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/c(i)) curve. After 11 months of exposure, the grasses displayed a downward acclimation in the decreased initial slope of the A/c(i) response curve and similar A at high CO2 concentrations in plants grown at high CO2 concentartion (HCO2 plants). Transpiration decreased with an increase of c(i) in the grass species, while in the dicot species it was not affected by any change in c(i). 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/c(i) curved did not reach saturation. The dicot species showed upregulation regarding either the Rubisco capacity or P(i)/RuBP regeneration capacity. In the short term, monocot species are more responsive than the dicot ones. Further, acclimation of photosynthesis in P(i)/RuBP regeneration capacity is an earlier response than that of Rubisco activity/amount. In the long term, HCO2 treatment caused alleviation of the P(i) regeneration limitation at high CO2 concentrations, while in LCO2 plants the A/c(i) 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.
|Number of pages||8|
|Publication status||Published - Dec 1 1997|
- C3 plant
- Carbon dioxide enrichment
- Long-term change
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)