Effects Of Alkaline Salt Stress On Seedling Growth And Rhizosphere Soil Environment Of Rapeseed

As one of the main oil crops in the world,rapeseed has a certain saline-alkali tolerance.There are a lot of saline-alkali cultivated land in northern China,especially in Inner Mongolia,which has a prospect of development and utilization.To study the changes of seedling growth and rhizosphere soil environment of rapeseed under alkaline salt（the mixture of Na HCO₃ and Na₂CO₃ with a molar ratio of 2:1）can look for crops suitable for saline-alkali soil,which is of great significance for the development and utilization of salinized and alkaline land.In this study,8 rapeseed germplasm were screened for salt and alkali resistance by fuzzy mathematics membership function analysis,and two rapeseed germplasm with the strongest and weakest resistance to alkali salt were selected.Four treatments were set by pot-grown experiment,the concentration of alkaline salt in the soil was 0,2,4 and 6 g/kg.The dry and fresh weight of shoot and root,root morphology,content of crude protein,NDF and ADF,antioxidant enzyme activity of root,content of soil available nutrients,soil enzyme activity,organic acid content and microbial community structure were measured under different concentrations of alkaline salt stress.The main results are as follows:1.The order of comparison of salt and alkali tolerance of 8 rapeseed germplasm was as follows:Huayouza 62>Huashuang No.5>Chong 2>16-P22 wai>Qingza No.9>Jinyou 158>17 chong 1>16-p32 wai.2.With the increase of alkaline salt concentration,the dry and fresh weight of shoot and root,root morphological indexes of both rape germplasm decreased in the early seedling stage,but increased first and then decreased in the late seedling stage,and reached the peak value under A2 treatment.The dry and fresh weight of shoot and root,root morphological indexes and crude protein content of two rape germplasm were significantly decreased while the contents of neutral detergent fiber（NDF）and acid detergent fiber（ACF）were significantly increased under high concentration alkaline salt stress at two stages.Under alkaline salt stress,the dry and fresh weight of shoot and root and root morphological indexes of Huayouza 62 were less inhibited than those of16-P32wai,but the contents of crude protein and neutral and acid detergent fiber were not significantly different.3.The activities of antioxidant enzymes in roots of two rapeseed germplasm increased first and then decreased with the increase of alkaline salt concentration,and reached the peak under A4 treatment.The activities of SOD and POD in roots of two rapeseed germplasm decreased in the late seedling period compared with the early seedling period,while the activities of CAT increased.In the process of resisting osmotic stress and reactive oxygen damage caused by alkaline salt stress,the antioxidant capacity of Huayouza 62 is generally stronger than that of 16-P32wai.4.Under alkaline salt stress,the content of available P and available K in the rhizosphere soil of two rapeseed germplasm increased first and then decreased with the increase of alkaline salt concentration,while the content of alkali-hydrolyzed N showed a decreasing trend.The content of soil available nutrients in the late seedling period was lower than that in the early seedling period,and the content of soil available nutrients in the rhizosphere of Huayouza 62 was generally higher than that OTUside 16-P32wai.The activities of soil enzymes in the rhizosphere of Huayouza 62 increased first and then decreased with the increase of alkaline salt concentration,while the activities of alkaline phosphatase in 16-P32wai decreased with the increase of alkaline salt concentration.The enzyme activities of rhizosphere soil in Huayouza 62 were generally higher than those 16-P32wai.5.Under alkaline salt stress,oxalic acid,tartaric acid,formic acid,malic acid,ascorbic acid,acetic acid,citric acid and succinic acid were detected in two rapeseed rhizosphere soil.Oxalic acid plays a more important role in response to p H stress.The contents of tartaric acid,acetic acid and ascorbic acid in some treatments were decreased compared with the control,while the contents of other acids were increased.The organic acids secreted by roots of rapeseed germplasm with strong resistance to alkali salt and with weak resistance to alkali salt were different.The contents of oxalic acid and malic acid in the rhizosphere soil of Huayouza 62 were higher than those 16-P32 wai under high alkaline salt stress,formic acid and tartaric acid were lower than those 16-P32wai,and the contents of citric acid,succinic acid and acetic acid were higher than those OTUside 16-P32 under all treatments.6.The abundance of bacteria and fungi in the rhizosphere soil of the two rapeseeds germplasm increased first and then decreased with the increase of alkaline salt concentration,and reached the peak under A2 treatment.High concentration alkaline salt stress can reduce the abundance of bacteria and fungi.The abundance of bacteria and fungi under all treatments was higher than 16-P32wai.Proteobacteria were dominant strains of two rape germplasm under alkaline salt stress.Apart from the"unclassified"flora,Ascomycetes were dominant fungi under alkaline salt stress of the two rape germplasm.Proteobacteria and Ascomycetes were negatively correlated with the contents of alkali-hydrolytic nitrogen,available phosphorus and available potassium in rhizosphere soil.Oxalic acid,citric acid and succinic acid were positively correlated with the dominant bacteria in the rhizosphere soil of the two rapeseed germplasm under alkaline salt stress.