Grain Sorghum Crop Responses to Diversity in Rooting Architecture Among Plants Compared with Contrasting Monocultures and Interactions with Nitrogen.

The genetic uniformity of monocultures extends belowground to the architectural configuration of the roots. This uniformity among plants may encourage inefficiency in resource acquisition and/or intensify competition. In contrast, architectural diversity may improve efficiency such as observed in natural systems. Here we investigated the rooting character and responses of sorghum monocultures selected to contrast in rooting architecture and biodiverse mixtures (three, six, nine, and 12 genotypes) at four nitrogen rates. Significant differences, particularly in root mass density and specific root length, were observed between “shallow” and “deep” rooted monocultures in two soil profiles, demonstrating intra-species architectural contrasts often illusive in field conditions. The biodiverse cultures did not significantly differ in rooting architecture from each other, but on average fell between monocultures. This showed that, while containing extreme architectures to make the crop adaptable, the overall rooting character of a biodiverse crop was moderate. There was no evidence that root competition was affected by rooting architecture makeup in the system, as changes in crop root investment were mostly related to nitrogen availability. Variability in aboveground biomass yield systematically decreased as diversity in rooting architecture increased, suggesting that this diversity may impart yield stability to sorghum. Yield stability would be achieved as the crop, through biodiversity, gains access to soil resources despite environmental heterogeneity.