Responses Of Leaf Litter Decomposition And Nutrient Release To Precipitation And Nitrogen Addition

Litter as the important component of the carbon and nutrient pools in the terrestrial ecosystem,which plays an important role in the process of material cycle and structure and function maintainment in the ecological system.The process of litter decomposition and nutrient release not only change the cycle of carbon and nutrient in the terrestrial ecosystem and the response to the environment changes,but also has important influence to the accumulation of soil organic carbon and the dynamics and effectiveness of main nutrients.Therefore,understanding of the general rule of nutrient release in the litter decomposition and the response characteristics of nitrogen in water environment,is the foundation to predict the process of terriestrial ecosystem biogeochemical cycle.Through long-term field simulation test in this study,with different leaf litters in the Loess Plateau(typical terrestrial ecosystem of leaf litter accounted for more than 60% of the total litter,select leaf litter)as materials,study on litter decomposition in carbon flow pathway and flux,and the influence of different soil water content and nitrogen addition on the litter decomposition characteristics,finally investigated the decomposition characteristics of mixed leaf litter.The main conclusions of this study are as follows:(1)The mass loss,litter decomposition constant(k),the release of CO2 and dynamics of element in the process of litter decomposition affected by annual precipitation type and the source of litter.The high precipitation can accelerate the decomposition of the Populus,Cedrus,P.orientalis,P.serrulata,S.psammophila,H.annuus,Z.mays,G.max Merr and O.sativa,while the low annual precipitation can accelerate the decomposition of B.latyphylla,Q.liaotungensis and M.pumila.(2)The release of CO2 in the process of litter decomposition affected by annual precipitation type and litter type,which was highest in P.serrulata and lowest in P.tabuliformis Carrière and G.max Merr in high precipitation,highest in S.psammophila and lowest in P.tabuliformis Carrière in normal precipitation,and highest in G.max Merr and M.pumila and lowest in P.tabuliformis Carrière and P.serrulata in low precipitation.(3)In high precipitation,the residual rate of C and N were lowest in maize and highest in P.tabuliformis Carrière,and the residual rate of P and K were lowest in maize and highest in Platycladus orientalis.In normal precipitation,the residual rate of C,N and P were lowest in G.max Merr and highest in Platycladus orientalis,and the residual rate of K was lowest in Populus and G.max Merr and highest in Platycladus orientalis.In low precipitation,the residual rate of C,N,P and K were lowest in M.pumila and highest in Platycladus orientalis.(4)Adding N decreased the decomposition of litter,which depended on annual precipitation type and litter type.Adding N has stronger impact on the decomposition of H.annuus and maize in high precipitation,of black locust,P.tabuliformis Carrière and millet in normal precipitation,and of Stipa orientalis and M.pumila in low precipitation.(5)Adding N significantly changed the release of nutrient of the decomposition of litter,which depended on annual precipitation type,litter type and element type.After 12 months decomposition,among the annual precipitation type,adding N can suppress the release of C,N and P,which was highest in Populus and lowest in P.tabuliformis Carrière and P.orientalis.Adding N can increase the release of K in S.capillata.and decrease the release of K in Z.mays,S.italica and M.pumila.(6)The effect of mixing leaf litters on decomposition depended on litter type and precipitation.Among the precipitation type,R.pseudoacacia+ Populus promoted decomposition and S.capillata and P.orientalis inhibited decomposition.In high precipitation,R.pseudoacacia+ Cedrus,S.capillata+ Q.liaotungensis,Populus+ Cedrus inhibited decomposition.In normal precipitation,S.capillata+ Q.liaotungensis inhibited decomposition.In low precipitation,R.pseudoacacia+ Cedrus inhibited decomposition.(7)The effect of mixing leaf litters on the release of nutrient depended on mixing litter type,precipitation and element type.The release of C decreased in R.pseudoacacia+ Cedrus andS.capillata+ Q.liaotungensis in high precipitation and in R.pseudoacacia+ Populus,R.pseudoacacia+ Cedrus,S.capillata+ Q.liaotungensis andS.capillata+ P.orientalis in low precipitation.While in normal precipitation,the effect of mixing leaf litters were not significant.R.pseudoacacia+ Populus,R.pseudoacacia+ Cedrus,Populus+ Cedruspromoted the release of N,and S.capillata+ Q.liaotungensis,S.capillata+ P.orientalis inhibited the release of N.Mixing litter promoted the release of P.R.pseudoacacia+ Populus,R.pseudoacacia+ Cedrus Populus+ Cedrus inhibited the release of K in high precipitation,but promoted those in low precipitation.