Diurnal Dynamic Characteristics And Driving Factors Of Soil Respiration In Typical Grassland Of Inner Mongolia

Soil respiration(R_S)is one of the key processes of the carbon cycle in terrestrial ecosystems.It has a large flux,rich substrate sources,and is very sensitive to the changes of soil temperature and moisture and other environmental factors.Under the influence of these environmental factors,soil respiration shows a significant diurnal dynamic change,and its diurnal dynamics have significant seasonal differences.The typical grassland in Inner Mongolia is an important part of Eurasian grassland.At present,most of the researches on soil respiration in this area are based on large time scales such as seasonal or inter-annual,while the research on the diurnal dynamics of soil respiration is relatively rare.It limits our understanding of the diurnal changes in soil respiration and its driving factors.This study was based on the analysis of soil respiration rate,soil temperature and moisture data measured by a soil respiration automatic monitoring system at an interval of 1 hour in the growing season from2016 to 2020.We mainly studied the method of parameterization of soil respiration diurnal dynamics,and the seasonal variation trend and driving factors of diurnal dynamic characteristics of soil respiration.In addition,we also studied the error of traditional manual measurement in estimating soil respiration flux and its response to climate change,and obtained the best period for manual measurement of soil respiration rate in this region.The main results were as follows:(1)In this region,soil respiration rate during the growing season has obvious diurnal dynamic characteristics with a“single peak”trend.Four parameter Gaussian equation is the best parameterized fitting model and the parameters of this equation can directly reflect four different characteristics of diurnal dynamics of soil respiration.(2)Driven by soil temperature or moisture,the diurnal dynamics of soil respiration have obvious seasonal changes.The daily minimum and maximum soil respiration rate,the amplitude of diurnal dynamics,and the time soil respiration reaches the peak value are higher in the middle of the growing season,but lower in the beginning and end of the growing season.(3)Traditional manual measurement method will overestimate the daily average value of soil respiration flux,and 6:00am to 10:00am is the best time to measure soil respiration rate in this region.Besides,the ratio of soil respiration means manually measured in different measurement periods to the daily soil respiration means has a significant negative correlation with soil moisture.It means that when studying the response of soil respiration rate to changes in precipitation,manual measurement methods will generate deviation to the research results,which may underestimate the response of soil respiration rate to reduced and increased precipitation.