Excessive application of phosphate fertilizer is common in vegetable fields and causes deterioration of the rhizosphere environment, that is, the soil oxygen (O₂) environment, which further constrains root morphology construction and limits vegetable yield. Nevertheless, the interaction between root morphology and the response of the rhizosphere O₂ environment to vegetable P utilization has rarely been reported. Therefore, we carried out an experiment applying different concentrations of O₂ generator, 10%, 30%, 50%, and 80% urea hydrogen peroxide (as pure nitrogen) instead of urea as a top dressing in the rhizosphere, to study the effect on root morphology and P adsorption, and its mechanism. We found that there were O₂-deficient and P-deficient zones in the rhizosphere, and oxygenation could alleviate the rhizosphere O₂ and P consumption in roots. The rhizosphere O₂ concentration was maintained at approximately 250.6 μmol L⁻¹, which significantly promoted total root length, root volume, average diameter, and root activity by 29.0%, 30.9%, 3.9%, and 111.2%, respectively. Oxygenation promoted organic P mineralization and increased the Olsen-P content in the rhizosphere. The characteristics of root morphology and increased available P in the rhizosphere jointly contributed to high P absorption and utilization, and the P use efficiency was improved by 9.3% and the shoot P accumulation by 10.9% in the 30% urea hydrogen peroxide treatment compared with CK. Moreover, this treatment also improved yield and quality, including vitamin C and the soluble sugar content. However, at a still higher O₂ concentration (260.8 μmol L⁻¹), vegetable growth exhibited O₂ damage, resulting in reduced yield and quality. Our study provided new insights into constructing efficient root morphology by regulating the rhizosphere O₂ environment to improve vegetable yield and quality, as well as to increase P use efficiency in vegetable fields.

Soil salinization is a major threat to agricultural sustainability. Poly-gamma-glutamic acid (γ-PGA), a biopolymer produced by microbial fermentation, has received attention as a biostimulant due to its positive effects on crop performance. However, the function of γ-PGA in crop salt stress tolerance and its effect on the rhizosphere are unclear. This study explores the effects of γ-PGA application on rhizosphere soil nutrients and the soil–physical environment and examines the salt tolerance response of maize seedlings grown in saline–alkali soil under such an application regime. The results show a significant promotion of maize seedling growth and of nutrient accumulation with γ-PGA application under salt stress; plant dry weight, stem diameter, and plant height increased 121%, 39.5%, 18.4%, respectively, and shoot accumulation of nitrogen, phosphorus, potassium, and carbon increased by 1.38, 2.11, 1.50, and 1.36 times, respectively, under an optimal-concentration γ-PGA treatment (5.34 mg kg⁻¹ (12 kg ha⁻¹)) compared with the control. γ-PGA treatment significantly decreased rhizospheric pH and soil electrical conductivity and significantly increased nutrient availability in the rhizosphere, especially available nitrogen (AN) and available potassium (AK). Compared with the control, AN, available phosphorus (AP), and AK increased by 13.9%, 7.70%, and 17.7%, respectively, under an optimal concentration treatment with γ-PGA. γ-PGA application also significantly increased the activities of urease, acid phosphatase, alkaline phosphatase, dehydrogenase, and cellulose in rhizosphere soil by 35.5–39.3%, 35.4–39.3%, 5.59–8.85%, 18.9–19.8%, and 19.2–47.0%, respectively. γ-PGA application significantly decreased Na⁺ concentration and increased K⁺ concentration in shoots, resulting in a lowering of the Na⁺/K⁺ ratio by 30.5% and an increase in soluble sugar and soluble protein contents. Therefore, rhizosphere application of water-soluble and biodegradable γ-PGA facilitates the creation of an optimized rhizospheric environment for maize seedling and overcomes osmotic and ionic stresses, offering possibilities for future use in drip-irrigation systems in the cultivation of crops on saline-alkali land.