Microbial biomass carbon and phosphorus are altered differently in the rhizosphere of intercropped and monocropped cereal and legumes

International audienceAims and Background: Microbial biomass carbon (C) is known to increase in the rhizosphere, while change of microbial biomass phosphorus ( P) is less documented. Microbial biomass is how ever a dynamic component of P cycling and thus a labile P pool that is potentially available to plants. Little is known about how it is controlled in the rhizosphere of crop species, either monocropped or intercropped. Methods: Durum wheat, chickpea and lentil were grown alone or as cereal/legume intercrops in a field experiment and their rhizosphere were collected at the legume flowering stage, with the corresponding bulk soils. The microbial biomass C and P were measured by chloroform fumigation-extraction technique. Results : Microbial biomass C systematically increased in the rhizosphere, the largest increase being observed in the rhizosphere of the legumes, when intercropped. In contrast, microbial biomass P seldom increased significantly in the rhizosphere. This occurred only in intercropped durum wheat/chickpea, both in the rhizosphere of chickpea and in that of durum wheat. No such change w as observed in these species when monocropped. Conclusion: The significantly increased microbial P in the rhizosphere of durum wheat/chickpea intercrops question its role in controlling P availability. Why did such an increase occur remains an open questio