Table of Content

10 March 2016, Volume 35 Issue 3

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Litter carbon stock and spatial patterns of main forest types in Tibet.

YANG Yang, WANG Gen-xu*, RAN Fei, CHANG Rui-ying

2016, 35(3):  559-566. 

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Litter is an important linkage between plant and soil in nutrient cycles because it is not only a key component consisting of forest ecosystems, but also is the essential carrier for nutrients. Thus, changes of carbon stock in litter can directly affect the carbon stocks in soil and forest ecosystems. In this study Abies georgei var. smithii, Picea asperata, Pinus densata, Pinus yunnanensis, Quercus semecarpifolia, Cupressus funebris forests in the Tibetan Plateau were selected as target vegetation types, and a direct harvesting method was employed to collect litter in the study sites. In general, carbon storage of litter showed a tendency of higher values with increasing stand ages. Additionally, the carbon storage of litter firstly increased with increasing elevation, and then a subsequent decrease in carbon storage occurred with increasing elevation. The largest carbon storage value was observed in sites with elevations ranging from 3200 to 3600 m. Spatially, the largest carbon storage value occurred in Linzhi, followed by Shannan and Shigatse, and the lowest in Changdu.

Stoichiometry of leaf C, N and P across 152 woody species of a monsoon broad-leaved evergreen forest in Pu’er, Yunnan Province.

HUANG Xiao-bo1,2, LIU Wan-de1,2, SU Jian-rong1,2*, LI Shuai-feng1,2, LANG Xue-dong1,2

2016, 35(3):  567-575. 

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The monsoon broad-leaved evergreen forests are one of the zonal vegetation types with most complex structure, highest productivity, and most abundant biodiversity. Thus, clarifying the changes in stoichiometric characteristics of forests is critical to understanding nutrient cycling, limiting factors and stability mechanisms of the ecosystem. We analyzed the leaf carbon (C), nitrogen (N), and phosphorous (P) concentrations of 152 wood species from 29 plots (30 m×30 m in size) in Pu’er, Yunnan Province. The results showed that the arithmetic means of leaf C, N and P concentrations of the 152 species were 458.17, 20.88 and 1.42 mg·g^-1, with the coefficients of variation of 7.12%, 34.89%, 51.81% respectively. The arithmetic means of leaf C/N, C/P and N/P were 24.96, 394.74 and 16.50, with the coefficients of variation of 33.46%, 38.79% and 51.44% respectively. Leaf C concentration was significantly negatively correlated with leaf N concentration (P=0.005). Leaf N concentration was significantly positively correlated with leaf P concentration (P<0.001). However, no significant relationship was found between C and P concentration (P=0.078). The variations of leaf N, P and C/N, C/P, N/P in different families were relatively large, compared with that of leaf C. Except for leaf C, significant differences of leaf N, P, C/N, C/P, and N/P were observed between trees and shrubs, and between trees and lianas (P<0.05). N and P concentrations of trees were significantly lower than those of shrubs and lianas. The relatively high N/P ratio (16.50) of the overall 152 woody species implied that P was a limit factor of monsoon evergreen broad-leaved forest in Pu’er, Yunnan Province.

Transpiration of Eucalyptus grandis × E. urophylla and Pinus massoniana in typical reservoir watershed in Guangxi.

TAN Juan1, GUO Jin-chuan2*, WU Jian-qiang1, LI Rong-hui2, WANG Min1, WANG Qing1, RUAN Jun-jie1

2016, 35(3):  576-583. 

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Field measurements of transpiration rate (T_r), leaf area index (LAI), and related environmental factors were conducted for two typical woody plant communities (Eucalyptus grandis × E. urophylla and Pinus massoniana) in the watershed of the Gongjing Reservoir in Guangxi, China. Results showed that the seasonal change of T_r of Pinus massoniana was 0.14-0.69 μmol·m^-2·s^-1, and that of <2year-old and >4year-old Eucalyptus was 1.65-3.76 μmol·m^-2·s^-1 and 1.05-2.04 μmol·m-2·s-1, respectively. The Tr of <2yearold and >4yearold Eucalyptus was 6 times and 3.4 times that of P. massoniana, respectively. The T_r was highest in summer and lowest in winter for all plants, and T_r in summer was nearly twice as high as in winter. Significant positive correlations were found between T_r and LAI, soil water content and air temperature (P<0.01); all factors influencing transpiration were not independent. Path analysis results showed that air temperature and soil water content were the key variables for transpiration in P. massoniana. LAI had the greatest effect on transpiration of younger Eucalyptus, while soil water content was the key variable for older Eucalyptus.

Effects of rain supplementation on the temperature sensitivity of soil respiration in Nitraria sphaerocarpa community in a hyperarid area of Dunhuang, China.

LIU Dian-jun1, ZHANG Jin-xin2,3, LU Qi2*, LI Xu1， WU Zhe4

2016, 35(3):  584-590. 

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In order to analyze the effects of rain supplementation on soil respiration rate of Nitraria sphaerocarpa community, we measured the temperature sensitivity of respiration (Q₁₀) from bare and vegetated soils in a hyperarid area (Dunhuang) during the growing season. The results showed that Q₁₀ was enhanced significantly with the increase in rain supplementation in the bare soils, but there was no obvious influence on Q₁₀ of the vegetated soils. The rain supplementation (16 mm, 200% of the control) significantly increased the Q₁₀ of the bare soils by 28% (P<0.05). There was a significant positive correlation between Q₁₀ and soil water content during the growing season (P<0.001), and the sensitivity of Q₁₀ to soil water content was higher in the bare soils (1.94) than in the vegetated soils (1.57).

Stoichiometric characteristics of soil C, N and P in subtropical forests along an urbantosuburb gradient.

HE Jun-jie, CHEN Xiao-mei*, FENG Si-hong, YAO Ting-yu, LIANG Qian-wen, FU Jia-ming

2016, 35(3):  591-596. 

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With increasing urbanization, more and more attention has been paid on the structure and functions of urban forests. The changes in ecosystem structure and function can be reflected by those in stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P). In order to explore potential influences of urbanization on the stoichiometric characteristics of C, N and P, soil samples (0-10 and 10-20 cm) were collected from six subtropical forests along an urbantosuburb gradient in the Pearl River Delta that has been experiencing an unprecedented level of urbanization. The results showed that soil C and N concentrations in layers 0-10 cm  and 10-20 cm were significantly higher in the suburb forests than in the urban forests. There was no significant difference in soil P concentrations in 0-10 cm layer between the urban and suburb forests (P=0.226). However, soil P concentrations in 10-20 cm were significantly greater in the suburb forests than in the urban forests (P=0.001). Both soil N∶P and C∶P were significantly higher in the urban forests than in the suburb forests but soil C∶N was not significantly different. Our results suggested that rapid urbanization changed nutrient cycling in subtropical forests, which would reduce the stability of structure and function of urban forests.

Soil water infiltration characteristics and their influence factors on karst hill slopes under different vegetation types.

HU Yang1,2,3, DENG Yan1,2*, JIANG Zhong-cheng1,2, LI Yan-qing1,2, LAN Fu-ning1,2

2016, 35(3):  597-604. 

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Based on field survey and laboratory analysis, we studied soil water infiltration and its influence factors in wasteland, grassland, bushwood, and forestshrub land on typical karst hill slopes in Guohua, Pinguo, Guangxi. The results showed that no significant difference in initial infiltration rate was found among wasteland, grassland, and bushwood, but their initial infiltration rates were obviously lower than that in the forest-shrub land. The initial and steady infiltration rates in the study area were very low (<1 mm·min^-1), and decreased gradually with the increase of soil depth. The permeability coefficient and cumulative water seepage did not differ in wasteland, grassland and bushwood, and decreased with the increase of soil depth, but they were obviously lower than those in the forest-shrub land. The steady infiltration rate and permeability coefficient were significantly negatively correlated with soil depth, soil bulk density, clay content and initial water content, while significantly positively correlated with soil organic carbon content, non-capillary porosity, silt proportion and water temperature. Soil non-capillary porosity and clay content (<0.002 mm) were the major factors influencing soil water infiltration ability.

Physiological response of four epyphytic lichens in Shennongjia Natural Reserve to different nitrogen stress.

GUO Hua1,2, WANG Chuan-hua1*, YANG Lin1

2016, 35(3):  605-611. 

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In order to explore the potential impact of increasing nitrogen deposition on lichen diversity in the Shennongjia Natural Reserve, four common epiphytic lichens (Lobaria pulmonaria, L. orientalis, Usnea luridorufa and U. dasopoga) in this area were collected, then they were soaked in deionized water and KNO₃ (0.05, 0.5 mol·L^-1), NH₄NO₃ (0.05, 0.5 mol·L^-1), and (NH₄)₂SO₄ (0.025, 0.25 mol·L^-1) solutions for half an hour. The fluorescence induction curve parameter, solution electrical conductivity (RE, namely cell membrane integrity) and chlorophyll degradation (OD₄₃₅/OD₄₁₅) were measured. The sensibilities of the four lichens to nitrogen additions and the stress of ammonium nitrogen, nitrate nitrogen and mixed nitrogen on F_v/F_m, RE and OD₄₃₅/OD₄₁₅ were analyzed. The results showed that: (1) There were significant differences among the responses of lichens to different nitrogen forms. The toxicity of different nitrogen forms to F_v/F_m, Y(Ⅱ) and OD₄₃₅/OD₄₁₅ were in the order of mixed nitrogen > ammonium nitrogen > nitrate nitrogen, and their toxicity to cell membrane integrity presented as ammonium nitrogen > mixed nitrogen > nitrate nitrogen, while nitrate nitrogen alone had little toxicity to F_v/F_m, Y(Ⅱ), OD₄₃₅/OD₄₁₅ of these four lichens. (2) Nitrogen sensitivities of these four lichens were speciesspecific. When treated with nitrate nitrogen, OD₄₃₅/OD₄₁₅ of U. dasopoga appeared more sensitive than that of L. pulmonaria. If mixed nitrogen was used, the toxicity to F_v/F_m was in the order of L. pulmonaria≈L. orientalis>U. luridorufa≈U. dasopoga, while the toxicity to RE was L. pulmonaria≈L. orientalis<U. luridorufa≈U. dasopoga. When they were treated with ammonium nitrogen, the toxicity to F_v/F_m was in the order of U. luridorufa≈L. orientalis>U. dasopoga≈L. pulmonaria, and the toxicity to OD₄₃₅/OD₄₁₅ presented as L. pulmonaria≈L. orientalis<U. luridorufa≈U. dasopoga. Under an increasing nitrogen deposition background, our result is of special importance in lichen diversity protection and management in Shennongjia Nature Reserve.

Effects of biological soil crusts on soil seed bank diversity and distribution characteristics in Gurbantunggut Desert.

XING Xu-ming1,2, MA Xiao-dong1, ZHANG Yuan-ming2*

2016, 35(3):  612-620. 

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Biological soil crusts are widely distributed on the surface soil in the Gurbantunggut Desert. Studies on soil seed bank with the coverage of biological soil crusts can facilitate our understanding of the ecological functioning of biological soil crusts and vegetation renewal and succession. In this study, we focused on three types of biological soil crusts (cyanobacterialalgal crusts, lichen crusts and moss crusts) regarding the dominant functional group in crusts and investigated soil seed bank diversity and distribution in the Gurbantunggut Desert. In the horizontal distribution of soil seed bank, soil seed bank density was significantly higher in biological soil crusts than in bare sand, and it differed among the three types of crusts. Soil seed band density was highest in lichen crusts (5905±778 seeds·m^-3), suggesting lichen crusts has the largest potential to entrap seeds. Seed bank density in moss crusted soil was 1138±380 seeds·m^-3; cyanobacterialalgal crusts showed no difference in seed bank density with bare sand. The degree of biological soil crust development, the seed morphology, the spatial distribution difference of different biological soil crusts were the reasons for the difference of the horizontal distribution of soil seed bank. Seeds were primarily distributed in the shallow soil layer of 0-2 cm in biologically crusted soil, consistent with that in bare sand. This demonstrates that biological soil crusts exert no impacts on the vertical distribution of seeds. The similarity index of soil seed bank with vegetation was very low, ranging from 0.14 in bare sand to 0.29 in moss crusted soil. The species diversity and abundance in seed bank were lower than those of the plant community. This result, to some extent, suggests a limited role of soil seed bank in vegetation restoration in this region. However, the inhabitation of biological soil crusts facilitates the reservoir of soil seed bank and is important to sustain species diversity and ecosystem stability in the deserts.

Effects of topographic factors and land use on the spatial variability of topsoil nutrients in HunTai river basin.

ZHU Ju-lan1,2, LIU Miao2*, ZHANG Yang1, GONG Ji-ping2,3, SUI Jin-ling2,3

2016, 35(3):  621-629. 

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Based on the GIS, statistics and geostatistics method, this study simulated the spatial distribution of surface soil nutrients, and explored the effects of topographic factors, land use types and their interaction in HunTai river basin. The results indicated that elevation and slope were positively correlated with soil organic matter (SOM), total nitrogen (TN) and total phosphorus (TP) concentrations, while negatively correlated with total potassium (TK) concentration. Aspect had no significant effects on these soil nutrient properties. Forest and grassland had higher SOM and TP concentrations. Paddy field and cropland had higher TK concentration. Land use and topographic factors interactively affected soil nutrient properties. Higher SOM, TN and TP concentrations were distributed in the forest and grassland with higher elevation and greater slope. Topographic conditions and land use types can explain the spatial variability of soil nutrients in the study area.

Spatial variability of soil organic matter at different sampling scales in Inner Mongolia Hetao irrigation area.

ZHANG Na1, ZHANG Dong-liang1, QU Zhong-yi1*, LYU Shi-jie2, LIU Quan-ming1

2016, 35(3):  630-640. 

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Taking the Hetao irrigation region in Inner Mongolia as the research subject, with methods of classical statistics and geostatistics, we analyzed the spatial variability and scale effect of soil organic matter at different soil layers (0-20, 20-40, 40-70 and 70-100 cm) and sampling scales (1, 4 and 8 km). The results of classical statistics showed that the variation of mean organic matter contents increased with the increase of soil depth at all sampling scales; the coefficients of variations of organic matter contents at soil depths of 0-20 cm and 20-40 cm increased with increasing the sampling scale. Geostatistics indicated that there existed strong spatial autocorrelations in soil organic matter contents in different soil layers and at different sampling scales, and soil type was the dominant factor influencing its spatial distribution. There were certain anisotropic effects in the spatial patterns of organic matter content at different soil layers at all sampling scales. At small scale (1 km), this anisotropic effect presented a strip variation on eastwest direction at each soil layer. At moderate (4 km) and large scale (8 km), corresponding spatial variability was intensive in terms of eastwest and northwestsoutheast gradients at the top soil layer. The cross validation of ordinary Kriging applied on organic matter at the three scales showed that the root mean square errors were less than 1, indicating that the spatial variability of samples was overestimated. Our results highlight great significance for understanding the spatial distribution of soil organic matter, providing a scientific basis for sampling system design in agricultural technology research.

Content of soil dissolved organic C along an altitude gradient in Daweishan Mountain of eastern Hunan Province.

MA Xin, SHENG Hao*, WEI Liang, PAN Bo, LUO Lan-fang, ZHOU Qing, ZHANG Yang-zhu

2016, 35(3):  641-646. 

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In order to understand soil dissolved organic C (DOC) content along an altitude gradient in mountain area, soils derived from granite along an elevation gradient (179-1573 m) in Daweishan Mountain of Hunan Province were collected. Soil profiles were excavated down to parent material or rock horizon, and the effects of altitude and soil depth on DOC content were investigated. The results showed that DOC content ranged from 9 to 5326 mg·kg^-1, and increased with increasing the altitude both in top soil and subsoil. Soil organic C (SOC) and moisture can well explain the alteration of DOC content along the altitude gradient. DOC to SOC ratio ranged from 0.8% to 34.9%, and was similar at the foot and on the mountain peak. DOC to SOC ratio generally peaked in subsoil. At the same altitude, typical yellow soil with deep B horizon showed higher DOC content and DOC to SOC ratio in subsoil, while yellow soil with indistinct B horizon had lower DOC content and DOC to SOC ratio in subsoil. This study suggests that soil C content and composition varied differently with increasing altitude in top and subsoil. Deep subsoil should be considered in assessing mountain soil C pools.

Effects of low-dose biochar on the enhancement of fertility and yield in upland red soils.

ZHANG Wen-feng1, ZHOU Ji-hai1,2*, YUAN Ying-hong1,3*, HUANG Jing1,4, LI Cong-lei1, HUANG Qian-ru3, CHENG Yan-hong3

2016, 35(3):  647-654. 

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To resolve the problems of hardening of heavy clay and low fertility in upland red soils in Jiangxi Province, a field experiment was conducted to study the effects of low doses of biochar on fertility and production of upland red soils. The experiment included three doses of biochar: 0, 758 and 1515 kg·hm^-2·a^-1 (denoted as CK, BC1 and BC2, respectively). The results showed that, compared with CK, soil bulk density under BC1 and BC2 treatments decreased by 0.57%-2.05% and 0.87%-4.88%, soil pH increased by 2.51%-13.66% and 8%-12%, and soil cation exchange capacity increased by 3.73%-6.45% and 4.91%-7.13% in 0-60 cm, respectively. Application of low doses of biochar is beneficial to increasing the contents of organic carbon and N, P, and K in upland red soils, and the contents of organic carbon, total K and soil available K increased with increasing the dose of biochar. The crop yields under BC1 and BC2 treatments increased by 19.08% and 23.68% in 2013, and 18.01% and 22.98% in 2014, respectively. Therefore, application of low doses of biochar shows great prospects in increasing agricultural production by improving physical and chemical properties, nutrient utilization efficiency of upland red soils, and soil fertility. From the viewpoint of comprehensive input/output, continuous application of lowdose biochar exhibits more practical values and prospects.

The relationship between seed size and main reserve contents of seeds in 41 Asteraceae species of alpine meadow in the northeastern QinghaiTibet Plateau.

YANG Hui-xian, BU Hai-yan*, GE Wen-jing, WANG Xue-jing, XIA Yu-bin, MA Bing

2016, 35(3):  655-660. 

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The components and contents of nutrients in seeds play important roles in seed germination and subsequent seedling establishment; the difference in reserve contents may lead to seed take different strategies in germination and seedling growth. In this study, the relationship between main reserve contents and seed weight of 41 Asteraceae species on the northeast QinghaiTibet Plateau was analyzed, to clarify the adaptation variation of alpine plants with seed weight. The contents of crude fats, sugar and starch, and protein were determined by Soxhlet extraction, anthrone colorimetric method, and Coomassie Brilliant Blue G-250. The results showed that the contents of proteins and crude fats were decreased significantly with increasing seed weight, but the contents of soluble sugar and starch had no significant correlations with seed weight. No significant change of the contents of soluble sugar and starch in larger seeds might  result from the thicker coats of larger seeds. Relatively higher percentages of fat and protein in smaller seeds might provide enough energy for faster growth of seedlings, which could help the smallerseed species to gain temporal and spatial advantages and might be a tradeoff to overcome the disadvantages of smaller seedlings produced by smaller seeds.

The relationship of characteristics of meadow communities with soil moisture and temperature in the northern slope of Qilian Mountains.

JIA Wen-xiong1*, CHEN Jing-hua1, ZHANG Yu-shun1, CAO Wen-xia2

2016, 35(3):  661-667. 

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Environmental factors play key roles in structure and function of grassland ecosystems. This paper analyzed the variation of species diversity and aboveground biomass of meadow communities, and the relationship between aboveground biomass and soil moisture/temperature through field investigation and laboratory analysis in the northern slope of Qilian Mountains during the growing season in 2013. The results indicated that single peaks were found in species richness, diversity and evenness from May to September. Among different meadow communities, significant differences were found in species richness and diversity, but not recorded in species evenness in May, July and September. The species between meadow steppe and upland steppe were moderately dissimilar, but those were extremely dissimilar among different meadow communities, reflecting the obvious replace of different types of plant communities along the elevation. The variations of aboveground biomasses for different meadow communities displayed a single peak in July for alpine meadow and desert steppe, and in August for meadow steppe and upland steppe. In different meadow communities, the accumulations of aboveground biomasses were positively related to soil temperature under 0-10 cm, while were not related to soil moisture.

Allocation of photosynthetically fixed carbon in Pedicularis kansuensis in three types of alpine grassland.

XU Long-hua1,3, YAO Bu-qing1, ZHANG Chun-hui1,3, MA Zhen1, WANG Wen-ying2, WANG Hui-chun2, ZHOU Hua-kun1*

2016, 35(3):  668-674. 

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The insitu ¹³CO₂ pulse labeling technique was used to trace the translocation and allocation of ¹³C in Pedicularis kansuensissoil system and assess the dynamic changes of photosynthetically fixed carbon in P. kansuens growing in natural meadow, severely degraded alpine meadow (black beach) and artificial grassland established 5 years in the army ranch of Guoluo Prefecture in the Three Rivers Headwaters region. Results showed that, on the day when carbon was labeled, 39%-71% of the ¹³C was assimilated in the three types of grassland, suggesting that the labeling was in high efficiency and had a great allocation difference. On average, 8.6% of carbon was allocated to soil in the three types of grassland, indicating that the carbon was quickly translocated and allocated unevenly in the P. kansuensissoil system. The δ¹³C values declined in shoots and roots and 5%-27% of the assimilated ^13C was transferred to soil pools after labeling 21 days. The amount of fixed ^13C translocated in soil increased significantly five years after the conversion of “black beach” to artificial grassland. While P. kansuensis has a certain ecological significance for maintaining the diversity and stability of the community, it should be eliminated rationally according to the economic utilization of grassland.

Species abundance pattern in Stipa breviflora desert steppe under different stocking rates.

DU Yu-fan, GU Chen, WU Li-ji, XUE Wen-jie, CHEN Wan-jie, LI Zhi-guo*, ZHAO Meng-li WANG Jing

2016, 35(3):  675-683. 

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The species abundance pattern of plant community was analyzed under different stocking rates in Inner Mongolia Stipa breviflora desert steppe by using filed investigation and geometric model, segmentation model and niche overlap model, in order to know species interrelation and community pattern, and to reveal the effect of overgrazing on desert steppe community. The results showed that the geometric model well fitted the species abundance pattern of plant community under different stocking rates in S. breviflora desert steppe. With the increasing stocking rate, the species abundance pattern didn’t change, but the plant frequency decreased. The species numbers were lower in moderate and heavy grazing treatments than in the control and light grazing treatments. The dominant species S. breviflora played a key role in plant community pattern in desert steppe. Heavy grazing decreased the overall community frequency but increased the dominant species frequency.

Stoichiometric characteristics in root, stem and leaf of Phragmites australis in different habitats in the southern marginal zone of Tarim Basin.

LUO Yan1,2, GONG Lu1,2

2016, 35(3):  684-691. 

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The ecological stoichiometry of root, stem and leaf of Phragmites australis in different habitats of Keriya River of the southern marginal zone of Tarim Basin, Xinjiang was studied, to explore the effects of habitats and organs on stoichiometry. The results showed that the mean concentrations of C, N and P in P. australis organs were in order of leaves > stems > roots, the C∶N and C∶P ratios were in order of roots > stems > leaves, whereas the N∶P ratio was in order of leaves > stems > roots. The concentrations of C, N, P and their stoichiometric ratios in roots, stems and leaves differed with habitat. The concentrations of C in root, stem and leaf were significantly higher in riverbank than in oasis and desert. Stem N concentration was significantly lower in desert than in riverbank and oasis, while the concentrations of N in leaf and root were not significantly different among the three habitats. Leaf P concentration in oasis was significantly higher than in desert, and the concentrations of P in stem and root were significantly higher in riverbank than in oasis and desert. There was no significant difference in C∶N ratio among root, stem and leaf. The C∶P ratios in stem and root differed between riverbank and desert, while the ratio of N∶P did not differ among the three habitats and was less than 14, which indicated that the growth of P. australis was mainly limited by N. The N concentration was positively correlated with the P concentration, indicating a consistent demand of N and P during P. australis growth. According to the factorial analysis of GLM, we concluded that the C and N concentrations and C∶N and N∶P ratios were mainly affected by the organs, while the P concentration and C∶P ratio were mainly determined by the habitats.

Nitrogen and phosphorus resorption of six dominant plant species in Poyang Lake wetlands.

GUO Chao1, CAI Jia-yan1, JIN Qi1, ZHOU Hong-yan1, LI Min1, HU Qi-wu1,2*

2016, 35(3):  692-697. 

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In this study, six dominant plant species, including Phragmites australis, Triarrhena lutarioriparia, Zizania latifolia, Carex cinerascens, Carex Argyi and Polygonum hydropiper, were selected in Nanji Wetlands National Nature Reserve in Poyang Lake. Subsequently, mature and senescent leaves were sampled for analyzing N and P concentrations at biomass peaking and the end of growing season, respectively. The objective of this study was to clarify the characteristics of N and P resorption of the six dominant plant species in Poyang Lake wetlands. The results showed that the N resorption efficiency (NRE) of the six plant species ranged from 8.2% to
46.6%, whereas the P resorption efficiency (PRE) varied from 18.9% to 44.5%. Among the six plant species, C. cinerascens had the minimum NRE and PRE. Moreover, the mean NRE and PRE were 41.3% and 38.5% for emergent plants, but 19.9% and 26.0% for hydromorphic plants, respectively. NRE and PRE were positively correlated with N and P concentrations in mature leaves. In addition, NRE was positively correlated with N∶P ratio in mature leaves. According to their nutrient resorption proficiency, the six plant species in the Poyang Lake wetlands could be recognized as low N resorption plants.

Effect of chitosan on tobacco root growth under soil cultivation condition.

QI Shuai1, LAI Yong-lin1, WANG Jun2, WANG Hang2, SHEN Hong1*

2016, 35(3):  698-708. 

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The impacts of different concentrations of chitosan (0, 20 and 40 mg·L^-1) on root growth dynamics of tobacco seedlings were measured in three soil types (ox liver soil, sand field soil, and purple soil) of Nanxiong, Guangdong Province using rhizobox device. The results showed that the rhizobox device was suitable for the observation of dynamic root growth in the three types of tobaccoplanting soils. By observing root growth on the transparent panes of the growth chamber, it was found that applying chitosan increased the total root length and root number of tobacco plants significantly in the three types of soils, and the total root length was positively correlated to the total root number. In particular, treatment with 40 mg·L^-1 chitosan showed better effects, enhancing the total root length in 20-30  and 50-60 cm soil layers of ox liver soil, and in 0-10  and 20-60 cm soil layers of purple soils, while in sand field soil, treatment with 20 mg·L^-1 chitosan was the best, increasing the total root length in 10-40 cm soil layer effectively. On day 24 after transplanting, the elongation rate of tobacco roots and the increasing rate of root number showed a growth peak under 20 and 40 mg·L^-1 chitosan treatments, being higher than those under the control. The above results indicated that chitosan could promote root growth of tobacco seedlings under soil cultivation conditions.

Level indicators and temporal-spatial distribution features of early rice flood disaster in Hunan Province based on different growth stages.

WANG Tian-ying1,2，3, HUO Zhi-guo1,2*, LI Xu-hui4, YANG Jian-ying2, WU Li2, ZHANG Gui-xiang2

2016, 35(3):  709-718. 

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Meteorological indicators of early rice flood are recognized to be of realistic importance to the disaster monitoring, prewarning and assessment of early rice flood. Taking early rice in Hunan Province as research object, 385 flood rainfall amount data samples from 9 early rice flood disaster sample sets based on different rice growth stages (transplantingjointing, bootingblooming, milkmaturity) and flood levels (light, moderate, severe) were built in this paper, integrating daily precipitation data (1961 to 2010) from 68 meteorology stations, flood disaster historical data and phenophase data in Hunan Province. K-S test and Student’s tdistribution were employed for the goodnessoffit test and parameters determination, and thus, rainfall thresholds for flood levels were determined based on the confidential intervals of 9 sample sets, and verified by independent samples. Afterwards, temporalspatial characters of early rice flood disaster in Hunan Province were analyzed based on the constructed flood level indicators and ArcGIS. The thresholds of early rice flood disaster were 129, 154 and 241 mm for light, moderate and severe floods in transplantingjointing stage, 135, 170 and 260 mm in bootingblooming stage, and 145, 190 and 295 mm in milk-maturity stage, respectively. Rice flood level indicators were detected to be basically consistent with the historical occurrence levels of rice flood disasters, according to the verification results. Total flood disaster frequency of early rice showed an increasing tendency since 1961, and furthermore, severe floods mainly located in northern Yueyang and southern Chenzhou. South and east regions of Hunan were detected with high frequencies of flood in transplantingjointing. Flood in bootingblooming stage mainly happened in east and central regions of Hunan, while milk-maturity flood occurred mainly in the north region of Hunan. Considering the frequency and intensity of flood, early rice flood disasters were most serious in the 1990s in Hunan. Central Hunan and east to south region of Hunan were the floodprone area during transplantingjointing and milk-maturity stage respectively, in recent 10 years.

Identification and evaluation of tomato rootstock seedlings for drought tolerance.

ZHANG Zhi-huan, HAN Min, ZHANG Yi, WANG Yun, XU Kun*

2016, 35(3):  719-725. 

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In order to obtain the indexes which can be conveniently used to identify the drought tolerance of tomato rootstocks and to screen out tomato rootstocks with strong drought tolerance from thirtytwo tomato rootstocks, we measured the changes of root fresh weight, stem fresh weight, leaf fresh weight, leaf water potential, root activity both before and after soil dehydration treatment, then evaluated the drought tolerance of tomato rootstock seedlings through comprehensive comparative analysis. It was found that, with increasing the duration of soil dehydration, the average value of drought damage index of tomato rootstock seedlings increased, while the coefficient of variation of drought damage index decreased. However, after the seedlings were watered, the changes were opposite. In the regression model of drought damage indexes, only root fresh weight, leaf water potential before soil dehydration treatment and the relative increment value of root fresh weight were selected. Tomato rootstocks could be divided into three classes by clustering analysis based on each of all variable factors of the model. With the exception of the relative increment value of root fresh weight, the other factors had same results on the grouping. So root fresh weight and leaf water potential of seedlings before soil dehydration treatment could be used as convenient indicators identifying tomato drought tolerance, and 606, AnkaT, 060813 and 0301112 were screened out as droughttolerant rootstocks of tomato.

Spatial structure of Syzygium hancei community along coastline of Guangxi.

LI Yuan-fa, WANG Lei, YU Su-fang, YE Shao-ming, LU Dao-diao*

2016, 35(3):  726-732. 

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Spatial structure to a large extent discloses the habitat of individual trees in a community and the quota of environmental resources they have. It is very important for maintaining the stability of plant community, and for analyzing interspecific competition and individual survival. In this study, a plot of 65 m×40 m with every tree positioned was established in the coastal zone of Fangchenggang, Guangxi Province, with the purpose to detect the spatial characters of natural Syzygium hancei Merr. et Perry community. The whole plot and trees with different sizes were analyzed by the bivariate distribution of structural parameters. The results showed that S. hancei population had a distinct advantage in both biomass and the number of individuals when compared with other species. Simultaneously, most individuals were randomly distributed and lowly mixed, regardless of the whole community, big or small trees. Only few trees belonged to high mixture, regular or cluster distribution. For the whole plot, trees with different superiority had a similar mixture and distribution pattern. Most big trees were in a superior status and low mixture, only a few belonged to middle or inferior trees. Almost all small trees were inferior individuals with low mixture, and they were in a state of random distribution and disadvantage at the same time. These features revealed that the community had a very complex structure and may be in a stable state. Our results could be beneficial to the protection and restoration of S. hancei community, and also provide a reference for the construction of structure system of protection forest in the coastal zone.

Zooplankton community structure and its relationships with environmental factors in Datong Lake of Hunan Province.

GAO Zi-han1, ZHANG Jian1, PI Jie1, ZHANG Ting2, LI De-liang1*, XIAO Tiao-yi1

2016, 35(3):  733-740. 

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In this study, zooplankton and environmental factors in Datong Lake of Hunan Province were investigated monthly. Zooplankton community structure and its relationships with environmental factors were analyzed by canonical correspondence analysis (CCA) to provide reference for fisheries sustainable utilization in Datong Lake. The characteristics of water nutritional levels, trophic state index (TSI-M) and dominant zooplankton species indicated that the lake was under accelerated eutrophication status. A total of 46 species from 20 genera were identified, which consisted of 18 species of Protozoa, 19 species of Rotifera, 4 species of Cladoera and 5 species of Copepoda. According to the abundance and occurrence, Tintinnopsis sinensis, Brachionus diversicornis, Asplanchna priodonta, Polyarthra trigla, Filinia longiseta, Bosmina longirostris and Cyclops strenuous were considered as the dominant species. The mean annual abundance and biomass of zooplankton were 1013±125 ind·L^-1 and 5.12±0.96 mg·L^-1, respectively. The abundance and biomass were both relatively high from October to March 2014, and lowest in April, with a spatial pattern of decreasing from South to North. The Shannon index (H), abundance index (D), and Pielou index (J) of the zooplankton community were 0.31-1.88, 0.11-1.39, and 0.45-0.90, respectively. The CCA results indicated that water temperature and total phosphorus concentration were the two main environmental factors affecting the zooplankton community structure in the Datong Lake. The stocking of silver carp and bighead carp as well as the spatial distribution pattern of Mollusca might also play an important role in determining the zooplankton community structure in this shallow lake.

Composition and nutritional evaluation of amino acids of peanutworm Sipunculus nudus dry body from five sea areas of Beihai, Guangxi.

LIU Xu-jia*, PENG Yin-hui, HUANG Guo-qiang

2016, 35(3):  741-746. 

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Sipunculus nudus is a special species distributed in the Beihai Gulf, and it is also a kind of precious sea food. In order to exploit its economic value, the content of amino acids of S. nudus was measured. Nutritional values of amino acids were evaluated according to amino acids grade standard mode of FAO/WHO. The investigation was conducted in February, May, August and November 2013 in five sea areas including Shankou, Beimu, Yingpan, Daguansha and Zhulin. Then the amino acids content and composition were analyzed. The result showed that the average content of amino acids of S. nudus in Beimu was highest, being 68.02%±0.50%. The contents of amino acids, essential amino acids and nonessential amino acids presented a trend of increase first and decrease later over seasons in the five sea areas. 16 kinds of amino acids were detected in S. nudus, and the content of glutamic acid was highest, which could reach 17.34%±0.61%. The ratio of essential amino acids to total amino acids and the ratio of essential amino acids to nonessential amino acids approached the FAO/WHO standard. Our results provided theoretical basis and technical support for the development of S. nudus with high edible and medicinal values.

Measurable characters, population structure and density effect of Pomacea canaliculata in different habitats.

FANG Miao1,2, XU Meng1, LUO Du1, MU Xi-dong1, GU Dang-en1, HU Yin-chang1, ZHANG Jia-en3, LUO Jian-ren1*

2016, 35(3):  747-754. 

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A comparative study on measurable characters, age structure, sex ratio and density dependence of Pomacea canaliculata populations from 4 habitats in 11 areas of Guangdong Province were conducted. The results showed that measurable characters of P. canaliculata significantly differed among habitats (P<0.05). The relationship between body mass and shell height conformed to the allometric equation with different allometric indexes in different habitats. The age structure of P. canaliculata was different among different habitats, with expanding populations in the paddy fields and ditches and stable populations in the waste paddy fields and ponds. The habitat did not significantly affect sex ratio (P>0.05), but it significantly influenced the relationship between sex ratio and body weight (P<0.05). The population growth of P. canaliculata was densitydependent and the effect of density dependence was different among 4 habitats with the smallest value in the ditch, middle in the paddy field and waste paddy field, maximum in the pond. Our study suggested that the measurable characters and population structure of P. canaliculata populations were significantly affected by habitat conditions. Given its different growth potentials in different habitats, specific prevention and control measures should be drafted to manage this invasive species.

Effects of tourist numbers on the behavior of captive wolves.

LIU Bing-wan1*, CHEN Lu-wen1, LI Ruo-nan2, HE Xiang-bao2, Timothy R. VAN DEELEN3

2016, 35(3):  755-758. 

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Effects of humans on the behaviors of wildlife are a focal issue for ethology and tourist numbers are an important factor that affects behaviors of captive wildlife in zoos. To improve welfare of captive wolves, we studied the effects of the tourist numbers on the behavior of captive wolves using group scan sampling before, during and after China’s National Day in Harbin Northern Forest Zoo from September to November in 2014. The proportions of active, static, conflict and stereotyped behaviors of captive wolves differed significantly among the three periods (P<0.05), while the proportions of friendly and other behaviors did not (P>0.05). The proportions of active and friendly behaviors of captive wolves were positively associated with the number of tourists significantly (P<0.05), while the proportions of static and stereotyped behaviors were negatively associated with number of tourists significantly (P<0.05). Proportions of conflict and other behaviors of captive wolves were not associated with number of tourists significantly (P>0.05). Our results indicate that tourist number affects the behaviors of the captive wolves in zoos and zoo managers could improve the welfare of captive wolves by managing tourist numbers.

Impact of food availability on seasonal diet composition of whiteheaded langur.

LU Shi-yi1, LU Chang-hu1*, LI You-bang2

2016, 35(3):  759-766. 

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Study on the impact of food availability in limestone habitat on dietary diversity and monthly similarity is crucial to understand animal’s adaptation to specific habitat. We collected data on food species, items and feeding time of whiteheaded langur (Trachypithecus leucocephalus) via instantaneous scanning sampling method, and monitored food availability by fixed transect in their home range each month. The results showed that annual dietary diversity index was 4.02. There was no significant monthly variation in dietary diversity (P=0.89), and there was a significant negative correlation between dietary diversity and availability of young leaves of staple food (P<0.05). Eight species were used by the langurs in all months, whereas others were consumed seasonally, despite of their higher availability. Food species overlap between months ranged from 0.36 (March and April) to 0.75 (September and October). Moreover, we found a significant positive correlation between food availability similarity and dietary species similarity among months (P<0.05). This study suggested that langurs inhabiting limestone hills diversified food species to meet nutrient demand by being selective in food species available in all months and consuming some seasonally available food species.

Factors affecting Hyphantria cunea supercooling point.

DENG Yu, SUN Shou-hui*, QI Jin-yu, YIN Da-chuan, LI Fei

2016, 35(3):  767-771. 

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As an alien invasive species in China, Hyphantria cunea is an important international quarantine pest and its distribution is spreading. The supercooling point (SCP) is an important physiological indicator for studying its potential distribution area. In this study, we analyzed the relationships between SCPs and larvae instars, host plants, low temperature acclimation time and geographical population. It was found that the SCP of H. cunea differed with larvae instars (P<0.001). The lowest SCP was found in pupae (-15.91 ℃) and the highest SCP was found in 5th instar (-6.97 ℃); SCP increased with the increase in age of larvae instars. The averaged SCP of H. cunea pupae feeding on the leave of Platanus acerifolia (-16.09 ℃) was significantly lower than that of pupae feeding on the leave of Acer negundo (-14.61 ℃) (P=0.002). There was no significant difference in SCP of non-diapause pupae after acclimating 24, 48 and 72 h at 6 ℃ (P=0.846). Significant differences of SCP were found among 6 geographic populations (Wuyi, Neihuang, Puyang, Dongying, Shouguang and Shenyang). Particularly, the SCP of Dongying samples was the highest (-15.35 ℃) and the SCP of Neihuang was the lowest (-21.39 ℃).

Source-sink theory based distribution characters of soil heavy metals along an urban-rural gradient in Pudong New District.

FANG Shu-bo1,2, CUI Qu1, PANG Hui-huan1, YIN Chun-sheng1, LUO Xing-zhang2*

2016, 35(3):  772-780. 

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By using the moving windows method, the mean concentration and range of soil heavy metals including Cu, Cd and Pb in forest and builtup patches along an urbanrural gradient in Pudong New District, Shanghai were analyzed based on the sourcesink theory. The linear regression analysis and correlation analysis were applied to distinguish the major factors affecting the spatial distribution of soil heavy metals concentrations. With the selected factors affecting the spatial variation of heavy metals, the priority management areas associated with potential risks of heavy metals were identified by raster layer computation. The results showed that the mean and range values of heavy metals in the forest patches were higher than those in the builtup patches. The mean concentrations of forest soil Cu and Cd decreased significantly at the distance of 27 km from the urban center, while those of soil Pb had a peak value at the distance of 30 km from urban center. The linear regression analysis and the correlation analysis showed that road density, builtup area percentage, and population change index that reflects the industrial development process could significantly affect the spatial distribution of soil heavy metals. A multitarget forest management strategy should be applied to respond to the identified potential priority areas for risk management of heavy metals.

Assessment of the impact of climate change on vulnerability of farmer households’ livelihood in an ecologically vulnerable alpine region: Taking Gannan Plateau for example.

ZHANG Qin1, ZHAO XUE-yan1*, LUO Li1, WANG Ya-ru1， XUE Bing2

2016, 35(3):  781-790. 

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Climate change is one of the most serious challenges to human in the 21st century, which exacerbates the vulnerability of many countries and regions, especially for the agricultural population who relies on natural resources for their livelihoods. Clarifying the impacts of climate change on farmers’ livelihood vulnerability is of great significance for making effective adaptive strategy and strengthening the farmers’ adaptability and mitigating livelihood vulnerability to climate change. This paper takes Gannan Plateau, a representative ecologically vulnerable alpine region, as the study area, and establishes an index system for evaluating farmer households’ livelihood vulnerability to climate change. Based on 539 questionnaires of farmer households, we analyzed the impacts of climate change on farmers’ livelihood vulnerability in Gannan Plateau and the key factors affecting farmers’ livelihood vulnerability by using the multivariable linear regression model. The results show that: (1) The impacts of climate change differ with different types of households in Gannan Plateau, of which, the vulnerability of households with young householders is the strongest, and the vulnerability of households with middleaged householders is the least. The vulnerability of farmers’ livelihood to climate change tends to decrease from the low income households to the high income households, from the households with low education level to the households with high education level, from the households with less than 10% of their income from nonfarming to the households with more than 90% of their income from nonfarming, but to increase from the households with low dependency ratio to the households with high dependency ratio; (2) The impacts of climate change on the livelihood of farmers differ in different regions, of which, the vulnerability of households living in pure pastoral area is the strongest, and the vulnerability of households living in the farming areas is the least. (3) The vulnerability of farmers’ livelihood to climate change is negatively correlated with the age and the education level of householders, the income per capita of households and the level of nonfarming and livelihood diversification, while positively correlated with the dependency ratio. Finally, suggestions are proposed to reduce the vulnerability of the farmers’ livelihood to the climate change.

Landscape ecological risk assessment and landscape security pattern optimization in Shule River Basin.

PAN Jing-hu*, LIU Xiao

2016, 35(3):  791-799. 

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Taking Shule River Basin as a case, this paper analyzed landscape ecological risk variability by establishing a risk index based on landscape pattern and process using GIS and RS technology. Spatialtemporal processes and aggregation characteristics of ecological risk were analyzed. Minimum cumulative resistance model was used to build river basin ecological security pattern with taking natural reserves, waters, forest lands as the “source”, and ecological security level, elevation and slope as resistance factors to generate resistance surface. The potential corridors and nodes were identified and the optimized ecological security network was established. Results showed that the ecological risk level in the north of Shule River Basin was higher than that in the south. In general, the ecological security level in the Shule River Basin had been improved in recent 30 years. From 1980 to 1995, the areas of Shule River Basin with degraded ecological security level were mainly located in the southwest and the east; the area with degraded ecological security level during 1995-2010 was less than that during 1980-1995. The landscape risk index presented a positive spatial autocorrelation. The spatial autocorrelation degree weakened during the past 30 years, which indicated a reduction in spatial convergence. The optimized ecological network made full use of the existing river system to get through the corridors, and avoid urban industrial land, mining land and transportation lines. Also, the optimized ecological network combined ecological source region, potential corridors, potential nodes and other landscape components, and set up key points in the ecologically fragile regions as the “pedals” of species dispersal.

Adaptability of WOFOST model to simulate the whole growth period of maize in Hetaoirrigation region of Inner Mongolia.

SUN Lin-li1, HOU Qiong2, MA Yu-ping3, ZHAO Hui-ying4*, ZHAO Fang4, ZHANG Fu-chao4

2016, 35(3):  800-807. 

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Introducing a mature crop model and validating its adaptability can provide a basis for further study of maize growth monitoring and yield estimation in Hetao irrigation region. Based on the observed maize data in 2012, as well as the local weather and soil data, the WOFOST crop model developed by Wageningen University was calibrated and verified by the crop data of 2013 and agrometeorological observation data from 2001 to 2011 at Bayannur agrometeorological experiment station. The basic crop parameters were obtained, which included specific leaf area, maximum rate of CO₂ assimilation, lightuse efficiency of single leaf, etc. The result showed that after parameters were calibrated, WOFOST model could simulate LAI expansion and biomass accumulation well, and the simulated values on LAI, biomass of organs and yield fitted well with the observed ones. The average absolute deviation of LAI was 0.75, and the normalized root mean square errors (NRMSE) for dry weight of leaves, stems, storage organs, total aboveground biomass and yield were 33%, 26%, 17%, 18%, and 13%, respectively. The NRMSE for the simulated yield from 2001 to 2011 was 7.5%. Therefore, it was reasonable and practical to simulate LAI, biomass of organs and yield by the calibrated model. WOFOST model was suitable for the diagnosis and assessment of physiological and ecological factors during maize production in the Hetao irrigation region.

Phenology mismatch induced by global warming and the adaptation mechanisms of organisms.

WANG Wei-wei, ZHANG Shu-ping*

2016, 35(3):  808-814. 

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Changes in the phenology of organisms induced by global warming can cause mismatches between the phenology of different species. Such mismatches can disturb interspecific relationships, thereby influencing species’ population size and distribution. In this paper, we introduce the ecological effects of phenological mismatches on interspecific relationships such as predation, symbiosis, parasitism, and competition, as well as the mechanisms by which organisms adapt to phenological change. We suggest that adaptation to phenology mismatch induced by global warming should be studied from the perspective of behavioral adjustments and microevolution, and that comprehensive understanding of the additional ecological effects of phenological mismatches on ecosystems will require extensive monitoring and the use of predictive models.

Recent advances in the study of plant growth-promoting rhizobacteria in China.

LIU Dan-dan, LI Min, LIU Run-jin*

2016, 35(3):  815-824. 

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The rhizosphere and plant growthpromoting rhizobacteria (PGPR) are important concepts in biology, and become one of research hotspots in soil microbiology and microecology. Total 53 species (isolates) belonging to 27 genera of PGPR were isolated from food crops, economic crops and other plants grown in China, of which isolates in Bacillus, Pseudomonas, Enterobacter and Burkholderia are common and widely distributed PGPR. It is well documented that PGPR can activate soil nutrients, improve soil physical and chemical characteristics, increase soil fertility, antagonize pathogens, decrease plant diseases, enhance plant resistance to diseases, salt stress, coldness and heavy metal toxicity, improve crop growth, development, yield and quality through directly synthesizing hormones, antibiotics and other secondary metabolites, and by regulating plant related gene expressions and other living organisms community structure in rhizosphere. All of these effects are influenced by PGPR species or isolates, other living organisms, soil conditions and agricultural measures. Several PGPR agents developed have been commercialized, produced and applied for enhancing plant growth and controlling soilborn diseases with superior effects. In addition, whole genome sequencing analysis of several species and isolates of PGPR were finished in China. It is concluded that great achievements have been obtained in basic application research, and a solid foundation for realizing the industrialization and application of PGPR has been laid in China. There are broad application prospects for PGPR solving some difficult problems in crop production and promoting the sustainable development of agriculture, forestry and animal husbandry.

A review on social behavior-kinship linkage mechanisms in population regulation of small mammals.

DENG Ke, LIU Wei*, WANG De-hua

2016, 35(3):  825-833. 

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The intrinsic mechanisms underlying population fluctuations especially in small mammalian species have received much attention from ecologists and evolutional biologists. According to the polymorphic behavior hypothesis and kin selection theory, integration between social behavior and kinship may play a major role in driving animals’ population fluctuations, which has become one of the frontier topics in the field. However, controversies still exist mainly due to the lack of convincing data demonstrating the underlying mechanisms. In the present review, we introduce some of the new methodological tools available for studying social behavior and kinship, review related theories, and discuss the current literature with respect to the behavior-kinship linkage models and possible future directions.

Connotation and differentiation of terminology on main kinds of wetlands in English.

LUO Ling1,2, WANG Zong-ming1, MAO De-hua1, ZHANG Bai1*, LU Chun-yan1,2, MAN Wei-dong1,2

2016, 35(3):  834-842. 

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Wetland plays an important role in the global ecological balance and ecological safety. Comparatively, wetland has higher ecosystem diversity and structure complexity, and its classification is more difficult. All of these make misuses of English vocabulary for wetland terms common in related researches, which seriously impact the spreading and correct use of scientific research results. Based on the classic academic data in the field of wetland science, combining with field working experience, we describe the connotations of English vocabulary of wetland terms (swamp, marsh, peatland, mire, bog, fen), reveal the main distinguishing features through pairwise comparison of similar types of wetlands, and then sum up the main causes of confusion for wetland terms as follows: (1) language differences between different countries or regions; (2) differences in culture and research habits between different countries or regions; (3) difficulty in distinguishing the uniqueness of some wetlands; (4) changes in understanding of wetlands in different periods. This paper can provide scientific basis for the scholars and related persons who are engaged in wetland research and management to better promote the proper, wide spread of research results in the field of wetland science.