| Forest recovery has been a hot subjest in restoration ecology. Although ecologists have a knowledge and understanding to plant species selection, community building, soil nutrients as well as other basic physical and chemical properties of soil in the process of forest ecosystem restoration. It is not clear about the quantitative extent to which clear cutting affects bacterial and archaeal community diversity and composition. It is also unclear to what extent the observed shifts in community structure and function are dependent on the altered soil properties. microorganisms mediate biogeochemical cycles of carbon and nitrogen various metals, and play critical roles in forest ecosystem structure and function. Understanding the change and regulatory mechanisms of soil microbial community composition, structure, function and diversity in restoration ecology is critical to scientifically identify the ecosystem fuction and community assembly processes of soil microbial community in the different recovery stages or recovery stand types. In our study, we examined the effects of forest successional restoration and artificial restoration on soil bacterial and archaeal community composition, structure, diversity and community assembly processes using high throughput 16 S rRNA gene sequencing. We aim to understand the recovery mechanisms of soil micrbobial communities and the effect of tree species mixture on soil microbial coummunity structure, function and stability. The main conclusions in this paper are as follows:This study utilized a chronosequence of developing typical virgin vegetation forest ecosystems, rehabilitated after clear cutting(“3-year-old rehabilitation”, “35-year-old rehabilitation” and “intact primary forest”), to examine changes in soil prokaryotic community composition, structures and diversity. Our results demonstrated that archaea accounted for 10.9?13.4% of total prokaryotes, and no significant shifts of archaeal community composition and structure occurred in response to clear cutting. Our results demonstrated that clear-cutting significantly altered soil bacterial community structure, and became similar to those of surrounding intact primary forest with natural regeneration. These findings suggest that bacterial community dynamics may be predictable during the natural recovery process. The ‘restoration ecology’ theory, which assumes that ecosystem degeneration is not irreversible and the recovery after disturbance will proceed toward a primary, unperturbed-state, is true in this soil bacterial case. It indicates that the bacterial communities could rebound to its original state after clear cutting disturbance under certain mechanisms. In fact, the time frame we present for the recovery of soil bacterial community may require at least 30 years.Clear cutting decreased bacterial community diversity in the shrub-grassland, but after 35-year recovery, these parameters were significantly higher in the secondary forest than those in primary forest. This supports the intermediate disturbance hypothesis proposes that species diversity should be low after high disturbances, very low disturbances, species diversity should increase to a maximum under appropriate disturbances.Bacterial and archaeal community assembly processes were assessed by net relatedness index(NRI) and nearest-taxon-index(NTI). There were significant shifts in NRI and NTI values in response to clear-cutting for bacteria, which indicated clear-cutting significantly increased niche-based processes. In the secondary forests, however, both indices were not significantly different compared to the intact primary forest. Redundancy analysis revealed that soil pH had a weak effect on the bacterial community composition among all the measured soil chemical parameters, of which NO3--N and C/N have an important role in shaping soil bacterial communities. clear-cutting increases the importance of niche-based processes working as a dominant role of environmental filtering due to the low or extreme resource environment)s induced by clearcutting.There were no significant shifts in NRI and NTI values in response to clear-cutting for archaea. Redundancy analysis showed that soil factors had no effects on archaeal community composition.The results of soil microbial communnity composition and structure under pure plantation of Pinus massoniana(PM), pure plantation of Castanopsis hystrix(CH), pure plantation of Eucalyptus urophylla(ES), pure plantation of Erythrophleum fordii(EF), pure plantation of Gmelina Arborea(GA), mixed plantation of Pinus massoniana and Castanopsis hystrix(MPC), mixed plantation of Eucalyptus urophylla and Erythrophleum fordii(MEE) and mixed plantation of Gmelina Arborea and Erythrophleum fordii(MEG) suggested: the overall microbial community structure was largely altered in the mixed plantations, the community structure form the three mixed plantations became similar. The results of permutation-based multiple regression on distance matrices the glucose of soil DOC, soil C mineralization, free amino acids, NH4+-N, AP, NO3--N, DOC, C/N, and phenolics had a significant effect, of which LMW compounds and C mineralization was the strongest factor, whereas other variables(that is, pH, TOC and TN) revealed weaker effects on the community composition. Network interactions between environmental parameters and microbial taxonomic community nodes suggested that glucose of soil DOC and soil C mineralization play an important role in maintaining the network structure and topology.To understand the ecological consequences of altered bacterial communities, We used linear regression to analyse the relationship between the relative abundance of these largely changed phylum and soil properities. There was a significant, positive, relationship between soil C mineralization rate and the relative abundance of Proteobacteria and Bacteroidetes, while the abundances of Acidobacteria were negatively correlated with C mineralization rates. our results demonstrated the changes of soil bacterial composion caused by tree species mixture would alter soil carbon cycling processes.Soil bacterial communities stability were significantly higher in MPC, MEE and MEG than their corresponding PM CH, ES, EF and GA. Phylogenetic diversity was significantly higher in the mixed plantationes than pure plantationes. Shannon’s indices and species richnesss did not show significantly differ among the different plantations(including pure and mixed plantations). Futhermore, NRI and NTI values in the mixed plantation MPC, MEE and MEG were dramatically lower than that in pure plantations PM, CH, ES, EF and GA, meaning there were distantly related species and more niches in mixed plantation. However, no significant difference on species richess between pure and mixed plantations was observed. This case only occur under one condition that there were more niche overlaps in pure plantations. Consistent with this is the finding that molecular ecological networks(MENs) suggested that, indeed, more overlaps were found in pure plantations.The relationships between phylogenetic structure and soil bacterial the difference niche differentiation of cummnities explain the variation in ecosystem function and stability rather than species richness,suggesting that tree species mixture increased the community stability by increasing ecological niche differentiation. |
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