COS 229-5 - Different degrees for different trees: variation in the acclimation of photosynthetic capacity to climate change among seedlings of three boreal trees

Thursday, August 18, 2022

11:00 AM – 11:15 AM EDT

Location: 513E

Presenting Author(s)

JH

Julia Hammer

University of Western Ontario, Canada

Coauthor(s)

AC

Andrew Cook

Graduate Student
University of Western Ontario
London, Ontario, Canada
KL

Kiana Lee, BSc

University of Western Ontario, Canada
SS

Stephanie Schmiege

Michigan State University, University of Western Ontario, Canada
RS

Robyn Swartman

University of Western Ontario, Canada
PR

Peter B. Reich

Professor
University of Minnesota, Minnesota, United States
DW

Danielle A. Way, BSc, PhD

Associate Professor
University of Western Ontario
London, Ontario, Canada

Background/Question/Methods

Boreal forests provide crucial ecological and economic services and are important ecosystems for modelling global carbon dynamics. We expect anthropogenic CO₂ emissions to warm boreal regions by up to 8ºC by 2100, yet we have relatively little data on the physiological responses of boreal trees to these climatic changes. In particular, we do not know the extent to which photosynthetic capacity in boreal trees will acclimate to changes in atmospheric CO₂ and warming. To resolve this, we grew three species of North American boreal tree (paper birch, tamarack, and black spruce) from seed at either ambient (AC, 400 ppm) or elevated CO₂ (EC, 750 ppm), and at either ambient temperatures (T0) or with +4ºC (T4) or +8ºC (T8) warming. After four months, we measured the maximum rate of Rubisco carboxylation (V_cmax) at multiple leaf temperatures.

Results/Conclusions

Each species showed unique responses. In paper birch, the temperature response of V_cmax was unaffected by warming, and only weakly acclimated (i.e. decreased when measured at a common leaf temperature) to elevated CO₂. In tamarack, V_cmax acclimated to warming under current CO₂, but was enhanced by moderate warming (T4) under high CO₂. V_cmax also acclimated to warming under current CO₂ in black spruce, but decreased in T0 plants and increased in T8 plants when grown under high CO2. These results suggest that different boreal tree species have different photosynthetic responses to climate change. This has implications for our models of CO₂ exchange between boreal trees and the atmosphere, and for the composition and productivity of Canada's boreal forests in the future.