Spatial and temporal patterns of forest water-use efficiency in Switzerland

Link To Share This Poster: https://cdmcd.co/bYGbLm

Brandon Bernardo, Schmid College of Science and Technology, Chapman University, Orange, CA, Sabine Braun, Institute for Applied Plant Biology, Switzerland and Gregory Goldsmith, Grand Challenges Initiative, Chapman University, Orange, CA

Background/Question/Methods
Plant water-use efficiency (WUE) is defined as carbon gained via photosynthesis per unit water lost through transpiration. Given that WUE captures the coupled patterns in both carbon and water cycling, it has the potential to serve as a compelling measure of plant function in response to both current and future environmental conditions. Historically, our ability to effectively measure WUE over time and space has been limited by the intensive nature of available methods. However, advances in remote sensing instrumentation have created new opportunities to observe WUE. In particular, NASA’s new ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS), provides estimates of water-use efficiency at 70 m resolution every few days. We sought to use these advances in available WUE data to determine 1) how WUE varies across space and time and 2) test for relationships between WUE and environment. We ask these questions in Switzerland, a country where nearly all of its forests are closely managed for timber production; thus, measures of plant function that can inform management now and in the future are a high priority for decision makers. In particular, we studied how WUE varies during the summer growing seasons (2018-2020) among forests that vary in temperature, precipitation, elevation, and soil nitrogen deposition. To do so, we used ground-based observations from 182 sites that are part of a long-term forest monitoring program.
Results/Conclusions
Mean WUE among sites was 2.85 ± 1.50 g C kg-1 H2O and varied on average by 4.82 g C kg-1 H2O within a site over the growing season. Thus, temporal variation in WUE within a site is as high spatial variation across sites. Sites with higher mean annual temperature and lower mean annual precipitation at lower elevations demonstrated significantly higher inter- and intra-site variability in WUE. This corresponds to differences in the WUE of the predominant tree species at different sites, whereby oak (3.68 ± 2.56 g C kg-1 H2O) is restricted to the hottest and driest low elevation sites, beech predominates (2.58 ± 0.75 g C kg-1 H2O) at intermediate sites, and spruce (2.40 ± 0.88 g C kg-1 H2O) primarily occurs at the coldest and wettest high elevation sites. Surprisingly, WUE did not vary with atmospheric nitrogen deposition from anthropogenic pollution. Our results are consistent with observations that changes in climate are likely to exert control over changing WUE in the future.