Abstract: Carbon and nitrogen contents in aggregates are influenced greatly by human disturbance and land use. However, it is uncertain how disturbance and land use affect carbon and nitrogen in aggregates, especially for calcareous soil in karst region in southwest China, where is extremely vulnerable to human disturbance. Based on a longterm field trial in Huanjiang Observation and Research Station, this study identified the distribution characteristics of carbon and nitrogen in calcareous soil aggregates under five kinds of disturbance and land use treatments (enclosure, cutting, burning, pasture, and maize cropland). The results showed that the aggregate composition was dominated by particles >5 mm and 2-5 mm under the different disturbance and land uses. The aggregates of enclosure and cutting lands showed significantly higher values in particles >5 mm than those of the other three landuse patterns, while burning land and maize cropland had high values in <2 mm fraction. In whole soil and all size classes of aggregate particles, enclosure had the highest values of organic carbon and total nitrogen, followed by burning and cutting, while the values of organic carbon and total nitrogen in pasture and maize cropland were relatively lower. The distribution patterns of carbon in different aggregates were variable: enclosure and cutting presented an undulation distribution, and maize cropland showed an inverted “V” shape. The lowest values of organic carbon and total nitrogen appeared in particles 0.054-0.25 mm. The contribution of organic carbon and total nitrogen in >5 mm fraction under enclosure and cutting was significantly higher than that under the other three landuse patterns. Most of the organic carbon and total nitrogen were accumulated in >5 mm and 2-5 mm fractions, which both accounted for 60%-82%. The results suggest that particles of aggregate size >2 mm hold the major parts of the soil carbon and nitrogen in karst calcareous soils. Our findings could provide fundamental information for choosing proper management practices to improve soil fertility as well as carbon and nitrogen sequestration.

Key words: photosynthesis characteristics, non-structural carbohydrate (NSC), alpine treeline, antioxidant system, nutrient characteristics