Timing of connection to mycorrhizal networks matters: Nutrition, N fixation, and transfer of fixed N in maize-bean intercropping

Abstract

The mycorrhiza-mediated transfer of nutrients to plants connected through mycorrhizal networks may be managed through the timing at which plants integrate to the networks and the integrity of those networks. This is particularly relevant for intercropping agrosystems. We used soil tillage to disrupt mycorrhizal networks and sowing time treatments to manipulate the connection time of maize and bean in a field experiment. We hypothesized that 1) the benefits from connecting to mycorrhizal networks would be greater for the crop that is established first and retrieved resources from the network without competition, and 2) tillage disruption delaying colonization and connection to preserved mycorrhizal networks would reduce mycorrhizal colonization in roots and soil, crop nutrition, N fixation by beans, and transfer of fixed N to maize. Mycorrhizal network disruption with tillage reduced early mycorrhizal development in roots and soil, and N and P nutrition of both crops. In general, sowing time had no effect in maize but tillage increased plant density, growth, and the yield of maize by alleviating soil compaction. Reduced tillage and early sowing increased nutrition, development, N fixation and yield of bean. N derived from symbiotic fixation in bean and transferred to maize were higher with bean sown before maize under reduced tillage. Early connection to mycorrhizal networks favored mostly bean and made little difference to maize regardless of sowing time, contrary to our expectations. The greatest overall benefit for both crops was obtained when bean was sown before maize and connected early to preserved mycorrhizal networks under reduced tillage.