Effects Of Precipitation On Litter C:N:P Ecological Stoichiometry In A Desert Steppe In Northwestern China

As the consequence of global climate warming,the global and regional precipitation patterns have been changed,directly affecting soil water availability,and then posing great effects on plant growth,litter decomposition,as well as the structure and function in plant-soil systems.Desert steppes are characterized by low precipitation and uneven seasonal distribution of precipitation and their stabilities are mainly limited by precipitation.Therefore,desert steppes are sensitive to changing precipitation patterns.Litters are the links between plants and soils.The releases of C,N,P,and other elements during litter decomposition directly affect soil nutrient availability and plant nutrient use strategy.In this study,we conducted a simulated field experiment of precipitation change involving five treatments(1.e.50%reduction in mean annual precipitation,30%reduction in mean annual precipitation,natural precipitation,30%increase in mean annual precipitation,50%increase in mean annual precipitation)in a desert steppe in Ningxia,northwestern China in 2015.Based on a 480-days of litter decomposition sub-experiment since November,2016,we studied the effects of precipitation on litter mass residual rate,decomposition rate,and C:N:P ecological stoichiometry,monitored the characteristics of soil water content,temperature,pH,conductivity,urease activity,catalase activity,invertase activity,and C:N:P ecological stoichiometry,explored the influencing factors of litter decomposition rate and C:N:P ecological stoichiometry,and also analyzed the relationship between litter and soil C:N:P ecological stoichiometry.Our results will provide basic data for a better understanding of elemental cycling in plant-soil system in desert steppe under changing precipitation patterns.The important findings are as follows:(1)Changing precipitation had little effects on litter decomposition mass residual rate and C:N:P ecological stoichiometry but altered decomposition rate both at community and population levels.Mass residual rate decreased with decomposition time.Higher mass losses at both community level and population level mainly showed before 180 d,while faster decomposition rates displayed on 60 d and 240 d.Between two levels and among four species,the mass loss and decomposition rate of Artemisia scoparia were the fastest,while those of Pennisetum centrasiaticum were the slowest.In most cases,compared with natural precipitation treatment,increased precipitation treatments significantly increased litter decomposition rates of most species populations,while reduced precipitation treatments greatly decreased litter decomposition rates of several species populations.Litter C,N,and P concentrations also decreased with decomposition time,and the release rate of C were lower than those of N and P.Being influenced by the changes in C,N,and P,litter C:N,C:P,and N:P increased firstly and then decreased;(2)Changing precipitation had little effects on soil temperature,pH,conductivity,alkali-soluble N content,NH4+-N content,catalase activity,and C:N:P ecological stoichiometry,while it greatly altered soil water content,NO3--N content,available P content,urease activity,and invertase activity and the effects were different among decomposition time.Compared with natural precipitation treatment,50%increase in precipitation treatment significantly increased soil water content on 120 d,180 d,and 480 d,50%reduction in precipitation treatment significantly decreased soil water content on 240 d.In most cases,50%reduction in precipitation treatment significantly raised NO3--N content,50%increase in precipitation treatment significantly reduced available P content.Increased precipitation greatly increased urease activity on 180 d,240 d,and 360 d,while both increased and reduced precipitation increased invertase activity on 0 d,180 d,and 360 to certain extents;(3)Litter decomposition rate and C:N:P ecological stoichiometry were mainly affected by litter initial chemistry.During the whole decomposition time,litter decomposition rate was positively related to initial P concentration and negatively related to both initial C:P and N:P.Litter C:N:P ecological stoichiometry was also closely related to initial chemistry.Litter decomposition rate and C:N:P ecological stoichiometry were correlated with various soil factors in varying degrees:litter decomposition rate and C:N:P ecological stoichiometry were strongly correlated with soil conductivity,urease activity,catalase activity and invertase activity;(4)Litter C:N:P ecological stoichiometry was closely related to soil C:N:P ecological stoichiometry on 180 d,indicating that nutrient release in early decomposition time will pose direct influence on soil nutrient supply,and further pose great effects on the nutrient use of plants and also the structure and function in plant-soil system of desert steppe.