Simulated organic–inorganic nitrogen deposition changes the growth rate, leaf stoichiometry, and phenolic content of Cyclocarya paliurus

Abstract

Atmospheric nitrogen (N) deposition is composed of both organic nitrogen (ON) and inorganic nitrogen (IN), and these sources of N affect plant growth, the balance of elements, and the accumulation of secondary metabolism substances; however, how these plant traits respond to ON–IN N deposition remains unclear. Here, we explored the effects of N addition with different ON:IN ratios on the growth rate, biomass allocation, leaf N and phosphorus (P) concentration, and leaf phenolic content of Cyclocarya paliurus in a short-term field experiment. Compared with the control, the growth rate (μ) and biomass accumulation of C. paliurus showed a decreasing trend in the 2 years after different N addition treatments. Higher ON:IN ratios not only resulted in higher leaf N content but also significantly increased the leaf P content. In addition, N addition with different ON:IN ratios induced more biomass accumulation allocated to the underground part of C. paliurus, which may be related to the nutrient acquisition strategy. Increased leaf N:P ratios indicated that stoichiometric imbalance occurred and that N and P limitation conditions of C. paliurus changed after different ON–IN N treatments. The growth rate (μ) of C. paliurus showed a trend of first decreasing (14 < leaf N:P ratios < 16) and then increasing (16 < leaf N:P ratios). However, compared with the growth rate, the leaf phenolic content showed an opposite trend to that of leaf stoichiometry, which indicated that leaf stoichiometry significantly affected both the primary growth and secondary metabolism of plants. Our results suggest that simulated N addition with different ON:IN ratios caused stoichiometric imbalance and changed the plant growth rate and accumulation of biomass and secondary metabolism substances. In addition, our study highlights that the type of nutrient limitation and the variation in N deposition components should be considered when predicting the future responses of plant functional traits to N deposition.