Effects Of Water Deficit And Rehydration At Seedling Stage On Root Development And Root Zone Soil Of Soybean

Using drought-sensitive soybean Suinong 26 and drought-tolerant soybean Heinong 54 as materials,we set the soil water content at 70% ± 5% of the field water holding capacity(normal water supply,CK),60% ± 5%(mild water deficit,T1),50% ± 5%(moderate water deficit,T2)and40% ± 5%(severe water deficit,T3)at the soybean seedling stage(V1)in a pot experiment.The effects of different degrees of water deficit and rehydration at seedling stage on root characters,root physiological characteristics,root nutrient uptake,soil nutrient content,soil enzyme activity,soil microbial diversity and yield of soybean were studied systematically,the response characteristics of soybean root and soil related indexes to water deficit and the compensation effect after rehydration were clarified in order to provide theoretical basis for drought-resistant cultivation and stable and high yield techniques of soybean.The main results of the study were as follows:1.The root morphological growth and development and root vitality were inhibited by different degrees of water deficit treatments in soybean V1.The root length of Suinong 26 under mild,moderate and severe water deficit treatments decreased by 8.31%,17.60% and 25.18%,respectively,compared with the control,and the root diameter of each treatment decreased by up to 12.66% to 21.99% compared with the control,while the root volume was significantly reduced by 19.16% and 30.84% under moderate and severe treatments compared to the control.The root length of Heinong 54 was reduced to a lesser extent compared with the control in all treatments,and only the severe water deficit treatment significantly decreased by 18.92% compared to the control,root diameter was reduced by 15.59% and 19.77% in the moderate and severe water deficit treatments,root volume was significantly increased by 21.59% compared to the control by mild water deficit treatment.Root vitality was reduced by 7.17%,12.72% and 17.73% for each treatment of Suinong 26 and reduced by 3.65%,10.29% and 12.76% for Heinong 54 compared to the control.After rehydration,the root systems of both soybean varieties grew rapidly and the root morphology of all treatments recovered to some extent compared to the previous ones.2.Soybean V1 treatments with different degrees of water deficit had significant effects on dry matter accumulation and root nutrient content,with the decrease of water content,root dry matter accumulation showed a trend of increasing and then decreasing,all of them had the highest dry matter quality under mild water deficit,in which Suinong 26 significantly increased by 22.73%compared with the control,while Heinong 54 significantly increased by 27.54% compared with the control,and the trend of dry matter quality remained unchanged after rehydration.The reduction in soil moisture content led to a decrease in total nitrogen,phosphorus and potassium content in the root system,with Suinong 26 showing a significant increase of 5.80% in total nitrogen content under mild water deficit treatment compared to the control,the total phosphorus content of each treatment was reduced by 6.90%,13.79% and 20.69%,respectively,and the total potassium content was reduced by up to 5.07% to 13.77% compared to the control.For Heinong54,the root total nitrogen content of each treatment was reduced by 2.26%,6.77% and 20.30%respectively compared to the control,the total phosphorus content was reduced by 3.23%,12.90%and 16.13% respectively for each treatment compared to the normal water supply,and the total potassium content was reduced by up to 6.03% to 18.10% compared to the control.The recovery effect of mild water deficit treatment after rehydration was the best,which could produce a certain compensation effect on nutrient absorption of roots.3.The root membrane structure was severely damaged by different degrees of water deficit treatments in soybean V1,and the root MDA content increased significantly with the increase of water deficit,among which Suinong 26 showed a significant increase of 18.01%,50.29% and69.55% in mild,moderate and severe water deficit treatments,respectively,compared with the control,and Heinong 54 showed an increase of 13.64%,31.39% and 66.83% compared with the control.In order to resist the adversity,the antioxidant enzyme activity and osmoregulatory substances in the root system were increased,and in general,the protective enzyme activity and osmoregulatory substances were higher in Heinong 54 compared with Suinong 26.After rehydration,all physiological indexes of the root system were compensated,among which the compensation effect of mild and moderate water stress was better,and the compensation ability of drought-resistant varieties was higher than that of drought-sensitive ones.4.The water deficit treatment during soybean V1 had certain effects on soil nutrient content,and the content of alkali hydrolyzable nitrogen of Suinong 26 increased significantly by 5.64%compared with the control under the treatment of mild water deficit,the available phosphorus content was significantly reduced by 11.05% under the severe water deficit treatment compared to the control,and the available potassium content was significantly increased by 6.90% under the mild water deficit treatment compared to the severe deficit treatment.In comparison between varieties,the soil nutrient content of Heinong 54 was slightly influenced by moisture.After rehydration,soil nutrients had largely returned to the same level as the control by late in the reproductive stage.5.Water deficit treatment in the appropriate range at V1 stage could effectively promote soil enzyme activity and change the soil microenvironment.The urease activity of Suinong 26 was highest under mild water deficit treatment with a significant increase of 6.83% compared to the control,sucrase activity decreased by 13.89%,20.73% and 21.94% in each treatment compared to the control,catalase activity increased significantly by 8.87% under severe water deficit compared to the control,the phosphatase activity decreased significantly with the decrease of moisture content,and the decrease of each treatment compared with the control ranged from 10.36% to23.53%.The urease activity of Heinong 54 was significantly increased by 4.48% under the mild water deficit treatment compared to the control,sucrase activity was significantly reduced by 10.11%and 14.90% under moderate and severe deficiency treatments compared to the control,the catalase activity of each treatment increased by 1.70%,7.59% and 9.98%,respectively,compared to the control,the phosphatase activity was significantly reduced by 5.78%,12.92% and 14.16% for each treatment respectively compared to the control.And the promotion effect of rehydration on each soil enzyme activity continued for some time.6.At the bacterial phylum level,Proteobacteria,Acidobacteria and Actinobacteria were the dominant phyla under different water deficit treatments,while at the fungal phylum level,Ascomycota and Basidiomycota were the dominant phylum under different water conditions.For Suinong 26,soil urease activity was significantly negatively correlated with bacterial Chao1 and ACE index,soil catalase activity was significantly positively correlated with bacterial Simpson and Shannon index,and soil urease activity was positively correlated with fungal Chao1 and ACE index.However,there was a highly significant positive correlation between soil urease activity and bacterial Simpson index in Heinong 54,and a significant positive correlation between soil catalase activity and bacterial Chao1 and ACE index.In addition,urease,sucrase and phosphatase activities were significantly positively correlated with fungal Chao1 and ACE index,and fungal Simpson index was positively correlated with soil phosphatase activity.7.The analysis of yield in 2021-2022 showed that water deficit treatment in soybean V1 had a significant effect on yield,and the findings were generally consistent between the two years.For2022,rehydration after mild water deficit treatment had the best effect on yield improvement of soybean Suinong 26 with a slight increase of 1.11% compared to normal water supply,while rehydration of Heinong 54 under moderate water deficit treatment had the highest effect on yield improvement per plant,with a significant increase of 7.71% compared to normal water supply.