Observational Study On Characteristics Of Grassland Soil Respiration And Its Influencing Factors In A Semi-arid Regions

The soil respiration rate,soil temperature and soil water content of grassland ecosystem in semi-arid area of Loess Plateau were continuously observed by Li-8100A soil carbon flux analyzer.The diurnal and monthly variation of soil respiration were comprehensively analyzed,and the effects of hydrothermal factors on soil respiration rate were studied.The results show that:(1)The diurnal dynamics of soil respiration under typical weather conditions in dry growing season showed a single-peak curve,with significant diurnal variation in different weather conditions.The variation range(0.35-1.4?molm^-2s^-1)and the daily mean(0.64?molm^-2s^-1)in sunny days were larger than those in cloudy and cloudy days,and the maximum value in sunny and cloudy days generally appeared at 12:00 noon.However,there was a delay of 2 hours in overcast days.The daily mean values of the three typical weather conditions were close to the observed values of 9:00 and 17:00 to 18:00.After precipitation,the diurnal variation of soil respiration rate in sunny days was still"single-peak type".The maximum occurrence time of soil respiration rate in cloudy days was greatly affected by solar radiation,but there was no obvious diurnal variation in cloudy days.Compared with dry days,the diurnal variation of soil respiration rate after precipitation was significantly enhanced.The diurnal variation of soil respiration rate on sunny days in non-growing season still maintained a"single peak"curve,and the intensity was greater than that on cloudy days and cloudy days,and the maximum occurrence time of the latter two days was regulated by solar radiation.Negative flux appeared at night during the non-growing season,indicating that soil would absorb carbon dioxide during this period.(2)The seasonal variation characteristics of soil respiration rate were that it gradually increased from the vegetation returning stage,reached the maximum value in the peak growth stage(July-August),and then remained in a downward trend from the yellowing stage(September)to the non-growing season.The decline tended to be gentle in December,and reached the lowest value in the following January.Interannual comparison showed that soil respiration rate was stronger in the years with better hydrothermal conditions and stronger solar radiation in the growing season,while the interannual difference gradually decreased in the non-growing season.(3)When water was the limiting condition,soil moisture was the main controlling factor affecting the diurnal variation of soil respiration rate under three typical weather conditions,soil temperature and soil moisture were the main controlling factors affecting the diurnal variation of soil respiration rate after precipitation on sunny and cloudy days,respectively,while the effects of the two environmental factors on cloudy days were relatively low.Soil temperature and water content had a certain contribution to the diurnal variation in sunny and cloudy days in non-growing season,and the contribution of the two environmental factors had little difference.In cloudy days,soil water content had a more significant effect on the diurnal variation(R~2=0.78).(4)Soil temperature was the main controlling factor affecting the seasonal variation of soil respiration in the growing season,but the univariate model was not sufficient to fully explain the dynamic change of soil respiration in the growing season.The bivariate nonlinear model combined with soil temperature and water content could better fit the soil respiration rate and explain 74%of the variation.The fitting effect of non-growing season bivariate model is worse than that of soil temperature univariate model.(5)The variation pattern of the temperature sensitivity indices Q₁₀value in different years is similar.It starts to decrease from may to July when vegetation returns to green,and then shows an upward trend until yellowing stage.The Q₁₀values in the growing season from 2017 to 2020 ranged from 0.92 to 1.28,1.47 to2.40,1.51 to 2.16,and 1.33 to 1.79,with average values of 1.10±0.18,2.03±0.65,1.74±0.25,and 1.52±0.16,respectively.