Community Composition And Diversity Of Soil Nematodes And Microorganisms In Different Forest Chronosequences

Plants and soil organisms are tightly associated,and plants can provide energy for soil organisms.Thus,changes in the quantity and quality of plant resources input to belowground ecosystems at different spatial and temporal scales may affect the composition community and diversity of soil organisms.Nematodes and microorganisms have extremely high abundance and richness in soil,they occupy several trophic levels in soil food webs,and play a key role in biogeochemical cycles and energy transfer.A few case studies have found significant differences in the community composition and diversity of soil nematodes and/or microorganisms with chronosequence of vegetation.However,it is not clear whether the above findings are universal at a large spatial scale.Therefore,we selected three nature reserves in China(Dinghushan,Baotianman and Changbaishan)with different vegetation types and climate types as the representative study areas in low,middle and high latitudes.We used a spatial-to-temporal approach to select forests in each reserve at three different age stages,hereinafter referred to as: earlier(stage1),middle(stage2),and later(stage3)stage.For each reserve,three repeated plots were selected in each stage of forest,and the soil and litters collected from each plot to analyze soil biological(nematodes and microorganisms)and(soil physical-chemical and litter properties).The aim was to investigate the dynamic characteristics of the communities and diversity of soil nematodes and microorganisms in different chronosequence of forest,and to better understand the interaction between aboveground and underground ecosystems at a larger spatial and temporal scale.The results obtained from this study were as follows:(1)Dinghushan(low latitude): 1)The process of forest chronosequence had a great influence on the abundance of total soil nematodes and the abundance of different trophic and functional groups of nematodes.The ratio of fungal-feeding nematodes to bacterial-feeding nematodes increased firstly and then decreased,the dominant genera of nematodes changed with the forest chronosequence,and the community composition of soil nematodes in the earlier stage was significantly different from that in the later stage of forest;The diversity of soil nematodes increased with the forestage,the diversity of plant-feeding and omnivorouspredatory nematodes were the highest in the middle and later stage of forest,and the diversity of fungal-feeding nematodes was the lowest in the middle stage of the forest,the total diversity of nematodes in the whole forest chronosequence was positively correlated with the diversity of plant-feeding and omnivorous-predatory nematodes,respectively.2)The total soil microbial PLFAs and soil bacterial PLFAs,actinomycetal PLFAs,gram-positive and gram-negative bacterial PLFAs changed obviously of forest chronosequence.The biomass ratios of fungi to bacteria increased firstly and then decreased with the forest chronosequence.The community composition of bacteria and fungi were significantly different among the three stages of forestage,and the difference of community composition of archaea was relatively small.There was no significant change in the diversity of bacteria.The fungal diversity increased significantly in the later stage of forest,and the archaeal diversity was higher in the middle stage of forest.(2)Baotianman(middle latitude): 1)The process of forest chronosequence had little influence on the total abundance of soil nematodes and the abundance of different trophic and functional groups of nematodes.The ratio of fungal-feeding nematodes to bacterial-feeding nematodes was higher in the earlier stage of forest,the dominant genera of nematode had not been replaced with the forest chronosequence,and the composition community of nematodes was relatively similar in different age stage of forest;The diversity of soil nematodes increased with the forest chronosequence,the diversity of plant-feeding nematodes was higher in the later stage of the forest age,there was a significant positive correlation between the diversity of plant-feeding nematodes and the total diversity of soil nematodes during the process of forest chronosequence.2)The total soil microbial PLFAs and the bacterial PLFAs,actinomycetal PLFAs,gram-positive and gram-negative bacterial PLFAs changed significantly.There was no significant difference in the ratio of fungi to bacteria.The community composition of bacteria,fungi and archaea in the three forest stages were similar.The diversity of bacteria was higher in the later stage,and the diversity of fungi marginally increased in the later stage,the diversity of archaea had no obvious change.(3)Changbaishan(high latitude): 1)The process of forest chronosequence had little influence on the total abundance of soil nematodes and the abundance of different trophic and functional groups of nematodes.The ratio of fungal-feeding nematodes to bacterial-feeding nematodes marginally increased in the later stage,the dominant genera of nematode had not changed of the forest chronosequence,and the composition community of soil nematodes had a certain difference in the later stage than in the earlier stage;The diversity of soil nematodes and bacterial-feeding nematodes were the highest in the middle stage,decreased significantly in the later stage.The diversity of plant-feeding nematodes was the highest in the middle stage,total diversity of soil nematodes was positively correlated with the diversity of bacterial-feeding nematodes and plant-feeding nematodes,respectively.2)It was no significant change in soil microbial PLFAs as a whole,only the fungal PLFAs decreased with the forest chronosequence,the ratio of fungi to bacteria decreased with the forest chronosequence,community composition of bacteria and archaea were different in the earlier stage and the middle,later stage,fungal community composition was significantly different in the later stage and earlier,middle stage;There was no significant change in bacterial diversity,fungal diversity as a whole increased with the forest chronosequence,the change of archaea diversity was the opposite.In general,our results showed that the process of forest chronosequence affected the community composition and diversity of soil nematodes and microorganisms.The community composition of soil nematodes and microorganisms changed with forest development when the plant communities changed obviously in different age stages of forest,and soil and litter properties also changed due to the shift of plant communities.Although soil and litter properties also influenced the community composition of soil nematodes and microorganisms,if possible,other factors(e.g.the characteristics of plant community composition,dominant species,etc.)affected the community composition of soil nematodes and microorganisms should be taken into account in future studies.In addition,we found that the diversity of total soil nematodes and plant-feeding nematodes changed significantly of the forest chronosequence,there were significant positive correlations between the diversity of plant-feeding nematodes and the total soil nematodes in each study area,which indicated that the changes in the diversity of plantfeeding nematodes have potential influence the changes of the diversity of soil nematodes.We thought that the diversity of plants in different stages of forest might cause the changes of the diversity of soil nematodes by affecting the diversity of plant-feeding nematodes.We also found that the fungal diversity increased in the later stage.The findings of these results are helpful for us to better understand the factors that affect the composition and diversity of soil organisms,and provide important information on driving factors of the changes soil communities during of forest chronosequence.