Leaf physiological plasticity in Schima superba and Schima argentea is related to ecological niche width under varied altitude gradients

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 (RDPIs) showed
that the RDPIs of physiological traits in S. argentea
were significantly greater than thanthoset of morphological traits, and
the RDPIs of most physiological traits were greater than that of S.
superba, mainly due to the RDPIs 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.