Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 109, Issue 22, Pages 8612-8617Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1119131109
Keywords
day length; gross primary productivity; carbon sequestration; leaf area index; evapotranspiration
Categories
Funding
- US Department of Agriculture [2009-51181-05768, 58-6618-2-0209, 2011-67003-30222]
- Horticulture Research Institute
- Tree Research & Education Endowment Fund
- South Carolina Association
- Virginia Nursery and Landscape Association
- Colorado Experiment Station
- South Carolina Experiment Station
- US Department of Energy, Office of Science, Biological and Environmental Research
- Natural Sciences and Engineering Research Council of Canada
- Department of Energy [DE-AC05-00OR22725]
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Although temperature is an important driver of seasonal changes in photosynthetic physiology, photoperiod also regulates leaf activity. Climate change will extend growing seasons if temperature cues predominate, but photoperiod-controlled species will show limited responsiveness to warming. We show that photoperiod explains more seasonal variation in photosynthetic activity across 23 tree species than temperature. Although leaves remain green, photosynthetic capacity peaks just after summer solstice and declines with decreasing photoperiod, before air temperatures peak. In support of these findings, saplings grown at constant temperature but exposed to an extended photoperiod maintained high photosynthetic capacity, but photosynthetic activity declined in saplings experiencing a naturally shortening photoperiod; leaves remained equally green in both treatments. Incorporating a photoperiodic correction of photosynthetic physiology into a global-scale terrestrial carbon-cycle model significantly improves predictions of seasonal atmospheric CO2 cycling, demonstrating the benefit of such a function in coupled climate system models. Accounting for photo-period-induced seasonality in photosynthetic parameters reduces modeled global gross primary production 2.5% (similar to 4 PgC y(-1)), resulting in a >3% (similar to 2 PgC y(-1)) decrease of net primary production. Such a correction is also needed in models estimating current carbon uptake based on remotely sensed greenness. Photoperiod-associated declines in photosynthetic capacity could limit autumn carbon gain in forests, even if warming delays leaf senescence.
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