Soil carbon and climate warming in tropical forests: using experimentation and elevation to reveal responses across space and time

Climate change is predicted to release carbon stored in terrestrial ecosystems, causing a major acceleration of future climate change. This carbon release is predicted to occur through increased rates of decomposition and respiration by plants and soil microorganisms under warming. However, the acceleration could be constrained in the long-term if microorganisms adjust their community-wide physiology to metabolise less carbon under higher temperatures. Despite the significance of this potential feedback, we have little information on the magnitude and mechanisms by which it occurs in tropical forests, which contain two-thirds of global terrestrial plant biomass and a third of global soil carbon. I address this uncertainty, by combining a unique tropical forest soil warming experiment with a series of 'natural' experiments along tropical forest elevation/temperature gradients. I will use cutting-edge techniques in soil biogeochemistry and microbiology to determine the magnitude and mechanisms of carbon release from these soils under warming, and the mechanisms by which it may be constrained, particularly by the physiological and community-wide changes in microbial communities. By combining experimental study of short-term microbial responses and observational study of long-term responses across elevation gradients, I will gain unique integrated insights, enabling the extrapolation of findings to landscape scales, and providing key information urgently needed by Earth-system models. In summary, this project will directly address what has been identified as the most significant cause of uncertainty in predicting the feedbacks between climate change and terrestrial ecosystems: the magnitude and mechanisms for tropical forest soil carbon release under climate warming, and the role of microbial communities in constraining this release.

The project 'Climate warming effects on tropical forest soil carbon: below-ground responses to experimental warming and elevation' will have significant academic, social and economic benefits for the UK, the partner countries and the world. The impacts will be wide reaching and continue beyond the duration of this proposal.

The project will directly address a major knowledge gap identified in the fifth assessment by the Intergovernmental Panel on Climate Change (2013), the magnitude and mechanisms for Earth-climate carbon-exchange feedbacks in tropical regions. The results from this project will, therefore, be of high interest to the global research community, governments and policy makers.

Scientists will benefit from the experiment, as outlined in the Academic Beneficiaries section. The immediate beneficiaries will be the already extensive network of international research collaborators and institutes - with UK scientists and institutes leading the work. The beneficiaries will develop and extend beyond these, as the project will develop and explore further aspects of climate change impacts in tropical forests, including climate modellers, community ecosystem ecologists, plant physiologists, researchers working at different trophic levels and scales. These developments will be made during the course of the project as our preliminary findings are presented at international conferences and published in peer-reviewed journals.

The SWELTR experiment will have a long-lasting scientific and education legacy, providing opportunities for research and student projects, education to students and lay audiences. The high profile of the experiment will provide opportunities for outreach work on climate change, including talks, tours and articles in newspapers and magazines, to UK, Scottish and international audiences. The project has already attracted media attention (recently conducted interviews for general interest publications 'Tropicos' and 'The Smithsonian Magazine') and was announced in a White House Press Release by the Obama Administration on World Soils day 2016.

The elevation gradient studies will have societal impacts that will benefit the field site countries (Panama, Peru, Colombia) by providing research opportunities and building research capacity, especially in the developing economies of Peru and Colombia. I will develop this work and to build UK-partnerships through applications to host workshops and student exchange programs through the Newton fund, which has prioritized development of climate change and biodiversity research in these countries. I will develop outreach programs in the vicinity of the research sites, including a school program to engage in talks and activities on climate change and environmental education themes. The elevation gradient studies will be long-term research assets for the respective countries, by engaging with local universities and supervising local student researchers. This approach was successfully implemented for the elevation gradient studies in Peru (led by Prof Silman, Prof Malhi, Prof Meir), leading to numerous Peruvian graduates and PhDs and new research grants led by The Catholic University of Lima. This model would be replicated for the Colombian elevation gradients in this proposal, stimulated by a new initiative by the Colombian government to develop natural reserves and prioritize ecological research in areas of tropical forest.