Study on Photosynthesis of Different Position Leaves of Cucumber in Solar—Greenhouse

The photosynthetic rate (Pn) and carboxylation efficiency (CE) were observed to be the highestin mid-position leaves of cucumber in solar-greenhouse, second in upper and middle-lower position leaves, andlowest in lower-position leaves. The saturation light of the mid-position leaves was also the highest, while thephoto compensation points of the upper, middle and lower position leaves decreased as the leaf-position descen-ded. During the growth period, the Pn of most leaves enhanced as PFD increased. Pn curves of diurnal varia-tion in different position leaves had single-peak which appeared at 12:00 a.m. As the plant density increased,the PFD of different layer leaves decreased, especially of the lower position leaves. The effect of plant densityon the Pn of the upper-position leaves was not visible, but on the light compensation points was obvious. As tolower position leaves, the Pn and saturation light decreased as the plant density increased, but the light com-pensation points were not obviously affected. Cucumber leaves had certain capacity of adaptation and adjust-ment to light intensity which expressed as the lower the PFD, the higher the apparent quantum yield (AQY).So the AQY increased as the leaf position descended and plant density increased.