The Pacala, Sarmiento, Morel, and Bender groups are using models and laboratory experiments to understand how climate change will impact the terrestrial and marine biospheres.

 

Terrestrial ecosystem response to climate change

In the past year, Anping Chen’s research focused on how terrestrial ecosystems respond to climate change. With remote sensing techniques and modeling, Chen and colleagues have found:

  •  vegetation growth responses to asymmetric daytime and night-time warming cause important variations in carbon uptake currently not captured in most models;
  • the sensitivity of atmospheric CO2 growth rate to variations in tropical temperature has doubled over the last 50 years, but is not reproduced in model simulations; and
  • under the Intergovernmental Panel on Climate Change (IPCC)-projected future climate scenarios, General Circulation Models (GCMs) used in the IPCC’s latest assessment report predict decreases of 1-15% in the extents of tropical forests by 2100.

In addition, the researchers evaluated the potential impact of future climate change on global biodiversity conservation priority areas. The research highlights a heterogeneous but highly sensitive ecosystem and carbon cycle response to climate change.

 

The impact of increasing CO2 levels on photosynthesis and respiration

Because of experimental challenges, the rate of photosynthesis has never been measured directly in plants. Plants, like humans, respire to make energy, but this rate has never been measured in the daytime (in the light). Postdoctoral fellow Paul Gauthier, working with Michael Bender, has built an apparatus for making these measurements (Figure 5). Air is passed through a chamber containing a leaf which water has been “labeled” with the heavy oxygen isotope 18O. The rate of photosynthesis, and respiration in the light, are determined by analyzing the change in the concentration of O2, and its isotopic composition, as air passes through the chamber

Gauthier has conducted preliminary experiments documenting a linear increase of photosynthesis with light, as indicated by theory, and increased rates of respiration as illumination falls. In the coming year, experiments are planned to investigate the influence of atmospheric CO2 concentration on the energetics of plant growth.

 

Compression of marine habitats

The vertical range (thickness) of the habitat that can be used by organisms living in pelagic marine ecosystems is limited by the availability of oxygen. Recently, shallowing of oxygen depleted waters has been observed in many locations throughout the ocean, compressing the vertical habitat structure of marine ecosystems.

Figure 5. A detached leaf inside the apparatus. The rates of photosynthesis and respiration are measured from changes in the composition of air passing through the cuvette. This instrument has been used to make the first measurements of rates of photosynthesis and respiration in leaves at ambient conditions. The researchers are carrying out experiments to understand, among other things, how the rate of metabolic reactions in leaves will change as the CO2 concentration rises.

In an ongoing project, the Sarmiento group is developing new approaches to predict the extent of compression for many different species, as well as evaluating what impact additional environmental stressors such as ocean warming will have on oxygen acquisition in pelagic habitats. In particular, they will identify which physiologies will be most susceptible to changes in oxygen and other environmental stressors, with commercially fished species being of particular concern.

 

Response of high-latitude phytoplankton to global change

Marine phytoplankton are responsible for nearly half of Earth’s primary production but we have little understanding of how they will respond to global change. The most rapid changes are occurring in the highly productive waters of the Antarctic. François Morel and colleagues are using recent data from a six-month deployment at Palmer station in the Western Antarctic Peninsula (Figure 6), complemented with laboratory experiments with model species, to provide new insights into the adaptations responsible for the high productivity of phytoplankton in cold waters (< 0°C). This information will provide a basis for predicting the likely responses of the Antarctic flora to changing environmental parameters, such as increases in temperature and CO2 concentration.

In early December, continuous recording of gas concentrations quantified a massive diatom bloom that drove the ambient CO2 concentration to nearly zero. Physiological and biochemical data showed that the organisms had a very high protein content to compensate for slow enzyme kinetics, and that particularities of their photosynthetic apparatus resulted in very low respiration rates. The net result is a much higher ratio of net/gross production compared to more temperate marine ecosystems. However, as high latitude temperatures warm, an increase in respiration is likely to more than offset the increasing rate of photosynthesis (gross production), lowering the net production in high latitude oceans. If confirmed, this result could have large implications for higher trophic levels, including krill and the large animals that feed on it.

Figure 6. Jodi Young (Princeton) and Elizabeth Asher (UBC) sampling water from a range of depths using niskin bottles on a wire. Near-shore at Palmer Station, Western Antarctic Peninsula, austral summer 2012/13. (photo credit Kim Bernard)