Does Legume Root Exudation Facilitate Itself P Uptake in Intercropped Wheat?

The purpose of the study is to assess the ability of three different grain legume species to facilitate phosphorus (P) uptake by intercropped wheat and to evaluate the differences in root exudation and phosphatase activity that each grain legume species can induce in the soil. In a pot experiment under controlled climatic conditions, lupin, pea, and faba bean intercropped with durum wheat and respective sole crops were grown at high and low phosphorus availability. At the flowering time of each grain legume, intercrop and sole crops were sampled. Intercropping favored wheat P uptake more at low P availability than at high P availability. Compared to the sole crop, wheat P uptake was greater in intercropping with pea both without and with the addition of phosphorus and with lupin when phosphorus was not added. Phosphatase activity, which was generally high, was highest in soil with lupin and faba bean sole crops. In the rhizosphere of faba bean, the highest total carboxylate concentration was also measured, followed by pea and lupin. Root exudation was favored by P supply, showing greater values in intercropped wheat than in the respective sole crops. P uptake by wheat was not directly linked to greater root exudation in the tested intercropping systems. Even if root exudation and available phosphorus were generally greater with legumes both in sole crop and in intercropping, other interactions such as complementarity and competition were involved, hiding potential facilitation exerted by faba bean and bringing out the benefits from the wheat/pea combination.