RHIZOSPHERIC PROCESSES INFLUENCING THE BIOGEOCHEMISTRY OF FOREST ECOSYSTEMS

In the rhizosphere, biotic and abiotic processes interact to create a zone distinct from the bulk soil that may strongly influence the bioge ochemistry of forest ecosystems, This paper presents a conceptual mode l based upon three operationally defined soil-root compartments (bulk soil, rhizosphere and soil-root interface) to assess nutrient availabi lity in the mineral soil-root system. The model is supported by chemic al and mineralogical analyses from bulk and rhizosphere soils collecte d from a Norway spruce forest. The rhizosphere was more intensively we athered and had accumulated more acidity, base cations and phosphorus than the bulk soil. The quantity and quality of organic matter regulat e the reciprocal relationships between soil and roots with their assoc iated biota, However, the biogeochemical role of organic matter in the rhizosphere still remains as an area in which more future research is needed. The mechanisms that may regulate nutrient availability in the rhizosphere are also discussed and related to nutrient cycling and ad aptation of forests growing under nutrient poor or perturbed condition s, We suggest that the rhizosphere is not an ephemeral environment in the soil, but persists over time and is resilient against perturbation as evinced by consistent differences between rhizosphere and bulk che mistry and mineralogy over wide range of field treatments.