Biology subjects

Burghardt, L.

Publications and source records attributed to Burghardt, L..

5 recordsLinked to original sources

bioRxiv2026

Alfalfa varieties can weakly choose beneficial nitrogen-fixing bacteria from a population isolated from a single field

O_LIIn natural and agricultural systems, legumes recruit rhizobia from diverse soil populations to fix nitrogen in root nodules. A few legumes, including the model legume Medicago truncatula, can select and enrich beneficial rhizobia. Here, we investigated whether its perennial relative, Medicago sativa (alfalfa), a globally important forage crop, also possesses this ability. C_LIO_LIWe developed a genetically variable collection of 117 Sinorhizobium meliloti strains sampled from three field-grown alfalfa varieties, performed multi-strain and single-strain inoculations in a nitrogen-free greenhouse experiment across the same hosts, and evaluated plant benefits and relative strain fitness in nodules. C_LIO_LIAlfalfa varieties differed in which strains best promoted plant growth and which strains had high fitness in nodules. Regressing strain fitness and host benefit revealed that two of three alfalfa varieties selected and enriched more beneficial strains during symbiosis, though the strength of selection was weak. In alignment with these results, no variety produced as much biomass in mixed inoculation as it did with the best-performing single strain. C_LIO_LILegumes ability to enrich beneficial rhizobial populations from field-representative strain diversity warrants further study to develop optimized varieties. Ultimately, identifying crop varieties that naturally select for beneficial bacteria could reduce the need for repeated inoculant applications. C_LI

Plant Biology↗

bioRxiv2025

Cover crop microbiomes affect legume cash crop growth but not consistently through enriching nitrogen-fixing rhizobia

Harnessing plant-microbe interactions offers a promising path to reduce chemical inputs and enhance crop resilience in agricultural systems. However, microbial inoculants often fail to persist or function consistently across soils, which limits their broad utility. Here, we explore whether legume cover crops can be used to create microbial legacies that improve nodulation and nitrogen fixation in downstream legume cash crops. In a greenhouse experiment, we inoculated four cash crops with rhizosphere and nodule microbiomes derived from different legume cover crops, then used 16S rRNA and nifH amplicon sequencing to profile bacterial and diazotroph communities, respectively. Host identity shaped cover crop rhizosphere and nodule microbial communities, and specific taxa within these communities predicted nodulation and growth in some cash crops. Host specificity varied widely across cash crops, with alfalfa narrowly dependent on a specific symbiont and common bean and fava bean forming more permissive, taxonomically diverse nodule communities. Increased nodulation did not consistently improve biomass, and outcomes in some cash crops depended on more than symbiont compatibility alone. In particular, common bean growth was predicted by both rhizobial and non-rhizobial taxa, while soybean nodulation was shaped by its compatible symbiont as well as a mismatched rhizobial taxon associated with other hosts. Together, these results suggest that cover crops can shape cash crop microbiomes and productivity in host-specific ways, requiring precise symbiont matching in selective hosts but offering more flexible, multi-taxon management opportunities in permissive hosts.

plant biology↗

bioRxiv2025

Rapid adaptation and extinction across climates in synchronized outdoor evolution experiments of Arabidopsis thaliana

Climate change is threatening species with extinction, and rapid evolutionary adaptation may be their only option for population rescue over short ecological timescales. However, direct observations of rapid genetic adaptation and population dynamics across climates are rare across species. To fill this gap, we conducted a replicated, globally synchronized evolution experiment with the plant Arabidopsis thaliana for 5 years in over 30 outdoor experimental gardens with distinct climates across Europe, the Levant, and North America. We performed whole-genome sequencing on [~]70,000 surviving reproductive individuals and directly observed rapid and repeatable adaptation across climates. Allele frequency changes over time were parallel in experimental evolution replicates within the same climates, while they diverged across contrasting climates--with some allele frequency shifts best explained by strong selection between -46% to +60%. Screening the genome for signals of rapid climate adaptation identified a polygenic architecture with both known and novel adaptive genetic variants connected to important ecological phenotypes including environmental stress responses, CAM5 and HEAT SHOCK FACTORs, and germination and spring flowering timing, CYTOCHROME P450s and TSF. We found evolutionary adaptation trends were often predictable, but variable across environments. In warm climates, high evolutionary predictability was associated with population survival up to 5 years, while erratic trends were an early warning for population extinction. Together, these results show rapid climate adaptation may be possible, but understanding its limits across species will be key for biodiversity forecasting.

evolutionary biology↗

bioRxiv2024

Temperature and host plant ecotype drive nitrogen fixation, but not nodule community composition, in hairy

Hairy vetch (Vicia villosa Roth) is a commonly grown cover crop throughout the U.S., which can contribute nitrogen for subsequent cash crops through biological nitrogen fixation (BNF) in association with Rhizobium leguminosarum biovar viciae (Rlv) bacteria. Hairy vetch is one of the few cover crops sufficiently cold-tolerant to over-winter in the Upper Midwestern U.S. However, nitrogen contributions by hairy vetch vary across locations, potentially due to cold impacts on the legume/rhizobia symbiosis. The traditional route to improve BNF in legumes involves selecting superior rhizobia strains to create more effective inoculants to apply at planting, but inoculants often fail to compete and survive in agricultural soils. Instead, this study tested the effects of temperature and host plant ecotype on hairy vetch BNF and Rlv community composition in nodules, with the goal of potentially identifying vetch ecotypes able to select beneficial Rlv strains from the soil community. Four hairy vetch ecotypes trapped Rlv from three Minnesota soils, at warm or cold temperatures. Vetch ecotype was a key driver of BNF and nodule formation under warm and cold conditions. However, temperature and plant ecotype did not drive Rlv community composition in nodules, and Rlv community composition did not affect plant productivity. Taken together, these results suggest that the best strategy to improve BNF at low temperatures in hairy vetch likely depends on breeding for improved biomass accumulation and nitrogen fixation in host plants, rather than focusing on host plant selection of beneficial rhizobia.

plant biology↗

bioRxiv2024

A Multitrait Genome-Wide Association Study Reveals a Requirement for the Strigolactone Receptor DWARF14 in Optimal GOLVEN10 Signaling

GOLVEN/ROOT MERISTEM GROWTH FACTOR family of signaling peptides have been shown to control root lateral organ number, density and positioning in plants, although the signaling pathways involved remain obscure. A diverse set of 171 Medicago truncatula HapMap accessions with variation in responses to the GOLVEN 10 peptide, GLV10, were used to identify 74 significant loci controlling seven traits related to nodule formation and root architecture. Importantly, a single nucleotide polymorphism (SNP) in the upstream region of the MtGLV10 peptide-inducible strigolactone receptor gene, MtDWARF14 was significantly associated with insensitivity of nodule density to GLV10, suggesting a link between strigolactone signaling and GLV10 responsiveness. Three independent d14 mutants of the DWARF14 gene were found to hypernodulate, while overexpression of the gene led to reduction in nodule number, phenocopying GLV10. A null mutant, mtd14-1, remained sensitive to GLV10s effect on nodule density. However, at the transcriptional level, the mutant failed to effectively induce the expression of the GOLVEN marker genes, MtPLETHORA3 and MtPINLIKES2. Our study uncovers a hitherto unknown link between the strigolactone and GLV peptide signaling pathways using genotype x environment analysis of Medicago HapMap lines and provides a putative molecular mechanism for recovery from frost damage to fine roots.

plant biology↗