Seasonal changes in pigment content in overwintering and current-year leaves of Sasa senanensis from snowmelt to before leaf-fall of canopy deciduous trees.

Sasa senanensis (a dwarf bamboo), an evergreen herbaceous plant native to the cool temperate regions of eastern Asia, endures seasonal temperature fluctuations and significant variations in light intensity typical for understory plants. Following snowmelt in early spring, the light intensity received by Sasa leaves surges, then diminishes as the canopy of upper deciduous trees develops. The current-year leaves of S. senanensis unfold under these shaded conditions, rendering the preservation of overwintering leaves vital for maintaining photosynthetic productivity in early spring. This study investigated the adaptations of overwintering leaves of S. senanensis to the low temperatures and elevated light conditions typical of early spring, examining whether these leaves dissipate absorbed light energy as heat and/or reduce their antenna size in response to increased light levels. Comprehensive analyses of Fv/Fm and photosynthetic pigment compositions were conducted throughout the spring to autumn seasons from 2014 to 2017. Our results indicate that Fv/Fm in overwintering leaves was initially low in early spring but increased gradually before the onset of shading, maintaining high levels under shaded conditions across all examined years. The chlorophyll a/b ratio increased post-snowmelt and decreased with intensified shading annually, with the exception of 2015, suggesting that reductions in antenna size are not essential for Fv/Fm recovery. Furthermore, the quantities and de-epoxidation state of xanthophyll cycle pigments increased after snowmelt despite rising temperatures, then decreased with progressive shading each year, indicating that overwintering leaves adapt to early spring conditions by modulating their xanthophyll cycle pigments. This study demonstrates that the overwintering leaves of S. senanensis exhibit a flexible response in photosystem pigments to variations in the light environment.