Phosphorus feedbacks determining forest resilience in Singapore

Tropical forests are important for the world’s biodiversity and carbon and water cycles. These globally important ecosystems are facing increasing threats from human activities and nutrient imbalances caused by global changes. Nutrients regulate forest productivity and species composition. Therefore, alteration of carbon and nutrient cycles may have disproportionally large effects in tropical forests. Soil phosphorus is a key nutrient that is particularly low in availability in old, highly weathered soils, such as those found in Singapore and other tropical forest regions. Thus, it is hypothesized that soil phosphorus availability will ultimately determine tropical forest resilience to global changes. However, current model projections for tropical forest responses to global change diverge, with some suggesting increased productivity and others suggesting catastrophic die-back. This research project aims to address key research gaps for understanding tropical forest resilience to global changes by examining potential mechanisms for overcoming phosphorus limitation and phosphorus feedbacks on carbon cycling. By focusing on fundamental processes, such as how plants and soil microbes 1) take up soil phosphorus, 2) use and recycle phosphorus, and 3) trade-offs between efficient phosphorus uptake and use, the proposed research will provide a novel framework for how phosphorus feedbacks may affect Singapore and Southeast Asian tropical forest resilience to global changes.

Large-scale soil nutrient addition experiment in Amazonia (AFEX)

The first large-scale nutrient manipulation experiment in Central Amazonia, the Amazon Fertilization Experiment (AFEX), is based in Manaus, Brazil. The longterm experiment is originally funded by the Natural Environment Research Council (NERC 2014-2020) to Drs. Iain Hartley, Lina Mercado, Luis Aragão (University of Exeter), Patrick Meir (University of Edinburgh/Australian National University) and local collaborator Dr. Carlos Alberto Quesada (Instituto Nacional de Pesquisa da Amazônia). Located at a low soil fertility site, AFEX focuses on the mechanistic underpinnings of how soil nutrients, including nitrogen (N), phosphorus (P) and cations, influence plant and ecosystem processes across a diverse group of sympatric plant species. Due to the high biodiversity of the Amazon, our approach focuses on comparing the process-based responses across a wide taxonomic array of common species-rich tropical families.

Plant functional diversity feedbacks on ecosystem processes

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Are there home-site advantages in above- and below-ground decomposition? Functional traits influence community assembly and feedback on ecosystem function. Acquisitive species generally have nutrient rich leaves to support high photosynthetic and growth rates, whereas conservative species have well-protected leaves to promote longer leaf longevity and survival rates. How traits strategies equate to above- vs. below ground trade-offs has implications for ecosystem function, such as nutrient turnover and carbon fluxes. I am collaborating with Dr. Nina Wurzburger (University of Georgia) on a project looking at the influence of specific plant species and their mycorrhizal and soil microbial communities on carbon and nutrient cycling. This project examines rates of leaf and root decomposition on above- and belowground nutrient and biomass turnover rates of species with diverse nutrient acquisition strategies using reciprocal litter transplant experiments in mixed hardwood temperate and tropical lowland forests.

Understory palm communities in tropical montane forests

I obtained my PhD in Biology from the University of Illinois, Urbana under the direction of Dr. James Dalling. My dissertation research on closely related understory palm species examined functional trade-offs that influence distribution patterns along soil gradients in lower montane tropical forests of the Fortuna Forest Reserve, western Panama. Soil cation and nitrogen (N) availability influences both species- (Andersen et al. 2010, J. Biogeography) and trait-based (Andersen et al. 2012, Oecologia) understory palm community assembly. Across a soil fertility gradient, coordinated shifts in functional traits and strong home-site performance advantages for transplanted seedlings of low-nutrient species support soil-based habitat filtering of the palm community (Andersen et al. 2014, Ecology). Additionally, an N isotope tracer field experiment indicates that low fertility species have lower N uptake rates than species occurring at higher fertility sites, but palm species do not partition N chemical forms (Andersen & Turner, J. Ecol. 2013).

I am also collaborating with the Dalling Lab (UIUC) and STRI Soils Lab in continuing research in the tropical montane forests of the Fortuna Forest Reserve, Panama. The current focus of our research is an assessment of carbon storage in the Fortuna Reserve, Panama.


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