Variations in the natural 13C and 15N abundance of plants and soils under long-term N addition and precipitation reduction: interpretation of C and N dynamics
Guoyong Yan, Shijie Han, Mingxin Zhou, Wenjing Sun, Binbin Huang, Honglin Wang, Yajuan Xing, Qinggui Wang
Abstract
Abstract 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.