Effect of Ammonia-Oxidizing Bacterial Strains That Coexist in Rhizosphere Soil on Italian Ryegrass Regrowth

Abstract

Potted Italian ryegrasses (Lolium multiflorum L.) were used to investigate the effect of ammonia-oxidizing bacterial (AOB) strain that coexisted in rhizosphere soil on Italian ryegrass regrowth. The results showed that the isolated and screened AOB strain (S2_8_1) had 100% similarity to Ensifer sesbaniae. The inoculation of S2_8_1 on day 44 before defoliation caused its copy number in rhizosphere soils to increase by 83–157% from day 34 before defoliation to day 14 after defoliation compared with that in Italian ryegrass without S2_8_1 inoculation, indicating that S2_8_1 coexisted permanently with Italian ryegrass. The coexistence promoted the delivery of root-derived cytokinin to leaves and to increase its cytokinin concentrations; thus, the Italian ryegrass regrowth accelerated. During the 14-day regrowth period, the S2_8_1 coexistence with Italian ryegrass caused its leaf and xylem sap cytokinin concentrations, rhizosphere soil nitrification rates, net photosynthetic rates, and total biomass to increase by 38%, 58%, 105%, 18%, and 39% on day 14 after defoliation, respectively. The inoculation of S2_8_1 on day 2 before defoliation also increased the regrowth of Italian ryegrass. Thus, the coexistence of AOB with Italian ryegrass increased its regrowth by regulating the delivery of cytokinins from roots to leaves.

Unveiling the dual role of heterotrophic ammonia-oxidizing bacteria: enhancing plant regrowth through modulating cytokinin delivery

“…Previous studies primarily focused on their vital role in nitrification processes within aquatic and soil environments ( Taylor et al, 2009 ; Kouki et al, 2011 ; Matsuno et al, 2013 ; Soliman and Eldyasti, 2018 ; Fang et al, 2019 ). A limited body of research has revealed that HAOB strains promote soil nitrification in the rhizosphere, leading to the release of nitrate nitrogen from the soil ( Wu et al, 2022 , 2023 ). However, our study introduces a novel perspective by exploring their role in enhancing plant growth.…”

“…This addition aimed to inhibit soil nitrification during the regrowth phase and was applied to all treatments except DA. This approach was based on previous research, which indicated a lag time of approximately 3 days for the inhibitory effect of DMPP on Italian ryegrass regrowth ( Wu et al, 2022 ). Throughout the regrowth period, soil water content was maintained at 65–70% of field capacity by adding either NO 3 − solutions or water to the treatments.…”

“…Soil NO 3 − , in turn, triggers cytokinin synthesis in plant roots, thereby influencing overall plant growth ( Landrein et al, 2018 ; Poitout et al, 2018 ; Wang et al, 2018 ). In a recent study ( Wu et al, 2022 ), a heterotrophic ammonia-oxidizing bacteria (HAOB) strain exhibited a strong correlation with the transport of cytokinins from roots to leaves. This correlation resulted in an elevation of leaf cytokinin content, subsequently contributing to the regrowth of Italian ryegrass following defoliation.…”

Enhanced Post-Drought Compensatory Growth and Water Utilization in Maize via Rhizosphere Soil Nitrification by Heterotrophic Ammonia-Oxidizing Bacteria

“…Therefore, ammonia-oxidizing bacteria typically inhabit the rhizospheric soil of plants and tend to be heterotrophic. In a recent study, a strain of heterotrophic ammonia-oxidizing bacteria (HAOB) was found to have a strong correlation with the transport of cell division hormones from the roots to the leaves [18]. However, limited research explores how soil microorganisms induce compensatory growth in maize through roots under limited rewatering after drought.…”