Impacts of underground competition and establishment on growth and root architecture of breadfruit (Artocarpus altilis) and māmaki (Pipturus albidus)

Abstract

Replacing conventional monocultures with more diverse agroecosystems can positively impact environmental quality, but their adoption is limited, in part, due to inadequate understanding of how these systems operate regarding belowground competition. We examined how root competition between breadfruit (Artocarpus altilis) and māmaki (Pipturus albidus) affected aboveground performance. Our 2 × 3 factorial design consisted of two competition treatments and the three establishment treatments. Plants were grown together on either side of 47-gallon pots. For non-competition groups, a sheet of vinyl plastic was used to keep the roots of each species separate while maintaining above ground conditions. We used root cores to quantify the spatial allocation of root biomass to explore competition strategies of the two crops and measured biomass production to determine how growth was affected by competition. The two species demonstrated different responses to below-ground competition, with above ground biomass (AGBM) decreased for breadfruit but increased for māmaki. Below ground biomass increased for both plants under competition. Prior establishment enhanced māmaki's response to competition, while breadfruit's response to competition was exacerbated by post establishment and mitigated by simultaneous establishment. We suggest that māmaki's response is due to a more aggressive strategy that targets resource patches, while breadfruit is unable to compete within established māmaki zones and employs an avoidance strategy for root allocation.