Assistant Professor

Ph. D., Cornell University, 2005
Post-doctoral Research: Duke University, 2005-2007

Program Affiliation: Evolution, Ecology and Behavior |Microbiology | Plant Biology

Research Groups Affiliation: Ecology | Microbiology | Plant Biology

Phone: 812/855-xxxx
Fax: 812/855-6705
Email Rich

Arriving Spring 2008

My research broadly seeks to quantify and better understand how plants and soil microbes influence biogeochemical cycling in terrestrial ecosystems in the wake of human-accelerated environmental change.  Of particular interest is the degree to which root-microbial interactions in forest soils influence feedbacks to regional and global change through their effects on ecosystem carbon (C) storage and nitrogen (N) and phosphorus (P) retention. 

Most belowground processes are poorly understood owing to difficulties of quantifying spatially heterogeneous and temporally dynamic processes.  I use a complimentary suite of approaches that integrate field observations with novel techniques (e.g. stable and radioactive isotopes) and controlled environmental systems (e.g. growth chambers, FACE sites) to address questions that intersect plant physiological ecology and soil microbial ecology in an ecosystem context. 

There are three broad themes to my research:

Coupling of plant and microbial productivity.  In terrestrial ecosystems, plants and soil microbes are highly interdependent as plants rely on microbes to transform nutrients to an “available” form, and microbes rely on plants to provide reduced C for metabolism.  Despite the apparent simplicity of the interaction, there are significant gaps in our understanding of factors that mediate the coupling of C and nutrient cycles.  It is often assumed leaf litter quality controls nutrients availability in soils.  However, plants also release appreciable amounts of C from roots via exudation, cell sloughing, and root turnover, and root exudates may have a disproportionate effect on nutrient availability if they are pulsed to soil continuously, and stimulate microbial transformations of nutrients in the zone of soil adjacent to roots (i.e. the rhizosphere).  A theme of my research is to better understand the role of roots in influencing the coupling of plant and microbial productivity through their effects on nutrient cycling.  Some key questions include:

• How do rhizosphere C fluxes vary in space and time? 
• How does the chemical composition of exudates affect the availability of N to plants? 
• How much plant N is acquired through this mechanism? 

Species effects on nutrient cycling.  A fundamental question in ecology is the role of species in influencing ecosystem processes.  This question has become increasingly important given the loss of species, increases in non-indigenous species, and predicted shifts in the distribution and abundance of species owing to global climate change.  In forests, most research has focused on tree species effects on ecosystem processes through differences in aboveground traits, with little consideration of species differences in belowground C allocation and nutrient acquisition strategies.  Most C allocated belowground is used to support root growth, but a large portion of C is also allocated to mycorrhizal fungi and released to soil as root exudates.  My research seeks to improve upon our understanding of species effects on nutrient cycling by examining differences in belowground C allocation and nutrient acquisition strategies among tree species, with a focus on root-induced alterations of rhizosphere bacteria and fungi.  Some key questions include:

• How do tree species vary in their proportional allocation of C? 
• Are there fundamental differences in allocation and acquisition strategies between tree species colonized by arbuscular mycorrhizal and ectomycorrhizal fungi? 
• What are the consequences of such differences for the cycling of N, P, and base cations?

Plant-soil-microbial feedbacks to global change.  Interactions between plants, soils, and microbes mediate the flow of energy and nutrients through ecosystems with the potential to feed-back to primary production through effects on C sequestration in biomass and soils.  This has led to speculation that terrestrial ecosystems – particularly forests – may mitigate elevated levels of atmospheric CO2 through increases in productivity.  However, the persistence of forests as C sinks over the long-term will likely depend on the degree to which trees increase access to soil N. 
A broad theme of my research is to quantify the degree to which plant-soil-microbial interactions mediate ecosystem-responses to global environmental change.  Some key questions include: 

• What are the mechanisms by which trees increase access to soil N and delay the onset of progressive N limitation? 
• How do other global change factors (e.g. atmospheric ozone, N deposition, persistent drought, etc) affect plant-microbial interactions and influence these feedbacks?

Phillips, R.P. and T.J. Fahey.  2008. Fertilization suppresses rhizosphere effects in northern hardwood forest soils.  Soil Science Society of America Journal 72: 453-461.

Phillips, R.P. and T.J. Fahey.  2007.  Fertilization effects on fine root biomass, rhizosphere microbes and respiratory fluxes in hardwood forest soils.  New Phytologist 176: 655-664

Phillips, R.P.  2007.  Towards a rhizo-centric view of plant-microbial feedbacks under elevated atmospheric CO2.  New Phytologist 173: 664-667

Phillips, R.P. and T.J. Fahey.  2006.  Tree species and mycorrhizal associations influence the magnitude of rhizosphere effects. Ecology 87: 1302-1313

Phillips, R.P. and T.J. Fahey.  2005.  Patterns of rhizosphere C flux in sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) saplings. Global Change Biology 11: 983-995.

Yanai, R.D. Phillips, R.P., Arthur, M.A., Siccama, T.G. and E.N. Hane.  2005.  Spatial and temporal variation in calcium and aluminum in northern hardwood forest floors.  Water, Air, and Soil Pollution 160: 109-118.

Phillips, R.P. and R.D. Yanai. 2004.  The effects of AlCl3 additions on rhizosphere soil and fine root chemistry of sugar maple (Acer saccharum). Water, Air, and Soil Pollution 159: 339-356.