Zhang C, JA Postma, LM York, JP Lynch


Annals of Botany (2014)

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Background and Aims Since ancient times in the Americas, maize, bean, and squash have been grown together in a polyculture known as the "three sisters". This polyculture and its maize/bean variant have greater yield than component monocultures on a land equivalent basis. Here we show that belowground niche complementarity may contribute to this yield advantage.

Methods In two seasons we grew monocultures and polycultures of maize, bean and squash in field plots differing in nitrogen (N) and phosphorus (P) availability. Root growth patterns of individual crops and entire polycultures were determined using a modified DNA-based technique to discriminate roots of different species.

Key Results The maize/bean/squash and maize/bean polycultures had greater yield and biomass production on a land equivalent basis than the monocultures. Increased biomass production was largely caused by a complementarity effect, rather than a selection effect. The differences in root crown architectures and vertical root distribution among the components of the "three sisters" suggest that these species have different, possibly complementary, nutrient foraging strategies. Maize foraged relatively shallower, common bean explored the vertical soil profile more equally, while the root placement of squash depended on P availability. The density of lateral root branching was significantly greater for all species in the polycultures than in the monocultures.

Conclusions We conclude that species differences in root foraging strategies increase total soil exploration, with consequent positive effects on the growth and yield of these ancient polycultures.