THE CONTRIBUTION OF PLANT-ROOTS TO CO2 FLUXES FROM ORGANIC SOILS

The CO2 released in soil respiration is formed from organic matter whi ch differs in age and stability, ranging from soluble root exudates to more persistent plant remains. The contribution of roots, a relativel y fast component of soil cycling, was studied in three experiments. (1 ) Willows were grown in a greenhouse and CO2 fluxes from the substrate soil (milled peat) and from control peat were measured. (2) CO2 fluxe s from various peatland sites were measured at control points and poin ts where the roots were severed from the plants. (3) CO2 fluxes in cul tivated grassland established on peatland were measured in grassy subs ites and in subsites where the growth of grass was prevented by regula r tilling. The root-derived respiration followed the typical annual ph enology of the vegetation, being at its maximum in the middle and late summer. All the experiments gave similar results, root-derived respir ation accounting for 35-45% of total soil respiration in the middle an d late summer at sites with an abundant vegetation. The root-derived r espiration from the virgin peatland sites correlated well with the tre e biomass, and also partly with the understorey vegetation, but in the drained sites the root effect was greater, even in the presence of le ss understorey vegetation than at virgin subsites.