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Acclimation of dicot and monocot temperate grassland species to long-term elevated CO₂ concentration
Z. Nagy, K. Szent and Z. Tuba
Vol. 21, No. 2, Special issue: Grassland ecology and ecophysiology under elevated atmospheric CO₂ and temperature (1997), pp. 297-304
Published by: Akadémiai Kiadó
Stable URL: http://www.jstor.org/stable/43519245
Page Count: 8
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Net CO₂ assimilation (A), transpiration (E) and water use efficiency (WUE) were compared in two C₃ grasses and two C₃ dicot herbs of a xeric temperate loess steppe after exposure in open top chambers for 1, 2, 11 and 36 months to present (350 µmol mol⁻¹, LCO₂) and elevated (700 µmol mol⁻¹, HCO₂) levels of CO₂. Acclimation of A to elevated CO₂ varied both between species and over the course of the period of exposure. In the first month of exposure photosynthesis of Festuca rupicola grown at elevated CO₂ concentration showed a significant upward regulation. Salvia nemorosa did not show acclimation of photosynthesis after the first month of exposure. After the 2nd month of exposure, F. rupicola maintained its upward acclimation. S. nemorosa also showed upward acclimation of net photosynthesis both in the initial slope and the plateau of the CO₂ assimilation vs intercellular CO₂ concentration (A/ci) curve. After 11 months of exposure, the grasses displayed a downward acclimation in the decreased initial slope of the A/ci response curve and similar A at high CO₂ concentrations in plants grown at high CO₂ concentartion (HCO₂ plants). Transpiration decreased with an increase of Ci in the grass species, while in the dicot species it was not affected by any change in Ci. Long term exposure to high CO₂ causes a similar acclimation of stomatal regulation and transpiration to that of photosynthesis. Instantaneous WUE significantly increased in all species grown at elevated CO₂. After 36 months of exposure the monocot species showed a downward acclimation in Rubisco capacity and its A/ci curve did not reach saturation. The dicot species showed upregulation regarding either the Rubisco capacity or Pi/RuBP regeneration capacity. In the short term, monocot species are more responsive than the dicot ones. Further, acclimation of photosynthesis in Pi/RuBP regeneration capacity is an earlier response than that of Rubisco activity/amount. In the long term, HCO₂ treatment caused alleviation of the Pi regeneration limitation at high CO₂ concentrations, while in LCO₂ plants the A/ci curve showed saturation in all of the species. Species responded at different time scales and in different ways to exposure to HCO₂ treatments. The grass species responded earlier and maintained their response characteristics after the first month of exposure, while the dicot species responded later and their response characteristics changed with the advance of exposure to HCO₂ treatment. These differences can partly be attributed to probable sink limitation in the monocot species, which was apparently absent or smaller in the dicots.
Abstracta Botanica © 1997 Akadémiai Kiadó