| The simplification and mechanization of rice planting is the inevitable trend of the modernization of planting production.The mechanization of rice production requires a relatively short growth period,and at the same time requires more dry matter producing in a short period to ensure the matter basis required for high yield.Improving the matter producing efficiency of rice varieties is an urgent problem to be solved for the sustainable development of rice producing.The high-efficiency rice producing includes two aspects:high efficiency of matter producing and high efficiency of resource utilization.At present,the research on high-efficiency rice varieties mainly focuses on the high-efficiency characteristics of fertilizer utilization,while the research on highefficiency matter producing of varieties is relatively few,and there is a lack of mechanism analysis on the formation of high-efficiency matter producing capacity of rice varieties.There is also a lack of necessary in-depth research on the synergistic mechanism of high-yield and high-efficiency formation of rice.In this study,hybrid rice and conventional japonica rice varieties with different matter producing efficiency were selected as materials.Through field experiments and pot experiments,different nitrogen supply levels were treated to observe the yield formation and matter producing characteristics of each variety under different nitrogen levels.Physiological basis including leaf photosynthetic producing capacity,root morphological and physiological characteristics and nitrogen metabolism performance as well were further analyzed,the performing characteristics and physiological mechanism of high-yield and highefficiency varieties were discussed.The results of this study can provide theoretical basis for the breeding and cultivating regulation of high-yield and high-efficiency rice varieties.The main results are as follows:1.High-yield and high-efficiency rice varieties first showed large sink capacity,hybrid rice varieties are characterized by higher number of grains per panicle,and conventional japonica rice varieties are characterized by relatively high number of effective panicles,they obtained higher seed setting rate through strong matter producing during the fruiting period,thus showed higher yield.The stem-sheath translocation amount,stem-sheath translocation rate and spike matter increasing of high-yield and high-efficiency rice varieties were significantly higher than those of general varieties,indicating that their individual and population matter producing capacity was strong,especially the matter producing and transportation during the fruiting period.Compared with the general varieties,it has obvious advantages.The high-yield and high-efficiency rice varieties have developed roots,and the root activity was higher.The rapid occurrence of tillering is the main manifestation of its early growth.The high-yield and high-efficiency rice varieties had stronger response to nitrogen,and still showed higher producing capacity at higher nitrogen levels.2.The high-yield and high-efficiency rice varieties showed higher leaf net photosynthetic rate at heading stage,and leaf stomatal conductance,intercellular CO2 concentration and transpiration rate were significantly higher than those of general varieties,indicating that the leaf transpiration of high-yield and high-efficiency rice varieties was stronger,which can increase the supply of photosynthetic substrates and provide guarantee for stronger photosynthetic capacity.The photosynthetic rate of leaves decreased significantly at the middle stage of grain filling(20 days after heading),but the decrease of photosynthetic rate of leaves in high-yield and high-efficiency rice varieties was relatively small.However,there was no significant difference in stomatal conductance between the high-yield and high-efficiency rice varieties and the general varieties,and the intercellular CO2 concentration of leaves was consistent with the stomatal conductance of leaves,indicating that the supply of photosynthetic substrates may not be the direct limiting factor for the decline of photosynthetic capacity of varieties.The high-yield and high-efficiency rice varieties had strong root physiological activity during the fruiting period,the chlorophyll content of leaves decreased slightly,and the senescence rate was slow,which may be the main reason for maintaining high photosynthetic producing efficiency.The high-yield and high-efficiency rice varieties had higher antioxidant protective enzyme activities in the middle and late fruiting stages,which relatively delayed leaf senescence and maintained relatively strong photosynthetic capacity in the middle and late fruiting stages.3.The high-yield and high-efficiency rice varieties showed higher nitrogen use efficiency,especially the nitrogen absorption and utilization efficiency were significantly higher than that of the general varieties.With the increasing of nitrogen level,the indexes of nitrogen agronomic utilization efficiency,nitrogen partial productivity and nitrogen physiological utilization efficiency decreased,and the total nitrogen uptake increased.Under high nitrogen level,the nitrogen utilization efficiency of high-yield and high-efficiency rice varieties in hybrid rice was greatly affected by nitrogen level,while the high-yield and high-efficiency rice varieties in conventional japonica rice still showed relatively high nitrogen absorption and utilization efficiency.Under high nitrogen level,the response degree of nitrogen utilization efficiency of highyield and high-efficiency rice varieties in hybrid rice to nitrogen level was relatively low,and the decrease of each efficiency index was small.There was no significant advantage in nitrogen absorption and utilization efficiency of high-yield and highefficiency rice varieties in conventional japonica rice.The activities of glutamine synthetase(GS)and glutamate synthase(GOGAT)in leaves were higher than those of general varieties,indicating that the assimilating ability of ammonium nitrogen was higher than that of general varieties.The decrease of GS and GOGAT enzyme activity in the middle and late filling stage was relatively small.4.Under the low light stress during the fruiting period,the high-yield and highefficiency rice varieties still have relatively high seed setting rate,so the yield decline was small.Compared with the general varieties,the dry matter accumulating of highyield and high-efficiency rice varieties decreased less under low light stress,the stem and sheath transport amount and transport rate were relatively low,and the spike increasing was relatively larger.Under low light stress,it still maintained high matter producing capacity.Low light stress reduced the net photosynthetic rate and the activities of the key enzymes involved in leaf nitrogen metabolizing.In the middle stage of grain filling,low light stress reduced the net photosynthetic rate and key enzyme activities of nitrogen metabolism in leaves,but the decrease of high yield and high efficiency rice varieties was smaller.Under low light stress,the leaf chlorophyll content of high-yield and high-efficiency rice varieties increased significantly and the advantages were obvious.The leaf senescence was relatively delayed and had good resistance to low light stress. |
