关键词: 沙棘, 坡位, 分形维数, 坡度, 砒砂岩区

Abstract: The objectives of this experiment were to study the response of seeds to digestion in the rumen of sheep and to discuss the significance of seed heteromorphism phenomenon of Chenopodiaceae plants. The seeds were from the following species: Ceratocarpus arenarius L.,Halogeton glomeratus C. A. Mey.,Atriplex aucheri Moq. and Salsola affinisC. A. Mey.; each plant can produce two different types of seeds. After determining their morphological characteristics, the seeds were put into nylon bags which were then placed in the rumen of sheep through a fistula. The bags were removed at different times and then the seed length, width and thickness and germination rates were determined. The results showed that the seeds became dark after digestion, the seed appendix structures (such as bracts, seed trichomes and seed wings) of all four species were digested by rumen fluid of sheep and the internal annular embryos were exposed. Digestion time had significant effect on the seed length, width, thickness and 1000seed weight of the four plant species (P<0.05). The relationships between seed length, width, thickness, weight of 1000 seeds and digestion time were described by the equationsY=1.00+7.92e^-0.04X(R²=0.92, P<0.0001), Y=1.28+4.63e^-0.11X(R²=0.91, P<0.0001),Y=0.70+1.36e^-0.09X(R²=0.92, P<0.0001) and Y=1.48+9.57e^-0.20X(R²=0.36, P<0.0001) respectively, whereX is time in hours. Sheep rumen digestion could break the seed dormancy of  Chenopodiaceae plants, significantly improving seed germination rates (P<0.05). In addition to the gradually increased germination rate of A. aucheri smallbract seeds with the extension of rumen digestion time, the seed germination rates of the rest seeds decreased after an initial increase. The seed germination rates were all >40% when digestion time was >12 h, which increased significantly compared with seeds that were not digested (P<0.05). These eight kinds of Chenopodiaceae seeds all can disperse by sheep digestive tract. This study indicates that different types of seeds produced by the same species can respond to sheep rumen digestion in convergence. Chenopodiaceae plants not only can reproduce by “bet hedging” strategy to adapt to the harsh desert environment, but also can spread by grazing sheep digestive tract to increase the opportunity of population dispersal. This is a survival way of plants to adapt to changing environment in desert.

Key words: fractal dimension, Pisha sandstone area, slope, slope position., seabuckthorn