Effects Of Changing Precipitation In Different Periods Of Growing Season On Soil Respiration Of Typical Steppe Ecosystems In Northern China

Global warming exacerbates hydrological cycles.The model predicts that the future precipitation will show greater changes.According to the pattern of precipitation in the northern China in recent decades,there are a decreased trend in summer precipitation.As an important carbon cycle pathway,the response of soil respiration to precipitation changes will greatly affect carbon sequestration in terrestrial ecosystems.In order to clearly understand the response of carbon cycle processes to more complex precipitation patterns in the future,it is necessary to conduct manipulative experiments in arid and semi-arid grassland ecosystems to study the effects of changing precipitation in different periods of growing season on soil respiration.In the typical grassland ecosystem of northern China,an experiment was conducted to change precipitation amount and its timing.The experimental treatments include: control,60% precipitation reduction in the early growing season,60% increase in the early growing season,60% decrease in the late growing season,60% increase in the late growing season,60% decrease in the growing season and 60% increase in the growing season.We mainly focus on:(1)Response of soil respiration to precipitation changes in different periods.(2)Response of biological and abiotic factors to precipitation changes in different periods of the growing season.(3)Biological and abiotic mechanisms that determine the effects of changing precipitation in different periods of the growing season on soil respiration.Increasing precipitation in the early growing season reduced microbial carbon and nitrogen content.In contrast,increasing precipitation in the late growing season had little effect on microbial carbon and nitrogen content.Both decreasing precipitation in the early and late growing season reduced soil respiration.Increasing precipitation in the early growing season increased soil respiration while increasing precipitation in the early growing season had no significant effect on soil respiration.The response of soil respiration to precipitation increase and decrease is asymmetrical.Compared with precipitation increase,soil respiration is more sensitive to precipitation reduction.The negative effect of decreasing precipitation in the early growing season on soil respiration is less than that of decreasing precipitation in the late growing season.In contrast,the effect of increasing precipitation in the early growing season on soil respiration was greater than that of increasing precipitation in the late growing season.The data of soil heterotrophic respiration in 2018 showed that decreasing precipitation in the late growing season reduced heterotrophic respiration while decreasing precipitation in the early growing season had little effect on heterotrophic respiration.In contrast,neither increasing precipitation in the early growing season nor in the late growing season affected heterotrophic respiration.Under precipitation reduction scenario,soil respiration was positively correlated with soil moisture both in the early growing season and in the late growing season.Soil respiration was negatively correlated with soil temperature in the late growing season,but not with soil temperature in the early growing season.Soil respiration was positively correlated with forbs cover,shrub and semi-shrub cover,soil microbial biomass carbon,soil microbial biomass nitrogen,belowground net primary productivity and community cover.Soil respiration was not significantly correlated with grasses cover,annual and biennial cover.Heterotrophic respiration was positively correlated with soil moisture,forb cover,microbial carbon content,microbial nitrogen content and community cover in the late growing season,but not correlated with soil moisture and soil temperature in the early growing season,soil temperature in the late growing season,grasses cover,shrub and semi-shrub cover,annual and biennial cover and belowground net primary productivity.Under precipitation increases scenario,soil respiration was positively correlated with shrub and semi-shrub cover and community coverage,and negatively correlated with soil microbial carbon content.Soil moisture in the early and late growing season,soil temperature in the early and late growing season,forb cover,grass cover,annual and biennial cover,soil microbial biomass nitrogen and belowground net primary productivity were not significantly correlated with soil respiration.In conclusion,the response of soil respiration to precipitation reduction is more sensitive than that to precipitation increase in typical grasslands in northern China.Compared with the decreasing precipitation in the early growing season,decreasing precipitation in the late growing season has a greater impact on soil respiration.In contrast,the effect of increasing precipitation in the early growing season on soil respiration was greater than that of increasing precipitation in the late growing season.The experiment highlights the effect of changing precipitation in different periods of growing season on terrestrial ecosystem carbon cycle,and providing data support for the study of the response of terrestrial ecosystem carbon cycle to changing precipitation pattern in the future.