Phylogeographic distribution of rhizobia nodulating common bean (Phaseolus vulgaris L.) in Ethiopia

Vegetation communities and soil properties along the restoration process of the Jinqianghe mine site in the Qilian Mountains, China

The study explores the impact of mine grassland restoration on plant communities and soil properties in alpine grasslands, a subject of significant interest due to the observed relationship between grassland changes, plant communities, and soil properties. While prior research has mainly focused on the consequences of grassland degradation on plant diversity and soil characteristics, the specific effects of varying restoration degrees in alpine mining grasslands at the regional scale remain poorly understood. To address this knowledge gap, we established 15 sampling plots (0.5m×0.5m) across five different restoration degrees within alpine mining grasslands in the Qilian Mountains, China. Our objective was to assess the variations in plant diversity and soil properties along these restoration gradients. We conducted comprehensive analyses, encompassing soil properties [soil water content (SWC), available nitrogen (AN), total phosphorus (TP), nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N), total nitrogen (TN), available phosphorus (AP), soil organic carbon (SOC), nitrate nitrogen, soil pH, and electrical conductivity (EC)], plant characteristics (height, density, frequency, coverage, and aboveground biomass), and plant diversity indices (Simpson, Shannon-Wiener, Margalef, Dominance, and Evenness indexes). Our findings included the identification and collection of 18 plant species from 11 families and 16 genera across the five restoration degrees: Very Low Restoration Degree (VLRD), Low Restoration Degree (LRD), Moderate Restoration Degree (MRD), High Restoration Degree (HRD), and Natural Grassland (NGL). Notably, species like Carex duriuscula, Cyperus rotundus, and Polygonum viviparum showed signs of recovery. Principal component analysis and Pearson correlation analysis revealed that soil pH, SWC, SOC, NO3-N, and AN were the primary environmental factors influencing plant communities. Specifically, soil pH and EC decreased as restoration levels increased, while SWC, AN, TP, NH4-N, TN, AP, SOC, and NO3-N exhibited a gradual increase with greater restoration efforts. Furthermore, the HRD plant community demonstrated similarities to the NGL, indicating the most effective natural recovery. In conclusion, our study provides valuable insights into the responses of plant community characteristics, plant diversity, and soil properties across varying restoration degrees to environmental factors. It also elucidates the characteristics of plant communities along recovery gradients in alpine grasslands.

Diversity of common bean rhizobia in blackland of northeastern China and their symbiotic compatibility with two host varieties

The common bean (Phaseolus vulgaris L.) is an important crop in the world that forms root nodules with diverse rhizobia. Aiming to learn the rhizobial communities associated with the common bean in the black soil of Northeast China, 79 rhizobia were isolated from root nodules of two host varieties (Cuican and Jiadouwang) grown in two sites of blackland and were characterized by comparative sequence analyses of 16S rRNA, recA, atpD, nodC, and nifH genes, and whole genome. As a result, Rhizobium indigoferae, R. anhuiense, and R. croatiense as minor groups and three dominant novel Rhizobium species were identified based on their average nucleotide identity and DNA-DNA hybridization values to the type strains of relative species. This community composition of rhizobia associated with the common bean in the tested black soils was unique. Despite their different species affiliations, all of them were identified into the symbiovar phaseoli according to the phylogenies of symbiotic genes, nodC and nifH. While the phylogenetic discrepancies found in nodC, nifH evidenced that the evolutions of nodulation (nod) and nitrogen fixation (nif ) genes were partially independent. In addition, only one dominant rhizobial species was shared by the two common bean varieties grown in the two soil samples, implying that both the plant variety and the soil characteristics affected the compatibility between rhizobia and their hosts. These findings further enlarged the spectrum of common bean-nodulating rhizobia and added more information about the interactions among the soil factors, rhizobial species, and host plants in the symbiosis.

MGEs as the MVPs of Partner Quality Variation in Legume-Rhizobium Symbiosis

Despite decades of research, we are only just beginning to understand the forces maintaining variation in the nitrogen-fixing symbiosis between rhizobial bacteria and leguminous plants. In their recent work, Alexandra Weisberg and colleagues use genomics to document the breadth of mobile element diversity that carries the symbiosis genes of Bradyrhizobium in natural populations. Studying rhizobia from the perspective of their mobile genetic elements, which have their own transmission modes and fitness interests, reveals novel mechanisms for the generation and maintenance of diversity in natural populations of these ecologically and economically important mutualisms.

Re-vegetation Improves Soil Quality by Decreasing Soil Conductivity and Altering Soil Microbial Communities: A Case Study of an Opencast Coal Mine in the Helan Mountains

Microbial communities constitute a diverse genetic resource pool in the soil and are key indicators of soil health and quality. How re-vegetation affects soil microbial diversity and community composition at the dump of an opencast coal mine is largely unknown. Using high-throughput sequencing, we performed a comparative study of the bacterial and fungal communities from non-vegetated (bare land) soil and from areas re-vegetated by Astragalus laxmannii, Halogeton arachnoideus, and Artemisia desertorum at an opencast coal mine in the Helan Mountains in western China. These results indicated that re-vegetation significantly reduced soil conductivity. The soils re-vegetated by all three plant species showed greater richness of bacterial species than the bare land, and soils re-vegetated with A. desertorum and A. laxmannii showed significantly greater richness of fungal species than bare land. The bacterial and fungal β-diversity values differed significantly between vegetated and non-vegetated soil, and these differences were more pronounced for bacterial communities than for fungal communities. Re-vegetation significantly increased the relative abundances of Proteobacteria and Bacteroidota and decreased the relative abundance of Chloroflexi. The decreasing soil conductivity that occurred with re-vegetation was found to be an important environmental determinant of the soil microbial community. This study provides evidence that re-vegetation may enhance soil quality via decreasing soil conductivity and altering the soil microbial community, and A. laxmannii was found to be a more effective species than H. arachnoideus or A. desertorum with respect to decreasing soil conductivity and altering the soil microbial communities in the Opencast Coal Mine arid region. This work may provide a helpful guideline for selection of plant species for re-vegetation projects.

Phylogenetic diversity and plant growth-promoting activities of rhizobia nodulating fenugreek (Trigonella foenum-graecum Linn.) cultivated in different agroclimatic regions of India

Fenugreek (Trigonella foenum-graecum Linn.), is an extensively cultivated legume crop used as a herb, spice, and traditional medicine in India. The symbiotic efficiency and plant growth-promoting potential of fenugreek rhizobia depend on the symbiont strain and environmental factors. We isolated 176 root-nodulating bacteria from fenugreek cultivated in different agroclimatic regions of India. MALDI-TOF MS-based identification and phylogenetic analyses based on 16S rRNA and five housekeeping genes classified the fenugreek-rhizobia as Ensifer (Sinorhizobium) meliloti. However, the strains represent separate sub-lineages of E. meliloti, distinct from all reported sub-lineages across the globe. We also observed the spatial distribution of fenugreek rhizobia, as the three sub-lineages of E. meliloti recorded during this study were specific to their respective agroclimatic regions. According to the symbiotic gene (nodC and nifH) phylogenies, all three sub-lineages of E. meliloti harboured symbiotic genes similar to symbiovar meliloti; as with the housekeeping genes, these also revealed a spatial distribution for different clades of sv. meliloti. The strains could nodulate fenugreek plants and they showed plant growth-promoting potential. Significant differences were found in the plant growth parameters in response to inoculation with the various strains, suggesting strain-level differences. This study demonstrates that fenugreek rhizobia in India are diverse and spatially distributed in different agro-climatic regions.