CONTROL ID: 1466435
TITLE: Seasonal patterns of photosynthetic capacity: photoperiodic control and its carbon cycling implications
AUTHORS (FIRST NAME, LAST NAME): William Bauerle1, Ram Oren2, Danielle Way3, 2, Song Qian5, 2, Paul C Stoy4, Peter E Thornton6, Joseph Bowden1, Forrest M Hoffman6, Robert Reynolds7
INSTITUTIONS (ALL): 1. Horticulture, Colorado State University, Fort Collins, CO, United States.
2. Duke University, Durham, NC, United States.
3. University of Western Ontario, London, ON, Canada.
4. Montana State University, Bozeman, MT, United States.
5. The University of Toledo, Toledo, OH, United States.
6. Oak Ridge National Laboratory, Oak Ridge, TN, United States.
7. Clemson University, Clemson, SC, United States.
ABSTRACT BODY: While 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, while 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 photoperiod-induced seasonality in photosynthetic parameters reduces modeled global gross primary production ~4 PgC y-1, resulting in a ~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. Assessments of late season carbon sequestration under a changing climate should focus on potential adverse impacts of warming via increased ecosystem respiration.
KEYWORDS:  BIOGEOSCIENCES / Carbon cycling,  BIOGEOSCIENCES / Modeling.
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Previously Presented Material: A portion of the material was presented as a late breaking poster at the Ecological Society of America annual meeting in August, 2012.
The material is based on the very recent publication
Bauerle, W.L., R. Oren, D.A. Way, S.S. Qian, P.C. Stoy, P.E. Thornton, J.D. Bowden, F.M. Hoffman, and R.F. Reynolds. 2012. Photoperiodic regulation of the seasonal pattern of photosynthetic capacity and the implications for carbon cycling. Proceedings of the National Academy of Sciences of the United States of America, 109:8612-8617.
CONTACT (NAME ONLY): William Bauerle
CONTACT (E-MAIL ONLY): bauerle at colostate dot edu
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