Effects of Increased N Deposition on Leaf Functional Traits of Four Contrasting Tree Species in Northeast China

Northeast China is persistently affected by heavy nitrogen (N) deposition. Studying the induced variation in leaf traits is pivotal to develop an understanding of the adaptive plasticity of affected species. This study thus assesses effects of increased N deposition on leaf morphological and anatomical traits and their correlation among and with biomass allocation patterns. A factorial experiment was conducted utilizing seedlings of two gymnosperms (Larix gmelinii, Pinus koraiensis) and two angiosperms (Fraxinus mandshurica, Tilia amurensis). Leaf mass per area and leaf density decreased and leaf thickness increased under high N deposition but trait interrelations remained stable. In gymnosperms, leaf mass per area was correlated to both leaf thickness and area, while being correlated to leaf density only in angiosperms. Epidermis, mesophyll thickness, conduit and vascular bundle diameter increased. Despite the differences in taxonomic groups and leaf habits, the common patterns of variation suggest that a certain degree of convergence exists between the species' reaction towards N deposition. However, stomata pore length increased in angiosperms, and decreased in gymnosperms under N deposition. Furthermore, biomass and leaf mass fraction were correlated to leaf traits in gymnosperms only, suggesting a differential coordination of leaf traits and biomass allocation patterns under high N deposition per taxonomic group.