Jed Sparks
Research
The exchange of compounds at the boundary between the atmosphere and terrestrial ecosystems has profound and controlling effects on plant ecophysiology, ecosystem function and the chemical composition of both the biosphere and atmosphere. Further, the magnitudes of the fluxes between the earth and the atmosphere often control the pool sizes of important elements and compounds held in each, the balance of which are intrinsic to the maintenance of life on earth (e.g., carbon dioxide, nitrogen, ozone and other oxidants, and many others). For example, fluxes of various reactive trace gases between terrestrial ecosystems and the atmosphere exert significant influences on plant performance, tropospheric photochemistry, terrestrial biogeochemistry and the maintenance of clean air, water and soil. The study of fluxes between the biosphere and atmosphere requires skills in plant ecophysiology, with its emphasis on the mechanistic controls over flux; biogeochemistry, with its emphasis on the mass balance of biogeochemical cycles; and atmospheric chemistry, with its emphasis on the reactivity and control over turnover times of various atmospheric constituents. My research program at Cornell University focuses on the plant and soil-mediated exchange of compounds at the Earths surface with special emphasis on plant and soil based mechanisms of transfer.
Reactive gas-phase nitrogen compounds [NOy = NO, NO2, peroxyacetyl nitrate (PAN), HONO, HNO3-, N2O5 and various organic nitrates] are present in the atmosphere from both natural processes (soil driven processes and lightning) and industrial sources. In my own research, I am interested in the ecological importance of the interaction between reactive oxidized nitrogen and vegetation at scales from single genes to ecosystem level fluxes. This multiple scale approach is appropriate because the overall effect of reactive nitrogen is very much scale dependent (e.g., a beneficial fertilization effect observed at the leaf level may be offset by changes in litter quality at the ecosystem scale or changes in the oxidative chemistry of the atmosphere at the regional scale). Reactive oxidized nitrogen compounds are of particular interest for three reasons. At high concentrations reactive oxidized nitrogens are known to be phytotoxic to plants causing necrosis, decreased photosynthetic rates and reductions in growth. Interestingly, at lower concentrations reactive oxidized nitrogen compounds have been shown to act as an atmospheric fertilizer increasing plant growth in some cases. Therefore, understanding the basic interactions between vegetation and reactive oxidized nitrogen is of great importance to understanding basic plant ecophysiology.
Further, the input of reactive gaseous nitrogen directly to plants through foliar uptake is a pathway not normally considered in ecosystem nitrogen cycling. Multiple studies have addressed the ramifications of increased nitrogen inputs to ecosystems, but most have been limited to consideration of wet deposition of nitrate or ammonium to the soil system. Additionally, most of the data available for atmospheric nitrogen deposition has been obtained via networks where wet deposition is collected in buckets placed in open areas. Therefore, few studies of nitrogen deposition have considered the role of direct foliar uptake, and no studies have yet been undertaken to fully evaluate the speciation of deposited nitrogen. Additionally, the long-term indirect ramifications of direct foliar uptake of nitrogen on other aspects of ecosystem function, particularly carbon cycling, has yet to be fully explored.
Finally, nitrogen oxides (NOx) play a central role in controlling the oxidative chemistry of the lower atmosphere-by catalyzing the formation of ozone and therefore influencing the total radical level in the atmosphere. This, in part, regulates the atmospheric concentrations of nitric acid and organic nitrates. Transformations of NOx into other forms of oxidized nitrogen compounds affect the rate at which ozone and other oxidants are produced. Current atmospheric chemistry models utilize measured soil, industrial and agricultural NO emission rates as a primary input and assume that photochemical transformations of NO to the other components of NOy occurs well above the influence from plant canopies. This practice ignores the possibility that plants can affect local photochemistry by assimilating, emitting or transforming certain forms of NOy. Past studies from tropical forests in Brazil and Panama suggest that 30 - 60% of the soil-emitted NO can be transformed and assimilated by the overlying canopy. Therefore, understanding the interactions between NOy compounds and vegetation is of great importance to regional and global atmospheric chemistry.
Courses Taught
BioEE 3610 Advanced Ecology
BioEE 4660 Physiological Plant Ecology
BioEE 4661 Physiological Plant Ecology Laboratory
BioEE 6601 Tropical Field Ecology
BioEE 6602 Graduate Field Course in Ecology
