Temporal variation in soil bacterial communities can be confounded with spatial variation

Two rice cultivars recruit different rhizospheric bacteria to promote aboveground regrowth after mechanical defoliation

Plants have evolved the ability to regrow after mechanical defoliation and environmental stresses. However, it is unclear whether and how defoliated plants exploit beneficial microbiota from the soil to promote aboveground regrowth. Here, we compared the defoliation-triggered changes in the root exudation and bacterial microbiome of two rice cultivars (Oryza sativa L ssp.), indica/xian cultivar Minghui63 and japonica/geng cultivar Nipponbare. The results show that reciprocal growth promotion existed between defoliated Minghui63 seedlings and soil bacteria. After the leaves were removed, the Minghui63 seedlings displayed approximately 1.5- and 2.1-fold higher root exudation and leaf regrowth rates, respectively, than did the Nipponbare seedlings. In field trials, Minghui63 and Nipponbare enriched taxonomically and functionally distinct bacteria in the rhizosphere and root. In particular, Minghui63 rhizosphere and root communities depleted bacteria whose functions are related to xenobiotics biodegradation and metabolism. The microbiome data implied that the bacterial family Rhodocyclaceae was specifically enriched during the regrowth of defoliated Minghui63 rice. We further isolated a Rhodocyclaceae strain, Uliginosibacterium gangwonense MDD1, from rice root. Compared with germ-free conditions, MDD1 inoculation promoted the aboveground regrowth of defoliated Minghui63 by 61% but had a weaker effect on Nipponbare plants, suggesting cultivar-specific associations between regrowth-promoting bacteria and rice. This study provides novel insight into microbiota‒root‒shoot communication, which is implicated in the belowground microbiome and aboveground regrowth in defoliated rice. These data will be helpful for microbiome engineering to increase rice resilience to defoliation and environmental stresses.IMPORTANCEAs sessile organisms, plants face a multitude of abiotic and biotic stresses which often result in defoliation. To survive, plants have evolved the ability to regrow leaves after stresses and wounding. Previous studies revealed that the rhizosphere microbiome affected plant growth and stress resilience; however, how belowground microbiota modulates the aboveground shoot regrowth is unclear. To address this question, we used rice, an important crop worldwide, to analyze the role of rhizosphere microbiota in leaf regrowth after defoliation. Our data indicate mutual growth promotion between defoliated rice and rhizosphere bacteria and such beneficial effect is cultivar specific. The microbiome analysis also led us to find a Uliginosibacterium gangwonense strain that promoted rice cv. MH63 leaf regrowth. Our findings therefore present a novel insight into plant-microbiome function and provide beneficial strains that potentially enhance rice stress resilience.

Soil bacterial community composition is more stable in kiwifruit orchards relative to phyllosphere communities over time

BACKGROUND

Soil and phyllosphere (leaves and fruit) microbes play critical roles in the productivity and health of crops. However, microbial community dynamics are currently understudied in orchards, with a limited number incorporating temporal monitoring. We used 16S rRNA gene amplicon sequencing to investigate bacterial community temporal dynamics and community assembly processes on the leaves and fruit, and in the soil of 12 kiwifruit orchards across a cropping season in New Zealand.

RESULTS

Community composition significantly differed (P < 0.001) among the three sample types. However, the communities in the phyllosphere substrates more closely resembled each other, relative to the communities in the soil. There was more temporal stability in the soil bacterial community composition, relative to the communities residing on the leaves and fruit, and low similarity between the belowground and aboveground communities. Bacteria in the soil were more influenced by deterministic processes, while stochastic processes were more important for community assembly in the phyllosphere.

CONCLUSIONS

The higher temporal variability and the stochastic nature of the community assembly processes observed in the phyllosphere communities highlights why predicting the responsiveness of phyllosphere communities to environmental change, or the likelihood of pathogen invasion, can be challenging. The relative temporal stability and the influence of deterministic selection on soil microbial communities suggests a greater potential for their prediction and reliable manipulation.