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Harvard Forest Symposium Abstract 2017

  • Title: Improving the understanding of the effect of carbon substrate availability on wood formation
  • Primary Author: Tim Rademacher (Harvard University)
  • Additional Authors: David Basler (Harvard University); Mariah Carbone (NCEAS); Andrew Richardson (Northern Arizona University)
  • Abstract:

    Wood constitutes the largest reservoir of carbon in terrestrial vegetation with wood growth being a major sink of atmospheric carbon every year (Pan et al., 2011). While wood formation requires carbon as a substrate, there is increasing evidence that wood formation is not simply driven by photosynthesis or trivially related to photosynthetic activity or local carbon substrate availability (Körner, 2003; Palacios et al., 2014). Hence, changes in the environmental matrix (e.g. atmospheric CO2) might affect photosynthesis and wood growth differently. Therefore, it is crucial to understand the exact dependency of wood growth on carbon substrate availability and potential feedbacks. To advance our understanding of the controls of wood growth we propose a combined observational, experimental and modelling study on three species with varying physiological and phenological characteristics (e.g. Pinus strobus, Quercus rubra and Acer rubrum) in Harvard Forest over three growing seasons starting in 2017. Wood formation (xylogenesis) will be observed at a cellular scale via repeated microcoring, while carbon supply will be inferred from monthly non-structural carbohydrate (NSC) concentrations in foliage, branches, stemwood and roots. The experimental component involves restricting the phloem transport using a cooling collar to manipulate the supply of carbon to different regions along the stem. Using the observational and experimental data we will constrain a model to scale our findings to the stand level and beyond. In this study we will test the hypotheses that (i) carbon sequestration over each growing season is limited by concurrent photosynthetic activity, (ii) the extent to which growth is controlled by carbon sources or sinks is closely related to the relative proportions of early and latewood, (iii) downregulation of photosynthesis occurs as a result of the built-up of phloem carbon, and (iv) observed variance in carbon sequestration across years, species and treatments can be captured sufficiently well by our model of xylogenesis. Thus, the aim of our study is to improve our understanding of wood growth and compare projections of our model of xylogenesis to the pervasive current paradigm of photosynthesis-driven plant growth in terrestrial vegetation models (TVM). Given the strong fertilization effect of projected increases in atmospheric CO2 on photosynthesis by current TVM, our model has the potential to produce radically different projections of the global carbon cycle.

  • Research Category: Physiological Ecology, Population Dynamics, and Species Interactions, Forest-Atmosphere Exchange

  • Figures:
  • Project_Chill_abstract_Harvard_Forest_Research_Symposium.pdf