The University of Arizona

Tropical forest responses to climate change

Despite their key influence in global carbon cycles, elucidating the carbon cycle of tropical rainforests has been an elusive quest. In addition, we have little ability to predict responses of tropical rainforest to climate change because of the difficulties of developing experiments that control precipitation and temperature in the field.  We are developing a new avenue to study the future of Amazon forests under climate change by integrating observations of Amazon forest response to droughts with experiments in the enclosed Tropical Forest biome of the University of Arizona's Biosphere 2. By a combination of warming and drought experiments in this controlled ecosystem we plan to gain a more mechanistic understanding of future responses of tropical rainforests to climate change, ranging from the level of individual plants to the entire ecosystem. Long-term field observations in the Amazonian forests coupled with experiments at Biosphere 2 will be integrated with modeling exercises at both sites, in order to validate computer simulations using the results of experimental manipulation. This research program partners with the office of Partnership for International Research and Education (PIRE) of the National Science Foundation (NSF) in order to transform science education by establishing an innovative model for international collaboration as a basis for education and training of science students in both the U.S. and Brazil. These international activities involve field courses, graduate and undergraduate research opportunities, and workshops involving the community of experts in tropical rainforest science.

Current projects:

Simultaneous modeling of rainforest behavior in the field and in Biosphere 2

Canopy profiles are being installed at Biosphere 2’s tropical rainforest biome to obtain micrometeorological measurements. Ultimately, the collected data will be used to simulate the ecohydro-meteorology of the B2 tropical rainforest biome and provide a simplified comparison to a primary rainforest in the Amazon.

In spring 2009, we installed a measurement station with light, temperature, and wind-speed sensors in a central location to provide some missing data components for the model.  Over the summer researcher Rafael Rosolem ran a simulation model and submitted for peer review a paper describing the results. All the programming for the profiles is complete and sensors are being calibrated and installed.

For questions contact Rafael Rosolem rosolem@email.arizona.edu.

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Influence of light, temperature and water availability on carbon and nutrient cycling in the plant-soil continuum of the tropical rainforest biome: a seedling-scale experiment

We plan to start a five-year potted-seedling experiment in the B2 rainforest. Through this seedling-level the experiment, we aim to gain valuable insight into how light, temperature, and VPD interact and affect carbon and nitrogen cycling both above and below ground in a selection of tropical forest tree species, beginning at the newly-emerged seedling stage. The results of this experiment will add to the growing body of knowledge on how tropical forests will respond to global climate change, but most importantly will fill in critical gaps by isolating variables such as temperature and moisture that have proven difficult to independently characterize in recent experimentation.

We have started the seed germination tests with seeds from the USDA seed depository in Puerto Rico. The species available through this depository provide some overlap with species already present inside Biosphere 2 (Pterocarpus indicus and Parichia ) and species for genera that are common in Brazil.  The initial germination results were poor, we expect mainly as a result of the relatively low light conditions of the location used in the B2 rainforest and high soil pH.  We have expanded the germination tests to the greenhouse and the lab using incubators and germination paper in order to test a range of conditions to improve germination yields.

For questions contact Joost van Haren jvanhare@email.arizona.edu or Greg Barron-Gafford gregbg@email.arizona.edu.

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Monitoring of below-ground productivity in the tropical rainforest biome at Biosphere 2

In order to elucidate the mechanisms of how rainfall and temperature can impact below-ground productivity in tropical rainforests, we propose to monitor fine-root demography (productivity, mortality and decomposition) in the tropical rainforest biome at Biosphere 2 in response to variation in rainfall and temperature (drought and/or high temperature treatments). Fine-root demography will be assessed with minirhizotron tubes (root observation devices) and soil observation pits installed at different depths together with root observation windows inside soil pits; these will complement other below- and above-ground measurements in order to provide better understanding of the flow of carbon in the ecosystem. These measurements in the enclosed system will be compared with fine-root demography datasets from other tropical rainforest sites in Brazil and Costa Rica.

For questions contact Brad Christoffersen bchristo@email.arizona.edu or Joost van Haren jvanhare@email.arizona.edu.

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Monitoring of above-ground productivity and gas exchange in the tropical rainforest as a response to environmental variation

In order to elucidate the mechanisms of how rainfall and temperature can impact above-ground productivity in tropical rainforests, the tropical rainforest biome at B2 will be subjected to different regimes of drought and temperature. The exchange rates of carbon and water will be studied by sampling air from canopy profiles in the forest and simultaneous analysis of carbon and water concentrations in the air with infrared gas analyzers, and sampling carbon and water isotopic compositions with novel laser-based spectrometers.

For questions contact Kolby Jardine jardine@email.arizona.edu.

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Studies on below-ground gas exchange

The production of greenhouse gases from tropical rainforest soils, specifically the emissions of carbon dioxide, methane and nitrous oxide will be measured from the soil surface and at different soil depths using surface chambers and soil pits in the tropical rainforest biome. The forest-wide response to environmental manipulation at B2 will be compared to field measurements in the Amazons and to species-specific data to elucidate potential mechanisms of ecosystem flow.

We installed soil probes at 15 cm depth on a 5 by 5m grid and have conducted three sampling rounds to determine the spatial variability changes with the increased rainfall regime in the B2 tropical forest.  Initial results suggest that the soil CO2 and N2O concentrations are low and less consistent than during the CU days. We expect that with a more constant and increased rainfall regime, more consistent patterns will develop.

For questions contact Joost van Haren jvanhare@email.arizona.edu.

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Investigating sesquiterpene dynamics: from leaf biochemistry to scaling theory

Sesquiterpenes are a subclass of hydrocarbons produced primarily by plants, and are a major component of many essential oils. Biosphere 2 is an ideal location for investigations into sesquiterpene land-atmosphere dynamics because it allows the coupling between a state-of-the art 21st century analytical chemistry lab with large-scale enclosed systems such as the tropical rainforest biome. Using a mass balance approach with a flow-through system, it may be possible to provide the first direct ecosystem scale emission estimates of sesquiterpenes using the Biosphere 2 facility.

For questions contact Kolby Jardine jardine@email.arizona.edu. and see http://en.wikipedia.org/wiki/Sesquiterpenes

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