Effect of root mucilage and modelled root exudates on soil structure

Plant roots release in the rhizosphere diverse organic materials which may have different effects on soil structure. We have evaluated the effect of n atural and modelled root-released materials on soil aggregates and the biod egradation of carbon from roots in the soil. The effects of root mucilage f rom maize and of a modelled soluble exudate were compared with those of sim ple compounds (glucose, polygalacturonic acid). For all treatments, soil wa s amended with 2 g C kg(-1) soil and incubated for 30 days at 25 degreesC. The biodegradation of mucilage was similar to that of polygalacturonic acid , and slower than the decomposition of modelled exudates and glucose. Addit ion of all substrates increased the stability of aggregates, but the durati on of this effect depended on the chemical nature of the material. Compared with the control, the proportion of stable aggregates after 30 days of inc ubation was multiplied by 3.8 for root mucilage, by 4.2 for modelled solubl e exudates, by 2.5 for polygalacturonic acid and by 2.0 for glucose. The di fferent fractions of root exudates in the rhizosphere evidently affected th e aggregate stability.