Abiotic and biotic processes may both affect plant community assembly. Our objective is to explore the relative influence of environment and phylogenic background on variations in plant functional traits in the Yanhe River catchment, Shaanxi, China. The goal is to provide helpful information related to understanding the mechanisms and interactions influencing plant adaptation as they relate to environmental factors.
This study measured six leaf traits and three fine root traits of 107 species belonging to 35 families in 31 sample plots in three vegetation zones (forest, forest-steppe, steppe) on the Loess Plateau. One-way ANOVA was used to describe the variation among three vegetation zones and plant families. We then used redundancy analysis (RDA) to analyze the relationships between plant functional traits and meteorological factors. Principal component analysis (PCA) was used to detect important relationships between plant functional traits and plant families. Finally, we used a General Line Model (GLM) to evaluate the relative contribution of environmental factors and plant phylogenic background to variations in plant functional traits.
The results show: (1) There were no significant differences in leaf nitrogen concentration per mass (LN) and fine root nitrogen concentration per mass (RN), but significant differences were found in leaf thickness (LT), specific leaf area (SLA), leaf tissue density (LTD), leaf phosphorus concentration per mass (LP), the ratio of leaf nitrogen concentration per mass and leaf phosphorus concentration per mass (LN:LP), specific root length (SRL), fine root tissue density (RTD)between the three vegetation zones. The values of these various parameters increased from the south to the north as climatic aridity intensified, plants adjusted plant functional traits to adapt to different environmental conditions. Plants in the forest zone had higher competitive ability with more rapid leaf growth rates and with roots having a higher resistance to stress and damage. Plants in the forest-steppe zone had higher root growth rates and had leaves with greater resistance to stress and damage. (2) Plants from different plant families used different strategies to adapt to environment; that is different species perform differently when provided with the same resources and environmental gradients; for example, leaf nitrogen concentration per mass and root nitrogen concentration per mass of Leguminosae was far greater than that of other families, but the nutrient absorption efficiency of species in the Leguminosae was not high. (3) Average annual precipitation and the mean temperature of the warmest month were two main factors which had significant effects on variations in traits along environmental gradients in the area; for example, 16.26% of the observed variance in SLA can be explained by average annual precipitation and 4.02% can be explained by plant family. The explained variance of plant functional traits varied as those same functional traits varied and there were obvious environmental screening effects in the process of the formation of plant communities in the Yanhe River watershed. Six traits, LT, SLA, LTD, LP, SRL, and RTD were sensitive to climatic aridity at the species level; the spatial variation was caused primarily by environmental differences. In conclusion, environmental heterogeneity must be considered during vegetative restoration on the Loess Plateau.