Effects of shading on the growth and physiological characteristics of Citrus in solar greenhouse

In order to study the effects of different shading treatments on the canopy microclimate condition, shoot growth and some leaf physiological metabolism of citrus under solar greenhouse, 4-year-old seedlings of Shatangju tangerine (Citrus reticulate‘Shatangju’) on the stock of trifoliate orange (Poncirus trifoliata Raf.) was selected as materials. Results showed that the PAR and temperature of greenhouse were high, the relative humidity was very low, and the curve of diurnal variation of net photosynthetic rate ( Pn ) was demonstrated two peaks with midday depression of photosynthesis under un-shading treatment. Shading markedly decreased canopy PAR and temperature, increased the relative humidity. The curve of diurnal variation of net photosynthetic rate ( Pn ) was demonstrated single peak with shading. Shading inhibited the growth of new germination summer shoot. With the transmittance reducing, new shoot number, diameter and length decreasing. Shading markedly increased leaf area and decreased leaf thickness. Compared with CK, the Chl b of leaves declined and Chl a/b decreased under shading. The young fruit set with a layer of shading treatment increased 16.44%, while the young fruit set was 0 under two layers of shading treatment.