| As the loess plateau is one of the regions with the largest fluctuation of global rainfall,the change of rainfall will inevitably cause the change of vegetation community structure and function,and then change the community's response to carbon exchange.At present,although there are studies on soil respiration characteristics in the loess plateau under the change of rainfall pattern,the long-term scale and fixed-point observation of soil respiration characteristics in the loess hills under a variety of rainfall gradients remains to be further studied.In this paper,the grassland community in loess hilly region of Ansai county,Shaanxi province was taken as the research object,set 7 precipitation gradients(DP60:-60%,DP40:-40%,DP20:-20%,CK:-0%,IP20:+20%,IP40:+40% and IP60:+60%).Based on the observation data of soil respiration of grassland community under different rainfall gradients in the loess hilly area from May to October 2019.The response of grassland soil respiration to simulated rainfall in loess hilly area was analyzed,the following conclusions were obtained:(1)The diurnal variation of soil respiration and soil temperature of grassland communities(Natural restoration communities and Bothriochloa ischaemum communities)under different precipitation gradient showed a single peak curve.During the observation period,the minimum values of soil respiration and soil temperature under different precipitation gradient appeared between 6:00-8:00.Most of the daily maximum soil temperature occurred between 14:00-16:00,and the maximum soil respiration occurred between 12:00-14:00.In the natural restoration community,the daily average soil respiration rate of IP20 has the smallest increase,and CK was the largest in August;the daily average soil respiration rate of DP60 has the smallest decrease,and CK was the largest in September.In Bothriochloa ischaemum communities,the daily average soil respiration rate of DP20 has the smallest increase,and CK was the largest in August;the daily average soil respiration rate of DP60 has the smallest decrease,and IP20 was the largest in September.(2)Monthly changes of soil respiration and soil temperature of grassland communities(Natural restoration communities and Bothriochloa ischaemum communities)under different precipitation gradient showed a single peak curve.The peak of soil respiration rate under precipitation gradient appeared in July,and the lowest values appeared in October.But the monthly changes in soil volumetric water content showed an upward trend.In natural restoration community,the average soil respiration rate of the whole growing season under different precipitation gradient was from IP20 > IP60 > CK > IP40 > DP20 > DP40 > DP60,and the average soil respiration rate of IP40,DP20,DP40 and DP60 was significantly lower than that of CK(P <0.05),and precipitation decrease(DP20,DP40 and DP60)significantly reduced the soil respiration rate.In Bothriochloa ischaemum communities,the average soil respiration rate of the whole growing season under different precipitation gradient was from IP60 > IP20 > IP40 > CK > DP20 > DP40 > DP60,the average soil respiration rate of IP60 was significantly higher than that of CK;the average soil respiration rate of DP40 and DP60 was significantly lower than that of CK(P <0.05).(3)The exponential model and the quadratic curve model were used to perform regression analysis on soil respiration rate and soil temperature,soil respiration rate,and soil volume water content in grassland communities(Natural restoration communities and Bothriochloa ischaemum communities)under different precipitation gradient from May to October.In the natural restoration community,there was a significant exponential relationship between soil respiration and soil temperature under different precipitation gradient(P <0.05)(except DP60),and a significant quadratic curve with soil volumetric water content(P <0.05).Compared with soil temperature,soil volumetric water content has relatively low explanatory power for soil respiration.In Bothriochloa ischaemum communities,there was a significant exponential correlation between soil respiration and soil temperature under different precipitation gradient(P <0.05)(except DP60 and DP40),and a significant quadratic relationship with soil volumetric water content(P <0.05)(except IP60).The explanatory power of soil temperature and soil volumetric water content on soil respiration rate was the same.(4)The diurnal variation trend of soil temperature before and after rainfall in the grassland community(Natural restoration communities and Bothriochloa ischaemum communities)under different precipitation gradient was consistent,but the diurnal variation of soil temperature after rainfall was small.Rainfall significantly increased the soil volumetric water content of each precipitation gradient,and the soil volumetric water content gradually increased with the increase of rainfall.Affected by rainfall,the daily maximum and minimum values of soil respiration of each rainfall gradient of grassland communities(Natural restoration communities and Bothriochloa ischaemum communities)changed.After rainfall,the soil respiration rate of each precipitation gradient increased significantly.In the natural restoration community,the largest increase was IP60 and the smallest increase was DP60.In Bothriochloa ischaemum communities,the largest increase was IP60 and the smallest increase was DP60.(5)The daily soil respiration rate,monthly soil respiration rate,and daily soil respiration rate after rainfall of grassland community(Natural restoration communities and Bothriochloa ischaemum communities)all showed Natural restoration communities > Bothriochloa ischaemum communities. |
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