The rhizospheric environment

H. H. Rogers, G. B. Runion, and S. V. Krupa, Plant responses to atmospheric CO, enrichment with emphasis on roots and the rhizosphere. Environ Polhit. 155 (1994). 

The literature shows that many fewer data are available on dissolved than on solid-phase heavy metals at the soil-root interface. To date, several approaches have been used to acquire soil solution samples from the rhizospheric environment, includmg water displacement, water extraction, centrifugation, and microsuction cups. However, because of technical constraints, no single method appears to sample unaltered rhizosphere solution. 

The results from these complementary approaches showed that the rhizospheric environment accelerated the weathering of primary minerals. In situ weathering products contributed to the retention of trace metals at the soil-root interface. The reader is referred to Chapter 2 written by S6guin et al. (2005) for a detailed presentation of the methods used to measure weathering and for a comprehensive discussion of the results gathered as part of this project. 

Walton BT, Anderson TA. 1990. Microbial degradation of trichloroethylene in the rhizosphere Potential application to biological remediation of waste sites. Appl Environ Microbiol 56 1012-1016. 

Brazil GM, L Kenefick, M Callanan, A Haro, V de Lorenzo, DN Dowling, F O Gara (1995) Constrnction of a rhizosphere psendomonad with potential to degrade polychlorinated biphenyls and detection of bph gene expression in the rhizosphere. Appl Environ Microbiol 61 1946-1952. 

Notz R, M Maurhofer, H Dubach, D Haas, G Defago (2002) Fusaric acid-producing strains of Fusarium oxysporum alter 2,4-diacetylphloroglucinol biosynthetic gene expression in Pseudomonas fluorescens CHAO and in the rhizosphere of wheat. Appl Environ Microbiol 68 2229-2235. 

This chapter considers the various types of root products with a potential functional role in the usually tough environment of soil. Only direct effects of immediate benefit to plant growth—e.g., an increase in nutrient solubility—are considered here. Although root products of a plant species may have a direct effect on important groups of soil organisms, such as rhizobia and mycorrhizae. their effect on the plant is not immediate these and aspects related to microbial activity in the rhizosphere are not considered here (see Chaps. 4, 7, and 10). For an extensive and recent review of the microorganisms in the rhizosphere, the reader is referred to Bowen and Rovira (23). 

B. Dinkelaker, Rdmheld, V., and H. Mar.schner, Citric acid excretion and precipitation of calcium citrate in the rhizosphere of white lupin (Lupinus aihus L.). Plant. Cell Environ. /2 285 (1989). 

Extraction of rhizosphere soil (22,34,51,52) is an approach that can provide information about long-term accumulation of rhizosphere products (root exudates and microbial metabolites) in the soil. Culture systems, which separate root compartments from adjacent bulk soil compartments by steel or nylon nets (52-54) have been employed to study radial gradients of rhizosphere products in the root environment. The use of different extraction media can account for different adsorption characteristics of rhizosphere products to the soil matrix (22,34). However, even extraction with distilled water for extended periods (>10 min) may... 

By definition, all carbon (except above-ground littering) enters the soil via the rhizosphere, which is a highly dynamic and complex environment both in time and in space. As discussed in the Chaps. 2 and 4, the root excretions as well as root debris consist of a wide array of chemical compounds, most of which can be utilized by soil microorganisms (13). These compounds can be arbitrarily di-... 

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