| Litter decomposition is an important process of carbon and nutrient cycling in forest ecosystems.As the main decomposers of litters,the diversity and composition of microorganisms directly affect the decomposition process of litter.As pioneer colonizers,endophytes can preferentially occupy and utilize resources for their own better reproduction,and enter the saprophytic system with the apoptosis of plant tissues to participate in the decomposition process of litters.However,the mechanism of microbial community assembly involving endophyters in this process and its association with litter decomposition.Thus,Cinnamomum camphora,a common subtropical tree species,was taken as the research subject.The composition and diversity of microbial cmmunities during the growth and decomposition of C.camphora leaves were inverstigated by amplicon sequencing technology(including 16 S r RNA and ITS).Network analysis was used to get the keystone of microbial community in each period,and the microbiological mechanism of the decomposition process was further investigated by combining with the analysis of enzyme activity.Besides,the microbial phylogenetic combined the null model was used to analyze the endophytes and saprophytic microbial community assembly mechanism,respectively.The results of this study will help to understand the microbial community dynamics in the process of symbiotic turned to saprophytic of endophytic,as well as to get insight of the microbiological drivers of forest ecological processes(litter decomposition).The results are as follow:(1)The endophytic communities assemblely during the growth of C.camphora leaves were all dominated by stochastic processes,but endophytic bacterial communities were relatively more influenced by deterministic processes.The dominant taxa of the endophytic bacterial community were more stable and varied more uniformly than the endophytic fungal community.In contrast,the dominant taxa of endophytic fungal communities showed multiple patterns of variation.With the growth of leaves,the modularity of endophytic community structure was significantly enhanced,and the “small world” characteristics were gradually prominent.The key endophytic bacteria had better inheritance during the growth of C.camphora leaves,and their main keystone were Fibrella,Hymenobacter,and Spirosoma.The composition of key endophytic fungi varied greatly,among which the key endophytic fungi in child leaves were Acremonium,Bensingtonia,Colletotrichum,Exobasidium,Hyalopeziza,Simplocillium,Trichoderma,etc.The key endophytic fungi in mature leaves were Camarosporium,Chrysothrix,Exophala,Fusarium,Hydnopolyporus,Neonectria,Orbilia,Tubeufia,etc.In the senescent leaves,Chaetothyrina,Mycosphaerella,Exophala,Mycosphaerelloides,Phaeosphaeria occupied the key position in the community.(2)During the decomposition of C.camphora litter,the succession patterns of fungal and bacterial communities were significantly different.The relative abundance of the major taxa of the bacterial community,driven by nutrients,showed a trend of increasing and then decreasing.In contrast,the abundance of the major taxa of the fungal community showed polymorphism due to their different functions.There was a significant correlation between fungal diversity and soil available nitrogen content.Colletotruchum played a key role in the whole decomposition process.In addition,the community construction mechanism of different microbial groups showed completely different patterns.There is the bacterial community assembly was dominated by deterministic processes,while fungal community assembly was dominated by stochastic processes.(3)The decomposition process of C.camphora litter was strongly influenced by the external climate,and both mass loss and microbial enzyme activity decreased with the decrease of temperature.At different decomposition stages,the mass loss driven by different decomposition enzymes and influenced by environmental factors to different degrees.Among them,fungal diversity showed a strong association with mass loss only in the middle stage of decomposition.In contrast,the initial and last decomposition stages were mainly dominated by bacterial diversity and were strongly influenced by soil available phosphorus and litter quality,respectively.Meanwhile,we also found that most of the representative microbial were multifunctional,but only a few representative groups showed significant correlation with decomposition enzyme activity throughout the decomposition process,the correlation between endophytic and enzymes was significantly weaker than saprophytic,which implied that the dominance of endophytic was diminishing during the decomposition process.In conclusion,this study revealed that the community dynamics of endophytic bacteria during symbiosis and saprophylaxis in C.camphora leaves.In terms of dominant taxa,bacterial community composition is more stable than fungal community composition,and the keystone have better inheritance.As litter entered the saprophytic system,the bacterial community construction pattern gradually changed from stochastic process-dominated to deterministic process-dominated.On the whole,some endophytic bacteria played important roles in the decomposition of the litter,but their participation gradually weakened with the progress of decomposition. |
