Legumes provide multiple ecosystem services in agricultural systems. The objectives of this study were to evaluate the influence of different legumes through C rhizodeposition on the dynamics of C, N and P in soil and on microbial communities’ resource requirements. Legumes pea (Pisum sativum L.), faba bean (Vicia faba L.), white clover (Trifolium repens L.), crimson clover (Trifolium incarnatum L.) and non-legume wheat (Triticum aestivum L.) were grown in pots. Carbon rhizodeposition was quantified by using 13CO2 labeling, and six soil enzyme activities were measured: β-glucosidase (BG), arylamidase (ARYLN), N-acetyl-glucosaminidase (NAG), phosphatases (PHO) and alkaline and acid phosphatases (AKP and ACP). Enzyme stoichiometry approaches were applied. The results showed that BG, NAG and ACP activities were positively influenced by faba bean and clovers. Enzyme stoichiometry analysis revealed a limitation of microorganisms in C and P resources at the plant reproductive stage. These results were explained by plant functional traits. Plant biomass production, root total length, the ability of plants to rhizodeposit C and the C and N content of plant tissues were the main explicative factors. This study also shows that N and C nutrient supplies positively contribute to nutritional requirements and the growth of microorganisms and P availability in soil.

Legume crop production has many benefits for agricultural systems. Through the rhizodeposition process, they release a significant amount of C and N into the soil, increasing soil organic C and reducing the use of N fertilizer. Rhizodeposition is known as a dynamic process influenced by many factors. The aim of this study was to study the contribution of root exudation and root senescence to the rhizodeposition of atmospheric C and N during vegetative and reproductive growth in annual and perennial legumes and to understand how this is linked to the fixation capacities of C and N and root functional traits. An original approach that combined 13CO2 labelling and the 15N dilution method was developed to measure the rhizodeposition of atmospheric C and N throughout plant growth by two annual grain legumes (pea and faba bean) and two perennial forage legumes (white and crimson clovers). C rhizodeposition was found to increase proportionally with N rhizodeposition during reproductive development and the differences observed between species were related to the C and N fixation abilities. The use of root traits such as specific root length, root tissue density and root dry matter content suggests a strong contribution of root exudation to C rhizodeposition at vegetative growth and a strong contribution of root senescence to both C and N rhizodeposition during reproductive growth. Synthesis. Both C and N rhizodeposition appeared to be controlled by traits indicative of resource acquisition and root development.