| Carbonate dissolution is the main way of soil formation in karst area.Due to the low content of acid-insoluble matter in carbonate,the karst area has the characteristics of slow soil formation,shallow soil layer,fragile soil environment.Carbonate rock erosion makes the karst land surface to have a complex micro-geomorphology.This micro-geomorphic environment has strong spatial heterogeneity.For the convenience of research,scholars classify the micro-morphology into stone cavern,stone crevice,stone gully,stone groove,stone surfaces and top soil.Most of the soil in the karst area is distributed in these habitats,forming a feature of discontinuous soil layer.The soil retained in different types of habitats has strong spatial heterogeneity.Soil microbial communities and functions are extremely sensitive to the environmental changes and are important indicators for predicting the succession of ecosystem.However,reports are rare on the rock dissolution and soil microbial research of different habitats in karst area.This study was intended to find out the rock dissolution rate and morphology,soil microbial distribution and ecological function of different habitats'types,as well as the relationship among rock dissolution,soil formation and soil physical and chemical factors,microbes and habitat environment.Different microhabitats'types in Maolan Karst forest in Guizhou was selected as the research object,and a two-year rock erosion experiment was conducted.Also,the soil microbes in habitats using phospholipid fatty acid biomarkers and 16S rRNA were analyzed to explore the community structure and ecological function.Finally,the relationship between rock dissolution and bio-fabrication was discussed,aiming to provide a scientific basis for the protection of forest soil ecology and sustainable utilization of soil in karst areas.The main conclusions of the study are as follows:(1)The content of organic matter in habitats ranged from 60 to 546 g/kg,and the organic matter content in the stone groove was significantly higher than that in other microhabitats(P<0.05).The soil pH in different habitats types was significantly different,and the whole trend was in the sequence of stone crevice>stone cavern>stone groove>top soil>stone gully>sub-soil;the regulation of total carbon content in the habitats were consistent with that of organic matter content;the total nitrogen content of the stone groove was significantly higher than that of the stone gully,and total nitrogen content in the gully was significantly higher than that in other habitats;The C/N ratio of stone groove was significantly higher than that of the lower sub-soil,which was not significantly different from other habitats.(2)The results showed that:48 phospholipid fatty acids(PLFAs)were detected in six different microhabitat soils,among them,18 PLFAs were characteristic with microbes.Organic matter was the main factor controlling soil microbial communities,the contents of total microbial,bacteria,fungi and actinomycetes,G~+and G~-in different types of microhabitats followed the order of stone groove>stone gully>top-soil>stone cavern>stone crevice>sub-soil,simultaneously,the contents of microbial in all habitats followed the order of bacteria>actinomycetes>fungi.The values of G~+/G~-in all habitats presented as:stone groove>stone gully>top-soil>stone crevice>stone cavern>sub-soil.Fungal to bacterial ratio ranged from 0.14 to 0.16,and followed order of top-soil>stone crevice>stone gully>stone groove>stone cavern>sub-soil;The results of MRT clustering showed that karst forest microhabitat can be divided into four types:stone groove-stone gully type,stone cavern-stone crevice type,top-soil type and sub-soil type.(3)Soil bacteria 16S rRNA V3-V4 variable regions were performed by high-throughput sequencing technique,and Tax4Fun2 method was used to predicted functional enzyme of soil bacteria.Numerical ecology methods were used to study the effects of soil physicochemical factors on bacterial community and enzyme structure.The results showed that 25 phyla,94 classes,244 orders,376 families,536 genera,and643 species were detected in the soils from five types of microhabitats.Proteobacteria and Actinomycetes were the dominant bacterial phyla in high pH and low pH of habitats,respectively.There were differences in Alpha diversity of bacteria among the five habitats,but they did not reach significant levels.While there were significant differences in Beta diversity and ASV(amplicon sequence variant table(ASV))of bacteria distribution among habitats.The results of Redundancy analysis and relative importance analysis showed that the soil bacterial distribution at phyla level had different degrees of response to soil physical and chemical factors,and overall pH was the primary factor affecting bacterial distribution.The results of Tax4Fun2 showed that7828 functional enzymes were detected in the five habitat types.The distribution of these functional enzymes showed significant differences with the changes of soil environment,and their functional redundancy index was generally represented by the sequence of top soil>stone gully>stone groove>stone cavern>stone crevice,which was indicated that the top soil has a relatively stable ecological environment,while the environment of stone cavern and stone crevice were fragile and poor.(4)The dissolution rate of carbonate rock was different between the soil surface layer and the sub-surface layer.When the dissolution was carried out for 0.5 years:in the soil surface layer,the dissolution mainly occurred in the stone groove,stone surface and soil surface.The test pieces in the stone groove dissolved dramatically,whose rate was up to 0.01 mg/cm~2 a;the test pieces in gully were slightly dissolved,while there was no obvious dissolution in the stone cavern and stone crevice.Under the soil,the dissolution rate of the test piece in the stone groove was as high as 0.0250 mg/cm~2 a,And the dissolution rate of the test piece under the soil surface was also higher than that of the soil surface during the same period.This phenomenon lasted from 0.5 years to 2years.In general,there were significant changes in the dissolution rate and morphology of the test pieces in the stone groove,stone surface,stone gully and soil.The significant dissolution rate and morphology changes have not been seen of the test pieces in the stone cavern and the stone crevice.The dissolution rate of carbonate rock was significantly negatively correlated with soil pH,and was significantly positively correlated with water content,carbon,nitrogen and microbial abundance. |
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