| Popis: |
Boreal regions are undergoing rapid climate change but our understanding of the long-term consequences for forest processes is hampered by limited knowledge of how trees acclimate to rising atmospheric CO2 concentrations and temperature. This study used the detailed canopy flux model MAESTRA to simulate the effects of elevated CO2 (eCO2) and warming on net photosynthesis (An) and transpiration (E) of mature boreal Norway spruce, investigating how these effects are influenced by the observed acclimation of photosynthetic capacity, respiration, stomatal behavior, and phenology. Without any type of acclimation, eCO2 increased shoot and crown An during the non-frost growing season by 23-44%, while warming only had a minor effect (±2%). Photosynthetic downregulation greatly decreased the positive effect under eCO2. Under warming, both stomatal and phenological acclimation had substantial effects on An but in opposite directions. Transpiration at shoot and crown level was greatly decreased (23-50%) by eCO2 and increased by warming (27-42%) in the absence of acclimation. However, both these effects were largely cancelled by stomatal acclimation. Effects of eCO2 on An were generally smaller at entire crown compared to shoot level, as a result of photosynthetic stimulation being smaller in shaded canopy positions. In addition, upregulation of respiration in eCO2 had a considerably larger negative effect on An at crown compared to shoot level. Overall, tree physiological acclimation generally acted to dampen non-acclimated responses. We conclude that photosynthetic and respiratory acclimation greatly reduce the positive effect of eCO2 on tree CO2 assimilation, while stomatal and phenological acclimation are crucial for annual water consumption under warming. These results highlight the critical need to account for acclimation in models. |
