Difference In Response To Low Phosphorus Among Rice Varieties And Its Physiological Mechanism

Phosphorus is one of the essential elements for plant growth,and it is also the most used element next to nitrogen and potassium.But phosphorus is a nonrenewable resource.With the development of agricultural production,the shortage of phosphate fertilizer resources has become a global problem.Rice is not only one of the three largest cereal crops in the world,but also the most important grain crop in China.Therefore,exploration and utilization of rice varieties with tolerance to low phosphorus is an important way to save phosphate fertilizer resources and to achieve high yield and high efficiency of crops,which have great significance in promoting sustainable agricultural development.However,the difference in response to low phosphorous among rice varieties is not clear,and the agronomic and physiological characteristics of a variety with high phosphorus use efficiency(PUE)or a variety with tolerance to low phosphorus are not understood.To solve these problems,this study conducted hydroponic experiments and designed two concentrations of phosphorus,low phosphorus(LP)and normal phosphorus(NP,control),using 11 rice varieties which have been planted in Jiangsu Province in recent 70 years.According to the LP tolerance index[grain yield of LP treatment × LP tolerance coefficient(grain yield of LP treatment/grain yield of control)/average grain yield of LP treatment for all tested varieties],the tested varieties were divided into 3 categories:strong tolerance to low phosphorus,medium tolerance to low phosphorus,and weak tolerance to low phosphorus.Grain yield and main agronomic and physiological traits of rice varieties differing in tolerance to low phosphorus were investigated.The main results are as follows.1.The LP tolerance index was significantly and positively correlated with grain yield under low phosphorus treatment(r = 0.79**),indicating that LP index can reflect the tolerance for a rice variety to LP stress.With LP tolerance index as a screening index,the tolerance to LP of 11 varieties was evaluated:a variety with strong tolerance to LP was considered if LP tolerance index ?1,and a variety with medium tolerance to LP if 0.6<LP tolerance index<1,and a variety with weak tolerance to LP(W)if LP tolerance index<0.6.Based on the thresholds,the varieties Yongyou 2640 and Yanjing 2 were strong tolerance to LP;and Lianjing 7,Sidao 8,Jinnanfeng,Xudao 2,Huaidao 5,and Guihuahuang were medium tolerance to LP;and Guihuaqiu,Liming,and Zhendao 88 were weak tolerance to LP.The PUE was higher for a variety with strong tolerance to LP than for a variety with weak tolerance to LP.2.Compared with NP(control),LP decreased panicle number and grain number per panicle,whereas increased 1000-grain weight and seed-setting rate.However,increases in 1000-grain weight and seed-setting rate could not compensate for decreases in panicle number and grain number per panicle,resulting in reduction in grain yield.Under LP treatment,a variety with strong tolerance to LP had more panicle number and grain number per panicle than a variety with weak tolerance to LP,and consequently,the former produced higher grain yield than the later.3.Compared with a variety with weak tolerance to LP,a variety with strong tolerance to LP showed larger root biomass,ratio of root to shoot,root aerenchyma,and vascular catheter,earlier tillering,greater percentage of productive tillers,higher proportion of highly effective leaf area,and photosynthetic capacity,larger sink capacity and ratio of sink to source,more remobilization of non-structural carbohydrates from vegetative tissues to grains and more dry matter accumulation during the grain filling period,and higher nitrogen and potassium use efficiencies.Above traits accounted for achieving higher grain yield and higher PUE for a variety with strong tolerance to LP under the LP condition.