No acclimation: flexible responses of photosynthesis to different temperatures in American elm

Will photosynthetic processes of trees be able to keep up with future changes in temperature and precipitation under climate change?

Terrestrial plant photosynthesis and plant respiration represents the two largest fluxes of carbon between the atmosphere and the Earth’s surface. As such, any future changes in these processes will alter the rate and magnitude of climate change. Each of these processes is sensitive to changes in temperature. As temperatures rise, it is important that we understand this temperature sensitivity to accurately determine the rate and magnitude of the change in the future land carbon sink. Over short time periods (e.g. seconds to minutes), increasing leaf temperatures stimulate the enzymatic processes that underlie photosynthesis and respiration, which results in exponential increases in these process rates at low temperatures. At increasingly higher temperatures, this rate of increase slows and eventually peaks at an optimum temperature. Longer term responses (e.g. days to weeks), on the other hand, are less well understood due to temperature acclimation responses.

Measurement of photosynthetic properties of American elm using gas exchange at the Boston-Area Climate Experiment (BACE). Image credit: Smith et al.

In their new paper published in AoBP, Smith et al. measured photosynthetic acclimation to expected changes in temperature and precipitation in American elm (Ulmus americana). They monitored the rates of biochemical, stomatal and respiratory processes across different preset leaf temperatures throughout a growing season under two levels of canopy warming. They found that the flexibility of the photosynthetic systems of elm trees allowed them to maintain relatively stable rates of photosynthesis under altered climate conditions, without any acclimation. This stability resulted from decreases in rates of stomatal conductance and increasing respiration with temperature being balanced by an increased capacity for CO2 fixation. These results indicate that some plants may be able to withstand negative impacts of climate change without acclimation, and the costs associated with acclimation. The authors hope that further studies across larger spatial and temporal scales, and in other plant species will help us to understand whether their findings could apply to plant systems more generally.

Researcher highlight

Nick Smith grew up in Indiana, USA, where he developed an interest in environmental studies and Ecology in particular. He decided to use these interests to help society better prepare for and combat global change. He pursued a PhD in plant-climate interactions with Jeff Dukes at Purdue University. This work was extended to larger scales during a postdoc at Lawrence Berkeley National Lab with Trevor Keenan.

Nick now teaches and runs his own lab at Texas Tech University, where he is dedicated to mentoring the next generation of scientists. His group explores biosphere-atmosphere feedbacks, broadly defined. Recently, Nick has become interested in developing plant ecophysiological theory as a means to explore mechanisms ecological processes at the community and ecosystem scales. He will use his work to provide more reliable projections of future global change, leading to more informed policy decisions.