Effects of shading on photosynthetic characteristics of cotton at full bolling stage

This study aimed at disclosing the effects of shading at full bolling stage on photosynthetic characteristics and inherent mechanism of leaves in cotton.The cotton plants were grown in the field under three light treatments(shading 0%,50%,80%)in Baoding,and the response of chlorophyll,photosynthetic and light response curves of chlorophyII fluorescence were studied.The main results were as follows:(1)The results showed that shading could cause the increasing of chlorophyll concentration and improve the proportion of chlorophyll b.(2)When increasing the shading,the maximum net photosynthetic rate Pnmax light saturation point(LSP),light compensation point(LCP)and dark respiration rate(Rd)in cotton leaf were decreased,the apparent quantum yield(φ)was significantly increased.(3)The shading treatment and highlights decreased the quantum yield of PSⅡlinear electron(ΦPSⅡ),photochemical quench(qP),the non-photochemical quenching(NPQ)and electronic transfer rate(ETR)decreased when the actinic light intensity was higher than about 150μmol/(m2·s). Therefore,Shading can improve the fertility of the late cotton leaf chlorophyll content,reduce the consumption of dark respiration to produce a certain ecological adaptability to low light, and shading can lower the cotton leaf photochemical activity of PSII reaction center of the photosynthetic rate decline,leading to the decline of accumulation of photosynthetic products.