Study On The Difference Of Photosynthetic Phosphorus Efficiency And Physiological Mechanism Of Soybean At Different Acclimation Stages

Under the condition of P deficiency,plants can maintain photosynthetic rate by optimizing P allocation among leaf P components.Photosynthetic P-use efficiency（PPUE）is an important adaptive mechanism of phosphorus deficit habitats.Soybean domestication not only increased the grain yield of soybean,but also changed many agronomic traits of soybean.But did soybean domestication improve the photosynthetic phosphorus utilization rate of soybean?Is the increase of photosynthetic phosphorus utilization related to the change of phosphorus components in leaves?These questions remain to be answered.In this study,7 kinds of wild soybean species,7 kinds of local soybean species and 7 kinds of soybean varieties were developed high P（+P:20 mg P kg-1 sand）and low P(-P:0 mg P kg^-1sand).The net photosynthetic rate,stomatal conductance,transpiration rate,leaf anatomical structure,chlorophyll content and the contents of phosphorus components in leaves of soybean were determined.The changes of photosynthetic phosphorus utilization and the correlation between photosynthetic phosphorus and phosphorus components in leaves were analyzed during soybean domestication.The main research results are as follows:1)Under high P level,the root-shoot ratio,net photosynthetic rate,chlorophyll content and Leaf mass area（LMA）of local soybean species and cultivated soybean varieties were significantly higher than those of wild soybean,indicating that domestication increased the net photosynthetic rate,root-shoot ratio,LMA and chlorophyll content of soybean.The net photosynthetic rate,stomatal conductance and transpiration rate of wild soybean were decreased,while the root shoot ratio,chlorophyll content and LMA were increased in response to low phosphorus environment.Local soybean cultivars can adapt to low phosphorus stress by increasing chlorophyll content and root-shoot ratio,while soybean cultivars can adapt to low phosphorus stress by increasing net photosynthetic rate,stomatal conductance and root-shoot ratio,and reducing chlorophyll content and LMA.The correlation analysis showed that the photosynthetic rate had a significant positive correlation with chlorophyll content and root-shoot ratio.2)From wild soybean to cultivated soybean,the ratio of palisade tissue thickness to spongy tissue thickness of soybean leaves decreased gradually,indicating that spongy tissue thickness was gradually thickened during the domestication process,and leaf looseness（that is,the ratio of spongy tissue thickness to leaf thickness）was increased,and leaf tissue structure gradually became looser.There were significant differences in leaf thickness between three different stages of acclimation,and there was a significant positive correlation between leaf sponge tissue thickness and LMA.There was no significant correlation between leaf anatomical indexes and photosynthetic rate of soybean.3)Under high P level,photosynthetic P utilization rate of leaves from wild soybean cultivars to cultivated soybean cultivars increased gradually.Low P significantly increased photosynthetic P utilization,which was related to the decrease of primary metabolic P content and the increase of nucleic acid P content.4)Under the high P level,the proportion of P components in leaves of three domesticated soybean varieties was different,and the proportion of primary metabolic P content in total P content was the highest.Among three different domesticated soybean cultivars,the proportion of nucleic acid phosphorus in leaves of wild soybean cultivars was the highest,which was 21%.Under low P level,leaf primary metabolic P decreased by 17-26%and leaf nucleic acid P increased by 11-20%.The proportion of lipid phosphorus,nucleic acid phosphorus and residual phosphorus in total phosphorus content was positively correlated with photosynthetic phosphorus utilization rate（r=0.35,r=0.60,r=0.70）,and the proportion of primary metabolic phosphorus content in total phosphorus content was negatively correlated with photosynthetic phosphorus utilization rate（r=0.63）.The results indicated that soybean could respond to low P stress by decreasing the P distribution to primary metabolic P and increasing the P distribution to nucleic acid.In conclusion,soybean domestication increased photosynthetic phosphorus utilization,leaf chlorophyll content and root-shoot ratio increased leaf photosynthetic rate.The increase of photosynthetic phosphorus utilization was closely related to the allocation strategy of phosphorus components and photosynthetic rate of soybean leaves.Under low P stress,soybean reduced the distribution of primary metabolic P and more P was allocated to nucleic acid P to improve the utilization rate of photosynthetic P.