Physiological Mechanism Of Drought Resistance In Seedling Stage Of Elymus Sibiricus

As the most important abiotic stress for the growth and development of forage grass,drought seriously restricts the sustainable development of agriculture and animal husbandry and the construction of ecological environment in our country.To explore the drought resistance mechanism of crops and improve the drought resistance of crops have become an urgent research subject to be solved.Elymus sibiricus is an important economic species of Elymus L.It's a dominant grass species suitable for artificial grassland establishment and natural grassland improvement in Qinghai-Tibet Plateau,base on the characteristic of fast growth,developed root system,rich leaves,drought resistance,cold resistance etc.In this study,Firstly,52 wildtype Elymus sibiricus species were evaluated for drought resistance based on 13 physiological indexes of chlorophyll fluorescence and membrane permeability,from which one drought-resistant germplasm?DT?and one drought-sensitive germplasm?DS?were selected.Secondly,the physiological mechanism of drought resistance of Elymus sibiricus was explored by analyzing the root morphology and configuration of DT and DS under drought stress,the primary reaction in leaf photosynthesis,the process of electron transport and gas exchange,leaf water status,and the difference of ascorbate-glutathione?ASA-GSH?cycle metabolism in leaf antioxidant system.The results are as follows:1.In this study,the drought resistance of 52 germplasms were evaluated comprehensively of which used the membership function.Among them,the drought-resistance of E37 was relatively strong,represented by DT,and E23 was relatively weak,represented by DS.Based on the analysis of 13 physiological indexes,it was found that the drought variation index of relative conductivity?REC?and PS?maximum photochemical quantum yield?Fv/Fm?was significantly higher than that of the other11 physiological indexes.In further analysis of the two indexes,it was found that there was a significant negative correlation between them,and was closely related to the strength of plant drought resistance,so it was suggested that they should be used as the preferred index for drought resistance evaluation of a large number of germplasm resources.2.The study on the root morphology and configuration of DT and DS under drought stress?PEG-6000?showed that the total root length,surface area,volume,root tip number,bifurcation number,fractal dimension and topological index that decreased significantly.However,the DT was decreased more significantly than DS,indicating that higher root morphological characteristics such as root length,surface area and more lateral roots could maintained the ability to obtain nutrients from soil may be one of the important strategies for DT to deal with drought stress.3.The study on the photosynthetic system and water status of DT and DS under drought stress showed that the water potential??w?,osmotic potential??s?,net photosynthetic rate?Pn?,transpiration rate?Tr?,stomatal conductance?Gs?,water use efficiency?Pn/Gs?,stomatal limit value?Ls?,maximum photochemical quantum yield?Fv/Fm?,electron transport rate?ETR?and photochemical quenching coefficient?q P?in the leaves of DT and DS decreased significantly.The turgor pressure??t?increased significantly.The non-photochemical quenching coefficient?NPQ?of intercellular carbon dioxide concentration?Ci?increased significantly.Meanwhile,the magnitude of change in DT is less than DS.Showing that,compared with DS,DT has more stable water condition and stronger ability of photosynthesis metabolism under drought stress4.The study on the antioxidant system of DT and DS under drought stress showed that the contents of superoxide anion(O^2-),hydrogen peroxide?H₂O₂?,ascorbate?ASA?,mono-dehydroascorbate reductase?MDHAR?,dehydroascorbate reductase?DHAR?and the ratio of ascorbic acid to dehydroascorbic acid?ASA/DHA?in DT and DS leaves increased significantly,while the glutathione?GSH?content increased at first and then decreased.The content of ascorbate reductase?APx?decreased at first and then increased.And the change range of DT is less than that of DS.It shows that under drought stress,compared with DS,DT has stronger ability of anti-oxygen metabolism.The above results systematically revealed the physiological mechanism of Elymus sibiricus adaptation to drought stress.