Some controls on the release of dissolved organic carbon by plant tissues and soils

Soil and plant tissues were used to examine the effect on the release of di ssolved organic carbon (DOC) of rinsing over time at two temperatures and u nder oxic and anoxic conditions in a laboratory incubation. The release of DOC over 60 days of incubation ranged from 0.5 to 189 mg DOC g(-1) oven-dry material and was correlated inversely with the degree of decomposition of the material: fresh maple leaves > old maple leaves > Sphagnum moss > fibri c peat > hemic peat sapric peat > Inceptisol A horizon. Rates of DOC releas e were similar through the duration of the experiment, except for the fresh maple leaves, where release rates fell after 3 day. Rinsing, by the replac ement of water in the incubating samples after 20 day, produced slower rate s of DOC release, except in the Inceptisol A and sapric peat samples. There was no significant difference between DOC release under oxic and anoxic co nditions, except for the Inceptisol A soil, where DOC release was greater u nder anoxic than under oxic conditions. The rate of DOC release at 22 degre esC was an average of 2.4 times greater than at 4 degreesC, translating int o Q(10) values of about 1.6. At 22 degreesC under oxic conditions, DOC prod uction accounted for 14 to 58% (average 24%) of the total C released as DOC + CO2, with the highest proportion in the maple leaves. Under anoxic condi tions, DOC production accounted for 63 to 95% (average 82%) of the total C released as DOC + CO2 + CH4. Production of CH4 under anoxic conditions was minor, accounting for <1% of the total C released. Under oxic conditions at 22 <degrees>C, the incubations released between 2 and 107% of the organic C contained in the samples, the largest proportion of which was released fr om the plant tissues. Microbial utilization of DOC meant that some C was do uble-counted, both as DOC and as subsequently emitted CO2 Under anoxic cond itions, 0.0 to 49% of the sample organic C was mineralized. The release of DOC represents the balance between production, adsorption, and desorption a nd microbial utilization. This release differs clearly among samples and am ong treatment effects.