Influence Of Karst Outcrop Size And Geotechnical Distance On Soil Ecosystem Multifunctionality

Karst areas have shallow soils with many outcrops,and the exposed bedrock divides the soil into disjointed patches and creates a rock-soil coexistence pattern.These small,fragmented habitats around outcrops are characterized by spatial and ecological isolation,which are often regarded as negative features that do not enhance productivity significantly but occupy a large amount of space,while limiting the recovery of vegetation and hindering material dispersal and migration;however,the effects of outcrops on adjacent soils and plant communities have rarely been studied.In this paper,we investigated and compared soil chemical and biological parameters as well as ecological functions at different distances from outcrops in the karst area of Guangxi with different sizes of outcrops in order to assess their effects on the surrounding environment.Based on the systematic classification of the morphological characteristics of karst bedrock outcrops,a total of 31 independent karst outcrops with different side lengths of 0-5m were investigated and searched in the field,The outcrops were divided into five size gradients according to the side lengths of 0-1 m,1-2m,2-3m,3-4m,and 4-5m,and recorded as SL1,SL2,SL3,SL4,and SL5;then the peri-rock soils were collected at 20 and 50cm distances from the outcrops,and the chemical properties,microbial diversity,and enzyme activities of the soils were measured.The results of the study can provide important theoretical support for karst forest soil ecology,sustainable soil development and rock desertification.The main results are as follows:(1)Five size gradients of outcrops(SL1,SL2,SL3,SL4,SL5)had significant effects on soil organic carbon,total nitrogen,total phosphorus,fast-acting phosphorus,and exchangeable calcium and magnesium;among them,the highest values were found in the SL3 gradient of outcrop size,followed by the SL2 and SL4 size gradients,while the lowest values were found in the SL1 and SL5 size gradients,showing an overall The soil at 20 cm from the outcrop has higher contents of total N,total P,fast-acting P,soil organic carbon,nitrate N,fast-acting P,fast-acting P,total P,total N,and exchangeable Ca and Mg compared with the outcrop at 50 cm.(2)Different sizes of outcrops had significant effects on soil glucosidase.Different distances(20cm 50cm)of outcrops had significant effects on soil leucine aminopeptidase and acid phosphatase.Only the carbon to phosphorus ratio of enzyme activity was significantly different among all treatments.Rock size and rock-soil distance did not differ significantly on soil enzyme stoichiometry ratios.There was no significant difference in vector angle among treatments,and the overall trend showed a single-peaked distribution of increasing and then decreasing,which was similar to the overall distribution trend of soil chemical properties.(3)Soil microbial load and community composition structure were not significantly correlated with rock distance,while soil microbial load,diversity and community structure showed a more obvious trend of increasing and then decreasing with the increase of the gradient of rock size,and the highest value of each index was when the rock size was SL3 and SL4.(4)When the size of dew rock was SL3 and SL4,it significantly increased the single functional indexes of mycorrhizal fungi,microbial productivity and soil fertility;it showed that the size of dew rock had an influence on the ecosystem functionality,and the maximum value was when the size of dew rock was gradient SL3 and SL4.The relationship between ecosystem multifunctionality and microbial indicators is that bacterial community composition,bacterial and fungal diversity and bacterial and fungal biomass are important biological traits that affect ecosystem multifunctionality and have significant effects on ecosystem multifunctionality.In summary,ecosystem multifunctionality was better and the overall effect was higher when the outcrop size was SL3 and SL4 and the rock-soil distance was 20 cm;it proved the influence of outcrop microhabitat on ecosystem multifunctionality,and provided a new research method and idea to study and evaluate the role of outcrop in soil material cycle and its ecological function,which is important for the improvement of soil ecological chemometric theory and the scientific restoration and control of karst in southwest China.It is important for the improvement of soil ecological stoichiometry theory and the scientific restoration and control of rock desertification in southwest China.