| Soil moisture status is closely related to crop growth and development,which is critical for achieving high yield and good quality of crops.The majority of research between soil water and crops focuses on soil water content.However,the effects and mechanism behind the soil moisture stability on crop growth and yield is still not fully understood.In this study,tomato,a vegetable crop,and maize,a food crop with high water demand,were used as test material.Different stable and fluctuating soil moisture were created with negative pressure irrigation and conventional irrigation,respectively,through the water control experiments in a rainproof shelter.In the tomato experiment,four treatments were set up: SMW1(-10 k Pa),SMW2(-5 k Pa),FMW1(75%FC-55%FC),and FMW2(85%FC-65%FC).In the maize experiment,SL(-9 k Pa),SH(-3 k Pa),FL(70%FC-40%FC)and FH(90%FC-60%FC)were set up.The effects of soil moisture stability on the growth and physiological response of tomato and maize,as well as the changes of microbial communities were studied.The main findings of this paper were as follows:(1)Soil moisture stability significantly affected the growth and development,agronomic traits,root morphology,biomass and yield of tomato and maize,with stable soil moisture being more beneficial to most indices.Compared with fluctuating soil moisture,stable soil moisture significantly increased the plant height,stem diameter and other agronomic characters(21.4%-75.1%),and the difference was more obvious under the low water content conditions.Stable soil moisture increased the growth rate of maize plant height,stem diameter,leaf number and leaf area(7.0%-18.4%),but also increased the final plant height,stem diameter and leaf area(4.9%-11.2%).The root length,surface area,and volume of tomato and maize were greatly improved by stable soil moisture,which encouraged the growth and development of roots.However,the effects on average root diameter,specific root length and root-shoot ratio varied with different crop species and plant growth stages.Under stable soil moisture conditions,the yield and biomass of tomato increased by 112.1% and 118.1%-131.2%,respectively,and the yield and biomass of maize increased by 100.8% and 27.1%-49.4%,respectively.(2)The physiological indices of tomato and maize had obvious response to soil moisture stability.Stable soil moisture,versus fluctuating soil moisture,decreased the contents of abscisic acid in tomato and maize,improved plant osmotic regulation and antioxidant defense system,finally helped plants avoid or alleviate water stress.Under similar soil water content,stable soil moisture was more conducive to maintaining a higher water state and photosynthetic pigment contents of plant leaves,improving leaf photosynthetic rate and root activity,and the difference between the two was more pronounced under low water content.In the tomato,stable soil moisture greatly reduced the contents of free proline,soluble sugar,malondialdehyde,and abscisic acid in the roots,stems,and leaves,and significantly reduced the contents of soluble protein in roots and leaves.Even if the soil water content in stable soil moisture was lower than or equal to that in fluctuating soil moisture,there was no water stress in tomato under stable soil moisture,while the fluctuating soil moisture induced water stress.In the maize,stable soil moisture decreased significantly the contents of free proline and soluble protein in stem and leaves,the soluble sugar,malondialdehyde contents and peroxidase activity in all organs,decreased significantly the superoxide dismutase activity in roots and leaves,catalase activity in stems,and decreased significantly the contents of abscisic acid and salicylic acid in maize roots and leaves.However,it significantly increased the content of trans-Zeatin-riboside in the root.(3)Soil moisture stability had significant effects on the soil habitat of tomato and maize.There were significant differences in the microbial community structure between stable and fluctuating soil moisture.Compared with fluctuating soil moisture,stable soil moisture enhanced the rhizosphere soil enzyme activities and increased the availability of soil nutrients.Actinobacteriota,Proteobacteria,Chloroflexi,Acidobacteriota,and Firmicutes were the predominant bacterial phyla in the rhizosphere soil of tomato and maize,and Ascomycota,unclassified＿k＿＿Fungi,Mortierellomycota,Basidiomycota,and Chytridiomycota were the predominant fungal phyla.However,the response of rhizosphere soil community structure to soil moisture stability and water content was different between tomato and maize.In the tomato,the bacterial and fungal communities in the rhizosphere soil were significantly influenced by soil moisture stability,whereas the bacterial and fungal communities were not significantly influenced by soil water content.In the maize,soil moisture stability significantly influenced the structure of bacterial and fungal communities at the ten-leaf,milk,and physiological maturity stages(apart from the bacterial communities structure at physiological maturity stage and the fungal communities structure at ten-leaf stage),while soil water content significantly influenced the composition of bacterial and fungal communities at the three stages of maize.Under similar soil water content,compared with fluctuating soil moisture,stable soil moisture significantly increased the diversity,richness and evenness of bacterial community structure and the richness of fungal community structure in rhizosphere soil at tomato harvest.The same phenomenon was observed at maize harvest but the diversity and evenness of bacteria were significantly increased only under low water conditions and the richness of fungi only under high water conditions.Under stable soil moisture,the enzyme activities and available nutrient contents of tomato rhizosphere soil were increased by13.0%-21.2% and 25.3%-72.2%,respectively,and the enzyme activities and available nutrient contents of maize rhizosphere soil were increased by 4.0%-8.7% and 4.7%-29.6%,respectively.In conclusion,under similar soil water content conditions,stable soil moisture,versus fluctuating soil moisture,reduced abscisic acid contents in tomato and maize,improved osmotic regulation and antioxidant defense system,enhanced plant tolerance to water stress,and improved photosynthetic capacity and root activity of crops.Stable soil moisture also improved microbial community structure,enhanced rhizosphere soil enzyme activities and soil nutrient availability,and finally significantly improved crop yield. |
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