Response Of Multi-element Eco-stoichiometry To Grassland Degradation In Soil-plant System

The grasslands in west Jilin were rich in waters and vegetation,being a natural"green ecologic guard".In the last fifty decades,due to human intervention and global warming and other factors,this region has less vegetation coverage and lost many nutritious elements,becoming an ecotone.As one of highly productive and nutritional grasses for grazing,Leymus chinensis?L.chinensis?is widely distributed in west Jilin.For this reason,L.chinensis is mainly researched for exploring the causes and mechanisms of grassland degradation.Currently,the ecological stoichiometry studies on carbon,nitrogen and phosphor in L.chinensis have attracted attentions from many scholars.However,studies on other elements which are coupled with carbon,nitrogen and phosphor from ecological stoichiometry perspective,such as potassium,sulfur,manganese,magnesium,copper and zinc are less reported.In this paper,L.chinensis at five different coverage ratios in natural grasslands in west Jilin province were studied.The elements limiting L.chinensis growth at such five conditions were specified according to N/P ecological stoichiometry rate.Stepwise regression analysis was used to determine other major elements that affect such limitation elements,and path analysis was applied to quantify the influences of these elements.Homeostasis characteristics of these elements were further unveiled by using homeostasis model.Results in this paper may provide important reference for improving and fertilizing degraded grasslands.Study results have indicated that:?1?At five different coverage ratios,L.chinensis growth are all limited by N element.And six other elements,i.e.,K,Mg,S,Mn,Cu and Zn significantly affect N.?2?When coverage ratio is between 100%and 80%,between80%and 60%,between 60%and 40%,between 40%and 20%and between 20%and0%,the influencing elements and their sequences are S>Zn>Mg,where homeostasis index of S is H_S=4.99,Cu>K>Mn,where homeostasis indices of Mn and Cu are respective H_Mn=3.06 and H_Cu=0.91,S>Cu,where neither S or Cu has homeostasis,K>S,where neither K or S has homeostasis,and Mg alone where Mg has no homeostasis.?3?When improving and fertilizing degraded grasslands,nutritional elements which are strong at controlling N and have weak or no homeostasis should be highly paid attention to.When coverage ratio is between 100%and 80%,between 80%and 60%,between60%and 40%,between 40%and 20%and between 20%and 0%,elements requiring much attention are respectively Zn and Mg,Cu and K,Cu and K,S and Cu,K and S,and Mg.