Variations of soil metal content, soil enzyme activity and soil bacterial community in Rhododendron delavayi natural shrub forest at different elevations
Guizhou Baili Rhododendron Scenic spot is rich in the species of rhododendron, such as Rhododendron delavayi, Rhododendron agastum, Rhododendron irroratum and so on, forming various monodominant populations13. Among them, R. delavayi is the main dominant species of rhododendron community in Baili Rhododendron Nature Reserve. It has a wide ecological niche and is distributed in the area of 1400-1900 m, but R. agastum and R. irroratum are only distributed in the area of 1600-1800 m. R. delavayi can not only promote local economic development as an ornamental plant, but also prevent ecological degradation. At present, the research on R. delavayi has mainly focused on flower color formation, reproduction and breeding, the community structure and diversity, and changes in the structure of rhizosphere microbial and so on. However, little research has been done on how changes in soil bacterial communities help R. delavayi adapt to different elevation environment.Elevation, as a comprehensive environmental factor, causes drastic changes in water, temperature, light, oxygen and ultraviolet, which eventually affect the composition of plant community, soil properties, soil heavy metal content and soil enzyme activity, resulting in the difference of soil microbial community structure.. A study demonstrated that different elevations gradients had different plant types and contents of heavy metal. For example, Zn content in 1250 m was significantly higher than that in 380 m and 820 m, while Pb content in 380 m was higher than that in 820 m and 1250 m. Microorganisms are also an important indicator of soil health, they can predict the change of soil environmental quality earlier, because it is sensitive to external disturbance. Soil microbial community is principal composed of bacteria and fungi, but bacteria are more resistant to heavy metals than fungi. The diversity and structure of soil bacterial communities changed along different elevations, and the response of soil C- and N-cycling microbial structure was complex as plants adapted to different elevations. For example, the relative amount of psychrophilic heterotrophic bacteria, fungi and gram-negative bacteria increased with the increase of elevation in the Austrian Central Alps.Currently, studies on rhizosphere microorganisms of R. delavayi mainly focuses on the soil microorganisms community structure at single elevation or different elevations. However, it is unclear how the changes of soil bacterial community structure at different elevations, especially soil bacteria, help R. delavayi adapt to KRD environment. Therefore, it is of great significance to study the effects of soil enzyme activity and soil metal changes on soil bacteria structure along the change of elevation gradient for exploring the process of plant adaptation to different elevations in the karst areas. The purpose of our study was to understand (1) the effect of various elevations on soil mineral elements and soil enzyme activities, (2) the effect of different elevations on soil bacterial community structure of R. delavayi, (3) to explore the relationship between soil mineral elements, soil enzyme activities and soil bacterial community in R. delavayi.