Studies On Mechanisms Underlying The Effects Of Potassium Nutrition On Canopy Temoerature And Photosynthetic Capacity Of Photosynthetic Organs Of Brassica Napus

Winter oilseed rape(Brassica napus L.),one of the most important oil crops in China,is mainly distributed in the Yangtze River Basin.During the same period of rain and heat in this region,the multiple cropping index is high,and the soil potassium content is low.Farmers often neglect the input of potassium fertilizer in fertilization,resulting in different degrees of potassium deficiency in the Yangtze River Basin.Application of potassium fertilizer can promote the expansion of leaf area,increase the number of pods per plant,increase the photosynthetic area and rate,and also enhance the resistance of plants.In the face of the change of environmental temperature,the mechanism of potassium regulating the growth of photosynthetic organs and the change of photosynthetic capacity in oilseed rape is not clear at present.In this study,oilseed rape was taken as the research object,studied the effects of different potassium application on the yield and the succession of photosynthetic organs in the growth period of oilseed rape under the field conditions;on this basis,using infrared thermal imager to monitor the seasonal and daily changes of canopy temperature during the growth period of winter oilseed rape,and combining with the seasonal and daily changes of photosynthetic capacity of photosynthetic organs,analyzed the relationship between the changes of canopy temperature and photosynthetic capacity of oilseed rape under different potassium fertilizer application rates.Based on the energy balance model under dynamic environment conditions of leaves,analyzed the mechanism of K nutrition regulating canopy temperature.The main results are as follows:(1)There was no significant difference in the number of seeds per corner and 1000 grain weight between different potassium treatments,the application of potassium fertilizer significantly increased the number of pods per plant in winter oil menu and thus increased the yield of rapeseed.The above ground biomass and potassium accumulation increased with the increase of potassium application rates,but there was no significant difference when the potassium application rates more than 120 kg/ha.Leaf area index increased slowly in seedling stage and over-wintering stage,increased rapidly in bolting stage,reached the maximum value in flowering stage,decreased rapidly after flowering stage,and the silique area index increased rapidly and became the main photosynthetic organ,there was no significant difference between leaf area index and silique area index at the maximum value.With the increase of potassium application rates,leaf area index and silique area index increased significantly,but did not increase significantly when potassium application was more than 120 kg/ha.Correlation analysis showed that leaf and silique area index were positively correlated with biomass and yield.The application of potassium fertilizer increased the photosynthetic area of photosynthetic organs,increased the number of pods per plant,and promoted the yield.(2)At different growth stages,K application rates can significantly improve the stomatal conductance,transpiration rate and net photosynthetic rate of photosynthetic organs,and reduce the difference between canopy temperature and ambient temperature.The diurnal variation of photosynthetic capacity and canopy temperature showed that the differences of net photosynthetic rate,stomatal conductance,transpiration rate and canopy temperature were the largest in different treatments at noon,and the differences of net photosynthetic rate,stomatal conductance and transpiration rate increased with the increase of potassium application,while the differences of canopy temperature and ambient temperature decreased with the increase of potassium application.In the morning and evening,there was no significant difference in photosynthetic capacity and canopy temperature between different K treatments,and the variation range of canopy temperature decreased with the increase of K application.In different growth stages,net photosynthetic rate,stomatal conductance and transpiration rate of photosynthetic organs were negatively correlated with canopy temperature.The stability of potassium nutrition regulating canopy temperature,in the over-wintering stage,bolting stage and podding stage,the daily range of canopy temperature decreased by 0.37 ?,0.54 ? and 0.83 ? for every 1% increase of potassium content,with the increase of environmental temperature,the effect of Potassium Fertilizer on maintaining the stability of canopy temperature is more obvious.It can be seen that the application of potassium fertilizer can significantly reduce the variation of canopy temperature,so as to promote photosynthetic organs to maintain higher photosynthetic capacity.(3)There were significant differences in stomatal conductance,transpiration rate and leaf temperature response to light in different potassium supply levels,adequate potassium supply could reduce response time to a stable state.Under the light dynamic change,the leaf temperature obtained by the energy balance model is consistent with the measured leaf temperature change trend,When the light intensity step increases,the leaf temperature increases rapidly to the maximum value,and then decreases slightly to a stable state;when the light intensity step decreases,the leaf temperature decreases rapidly to the minimum value,and then increases to the temperature before the initial change of light intensity.According to the energy balance model,the mechanism of potassium regulating temperature change was explored.The results showed that adequate potassium supply could reduce the response time of stomatal conductance and quickly reach a stable state;under adequate potassium nutrition,transpiration rate was strong,which reduced leaf heat;adequate potassium supply increased leaf specific heat capacity and reduced leaf temperature variation.In conclusion,under adequate potassium supply,stomatal response time to environmental change was reduced,transpiration rate and specific heat were kept high,and canopy temperature and its variation degree were reduced.