Photosynthetic Physiological Characteristics Of Cotton Canopy "Boll-leaf System" And The Response To Drip Irrigation Amount

Photosynthesis is the basis for yield formation.Improving the potential of crop photosynthetic performance and the utilization of light energy under water deficit are keys to improving yield.The cotton canopy“boll leaf system”is composed of main stem leaf,boll subtending leaf and capsule wall.Its photosynthetic performance reflects the ability of the plant to exchange material and energy with the outside world.Exploring the differences in photosynthetic capacity of each component in“boll leaf system”and the response to moisture is important to enrich cotton biological water-saving theory and construct water-saving and high-yield cultivation technology system in arid areas.The research was carried out at the Experimental Station of Agricultural College of Shihezi University in 2017-18.A Xinluzao 45?Gossypium hirsutum L.?cultivar was used,and three treatments were set as follows:W₁(conventional drip irrigation,4800 m³·ha^-1),W₂(limited drip irrigation,3840 m³·ha^-1),W₃(deficit Drip irrigation,2880 m³·ha^-1).We used the“boll-leaf system”as the research subject to determine gas exchange parameters and photosynthetic key enzyme activities,stomatal characteristics and anatomical structure,chlorophyll fluorescence parameters and antioxidant enzyme systems,biomass accumulation,yield and quality,as well as the response to drip irrigation amount.The main research conclusions are as follows:1.The changes of chlorophyll content?Chl?,gas exchange parameters,photosynthetic area,ribulose-1,5-bisphosphate carboxylase?RUBPC?,phosphoenolpyruvate carboxykinase?PEPC?of each component in canopy“boll leaf system”and the response to drip irrigation amount were studied.The Chl,net photosynthetic rate?Pn?,RUBPC and PEPC?during 28-42 days after anthesis?of boll suntending leaf were higher than those of main stem leaf under each treatment.Under W₂ treatment,it was 8.3-24.6%,10.5-38.7%,4.4-22.7%,and 7.6-15.3%higher than the main stem leaf,respectively.There were no significant differences in Pn?during 7-49 days after anthesis?,Chl?during 21-35 days after anthesis?and photosynthetic key enzyme activities?during 21-49 days after anthesis?of boll suntending leaf between W₁ and W₂ treatments.The Chl and photosynthetic area of capsule wall were in a rapid growth period during 21-35 days after anthesis.Compared with W₁ treatment,they were reduced by 7.2-13.4%and 3.8-16.2%under W₂ treatment,13.7-16.1%and 18.2-31.5%under W₃ treatment.Therefore,under limited drip irrigation,the photosynthetic performance of the main stem leaf was inhibited during 21-49days after anthesis.However,cotton has maintained the photosynthetic performance of the“boll leaf system”by enhancing the photosynthetic capacity of boll subtending leaf and capsule wall during 28-42 days after anthesis.2.The changes of stomatal characteristics and anatomical structure of each component in canopy“boll leaf system”and the response to drip irrigation amount were studied.The thickness of the capsule wall was significantly larger than that of the leaf,while the stomatal density was significantly lower than that of the leaf.As the drip irrigation amount decreased,the stomatal length and width of each component decreased,and the stomatal density increased.The stomatal densitiy of main stem leaf,boll suntending leaf,capsule wall under W₂ and W₃ treatments?during 21-35 days after anthesis?were increased by 13.4-27.9%?23.5-35.4%?7.5-17.9%and22.1-46.1%?32.740.6%?8.9-24.1%than W₁ treatments,respectively.Compared to W₁ treatments,the palisade tissue thickness?PT?of the main stem leaf and boll suntending leaf under W₂treatment?at 35 days after anthesis?increased by 4.2%and 7.7%,respectively.And the ratio of palisade tissue thickness to sponge tissue thickness?P/S?of boll suntending leaf?during 21-49after anthesis?increased by 3.6-10.2%under W₂ treatment.Correlation analysis showed that the total leaf thickness?TT?,PT,and P/S had extremely significant linear correlations with Pn,respectively.Therefore,under limited drip irrigation,cotton improved light suitability of the“boll leaf system”by adjusting the stomatal characteristics of each component,increasing the TT of boll suntending leaf and capsule wall and improving the P/S of boll suntending leaf.3.The changes of relative water content?RWC?,carotenoid?Car?content,chlorophyll fluorescence parameters,antioxidant enzyme activity and lipid membrane peroxidation of each component in canopy“boll leaf system”and the response to drip irrigation amount were studied.SOD activity of leaf was enhanced in the early stage?during 7-28 days after anthesis?,and POD and CAT activities were enhanced at later stages?during 28-49 days after anthesis?to clear the active oxygen.Compared to W₁ treatment,the SOD,POD and CAT activities of each component increased significantly under W₂ and W₃ treatments,the Car content of main stem leaf and boll suntending leaf increased by 10.6-43.6%,8.7-17.8%?except 49 days after anthesis?and19.4-74.6%,0.5-33.5%under W₂ and W₃ treatments,respectively.The RWC of capsule wall was higher than that of leaf under each treatment,but the antioxidant enzyme activity,MDA and H₂O₂ content were significantly lower than those of leaf.Compared to W₁ treatments,the NPQ of capsule wall increased by 0.71-10.1%?except 49 days after anthesis?and 8.0-17.5%,and the Car content of capsule wall increased by 26.23%and 44.86%under W₂ and W₃ treatments,respectively.Therefore,under water deficit,the main stem leaf and boll suntending leaf mainly relied on strong antioxidant enzyme system and high Car content to adapt to water deficit stress,while the capsule wall mainly maintained high Car content and heat dissipation ability to quench the excess light energy,thereby protecting the photosynthetic mechanism.4.The effects of different drip irrigation amount on boll growth index,biomass accumulation,water productivity?WP?,cotton yield and quality were studied.The boll growth index,biomass accumulation and yield decreased with the decrease of drip irrigation amount,but the fiber quality changed slightly.It prolonged the rapid growth duration of biomass accumulation of main stem leaf and boll subtending leaf?T,6.9 d and 22.1 d?and increased the maximum growth rate of seed cotton biomass(Vx,0.195 g?d^-1)under W₂ treatment.Compared with W₁ treatment,the seed cotton yield under W₂ and W₃ treatments decreased by 4.8%and22.2%,respectively,and there was no significant difference between W₁ and W₂ treatments.In addition,the WP under W₂ and W₃ treatments increased by 18.9%and 21.4%than W₁ treatment,respectively.Correlation analysis showed that Pn,gs,Chl,PT of the main stem leaf and boll substending leaf as well as the seed cotton weight showed significant or extremely significant positive correlations with biomass accumulation,respectively.Therefore,under limited drip irrigation,the rapid growth duration of the biomass accumulation of the main stem leaf and boll substending leaf has been prolonged,which ensured the supplyment of photoassimilation for the growth of capsule wall and seed cotton,and improved WP without significantly reducing the yield.