The Contribution of Root - Rhizosphere Interactions to Biogeochemical Cycles in a Changing World

This chapter discusses how elevated atmospheric CO2 and atmospheric N deposition influence the physiology and growth of fine roots, as well as how the changes in the form and function of the root system can influence rhizosphere processes, which scale up to alter biogeochemical cycles. Elevated atmospheric CO2 increases the growth of small-diameter roots across a range of species and experimental conditions. The poor understanding of the relationship between fine root biomass and soil N availability is partly because of the inconsistent relationship in literature between soil N availability and root turnover. Fine root turnover refers to the flux of carbon and nutrients from plants into soil per unit area per unit time, and it is a major component of forest ecosystem carbon and nutrient cycling. The effects of increased soil N availability, induced by atmospheric N deposition, on fine root lifespan are not at all clear, in spite of considerable research and years of debate in the literature. Root respiration is a major component of total soil CO2 efflux, usually accounting for at least 50% of soil respiration. The response of ecosystems to elevated atmospheric CO2 and O3 provides another interesting example of how altered primary productivity cascades through the root system to influence C storage in the soil. Field studies have shown that elevated atmospheric CO2 increases the concentration of soil CO2. The impact of the interaction between elevated atmospheric CO2 and O3 on soil C storage clearly demonstrates why it is important to examine the interacting effects of our changing atmosphere. © 2007 Elsevier Inc. All rights reserved