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Background:The nitrogen isotope natural abundance (δ 15 N) provides integrated information on ecosystem N dynamics, and carbon isotope natural abundance (δ 13 C) has been used to infer how water-using processes of plants change in terrestrial ecosystems. However, how δ 13 C and δ 15 N abundances in plant life and soils respond to N addition and water availability change is still unclear. Thus, δ 13 C and δ 15 N abundances in plant life and soils were used to investigate the effects of long-time (10 years) N addition (+ 50 kg N•ha − 1 •yr − 1 ) and precipitation reduction (− 30% of throughfall) in forest C and N cycling traits in a temperate forest in northern China. Results: We analyzed the δ 13 C and δ 15 N values of dominant plant foliage, litterfall, fungal sporophores, roots, and soils in the study. The results showed that δ 15 N values of foliage, litterfall, and surface soil layer's (0-10 cm) total N were significantly increased by N addition, while δ 15 N values of fine roots and coarse roots were considerably decreased. Nitrogen addition also significantly increased the δ 13 C value of fine roots and total N concentration of the surface soil layer compared with the control. The C concentration, δ 13 C, and δ 15 N values of foliage and δ 15 N values of fine roots were significantly increased by precipitation reduction, while N concentration of foliage and litterfall significantly decreased. The combined effects of N addition and precipitation reduction significantly increased the δ 13 C and δ 15 N values of foliage as well as the δ 15 N values of fine roots and δ 13 C values of litterfall. Furthermore, foliar δ 15 N values were significantly correlated with foliage δ 13 C values, surface soil δ 15 N values, surface soil C concentration, and N concentrations. Nitrogen concentrations and δ 13 C values of foliage were significantly correlated with δ 15 N values and N concentrations of fine roots. Conclusions: This indicates that plants increasingly take up the heavier 15 N under N addition and the heavier 13 C and 15 N under precipitation reduction, suggesting that N addition and precipitation reduction may lead to more open forest ecosystem C and N cycling and affect plant nutrient acquisition strategies.

Secondary forest succession after clear‐cutting is one of the foremost ecosystem restoration strategies, while soil microbes play essential roles in the processes by modulating nutrient cycling. However, the assembly processes and driving factors of soil microbial communities across secondary forest succession remain unclear. Here, we studied the assembly processes of soil microbial communities and examined shifts in soil microbial community‐associated functional dynamics across secondary forest succession. Our results showed that the stochastic process was more important in shaping bacterial community assembly throughout the successional process [modified stochasticity ratio (MST) > 50%], while the fungal community assembly was initially governed by deterministic processes (MST < 50%), but there was a progressive increase in stochastic selection as succession proceeded. Soil organic carbon and pH were principal factors for the explanation of changes in the bacterial community structure (total explained 43% change), and tree richness and productivity were principal factors for the explanation of shifts in the fungal community structure (total explained 17% change). The relative abundance of nitrogen transformation and saprotroph functional groups increased gradually with succession, whereas ectomycorrhizal fungi significantly declined. The results suggested that microbial community succession might accelerate the soil carbon and nitrogen turnover rates. Used together, the mechanisms shaping fungal and bacterial community structure are different in secondary forest succession and highlight that those fungi and bacteria are primarily controlled by plant traits and soil properties, respectively. Variations in microbial functional groups provide new insight into the mechanisms underlying the soil microbe‐driven soil nutrient cycles during secondary forest succession.