The Amazon Fertilisation Experiment (AFEX)

Terrestrial ecosystems currently absorb one quarter of the carbon dioxide that Humankind releases into the atmosphere, thus reducing the rate of climate change. In this context, Amazon rainforest is extremely important, absorbing more than half a billion tonnes of carbon per year. This represents more than the combined emissions from the USA and China. However, we have limited understanding of how the productivity of Amazon forests is controlled, and this reduces our ability to predict what will happen in the future as atmospheric CO2 concentrations continue to rise and the climate changes.

One of the main paradigms in ecology is that the productivity of tropical ecosystems, which occur on old, highly-weathered soils, is limited by the availability of phosphorus. This contrasts with more temperate ecosystems whose productivity has been shown to be limited by nitrogen availability. However, the phosphorus paradigm has not been tested in detail as there have been very few nutrient manipulation studies in tropical forests, and no large-scale study has been carried out in Amazon forest. This is a major issue because soil nutrient availability in most of Amazonia is substantially lower than in Panama, the location of the only ongoing fertilisation experiment in tropical lowland rainforest. Thus, the Panama findings may not be representative of large areas of Amazonia, and, therefore, our understanding of the role soil fertility plays in controlling tropical forest productivity is incomplete.

Testing the phosphorus paradigm in Amazonia is critical for two reasons. Firstly, eastern and central Amazonia, the area which contains the lowest fertility soils, is considered to be at risk from the adverse effects of climate change, with widespread dieback predicted by some scientists. The resilience of these forests is considered to be highly dependent on whether trees are able to increase their growth in response to rising atmospheric CO2 concentrations, and this ability is likely to depend on the extent to which their growth is currently limited by soil nutrient availability. Secondly, there is growing evidence that the response of ecosystems to global change may differ depending on which nutrient limits their productivity. Therefore, establishing the first large-scale nutrient manipulation study in Amazonia should represent one of greatest priorities for ecosystem and climate change research.

We will do just that, manipulating nitrogen, phosphorus and cation availability in central Amazon forest, at a site representative of the most common soil type in the Basin, and will quantify the response of key forest processes. We will determine the impacts on photosynthesis, plant respiration, biomass production and turnover, and decomposition, ultimately allowing us to take a full-ecosystem approach to establish how carbon storage has been affected. The new knowledge and understanding which we generate will be used to improve Amazon process representation in the Joint UK Land Environment Simulator (JULES). This will be the first time that multi-nutrient control of tropical forest function has been included in a dynamic global vegetation model, allowing for more realistic simulation of the response of the Amazon carbon cycle to environmental change. This will improve our ability to predict how the Amazon rainforest will change during the 21st century and what the implications will be for rates of regional and global climate change.

In summary, our project will address a fundamental ecological question and will improve greatly our understanding of an issue that contributes substantially to uncertainty in predictions of rates of 21st century climate change; namely, how the productivity of one of the most important natural carbon sinks on the planet, the Amazon rainforest, is controlled.

Our ultimate aim is to improve understanding of how Amazon forest productivity is controlled, and thus how it may be affected by global change. Given the globally significant role the forest plays in the carbon cycle, as well as the ecosystem services it provides to the people living in Amazonian states and beyond, this work is likely to be of great interest to the IPCC and the Brazilian Panel on Climate Change (PBMC). Our work also has implications for local Environmental Protection Agencies (including those involved in climate change mitigation and the regional implementation of the UN REDD programme), and local communities in Manaus, the nearest major city. Finally, the experimental manipulation of nutrient availability in Amazon rainforest is likely to be of great interest to the general public.

The IPCC is placing a greater emphasis on earth system modelling and in particular climate-carbon cycle feedbacks. Given that Amazonia represents a globally significant carbon sink, the aims of our project are highly relevant to IPCC Working Group 1. In addition, our work will also provide valuable information on ecosystem resilience to global change in one of the IPCC focal regions, Latin America. This is therefore within the scope of IPCC Working Group II. The modelling in our project uses the Joint UK Land Environment Simulator (JULES) which is the land component of the Met Office Hadley Centre's flagship family of Earth System Models, HadGEM2 & 3, and thus developments in this project will directly lead to improvements relevant to IPCC-facing, coupled climate-C-cycle modelling. We enjoy excellent links with Met Office scientists; PI Hartley runs a joint Exeter University-Met Office carbon cycle research group, and CoI Mercado is the theme leader in plant physiology for JULES. We will also make our results available to our collaborators on the board of directors of the PBMC, including Prof. Jose Marengo and Prof. Carlos Nobre.

Our links with key Brazilian Project Partners, and CoI Aragao's proven track record in communicating his science to local government and environmental protection agencies, ensures that the key local beneficiaries of the science will be informed of the implications of our science. We will give public lectures in Portuguese at Partner Institutions to reach a broader audience including local people and governmental organisations. Furthermore, we will run a workshop at INPA, with a 3-day visit to the field station, for environmental studies students, and local environmental agency and local government agency representatives. Our project partners will help identify the key individuals to invite and will actively advertise the workshop.

We expect the project to be of great interest to the general public, and to be an excellent opportunity to promote NERC science and to outline the impacts that environmental change will have on the tropical forests. The investigators are committed to, and have strong track records in, communicating science to the general public through various media outlets. We will join three successful initiatives that promote dissemination of tropical science: (1) the NERC-funded Global Ecosystems Monitoring Web Portal (see Letter for Support from Prof. Malhi) (2) the RAINFOR network, and (3) the prize-winning public science web site 'Climate Kaleidoscope'. Finally, we will set up a website actively promoting the project.

In summary, together with our plans for academic dissemination, our impact plan will ensure our results have the maximum possible impact in terms improving the representation of the Amazon in IPCC-facing modelling, and we will give lectures and run a workshop to outline our findings to the local community and local government and environmental protection agencies. Furthermore, we will use various media, to ensure that our research reaches the wider society.