Studies On The Ecosystem Engineering Effect Of Cushion Plants In Alpine Cold Desert At The Northern Margin Of Tibetan Plateau

Alpine cold desert is always with harsh climate conditions and vulnerable environment,a few of plant species survive in such area, and the vegetation is also rare. Cushion plants arewidely spread in alpine cold desert, they are a type of ecosystem engineer in alpine regions.Taking cushion plants, Thylacospermum caespitosum, Krascheninnikovia compacta,Saussurea subulata and Androsace tapete in the alpine cold desert at the northern margin ofTibetan Plateau as target plants, their ecosystem engineering effects were studied, and themain conclusion were as follows.The cushion plants in the alpine cold desert at the northern margin of Tibetan Plateauchanged the availability of resources in their microenvironment, improved the conditions ofsoil, created a superior microenvironment for themselves and other species, and they arewell known as ecosystem engineer.The cushions improved the soil nutrients under their canopies, all the four cushion plantsimproved the organic matter, total nitrogen, available nitrogen, available phosphorus andavailable potassium content in the soil beneath them. Meanwhile, the cushions changed thephysical structure of soil under their canopies, compared with open areas, soil bulk densitydecreased, noncapillary porosity, capillary porosity, total porosity and aeration porosityincreased respectively. In addition, the cushions improved the water condition of soil beneaththem, pondage was improved most, but soil water content was not increased much. Moreover,the cushions maintained relatively constant temperature environments under their canopies,they increased the extreme low temperature and decreased the extreme high temperature ofsoil beneath them, and made the soil temperature under their canopies not to change muchduring a day.However, the improvement of cushion plants changed with cushion type, cushion sizeand altitude. Comparison studied showed that the modification effects on soilmicroenvironment increased with cushion size and altitude, which of the compact typecushion was much better than that of loose type cushion, this indicated that the compactcanopy was more beneficial to the modification effects.The cushion plants leads to the creation and maintenance of new habitat patches in thelandscape, with quite different physicochemical conditions compared to the surrounding unmodified habitat matrix. Such a change in habitat conditions may directly affect thedistributions of other species, and also improved the species diversity of the community. Inthis study, the cushion plants added new species to landscape, change the speciescomposition and enhanced species diversity of community, and also changed the abundanceof some species. And the cushion plants also showed their potential to maintain speciesdiversity.Consequently, ecosystem engineering effect of cushion plants lead to the changes ofecosystem function of alpine cold desert, they improve the biomass of some plant growinginside them, and increase the total biomass of the community, but the average biomass of unitarea was not improved. Meanwhile, total biomass of plants inside per cushion increased withtheir species number, and they were in a significant positive correlationship.