Exogenous Streptomyces spp. benefit naked oat growth under dry farming conditions by modifying rhizosphere bacterial communities

Manipulation of rhizosphere microbiota is an effective strategy to facilitate crop growth in dry farming systems. Actinobacteria, such as Streptomyces spp., have the potential to alleviate plant damage induced by drought stress. However, whether exogenous actinobacteria can promote naked oat (Avena nuda L.) growth in drylands by reshaping rhizosphere bacterial community structure is still unclear. This study evaluated the effects of S. albidoflavus T4 and S. pactum Act12 on the growth and yield of naked oat through a two-year field experiment conducted in Taigu, Shanxi Province, China. Streptomyces-mediated shifts in rhizosphere bacterial diversity and community composition were analyzed based on 16S ribosomal RNA gene sequencing. Both T4 and Act12 inoculation improved plant growth and grain yield by 21.5 %-27.4 % compared with the uninoculated control. Despite no significant changes in the alpha diversity of rhizosphere bacteria, their community composition varied in different patterns following inoculation. In T4-treated soils, there were increased proportions of Chloroflexi (rare phylum), Stenotrophomonas (abundant genus), and Acidovorax (moderate genus), along with a decreased proportion of Polycyclovorans (moderate genus). These differential taxa were closely related to increased soil available phosphorus and potassium contents as well as alkaline phosphatase activity, thereby contributing to plant growth. Act12-treated soils showed increased proportions of Lachnospiraceae_NK4A136 (abundant genus), Pantoea (rare genus), and Kluyvera (rare genus), in contrast to the decreasing trend of Microvirga (moderate genus). These differential taxa were mainly associated with enhanced soil sucrase and leaf catalase activities, which indirectly increased plant biomass and grain yield. The findings demonstrate that inoculation with S. albidoflavus T4 and S. pactum Act12 conveys benefits to naked oat growth under dry farming conditions as an indirect consequence of alterations in key taxa abundance in rhizosphere microbiota coupled with changes in soil chemical environment and plant antioxidant activity.