摘要：Photosynthesis, as the basis of most food chains and a crucial global carbon sink, makes chief contributions to overall ecosystem carbon budgets, but specific responses of the plant component cannot be obtained from such budgets. To gain much-needed further information on possible interspecies differences in seasonal patterns of photosynthesis, capacities for light- and CO 2 -saturated rates of oxygen evolution at 25°C (photosynthetic capacity) were determined during the summer-fall-winter transition for five conifer species over their natural distribution along a steep altitudinal gradient. Findings include (i) a transient upregulation of photosynthetic capacity during the summer-to-fall transition in all five conifer species that preceded the previously reported winter downregulation in conifers. However, there were (ii) interspecific differences in this response at the highest altitudes, with higher maximal photosynthetic capacities displayed by pine and spruce species compared to fir species. Lastly, the winter downregulation of photosynthetic capacity was not as complete in the present study (winter of 2006) as that which has been reported for previous winter seasons, which has implications for the winter survival strategy of conifers in response to global warming.
