Study On The Systemic Regulation Of Photosynthesis In Cotton Leaves And Its Response To Plant Density

Xinjiang is the major areas of cotton cultivation and production in China,high density planting pattern is an important means to obtain high yield of cotton in Xinjiang.However,in agricultural production,the increase of planting density often leads to the occurrence of different degree of shading between the middle and lower mature leaves of the plant,so that the middle and lower mature leaves are in low light environment,while the top leaves are still in the strong light environment,resulting in heterogeneous light environment.Therefore,under different light conditions,the growth and photosynthetic performance of leaves in different parts of the crop need to be further studied.In this study,the effects of shading on the anatomical structure,pigment content and photosynthetic fluorescence characteristics of young leaves and mature leaves of cotton were studied.The mechanism of physiological and physiological characteristics of young leaves and mature leaves and the response mechanism of photosynthetic performance to different light environments were clarified.The mechanism of photosynthetic system regulation between young leaves and mature leaves.The effects of different planting densities on the leaf anatomical structure,pigment content and photosynthetic fluorescence characteristics of cotton canopy were studied.The mechanism of photosynthesis in different parts of cotton under high density cultivation was studied,and the field environment and indoor simulation were also analyzed,in order to reveal the optimization of photosynthesis of cotton leaves under tight condition.The main contents and results are as follows:1.This study showed that the mature leaves light environment changes,the stomatal density,leaf thickness,palisade tissue thickness and leaf mass per area of the young leaves were significantly decreased,the content of chlorophyll was increased significantly,the net photosynthetic rate,stomatal conductance and stomatal limitation were significantly decreased,intercellular CO2 concentration was significantly increased,and these indexes of mature leaves had similar trends.That growth and photosynthesis of young leaves were regulated by signal system of mature leaves light environment.However,the change of chloroplast ultrastructure in different parts of cotton is closely related to the light environment in which it is located.2.This study showed that the mature leaf light environment changes,Chla,Chlb and Chla+b content of young leaves were increased significantly,the Chla/Chlb value was decreased significantly,the LCP,Pmax and Rd were decreased and AQY was increased significantly,the Gs and Ls were decreased and Ci was increased significantly,the LSP,Pm and Ik were decreased significantly,the α was increased significantly,the Y(II)and qP were decreased significantly,the NPQ and Y(NPQ)were increased significantly,and these indexes of mature leaves had similar trends.Therefore,the light environment of the lower matureleaves of the cotton has a systematic regulation on the energy utilization of the top leaves.Young leaves through the xanthophyll cycle of heat dissipation and other optical protection mechanisms to dissipate excess light energy,balanced the regulation of systemic irradiance signal from lower shade leaves and effects of its own light environment.3.The study showed that the photosynthetic active radiation of canopy in the middle and lower leaves of cotton decreased significantly with the increase of planting density,the net photosynthetic rate of the upper and lower leaves decreased significantly,the content of chlorophyll was increased significantly,the leaf thickness and specific leaf weight were decreased significantly.The results showed that under the close planting condition,the lower leaves of cotton played a significant role in regulating the development and photosynthetic properties of upper leaves.4.The study showed that the leaf mass per area of the upper and lower leaves of cotton was significantly positively correlated with leaf density and leaf thickness,and the leaf mass per area of the middle leaves was positively correlated with the leaf density.The results showed that the leaf mass per area of upper and lower leaves was regulated by leaf density and thickness,and the leaf mass per area of middle leaves was regulated by leaf density.