GLOBAL CHANGE AND ROOT FUNCTION

Global change includes land-use change, elevated CO2 concentrations, i ncreased temperature and increased rainfall variability. All four aspe cts by themselves and in combination will influence the role of roots in linking below- and above-ground ecosystem function via organic and inorganic resource flows. Root-mediated ecosystem functions which may be modified by global change include below-ground resource (water, nut rients) capture, creation and exploitation of spatial heterogeneity, b uffering of temporal variations in above-ground factors, supply and st orage of C and nutrients to the belowground ecosystem, mobilization of nutrients and C from stored soil reserves, and gas exchange between s oil and atmosphere including the emission from soil of greenhouse gase s. The theory of a functional equilibrium between root and shoot alloc ation is used to explore predicted responses to elevated CO2 in relati on to water or nutrient supply as limiting root function. The theory p redicts no change in root:shoot allocation where water uptake is the l imiting root function, but substantial shifts where nutrient uptake is (or becomes) the limiting function. Root turnover will not likely be influenced by elevated CO2, but by changes in regularity of water supp ly. A number of possible mechanisms for root-mediated N mineralization is discussed in the light of climate change factors. Rhizovory (root consumption) may increase under global change as the balance between p lant chemical defense and adapted root. consuming organisms may be mod ified during biome shifts in response to climate change. Root-mediated gas exchange allows oxygen to penetrate into soils and methane (CH4) to escape from wetland soils of tundra ecosystems as well as tropical rice production systems. The effect on net greenhouse gas emissions of biome shifts (fens replacing bogs) as well as of agricultural land ma nagement will depend partly on aerenchyma in roots.