Dynamic Of Pasture Soil Carbon Sequestration And Change Mechanism Of Microbial Community Composition And Function In Crop-pasture Rotation System

Global change has a profound impact on sustainable development of human economy,society and ecosystem.Soil is the largest terrestrial sink for carbon?C?on the planet,enhancing C storage in soils contribute to the mitigation of global climate change.Change of land use and management is the important factor influencing soil C sequestration or emission.Crop-pasture rotation is a predominant land use strategy for sustainable agriculture in temperate areas of the world.The pasture phase in crop-pasture rotation is beneficial for reducing the soil degeneration caused by previous tillage,improving soil physicochemical and biological conditions,and increasing soil C concentrations.Revealing the temporal dynamics of soil C pools and the mechanisms in pasture rotations is the key to fully understand and maintain this sustainable agricultural production system under global change background.In this study,a space-for-time approach was used to assess the response of soil C sequestration and microbial community composition during a five-year grazed pasture rotation following three years of low input vegetable production on an organic farm in the central east of the United States.The objectives of this study were to measure the change in soil organic carbon?SOC?and nitrogen?N?of different soil organic matter fractions in pastures 1 to 5 years old,evaluate the effect of pasture rotation year on mineralization of the labile carbon pool,analyze the effects of time in pasture and seasonal changes on the microbial biomass and community,and explore the relationships between soil microbial and physicochemical parameters and C sequestration and stabilization.The main findings are as follows:1.Particulate organic matter?POM?sensitively indicates the change of soil organic matter.Soil organic matter increased gradually with increasing pasture rotational year mainly due to increasing proportion of POM in soil organic matter.SOC increased 20.6%over 5 years in pasture rotation,and close to that observed in the permanent pasture.Particulate organic matter C?POC?and non-POC fractions increased 53.5%and 17.6%,respectively.Similar trend was observed for the content of soil organic N in pasture rotation.Soil organic N accumulation promoted the SOC stabilization.2.Results from the lab-incubation indicated that the carbon mineralization?CM?rates declined with soil incubation time.After an initial incubation period,during which CO₂release rate was relatively high,CM rate reduced and stabilized in each pasture rotation year until the end of the experiment.The potential release of CO₂ significantly increased after 4 years pasture rotation and became similar to the average level of permanent pasture.Average soil CM rate in the fall was lower than that in the spring,summer and winter.Pasture rotation enhanced soil CM potential,promoted C cycling and availability,delayed half-life time of SOC,and resulted in the soil C pool stabilization.3.Soil total microbial biomass and the diversity of phospholipid fatty acid increased over pasture rotation years,with declining gram positive to negative ratio and raising fungi to bacteria ratio.Microbial community composition changed after 4 years of pasture rotation and became similar to the microbial community of permanent pasture.Both CM and POM were the key factors driving the assemblage and structure of microbial communities.The change of soil microbial community across pasture rotation affected SOC sequestration potential and availability.The difference of microbial community composition among seasons resulted in the variation of C mineralization potential.4.SOC pool storage and stability were enhanced over 5 years pasture rotation.The change of soil physical,chemical,and biological properties closely correlated between each other.The factors with higher correlation to C storage were ranked as soil bacteria,total microbial biomass,actinomycetes,bulk density,sand proportion,POM,available phosphorus,fungi,and cumulative CM.The change of soil physical structure,chemical composition,and microbial community in pasture rotation showed different strength of direct or indirect effects on C pool stability.The accumulation of non-POM and fungi biomass significantly correlated to the enhancement of SOC stabilization.Based on above findings,the dynamic process and mechanisms of soil organic carbon affected by pasture rotation have been preliminarily revealed.However,the nature of carbon sequestration and stabilization,and the exact pathway of influence from correlative factors still wait for further study.