Increasing atmospheric CO₂ will likely affect both the hydrologic cycle and ecosystem productivity. Current assumptions that increasing CO₂ will lead to increased ecosystem productivity and plant water use efficiency (WUE) are driving optimistic predictions of higher crop yields as well as greater availability of freshwater resources due to a decrease in evapotranspiration.

The Sevilleta LTER is located at the intersection of several aridland ecosystem types. Although it is axiomatic that water is the key limiting resource in aridland ecosystems, most arid land soils are also chronically low in nutrients and organic matter. Resource availability is a function of the frequency and size of precipitation events as well as the time between events. As a consequence, NPP and organic matter decomposition are often decoupled in space and time, and soil nutrient supply rates may limit NPP during periods when soil moisture is sufficient for plant growth.

If long-term responses of plant photosynthesis to rising atmospheric carbon dioxide (CO₂) levels are similar or predictably different among species, functional types, and ecosystem types, general global models of CO₂ fertilization effects can effectively be developed. To address this issue we measured gas exchange rates of 13 perennial grassland species from four functional groups exposed to eleven years of long-term free-air CO₂ enrichment (eCO₂, +180 ppm above ambient CO₂, BioCON).

The goal of the Arctic LTER is to predict the future ecological characteristics of Arctic Alaska based upon our knowledge of the controls of ecosystem structure and function as exerted by physical setting and geologic factors, climatic factors, biotic factors, and the changes in fluxes of water and materials from land to water.

Drought-related tree mortality occurs worldwide, including recent episodes in piñon-juniper woodlands of the American west. Although the physiological mechanisms of mortality are poorly understood, carbon starvation may occur in trees that limit transpiration (E) to avoid hydraulic failure.

It has been hypothesized that the range limits of woody plants are determined by a trade-off between freezing tolerance and growth rate, such that species with high freezing tolerance have low growth rates. However, willows (genus Salix) appear to be an exception to this pattern as they have high growth rates and high freezing tolerance. To determine whether there is evidence for this trade-off in willows, I compared the growth and freezing tolerance of twenty-eight  willow species collected across North America.

The hydraulic architecture of parallel veined monocots is fundamentally different from the branched networks of dicot leaves. The functional significance of this difference on leaf level gas exchange is not well understood. In order to investigate how the hydraulic architecture of monocots affect gas exchange we measured the axial hydraulic conductivity and leaf level gas exchange from the base to tip of 7 grass species. Stomatal conductance (g_s) and photosynthesis (A) increased but hydraulic conductivity (K_h) declined along the length of the blade.

Barrier islands may represent an underestimated sink for atmospheric carbon because they combine potential for high above-ground primary productivity (ANPP) with young, infertile soils capable of sequestering significant amounts of carbon. Ecosystem ANPP on many barrier islands of the Virginia Coast Reserve (VCR) has been further enhanced by the rapid expansion of woody shrubs. Compared to adjacent grasslands, shrubs in coastal systems combine high leaf area index with high photosynthetic rates.

Due to fragmentation, where there were once contiguous populations of grasslands, core and edge populations remain, often times separated by large distances and located in different climates. Previous research has largely overlooked edge populations and focused on dominant species in core populations. The purpose of this study is to compare core and edge populations of two dominant C4 grasses, Bouteloua gracilis and Andropogon gerardii, in a reciprocal transplant experiment.

Konza prairie contains over 550 vascular plant species, of which, only a few have been closely studied. Predicted impacts of climate change on the tallgrass prairie region increase the importance of understanding how native tallgrass prairie species are likely to respond to future changes in water availability and increased air temperatures. Understanding which traits are the best predictors of relative abundance along a continuum of water availability (well watered to water stressed) will aid in the prediction of plant community structure under altered temperature-precipitation regimes.