Effects Of Potassium Management On Leaf Photosynthetic Characteristics And Grain Yield Of Rice Under Shading Stress

Sichuan basin is a typical low-light region in China.The low-light condition is one of the key obstacles to rice production in Sichuan.Potassium is one of the top three necessary nutrient elements for plant growth and development,which plays an important role in optimizing leaf photosynthetic performance,promoting dry matter accumulation and transportation,and improving plant resistance.However,the regulatory effect of potassium fertilizer on leaf photosynthetic characteristics and yield of rice under shading stress is unclear.Therefore,the field light control experiment in heading stage was conducted to investigate the effects of the single application of potassium fertilizer at basal(K_90,0)and single application of potassium fertilizer at jointing(K_0,90),the application of potassium fertilizer at basal and jointing(K_90,90)on leaf photosynthetic characteristics,accumulation and transportation characteristics of dry matter and potassium,and yield formation of rice.The results showed that:（1）Compared with natural light control,shading stress significantly increased the green leaves number of other leaves of rice（except the top three leaves）at 20 days after heading,which resulted in a significant increase in total number of green leaves per hill.Shading stress also increased the single leaf area of the top three and other leaves,which contributed to significant increase in leaf area index of high efficiency leaves and total leaves.The application of potassium fertilizer effectively increased the high efficiency leaf area of rice,and then significantly increased the leaf area index of high efficiency leaves and total leaves of rice,while compared to no potassium fertilizer control.Compared with K_90,0 and K_0,90,K_90,90increased the leaf area index of high efficient leaves and total leaves by 5.3%-9.8%and 7.6%-10.7%under shading stress,respectively.（2）Shading stress markedly increased the contents of chlorophyll a,chlorophyll b,total chlorophyll,and K⁺in the top three leaves after heading,but decreased the chlorophyll a/b of flag leaf after heading and the K⁺/Na⁺of flag leaf at 30 days(except K⁺/Na⁺of K₀ and K_0,90).This led to a decrease in actual photochemical efficiency,apparent electron transfer rate,and photosynthetic rate of flag leaf in 2021,as well as sucrose content in top three leaves and starch content in flag leaf in 2022.Compared with no potassium fertilizer control,The application of potassium fertilizer effectively improved the total chlorophyll content of flag leaf and the contents of K⁺and Na⁺of the top third leaves,but reduced the Na⁺content of the top third leaves.This resulted in an increase in the actual photochemical efficiency and apparent electron transfer rate of flag leaf,which contributed to an increase in the photosynthetic rate in both years(except K_90,90 under natural light in 2022)by 6.1%-24.0%and 7.0%-25.8%respectively.The application of potassium fertilizer also increased the content of sucrose and starch of flag leaf at 20-40 days after heading by 1.7%-9.4%and 3.3%-24.6%,respectively,but decreased the sucrose/starch by 1.0%-25.0%.In addition,compared with the K _90,0 and K _90,90 treatments,the K _0,90 could effectively increase the net photosynthetic rate of flag leaf under shading stress,and then increase the starch content of the top three leaves at 30 and 40 days after heading.（3）Shading stress markedly hindered the dry matter accumulation of rice after heading,which resulted in a 23.0%-30.7%and 2.5%-31.5%decrease in dry matter accumulation rate of panicle in 2021 and 2022,respectively.This significantly reduced the plant dry matter accumulation at maturity.Shading stress also significantly reduced rice seed setting rate and1000-grain weight,resulting in a 16.2%-19.3%and 25.4%-28.6%significant decrease in rice yield in 2021 and 2022,respectively.Compared with the control without fertilization,the application of potassium fertilizer effectively increased the total dry weight at each period,as well as the dry matter remobilization amounts of leaves and stem sheaths.This contributed to the effective increase in dry matter accumulation of panicle,which resulted in a 5.6%-13.9%and 6.4%-17.3%significant increase in grain yield in 2021 and 2022,respectively.Compared with the K_90,0 and K_0,90,K_90,90 markedly increased the dry weight of shoot in both years,which led to an 4.5%-4.8%and 1.9%-4.1%increase in yield in 2021 and 2022,respectively.（4）Shading stress significantly increased the K⁺content of leaf and panicle at each period,but decreased the K⁺accumulation of shoot in 2021 and the remobilization amount of K⁺in both years.Therefore,the partial productivity of potassium fertilizer in two years and the potassium harvest index in 2021 were significantly reduced by 19.3%-25.5%and 12.6%-17.9%,respectively.Compared with no fertilization,the application of potassium fertilizer significantly increased the K⁺content in each part of plant and the K⁺accumulation of shoot in both years,as well as the remobilization amount of K⁺in leaves and stem plus sheaths.This resulted in a23.7%-63.8%increase in potassium harvest index.Furthermore,the K_0,90 could effective improve the partial productivity and agricultural utilization rate of potassium fertilizer.（5）Correlation analysis showed that the net photosynthetic rate of flag leaf was significantly positively correlated with single leaf length of flag leaf,single leaf length of second leaf,single leaf area of second leaf,high efficiency leaf area index and total leaf area index in two years,as well as the contents of total chlorophyll（except flag leaf）,K⁺and Na⁺（except flag leaf）of top three leaves in 20 days after heading in 2021.rice yield was significantly and positively correlated with the dry weight of shoot and the remobilization amount of dry matter of leaf in both years,net photosynthetic rate,actual photochemical efficiency,apparent electron transfer rate and potassium accumulation of shoot in 2021,and chlorophyll a/b,contents of sucrose and starch,and sucrose/starch in flag leaves at 20 days after heading in 2022.Meanwhile,yield of rice was negatively correlated with the remobilization amount of dry matter of stem plus sheath in 2021 and the total chlorophyll and Na⁺content of flag leaf at 20 days after heading in 2022.The application of potassium fertilizer could optimize the photosynthetic performance of leaves under shading stress by increasing the photosynthetic area and the physicochemical properties of leaves.Potassium fertilizer also coordinated the accumulation and remobilization of dry matter and potassium and promoted panicle growth and development.This resulted in a significant increase in rice yield.In addition,the K_0,90 and K_90,90were better for improving the photosynthetic characteristics of leaves and dry matter accumulation and remobilization of rice.