Interaction between Medicago truncatula and Pseudomonas fluorescens: evaluation of costs and benefits across an elevated atmospheric CO(2)

Carbon fluxes and environmental interactions during legume development, with a specific focus on Pisum sativum

Grain legumes are major food crops cultivated worldwide for their seeds with high nutritional content. To answer the growing concern about food safety and protein autonomy, legume cultivation must increase in the coming years. In parallel, current agricultural practices are facing environmental challenges, including global temperature increase and more frequent and severe episodes of drought stress. Crop yield directly relies on carbon allocation and is particularly affected by these global changes. We review the current knowledge on source-sink relationships and carbon resource allocation at all developmental stages, from germination to vegetative growth and seed production in grain legumes, focusing on pea (Pisum sativum). We also discuss how these source-sink relationships and carbon fluxes are influenced by biotic and abiotic factors. Major agronomic traits, including seed yield and quality, are particularly impacted by drought, temperatures, salinity, waterlogging, or pathogens and can be improved through the promotion of beneficial soil microorganisms or through optimized plant carbon resource allocation. Altogether, our review highlights the need for a better understanding of the cellular and molecular mechanisms regulating carbon fluxes from source leaves to sink organs, roots, and seeds. These advancements will further improve our understanding of yield stability and stress tolerance and contribute to the selection of climate-resilient crops.

Priority effects alter interaction outcomes in a legume-rhizobium mutualism

Priority effects occur when the order of species arrival affects the final community structure. Mutualists often interact with multiple partners in different orders, but if or how priority effects alter interaction outcomes is an open question. In the field, we paired the legume Medicago lupulina with two nodulating strains of Ensifer bacteria that vary in nitrogen-fixing ability. We inoculated plants with strains in different orders and measured interaction outcomes. The first strain to arrive primarily determined plant performance and final relative abundances of rhizobia on roots. Plants that received effective microbes first and ineffective microbes second grew larger than plants inoculated with the same microbes in the opposite order. Our results show that mutualism outcomes can be influenced not just by partner identity, but by the interaction order. Furthermore, hosts receiving high-quality mutualists early can better tolerate low-quality symbionts later, indicating that priority effects may help explain the persistence of ineffective symbionts.

Long-term non-invasive and continuous measurements of legume nodule activity

Symbiotic nitrogen fixation is a process of considerable economic, ecological and scientific interest. The central enzyme nitrogenase reduces H(+) alongside N2 , and the evolving H2 allows a continuous and non-invasive in vivo measurement of nitrogenase activity. The objective of this study was to show that an elaborated set-up providing such measurements for periods as long as several weeks will produce specific insight into the nodule activity's dependence on environmental conditions and genotype features. A system was developed that allows the air-proof separation of a root/nodule and a shoot compartment. H2 evolution in the root/nodule compartment can be monitored continuously. Nutrient solution composition, temperature, CO2 concentration and humidity around the shoots can concomitantly be maintained and manipulated. Medicago truncatula plants showed vigorous growth in the system when relying on nitrogen fixation. The set-up was able to provide specific insights into nitrogen fixation. For example, nodule activity depended on the temperature in their surroundings, but not on temperature or light around shoots. Increased temperature around the nodules was able to induce higher nodule activity in darkness versus light around shoots for a period of as long as 8 h. Conditions that affected the N demand of the shoots (ammonium application, Mg or P depletion, super numeric nodules) induced consistent and complex daily rhythms in nodule activity. It was shown that long-term continuous measurements of nodule activity could be useful for revealing special features in mutants and could be of importance when synchronizing nodule harvests for complex analysis of their metabolic status.

(34)S and (15)N labelling to model S and N flux in plants and determine the different components of N and S use efficiency

In order to highlight our understanding on ecosystems functioning and resource sharing/competition, either in artificial environment or agrosystems, according to changes in the climatic conditions, it is necessary to measure accurately element fluxes within plants. Stable isotopes allow tracking safely and accurately on a short time frame the behavior of elements in plants. After a short review devoted to isotopic studies of elemental flux within plants, we explain how a direct multiple labelling study might be conducted in a plant, so as to measure over short time nitrogen and sulfur acquisition, and assimilates arising from a labelled source.