Uma J Nagendra
Research
Overview
My research focuses on the impacts of wind disturbances on plant-soil interactions. I use a combination of greenhouse and field experiments to investigate how tornadoes can change not only *what* plants grow in an area, but also *how* they interact with each other-- through the soil. This research will contribute to our knowledge of plant-soil feedbacks by adding a field-based non-equilibrium view. As strong disturbances become more frequent, it becomes more important for us to examine how ecological processes respond to abrupt environmental changes.
For a short and simple explanation of what I do and why, see my three minute thesis video!
(voted "best graduate student entry" for the UGA Plant Biology competition)
Projects
Do disturbances change plant-soil feedbacks?
Blowdown gaps favor early successional microbial communities which are often not specialized to one plant species. Strong feedbacks are more likely to occur with species-specific plant-microbial interactions. In addition, the documented decrease in pathogen loading in windblown plots could possibly release previously pathogen-limited seedlings. I proposed that plant-soil feedbacks will be weaker (more neutral) in windblown plots than in intact forest plots.
In Spring/Summer 2012, I conducted a greenhouse experiment to examine the direct impacts of post-disturbance soil changes to plant-soil feedbacks. I grew seedlings of three species in soil collected from the base of mature trees in either wind-damaged forest, or nearby intact forests.
Although black gum (Nyssa sylvatica) and white oak (Quercus alba) both showed significant changes in their plant-soil feedbacks after wind damage, their feedbacks changed in different directions.
How does the post-disturbance environment affect plant-soil feedbacks?
Tornadoes and other disturbances cause sudden, substantial changes to the forest environment-- namely, increasing canopy openness and solar radation. Plant-soil feedbacks are notoriously context-dependent. In addition to directly changing soil biotic communtites, tornadoes may also cause indirect effects on plant-soil feedbacks by changing the environmental context. In order to tease apart the effects of soil changes and the effects of the light environment, I am conducting a field-based soil transplant experiment in North Georgia. Soil transplants allow me to isolate the effect of soil changes from the other major environmental changes after a tornado.
How do disturbances affect soil parameters?
Natural disturbances temporarily alter ecosystem characteristics, causing shifts in key ecological processes. Changes to rates of decomposition, respiration, and production affect carbon and nutrient cycling. How long these changes persist is not understood. Characterizing the magnitude and duration of post-disturbance changes is important for global carbon models as well as our understanding of ecosystem ecology.
We are monitoring soil temperature, moisture, and respiration in our north Georgia field site in order to understand changes to a few components of the carbon cycle. Undergraduate helpers are also working on leaf litter fall and decomposition.
Although we expected soil temperature, moisture, and respiration to scale with plot disturbance severity, so far none of these parameters have shown a consistent response to disturbance. Altogether, the data suggest potentially rapid ecosystem recovery after these types of wind disturbances, indicating that certain ecosystem processes may be more resilient to disturbances than previously thought.