Response of Eriophorum vaginatum to CO2 enrichment at different soil temperatures: Effects on growth, root respiration and PO43-
In a phytotron experiment, we examined responses of a tussock sedge, Eriophorum vaginatum L., to changes in atmospheric CO2 concentration and soil temperature. We were particularly interested in phosphorus (P) acquisition and below ground plant characteristics that regulated its uptake in response to CO2 enrichment. Plants were grown at two CO2 partial pressures, 35 and 70 Pa, three soil temperature regimes, 5, 15 and 25 °C and a constant ambient air temperature of 15 °C. Elevated CO2 increased total plant biomass production, but decreased tissue P concentration. Although high CO2 enhanced root carbohydrate concentration, it inhibited root respiration with no significant effect on root PO43- absorption capacity or root: shoot ratio. Surprisingly, there were no significant interactions between CO2 and soil temperature. The inability of Eriophorum to exhibit root-level compensatory adjustments, e.g. increased root:shoot ratio or PO43- absorption capacity, was largely responsible for the observed decline in tissue P concentration under elevated CO2 conditions. This could ultimately limit long-term growth responses of Eriophorum to CO2 enrichment in the field where P availability is limiting. We found that uptake of PO43- in response to elevated CO2 was independent of changes in root respiration, but changes in root respiration could have important implications for ecosystem carbon budget under elevated CO2 levels. Our data indicated that although root respiration on a per unit biomass basis declined in response to CO2 enrichment, this effect was counterbalanced by increased root biomass, so that high CO2 stimulated root respiration on a whole-plant basis by 30%. This might help to explain why long-term exposure to high CO2 increases CO2 efflux from Eriophorum-dominated ecosystems.
Bassirirad, H; Tissue, DT; Reynolds, JF; Chapin, FS
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