COLLABORATORSFACE: Emily Bernhardt, Duke University
Forests slow global climate change by absorbing and storing CO2, but the extent to which these ecosystems will persist as carbon sinks is unknown. We are currently investigating the mechanisms by which trees and soil microbes mediate carbon retention and loss in forests. Specifically, we’re testing the hypothesis that roots play a critical role in stimulating microbes to release nutrients from soil organic matter - a process that increases plant growth, alters long-term soil carbon storage, and potentially affects feedbacks to climate.
We’ve been adding microbial substrates to soils (in field plots) via a sustained, low-volume drip from an artificial root which we call a “rhizosphere simulator”. This technique permits us to alter the timing and chemistry of exudate inputs, and to quantify their effects on nutrient dynamics in ecosystems. We have conducted these studies in multiple sites, including a climate change manipulation, the Boston Area Climate Experiment. We’re using the results from these experiments to refine mathematical models of rhizosphere dynamics under changing climates.
Forest productivity is generally increased by increases in atmospheric CO2. However, the magnitude of this growth enhancement is strongly regulated by soil nutrient availability. We’ve been investigating how trees exposed to elevated CO2 make physiological adjustments to enhance nutrient scavenging and nutrient mining from soil. We’ve been conducting much of this research at the Duke Forest FACE site, where loblolly pine and understory hardwood trees were fumigated with exogenous CO2 (200 ppm in excess of ambient levels) for 15 years.