EGU2020-13361
https://doi.org/10.5194/egusphere-egu2020-13361
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Live fast-die young: Scaling CO​2 fertilization effects from leaf to ecosystem levels

Laura Marques1, Ensheng Weng2, and Benjamin Stocker1
Laura Marques et al.
  • 1Department for Environmental Systems Science, Institute for Agricultural Sciences, ETH Zürich, Switzerland
  • 2Center for Climate Systems Research, Columbia University, New York City, United States

Global environmental changes are rapidly altering the functioning and structure of terrestrial ecosystems.Particularly, rising CO2 atmospheric concentrations have been reported to increase photosynthesis by increasing carbon assimilation and water-use efficiency. This leaf-level COfertilization effect may lead to an increase in the biomass stock in forest stands. However, previous studies argued that an enhanced tree growth rate is associated with a reduction in the longevity of trees, thus reducing the ability of forest biomass to act as carbon sinks over long timescales. In addition, faster growth may lead to an acceleration of self-thinning whereby tree density in the stand is reduced due to progressive mutual shading as tree crowns expand and a resulting increase in shaded individuals’ mortality. Nevertheless, previous results relied on empirical relationships between tree growth rates and longevity, without considering any positive effects of elevated CO​on individual tree’s carbon balance. Individual-based forest datasets such as tree ring width data and forests inventories have been widely used to monitor long-term changes in forest demography. Yet, the mechanistic underlying these processes remains poorly understood and challenges persist in upscaling from individual measurements to higher level of organization.

Here, we use a vegetation demography model (LM3-PPA) which simulates vegetation dynamics and biogeochemical processes by explicitly scaling from leaf up to ecosystem level by resolving leaf-level physiology, growth, and height-structured competition for light, using the perfect plasticity approximation (PPA). Using this simulation model, we investigate the links between individual trees’ carbon balance under rising COlevels, their longevity under alternative mortality parametrizations, and the implications for forest dynamics and self-thinning rates. Inventory data from long-term forest reserves is used to assess empirical support for these simulated links. Specifically, we test the hypothesis of faster growth-earlier death in order to assess forests’ capacity to store carbon under environmental changes. This provides key mechanistic insights to reveal whether increased COfertilization on leaf-level photosynthesis positively affects tree’s C balance and thereby reduces the mortality under competition for light in the canopy.

 

How to cite: Marques, L., Weng, E., and Stocker, B.: Live fast-die young: Scaling CO​2 fertilization effects from leaf to ecosystem levels, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13361, https://doi.org/10.5194/egusphere-egu2020-13361, 2020

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Display material version 1 – uploaded on 05 May 2020
  • AC1: Response to comments in chat, Laura Marques, 05 May 2020

    In response to:

    Jennifer Holm (16:55) @ Laura - very nice to see your study. I work with the FATES demographic model, with also uses PPA. We have the same "live-fast, die-young" aka RockStars. Have you looked into respiration of plants in the understory, and also how much of a distinction do you get between canopy and understory trees, or multiple canopy layers? Maybe respiration needs to be throttled back to represent those slow growing trees that bide their time in the understory waiting for gaps. Also is C starvation the main mode of mortality in LM3, are the other modes of mortality?

    Laura Marques: @Jennifer, thank you very much for your comment! We are in the process to analyse differences between the understory vs. the canopy. Mortality in LM3-PPA is formulated as a function of DBH (high mortality rate for large trees), and carbon starvation if NSC pool falls to zero is also included. We want to include other mortality formulations, such as mortality as a function of basal area of larger trees or as a funtion of growth rate.