Abstract
Changes in gross canopy photosynthetic rate (PGc), produced by long-term exposure to an elevated atmospheric CO2 level (626±50 µmol mol-1), were modelled forLolium perenne L. cv. Vigor andTrifolium repens L. cv. Blanca, using a simple photosynthesis model, based on biochemical and physiological information (leaf gross CO2 uptake in saturating light, Pmax, and leaf quantum efficiency, α) and structural vegetation parameters (leaf area index, LAI, canopy extinction coefficient, k, leaf transmission, M). Correction of PGc for leaf respiration allowed comparison with previously measured canopy net CO2 exchange rates, with the average divergence from model prediction amounting to about 6%. Sensitivity analysis showed that for a three-week old canopy, the PGc increase in high CO2 could be attributed largely to changes in Pmax and α, while differences in canopy architecture were no longer important for the PGc-stimulation (which they were in the early growth stages). As a consequence of this increasing LAI with canopy age, the gain of daytime CO2 uptake is progressively eroded by the increasing burden of canopy respiration in high-CO2 grownLolium perenne. Modelling canopy photosynthesis in different regrowth stages after cutting (one week, two weeks,...), revealed that the difference in a 24-h CO2 balance between the ambient and the high CO2 treatment is reduced with regrowth time and completely disappears after 6 weeks.
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Abbreviations
- C350:
-
ambient CO2 treatment
- C625:
-
high CO2 treatment
- k :
-
canopy extinction coefficient
- LAI:
-
leaf area index
- LAImax :
-
fitted LAI-maximum
- M:
-
leaf transmission
- NCER:
-
net CO2 exchange rate
- PGc:
-
gross canopy photosynthetic rate
- Q:
-
photosynthetic photon flux density
- Q0 :
-
photosynthetic photon flux density at the top of the canopy
- RDc:
-
canopy dark respiration rate
- RDl:
-
leaf dark respiration rate
- t :
-
regrowth time after cutting
- T :
-
air temperature
- α:
-
leaf quantum efficiency
- αLAI :
-
rate of initial LAI-increase with time
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Nijs, I., Impens, I. Effects of long-term elevated atmospheric carbon dioxide onLolium perenne andTrifolium repens, using a simple photosynthesis model. Vegetatio 104, 421–431 (1993). https://doi.org/10.1007/BF00048171
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DOI: https://doi.org/10.1007/BF00048171