Effect Of N,P Addition On Decomposition Of Soil Organic Carbon In Alpine Meadows On The Qinghai-Tibetan Plateau

Plant growth is limited by the condition of nitrogen(N)and phosphorus(P)in terrestrial ecosystem.Because of its environmental conditions and the slow mineralization,plant growth is much more limited by the condition of nutrient in alpine meadows than other grasslands.N and P addition could increase plant productivity,and it could also influence the decomposition of soil organic carbon via altering the chemical structure of soil and plant.In this study,we investigated the effects of N and N+P fertilization on the chemical structure of soil and plant.We also analyzed the correlation between chemical structure and cumulative C mineralization in different stages.The results showed that:1.N,P addition significantly decreased the SOC.2.N10P10 addition significantly increased soil N content;N+P fertilization significantly increased soil P content.3.N fertilization decreased soil C/N(except N10)and C/P but the differences were not remarkable;N+P fertilization significantly decreased soil C/N and C/P.4.N+P fertilization significantly increased N content of Potentilla anserine,but decreased N content of Elymus nutans,Poa annua L(except N10P10),Geranium pylzowianum and Polygonum viviparum;N+P fertilization significantly increased plant P content except Oxytropis ochrocephala,and significantly decreased their C/N and C/P.5.N10P10 and N15P15 significantly decreased the lignin content of five species except Elymus nutans.6.N15P15 fertilization significantly increased cumulative C mineralization of soil in both earlier stage and later stage(except soil with Elymus nutans).In the whole process of decomposition,the effect of N,P addition on cumulative C mineralization was the same as the earlier stage.7.Cumulative C mineralization of soil was positively related to soil N,but negatively related to soil C/N,cellulose and lignin content;Except in the earlier stage of decomposition,cumulative C mineralization of soil with forbs was related to plant N,and C/N.Cumulative C mineralization was mostly influenced by soil N,soil C/N and the content of cellulose and lignin.Based on the above results,we drew the following conclusion:1.Plant growth is mosly limited by the condition of nitrogen in alpine meadow on the Qinghai-Tibetan Plateau.N fertilization at high rate(N15)could alleviate N contraintst.2.In the whole stage of decomposition,cumulative C mineralization was postively related to soil N,negetively soil C/N and content of lignin,but not related to microbial biomass.3.Because N,P addition generally decreased soil C/N and the content of lignin,it could increased cumulative C mineralization and stimulated the decomposition SOC and was not good to SOC accumulation.