Biology subjects

Frossard, E.

Publications and source records attributed to Frossard, E..

6 recordsLinked to original sources

bioRxiv2026

Combing agronomic biofortification with a Zn-efficient wheat line synergistically increases grain Zn concentrations with varied effects on Cd in wheat grains

(Background and aims) Wheat grains are often too low in zinc (Zn) compared to human dietary needs, and are a major dietary source of highly toxic cadmium (Cd). Biofortification strategies can increase Zn in edible grain, but must not increase grain Cd. (Methods) We investigated the individual and combined effects of genetic and agronomic biofortification on Zn and Cd in wheat grains. Non-transgenic Bobwhite (BW-NT) and an OsNAS2-expressing line (BW-NAS) were grown in a pot experiment with isotope-labeled mineral Zn (70Zn) and green manure (70Zn, 106Cd). At flowering and maturity, Zn and Cd were quantified in wheat biomass. Wheat contents of Zn and Cd derived from inputs versus soil were determined using stable isotope analyses. (Results) Individually, the OsNAS2-expressing wheat and input application increased grain Zn. Combined OsNAS2 expression and input application led to grain concentrations of 76{+/-}4 mg kg-1 with mineral Zn application and 61{+/-}7 mg kg-1 with green manure. This was 154-217% higher than the 24{+/-}1 mg kg-1 observed in the BW-NT control and significantly higher than the additive effects of each strategy individually. The OsNAS2-expressing line increased grain Cd to 0.214{+/-}0.002 mg kg-1 under green manure, compared to 0.12{+/-}0.01 mg kg-1 in the BW-NT control. No other treatment increased grain Cd. (Conclusions) Our results encourage development of integrated genetic and agronomic biofortification strategies to increase grain Zn. They also underscore the need for careful monitoring of grain Cd concentrations when organic amendments are paired with genetic biofortification strategies.

plant biology↗

bioRxiv2026

The effect of organic amendment composition on zinc and cadmium availability and uptake in wheat crops

Organic amendments provide crops with nutrients, but can also add pollutants. Yet the fate of micronutrients such as zinc (Zn) and pollutants such as cadmium (Cd) in soil-crop systems is difficult to predict because of the complexity of amendments added to soils. We performed pot and incubation experiments to determine whether the soil availability, uptake and transfer to grain of Zn and Cd in wheat (Triticum aestivum) are linked to the composition of amendments. Three amendments with highly diverse chemical properties, including varied organic matter (OM) degradability, were applied to a non-contaminated, arable soil. Stable isotopes of 70Zn and 106Cd were used to trace metals taken up from inputs versus soil in wheat biomass. We found the amendment most enriched in rapidly degradable OM (poultry manure) led to the highest wheat uptake of input-derived Zn i.e., 87{+/-}14 mg Zn (kg soil)-1. This was 2.5 times higher than input-derived Zn uptake from the most degraded amendment (compost). We did not observe an increase in soil available Zn with amendment application. Thus, biotic processes resulting from soil-plant-microbial interactions led to the increase in wheat uptake of input-derived Zn with amendment enrichment in rapidly degradable OM. Amendments led to minimal uptake of input-derived Cd in wheat and did not increase soil available Cd. Furthermore, we found no significant increase in grain Zn and Cd concentrations with amendments compared to the control. Our results highlight how amendment OM composition affects soil availability and wheat uptake of Zn and Cd with organic amendment application.

plant biology↗

bioRxiv2025

Interaction of Environment and Vineyard Management Effects Shape Microbial Functionality, Terroir, and Grape Qualities

Vineyards are complex agroecological systems, with geographically distinct microbial communities playing a central role in mediating vine health, grape quality, and ultimately local wine characteristics (terroir). However, the extent to which environmental factors and vineyard management practices interact to shape these microbial communities and their functions remains poorly understood. We implemented a multidisciplinary citizen science collaboration together with winegrowers to sample 19 Pinot Noir vineyards across two distinct Swiss regions (N=38 samples). This allowed us to evaluate how a combination of environmental conditions and management practices (such as cover cropping and fungicide use) collectively impact soil and grape microbiomes, soil enzymatic activities, nutrient concentration in leaves, and grape chemistry. Regional differences were the primary drivers of variation, but multivariate analysis revealed a distinct, secondary influence from management practices on soil and berries. Berry quality was linked to functional soil properties, including microbial activity, which were further associated with key fermentative yeasts likely involved in wine fermentation. These findings highlight the interconnected nature of environmental, microbial, and agronomic factors in grapevine systems and offer novel insights into functional aspects of microbial terroir.

microbiology↗

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↗