ORCID Profile
0000-0002-1806-2889
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Publisher: Oxford University Press (OUP)
Date: 21-07-2020
Abstract: There is interest in understanding how cultivation, plant genotype, climate and soil conditions influence the biogeography of root nodule bacterial communities of legumes. For crops from regions with relict wild populations, this is of even greater interest because the effects of cultivation on symbiont communities can be revealed, which is of particular interest for bacteria such as rhizobia. Here, we determined the structure of root nodule bacterial communities of rooibos (Aspalathus linearis), a leguminous shrub endemic to South Africa. We related the community dissimilarities of the root nodule bacteria of 18 paired cultivated and wild rooibos populations to pairwise geographical distances, plant ecophysiological characteristics and soil physicochemical parameters. Using next-generation sequencing data, we identified region-, cultivation- and farm-specific operational taxonomic units for four distinct classes of root nodule bacterial communities, dominated by members of the genus Mesorhizobium. We found that while bacterial richness was locally increased by organic cultivation, strong biogeographical differentiation in the bacterial communities of wild rooibos disappeared with cultivation of one single cultivar across its entire cultivation range. This implies that expanding rooibos farming has the potential to endanger wild rooibos populations through the homogenisation of root nodule bacterial ersity.
Publisher: Oxford University Press (OUP)
Date: 04-05-2020
Abstract: Understanding how plant-associated microbial communities assemble and the role they play in plant performance are major goals in microbial ecology. For nitrogen-fixing rhizobia, community assembly is generally driven by host plant selection and soil conditions. Here, we aimed to determine the relative importance of neutral and deterministic processes in the assembly of bacterial communities of root nodules of a legume shrub adapted to extreme nutrient limitation, rooibos (Aspalathus linearis Burm. Dahlgren). We grew rooibos seedlings in soil from cultivated land and wild habitats, and mixtures of these soils, s led from a wide geographic area, and with a fertilization treatment. Bacterial communities were characterized using next generation sequencing of part of the nodA gene (i.e. common to the core rhizobial symbionts of rooibos), and part of the gyrB gene (i.e. common to all bacterial taxa). Ecological drift alone was a major driver of taxonomic turnover in the bacterial communities of root nodules (62.6% of gyrB communities). In contrast, the assembly of core rhizobial communities (genus Mesorhizobium) was driven by dispersal limitation in concert with drift (81.1% of nodA communities). This agrees with a scenario of rooibos-Mesorhizobium specificity in spatially separated subpopulations, and low host filtering of other bacteria colonizing root nodules in a stochastic manner.
Publisher: Oxford University Press (OUP)
Date: 23-09-2019
Abstract: Mutualistic plant–microbial functioning relies on co-adapted symbiotic partners as well as conducive environmental conditions. Choosing particular plant genotypes for domestication and subsequent cultivar selection can narrow the gene pools of crop plants to a degree that they are no longer able to benefit from microbial mutualists. Elevated mineral nutrient levels in cultivated soils also reduce the dependence of crops on nutritional support by mutualists such as mycorrhizal fungi and rhizobia. Thus, current ways of crop production are predestined to compromise the propagation and function of microbial symbionts, limiting their long-term benefits for plant yield stability. The influence of mutualists on non-native plant establishment and spread, i.e. biological invasions, provides an unexplored analogue to contemporary crop production that accounts for mutualistic services from symbionts like rhizobia and mycorrhizae. The historical exposure of organisms to biotic interactions over evolutionary timescales, or so-called eco-evolutionary experience (EEE), has been used to explain the success of such invasions. In this paper, we stress that consideration of the EEE concept can shed light on how to overcome the loss of microbial mutualist functions following crop domestication and breeding. We propose specific experimental approaches to utilize the wild ancestors of crops to determine whether crop domestication compromised the benefits derived from root microbial symbioses or not. This can predict the potential for success of mutualistic symbiosis manipulation in modern crops and the maintenance of effective microbial mutualisms over the long term.
Publisher: Wiley
Date: 30-08-2021
Abstract: Soil microbial community coalescence, where entire microbial communities mix and interact under new conditions, is a widespread phenomenon whose applicability for targeted root microbiome assembly has not been studied. Whether soil mixing can lead to predictable outcomes for community assembly and functioning of specific functional groups, for ex le, N 2 ‐fixing rhizobia, remains unknown. Using a legume shrub adapted to nutrient‐poor soils, we tested the effects of community coalescence on plant nutrition and growth, and its influence on the rhizobial root nodule symbiosis. We grew seedlings of rooibos [ Aspalathus linearis (Burm.f.) Dahlg.] in in idual rhizosphere soils collected from cultivated and wild rooibos plants and their mixtures, and included a fertilization treatment. Portions of the taxonomic gyrB and the symbiotic nodA gene makers were sequenced to characterize rhizobial communities present in rooibos root nodules under the different soil conditions. Overall, community coalescence by soil mixing had positive effects on plant nutrition and growth, and interacted with fertilizer addition to concurrently change rhizobial taxonomic evenness and promote higher relative N 2 fixation. We identified particular rhizobia preferentially associated with rooibos plants that showed higher N fractions from N 2 fixation, raised in mixed fertilized soils. These findings indicate that soil bacterial community coalescence and fertilization can have synergistic effects on plant performance, while promoting the assembly of alternative symbiotic rhizobial communities that provide improved nutritional benefits to host plants. Synthesis and applications . The combination of soil mixing and fertilizer addition may be an important, but hitherto overlooked measure to improve the functioning of rhizobium symbioses in legume crops. Microbial community coalescence should gain recognition as a potentially effective mechanism to improve the functioning of plant microbiomes.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Josep Ramoneda Massague.