Root Exudates and Nutrient Cycling

Abstract

In addition to their role as organs for anchorage in soil, soil exploitation, and uptake of water and nutrients, plant roots can modify the physico-chemical conditions in the surrounding soil via alterations of root activity. The soil volume that is directly or indirectly influenced by the activity of plant roots is called the rhizosphere (Hinsinger 1998). As early as the beginning of the last century, the German phytopathologist Lorenz Hiltner (1904) recognised that the rhizosphere, as the interface between the soil matrix, plant roots and soil microorganisms, plays a critical role in nutrient cycling in ecosystems. Root-induced physico-chemical changes in the rhizosphere are major determinants of the plant availability of nutrients and toxic elements in soils. Organic compounds released from plant roots as rhizodeposits can have a direct impact on the solubility of mineral elements or can indirectly influence turnover and availability of nutrients by interaction with soil micro-organisms. Thus, rhizodeposition is a key factor determining fluxes and pool sizes of mineral nutrients in ecosystems.