The aim of this study is to investigate the effect of soil water stability on maize (Zea mays L.) yield, water use, and its photosynthetic physiological mechanisms, and to innovate the relationship between maize and soil water, which currently only considers soil water content and neglects soil water stability. An organized water experiment was conducted on maize. The effects of stable soil water (SW) at two water content levels were examined, with fluctuating soil water (FW) as a control. The assessed effects included leaf water, chlorophyll, gas exchange, leaf water use efficiency (WUE), stable carbon isotope ratio (δ13C), and yield of maize. Soil water stability had a significant effect on maize yield, yet it was slightly smaller than soil water content. Compared with FW, SW increased the maximum net photosynthetic rate, saturated light intensity, stomatal conductance, SPAD, leaf water content, and leaf WUE, and decreased δ13C, promoting dry matter assimilation and conversion into grain yield, ultimately increasing yield by 100.8%. Under the same soil water stability, 55% FC versus 75% FC weakened photosynthetic capacity and exacerbated stomatal limitation of maize leaves, making them more susceptible to light inhibition, which decreased photoassimilate accumulation, resulting in a significant decrease in yield. And the δ13C under 75% FC conditions decreased by 4.7–7.7% compared with 55% FC. In conclusion, SW exhibits a positive effect on maize leaf water content, photosynthetic carbon assimilation, and grain yields, regardless of soil water content. Compared to FW, SW increased leaf WUE and maize yield by enhancing photosynthesis, and SW has stronger discrimination against 13C during photosynthetic CO2 assimilation, thus decreasing leaf δ13C. This study fills a gap in understanding how soil water stability influences maize yield and gas exchange, and provides a fresh perspective on how to improve crop yield and WUE by managing soil water stability.

Weaker temporal variation of soil moisture can improve crop water use efficiency (WUE), but its physiological mechanism was still unclear. To explore the mechanism, an organized experiment was conducted in Beijing from June to September. From the jointing stage to maturity stage of maize, stable soil moisture (SSM) and fluctuating soil moisture (FSM) were established with Pressure Potential Difference-Crop Initiate Drawing Water (PCI) and manual irrigation (MI), respectively, to explore the physiological mechanism of SSM to improve maize WUE. Among them, PCI treatments were set with 3 pressure differences of -5, -10, and -15 kPa, and MI treatment was watering every 3 days with the irrigation amount of 9.3 mm. The results showed that (1) after water treatment, the average soil water content of PCI-5 kPa, PCI-10 kPa, PCI-15 kPa, and MI treatments were 53% field capacity (FC), 47, 38, and 78% FC, respectively. It was SSM with weak temporal variation under PCI treatments, and FSM with medium temporal variation under MI treatment. (2) PCI treatments reduced the content of proline, malondialdehyde, and abscisic acid in each organ of maize. (3) Compared with FSM 78% FC, the maize root activity at the filling stage of 53% FC SSM and 47% FC SSM increased significantly by 57.1 and 28.6%, respectively, and the carbon isotope discrimination value (Δ¹³C) in bracts of the two treatments increased by 18.3 and 10.4%, respectively. (4) There was a very significant positive correlation between WUE based on biomass (WUE_b) and Δ¹³C in bracts. In conclusion, a large temporal variation of soil moisture was an important factor that caused water stress in maize. Under SSM treatments, the accumulation of abscisic acid, proline, and malondialdehyde was synergistically reduced. SSM improved the WUE of maize by alleviating short-term soil water stress caused by the fluctuation of soil moisture.

The study investigated the response to five levels of potassium (K) fertilizer addition on tomato (Solanum lycopersicum L.) performance and soil bacterial communities by negative pressure irrigation (NPI) over two consecutive years. The application of K fertilization positively affected tomato performance under NPI, as indicated by increased yield, quality, growth, and nutrients’ contents of tomato compared with no K addition treatment. High-throughput sequencing of the rhizosphere soil revealed that K additions significantly affected in the bacterial diversity indices according to Chao1, Ace, and Shannon. K addition significantly increased the relative abundance of Gemmatimonadetes and decreased the level of Planctomycetes. There were very prominent increases in the levels of the genus Opitutus, but reduced the content of Sphingomonas and Bdellovibrio compared with no K addition treatment. Furthermore, application of 150 kg K ha⁻¹ (K150) was considered to be beneficial for plant growth and rhizosphere bacterial diversity of tomato. The tomato yield under K150 was considerably increased by 58% and 47% compared with no K addition treatment in 2016 and 2017, respectively. The K150 showed the highest K fertilizer utilization efficiency compared with other K treatments, with K contribution rate and K agronomic efficiency reaching 36.7 and 62.9 as well as 32.0 and 53.6 in 2016 and 2017, respectively. Therefore, these findings also demonstrate that K application under NPI not only promotes yield and quality of tomato fruits but also positively affects the rhizosphere microbiome.

Previous studies on soil water–plant relations have mostly focused on the soil water content (SWC), while the effect of soil moisture stability on plant growth has received surprisingly little attention. Potted tomato seedlings were used to examine the effect of stable soil moisture (SM) and fluctuating soil moisture (FM) on plant growth, development, and water use efficiency (WUE) in this study. The results showed that (i) soil moisture stability significantly affected the growth and development, photosynthetic characteristics, morphological traits, root morphology, and water physiological characteristics of seedling tomatoes, with SM being more conducive for most of these indices. (ii) SM improved the leaf WUE by reducing the content of abscisic acid in plants, regulating plant osmotic substances, maintaining a high gas exchange rate, and promoting plant morphology. (iii) SM could avoid water stress on tomato seedlings; even if the SWC of SM was equal to or lower than the SWC of FM, water stress would not occur under SM, whereas it would occur under FM. Overall, compared with FM, SM promoted beneficial plant morphology, maintained a high gas exchange rate, and did not induce water stress for tomato seedlings—ultimately improving WUE. This effect was more effective under low-SWC conditions than under high-SWC conditions. These findings provide a new perspective and theoretical basis for soil water–plant relations and indicate that SM has great potential in promoting plant growth and improving WUE.

Strawberry (Fragaria × ananassa Duch.) has a unique flavor and nutritional value. To investigate the effects of deficit irrigation on the growth, yield, quality, and water use efficiency of strawberries, “Zhangji” and “Hongyan” varieties were assessed in a greenhouse. Four irrigation levels were set as 95% (CK), 75% (LS), 55% (MS), and 35% (±5%) (SS) of the field capacity, respectively. Five successive plant growth stages were analyzed. The results indicate that the plants’ daily water consumption intensity, as well as fruit yield and titratable acidity, decreased with increasing water stress, while vitamin C (Vc), soluble sugar, soluble protein, the sugar–acid ratio, and water use efficiency increased. Yield significantly decreased under the MS and SS treatments compared with CK. Malondialdehyde, proline contents, and superoxide dismutase activity reached the highest values under SS. Our results indicate that the greatest effect of water restriction occurs during the seedling growth and fruit color-turning periods. Given the higher Vc, titratable acidity, soluble sugars, and soluble proteins, the “Zhangji” variety may be preferable to the “Hongyan” variety, and an irrigation level at 70~80% of field capacity is recommended for good strawberry yield and taste quality. Deficit irrigation can save water resources, improve water use efficiency, and promote agricultural sustainable development.