Effects of land use patterns on the limitation of soil microbial resources in the karst areas of Southwest China

XIAO Shuangshuang; CHEN Wurong; FU Wei; ZHANG Jianbing

doi:10.11932/karst20240507

Abstract：The experimental area is situated in the Mulian comprehensive experimental demonstration zone of Karst Ecosystem Observation and Research Station of Chinese Academy of Sciences,located in Huanjiang Maonan Autonomous County,Guangxi Zhuang Autonomous Region. This region falls within the subtropical monsoon climate zone. The average annual temperature is 19.9℃,with an extreme high of 38.7℃ and an extreme low of-5.2℃. The average annual rainfall is 1,380 mm,characterized by abundant precipitation that is unevenly distributed throughout the seasons;the rainy season accounts for more than 70％ of the total annual rainfall. The study area is characterized by a typical karst peak-cluster depression with an elevation of 272.0-647.2 m. The average bedrock exposure in the depression and the sloping land is 15％ and 30％,respectively,and their soil depths are 20-160 cm and 10-50 cm,respectively. The soil primarily consists of yellow-brown lime soil and brown lime soil,which have been developed from dolomite. The volume fraction of topsoil gravel can reach 10％-40％. The soil texture is composed of clay loam and clay,with the mass fraction of silt ranging from 25％ to 50％ and that of clay from 30％ to 60％,respectively. Soil microbial growth and activity are often limited by nutrient resources,and understanding which nutrients limit microbial activities is crucial for assessing ecosystem function and developing effective management strategies. Previous studies have shown that soil microorganisms are mainly limited by nutrient carbon © and phosphorus (P) during natural succession after the land has been left uncultivated in karst areas. However,measures such as fertilization in agricultural activities may change microbial resource limitations. In order to investigate nutrient resource limitations of soil microorganisms in agricultural land,this experiment selected four common land use patterns in Huanjiang,Guangxi,including enclosure,mowing,grass planting and corn planting,and analyzed enzyme activities related to C,nitrogen (N) and P in soil. Based on enzyme stoichiometry,the nutrient limitations of soil microorganisms were identified,and the influence of different land use patterns on the changes in microbial resource limitations in soil was clarified. This study could provide valuable guidance for the evaluation and management of different land use ecosystems. The results showed that soil enzyme activities changed significantly under different land use patterns,which was closely related to nutrients available in soil. Through enzyme stoichiometry,it was found that planting maize and grass significantly increased the nutrient C resource limitation of soil microorganisms,which was mainly caused by the reduction of soil organic carbon and microbial biomass carbon. The soil microorganisms of the four land use patterns were limited by N,but not by P. In addition,mowing and grass planting exacerbated the N limitation of microorganisms. Correlation analysis suggested that N resource limitation was associated with an increase in microbial biomass carbon,as microbial assimilation of carbon may require more nitrogen available in soil. In addition,microbial biomass C,N and P were significantly correlated with enzyme stoichiometry,which well explained the changes of microbial resource limitations under different land use patterns,and could be used as an effective index to assess microbial resource limitations in karst soil. In summary,this study indicates that changes in microbial resource limitations in soil should be fully considered in the evaluation and management of different ecosystems in karst areas,which was conducive to formulating more accurate and effective soil management strategies to promote the health and sustainable development of ecosystems. It is suggested to apply organic fertilizer such as manure or straw to alleviate the nutrient C resource limitation of soil microorganisms in karst areas where corn and forage are planted. In karst mowing areas,nitrogen fertilizer needs to be applied moderately to alleviate nutrient N resource limitation of microorganisms and to increase plant productivity.