Effects of nitrogen addition on leaf nutrient stoichiometry in an old‐growth boreal forest

Abstract

Boreal forests have been evidenced to be highly sensitive to enhanced nitrogen (N) deposition due to prevailing N limitations, and external N inputs from atmospheric deposition are expected to alter plant nutrient stoichiometry. Previous studies have mostly focused on the dominant tree species while neglecting understory plants that often play important role in the nutrient cycles in forest ecosystems. By conducting a six-year N-addition experiment with four treatments of 0 (control), 20 (low N), 50 (medium N), and 100 (high N) kg NÁha −1 Áyr −1 in a boreal forest in Northeast China, we assessed the responses of leaf nutrient stoichiometry (N, phosphorus [P], potassium [K], calcium [Ca], and magnesium [Mg]) for tree, shrubs, and grass. Although the responses of different species to N addition varied, six-year N addition, especially the medium and high N treatments, generally increased the leaf N concentration and decreased the leaf P and Ca concentrations.

Nonlinear responses of ecosystem carbon fluxes to nitrogen deposition in an old‐growth boreal forest

“…The annual effect of N additions on forest C balances also varied nonlinearly over time (Figure 5c). Consistent with the conceptual framework, N additions increased soil N availability (Du & Fang, 2014a; Xing et al, 2019) which increased plant N uptake and foliar N concentration (Du, 2017; Du & Fang, 2014a; Xu et al, 2021), resulting in increased photosynthesis and tree growth in the short term. However, high‐level N additions lead to foliar nutrient imbalances in the long‐term (Du & Fang, 2014a; Xu et al, 2021), which decreased the N effect on NPP and resulted in a nonlinear temporal pattern (Figure 5c).…”

“…Consistent with the conceptual framework, N additions increased soil N availability (Du & Fang, 2014a; Xing et al, 2019) which increased plant N uptake and foliar N concentration (Du, 2017; Du & Fang, 2014a; Xu et al, 2021), resulting in increased photosynthesis and tree growth in the short term. However, high‐level N additions lead to foliar nutrient imbalances in the long‐term (Du & Fang, 2014a; Xu et al, 2021), which decreased the N effect on NPP and resulted in a nonlinear temporal pattern (Figure 5c). However, the temporal dynamics of annual N addition effects on Rh were mediated by the N addition rates, resulting in a nonlinear temporal pattern under the low N but a linear decreasing trend under the medium‐ and high‐level N addition over time, attributable to changes in soil microbial biomass and community composition (Figure 5c).…”

“…Increased litter quality (Du & Fang, 2014a), microbial biomass and a shift in microbial community composition (Figures S5 and S7) stimulated Rh under low N additions (Figure 5b). Decrease in microbial biomass and changes in litter quality (Du & Fang, 2014a;Xu et al, 2021) suppressed Rh under high N additions (Figure 5b).…”

High‐level nitrogen additions accelerate soil respiration reduction over time in a boreal forest

“…Second, a recent meta‐analysis found evidence of P limitations of Rs since P addition stimulated Rs (Feng & Zhu, 2019). At our study site, N addition could have led to a P limitation, and the magnitude of P deficiency would increase with time (Du & Fang, 2014; Xu, Xing, et al, 2021), therefore, constraining Rs over the long term. Finally, the ability of plants to control soil organic matter dynamics through their rhizosphere activities (Henneron et al, 2020) is also an important aspect that requires further investigation.…”

Inconsistent stoichiometry and growth responses of two coexisting dominant species to various N and P supplies in a supratidal wetland of the Yellow River Delta

“…Notably, many previous studies have focused on green leaves (Mayor et al, 2014;Yan et al, 2018;Liu et al, 2021). Leaf nutrient dynamics are a more reliable indicator of plant adaptive strategies than total nutrient concentrations (Yang, 2018;Xu et al, 2021); moreover, their species-specific responses could explain the changes in community structure (Wan et al, 2020). To date, the effects of altered absolute nutrient availability on leaf N and P stoichiometry have been well demonstrated (Lü et al, 2013;Jing et al, 2017;Huang et al, 2018b).…”