Effect Mechanism Of Precipitation On Soil Respiration In A Desert Steppe In Northwest China

The change in precipitation pattern is one of the main aspects of global change.Being an important approach releasing CO2 from soils into atmospheres,soil respiration responding to changing precipitation may affect the carbon cycle in terrestrial ecosystems,and further will have a feedback on global change.However,there still lacks a consistent conclusion on how soil respiration responds to the changing precipitation,especially under extreme precipitation condition.To provide data supports for scientifically assessing carbon sink in desert steppes and regional carbon emission under global change,a field experiment involving five precipitation treatments(50%reduction,30%reduction,natural,30%increase,and 50%increase)was conducted in a desert steppe of Ningxia in 2014,the temporal dynamics(daily and monthly)of soil respiration rate were monitored from June to October in 2020,the effects of precipitation on soil properties(physical,chemical and biological)and plant community characteristics(biomass,diversity and C:N:P ecological stoichiometry)were explored in August,the relationships of soil respiration rate with soil properties and plant characteristics were analyzed too.The main findings are as follows:(1)Soil respiration rate increased first and then decreased in term of daily and monthly dynamics under the changing precipitation regimes.The peak value of daily dynamic approximately appeared at 9:30 or at 12:00,while that of monthly dynamic approximately appeared in late August or in early September.Compared with the natural precipitation,the decreasing precipitation tended to weaken soil respiration rate,while the increasing precipitation tended to increase soil respiration rate,especially the 50%increase in precipitation.However,the degrees of both influences were depended on the daily and monthly measuring times.In daily measuring time,generally,the decreasing precipitation had little effect on soil respiration rate,whereas the increasing precipitation had a greater effect.Accross the whole growing season,there was little difference in the decreasing precipitation impact among the measuring months,whereas the effect of the increasing precipitation was larger in the early stage than that in the late stage;(2)The influence of precipitation on soil properties was different.Compared with the natural precipitation,the 50%reduction in precipitation significantly reduced soil water content,organic carbon content and C:N,whereas it increased NO3--N concentration,microbial biomass carbon content and C:N.The 30%increase in precipitation significantly increased soil water content and electrical conductivity,whereas it decreased temperature.The 50%increase in precipitation significantly increased soil water content and electrical conductivity.In contrast,both the reduction and the increase in precipitation had no significant effects on other soil properties;(3)Precipitation had a great impact on plant biomass,whereas little impact on diversity and C:NP ecological stoichiometry.Compared with the natural precipitation,the 50%reduction in precipitation significantly reduced plant biomass,whereas it increased total nitrogen concentration.The 30%reduction in precipitation significantly reduced plant biomass.The 30%increase in precipitation significantly increased plant biomass.The 50%increase in precipitation significantly increased plant biomass and Patrick richness index,whereas it reduced total nitrogen concentration.In contrast,both the reduction and the increase in precipitation had no significant effects on other plant characteristics;(4)Under the changing precipitation regimes,soil respiration rate had different degrees of relationships with soil properties and plant characteristics.Soil respiration rate had a significantly and positively linear relationship with soil water content,temperature,electrical conductivity,organic carbon content,C:N,C:P,sucrase activity,urease activity and phosphatase activity,whereas a significantly and negatively linear relationship with NO3--N concentration.In contrast,it had not a significantly linear relationship with other soil properties.Soil respiration rate had a significantly and positively linear relationship with plant biomass and Patrick richness index,whereas an insignificant relationship with other plant characteristics.Further regression analysis showed that soil water content,soil C:N,soil sucrase activity,plant biomass and Patrick richness index had extremely and significantly positive effects on soil respiration rate.These results above indicate that,the decreasing precipitation has little effect on soil respiration rate in the studied desert steppe,reflecting the adaptability of soil respiration to arid environments;the increasing precipitation(especially extreme precipitation condition)may promote plant growth and microbial activity by improving soil water availability,stimulating soil enzyme activity,and regulating soil ecological stoichiometry,consequently stimulating soil respiration and carbon emission in desert steppes.