Effects Of Phosphorus Application Rate On Soil Respiration And Temperature Sensitivity Under Straw Returning

Soil respiration（Rs）is one of the key processes in the global carbon（C）cycle and the main way of soil C output.Accurate estimation and reasonable regulation of soil respiration and its temperature sensitivity are essential to fully understand the global C cycle and its role in climate change.Carbon and nutrient availability are important factors affecting soil respiration and its temperature sensitivity,but the responses of different components（autotrophic respiration,Ra,and heterotrophic respiration,Rh）to these factors may be inconsistent.In agricultural ecosystems,the studies on the response of soil respiration components and temperature sensitivity to C and nutrient availability are limited,which affects the accurate simulation of process-based C cycle model.In this study,a field experiment was carried out on a typical wheat-maize cropping pattern in North China with straw returning（no straw returning,S0,and straw returning,S1）combined with phosphorus（P）fertilizer（no P fertilizer,P0,low P fertilizer,P1,medium P fertilizer,P2,and high P fertilizer,P3）treatments.By regularly monitoring soil respiration,soil temperature and moisture,soil carbon fractions,soil microbial properties,and plant photosynthetic characteristics,the response and internal mechanism of soil respiration components and their temperature sensitivity to straw returning and P application were explored,expecting to provide parameters for C cycle model and provide basis for farmland soil C pool management.The main results are as follows:（1）Straw returning averagely increased Rs,Rh and Ra rates by 25.31%,19.77%and44.16%,respectively,in the two growing seasons.The effects of P application rate on soil respiration components were different with straw treatments and respiration components.Under the condition of without straw returning,P application rate tended to increase Rs rates,and low P application rate increased the most in maize season.There were no significant differences in the average Rs,Rh and Ra rates among different P levels under straw returning.（2）Under the condition of without P application,straw returning significantly increased the temperature sensitivity of soil respiration components,and the Q₁₀value of Rs,Rh and Ra increased by 35.30%,41.60%and 31.13%,respectively.However,its effect on the temperature sensitivity of Rh was not significant under P application.Under the condition of without straw returning,P application increased the temperature sensitivity of Rs and Rh,and the effect of low P application rate was the most obvious.The temperature sensitivity of Rh was negatively correlated with P application rates under straw returning.（3）Photosynthetic rate of straw returning treatments was 39.46%and 43.32%higher than those of non-straw returning treatments at wheat and maize filling stages,respectively,and intercellular CO₂concentration of straw returning treatments was 32.28%and 11.01%higher,respectively.Straw returning can not increase sucrose and starch contents in leaves,and it had a significant decrease effect on that under low P application rate.The photosynthetic rate and sucrose content of wheat leaf were significantly increased by P application at grain-filling stage,but starch content was significantly decreased.P application reduced photosynthetic rate,sucrose content and starch content in leaves at maize grain-filling stage.（4）Straw returning increased the contents of easily oxidized organic C,particulate organic C and the activities of C-related extracellular enzymes,and increased the soil microbial biomass C,N and P by 30.77%-50.90%,16.56%-78.55%and 8.50%-17.69%,respectively.Under different P application rates,soil microbial biomass C and N were the highest under medium P application rate,particularly in wheat season.The effects of P application rate on soil C-related enzyme activity and microbial community diversity varied with straw treatments.（5）Soil heterotrophic respiration rate is closely related to soil cellobiose hydrolase activity,plant sucrose content and soil moisture,while soil autotrophic respiration rate is mainly affected by soil temperature and soil microbial biomass nitrogen.