EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Temporal decoupling between carbon assimilation and tree growth in temperate oaks

Mukund Palat Rao1,2,5, Arturo Pacheco-Solana2, Kevin Griffin2, Johanna Elizabeth Jensen3, Neil Pederson4, Bar Oryan2, Troy Nixon2, Milagros Rocio Rodriguez Caton5, Laia Andreu Hayles1,2, Jeremy Hise6, Josep Peñuelas1, and Troy Magney5
Mukund Palat Rao et al.
  • 1Centro de Investigación Ecológica y Aplicaciones Forestales (CREAF), Barcelona, Spain
  • 2Lamont Doherty Earth Observatory, Columbia University, NY, USA
  • 3Ecology, Evolution, and Environmental Biology, Columbia University, NY, USA
  • 4Harvard Forest, MA, USA
  • 5University of California Davis, CA, USA
  • 6Hise Scientific, NY, USA

The ‘growing season’ of trees is often assumed to be coupled with climatology (e.g., summer vs winter) and visual canopy phenology cues (e.g., leaf emergence in spring and senescence in autumn). However, green leaves are not always photosynthetically active and actual tree radial growth via cambial cell division is ‘invisible’ since it is hard to see and occurs at micrometer resolution. Therefore, despite the presence of apparently green vegetation, trees may not be assimilating carbon or growing. Here, we study photosynthesis and tree-growth at near-instantaneous timescales using in-situ and satellite remote sensing, point dendrometers, quantitative wood anatomy, and Pulse Amplitude Modulated chlorophyll fluorescence. Tree and leaf-level measurements are being made on eight oak (Quercus spp.) trees in a temperate forest in southern New York, USA. We find that oak trees commence radial growth in the first week of April approximately one-month prior to canopy development that is not completed until the first week of May. Additionally, the development of foliar photosynthetic capacity lags leaf expansion by nearly two weeks. Further, we find that oak growth for the season is completed by late July while photosynthetic activity is maintained for three additional months until early November. Finally, we examine the growth climate sensitivity across a network of 16 oak tree-ring width chronologies distributed across the northeastern US. These relationships suggest that oak earlywood growth relies on carbon assimilated in prior year autumn while oak latewood relies on current year assimilated carbon. Therefore, photosynthesis and tree-growth in Northeastern US oaks occurs asynchronously, since trees don’t reach peak photosynthetic performance the moment leaves emerge or grow through the ‘growing season’.

How to cite: Rao, M. P., Pacheco-Solana, A., Griffin, K., Jensen, J. E., Pederson, N., Oryan, B., Nixon, T., Rodriguez Caton, M. R., Andreu Hayles, L., Hise, J., Peñuelas, J., and Magney, T.: Temporal decoupling between carbon assimilation and tree growth in temperate oaks, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8562,, 2023.