Effects Of Pulse Precipitation On Soil Respiration And Carbon Accumulation In Typical Grasslands

The carbon exchange between the soil carbon pool and the atmosphere caused by soil respiration is an important part of the carbon cycle of the ecosystem,and its small changes will have a huge impact on the soil carbon pool and atmospheric CO₂concentration.Precipitation events are an important driving factor for the biogeochemical cycle of terrestrial ecosystems.Precipitation causes rapid changes in soil moisture and may cause large amounts of CO₂ to be released from the soil in a short period of time.This phenomenon is called “precipitation pulse effect”.After precipitation,the increase of the availability of water and nutrients rapidly increased the soil microbial respiration rate to several times the normal water state,resulting in a large amount of soil CO₂ release,which affected the soil carbon balance and ecosystem carbon cycle process to a certain extent.In arid or semi-arid areas where water is scarce,this effect may be more significant.The process of rapid increase in soil moisture and loss due to precipitation is relatively short,and the response of microorganisms to precipitation pulses is a rapid process and regulated by various environmental factors.Therefore,there are few studies on the process,mechanism and influencing factors of rapid CO₂ release after precipitation from soils affected by large-scale spatial range.In this paper,the grassland ecosystem in arid and semi-arid areas of China is selected as the research object,and the meadow grassland-typical grassland-desert grassland of Inner Mongolia Plateau,Loess Plateau and Tibetan Plateau with water,nutrients and temperature as the main limiting factors was investigated.And conduct research on the response of soil respiration and CO₂ release to pulsed precipitation.Using "mass,continuous,high-frequency soil respiration rate measurement equipment" to achieve a 48-hour continuous simulation test to obtain the peak value of the unit soil microbial respiration rate(R_soil-max),the unit organic matter microbial respiration rate peak(R_SOC-max),to reach the peak respiration Time(T_Rs-max),unit soil carbon accumulation amount(A_Rsoil)and unit organic matter carbon accumulation amount(A_RSOC)are studied and analyzed.The results show:?1?The soil microbial respiration of the experimental grassland responded quickly and strongly to pulse precipitation.The peak of soil respiration appeared within 0.39-6.75 h after adding water,which was 1.34-14.86 times of dry soil.and the accumulation amount of respiration in soil is 1.22-8.00 times of that of dry soil in 48 hours;?2?There are significant differences in the peak grassland soil respiration rate and carbon accumulation in the three sample zones.The maximum unit soil respiration rate and accumulation are shown as: alpine meadow grassland> alpine typical grassland> alpine desert grassland,Inner Mongolian temperate grassland> Temperate meadow grassland> Temperate desert grassland,there is no significant difference between the temperate meadow steppe and the typical grassland on the Loess Plateau,both higher than the desert grassland;?3?The main limiting factors of Inner Mongolia Plateau,Loess Plateau and Tibetan Plateau are different,and the corresponding precipitation pulse response modes are also different.The peak of organic matter respiration in Inner Mongolia Plateau(0.16⁰.25 mg C g SOC^–1h^–1)and Loess Plateau(0.10⁰.20 mg C g SOC^–1h^–1)is significantly higher than that in Tibetan Plateau(0.07⁰.15 mg C g SOC^–1h^–1).The time to reach the peak of respiration in the Inner Mongolia Plateau is the shortest?1.19².26 h?and the relative duration is short.The soil microorganisms in Tibetan are not sensitive to precipitation,and the low temperature slows the evaporation of water,which takes longer time to reaching the peak of soil respiration?4.15⁴.86 h?.The lack of nutrients in the Loess Plateau has affected the rapid response of soil respiration to moisture.?4?The spatial difference of soil carbon emission in the three plots mainly comes from the spatial heterogeneity of environmental factors.The factors that affect the cumulative release of soil carbon mainly include soil physical and chemical properties,microbial community structure and climatic factors.The soil with humid climate,high organic matter content,high clay particle content and low bacterial-fungal ratio has a higher carbon emission per unit of soil.As the degree of drought increases,the accumulation of carbon per unit of organic matter increases significantly,and desert grasslands are significantly higher than the other two grasslands.Grassland soil microorganisms in arid areas may formed an adaptive mechanism for rapid water use,so changes in precipitation patterns in arid and semi-arid areas will have an important impact on the soil carbon cycle in grasslands and even terrestrial ecosystems.