Project Funding: 2014 - 2017

NRA: 2013 NASA: Carbon Cycle Science   

Funded by USGS, USDA FS, DOE

Abstract:
Integrated research approaches offer the best hope for improving our understanding of how ecosystem responses may have unintended feedbacks to climate. In turn, improving this understanding can greatly increase the confidence with which we can project future climate change. The project entitled ‘Effects of warming on tropical forest carbon cycling: investigating temperature regulation of key tropical tree and soil processes’ addresses this challenge by focusing on how increasing temperatures affect the way tropical rain forests cycle carbon. Tropical forests exchange more carbon with the atmosphere than any other biome. Due to these large fluxes, even subtle changes to the way tropical forests take in and release carbon dioxide (via photosynthesis and respiration, respectively) could have dramatic effects on atmospheric carbon dioxide concentrations and thus future climate. However, while these ecosystems are clearly important, our understanding of how tropical forest carbon cycling will respond to climatic change is notably poor, and this lack of understanding significantly impedes our ability to forecast climate. We strive to directly assess the effects of increasing temperature on tropical plant and soil carbon fluxes and storage over a range of time scales in order to reduce uncertainty and increase the confidence with which we can make global predictions of future climate. The proposed set of experiments will focus on both above- and belowground processes, and will mechanistically explore temperature controls over critical carbon cycling of tropical plants, soil, and microbes. In a wet tropical forest in Puerto Rico (El Yunque National Forest), we will use canopy access towers, novel leaf and branch warming techniques, micro-meteorological monitoring, and leaf chamber gas exchange measurements to assess the temperature sensitivity of mature tree foliage physiology. We will employ both field and laboratory manipulations to assess how plant roots and soil microbes respond to increased temperature and through what mechanisms. The field soil warming experiment will be the first of its kind in any tropical forest. Overall, this research strives to assess: (1) temperature responses and acclimation potential of mature tropical tree photosynthesis, leaf respiration, and root respiration and (2) temperature responses and acclimation potential of tropical soil processes: decomposition, microbial respiration, carbon use efficiency (how microbes partition carbon to their biomass vs. to carbon dioxide), and nutrient cycling (focusing on nitrogen and phosphorus). The results of this research would represent a significant step forward in our understanding and ability to effectively model tropical forest responses to a warmer world. The research addresses multiple goals highlighted by DOE and Carbon Cycle Science Theme 1: Carbon Research in Critical Regions. First, this work will make significant advances in our understanding of coupled biogeochemical processes in a globally important and relatively poorly understood biome. Second, the hypotheses were developed through ongoing collaborations with a cadre of modelers, and the study is designed to ensure that results will lead to invaluable improvements to the predictive capacity of existing models. Third, because we aim to focus not only on documenting responses but also on assessing the mechanisms regulating change, this work will allow us to extrapolate results beyond that of a single tropical forest site, leading to wide geographic applicability. Finally, the research strongly leverages existing support from multiple federal partners, including USDA Forest Service and the U.S. Geological Survey who share the same goal of improving our ability to forecast the effects of global warming on tropical forest ecosystems. This work will provide critical information regarding the vulnerability and adaptation potential of the only tropical forest in the US National Forest System.

Publications:

Cavaleri, M. A., Reed, S. C., Smith, W. K., Wood, T. E. 2015. Urgent need for warming experiments in tropical forests. Global Change Biology. 21(6), 2111-2121. DOI: 10.1111/gcb.12860

Kimball, B. A., Alonso-Rodriguez, A. M., Cavaleri, M. A., Reed, S. C., Gonzalez, G., Wood, T. E. 2018. Infrared heater system for warming tropical forest understory plants and soils. Ecology and Evolution. 8(4), 1932-1944. DOI: 10.1002/ece3.3780

Mau, A., Reed, S., Wood, T., Cavaleri, M. 2018. Temperate and Tropical Forest Canopies are Already Functioning beyond Their Thermal Thresholds for Photosynthesis. Forests. 9(1), 47. DOI: 10.3390/f9010047

Reed, S. C., Wood, T. E., Cavaleri, M. A. 2011. Tropical forests in a warming world. New Phytologist. 193(1), 27-29. DOI: 10.1111/j.1469-8137.2011.03985.x

Wood, T. E., Cavaleri, M. A., Reed, S. C. 2012. Tropical forest carbon balance in a warmer world: a critical review spanning microbial- to ecosystem-scale processes. Biological Reviews. 87(4), 912-927. DOI: 10.1111/j.1469-185X.2012.00232.x

More details may be found in the following project profile(s):

• North American Carbon Program (NACP) Project Profile