Effects of shading on photosynthesis and chlorophyll fluorescence characteristics of Toyonoka strawberry cultivar

Experiment was conducted with potted strawberry cultivar Toyonoka for studying effects of shading on its photosynthesis and chlorophyll fluorescence characteristics. The results showed that the petiole length, leaf area and the content of chlorophyll and carotenoid under shading condition were higher than those of control, but the specific leaf weight (SLW), carboxylation efficiency (CE), dark respiration (Rd), light saturation point (LSP) and light compensation point (LCP) became lower. Furthermore, shading increased the apparent quantum yield (AQY) and the CO2 compensation point (CCP), which represented that the plants would be more efficient to transfer light quantum into chemical energy under low light stress, but the affinity to CO2 was decreased. Because of shading, the highest sunlight intensity at noon, about 2000 μmol/m2·s, declined to 600 μmol/m2·s, and the diurnal variation, a double-peak curve, of net photosynthetic rate (Pn) of strawberry under nature environment became a single-peak, and the daily accumulation of photosynthate decreased about 38%. Shading increased the leaf stomatal conductance (Gs) but the transpiration rate was lower than that of control, which was the result of lower temperature under shading. Shading also decreased the minimal fluorescence (Fo) but promoted the PSⅡmaximal photochemical efficiency (Fv/Fm), implying that shading might protect integration of the photosynthetic membrane systems and photochemical efficiency against the strong light stress. The results above indicated that shading was indeed beneficial for strawberry growth and alleviated photosynthetic photoinhibition, but it should be noted to increase CO2 concentration for strawberry under low light environment.