不同海拔和放牧扰动下植物种间正相互作用的研究

Facilitation among plants is one of the hotspots in ecology, which plays an important role in community construction and ecosystem function. Stress gradient hypothesis (SGH), which is fundamental for facilitation, predicts that the intensity of facilitation increased with stress gradient. However, there is large controversy on this hypothesis, in particular for the net outcome among plants under high stress gradient. Also few studies have focused on SGH along different stress conditions. In this paper, we explored the facilitation among the shrub Dasiphora fruticosa and understory species at community, functional group and species levels, and the shift of facilitation along abiotic and biotic stress gradient by using a removal experiment in the meadow on the Tibetan plateau. We found: 1) D.fruticosa significantly changed the composition of understory community and increased the productivity of community due to the presence of facilitation. 2) Facilitation of shrub showed no difference between different elevation and grazing disturbance at the community and functional groups level. 3) Facilitation at community level did not increase with elevation or grazing disturbance, which maybe was due to the facilitation balanced each other at functional group and species level. 4) The variation of facilitation at species level was related to the strength and types of gradient. Our results reveal the variation of facilitation at the community, functional group and species levels, and differential responses of facilitation to differ stress types, which stress the importance of facilitation among D.fruticosa and its understory species in constructing community and maintaining diversity in the sub-alpine and alpine meadow.