Effects Of Water And Light Interaction On Growth And Physiological Metabolism In Welsh Onion

Welsh onion（Allium fistulosum L.）is an important seasoning vegetable in China with a long growth period.Welsh onion’s cultivation stubble mostly goes through summer,and welsh onion is easily affected by drought and strong light stress.To explore the response characteristics of welsh onions to drought and strong light,based on field experiments,the LED intelligent spectrum customized lights were used to simulate strong light,and 10%PEG-6000 Hoagland solution was used to simulate drought stress.The thesis studied the effects of different treatments（T1:0%PEG+800μmol/m²/s;T2:10%PEG+800μmol/m²/s;T3:0%PEG+1800μmol/m²/s;T4:10%PEG+1800μmol/m²/s）on the growth,yield and quality,secondary metabolism,photosynthetic capacity,and active oxygen metabolism of welsh onions,and aims to provide a theoretical basis for the innovation of summer cultivation techniques of welsh onions.The main findings are as follows:1.In the summer cultivation,the growth,photosynthetic capacity,nutritional quality,and yield of welsh onion decreased significantly under drought stress.The yield decreased by6.9%and 71.4%when the soil relative water content was 60%and 40%,respectively,compared with 80%.Shading could alleviate the damage caused by drought stress and promote the growth of welsh onions.The yield with 20%and 40%shading increased by39.04%and 35.85%,respectively.The results showed that shading could alleviate the damage caused by drought and strong light environment,promoted welsh onion growth,and significantly increased yield.2.Drought and strong light stress induced the‘granular’waxy crystals in the leaf epidermis of welsh onion,and the waxy crystals accumulated in the leaf epidermis.The wax content of leaves increased significantly.Compared with T1,T2,T3,and T4 increased by74.87%,36.04%,and 112.29%,respectively.The contents of ketones,alkanes,and alcohols were significantly increased;in particular,the increase of wax could form an effective cuticle transpiration barrier.The waxy substances of welsh onion leaves had the highest content of ketones,up to 65.47%.The ketones were mainly C29-ketones.The results showed that C29-ketones are the main substances in the waxy crystals of welsh onions leaves.3.Drought stress induced a significant increase in alcohols in welsh onion leaves.T2 and T4 increased 19.92 times and 19.10 times compared with T1,respectively,while sulfur content decreased significantly,reaching 60.09%and 52.54%.Strong light stress stimulated the leaf alkanes to increase significantly,and T3 increased by 63.39%compared with T1.The sulfur substances in leaves were mainly disulfides,accounting for 76%.Drought and strong light stress reduced the disulfides in leaves,while the proportion of trisulfides increased.For the pseudostem,drought and strong light stress caused a significant decrease in volatile substances’content.Compared with T1,T2,T3,and T4 were reduced by 29.4%,10.17%,and28.79%,respectively.The volatile matter of pseudostem is mainly sulfur and aldehydes.Drought and strong light stress caused a significant decrease in sulfur content.Compared with T1,T2,T3,and T4 were reduced by 29.58%,6.27%,and 32.7%,respectively.Besides,drought and strong light stress reduced the content of pyruvate,soluble sugar,and soluble protein in the edible part of welsh onions,while the content of crude fiber increased,resulting in reduced nutritional quality.4.Drought,strong light,and their interactive treatments resulted in a significant decrease in Fv/Fm of welsh onion leaves,and T2,T3,and T4 were reduced by 18.13%,13.45%,and21.3%,respectively,compared with T1.Drought and strong light stress caused a significant decrease in Y（II）and a significant increase in Y（NO）and Y（NPQ）of welsh onion leaves.With the extension of the stress time,the degree of photoinhibition gradually increased.The Y（I）of the leaves decreased slightly,and the Y（ND）and Y（NA）increased.The results showed that the PSI might be damaged.Drought and strong light stress induced an increase in the PQ pool of welsh onion leaves,and T2,T3,and T4 increased by 2.16 times,2.07 times,and 3.74 times respectively,compared with T1.The increase of ETR（I）/ETR（II）,CEF,and transmembrane proton gradients induced by drought and strong light stress accelerated the dissipation of excess excitation energy,thereby protecting the photosynthetic apparatus.The results showed that CEF was an important electron dissipation pathway in welsh onion leaves under drought and strong light stress.5.Drought,strong light,and their interaction treatments significantly inhibited welsh onions’growth,reduced leaf pigment content,and caused a significant decrease of Pn in leaves,and inhibited carbon and nitrogen assimilation.The contents of MDA and H₂O₂ in welsh onion leaves treated with T2,T3 and T4 increased significantly,while antioxidant enzymes such as SOD,POD,CAT,and APX and the content of antioxidant substances decreased significantly.The comprehensive analysis showed that drought and strong light stress caused the accumulation of ROS and MDA in the leaves of welsh onions,thereby destroying the ultrastructure of the leaves,reducing the photosynthetic capacity of the leaves,hindering the assimilation of carbon and nitrogen in the leaves,and ultimately inhibiting the growth of seedlings.