Effects of nitrogen addition on leaf traits of common species in natural Pinus tabuliformis forests in Taiyue Mountain,Shanxi Province,China

Aims Our objectives were to explore the effects of simulated nitrogen deposition on leaf traits and ecological stoichiometry characteristics of common species in natural Pinus tabuliformis forests.
Methods We conducted the experiment of nitrogen (N) addition from 2009 to 2013 in the natural Pinus tabuliformis forests in Taiyue Mountain, Shanxi, China. The levels of N addition were 0 (control), 50 (low-N), 100 (medium-N) and 150 (high-N) kg·hm^-2·a^-1, respectively. Eleven common plant species in 12 20 m × 20 m plots were selected, including Pinus tabuliformis, Quercus mongolica, Acer ginnala, Corylus mandshurica, Cornus bretschneideri, Spiraea salicifolia, Lonicera maackii, Carex callitrichos, Diarrhena mandshurica, Anemone tomentosa, and Polygonatum odoratum. Nine leaf traits were measured, including leaf thickness (LT), specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC), leaf phosphorus content (LPC), and other four.
Important findings We found that: 1) LT and SLA of Polygonatum odoratum significantly differed among four levels of N addition. Leaf area (LA) and LDMC of several species, such as Spiraea salicifolia, had significant difference among the N addition concentration. LNC of all species, chlorophyll content (CC) and LPC of most species increased significantly with the addition of N. Leaf N:P of 9 species varied significantly, and leaves with different types and ages showed different responses to N addition. 2) Leaf traits were significantly correlated with each other. For instance, SLA was significantly positively correlated with LNC and LPC. In contrast LT was negatively connected with LNC and LPC. In addition, the degree of correlation changed with the level of N addition. 3) The pattern of species distribution in leaf trait space was consistent with the prediction from the theory of Leaf Economic Spectrum (LES). N addition drove species moving along axis 1 in the trait space, and propelled them towards different directions along axis 2, which indicated that these species tended to take the “fast investment-return” strategy. These results suggested that with the change of environmental conditions, plants changed their survival strategy and adjusted resource allocation to maintain the stability of communities. This is the inherent characteristic of plants, thus the formation of LES did not depend on the environment change.