Phenotypic plasticity and genetic variation in leaf traits of Yushania niitakayamensis (Bambusoideae; Poaceae) in contrasting light environments.

Yushania niitakayamensis (Bambusoideae; Poaceae), a perennial grass distributed from mid to high elevations in Taiwan, is often found growing in exposed grassland or shaded forest understories. To answer the question how does Y. niitakayamensis cope with contrasting light availability of habitats, we compared (1) leaf ecophysiological traits between populations of Y. niitakayamensis growing in exposed and shaded habitats in four seasons, and (2) plasticity patterns of transplanted plants to two light treatments (full-sun and 70 % shading) in a phytotron. Significant differences in leaf morphological (leaf length, width, specific leaf area, stomatal density), anatomical (leaf thickness (LT), the frequency of cavity formed by collapsed fusoid cells), and biochemical (chlorophyll contents, nitrogen contents per unit area ([N]area) and stable carbon isotope ratio) features were found between populations across seasons. Common garden experiments suggested that most of the trait variations in field growing plants can be explained by the effect of growth light treatment but not by that of population. However, variations between the two populations in LT, [N]area, gas exchange parameters, and the degree of plasticity in LT and [N]area in responding to growth light regimes might have genetic basis. In comparison between transplants from different origins grown under same light regime, plants from the exposed population grown under full-sun expressed significantly higher LT, [N]area and light-saturated photosynthetic rates, whereas plants from the shaded population grown under shading had significantly higher water use efficiency. Accordingly, local specialization in populations of Y. niitakayamensis to particular environmental conditions might have arisen.