Influences Of Native Soil Available Organic Matter On Soil Priming Effects

In terrestrial ecosystems,soil is rich in carbon,and the decomposition of soil organic matter is a major source of atmospheric CO₂.Even small changes in the soil carbon pool may strongly change atmospheric CO₂ concentration,thus producing a positive feedback on global climate change.Numerous studies have shown that input of exogenous labile carbon to soil can become an important factor affecting soil organic carbon dynamics by accelerating or inhibiting the decomposition of soil organic matter,which is called"Priming effects".There are many factors affecting priming effect,mainly including biological factors such as soil microorganisms,plants,and soil animals,as well as abiotic factors such as soil structure,nutrients,water,and pH.Although the mechanisms responsible for the occurrence and maintenance of priming effects have been well understood,most previous studies only consider the impact of the input of exogenous available organic carbon on priming effects.It remains unclear how native soil available organic matter affect the direction and magnitude of priming effects.In this study,the mineral layer soil was collectd from a Chinese fir plantation in Qianyanzhou,Jiangxi.The concentrations of native available organic matter in the soil were adjusted by the vacuum soil solution extraction technology.Priming effect was quantified by adding ¹³C-labeled glucose at two different concentrations.We found that changes in the concentration of native available organic matter affected the native microbial biomass in the soil,which in turn altered the response of soil microorganisms to exogenous available organic carbon.When glucose was not added,soil with high concentration of native organic matter had relatively high soil microbial biomass carbon.The soil with native organic matter concentration of 200%has the highest microbial biomass carbon(110.00±4.62?g C g^-1 soil).After the addition of glucose,the soil microbial biomass increased,which promoted the decomposition of soil organic carbon and produced a positive priming effect.However,different glucose additions had no significant effect on the decomposition of soil organic carbon.At two glucose addition levels,the soil with the native available organic matter concentration of 50%showed significantly lower priming effect,the values were 1.00±3.10 mg C g^-1 SOC and 0.69±2.99 mg C g^-1 SOC,respectively.There was no significant difference in priming effects between other native available organic matter concentration treatments.The correlation between the concentration of native available organic matter and soil microbial biomass carbon,cumulative CO₂ emission from soil organic matter and the soil cumulative priming effect was analyzed,respectively,and the results showed that there was no significant linear relationship between them.At the same concentration of native available organic matter,in the two treatments with native available organic matter concentration of 0%and 100%,there was a significant linear relationship between exogenous glucose addition and cumulative CO₂ release from soil organic matter.These findings suggest that the influence of native available organic matter concentration on the soil priming effect may be much more complex than previously thought,and it is urgent to investigate it from the perspective of active microorganisms and soil enzyme activity.