Columbia University's Biosphere 2 Semester in Earth Systems Science and Astronomy

Biosphere 2 Research Semester
Projects Fall 2002

The following is a list of projects that students may choose from for the Fall 2002 session of the Biosphere 2 Research Semester. It is important to note that each mentor will only supervise one or two students (projects) irrespective of the number of projects they have listed. The intent is to provide students with a wide choice of projects but not all projects will end up being run. Acceptance into a project will be competitive so it is important for students to consider alternative projects/mentors. We anticipate accepting approximately 12 students for the Fall 2002 session.

Chemical ecology and natural products chemistry

1. Role of ultraviolet light on natural products chemistry, biosynthesis and biology.
Mentor: Dr. Leif Abrell.

This project will investigate the role UV light plays in the production of flavonoids by plants. Flavonoids are an important group of biological compounds that contribute to plant coloration, pollen germination, oviposition stimulation of butterflies, and screening UV irradiation. The Biosphere 2 provides a unique opportunity to study how UV light affects flavonoid production because the glass in the structure filters out UV light. In this project we will compare the types and amounts of flavonoids produced by plants growing outside the Biosphere 2 with those produced by the same types of plants growing inside the Biosphere 2.

2. Chemically mediated moth-host plant interactions.
Mentor: Dr. Leif Abrell.

In this project we will investigate the impacts of changes in environmental conditions on insect-host-plant interactions by identifying the volatile chemical cues used by the tobacco hawkmoth (Manduca sexta) to locate and oviposit on its host plant Datura wrightii (jimson weed). Once the chemical identities of the volatiles have been determined, our goal is to understand the effects that environmental parameters have on insect-plant interactions.

3. Chemical ecology of isoprene.
Mentor: Dr. Leif Abrell.

Plants and bacteria frequently emit a simple hydrocarbon called isoprene, but despite how common isoprene emission is, we don't have a good understanding of its biological or ecological implications. In this project we will explore a variety of hypotheses related to the chemical and ecological functions of isoprene. We will investigate whether isoprene-utilizing bacteria show positive chemotaxis in response to isoprene gradients, and will attempt to characterize their isoprene receptor proteins. We may also examine whether the tobacco hawkmoth (Manduca sexta) and ubiquitous crazy ants (Paratrechina longicornis) living in the Biosphere 2 display physiological and behavioral responses to isoprene.

4. Chemical communication and defense in a pantropical ant Paratrechina longicornis.
Mentor: Dr. Leif Abrell.

Since the completion of the Biosphere 2, a single species of ant, Paratrechina longicornis, has risen to dominate the insect community inside. We will explore the chemical, ecological and biological basis of the rise of P. longicornis to dominance. This will include a complete examination of its chemical signaling components, including alarm and recruitment pheromones, and poison gland contents. This research will be supported by electroantennogram measurements.

Organismal ecology, plant community ecology, and ecological/evolutionary modeling

5. On the coevolution of desert plants.
Mentor: Dr. Susan Schwinning.

The major constraint for plant growth, reproduction and ecosystem productivity in arid regions of the world is the availability of soil water. There is good support for the hypothesis that desert plants adapt to the prevailing precipitation patterns, but it is not clear whether plants also adapt to the presence of competitors for water. An important evolutionary question then is, would plant populations in a given environment evolve differently in the presence or absence of competitors for water? This question will be evaluated theoretically, based on a mathematical model of plant water uptake and use (Schwinning and Ehleringer 2001). An evolutionary algorithm will be used to identify adaptive optima in the presence or absence of competition.

6. On the functional diversity of desert plants.
Mentor: Dr. Susan Schwinning.

In this study, a mathematical model will be used to analyze the conditions that allow the coexistence of plant species on the resource water. We will simulate stochastic rainfall distributions and their effects on the growth of competing plant populations. The model will be based on an existing model of plant water uptake and use by an array of contrasting plant functional types (Schwinning and Ehleringer 2001). Students will have the opportunity to formulate research questions of their own interest. Among the possibilities are: Which inter-annual precipitation patterns create the most opportunities for coexistence? Do more or less species coexist when precipitation patterns vary from year to year? Is there a "limiting similarity" for coexisting plant functional types?

7. Ecological and evolutionary implications of sexual and asexual reproduction and hybridization in the cacti Opuntia spinosior, O. versicolor and O. fulgida.
Mentor: Dr. Andrew Peterson.

The cholla cacti Opuntia spinosior, O. versicolor and O. fulgida display varying levels of sexual and asexual reproduction and hybridization in the region around Biosphere 2. Theory on the tradeoffs between sexual and asexual reproduction suggests that these different modes of reproduction can confer quite different ecological and evolutionary costs and benefits. In addition, these three species of cholla display varying degrees of hybridization which also confers ecological and evolutionary costs and benefits. This project is part of an ongoing assessment of the physiological and evolutionary ecology of these three species. Students interested in this project will be able to focus on topics such as the energetic costs of sexual versus asexual reproduction, the relative advantages of sexual versus asexual reproduction in fluctuating environments, or the morphometric analysis of hybridization.

8. Does the benefit of resource translocation among connected ramets in clonal plants decrease with time?
Mentor: Dr. Andrew Peterson.

Many species of clonal plants have persistent rhizomes or stolons connecting ramets together to form highly integrated physiological units in which resources may be moved around to maximize growth in spatially variable environments. Recent theoretical developments suggest that the benefit of resource translocation may decrease with time. This hypothesis has not been tested experimentally, yet it has major implications for our understanding of the ecology and evolution of this important group of plants. In this project we will test this hypothesis using a variety of species in an attempt to determine if it is a taxonomically widespread phenomenon.

9. Effects of global climate change and elevated atmospheric CO2 on mechanisms of plant-species coexistence.
Mentor: Dr. Andrew Peterson.

Rising levels of atmospheric CO2 and climate variation are known to affect plant growth, reproduction and competition. However, it is only now coming to light that changes in CO2 and changes in climate variability may affect plants in complex, interactive, and nonlinear ways. This project will continue an ongoing investigation into how these nonlinear interactions may affect mechanisms of species coexistence in plant communities. We will use computer controlled growth chambers to investigate how competition between annual grass species may be affected by changes in CO2 concentration and different patterns of environmental variation aimed at simulating a future climate scenario. We will also incorporate a strong physiological approach to understanding how these variables affect plant growth in order to develop physiologically based models of plant competition.

Plant physiology, physiological ecology, and ecosystem ecology

10. Quantifying the interactive dynamics of photosynthesis and leaf growth using chlorophyll fluorescence and digital imaging technologies. Mentors: Drs. Uwe Rascher and Achim Walter.

The aim of this project is to investigate the spatio-temporal dynamics of the interaction between photosynthesis (measured using chlorophyll fluorescence) and leaf growth (measured using digital imaging technology) at the leaf and sub-leaf scales. This innovative approach to studying interactions between photosynthesis and leaf growth has great potential to give new insights into a wide range of questions in plant ecophysiology. Project details are in development.

11. Understanding the response of the tropical rainforest mesocosm of Biosphere 2 to drought episodes using stable isotope techniques.
Mentor: Dr. Guanghui Lin.
Technical assistants: Mr. Joost van Haren and Ms. Daniel Pierce.

There are two main foci for this project. The first is to test the utility of stable isotope techniques for identifying the contribution of plant respiration versus soil respiration to the carbon budget of the rainforest mesocosm. The second focus will be on using stable isotope techniques to understand the ecosystem-level effects of drought on CO2 and water vapor fluxes within this experimental mesocosm.

Marine ecology and biological oceanography

Several projects are currently in development and will be announced soon.

Astrophysics and fluid dynamics

12. Two-fluid shear flows, instability, droplets and spray formation. Mentor: Dr. Phil Yecko.

Our current understanding of the processes involved in the formation of sprays from liquids is limited. The conversion of liquid into spray is very important for a range of phenomena from ocean-atmosphere gas exchange to many industrial processes including combustion in liquid-fuel rocket engines. In this project the student will have the opportunity to work with and perhaps further the development of a state-of-the-art numerical simulation code (called SURFER) for the direct numerical simulation of two fluids. The primary goal is to perform numerical experiments on the breakup of liquids in a variety of configurations so as to better understand and ultimately quantify or develop a theory explaining this complex instability process. This project will involve significant work with graphical output and image analysis, familiarity with computer programming and knowledge of physics and fluids.

13. Theory and modeling of stellar pulsation.
Mentor: Dr. Phil Yecko.

In certain phases of evolution, many stars are observed to undergo large amplitude radial pulsations which lead to periodic changes of the star's luminosity. Physically, the star serves as a kind of acoustic cavity and the pulsations are sound waves - specifically the normal modes of that cavity. The mechanism by which stars pulsate (so-called kappa mechanism) is an instability that is driven by the temperature and density dependence of the star's opacity. In this project the student will develop, apply and explore the role of engineering-type models of turbulence in computer simulations of pulsating stars. Of particular interest is the role of turbulent convection in several as yet unexplained types of observed pulsation, including irregular or chaotic pulsators. An observational component may possibly be coupled to the primarily theoretical work.