Effects Of Long-term Nutrient Additions On Soil Microbial Respiration And Its Temperature Sensitivity In An Alpine Meadow On Tebetan Plateau

Soil is the largest carbon pool in terrestrial ecosystems.Soil microbial respiration releases about 60 Pg C to the atmosphere every year.Many experiments have shown that soil microbial respiration increased exponentially with temperature,which suggests that warming-induced increases in carbon dioxide release from soils represent may lead to positive climate feedback.As an important carbon pool of terrestrial ecosystem,the Tibetan Plateau is important in maintaining global carbon cycle.Due to the high altitude and cold climate,the vegetation and soil are very sensitive to the climate change.Currently,there are few researches on soil microbial respiration and its sensitivity to temperature change.This study took advantage of the research station of alpine meadow and wetland ecosystem in Lanzhou University,and conducted long term fertilization experiments,including NO(no fertilizer)?N5(N addition 5 gm-1)?N15(N addition 15 gm-1)?P0(no fertilizer)?P2(P addition 2 g m-1)?P8(P addition 8 g m-1)?NPO(no fertilizer treatment)?NP60(nutrient addition 60 g m-1)?NP120(nutrient addition 120 g m-1).We aimed to explore how soil microbial respiration and its sensitivity respond to increasing temperature under different fertilization treatments.The results as shown below:1)Long term application of nitrogen fertilizer and nitrogen&phosphorus combination,can significantly increase the content of soil nitrate(P<0.05);the application of phosphorus fertilizer can significantly increase the content of soil available phosphorus(P<0.05).2)Long-term nitrogen addition and nitrogen&phosphorus fertilizer significantly inhibited soil microbial respiration rate(P.<0.05),whereas P addition significantly increased soil respiration at high temperature(15?,25?)(P<0.05).3)Cumulative carbon soil respiration release significantly decreased long-term nitrogen and nitrogen&phosphorus addition(P<0.05),but significantly increased by long-term P addition(P<0.05).4)Long-term nitrogen and nitrogen&phosphorus addition,had no significant effects on temperature sensitivity(Q10)of soil microbial respiration(P<0.05),but long term P addition significantly increased the temperature sensitivity of soil microbial respiration(P<0.05).5)Long-term nitrogen addition significantly reduced the gram positive bacteria(GP)(P<0.05),but had no significantly effects on PLFAs(P>0.05);long term phosphate addition significantly reduced the soil gram negative bacteria(GN)and GP,fungi and arbuscular mycorrhizal fungi(AMF)content,but not the total PLFAs(P>0.05);long term nitrogen&phosphorus addition significantly reduced the GN?fungi,AMF content and the total PLFAs(P<0.05).6)The analysis of NMR,showed that nitrogen,phosphorus and nitrogen&phosphorus decreased labile carbon content,but increased recalcitrant carbon content.To sum up,temperature sensitivity of soil microbial respiration has different response to different fertilization treatment in the Tibetan Plateau alpine meadow.The results showed that nitrogen addition inhibited soil microbial respiration,while phosphorus addition stimulated soil respiration.Nitrogen and nitrogen&phosphorus addition may affect the temperature sensitivity of soil respiration through changing community structure and soil organic carbon structure.However applying phosphate fertilizers may more by changing the structure of soil organic carbon to influence soil respiration and its sensitivity to temperature.