Study in Biosphere 2 facility in Arizona reveals how tropical forests will respond to drought

The impacts droughts will have on features like carbon and water fluxes in tropical forests are a little clearer thanks to a study in an enclosed experimental forest ecosystem in Arizona. The results, which show how highly diverse drought responses within and among species determine overall ecosystem fluxes, may help improve predictions of the changes to forest ecosystems under future climate change conditions. Severe droughts, occurring more frequently and with greater severity worldwide, are threatening ecosystem functioning of many of Earth’s forests and potentially limiting their ability to sequester atmospheric carbon. This is particularly concerning for the planet’s large tropical forests, which are a major component of the terrestrial carbon sink; tropical forests also represent an important source of atmospheric biogenic volatile compounds (VOCs), which may play a critical role in global atmospheric chemistry and climate feedbacks. Given the complexity and size of tropical forests, developing an ecosystem-level mechanistic understanding of how droughts impact these regions has been challenging. Using the Biosphere 2 tropical Rainforest enclosed experimental ecosystem, a well-structured and diverse tropical forest ecosystem, Christiane Werner and colleagues evaluated how drought and drought recovery affected carbon, water, and VOC fluxes. Werner et al. imposed a 9.5-week drought on this system and continually monitored water, carbon, and VOC fluxes from all major forest components. They found that the forest ecosystem exhibited highly diverse drought responses within and among plant species and across forest structures. Drought-tol­erant and drought-sensitive tree species dif­fered substantially in how they contributed to carbon and water fluxes over the course of the drought and rewetting periods. The balance between individual strategies of distinct plant groups and their interactions with others modulated carbon and water fluxes, as well as VOC release. “The Werner et al. study exemplifies the potential of highly controlled enclosed facilities to explore the consequences of environmental change and unravel unique insights into the underlying mechanisms,” write Nico Eisenhauer and Alexandra Weigelt in a related Perspective.