Ecophysiological responses of tropical woody species to ambient and elevated temperatures

Abstract

Tropical forests exchange more carbon dioxide with the atmosphere than any other terrestrial biome on Earth. Yet, uncertainty in the projected global carbon balance over the next century is ~3 times greater for the tropics than for any other latitude. Our poor knowledge of tropical plant physiological responses to climate change – particularly photosynthetic responses – has been identified as one of the greatest sources of uncertainty in multiple efforts to estimate and forecast the global terrestrial carbon sink. Furthermore, tropical regions are expected to experience temperatures beyond their historical climate ranges within the next two decades, and evidence suggests that tropical forest canopies are already operating beyond thermal thresholds for photosynthesis. We used a meta-analytic approach to help reduce the gap in our understanding of tropical tree photosynthetic temperature sensitivity. We gathered 16 published and unpublished photosynthetic temperature response datasets from tropical biomes spanning different temperature, rainfall, and elevation gradients, representing 60 (net photosynthesis) and 33 (biochemical rates of photosynthesis) species. We investigated how photosynthetic parameters, including both net photosynthetic (Anet) and biochemical components of photosynthesis, maximum electron transport (Jmax) and maximum Rubisco carboxylation (Vcmax), responded to a suite of environmental drivers, including mean yearly temperature, yearly temperature range, and precipitation. Optimum temperatures for Anet increased with mean annual temperature (MAT), and the intercept and slope of this response was similar to global trends. Optimum temperature of Vcmax and Jmax also 17 increased with MAT; however, slopes and intercepts were lower than trends found globally. This suggests that separate algorithms should be used when including Jmax and Vcmax in tropical vegetation responses to temperature in global carbon models. Light played an important role in predicting Anet responses to temperature; however, we need more studies that include information on plant growth environment and strategy to more accurately model tropical photosynthetic responses to climate. In addition, we found that Jmax might play a more prominent role in limiting Anet than Vcmax in tropical forests, a trend that is divergent to global findings. This research will improve modeling efforts to quantify tropical ecosystem carbon cycling and provide more accurate representations of how these key ecosystems will respond to altered temperature and rainfall patterns under climate warming.

Citation

Carter, Kelsey R. 2019. Ecophysiological responses of tropical woody species to ambient and elevated temperatures. Doctoral dissertation. Michigan: Michigan Technological University, School of Forest Resources and Environmental Science. 248 pp.