Effects Of Drought Stress On Photosynthetic Characteristics And Physiological Mechanism Of Different Drought Resistance Rice

In recent years,the frequency and extent of drought in rice growing areas in the middle-lower reaches of the Yangtze river have increased.The annual yield reduction of rice in this region is about 0.5 billion kilograms,which causing losses to be the first of natural disasters.Photosynthesis decreased by drought was the main reason for rice yield reduction.Studying the response mechanism of photosynthesis to drought stressand revealing the physiological mechanism of drought stress affecting photosynthesis and yield,were great significance for exploring drought-resistant cultivation and rice breeding.Pot experiments were conducted with three different types of rice varieties,Huanghuazhan（general rice）,Hanyou113（water-saving and drought-resistant rice）and Zhonghan 3（upland rice）under four water treatments（control check,mild drought stress,moderate drought stress and severe drought stress）at the booting stage and heading stage.Leaf water potential,photosynthetic pigment content,photosynthetic parameters,photosynthetic response,chlorophyll fluorescence parameters and antioxidant enzyme system activitieswere analyzed.The main research results are as follows:1.Rice yield was significantly decreased under drought stress at booting stage and heading stage,and yield decreased with the increasing of drought stress.The yield of HHZ,HY113 and ZH3 decreased by 35.6%,30.7%,22.6%,respectively.Which means HY113 and ZH3 shows more stronger drought resistance.The main reason for yield decrease was the significantly decrease in spikelets per panicles,setting rate and grain weight.There was no significant effect on the rice quality in three rice cultivars at booting stage and heading stage under mild drought stress,but significantly reduced the rice milling,appearance and nutritional quality under moderate and severe drought stress.The milling and nutritional quality of ZH3 were less affected by drought stress,but the appearance quality was more affected by drought stress than HY113 and HHZ.2.Drought stress had significant effects on leaf chlorophyll content and SPAD.Compared with CK,the chlorophyll content of rice leaves decreased under drought stress at the booting stage and heading stage,and decreased with the increasing of drought stress.The main reason for the decrease of chlorophyll content under drought stress is the increase of chlorophyll b（Chb）decomposition,which lead to of Cha and Chb ratio.The SPAD value of ZH3 and HY113 increased under mild stress conditions,but the SPAD values of ZH3 and HY113 were higher than HHZ under severe drought stress.Drought stress significantly reduced the photosynthesis of three rice varieties.Compared with CK,the photosynthesis rate of rice was significantly reduced under drought stress at booting stage and heading stage,and the inhibition of photosynthesis rate by drought was dominated by stomatal limitation turn to non-stomatal limitation under severe drought stress.The photosynthesis of three types of rice varieties had significant differences in response to drought stress.The photosynthesis rate HY113and ZH3 under drought stress were better than HHZ.It indicated that the upland rice and water-saving and drought-resistant rice varieties could maintain good photosynthesis under drought stress and maintain certain material production.3.Drought stress at the booting stage and heading stage resulted in a significant increase in minimal fluorescence yield（F₀）and non-photochemical quenching（NPQ）,while significant decrease the Maximum quantum efficiency of PSII（F_v/F_m）,actual quantum efficiency of PSII（ΦPSII）,and photochemical quenching（q P）of all three rice cultivars.It is indicated that drought stress reduced the PSII proton storage（PQ）capacity of the leaves,and the PSII primary light energy conversion efficiency and PSII potential activity were directly inhibited,which directly affected the electron transfer and CO2 assimilation process of photosynthesis,thereby reducing the leaf photosynthesis.The light energy distribution ratio shows that the energy of the photochemical reaction（P）of ZH3 and HY113 is higher than that of HHZ,and the energy of the photochemical reaction（E）dissipates as HHZ is significantly higher than ZH3 and HY113,what indicating that energy utilization of upland rice and water-saving drought-resistant rice is higher than conventional rice.4.The antioxidant enzyme system in rice leaves was initiated by drought stress.The antioxidant enzyme activities of rice leaves increased with under mild drought stress,but decreased significantly under severe drought stress.The balance between the increase and elimination of reactive oxygen species is broken,leading to membrane lipid peroxidation and increased MDA content,which ultimately leads to the destruction of photosynthetic machinery membrane,which is also an important reason for non-stomatal limitation of rice photosynthesis under severe drought stress.The activity of antioxidant enzymes of ZH3 was higher than HY113,and the lowest was HHZ,but the MDA content of HHZ was significantly higher than that of ZH3 and HY113,indicating that the ability free radicals of antioxidant enzymes in the leaves of upland rice and drought-resistance rice were better than conventional rice,which better protects photosynthesis institutions from functioning properly.In summary,Drought stress can reduce rice yield by reducing leaf photosynthesis,and the yield reduction caused by drought stress at booting stage is significantly higher than that at heading stage.The yield reduction of upland rice varieties and water-saving and drought-resistant rice varieties is smaller than that of common rice varieties.Maintaining higher leaf water potential,photosynthetic rate,PSII primary light energy conversion efficiency,non-photochemical quenching coefficient（NPQ）,fluorescence photochemical reaction energy ratio and antioxidant enzyme activity for upland rice and water-saving drought-resistant rice are the main mechanism maintained relatively high photosynthesis.