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Soil carbon dynamics in an elevated CO2 world; a litter addition experiment in tropical forest

Supervisor: Edmund Tanner

Reference code: C143

Importance of the area of research:  Carbon in ecosystems is dynamically exchanging with CO2 in the atmosphere. About half the carbon in ecosystems is in the soil and the soil organic carbon is about 2-3 times the carbon in CO2 (Trumbore 2009). Increased CO2 in the atmosphere has increased forest growth and litter production (Finzi et al 2001). We have an experiment in tropical rain forest in Panama where we have doubled leaf litter input for 11 years (Sayer et al 2012);  40% of the extra C is in the soil. We propose a new, more realistic experiment where we add organic matter as carbon with very low nutrient concentrations (sugar cane waste) as compared to the higher nutrient leaf litter that we have been adding. The carbon in the sugar cane waste also has a 13C concentration different from the forest litter and forest soil organic carbon thus we will be able to trace the fate of the added sugar cane carbon.

What the project will involve:  We will set up new treatment within our existing litter manipulation experiment at the Barro Colorado Nature Monument administered by the Smithsonian Tropical Research Institute in lowland semi-evergreen rain forest in Panama. Sugar cane waste will be added monthly. Soil respiration and soil samples will be collected to determine changes in soil carbon dynamics and changes in soil carbon concentrations.

What the student will be doing:  The student will do the experiment in rain forest in Panama. They will set it up and add the sugar cane waste. They will collect a large set of samples to be analyzed for various carbon containing compounds in various labs both at the Smithsonian in Panama and in Cambridge. Many samples will be analyzed by mass spectrometry to determine 13C concentrations. The data will be used in a model of soil and litter carbon dynamics that we are currently developing.

Training that will be provided:  The student will be given training in design and execution of experiments in tropical forest. Training in soil chemical analysis (in Panama) and in use of a mass spectrometry (in Cambridge). Training in the use of models and in writing papers for publication will be an essential part of the Ph. D.


  1. Finzi et al. 2001 Forest litter production, chemistry, and decomposition following two years of free-air co2 enrichment. Ecology 82, 470–484.
  2. Sayer E J, et al.  2012 Variable Responses of Lowland Tropical Forest Nutrient Status to Fertilization and Litter Manipulation. Ecosystems 15, 387-400.
  3. Trumbore SE, Czimczik CI. 2008 An uncertain future for soil carbon. Science 321, 1455-1456.