Morphological plasticity, photosynthesis and chlorophyll fluorescence of Athyrium pachyphlebium at different shade levels

Athyrium pachyphlebium C. is a popular ornamental fern with considerable shade tolerance. The aim of this study was to investigate how the mature sporophytes acclimate to different light levels and to obtain an optimal light environment for their growth both in natural forest canopy and in urban landscapes. Plant growth and morphology, photosynthetic light-response curves and chlorophyll (Chl) fluorescence were measured at four different light levels (45% full sunlight, 30%, 20% and 8%). As the light intensities declined from 45% to 20%, seedling height, crown growth, foliage number and plant lifespan increased significantly. Seedlings grown at 20% light level were vigorous with great ornamental value. Plants grown in deep shade (8% light) showed severe symptoms of lodging and in 45% full sun, the plants showed highlight-stress symptoms. Seedlings in high light levels exhibited a higher light-saturated photosynthetic rate (P max), light compensation point (LCP), light saturation point (LSP) and a reduced ability for nonphotochemical quenching (NPQ) of excess light than those in low light levels. However, seedlings in low light exhibited greater efficiency in absorbing and utilizing light energy, characterized by higher chlorophyll b (Chl b) and electron transport rate (ETR). These results indicated that a light level of about 20% full sun appeared to be optimal for A. pachyphlebium when both physiological and morphological performance in the landscape were considered.