Effect of salinity and plant species on CO2 flux and leaching of dissolved organic carbon during decomposition of plant residue

Mitigation of increased concentrations of CO2 in the atmosphere by plants may be more efficient in saline systems with soils lower in organic matter than in other freshwater systems. In saline systems, decomposition rates may be lower and potential soil carbon storage higher than in fresh water systems. The effects of salinity, plant species and time on CO2 surface flux and dissolved organic carbon (DOG) leached during irrigation were determined in the laboratory in microcosms containing sand amended with residues of two halophytes, Atriplex nummularia and Salicornia bigelovii, and one glycophyte, Triticum aestivum. Surface flux of CO2 and DOC leached during decomposition were monitored for 133 days at 24 degrees C in microcosms containing different plant residue (5% w/w). Microcosms were irrigated every 14 days with distilled water or seawater adjusted to 10, 20, or 40 g L(-1) salts. CO2 flux and DOC leached were significantly higher from microcosms amended with A. nummularia residue compared to S. bigelovii or T. aestivum at all salinities and decreased significantly over time for all plant species. Irrigating with water of high salinity, 40 g L(-1), compared to distilled water resulted in a decrease in CO2 surface Aux and DOC in leachate, but differences were not significant at all sampling dates. Results indicate that plant residue composition, as well as increased salinity, affect CO2 surface flux and DOC in leachate during plant residue decomposition and may be an important consideration for C storage in saline systems.