Biology subjects

Gamper, H. A.

Publications and source records attributed to Gamper, H. A..

3 recordsLinked to original sources

bioRxiv2020

Ecological patterns of root nodule diversity in cultivated and wild rooibos populations: a community prediction approach

There is interest in understanding the factors behind the biogeography of root-associated bacteria due to the joint effects that plant host, climate, and soil conditions can have on bacterial diversity. For legume crops with remaining wild populations, this is of even more importance, because the effects of cropping on undisturbed root-associated bacterial communities can be addressed. Here, we used a community prediction approach to describe the diversity of the root nodule bacterial communities of rooibos (Aspalathus linearis), an endemic legume crop from South Africa. The goal was to reveal whether patterns of root nodule community composition in paired cultivated and wild rooibos populations could be related to geographical distance, plant traits, and plant population type (i.e. cultivated or uncultivated). We identified a core of dominant and widespread Mesorhizobium ZOTUs that each defined one of 4 different root nodule community classes. Rooibos cultivation impacted root nodule bacterial diversity at regional and local scales, while the geographical origin of the root nodule communities was the strongest predictor of root nodule community structure. Beyond impacts of cultivation on root nodule bacterial diversity, this study suggests a mixture of dispersal limitation and ecological drift regionally, and selection by different plant populations locally, define the biogeography of rooibos root nodule bacterial communities.

ecology↗

bioRxiv2020

Coalescence of rhizobial communities in soil interacts with fertilization and determines the assembly of rhizobia in root nodules

Soil microbial community coalescence, whereby entire microbial communities mix and compete in a new environmental setting, is a widespread phenomenon whose applicability for targeted root microbiome assembly has not been studied. Using a legume shrub adapted to nutrient poor soil, we tested for the first time how the assembly of communities of rhizobial root nodule symbionts is affected by the interaction of coalescence and fertilization. Seedlings of the rooibos [Aspalathus linearis (Burm.f.) Dahlg.], were raised in pairwise mixtures of soil from cultivated and uncultivated land of five farms, as well as the individual mixture components. A fragment of the symbiosis maker gene, nodA, was sequenced to characterize the taxonomic turnover of the rhizobia associated with all root nodules at the age of eight month. Soil mixing promoted taxonomic turnover in the rhizobial communities, while fertilization amplified such turnover by increasing the number of rhizobia that became more abundant after soil mixing. Soil mixing and fertilization had a synergistic effect on the abundance of a particular taxon, which was rare in the component soils but became highly abundant in fertilized plants raised in soil mixtures. These findings provide the first evidence that fertilizer addition can interact with soil microbial community coalescence, probably through increasing the chances for rare strains to prioritize root nodule colonization. The combination of soil mixing and fertilizer addition may be a still unexplored measure to (re)introduce root microbial mutualists in arable land.

ecology↗

bioRxiv2020

Different ecological processes drive the assembly of dominant and rare root-associated bacteria in a promiscuous legume

Understanding how plant-associated microbial communities assemble and the roles they play in plant performance are major goals in microbial ecology. For nitrogen-fixing rhizobia, assemblages are mostly determined by filtering by the host as well as abiotic soil conditions. However, for legumes adapted to highly variable environments and nutrient-poor soils, filtering out rhizobial partners may not be an effective strategy to ensure symbiotic benefits. As a consequence, this can lead to net increases in rhizobial diversity driven by stochastic (neutral) assembly processes. Here, we addressed whether symbiotic promiscuity of rooibos (Aspalathus linearis Burm. Dahlgren), reflects increases in rhizobial diversity that are independent of the environmental conditions, following a neutral assembly. We performed a common garden experiment to assess whether root system size and location- and habitat-specific rhizobial propagule pools of rooibos affected rhizobial community diversity and composition. We found a dominance of drift in driving taxonomic turnover in the root nodule communities, but operating at different scales in the dominant Mesorhizobium symbionts and the rest of bacterial taxa. Specifically, drift triggered differentiation between the core rhizobial symbionts of rooibos due to dispersal limitation on a regional scale, whereas it dominated the assembly of non-dominant rhizobial taxa at the root level. This suggests the existence of a significant neutral component in rhizobial community assembly when selectivity by the host plant is low. We conclude that in this promiscuous legume neutral processes govern bacterial community root nodule community assembly, but that these operate at different scales in dominant and rare rhizobial symbionts of the plant.

ecology↗