Root Rhizosphere Microbe Models and Experiments

As was noted in the discussion of primary production processes (Chapter 2), there are "hot spots" of activity, particularly of microbes in relationship to root surfaces and rhizospheres. When viewed as a transect through the rhizosphere, (e.g., 2 mm from the root surface or less,) there are arrays of rapidly growing bacteria and fungi, which have been called "fast" flora (Trofymow and Coleman, 1982) (Fig. 3.10). Moving up the root toward the shoot into older regions, one finds root hairs, then root cortical cells, which may be sloughing off into the surrounding soil. There are accompanying microbial and root grazers such as protozoa and nematodes, which are discussed in detail in Chapter 4. Out in the bulk soil, away from the rhizosphere (more than 4 mm from the root surface), occur some of the slower-growing, or "slow," bacteria and fungi, organic matter fragments, and some of the hyphae of either arbuscular mycorrhizal (AM) or ectotrophic mycorrhiza.

Legend

Litter from primary producers

Litter from consumers

Transect parameters-scales are unltless TP with individual T.P. maximums of 100% and minimums of 0%. PN.U Plant nutrient uptake

MN. Mineralized nutrient

GB Grazer biomass

MB Microflora biomass

SOC Soil organic carbon

Nutrient flow

Carbon flow

C^J High C/N. particulate substrate art Low C/N. particulate substrate

CO2 gas exchange

N2 gas exchange due to N-fixation and denitrification

NO3 input from precipitation g

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