Phosphorus availability drives the effect of legume-wheat intercropping on prokaryotic community interactions

Phosphorus (P) is a finite and pivotal resource in determining plant yield. Intercropping with legumes is
frequently proposed to improve P nutrition in many crops such as wheat, and the greater yield and P uptake observed are mostly attributed to legumes' root exudation of organic acids and phosphatases, which modify rhizosphere chemistry. The same rhizosphere modification drives the selection of specific bacterial communities by providing carbon sources such as organic acids and other metabolites. This study aimed to further understand the influence of P bioavailability on bacterial community selection and whether this can be extended to other crops through intercropping. Pea, lupin and wheat were grown as intercrops and as sole crops at four levels of P availability. This was achieved by using a low-P soil from the long-term experiment at Rothamsted Research,
amended with available and low-available forms of P. After 62 days of growth, 16S rRNA gene amplicon sequencing was performed from rhizosphere samples, and acid and alkaline phosphomonoesterase (PME) activity was measured. The plant species was the main factor determining the structure of the bacterial community followed by P availability. When P was unavailable or depleted, legume monoculture as well as intercropping, was associated with reduced bacterial species richness and diversity, which was partly explained by an increased relative abundance of Variovorax, Pseudomonas and Bradyrhizobium spp. The complexity and interconnections of
the bacterial community were increased in intercropping when P was unavailable as was alkaline PME activity, while the acid PME activity was more affected by the plant. In conclusion, wheat intercropping can generate a more complex and interconnected root-associated bacterial community, which can potentially contribute to the facilitation of P uptake.