Studies On The Mechanisms Of Rice Photosynthesis In Response To Fluctuating Light

Rice is one of the most staple crops for more than 50% of the population in the world.Due to the rapid growth of population and the limitation of arable land area,resources and other factors,the main technical way to ensure our country’s food security and increase the total grain production is to greatly increase the yield per unit area of grain crops,such as rice.Through high-yield breeding,reasonable water,fertilizer and cultivation management,the light absorption efficiency by the rice canopy and harvest index have gradually approached the theoretical upper limit.It is difficult to break through the yield potential of existing varieties by optimizing the above-mentioned ways.Therefore,improving the light use efficiency is an effective way to greatly improve crop yield.Under natural conditions,due to the change of the sun angle,clouds over,and shading from upper or adjacent leaves,the light intensity on the leaf surface changes very complex,resulting in a large amount of carbon loss and unnecessary water waste.Elucidating the mechanism of leaf photosynthesis in response to light fluctuations,and its water use strategy under fluctuating light will provide theoretical guidance for future rice breeding with high light use efficiency.According to the above objectives,the content of this research mainly includes the following five sections: 1)the relationship between steady-state and non-steady-state gas exchange parameters;2)how the stomata morphological characteristics affect the response of gas exchange parameters to fluctuating light,and thereby affecting the accumulation of plant biomass;3)the key limiting factors of leaf photosynthesis in response to fluctuating light among rice genotypes;4)the Effects and mechanisms of water managements on rice photosynthesis in response to fluctuating light;5)the Effects and mechanisms of different nitrogen supplements on rice photosynthesis in response to fluctuating light.The main results are as follows:1.There were significant differences in steady-state and non-steady-state gas exchange among different rice genotypes,and the variation of steady-state stomatal conductance between rice genotypes ranged from 0.09 mol m-2 s-1 to 0.28 mol m-2 s-1(gsi)and 0.46 mol m-2 s-1 to 0.88 mol m-2 s-1(gsf),and the variation of steady-state photosynthetic rate between rice cultivars was 4.36 mmol m-2 s-1 to 7.88 mmol m-2 s-1(Ai)and 24.7 mmol m-2 s-1 to 34.0 mmol m-2 s-1(Af).The response rate of stomatal conductance to fluctuating light ranged from 134 s to 434 s(P90g),and the response rate of photosynthetic rate to fluctuating light ranged from 224 s to 307 s(P90A)across rice genotypes.There was no obvious correlation between steady-state and non-steadystate gas exchange,and more studies may need to focus on the dynamic response of leaf gas exchange parameters under natural conditions in the future.2.There were large differences in stomatal morphology of different rice genotypes,among which the variation of stomatal size ranged from 224 mm2 to 491 mm2,and stomatal density ranged from 252 mm-2 to 730 mm-2.Higher density of smaller stomata contributed to the faster response of photosynthesis and stomatal conductance to light fluctuations,but reduced leaf water use efficiency.The response rates of stomatal conductance and photosynthesis to fluctuating light were significantly correlated to plant biomass,respectively,and the faster the response rate,the greater the plant biomass.3.Compared with diploid rice,tetraploid rice possessed larger and less stomata.There were no obvious differences in photosynthetic rate and stomatal conductance between tetraploid and diploid rice under constant light condition,while the response rate of stomatal conductance and photosynthetic rate in tetraploid rice is significantly slower than that in diploid rice under fluctuating light.Further analysis suggested that there were no difference in the response rate of biochemical processes to fluctuating light between tetraploid and diploid rice,thus stomatal opening is the main factor limiting rice photosynthesis in response to fluctuating light.4.The response rates of stomatal conductance and photosynthesis to fluctuating light in tetraploid rice were significantly slower than those in diploid rice under well water conditions,while there were no significant difference in the response rates of stomatal conductance and photosynthesis between tetraploid and diploid rice under Water deficit.Water deficit significantly increased the stomatal density and reduced the stomatal size of tetraploid rice,which accelerated the response of stomatal conductance and photosynthesis to fluctuating light,but had little effect on stomatal morphology in diploid rice.Further analysis suggested that stomatal opening was the main factor limiting photosynthetic induction under Water deficit.Meanwhile,Water deficit significantly reduced the stomatal conductance and photosynthetic rate of diploid rice under constant light conditions,but had less effect on gas exchange parameters in tetraploid rice.Therefore,compared with diploid rice,tetraploid rice exhibits a higher capacity of carbon assimilation under Water deficit.5.Higher nitrogen supply significantly improved the photosynthetic efficiency of rice under both constant and fluctuating light conditions,thereafter accelerating the accumulation of plant biomass.With the increasing supply of nitrogen,the response rate of stomatal opening,biochemical processes and photosynthetic rate to a stepwise increase in light intensity were all significantly increased in rice leaves.Limitation analysis indicated that biochemical processes was the main factor limiting rice photosynthetic induction among different nitrogen supplements.