| As a form of interference,forest gaps could promote the healthy and sustainable development of forest ecosystems.The artificial formation of gaps in the low-efficiency forest of weeping cypress can effectively increase biodiversity,enhance community succession and improve the ecological services in the hill region of the central Sichuan Basin.Fine root degradation is one of the important underground ecological processes in forest systems.Fungi are major contributors to plant degradation.Forest gaps affect the degradation of plant litter,but the effects of forest gap locations on fungal community structure during degradation and on the degradation of fine roots are not fully understood.In this study,the fine root degradation were monitored in different gap locations(gap center GC,gap border GB)of artificial forest gap(200 m~2)which were formed by the national“12th Five-Year”science and technology support project,and set a location in closed canopy(CC)as the control.A 2-yr positioning research of the decomposition of the fine root of 3-yr established Toona senensis forest which were introduced to artificial gaps as native broadleaf tree were carried out among gap locations.Fungal communities during each decomposition stage were obtained by using Illumina Miseq sequencing technique.Bioinformatics statistical analysis(Principal coordinated analysis,random rermutation test,permutational multivariate analysis,Redundancy Analysis,Mantel and partial Mante test,co-occurrence network analysis)were conducted in R to analyse the rate of fine root degradation,composition and variation of fungal community,community diversity and molecular network relationships combined with the environmental factors(physical properties of soil and nutrient content of fine root tissue).We aimed to reveal the effects of forest gap locations on fungal community of fine roots of Toona sinensis during the degradation.The main results were showed as below:(1)Gap locations significantly affected soil micro-environmental conditions(p<0.05)as well as environmental factors.Abiotic factors(like soil properties)were greatly affected by the gap locations,while biological factors(like nutrient content of fine root tissue)showed little effects by different gap locations.Soil temperature and soil water content showed obvious seasonal fluctuations and significant differences among gap locations(p<0.01).Soil p H showed little varition during the decomposition,but the difference among the gap locations was significant(p<0.05).The contents of TNP,SOC and STN varied with the degradation processes among gap locations,and there were significant differences at different stages(p<0.05).Gap locations influenced the degradation rate of fine roots of Toona sinensis differentially,and the degradation rate of fine roots in GB was significantly higher than that in GC and CC at the middle and the end of the experiment periods(p<0.05).The rates of degradation of GC and CC sites were basically the same.(2)At the phylum level,all the fungal communities were dominated by Ascomycota and Basidiomycota,and the relative abundances of fungal communities showed non-significant differences among different gap locations.Meanwhile,forest gap locations influenced the compositions and the relative abundances of the fungal communities.Eurotiales,Sordariales,Hypocreales,Chaetothyriales,Pezizomycotina＿ord＿Incertae＿sedis,Agaricales,Microascales were the dominant taxa with relative abundances>1%among different gap locations at the order level.Gap locations influenced the relative abundances of dominant spices differently.The relative abundance of Agaricales differed significantly between GB and CC(p<0.05);Chaetothyriales showed significant differences between GB and CC,GC and GB(p<0.05).The relative abundances of Microascales,Sordariales and Hypocrees showed different trends among gap locations,indicating that the three orders were sensitive to environmental conditions.The relative abundance of Eurotiales was highest,but there were no significant differences among different gap locations.Penicillium、Aspergillus、Chaetomium、Dactylonectria、Staphylotrichum were the dominant taxa with relative abundances>1%among different gap locations at the genus level.Staphylotrichum was a dominant specice with relative abundance>1%at all three locations.The relative abundances of Penicillium and Aspergillus showed significant differences among gap locations(p<0.05).The genera of Chaetomium,Dactylonectria,and Staphylotrichum were also with relative abundances>1%,moreover,they did not show significant differences among different gap locations during the experimental period of 2a,indicating that these three genera were not very sensitive to environmental condition changes.Most of the OTUs with relative abundances>1%were mainly from the Ascomycota,affiliated with Chaetothyriales,Eurotiales,Sordariales and Microascales.Some taxa were affiliated with Agaricales of Basidiomycete among different gap locations.(3)The alpha diversities of fungal communities showed nonsignificant differences among different gap locations.This might be due to the subtle differences in spatial scales of the gap locations in cypress plantation forest in the hill region of the central Sichuan Basin.However,environmental factors showed different influences on alpha diversity indices.Forest gap locations influenced the beta diversity of fungal community significantly(p<0.05).Due to the heterogeneity in local environments,the beta diversity of fungal community was highest at GB;the number of endemic species was lowest at GB,and the number of endemic species was highest at GC.The number of endemic species was lowest at GB,indicating that the local environments at GB had a wide range of niche supporting fungal communities.The soil properties at GC created relatively harsh environments where only some adaptable fungi could survive.This could explain the highest number of endemic species at GC.Forest gap locations influenced the beta diversity of fungal community by changing the local environments,and there was a positive response to the soil properties heterogeneity of beta diversity of fungal community.Mantel and partial Mantel test showed that p H、SWC、ST、SNP、STN were positively correlated with the fungal community.The suitable micro-environment at GB could provide good resources for the survival and colonization of fungal community,and the heterogeneity of fungal community was highest among gap locations.Fungi were strictly heterotrophic,and they heavily depended on the nutrient availability in soil.Based on the RDA analysis,gap locations influenced the beta diversity of fungal community by changing the heterogeneity of local environment factors.Compared with soil properties,there were little correlations between the nutrient content of fine root tissue and gap locations,while the nutrient content of fine root tissue could explain the variety of fungal community during the decomposition stages.(4)Ecological networks at different gap locations clearly showed greater network modularity than the corresponding random networks,and significant differences among gap locations.The modularity at GB was lowest,and GC was highest.Fungal co-occurrence patterns were clearly distinct at different gap locations.The network of GB had the most nodes and edges,followed by those of CC and GC,indicating that the fungal co-occurrence was stronger at GB than those at other locations.In summary,forest gap locations influenced soil properties and the fine roots decomposition of Toona senensis due to the micro-environmental heterogeneity,e.g.solar radiation and rainfall.The degradation process was the results of microbial-soil-plant interactions.The heterogeneity of local environments at different locations significantly influenced the compositions and relative abundances of fungal taxa.The diversity of fungal communities and networks showed significant differences among different gap locations.Due to the differences in ecological effects caused by the heterogeneity of forest gaps locations,the ecological effects embodied by the location of the edge of forest gaps are moderately considered,which was conducive to enhancing biogeochemical cycle and energy flow in forest gaps.These effects will have positive significances for the comprehensive improvement and upgrading of cypress low-efficiency forests. |
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