Eight years in the soil: temporal dynamics of wheat-associated bacterial communities under dryland and irrigated conditions

Authors: YANG, MING MING - Northwest A&f University; Schlatter, Daniel; WEN, SHANSHAN - Northwest A&f University; MAVRODI, DIMITRI - University Of Southern Mississippi; MAVRODI, OLGA - University Of Southern Mississippi; Thomashow, Linda; Weller, David; Paulitz, Timothy; Letourneau, Melissa

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: This work is unique in the literature because of the long temporal scale, both within the growing season and over multiple consecutive years. Using amplicon sequencing, we characterized bacterial communities in monocrop wheat over 8 years, both in the rhizosphere and the endosphere, under dryland and irrigated conditions. Our results show how the host plant can select and shift its microbial community over multiple seasons, as well as the role of moisture as an environmental driver. Several important unexpected conclusions resulted from our study. For example, Actinobacteria appeared to decline over time, both under irrigated and dryland conditions. Some Gram-negative bacteria such as Pseudomonas persisted over time on and in the roots under both dryland and irrigated conditions, while other genera, such as Sphingomonas, persisted in dryland but not irrigated conditions. Our results enabled us to propose models of microbial communities on wheat roots over time. This work is a capstone on over 30 years of research in our Unit on Pseudomonas and other bacteria in dryland wheat cropping systems.

Technical Abstract: Plants and their associated microbiomes are impacted by environmental factors that shape their interactions over time, but long-term trends in microbial community dynamics are not well characterized. We identified the seasonal and long-term population dynamics of root-associated bacterial communities over eight years in the rhizosphere and endosphere of monocropped wheat in adjacent dryland and irrigated plots in the low-precipitation region of central Washington State. Analyses throughout the first three years revealed genera with distinct annual periodicity in response to seasonal conditions. Further, bacterial richness and diversity were significantly greater in irrigated than in dryland wheat and in the rhizosphere than in the endosphere, apparently driven by the physiological state of the root and root exudates, and/or by soil water. Over eight years, copiotrophic Proteobacteria and Bacteroidetes (Pseudomonas, Variovorax, Chryseobacterium) maintained stable populations while Actinobacteria decreased in abundance independent of irrigation. Populations of some Bacteroidetes and Proteobacteria (Mucilaginbacter, Sphingomonas, Massilia, Burkholderia) were dryland adapted and persisted or increased in the dryland rhizosphere whereas others (Rhizobium, Acidovorax, Terremonas, Hyphomicrobium, Bdellovibrio) increased under irrigation. In contrast, endosphere taxa including Actinobacteria, declined in abundance regardless of irrigation, indicating that the maturing host, and not water, is the main driver of these populations. Our results provide insight into the long-term effect of desiccation on bacterial communities of wheat to guide future efforts to improve crop performance under drought conditions.