• My current research focus is on the biogeochemical cycling of mercury in response to different silvicultural practices aimed at restoring longleaf pine ecosystems. With undergraduate students, we are also examining how longleaf pine seedlings respond to various environmental stresses and what that means for restoring longleaf pine stands.  This team includes Martin Tsz-Ki Tsui, Alex Chow, Carl Tretting, Yener Ulus and me. Earlier in my career, I was part of a team that used the mass balance capability of the EcoCELLs to trace the flux of mercury demonstrating that most mercury enters the ecosystem through leaf fall and on direct atmospheric deposition to soils (with Mae Gustin and Steve Lindbergh).  You can see a narrated powerpoint of our May 2022 presentation "How does mercury methylation respond to intensive forest management and the creation of anoxia in floodplain soils?"  here:  https://uncg.box.com/s/m3j1mwdnd49xy0iykx5whruvf9o04eml
 
  • How leaf and plant development affect leaf biochemistry and susceptibility to insects and pathogens.  Using eastern cottonwood as a model system, we (Clive Jones, Bill Smith (Yale) and I) integrated the tremendous work of Phil Larson, Richard Dickson and Jud Isebrands who detailed the synchrony of form and function in eastern cottonwood seedlings, cuttings and trees, including mapping the vasculature system and clearly showing the physiological, biochemical and anatomical changes that occur as a leaf moves through it sink to source transition and then ages.  We used this basic understanding to demonstrate the ability of leaf beetles, caterpillars and aphids to track leaf development age, and we demonstrated how the strength of vascular connections between different leaves strongly influenced whether an undamaged leaf would induce defensive chemicals when another leaf was damaged.  We used  the knowledge of form and function relationships to examine whether environmental stress (using ozone as a model stress), changes plant chemistry and leaf development in such a way that it would change the susceptibility of plants to four different "pests" that feed in different ways and thus change the dynamics of the of insect and fungal pathogen community. We studied a leaf beetle that eats leaf tissue; an aphid that draws phloem fluid, a rust fungus which feeds from living cells, and a leaf spot fungus that only feed after cells have been killed. These data led Clive Jones and I to create what we called a "phytocentric perspective" of plant responses herbivores. I am currently revising a draft paper that describes a link between leaf development with patterns and phenology of leaf production in trees  (indeterminate vs. determinate) to life history and ecological traits of herbivores and pathogens in their community,  such as the likelihood of having insects with multiple generations/yr or those that experience boom or bust outbreaks. A paper that I wrote with an undergraduate at the time (A. Soren Leonard) demonstrated that there can be as much as 10-fold differences in the amount of leaf area missing from herbivory vs. the amount of leaf tissue eaten by herbivores.  Leaves develop by cells expanding, not the addition of new cells. So, if tissue from developing leaves is removed, the size of the hole will grow exponentially as the cells around the hole expand.  This does not occur in older, fully developed leaves.  To me, this was a very important finding about how leaf development process affect interpretations of missing leaf area. But, the plant-herbivore, net ecosystem productivity community has not found it very interesting.
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  • How plants allocate carbon and nutrients to roots, shoots, storage and reproduction in response to environmental stress, We (Kelly McConnaughay and I)  examined the importance of plant development and size dependency in interpreting whether adjustments in resource allocation (e.g., root:shoot ratio; N concentration in tissues) in plants to stressful environments follows the hypotheses of optimal partitioning, ontogenetic drift, or both. We tested whether data that supported optimal partitioning resulted from comparing traits of plants at a common age as opposed to at a common size.  Plants often develop as a function of their size, and not necessarily their age. Therefore, if one compares plant traits at a common time of a control vs. a stressed plant, then one will be measuring plants of different sizes because the control plant is likely to be bigger than the stressed plant. In such cases, any differences demonstrated in plant traits for plants of different sizes could be due to ontogenetic drift (the allometric relationships between different plant parts as a plant gets bigger), and not necessarily due to adaptive strategies of plants in response to stress.
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  • The role of low molecular weight heat shock proteins in protecting plants from heat stress and their evolutionary ecology. We (Scott Heckathorn, Craig Downs, and Tom Sharkey) were the first laboratory to demonstrate that low molecular weight chloroplast heat shock proteins protect photosystem II from heat stress. We started this work by examining the physiological cost to plants of making heat shock proteins, and whether that cost helps shape the pattern and amount of heat shock proteins produced by a single species within populations that are more or less adapted to experience acute heat stress. We also examined whether such differences correlated with the environment in which different species evolved.  We also demonstrated that there is resource cost (particularly N) to making low and high molecular weight heat shock proteins.
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  • How plants and ecosystems respond to rising carbon dioxide levels along with changing precipitation and deposition of nutrients and pollutants associated with climate change.  The Desert FACE (Free-air CO2 enrichment) site,  taught us (the main PIs were me, Stan Smith, Jeff Seemann, Bob Nowak, Jay Arnone, Yiqi Luo, Wexin Cheng, Paul Verburg, Dani Obrist, Tim Ball,  Dave Evans and Dale Johnson) a great deal about how elevated carbon dioxide affects photosynthesis,  ecosystem productivity, carbon cycling and carbon storage, invasive species, soil water and water use efficiency, and the role of the microbial crust that covers the desert floor. Laboratory experiments taught us a lot about closing the carbon cycle, the response of net ecosystem productivity over several years in response to one unusually warmer year, and the full carbon, nutrient and water fluxes and storage of ecosystems in response to elevated carbon dioxide using a nationally unique large mass balance mesocosm facility (EcoCELLs)  (https://www.youtube.com/watch?v=j_nYbGfU20c). The EcoCell work on the lagged response of soil respiration to an anomalously warm year was on the cover of Nature in 2008.

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