Seasonal patterns in the leaf C:N:P stoichiometry of four conifers on the northeastern Tibetan Plateau

Abstract

Research into leaf traits, especially carbon (C), nitrogen (N), and phosphorus (P), are essential for understanding the nutrient uptake strategies and ecosystem functions, such as the rates of photosynthesis, transpiration, and nutrient intake in plants. However, seasonal patterns of leaf C:N:P stoichiometry in arid and semiarid forest ecosystems remain unclear. In this study, temporal scale monitoring was conducted on four conifer species (Picea wilsonii, Pinus tabuliformis, Picea crassifolia, and Juniperus przewalskii) within the Qilian Mountains to determine the seasonal patterns of leaf C:N:P stoichiometry and their driving forces. The seasonal patterns of the leaf N and P contents were asynchronous among the species. The C content and C:N and C:P ratios in the leaves in Tulugou (relatively wet and fertile) were lower than those in Langchaigou (extremely infertile and dry), whereas the N and P contents in the leaves displayed an inverse pattern (p < 0.05). The results confirmed that the leaf economics spectrum gradually transitions from high resource acquisition to high resource conservation as the environmental stress increased. Additionally, the leaf N and P contents were found to be positively correlated with the precipitation and soil water content during the growing seasons (p < 0.01), whereas the soil temperature negatively impacted the leaf N and P contents (p < 0.01). A two-way analysis of variance indicated that the species was the main driving factor of variation in the leaf C:N:P stoichiometry in the four conifers. The redundancy analysis revealed that soil properties explained 50.9 % of the total variability in the leaf stoichiometry, with the soil N pool having the strongest effect on the leaf traits. Overall, our results indicated that the tree species and soil N pools were the key driving factors affecting the leaf stoichiometry of the conifers, and the trees adapted to the changing environment through a trade-off in the leaf functional traits. These findings provide a temporal and spatial perspective for understanding how the leaf functional traits of conifers respond to environmental changes in arid and semi-arid montane forest ecosystems.