What causes compositional change in freshwater plant communities? This central ecological question motivates experimental and descriptive inquiry in my lab, the Binghamton University research greenhouse, and in situ at organismal, population, and community levels.

     My students and I have concentrated for several years on the effects of lake acidification on underwater plants as we seek to understand why lakes of low pH tend to have different aquatic vegetation from lakes of high pH, and why different low pH lakes can also vary substantially from each other in their vegetation composition. Our experimental work has shown less plant growth (Grisé, Titus and Wagner 1986) and reproduction (Titus and Hoover 1993) at low pH.We have also learned, however, that the sensitivity of some species to low pH can be overcome with CO2 enrichment (Titus et al. 1990). This finding has shifted our focus to the ramifications of CO2 concentration ("[CO2]"), which we have found to vary several-fold among acidic lakes of the Adirondack Mountains (Titus et al. 1990, Pagano and Titus, unpublished data). Despite rapid photosynthetic down-regulation (Titus and Lawlis, manuscript in preparation), high [CO2] promotes growth and reproduction at low pH, and the accumulation of mineral nutrients by plants grown on diverse natural lake sediments (Titus 1992, Titus and Andorfer 1996). One result of this greater accumulation is that, in freshwater habitats characterized by high [CO2], aquatic plants release more key nutrients into lake water as they decay (Titus and Pagano 2002), thus potentially influencing water quality.

     We have learned recently that some freshwater plant species are not sensitive to CO2 enrichment(Pagano and Titus, manuscript in preparation), leading to our working hypothesis that low [CO2] favors species not sensitive to [CO2], and high [CO2] favors species responsive to CO2 enrichment.We are testing this hypothesis through a combination of greenhouse experiments determining the sensitivity of a wide range of plant species from Adirondack Mountain lakes and ponds to CO2 enrichment, and field studies (also in the Adirondacks) of CO2 availability and aquatic vegetation (determined by SCUBA diving). This research is currently sponsored by the National Science Foundation, which has provided partial support for a number of graduate students.

     CO2 concentration also can have other effects. For example, it can affect plant morphology: high [CO2] favors the development of underwater vs. floating leaves in heterophyllous water lilies (Titus and Sullivan 2001) . High [CO2], however, does not seem to influence aquatic plant decay rates, despite effecting a dramatic reduction in plant tissue quality (Titus and Pagano, 2002) .

We have pursued other endeavors not closely related to acidification or [CO2] issues: field studieshave revealed that both depth and patterns of water flow may limit successful pollination (Sullivan and Titus 1996), and that natural aquatic vegetation is not only extremely heterogeneous spatially (Carpenter and Titus 1984), but is also temporally dynamic even in the absence of pronounced environmental change (Titus, Grisé, Sullivan, and Stephens, manuscript in preparation). The vegetation has also changed remarkably in a softwater Adirondack Mountain lake with the invasion of an aggressive carnivorous plant species (Titus, manuscript in preparation).

     Wetlandecology isonce again loominglarger in myresearch program, following ahiatus of many years after an early project on Sphagnum ecology (e.g.,Titus and Wagner 1984). Jenny Kao recently completed her M.S. thesis, in which she showed that different wetland plant species vary substantially in their abilities to accumulate and retain nitrogen and phosphorus in a field site interposed between a dairy farm and a stream. I anticipate more projects on the effects of wetlands and underwater plant communities on water quality as joint projects develop with other members of the Rivers and Watersheds group -- comprised of environmental scientists from several disciplines here at Binghamton University. Finally, I have also initiated projects on forest succession and on the restoration of native spring wildflowers.

     Overall, my research program is comprised of a mix of physiological, population, and community ecology. My students and I rely on a host of techniques: pH drift and gas analysis to measure bicarbonate use and photosynthesis, pH-, [CO2]-, and temperature-controlled greenhouse tanks to measure growth under a wide range of conditions, transplants in situ to determine growth rates in natural lakes , standard measures of the abiotic environment (e.g., quantum sensors to measure water transparency, infrared gas analysis to measure CO2 availability, equilibrators and spectroscopy and/or an autoanalyzer to determine sediment nutrient availability...), plant digestion and analysis to determine plant tissue composition, SCUBA diving to quantify aquatic vegetation, and statistical tests ranging from linear regressions to multivariate analyses to help us interpret our diverse data sets.