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Seasonality of temperate forest photosynthesis and daytime respiration

Nature volume 534, pages 680683 (30 June 2016) | Download Citation


Terrestrial ecosystems currently offset one-quarter of anthropogenic carbon dioxide (CO2) emissions because of a slight imbalance between global terrestrial photosynthesis and respiration1. Understanding what controls these two biological fluxes is therefore crucial to predicting climate change2. Yet there is no way of directly measuring the photosynthesis or daytime respiration of a whole ecosystem of interacting organisms; instead, these fluxes are generally inferred from measurements of net ecosystem–atmosphere CO2 exchange (NEE), in a way that is based on assumed ecosystem-scale responses to the environment. The consequent view of temperate deciduous forests (an important CO2 sink) is that, first, ecosystem respiration is greater during the day than at night; and second, ecosystem photosynthetic light-use efficiency peaks after leaf expansion in spring and then declines3, presumably because of leaf ageing or water stress. This view has underlain the development of terrestrial biosphere models used in climate prediction4,5 and of remote sensing indices of global biosphere productivity5,6. Here, we use new isotopic instrumentation7 to determine ecosystem photosynthesis and daytime respiration8 in a temperate deciduous forest over a three-year period. We find that ecosystem respiration is lower during the day than at night—the first robust evidence of the inhibition of leaf respiration by light9,10,11 at the ecosystem scale. Because they do not capture this effect, standard approaches12,13 overestimate ecosystem photosynthesis and daytime respiration in the first half of the growing season at our site, and inaccurately portray ecosystem photosynthetic light-use efficiency. These findings revise our understanding of forest–atmosphere carbon exchange, and provide a basis for investigating how leaf-level physiological dynamics manifest at the canopy scale in other ecosystems.

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This research was supported by the US Department Of Energy (DOE), Office of Science, Terrestrial Ecosystem Science (TES) program (award DE-SC0006741), and the Agnese Nelms Haury Program in Environment and Social Justice at the University of Arizona. Soil chamber data were acquired with the help of K. Savage at the Woods Hole Research Center, under the DOE award. The Harvard Forest Environmental Measurements Site infrastructure is a component of the Harvard Forest Long-Term Ecological Research (LTER) site, supported by the National Science Foundation (NSF), and is additionally supported by the DOE TES program. Below-canopy PAR, soil temperature and soil moisture data were provided by E. Nicoll at the Harvard Forest, supported by the NSF LTER program. OCS data and SIF data were provided by the authors of refs 40 and 41, respectively.

Author information


  1. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USA

    • R. Wehr
    •  & S. R. Saleska
  2. School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA

    • J. W. Munger
    •  & S. C. Wofsy
  3. Aerodyne Research Inc., Billerica, Massachusetts 01821, USA

    • J. B. McManus
    • , D. D. Nelson
    •  & M. S. Zahniser
  4. Appalachian Laboratory, University of Maryland Center for Environmental Science, Frostburg, Maryland 21532, USA

    • E. A. Davidson


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S.R.S. conceived the study. S.R.S. and R.W. designed the study. R.W., J.B.M., D.D.N. and M.S.Z. developed and maintained the spectrometer. R.W. and J.W.M. set up and maintained the instrumentation and conducted the measurements. R.W. analysed the data and wrote the manuscript. R.W. and S.R.S. led the interpretation of the results with input from J.W.M., S.C.W. and E.A.D. All authors contributed to editing the manuscript.

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The authors declare no competing financial interests.

Corresponding authors

Correspondence to R. Wehr or S. R. Saleska.

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