Effects of Different Mulched Drip Irrigation Levels on the Soil Microorganisms and Yield of Greenhouse Tomatoes (Solanum lycopersicum L.)

It is imperative to investigate the impact of irrigation on the microorganisms inhabiting soil in greenhouses, as this understanding is crucial for the implementation of effective water conservation strategies and optimal soil health sustenance in greenhouse tomato production. To this end, a tomato-cultivating experiment was conducted in a greenhouse, with the control group receiving no planting or irrigation (W0), during the years 2021 and 2022 in the Taiyuan region of Shanxi Province, China. The experiment incorporated three irrigation levels: W1 (50–70% of the field capacity), W2 (60–80% of the field capacity), and W3 (70–90% of the field capacity). The objective of our study was to clarify the effects of different irrigation levels on soil bacterial and fungal community compositions and functions, as well as tomato yield and water use efficiencies, by analyzing the changes in community structural characteristics and potential functional composition of soil bacteria and fungi under different irrigation levels. Our results showed that in comparison with the control treatment, the W3 irrigation treatment exhibited the highest bacterial α-diversity, while its fungal diversity was the lowest. The r-strategy microbial community in tomato soil demonstrated increased abundance under the irrigation treatment. The relative abundance of common beneficial tomato bacteria increased by 0.32–1.70%, but that of beneficial soil fungi decreased by 0.09–3.75%. Among the different irrigation treatments, the relative abundances of Bacillus and Plectosphaerella changed the most. The functional structure of the bacteria in the irrigation treatment remained largely unchanged, while the saprotroph functional group of fungi was increased by 14.72–23.28%. With the increase in irrigation volume, the tomato yield of the W3 treatment increased, though the water use efficiency was not the greatest. The W2 treatment did not significantly reduce the yield, but it did increase the pathotroph functional groups of fungi, which may reduce the stress resistance of plants to soil-borne diseases. The findings of this study serve as a valuable reference point for the prediction of greenhouse soil health and the enhancement of tomato yields.