| Moss soil crusts(moss crusts)is a stable surface complex formed by the binding of soil particles to the pseudoroots of bryophytes.It occupies an important ecological niche in many fragile or damaged ecosystems and plays a crucial role in the structure and function of semi-arid and arid ecosystems.Moss crusts are also distributed in karst rocky desertification areas,and is one of the important factors affecting soil physical and chemical properties,enzyme activities and microbial communities in the preliminary stage of vegetation restoration.In this paper,we took Huajiang karst canyon,the typical karst rocky desertification area in Guizhou,China,as the research area.Using bare soil patches as a control,measured the nutrient content,enzyme activity and microbial community in different horizontal circles(central circle,middle circle,edge circle,peripheral circle)under different patche size of moss crusts(20 cm,35cm)and different vertical depths(crust layer,1～4 cm,4～7 cm,7～10 cm,10～15 cm,15～20 cm),we analyzed and revealed the interfering factors and changing patterns of different sizes of moss crust patches on the nutrients and microbial communities.The main results are as follows:(1)The physical and chemical properties in different horizontal circles of the two different moss patch size showed a general trend of gradually decreasing from the central to the peripheral circles,among which the decrease of soil water content and available nitrogen was significant(P<0.05).The main difference was that the soil water content increased significantly with the depth of soil layer,while the soil chemical properties such as organic carbon,total nitrogen,total potassium,available nitrogen,available phosphorus and available potassium decreased significantly with the depth of soil layer,and the crust layer was significantly higher than each soil layer under the crust.The chemical contents of bare soil patches did not change significantly except for the decrease of organic carbon,available nitrogen and available potassium.In addition,the content of organic carbon,total nitrogen,available nitrogen,and available potassium in shallow soil(<5cm)is significantly higher than that in bare soil patches.Suggesting that covering with moss crust can significantly increase the accumulation of surface soil nutrients in karst rocky desertification areas,but there is no significant difference in physical and chemical properties between 20 cm and 35 cm(2)Soil leucine aminopeptidase(LAP)、 N-acetyl-β-D glucosidase(NAG)and β-glucosidase(BG)all showed a significant decrease from the central to the peripheral circles;alkaline phosphatase(AKP)is irregular.The enzyme vector angle was less than 45°in all horizontal circles of the two different sized crust patches,and the peripheral circles were significantly higher than the remaining circles.Compared with the soil enzyme activities at each soil depth in the bare soil patches,β-glucosidase,leucine aminopeptidase,and N-acetyl-β-D glucosidase decreased significantly with the depth of soil layer in both different sizes of moss crust patches.Similar to the trend of soil nutrient content,there was a significant difference between the two biological soil crusts and bare patch in the shallow soil layer,indicating that the moss crust cover could significantly promote the accumulation of enzyme activity in the top soil layer.In addition the enzyme vector angle was less than 45° in the crust from the top layer of bare soil to 7～10 cm,which was limited by nitrogen,while it was greater than 45° in 10～15 cm and 15～20 cm,which was mainly limited by phosphorus.(3)α-diversity analysis showed that there were no significant differences in the abundance index(Chao1 index)and Shannon index of bacterial communities in two different moss patch size.The results of microbial(bacterial and fungal)co-occurrence networks showed that the size and complexity of the soil bacterial network structure decreased from the central to the peripheral circles,while there was no significant pattern in the fungal network structure.The results of two-factor network analysis and Mantel test of networks showed that p H and conductivity had significant effects on bacterial and fungal communities and networks in different circles of soils.The bacterial community composition of the two different sizes of crust patches was not significantly different compared to bare soil patches,and the dominant fungal phylum(Ascomycota)was significantly higher in bare soil patches than in 20 cm and 35 cm crust patches.The Chao1 index of bacterial and fungal community richness decreased significantly with soil depth in the crust patches,and the crust layer was significantly higher than the subcrust layer.The NMDS results showed significant differences in bacterial and fungal communities among different soil depths in the two crust patches,while the fungal communities in the bare soil patches clustered together without significant changes.The co-occurrence network results showed that the structural size and complexity of the soil bacterial network varied inconsistently in the three types of patches,while the structural size and complexity of the fungal network decreased significantly with soil depth.The results of two-factor network analysis of co-occurrence network and Mantel test showed that soil water content,organic carbon,and leucine aminopeptidase had significant effects on bacterial and fungal communities in crusted patches,and only soil water content had significant effects on bacterial and fungal communities in bare soil patches(P < 0.05).In summary,moss crusts have an agglomerative effect on soil nutrients,the farther away from the center of crust patches,the soil nutrient content will gradually decrease to a large extent.The presence of moss crusts can significantly improve the nutrients and enzyme activities of the top soil in karst rocky desertification areas,and play an important role in promoting the development of microbial communities.This study not only enriches the ecological studies of biocrusts under climate change scenarios,highlights the ecological functions of moss crust in degraded karstic rock desertification areas,but also provides data and theoretical support for the study of ecological processes of karst rock desertification,and a new ideas for the practice and construction management of rock desertification ecological restoration. |
