Leaf Physiological Plasticity in Schima superba and Schima argentea is Related to Ecological Niche Width Under Varied Altitude Gradients

Abstract

Plasticity magnitude may affect the distribution and adaptability of species in altitude gradients. The term is broadly defined as the adaptability of organisms to alter their morphological and physiological traits in response to varying environments. Morphological and physiological plasticity may have different mechanisms and resource costs. However, our understanding of the mechanisms by which plasticity affects species' adaptation to altitude changes is limited. This study focused on the differences in the leaf traits of Schima superba (narrow ecological niche) and S. argentea (wider ecological niche) in response to altitude gradients. It also explored the adaptive strategies and mechanisms behind the plasticity of morphological and physiological traits under similar environmental pressures. The interaction between altitude and species significantly impacted morphological traits, such as leaf thickness, width, and mass, and physiological traits, such as chlorophyll, carotenoids (Car), relative water, soluble sugar (SS), leaf nitrogen (LNC), and leaf phosphorus (LPC) contents, as well as the N/P ratio. The leaf traits of the two species responded similarly to altitude gradient changes, but the adaptive potential of S. argentea was higher. Compared with S. superba, the chlorophyll content of S. argentea at high altitude (1912 m) was remarkably greater than that at two lower altitudes (1375 and 1552 m). Moreover, it was affected by nitrogen and phosphorus limitation only when the altitude exceeded 1912 m. Quantitative analysis based on the simplified relative distance plasticity index (RDPI_s) showed that the RDPI_s of physiological traits in S. argentea were significantly greater than those of morphological traits, and the RDPI_s of most physiological traits were greater than those of S. superba, mainly due to the RDPI_s of its physiological traits-especially LNC (0.357), Car (0.328), and SS (0.319). Thus, physiological plasticity plays a critical role in adapting to environmental changes, especially in the case of vertical gradients.

Keywords: Nanshan National Park; Schima; morphological plasticity; physiological plasticity.

FIGURE 1

Map showing the study area and sampling plots.

FIGURE 2

Altitudinal variation in leaf length (LL; a), leaf width (LW; b), leaf thickness (LT; c), leaf area (LA; d), leaf mass (LM; e), and specific leaf area (SLA; f) for S. superba and S. argentea . Data are presented as means ± SE. Different letters indicate significant differences among elevations based on ANOVA followed by Tukey's HSD test (p < 0.05).

FIGURE 3

Altitudinal variation in chlorophyll a content (Chl a; a), chlorophyll b content (Chl b; b), total chlorophyll content (T‐Chl; c), carotenoid content (Car; d), relative water content (RWC; e), soluble sugar content (SS; f), leaf nitrogen content (LNC; g), leaf phosphorus content (LPC; h), leaf potassium content (LKC; i), and nitrogen‐to‐phosphorus ratio (LN/P; j) for S. superba and S. argentea . Data are presented as means ± SE. Different letters indicate significant differences among elevations based on ANOVA followed by Tukey's HSD test (p < 0.05).