Response Of Soil Phosphorus To Nitrogen Addition At Different Levels In Saline-alkali Grassland

Since the industrial revolution there has been a global increase in reactive nitrogen from industrial nitrogen fixation and the burning of fossil fuels,A large amount of these nitrogen compounds will lead to the continuous increase of atmospheric nitrogen deposition,which will have a huge impact on the relatively nitrogen-deficient grassland ecosystem.The availability of soil phosphorus was low,however,the effect of nitrogen deposition on soil phosphorus in saline-alkali grassland ecosystem is still unclear.To investigate the response of soil phosphorus to nitrogen addition in saline-alkali grassland.Eight treatments with different nitrogen levels(0,1,2,4,8,16,24 and 32 g N·m^-2·a^-1)were setted in the Youyu Loess Plateau Grassland Ecosystem Research Station in April 2017.In this study,nitrogen was applied at the beginning of each month during the 2018-2020 growing season（May-September）.Soil samples were collected from August 2018 to 2020,and soil total phosphorus（TP）,available phosphorus（AP）,microbial biomass phosphorus（MBP）,soil p H,soil anion,soil temperature（ST）at 10 cm depth,soil microbial（SM）,and soil microbial biomass carbon（MBC）and nitrogen（MBN）were analyzed.The main results are as follows:（1）Soil TP,AP and MBP were not significantly affected by nitrogen addition at different levels,and TP and AP showed a decreasing trend with soil depth increasing.（2）The inhibition effect of nitrogen addition on AP_sen increased gradually.N2 treatment had the strongest sensitivity to MBP_sen,and promoted MBP_sen.With the increase of nitrogen level,AP_sen and MBP_sen gradually weaken.MBP_sen。（3）Soil TP was negatively correlated with soil p H（P<0.01）,and positively correlated with CO₃^2-and microbial biomass nitrogen（P<0.05）.Soil AP had a significant positive correlation with soil p H（P<0.05）,and a significant negative correlation with soil ST and SM（P<0.05）.Soil MBC was significantly positively correlated with ST,SM,MBC and MBN（P<0.05）.（4）The results of redundancy analysis showed that MBN,MBC,Sm and CO₃^2-had a very significant explanatory degree（P<0.01）.