August 05, 2024

Boreal Tree Photosynthesis Acclimates to Climate Change Treatments

Spruce and tamarack trees increased photosynthetic capacity when exposed to soil and air warming in a boreal peatland.

A group of people stand behind scientific instruments on tripods.

Part of the team and their equipment during the intensive gas exchange campaigns. The team included undergraduate interns, graduate students, post-docs, technicians, scientists, and modelers representing multiple institutions and countries.

[Image courtesy Jeff Warren]

The Science

Boreal forests represent a key component within the global carbon cycle as, through photosynthesis, they absorb a significant amount of carbon from the atmosphere annually. Accurate representation of boreal forest photosynthesis within terrestrial biosphere models (TBMs) is, therefore, important to reliably predict both current and future global carbon cycling and associated climatic conditions. This study investigated the impact of increased growth temperature and elevated carbon dioxide (CO₂) on photosynthetic capacity in mature trees of two North American boreal conifers, tamarack and black spruce.

The Impact

The boreal region has already warmed more than twice than the global average, and predictions suggest that some regions could potentially warm by 6°C by 2100 compared to a global mean of about 4°C. Understanding changes in leaf characteristics, photosynthetic capacity, and efficiency with ecosystem warming is critical for correctly representing boreal plant carbon uptake in vegetation models that simulate impacts of future climate change.

Summary

There are two primary leaf parameters that represent the underlying biochemical processes of photosynthesis, the maximum rate of Rubisco carboxylation (V_cmax) and the maximum rate of electron transport (J_max). The V_cmaxand J_maxare key parameters in many TBMs that simulate current and future carbon uptake and sequestration. However, many TBMs do not currently incorporate long-term acclimation responses of both V_cmax and J_max to climate change variables such as warming and elevated CO₂, largely due to the lack of data, particularly for the boreal region. This knowledge gap limits models’ ability to reliably forecast the feedback between boreal forest carbon cycling and future climate.

This study investigated the acclimation of photosynthetic capacity (V_cmax and J_max) to warming and elevated CO₂ after 2 years of a whole-ecosystem experimental warming (up to +9°C above ambient temperature) combined with 1 year of elevated CO₂ (+430 to 500 parts per million above ambient atmospheric CO₂) in mature trees of North America’s boreal conifers (i.e., black spruce and tamarack) at their southern range of natural distribution. The photosynthetic capacity of mature trees of North American boreal conifers responded independently to warming and elevated CO₂ when exposed to both environmental factors. Data will be applied to improve representation of boreal tree photosynthesis in TBMs such as the DOE’s Energy Exascale Earth System Land Model.

Principal Investigator

Jeff Warren
Oak Ridge National Laboratory
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

Research was sponsored by the Biological and Environmental Research program in the U.S. Department of Energy’s (DOE) Office of Science and performed at Oak Ridge National Laboratory, which is managed by UT- Battelle, LLC, for DOE under contract DEAC05-00OR22725. Support was also received from the U.S. Geological Survey Climate Research and Development Program and the U.S. National Science Foundation Biological Integration Institutes grant DBI-2021898. Funding was also received from the Natural Sciences and Engineering Research Council of Canada Discovery and Strategic programs (RGPIN/04677-2019 and STPGP/521445-2018), the Research School of Biology at Australian National University, and DOE’s contract No. DE-SC0012704 to Brookhaven National Laboratory.

References

Dusenge, M. E., et al. "Photosynthetic Capacity in Middle‐Aged Larch and Spruce Acclimates Independently to Experimental Warming and Elevated CO₂." Plant, Cell & Environment Early View (2024). https://doi.org/10.1111/pce.15068.