Effects of elevated CO2 on below-ground processes in temperate marsh microcosms

Effects of elevated CO2 on upland vegetation have been widely studied, but limited information is available on the response of wetland vegetation. A laboratory-based experiment was conducted to determine effects of elevated atmospheric CO2 on the growth, root-derived DOC and phenolics, and extracellular enzyme activity for 110 days using Miscanthus sacchariflorus, Phragmites japonica, Phragmites communis, Zizania latifolia, Scirpus lacustris, Juncus effuses, and Typha latifolia. Elevated CO2 did not enhance the growth of any vegetation we assessed, but root-derived DOC and phenolics increased in the soil with M. sacchariflorus (phenolics, 45.0%, P < 0.05), P. communis (DOC, 25.5%, P < 0.1; phenolics, 52.6%, P < 0.1), Z. latifolia (DOC, 46.2%, P = 0.05; phenolics, 76.9%, P < 0.05), and S. lacustris (DOC, 142.0%, P = 0.001; phenolics, 42.9%, P < 0.05). Only a small number of enzymes exhibited changes under elevated CO2, and even such changes differed with the type of vegetation and enzymes. When all the data were combined, several enzyme activities were positively correlated with DOC in soils (phosphatase, r = 0.41, P < 0.05; arylsulphatase, r = 0.38, P < 0.05), but negatively with phenolics (beta-glucosidase, r = -0.30, P < 0.1) and the ratio of phenolics to DOC (arylsulphatase, r = -0.43, P < 0.05). Overall results of the present study suggest that elevated CO2 would not change vegetation growth but influence DOC and phenolics in soil.