Response Of Priming Effect And Mechanisms To Leaf Litter And Phosphorus Addition On In Pinus Massoniana Forest Soils

Priming effect(PE)plays a critical role in the storage and turnover of soil organic carbon(SOC)in forest ecosystems.The intensity and direction of priming effect,induced by litters,usually depend on the availability of limited nutrient(e.g.,phosphorus,P),especially in subtropical highly weathered forest soil.However,how phosphorus and litters addition affect soil priming effect in this region is far from clear.This study investigated the effects of litter and phosphorus addition on SOC mineralization and priming effect in subtropical low-phosphorus soils,in order to provide a theoretical basis for the study of carbon cycle in forest ecosystems in this region.Three kinds of ¹³C-labeled litter(Pinus Massoniana,Michelia macclurei and Liquidambar formosana)and P(KH₂PO₄)were added to P.Massoniana forest soil.Soil incubation of treated and control soils was conducted for 125-days in the laboratory.The physical and chemical properties,microbial properties and priming effect of the soils were determined after incubation,and the processes and mechanisms of leaf litter and phosphorus input affecting soil priming effect in subtropical forests were analyzed.The following main results were obtained:The results showed as follows:(1)The addition of leaf litter of P.Massoniana,M.macclurei and L.formosana increased soil cumulative CO₂ emissions by 24.64%,21.13%and 17.78%,respectively.This produced a strong positive priming effect at the early stage of incubation,then the priming rate decreased rapidly to a negative effect,and then gradually turned to a positive effect at the later stage of incubation.The intensity of cumulative priming effect was showed that P.Massoniana>M.macclurei>L.formosana;phosphorus addition decreased the intensity of priming induced by M.macclurei and L.formosana leaf litter.(2)Litter addition decreased the content of available nitrogen(AN),but increased the contents of microbial biomass nitrogen(MBN)and microbial biomass phosphorus(MBP).In addition,the activities of cellulolytic enzyme(CBH),?-N-acetylglucosaminosidase(NAG),acid phosphatase(ACP)and peroxidase(PEO)were significantly increased at the initial stage of incubation.Compared with the initial stage of incubation,the ratio of oxidase to hydrolase increased by 49.04%?97.25%at the end of incubation.Phosphorus addition increased the contents of total phosphorus(TP),available phosphorus(AP)and MBP,but inhibited the ACP activity induced by phosphorus addition in the early and middle stages of incubation.(3)The results of phospholipid fatty acid(PLFA)and ¹³C-PLFA showed that the ratio of fungi to bacteria and gram-positive bacteria to gram-negative bacteria increased at the end of incubation.However,¹³C from litter leaf litter was mainly used by fungi,Gram-positive bacteria and Gram-negative bacteria at the late decomposition stage.The results of high-throughput sequencing showed that the addition of leaf litter significantly changed the community structure of fungi at the early and middle stages of incubation,and the richness and community structure of fungi changed with incubation time.In addition,the addition of leaf litter and phosphorus promoted the enrichment of Sordariomycetes species.(4)The results of random forest model(RF)and stepwise regression analysis showed that soil C/N ratio,C/P ratio and N availability were important abiological factors,while the contents of MBN,MBP,NAG activity and the ratio of Gram-positive bacteria to negative bacteria were important biological factors affecting the change of priming effect.In conclusion,the following conclusions can be drawn:(1)the quality of litters influenced the intensity of the priming effect,and phosphorus addition may reduce the priming effect induced by litter with high ratio of C/P by relieving microbial"P mining".(2)According to the change of the direction of priming effect over time,it can be divided into three stages:"strong positive priming"in the early stage,"negative priming"in the middle stage and"positive priming"in the late stage.The microbial mechanism of priming effect is different in different stages and is accompanied by the change of microbial growth strategy and resource acquisition strategy.(3)Our results suggest that phosphorus availability is one of the important factors affecting soil carbon mineralization in subtropical low phosphorus forests,and the contribution of phosphorus should be considered in the regional carbon cycle prediction model.