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 (β-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.