Congratulations Dr. Cunha!

Dra. Hellen Fernanda Viana Cunha (aka Fernanda) successfully defended her PhD Thesis on October 25th, 2022. The “show” was was online, but Prof. Kelly got to celebrate in-person in Manaus, Brazil. Fernanda is the first PhD student to graduate from the extended Team Underground lab group. We wish Fernanda continued success in her career and look forward to many more collaborations over the years.

While in Manaus, some of the original AFEX group was around for discussions on papers and next steps. Several students who completed their master’s thesis on the short-term effects of nutrient additions are now continuing on in their PhD’s to look at the next phase of responses to large-scale nutrient additions. Many articles are in preparation, with more ideas to generate subsequent research and papers. Stay tuned for all the progress and insights coming from the AFEX project!


Nature paper update

Our paper, Cunha et al. 2022, is featured as one of SIX papers highlighting the importance of forest science and the urgent need for a better understanding of how global change will affect forest function, species distribution, and resilience in this week’s issue of Nature (Vol. 608, Issue 7923, 18 Aug 2022). An editorial summarizes the research papers. The online version of the editorial also emphasizes the importance of longterm, large-scale datasets, interdisciplinary research integrating remote sensing and modeling of responses over longer timescales and larger areas, and the difficulty in securing funding for these massive endeavors.

Here at Team Underground, we also want to emphasize the importance and difficulty of large-scale manipulation experiments, particularly in tropical forests. It took an enormous effort by all 31 authors, plus many more research technicians, friends and colleagues, to conduct the research and publish our initial findings from the AFEX project. We are super proud that this research is very much driven by Brazil-based researchers, as it should be.

New Paper from the AFEX project

Cunha, H.F.V., Andersen, K.M., Lugli, L.F. et al. Direct evidence for phosphorus limitation on Amazon forest productivity. Nature (2022).

Experimental plot adding phosphorus to a Central Amazonian Forest

Amazon’s growth limited by lack of phosphorus

Growth of the Amazon rainforest in our increasingly carbon-rich atmosphere could be limited by a lack of phosphorus in the soil, new research shows.

Higher concentrations of carbon dioxide (CO2) cause plants to grow more quickly, meaning they store more carbon.

This storage – especially in huge forests like the Amazon – helps to limit rising CO2 levels, slowing climate change.

However, plants also need nutrients to grow, and the new study shows that availability of a particular nutrient, phosphorus, could limit the Amazon’s ability to increase productivity (growth rate) as CO2 rises.

This could also make the rainforest less resilient to climate change, the researchers warn.

The study, published in the journal Nature, was carried out by an international team led by Brazil’s National Institute of Amazonian Research (INPA), the University of Exeter, and Nanyang Technological University.

“Our results question the potential for current high rates of carbon uptake in Amazonia to be maintained” said lead author Hellen Fernanda Viana Cunha, who is currently finishing her PhD at INPA. 

“About 60% of the Amazon basin is on old soils with low phosphorus content, but the role of phosphorus in controlling productivity was unclear because most fertilisation experiments in other parts of the world have been in more phosphorus-rich systems.

“Our experiment, the Amazon Fertilisation Experiment (AFEX), examined the effects of adding phosphorus, nitrogen and base cations (other potentially key nutrients) in an old-growth, low-phosphorus area of the rainforest.

“Only phosphorus led to increased productivity in the first two years of the experiment.” 

“Having such rapid and strong responses to phosphorus, both above and below ground, is an indication that the whole system was functioning under severe phosphorous limitation.” ~ Lead Author, Hellen Fernanda Viana Cunha

Soil in tropical regions such as the Amazon generally formed millions of years ago, and nutrients like phosphorus and cations, which come from chemical break down of rocks, can be lost over time.

While nutrients such as nitrogen can be absorbed from the air by micro-organisms associated with certain plants and soils, phosphorus is not available as a gas in the atmosphere – so once it is lost there is little opportunity for levels to increase. 

In the new AFEX experiment, two years with extra phosphorus caused significant increases in fine root growth (29%) and canopy productivity (19%). 

Stem growth did not increase. Ms Cunha said this may be because roots and leaves require more phosphorus than stems, and stem growth is a slower process. 

Long-term monitoring of the experiment is required to determine whether a stem wood productivity response becomes apparent.

The findings have major implications not only for carbon storage, but also for the forest’s resilience to global changes. 

“Plants grow faster with more CO2 in the atmosphere. However, results from AFEX suggest that the ability of the Amazon Forest to take advantage of increasing atmospheric CO2, which would enhance the forest’s resilience, will be ultimately limited by soil phosphorus availability,” said Assistant Professor Kelly Andersen, from Nanyang Technological University.

“Therefore, tropical forests growing on low nutrient soils may be experiencing increased risks caused by global change, with their resilience diminishing over time.

The AmazonFACE experiment – which is elevating CO2 at site near the AFEX experiment and whose international team includes researchers from the AFEX experiment– is working to address this key priority.

However, Dr Andersen said there is an urgent need to establish large-scale nutrient addition experiments across a range of tropical forest regions to better understand how soil nutrients control forest productivity and carbon cycling across the tropics. 

“Whether soil phosphorus, or other nutrients, determines tropical forest productivity in low soil nutrient forests of Southeast Asia, remains uncertain.” Dr. Andersen is working with colleagues to address this research gap.

The new study was funded by the Natural Environment Research Council.

The paper is entitled: “Direct evidence for phosphorus limitation on Amazon forest productivity.”

The paper is available at the following URL:

DOI: 10.1038/s41586-022-05085-2

An accompanying Nature News & Views article, by S. Joseph Wright, entitled “Low phosphorus levels limit carbon capture by Amazonian forests” is available at the following URL:

A version of this press release was published as a news blog by the College of Science, Nanyang Technological University:

Crescimento da Amazônia limitado pela falta de fósforo

O crescimento da Floresta Amazônica em uma atmosfera cada vez mais rica em carbono pode ser limitada pela falta de fósforo no solo, mostra uma nova pesquisa.

Concentrações mais altas de dióxido de carbono (CO2) fazem com que as plantas cresçam mais rapidamente, o que significa que elas armazenam mais carbono.

Esse armazenamento – especialmente em grandes florestas como a Amazônia – ajuda a limitar o aumento dos níveis de CO, desacelerando a mudança climática.

No entanto, as plantas também precisam de nutrientes para crescer, e o novo estudo mostra que a disponibilidade de um determinado nutriente, o fósforo, pode limitar a capacidade da Amazônia de aumentar a produtividade (taxa de crescimento) à medida que o CO2 aumenta.

Isso também pode tornar a floresta tropical menos resiliente à mudança climática, alertam os pesquisadores.

O estudo publicado na revista Nature, foi realizado por uma equipe internacional liderada pelo Instituto Nacional de Pesquisa da Amazônia (INPA), pela Universidade de Exeter e pela Universidade Tecnológica de Nanyang.

“Nossos resultados questionam o potencial para as atuais altas taxas de absorção de carbono na Amazônia serem mantidas” disse a principal autora Hellen Fernanda Viana Cunha, que está atualmente concluindo seu doutorado.

“Cerca de 60% da bacia Amazônica está em solos antigos com baixo teor de fósforo, mas o papel do fósforo no controle da produtividade não era claro porque a maioria dos experimentos de fertilização em outras partes do mundo foram em sistemas mais ricos em fósforo”

“Nosso experimento examinou os efeitos da adição de fósforo, nitrogênio e cátions base (outros nutrientes potencialmente importantes) em uma floresta tropical madura com baixo teor de fósforo”.

“Somente o fósforo levou ao aumento da produtividade nos dois primeiros anos do experimento”

“Ter respostas tão rápidas e fortes ao fósforo, tanto acima quanto abaixo do solo, é uma indicação de que o sistema estava funcionando sob severa limitação de fósforo”.

“Os solos de regiões tropicais como a Amazônia geralmente se formaram há milhões de anos, e nutrientes como fósforo e cátions, proveniente da decomposição química das rochas, podem ser perdidos com o tempo”.

Embora nutrientes como o nitrogênio possam ser absorvidos do ar por microrganismos associados a certas plantas e solos, o fósforo não está disponível como gás na atmosfera – portanto, uma vez esgotado, há pouca oportunidade para os níveis aumentarem. 

No novo experimento, dois anos com fósforo extra causaram aumentos significativos no crescimento das raízes finas (29%) e na produtividade do dossel (19%).

O crescimento do tronco não aumentou.  Cunha disse que isso pode ser porque raízes e folhas exigem mais fósforo do que o tronco, e o crescimento do tronco é um processo mais lento.

O monitoramento de longo prazo do experimento é necessário para determinar se a resposta da produtividade do tronco se torna aparente.

As descobertas tem grandes implicações não apenas para o armazenamento de carbono, mas também para a resiliência da floresta à mudança global.

“Para lidar e se recuperar de ameaças crescentes, como secas, precisamos que a floresta esteja crescendo melhor do que costumava” Disse o Professor Iain Hartley, do departamento de Geografia da Universidade de Exeter.

A fertilização com CO2 pode aumentar a resiliência da floresta, mas nossas descobertas sugerem que a disponibilidade de fósforo limitará esse efeito – e, portanto, os riscos causados pela mudança climática se tornam cada vez mais importante.

Em suma, partes da Floresta Tropical que crescem em solos de baixa fertilidade podem ser mais vulneráveis do que se reconhece atualmente.

O experimento AmazonFACE – que está elevando o CO2 em um local próximo ao experimento AFEX e cuja equipe internacional inclui pesquisadores do experimento AFEX – está trabalhando para atender a essa prioridade fundamental.

O novo estudo foi financiado pela NERC (Natural Environment Research Council). O artigo é intitulado: Evidência direta da limitação por fósforo na produtividade da Floresta Amazônica.

SG Traineeship Opportunity

Our lab is hiring a research trainee to participate in field and laboratory research to examine tree root traits, mycorrhizal traits, and soil nutrient availability led by the lab’s members and eventually take on leadership of one of the following:

  • Field collection of focal tree roots and soil
  • Laboratory sample processing of roots and soil, including cleaning, drying and grinding
  • Quantification of root morphological and physiological traits
  • Preparation of samples for nutrient analyses
  • Quantification of mycorrhizal colonisation and/or root nodules
  • Data processing and management, preliminary analysis of data in R

Candidates should have a bachelor’s degree in Biological Sciences, Environmental Sciences, Chemistry or related fields and have a basic understanding of research and laboratory experience. Knowledge and experience in R and data analyses are advantageous. Candidates should possess good communication skills and be a good team member.

Applications will close 20th August 2021. This position is a 6-month, full-time position for recent graduates or mid-career individuals in Singapore. Preferred start date will be 4th October 2021.

Please email Asst/P Kelly Andersen for any queries ( and apply officially directly through NTU here with a cover letter and CV.


I have several ongoing projects with research opportunities for students of various levels. Please email me ( with your interest.


1. Research Fellow on nutrient acquisition strategies in peatlands in Brunei

I am currently recruiting a Research Fellow (postdoc) to work in my lab on a funded project to examine nutrient acquisition strategies of tropical trees in peatlands and neighboring forests in Brunei in collaboration with colleagues in the Forest Ecology group at ASE and the SMART group. The Research Fellow will be responsible for helping establish a new research program revolving around nutrient limitation in tropical forests, with specific focus on phosphorus limitation and cycling. This will include extensive fieldwork in Brunei on root ecology and soil nutrients, nutrient analyses of field-collected plant and soil samples at the Forest Ecology labs in the Asian School of the Environment, Nanyang Technological University, Singapore. The Research Fellow will also be expected to contribute to the logistical planning for field work, provide research support for the other team-members in the lab and greater Brunei project team, and publish findings in peer-reviewed journalsCandidates with prior experience in tropical ecology, root ecology, or soil microbial ecology are preferred. Willingness to learn Malay is advantageous to communicate with our local collaborators in Brunei. Review of applications will begin on May 17, 2021. Please email me with your interest in the position, and apply officially directly through NTU including a cover letter, CV, and contact details of three potential referees.

Full job description

2. PhD student

Potential PhD students are welcome to contact me to discuss research interests in the areas of tropical forest ecology and biogeochemistry. Please include a brief summary of your research interests, past experiences and a C.V.

3. Student research experience

NTU offers several programs for enrolled students to conduct research in ongoing projects and to develop independent research projects as part of the curriculum. If you are an NTU student or visiting student interested in gaining research experience in tropical forest ecology and/or biogeochemistry, please email me with you interest. Kindly include your program and specialisation, year, and a list of relevant classes and grades.

B.I.G. News.

I got a job! After nearly 10 years moving from postdoc to postdoc, I finally found a tenure track position. I started as an Assistant Professor in the Asian School of the Environment at Nanyang Technological University, Singapore in January 2019. I am looking forward to growing my lab in Tropical Forest Ecology and Biogeochemistry over the coming years. I do not currently have openings in my lab, but if you have interest in joining us in Singapore to conduct an independent research project on nutrient limitation in tropical forests as a PhD student or Postdoctoral fellow, please email me your C.V. and research interests.