A5051626936- Plant Water Relations and Carbon Dynamics
- Atmospheric and Environmental Gas Dynamics
- Peatlands and Wetlands Ecology
- Climate variability and models
- Plant responses to elevated CO2
- Remote Sensing in Agriculture
- Tree-ring climate responses
- Coastal wetland ecosystem dynamics
- Fire effects on ecosystems
- Botany and Plant Ecology Studies
- Climate change and permafrost
- Geology and Paleoclimatology Research
- Isotope Analysis in Ecology
- Hydrology and Watershed Management Studies
- Soil Carbon and Nitrogen Dynamics
- Plant responses to water stress
- Methane Hydrates and Related Phenomena
- Groundwater and Isotope Geochemistry
- Hydrology and Sediment Transport Processes
- Forest ecology and management
- Ecology and Vegetation Dynamics Studies
- Lichen and fungal ecology
- Remote Sensing and LiDAR Applications
- Plant Stress Responses and Tolerance
- Species Distribution and Climate Change
University of Lethbridge
2014-2023
Institute for Biological Sciences
2005-2010
University of Utah
1989-2002
University of South Florida
1998
Carleton University
1991-1997
Carleton College
1997
University of Toronto
1985-1989
Harvard University
1988
McGill University
1988
Bellevue Hospital Center
1988
Analyses of carbon isotope ratios (δ13C) in soil organic matter (SOM) and respired CO2 provide insights into dynamics the cycle. δ13C analyses do not direct measures efflux rates but are useful as a constraint cycle models. In many cases, allow identification components well relative contribution to overall ecosystem fluxes. values unique tool for quantifying historical shifts between C3 C4 ecosystems over decadal millennial time scales, which relevant climate change land-use issues. We...
Photosynthesis and respiration impart distinct isotopic signatures to the atmosphere that are used constrain global carbon source/sink estimates partition ecosystem fluxes. Increasingly, “Keeling plot” method is being determine isotope composition of (δ 13 C R ) in order better understand processes controlling discrimination. In this paper we synthesize emergent patterns δ by analyzing 146 Keeling plots constructed at 33 sites across North South America. interpret results from disparate...
The Moderate Resolution Spectroradiometer (MODIS) sensor has provided near real-time estimates of gross primary production (GPP) since March 2000. We compare four years (2000 to 2003) satellite-based calculations GPP with tower eddy CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> flux-based across diverse land cover types and climate regimes. examine the potential error contributions from meteorology, leaf area index (LAI)/fPAR,...
Abstract Net ecosystem carbon dioxide (CO 2 ) exchange (NEE) was measured in a northern temperate grassland near Lethbridge, Alberta, Canada for three growing seasons using the eddy covariance technique. The study objectives were to document how NEE and its major component processes—gross photosynthesis (GPP) total respiration (TER)—vary seasonally interannually, examine environmental physiological factors influence annual C budget. greatest difference among years amount of precipitation...
In this paper we describe how a model of stable isotope fractionation processes, originally developed by H. Craig and L. I. Gordon ([1965] in E Tongiorgi, ed, Proceedings Conference on Stable Isotopes Oceanographic Studies Paleotemperature, Spoleto, Italy, pp 9-130) for evaporation water from the ocean, can be applied to leaf transpiration. The original was modified account turbulent conditions boundary layer. Experiments were conducted test factors influencing isotopic composition under...
Carbon flux models based on light use efficiency (LUE), such as the MOD17 algorithm, have proved difficult to parameterize because of uncertainties in LUE term, which is usually estimated from meteorological variables available only at large spatial scales. In search simpler entirely remote‐sensing data, we examined direct relationships between enhanced vegetation index (EVI) and gross primary productivity (GPP) measured nine eddy covariance tower sites across North America. When data winter...
Significance Terrestrial gross primary productivity (GPP), the total photosynthetic CO 2 fixation at ecosystem level, fuels all life on land. However, its spatiotemporal variability is poorly understood, because GPP determined by many processes related to plant phenology and physiological activities. In this study, we find that phenological properties can be integrated in a robust index—the product of length uptake period seasonal maximal photosynthesis—to explain over space time response...
Our current understanding of terrestrial carbon processes is represented in various models used to integrate and scale measurements CO 2 exchange from remote sensing other spatiotemporal data. Yet assessments are rarely conducted determine how well simulate across vegetation types environmental conditions. Using standardized data the North American Carbon Program we compare observed simulated monthly 44 eddy covariance flux towers America 22 biosphere models. The analysis period spans ∼220...
Abstract Many wetland ecosystems such as peatlands and wet tundra hold large amounts of organic carbon (C) in their soils, are thus important the terrestrial C cycle. We have synthesized data on dioxide (CO 2 ) exchange obtained from eddy covariance measurements 12 sites, covering 1–7 years at each site, across Europe North America, ranging ombrotrophic minerotrophic to ecosystems, spanning temperate arctic climate zones. The average summertime net ecosystem CO (NEE) was highly variable...
Significance Wetlands are unique ecosystems because they in general sinks for carbon dioxide and sources of methane. Their climate footprint therefore depends on the relative sign magnitude land–atmosphere exchange these two major greenhouse gases. This work presents a synthesis simultaneous measurements methane fluxes to assess radiative forcing natural wetlands converted agricultural or forested land. The net impact is strongly dependent whether managed. Here we show that conversion...
Abstract Comparisons were made among Douglas‐fir forest, aspen (broad leaf deciduous) forest and wheatgrass (C 3 ) grassland for ecosystem‐level water‐use efficiency (WUE). WUE was defined as the ratio of photosynthetic CO 2 assimilation rate evapotranspiration (ET) rate. The ET data measured by eddy covariance screened so that they overwhelmingly represented transpiration. three sites used in this comparison spanned a range vegetation (plant functional) types environmental conditions within...
ABSTRACT Measurements of the ratio deuterium to hydrogen (D/H) in stem xylem water were used determine relative uptake summer precipitation by four co‐occurring plant species southern Utah. The compared included two trees, Juniperus osteosperma and Pinus edulis , shrubs, Artemisia tridentata Chrysothamnus nauseousus. There significant differences among use precipitation. nauseosus had D/H ratios May through August 1990 that not significantly different from groundwater. In contrast, other...
Much of the past research in plant physiological ecology has focused on gas-exchange responses individual leaves (Pearcy et al., 1987). There been great progress developing models that link leaf biochemical properties with characteristics (Farquhar & von Caemmerer, 1982). Success also come understanding basis for ecological differentiation plants C3, C4 and CAM photosynthetic pathways (Osmond, Winter Ziegler, It recognized, however, further linking leaf-level, instantaneous to longer-term...
In presence of vegetation, the CO 2 –C produced by respiration activity in soils originates from plant C (rhizosphere respiration, R rh ) and soil (soil s ). Quantitative estimates each source are required many studies dynamics soil–plant system. this study, we (i) used measurements 13 value to separate total ( t into subcomponents a maize Zea mays L.) field under undisturbed conditions (ii) compared these with values obtained using root‐exclusion approach. The maximum contribution was 45%,...