| As the largest carbon pool in terrestrial ecosystems,soil fractions can be broadly divided into particulate organic carbon(POC,>53μm)and mineral-associated organic carbon(MAOC,<53μm).In recent years,an increasing work has highlighted the importance of fine root C inputs as sources to the soil carbon pool.Roots and mycorrhizal fungal hyphae are the main pathways for plant C to enter soil organic carbon pool compared to aboveground inputs.With intensified climate change,the subtropical regions of China maybe become more arid,which in turn will affect C inputs and decomposition(i.e.,root turnover and deposition).However,the relative contributions of roots and mycorrhizal fungi C inputs to soil organic carbon under different throughfall reduction treatments,and the effects of these C inputs on soil physicochemical properties,soil microorganisms and their priming effects on native soils are not clear.In this study,based on the Fujian Sanming Forest Ecosystem and Global Change National Field Scientific Observation and Research Station,mesh bags with different pore sizes(1 μm,45 μm,1000 μm)containing C4 soil were placed into different throughfall reduction plots(CT,-30%,-60%)for a one-year.We calculated the new C inputs from roots and mycorrhizal fungi as well as the change of native soil C,combined with the measurement of relevant soil physicochemical properties,soil enzyme activities and microbial communities to explore the effects of roots and mycorrhizal fungi on soil organic carbon formation and decomposition under the throughfall reduction.The results were showed as follows:(1)Higher DOC,DON and NH4+ concentrations resulting from root C input after throughfall reduction provided more C substrate and nutrients to microorganisms,which resulted in greater soil bacterial,fungal and total microbial biomass and soil enzyme activity.In contrast,lower soil bacterial,fungal and total microbial biomass and soil enzyme activity from new C input were found from mycorrhizal fungal source.(2)After one year of in-growth,C derived from roots was greater than C from mycorrhizal fungi in the control treatment,and root-derived C contributed more to newly sequestrated SOC,POC,and MAOC in the soil(63.0%,79.1%,and 77.8%,respectively).New SOC and MAOC derived from roots and mycorrhizal fungi were significantly lower after throughfall reduction,while POC derived from roots and mycorrhizal fungi did not change significantly.The amount of new SOC,POC,and MAOC derived from roots under the-30%and-60%treatments were greater than those from mycorrhizal fungi,and the contribution of root-derived C to new C in the soil remained significantly greater.(3)The greater contribution of roots during POC formation may be because roots contain more refractory compounds than mycorrhizal fungi and are more retained in the form of particles.For the greater contribution of roots during MAOC formation may be because of the higher DOC concentration due to root C than mycorrhizal fungi.Both new formed POC and MAOC after roots and mycorrhizal fungi inputs were significantly and positively correlated with DOC(p<0.05),and lower fine root biomass after throughfall reduction may lead to a decrease in DOC and consequently MAOC formation.(4)After one year of in-growth of roots and mycorrhizal fungi,the decomposition of native SOC in the control treatment was not different,and the decomposition was significantly lower after reduction of throughfall.The decomposition of native soil POC and MAOC after root C inputs(-11.8%and-34.2%)was significantly greater than those after mycorrhizal fungi inputs(-6.5%and-12.9%)in the control treatment,and the decomposition of native POC and MAOC after both C inputs diminished under throughfall reduction.(5)Compared to mycorrhizal fungal C input,the more intense decomposition of native POC and MAOC after root C input may be related to its leading to more microbial biomass.Regression analysis showed a significant negative correlation between the amount of native POC and MAOC alteration and DOC,MBC,bacterial and fungal biomass alteration(p<0.001).The weakening of decomposition after throughfall reduction was related to the reductions of C substrate and nutrients provided by root or mycorrhizal fungal C input and microbial biomass after throughfall reduction.In summary,roots play a more significant role in the decomposition of native organic carbon.Throughfall reduction decreased root or mycorrhizal fungal C input and the decomposition of native organic carbon.Throughfall reduction decreased the formation of new C by reducing fine root biomass and reduced the nutrient and energy supply to soil microorganisms,thus weakening the decomposition of native organic carbon.This is important for accurate prediction of soil-climate feedback under global climate change. |
