Abstract
Alternate drip irrigation (ADI) is a useful irrigation method for water conservation and the regulation of soil quality; however, knowledge about the underlying mechanism of soil-root-bacterium interactions is limited. To determine the mechanism by which ADI transforms soil nutrients and thereby promotes plant growth and to provide a basis for the reasonable selection of drip irrigation methodology, the present study investigated the effects of ADI on the composition and potential function of the bacterial community in tomato rhizosphere soils under greenhouse conditions and analyzed the soil-root-bacterium interactions under ADI. The results revealed that, compared with the soils of the plots treated with surface drip irrigation with plastic film mulching (DI-PFM), the soils of the plots treated with ADI presented an optimized bacterial community structure and optimized soil nitrogen (N) and phosphorus (P) metabolism. The soil available N contents under ADI with lower irrigation limits of 50%, 60%, and 70% of field capacity (A50, A60, and A70 treatments, respectively) were 1.48, 2.19, and 1.91 times greater than those under DI-PFM, respectively; similarly, the soil available P contents were 1.49, 1.65, and 2.91 times greater; the total phosphorus (TP) contents in the tomato roots were 1.06, 1.94, and 1.59 times greater, respectively; and the TP contents in the tomato plants were 1.03, 1.75, and 2.84 times greater, respectively. In addition, the total nitrogen (TN) contents in the tomato roots under ADI with lower irrigation limits of 60% and 70% of field capacity were 1.07 and 1.14 times greater than those under DI-PFM, and the TN contents in the tomato stems were 1.21 and 1.12 times greater than those under DI-PFM. However, compared with DI-PFM, ADI improved tomato yields by 24.23% under only 70% of field capacity. Therefore, ADI significantly enhanced soil-root interactions and stimulated the activation of soil N and P, but only a proper low soil moisture content (SMC) led to significantly increased tomato yields.
Highlights
Intensive agricultural irrigation and cropping in the greenhouse can lead to an imbalance in soil nutrients and can degrade soil quality [1,2,3]
The results showed that the structure of the bacterial communities in the A50 treatment was similar to that in the A60 treatment, whereas the structure of the bacterial communities in the A70 treatment was different from that in the CK and other treatments (Figures 1 and 2)
The results showed that the total copies of N metabolismand P metabolism-related genes in the Alternate drip irrigation (ADI) treatment (i.e., A50, A60, and A70) compared with the CK treatment increased, which indicated that ADI can optimize the bacterial community structure
Summary
Intensive agricultural irrigation and cropping in the greenhouse can lead to an imbalance in soil nutrients and can degrade soil quality [1,2,3]. ADI involves alternately irrigating the two sides of crop roots within a certain period of time to maintain one side of the crop roots as wet, whereas the other side is maintained as relatively dry. Compared with conventional drip irrigation, ADI significantly increases water-use efficiency and increases photosynthesis [7], increases crop yields, and improves fruit quality [8]. Frequent alternations of wet/dry conditions have several additional advantages, such as increasing soil microbial activity, accelerating the mineralization of soil organic matter (OM), altering the soil C/N ratio, increasing soil nitrogen (N) accumulation on the root surface, stimulating N uptake by roots [14], and increasing N fertilizer-use efficiency [15]. Knowledge about the changes in microbial community structure and function under ADI is limited, which could be used to determine the mechanisms by which ADI conserves water, regulates soil quality and promotes crop growth
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