The changes in diversity of vegetation and foliar stable isotopes during the terrestrial plant succession of a subtropical forest and their ecological implications

The disturbed forest system can be restored through successional processes, where changes in the diversity of plant species serves as key indicators of processes. Meanwhile plant water use efficiency and nitrogen dynamics are important factors influencing photosynthesis-water coupling and nutrient stress in plants, respectively, during forest recovery. Analyzing these factors is crucial for understanding forest recovery and promoting sustainable ecosystem development. In this study, traditional vegetation surveys and biodiversity indices, along with foliar stable carbon and nitrogen isotope analyses, as well as nitrogen content analyses, were conducted in a subtropical forest with various successional stages following human and natural disturbances in Sichuan province, China. These analyses were used to assess species diversity patterns, evaluate water use efficiency, and assess nitrogen dynamics in primary, secondary, and artificial forests. The results showed distinct stage-specific differences in succession among forest types. Primary forests exhibited the highest successional stage but were limited by water stress and high nitrogen competition, with the highest delta C-13 values (i.e., -29.0 parts per thousand), lowest delta N-15 values (i.e., -3.6 parts per thousand), and the lowest nitrogen contents (i.e., 3.6 %) on average. Artificial forests had the lowest species diversity due to species dominance and nitrogen competition, with the lowest delta C-13 values (i.e., -29.7 parts per thousand), relatively low nitrogen contents (i.e., 4.0 %), and high delta N-15 values (i.e., -1.8 parts per thousand). Secondary forests, with longer recovery periods, reached higher successional stage due to sufficient nitrogen and water, which is indicated by the highest delta N-15 values and nitrogen contents (i.e., -1.7 parts per thousand and 4.5 %), and the relatively low delta C-13 values (i.e., -29.4 parts per thousand), leading to accelerated vegetation growth. This study highlights not only the importance of analyzing plant diversity, but also the material cycles, especially water use efficiency, and nitrogen dynamics, to understanding forest recovery. These findings can support effective conservation and sustainable development of subtropical forest ecosystems.