Research Interests - John V.H. Constable

General Interests.  My research interests center on understanding how physiological processes of plants are affected by variations in resource availability (e.g., light. CO₂, nutrients) due both natural variability and those attributed to anthropogenic effects.  An understanding of how plants respond and integrate limitations and excesses of resources provides essential data for predicting future plant productivity and reproduction.  My research centers on acquisition of carbon (C) and nitrogen (N) and how the allocation and partitioning of these resources is affected by changes in climate.

Past Work.  Over the last several years I have worked on examining the impact of elevated CO₂ on plant processes and how increased C availability influences growth and the demand for other resources.  Elevated CO₂ conditions can occur naturally in many species, especially wetland plants such as cattail where CO₂ that diffuses internally from the sediments can serve as an important source of carbon (Figure 1) to support plant growth. However, the accumulation of CO₂ and pollutants in the atmosphere as the result of anthropogenic activities results in a complex series of physiological changes and ecological cascades making the effects on plants and ecosystems difficult to predict.  I have used modeling to examine how ponderosa pine (Pinus ponderosa L.) may respond to climate change and how their genetic differences between eastern (Rocky Mountains) and western (Sierra Nevada Mountains) varieties affects their response to tropospheric ozone. Additional studies have examined the monoterpene concentration and emission response of conifers to elevated CO₂ and other aspects of climate change at the single plant single (Figure 2) and continental scales (Figure 3). Currently, I am seeking to develop a better understanding of how growth at elevated CO₂ influences the uptake and assimilation of N, specifically nitrate (NO₃^-) comparing controlled small scale experiments (Figure 4) with large scale Free Atmosphere CO₂ Enrichment experiments (Figure 5 and Figure 6

Current Research.  Ongoing research in my laboratory addresses several direction mediated by my own interests and those of students within the lab.  Current interests and studies are outlined below

How tree carbon and nitrogen balance in the eastern hemlock (Tsuga canadensis) affect, and are affected by, the introduced pest the Hemlock Wooly Adelgid (HWA).  And why the western hemlock (Tsuga heterophylla) is resistant to HWA (Figure 7).

How photosynthetic and other physiological characteristics of the single leaf of Podophyllum peltatum changes during the seasonal transition from a high light to a low light environment (Figure 8).

Environmental influences on the induction and progression of senescence in Podophyllum peltatum (Figure 9)

Differential canopy carbon gain by leaves of different ages or positions as affected by variation in seasonal water availability.

Seasonal pattern of resource use and flood and drought tolerance by endemic vernal pool species

If these areas, or other aspects of plant environment interactions, interest you or you are interested in possible research opportunities in my laboratory please call or visit my office.