Response of Semi-natural Wet Meadow to Natural Geogenic CO2 Enrichment

A semi-natural wet meadow, dominated by Carex rostrata, experienced a natural geogenic CO2 enrichment of soil [CO2] and a small layer of air above the surface throughout the year, and occasional flooding in autumn. We expected such conditions to be tolerated by flood tolerant plant species, which might even benefit from CO2 enrichment. We examined the influence of elevated [CO2] and/or flooding on primary production of meadow vegetation and C. rostrata, measured through above-and below-ground biomass, LAI and photochemical efficiency (chlorophyll fluorescence Fv/Fm). Results showed that C. rostrata biomass increased under conditions of enhanced [CO2] and elevated soil water content (SWC). The positive effect of increased [CO2] was hampered by simultaneous increase in SWC. Additionally, patterns of C. rostrata senescence are changed, since dead biomass significantly decreased with the increase in [CO2] levels and the contrary was shown for higher SWC. These results explain why C. rostrata was the dominant species. In summer, Carex responded with enhanced growth on plots with higher SWC, which represented its optimal habitat, while on drier sites it benefited from elevated [CO2] because of improved water use efficiency. During autumn flooding, the positive effect of increased [CO2] on biomass production was hampered by and corresponded with increased root biomass. Carex rostrata, well adapted to waterlogged soil and hypoxia, was able to tolerate O-2 deficiency irrespective of its origin: waterlogging or geogenic CO2. Higher levels of [CO2] in the soil increased the photochemical use of Carex in the afternoon with low-light conditions, even though the changes in photochemical efficiency were best explained by the erectophile canopy. In crux, C. rostrata is the dominant species in this particular semi-natural meadow, can tolerate high levels of geogenic [CO2] in the soil and benefit from elevated [CO2] in the air during drought and low-light. (C) 2013 Friends Science Publishers