Root effects on soil organic matter decomposition. In: Roots and Soil Management: Interactions between Roots and the Soil (eds

Roots of higher plants, a key functional component of belowground systems and one of the main soil-forming agents (Jenny, 1941), interact with virtually all soil components. Processes that are largely controlled or directly influenced by roots and often occur in the vicinity of the root surface are often referred to as rhizo-sphere processes. These processes may include root production through growth and death (root turnover), rhizodeposition, root respiration, and rhizosphere mi-crobial respiration that is a result of microbial utilization of rhizodeposits. Rhi-zosphere processes play an important role in the global C cycle (Fig. 7–1). Ter-restrial ecosystems are intimately connected to atmospheric carbon dioxide (CO2) levels through photosynthetic fixation of CO2, sequestration of CO2 into biomass and soils, and the subsequent release of C through respiration and decomposition of organic matter. Considering all the pools and fluxes of C within ecosystems, C cycling belowground is increasingly being recognized as one of the most signifi-cant components (Jackson et al., 1997; Zak and Pregitzer, 1998). Globally, the input of C to the soil has been estimated to be as great as 60 ( 10−5 g yr−1 (Post e