Carbon Turnover in the Rhizosphere

Abstract

Considerable progress has been made during the last decade towards understanding and quantifying the input and turnover of plant carbon in the rhizosphere. This was made possible by the development (partially by the authors) and combination of appropriate new methods, such as: –homogeneous labelling of whole plants with 14C –distinction between root and microbial respiration –separation of soil zones of known distances from the roots –determination of microbial soil biomass. These methods were applied to study the following aspects: –release of organic plant carbon into the soil by growing roots –utilization of this plant carbon by the microbial biomass in the rhizosphere –related influence on the turnover of soil organic matter, and –spatial range of such root influence in the soil. About 19% of the total photosynthetic production of the investigated plants was released into the rhizosphere as organic material. Most of this (15%) was transformed by the rhizosphere microorganisms into CO2, while only a small fraction (4%) remained in the soil, mainly as microbial cells (2.5%). As a result, microbial rhizosphere biomass increased considerably. Relative to the organic C‐input, however, the incorporation of root derived carbon by the microbial biomass was remarkably low (13%). Along with the increase in microbial rhizosphere biomass, the presence of plant roots also enhanced the decomposition of soil organic matter and affected soil aggregate stability. Root carbon and root influences were even detected up to 20 mm away from the roots. This may be partially attributed to the contribution of root derived volatiles. Accordingly, both the actual volume of the rhizosphere and its metabolic significance is greater than what has so far been assumed. Possible interactions involving root, soil and microbial carbon are discussed.

Production of Oxalic Acid as Influenced by the Application of Organic Residue and Its Effect on Phosphorus Uptake by Wheat (Triticum aestivum L.) in an Inceptisol of North India

“…Increased secretion of oxalic acid with increase in crop growth interval has also been reported earlier [14]. It is largely accepted that up to 20-30 % of total carbon assimilated by higher plants is released in the rhizosphere as diverse exudates including CO 2 respired [15]. Varieties also had a significant effect on secretion of oxalic acid in soil.…”

Effect of nitrogen fertilisation on below‐ground carbon allocation in lettuce

“…Pulse 5,6 or continuous labelling of above-ground plant parts has frequently been used to distinguish between humus-derived and root-derived CO 2 and to quantify rhizodeposition. [7][8][9] Pulse labelling, compared with continuous labelling, has the advantage of being easier to handle, provides more information on the recent photosynthate distribution at specific developmental stages of plants, and can be used for kinetic investigations of 14 CO 2 evolution from the soil. The results obtained by pulse labelling correspond to the relative distribution of assimilated C at the moment of labelling.…”

Influence of an Elevated Atmospheric CO 2 Content on Soil and Rhizosphere Bacterial Communities Beneath Lolium perenne and Trifolium repens under Field Conditions

“…Under normal conditions, 12 to 54% of the carbon fixed by photosynthesis is released into the soil by the roots [26,27,36,46]. Lekkerkerk et al [32] showed that the root-derived, easily biodegradable compounds of wheat roots increased under a CO 2 -enriched atmosphere.…”