Effects of shade level and microenvironment on vegetative growth, physiological and biochemical characteristics of transplanted cucumber (Cucumis sativus)

Growing vegetables through transplantation under black shade nets is currently becoming popular to provide protection from high intensities of light and high temperatures. This study evaluated the effects of shade level on microenvironment, vegetative growth, photosynthetic pigments, chlorophyll a fluorescence, osmoprotectants, plant water status and leaf mineral nutrients of greenhouse-grown summer cucumber transplants at 25%, 50%, 63%, and 75% shade levels. Solar radiation and tempera-ture decreased with increased shading levels. Average daily temperatures were approximately decreased by 1.5oC under 75% shade nets compared to the 25% shade nets. Vegetative growth characteristics, photosynthetic pigments, chlorophyll a fluorescence (Fv/Fm, Fv/F0, and PI), dehydration tolerance and Leaf N, P and K concentrations increased when shade level increased. Chlorophyll a fluorescence (Fv/Fm, Fv/F0, and PI) reduced with the increase of solar radiation levels. Also, clear decreases in free proline, soluble sugars and total free amino acids in both experiments with increased shade level have been observed. Additionally, relative water content (RWC), membrane stability index (MSI) and electrolyte leakage (EL) of cucumber transplants were significantly affected in both experiments by shade level. Moreover Shade level affected leaf mineral nutrient but the effect differed among nutrients concentration. This study concluded that, nets with higher shading levels (63 and/or 75%) are a potential alternative to alleviate photo-inhibition and heat stress in cucumber transplants production