Brent Helliker

Associate Professor of Biology
328 Leidy Laboratories
helliker@sas.upenn.edu
215-746-6217
Ecology and Biodiversity
Plant Biology
Education: 

B.S., University of Kansas, 1995

MPhil, University of Newcastle upon Tyne, 1998

Ph.D., University of Utah, 2001

Research Interests: 

 

plant physiological ecology and global ecology

 

My lab’s approach to plant ecology and evolution is based on the underlying assumption that climate is a primary selective agent. Our goal is to improve our understanding of the physiological responses of plants to climate change, and to determine the ecological and biogeochemical consequences of those responses. Climate change is defined broadly, as we are interested in biotic-abiotic interactions from millennial scale climate change down to the seasonal progression of weather fronts. Our physical scale of study ranges from the subcellular to individuals, ecosystems and landscapes up to the regional level where physical and physiological processes modify the atmospheric boundary layer. The scope and scale of our research interfaces biochemistry, physiology, ecology, evolution and the earth sciences, and hence necessitates interdisciplinary collaboration that often includes, apart from biologists, meteorologists and geochemists.

 

Our research both examines natural processes and develops methods by which to measure them. A primary tool for elucidation of these processes is the analysis of natural abundance stable isotopes. Abiotic processes (e.g. precipitation and biomass burning) and biotic processes (e.g. photosynthesis and respiration) differentially affect the stable isotope abundance of atmospheric CO2, O2 and water. Hence, stable isotopes provide a tracer for biological activity from the scale of a chloroplast to the globe, and allow us to address questions of plant physiological ecology and climate on a variety of temporal and spatial scales. The analysis of stable isotopes both in atmospheric air and in plant material allows us to estimate plant and whole ecosystem responses to environmental change, partition terrestrial versus oceanic photosynthesis and assess changes in plant distribution and productivity over daily to geological timescales.

 

Some specific questions that motivate our research:

 

1) How do changes in abiotic inputs (e.g. CO2 concentration, precipitation, radiation) and the processes of photosynthesis and respiration affect the carbon and water cycles at whole plant to ecosystem scales?

 

2) How have changes in abiotic inputs affected plant ecology (distribution, competitive interactions) and evolution (selection for new photosynthetic pathways).

 

3) What are/were the selective forces behind the physiological and anatomical differences between C3 and C4 plants (particularly grasses)? How are these differences manifest in current and past distributions of C3 and C4 plants? How do intra-annual and inter-annual variations in C3 and C4 distribution affect carbon and water cycles?

 

4) What are the mechanistic explanations for observed differences in carbon and oxygen isotope signatures in plants? Can we use these observations and the underlying mechanisms to reconstruct plant and ecosystem responses to past climatic change?

 

5) Can we use measurements of CO2, H2O and their isotopes in the atmosphere to measure photosynthetic, respiratory and fossil fuel contributions to the global carbon cycle across a range of scales?

 

potential students

 

We are always looking for curious and motivated people to join us. If your interests broadly overlap the lab’s, then you are strongly encouraged to contact me and ultimately to apply.

 

Selected Publications: 

 

Out of 33 total:

 

Please contact me for reprints or questions concerning any of these publications.

 

Wiley E, Helliker BR. A re-evaluation of carbon storage in trees lends greater support for carbon limitation to growth. New Phytologist. In press.

 

Casper BB, Goldman R, Ariuntsetseg L, Helliker BR, Plante AF, Spence LA, Liancourt P, Boldgiv B, Petraitis PS. 2012. Legumes mitigate ecological consequences of a topographic gradient in a northern Mongolian steppe. Oecologia. In press.

 

Song X, Barbour MM, Saurer M, Helliker BR. 2011. Examining the large-scale convergence of photosynthesis-weighted tree-leaf temperatures through stable oxygen isotope analysis of multiple datasets. New Phytologist. 192: 912:924.

 

Helliker BR. 2011. On the controls of leaf-water δ18O in the atmospheric CAM epiphyte Tillandsia usneoides. Plant Physiology 155: 2096-2107

 

Aronson EL, Helliker BR. 2010. Methane flux in non-wetland soils in response to nitrogen addition: a meta-analysis. Ecology 91:3242-3251.

 

Helliker BR, Richter SL. 2008. Subtropical to Boreal convergence of tree-leaf temperatures: an isotopic analysis. Nature 454:511-514. With News and Views article by IF Woodward.

 

Helliker BR, Griffiths H. 2007. Towards a plant-based proxy for the isotope ratio of atmospheric water vapor. Global Change Biology. 13:723-733. doi: 10.1111/j.1365-2486.2006.01365-2486.2006.01325.x

 

Helliker BR, Berry JA, Betts AK, Davis K, Miller J, Denning AS, Bakwin P, Ehleringer J, Butler MP, Ricciuto D. 2004. Estimates of net CO2 flux by application of equilibrium boundary layer concepts to CO2 and water vapor measurements from a tall tower. Journal of Geophysical Research- Atmospheres, 109, D20106 10.1029/2004JD004532

 

Helliker BR, Ehleringer JR. 2002. Grass blades as tree rings: environmentally induced changes in the oxygen isotope ratio of cellulose along the length of grass blades. New Phytologist 155: 417.

 

Helliker BR, Ehleringer JR. 2000. Establishing a grassland signature in veins: 18O in the leaf water of C3 and C4 grasses. Proceedings of the National Academy of Sciences (USA) 97: 7894-7898.

 

Ehleringer JR, Cerling TE, Helliker BR. 1997. C4 photosynthesis, atmospheric CO2, and climate. Oecologia 112: 285-299.