Carbon input from plant to soil through root exudation in Digitaria adscendens and Ambrosia artemisiifolia

The amount of carbon released into soil through root exudation by Digitaria adscendens Herrm. and Ambrosia artemisiifolia L. var. elatior Desc., which often predominate at the early stages of secondary succession, was evaluated in a laboratory experiment conducted over a 60-day period. Differences in the amount of exuded carbon between these species and between the developmental stages were examined. The amount of carbon exuded increased with growth in both species. The percentage of exuded carbon to photosynthetically net fixed carbon, which was higher at younger stages (13%) in D. adscendens, decreased to 3.1% with time. On the other hand, no reduction in the amount of carbon exuded was observed in A. artemisiifolia (4.7-8.1% range). The total amount of carbon released through root exudation in D. adscendens and A. artemisiifolia was estimated at 3.1% and 6.9% of photosynthetically net fixed carbon, respectively. These results suggest the possibility that wild plants exude a considerable amount of carbon from their roots to the soil, and emphasizes the necessity for considering root exudation in the carbon cycle.