Agro-ecological aspects of the mycorrhizal, nitrogen-fixing legume symbiosis

Abstract

Vesicular-arbuscular mycorrhizal (VAM) fungi have fundamental effects on the ecophysiology of nodulated legumes, on the biota of the surrounding soil and on associated non-legumes. The effects are seen to be mediated through the direct transfer of nutrients from plant to plant by live hyphae of the soil mycelium, and through improving the competitiveness of legumes in nutrient uptake. As en-visioned, the main role of legumes, in the open source-sink system between associated plañís and the soil biota, is that of a nitrogen source. The expon of nitrogen may be balanced by flows of carbón and phosphorus from plant to plant along gradients of sink demand. Soil microbes are beneficíaries of inter-plant nutrient transport, utilizing exúdales as well as the soil mycelium as substrates, while the producís of microbial melabolism serve lo aggregale ihe abiotic component of the soil. Thus, the tripartile legume associalion is seen lo function not only as a self-conlained syslem, bul as one involved in nulrienl fluxes belween adjacenl plañís and Ihe soil ihal surrounds its roots.