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Pellegrini Group: Nutrient limitation of tropical savanna-forest biomes


Supervisor: Adam Pellegrini (Plant Sciences)

BrushThis project will take advantage of a nutrient fertilization experiment in Brazilian tropical savanna and forest biomes to test a general theory in biogeochemistry that disturbance can shift the nutrient limitation of tropical ecosystems.

Importance of work

What nutrients limit the productivity of plants is a long-standing and unresolved question in ecology. The current paradigm is that nitrogen limits growth in temperate and boreal regions while phosphorus limits growth in tropical regions because of constraints on nutrient supply. Disturbance by fire can change the type of limitation, however, because it volatilizes nitrogen to the atmosphere but recycles phosphorus to the soil. Given that fire regimes are changing dramatically across a large area of the globe, this has ramifications for nutrient limitation in a variety of ecological contexts. This project will conduct research in a tropical savanna-forest ecotone, located in central Brazil, where plots have undergone experimental manipulations of both fire and nutrients. A combination of field measurements and laboratory analyses will evaluate the growth of trees and grasses in the different treatments and the role of changes in plant physiology and soil chemistry in predicting the effect of fire and nutrient availability.

Project summary

The project will evaluate the response of tropical savannas and forests to nutrients using a field experiment in Aguas de Santa Barbara, Brazil. Sampling will be carried out on plots that have received different nutrient additions spanning ecosystems with different fire histories (recently burned savanna and fire excluded forests). In 2016, all trees were tagged, identified, and measured at the initiation of the experiment, and this PhD project will conduct follow-up surveys and detailed evaluation of the plant communities. Fieldwork will be conducted to evaluate the responses of plants, measure several important physiological traits (bark investment, leaf area, photosynthetic rates), and collect soils. Lab analyses will evaluate changes in soil chemistry.  

What the student will do

The project will combine both field and lab work.

  1. Fieldwork: Fieldwork will be carried out in Aguas de Santa Barbara (São Paulo state, Brazil) over the course of two field seasons during the first and second year of the PhD. Time will be spent conducting vegetation surveys (measuring tree stems, identifying species, and surveying leaf area) and collecting soil samples for future analyses in the lab. Follow-up analyses of plant traits will be conducted in the lab as needed.
  2. Labwork: Analyses of the amount and form of carbon and nutrients in the soil will be carried out in the lab using combustion and gas chromatography. Nutrient limitation of microbial communities will also be tested using multi-month incubations to measure CO2 respiration and microbial biomass.

Training to be provided

The student will be trained in field survey and sampling techniques, plant physiology, biogeochemistry (carbon and nutrient measurements in soils, organic matter chemistry), and microbiology (microbial biomass and respiration assays). Working in Brazil will provide insight into establishing collaborations in different countries, the potential to learn Brazilian Portuguese, and navigate logistics in a relatively remote field location.


  • A. F. A. Pellegrini, A. Ahlström, S. E. Hobbie, P. B. Reich, L. P. Nieradzik, A. C. Staver, B. C. Scharenbroch, A. Jumpponen, W. R. L. Anderegg, J. T. Randerson, and R. B. Jackson. 2018. Fire frequency drives decadal changes in soil carbon and nitrogen and ecosystem productivity. Nature 553:194–198.

  • A. F. A. Pellegrini. 2016. Nutrient limitation in tropical savannas across multiple scales and mechanisms. Ecology 97: 313-324.

  • A. F. A. Pellegrini, W. R. L. Anderegg, C. E. T. Paine, W. A. Hoffmann, T. Kartzinel, S. S. Rabin, D. Sheil, A. C. Franco, and S. W. Pacala. 2017. Convergence of bark investment according to fire and climate structures ecosystem vulnerability to future change. Ecology Letters 20:307–316.


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