Jillian Gregg

Oregon State University | OSU · Sustainability Double Degree Program

Globally, soils store two to three times as much carbon as currently resides in the atmosphere, and it is critical to understand how soil greenhouse gas (GHG) emissions and uptake will respond to ongoing climate change. In particular, the soil-toatmosphere CO2 flux, commonly though imprecisely termed soil respiration (RS), is one of the largest car...

The response of soil organic carbon (SOC) to increasing temperature is a critical and uncertain component of terrestrial ecosystems feedbacks to climate. To investigate warming impacts on soil and whole-ecosystem carbon cycling, we conducted a whole-ecosystem warming experiment in grassland mesocosms in Oregon, USA, with diurnal temperature profile...

potential impact of projected climate warming on the terrestrial hydrologic cycle is uncertain. This problem has evaded experimentalists due to the overwhelming challenge of measuring the entire water budget and introducing experimental warming treatments in open environmental systems. We present new data from a mesocosm experiment that examined th...

A critical challenge for ecohydrologists is to improve our knowledge of how the hydrologic cycle will respond to environmental stimuli such as climate warming. In particular, we have an incomplete understanding of how climate warming may impact the partitioning of annual precipitation to evapotranspiration (ET) and groundwater recharge (R). This pr...

Daily minimum temperature (Tmin) has increased faster than daily maximum temperature (Tmax) in many parts of the world, leading to decreases in diurnal temperature range (DTR). Projections suggest that these trends are likely to continue in many regions, particularly in northern latitudes and in arid regions. Despite wide speculation that asymmetri...

There has been considerable variation in the magnitude of change in diel temperature range due to on-going global warming and ecological responses are poorly understood. We compared the effects of +3.5C higher temperatures distributed either symmetrically (SYM, continuously +3.5C) or asymmetrically (ASYM, +5C dawn Tmin ramped to +2C midday Tmax and...

Global mean temperatures have increased 0.10 to 0.16°C per decade over the last 50 years, and continued increases in atmospheric greenhouse gas concentrations are expected to cause temperatures to increase by more than 3°C by the middle of the 21st century. While many warming experiments have been performed, most have determined impacts of equal in...

Canopies of adult European beech (Fagus sylvatica) and Norway spruce (Picea abies) were labeled with CO(2) depleted in (13)C to evaluate carbon allocation belowground. One-half the trees were exposed to elevated O(3) for 6 yrs prior to and during the experiment. Soil-gas sampling wells were placed at 8 and 15 cm and soil CO(2) was sampled during la...

Although extensive research has determined ecosystem responses to equal increases in day and night temperatures, current temperature increases have generally been asymmetrical, with increases in minimum temperature (Tmin) exceeding increases in maximum temperature (Tmax), or vice versa, depending on location. We conducted an ecosystem warming exper...

Previously we found that cloned cottonwood saplings (Populus deltoides) grew twice as large in New York, New York, USA, compared to surrounding rural environments and that soils, temperature, CO2, nutrient deposition, and microclimatic variables could not account for the greater urban plant biomass. Correlations between final season biomass and cum...

Stable isotope mixing models are often used to quantify source contributions to a mixture. Examples include pollution source identification; trophic web studies; analysis of water sources for soils, plants; or water bodies, and many others. A common problem is having too many sources to allow a unique solution. We discuss two alternative procedures...

Ozone concentrations in the Los Angeles (LA) basin were at historic highs in the late 1970s. Since that time Clean Air regulations have helped lower ozone, but little is known of the long-term vegetation responses. Extensive research has used tree-ring indices together with the physiological and environmental information stored in the delta 18C and...

Plants in urban ecosystems are exposed to many pollutants and higher temperatures, CO2 and nitrogen deposition than plants in rural areas. Although each factor has a detrimental or beneficial influence on plant growth, the net effect of all factors and the key driving variables are unknown. We grew the same cottonwood clone in urban and rural sites...

Stable isotopes are increasingly being used as tracers in environmental studies. One application is to use isotopic ratios to quantitatively determine the proportional contribution of several sources to a mixture, such as the proportion of various pollution sources in a waste stream. In general, the proportional contributions of n+1 different sourc...

The magnitude of hydraulic redistribution of soil water by roots and its impact on soil water balance were estimated by monitoring time courses of soil water status at multiple depths and root sap flow under drought conditions in a dry ponderosa pine (Pinus ponderosa Dougl. ex Laws) ecosystem and in a moist Douglas-fir (Pseudotsuga menziesii (Mirb....

Models of photosynthesis, respiration, and export predict that foliar labile carbon (C) should increase with elevated CO2 but decrease with elevated temperature. Sugars, starch, and protein can be compared between treatments, but these compounds make up only a fraction of the total labile pool. Moreover, it is difficult to assess the turnover of la...

The objective of this study was to determine if the O_3sensitivity of Phaseolus vulgaris L. changed with plant development. Plants exposed to charcoal-filtered air or elevated O_3 throughout the study were compared to those exposed only during the vegetative or reproductive stages. Effects of pod development on O_3 sensitivity were also examined by...

Stable isotopes have become an important tool for determining the relative importance of CO2 sources and sinks contributing to the global carbon budget. Of particular importance is estimating the terrestrial CO2 flux which is difficult to decipher without determining the relative importance of autotrophic and heterotrophic respiration from below-gr...

Stable isotope analyses are often used to quantify the contribution of multiple sources to a mixture, such as proportions of food sources in an animal's diet, or C3 and C4 plant inputs to soil organic carbon. Linear mixing models can be used to partition two sources with a single isotopic signature (e.g., δ(13)C) or three sources with a second isot...

Energy, economics, and the environment are interdependent. Land, water, atmospheric, and biological resources are being degraded by current high energy consumption. U.S. energy consumption is the highest in the world and the U.S. Department of Energy reports that the United States has only about 10 years of known and potentially discoverable oil re...