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.

Recent ¹⁵N tracing studies have highlighted the important role biotic assimilation plays in stream N retention, yet the fate of N following assimilation is not well understood. One potentially important fate is indirect denitrification, a process in which locally mineralized and nitrified N is denitrified before being exported to the water column. We conducted a series of in-situ chamber experiments in which patches of stream bottom were labeled with ¹⁵N to investigate the fate of assimilated N.

The Chronic Nitrogen Addition Experiment at the Harvard Forest was initiated in 1988 to better understand the process of forest N saturation due to anthropogenic N deposition. Presently, there is great interest in understanding and quantifying impacts of deliberate (forest fertilization) or inadvertent (atmospheric deposition) additions of nitrogen on forest growth as a means to enhance forest uptake of atmospheric C and subsequent storage within biomass and soil.

Denitrification is a key step returning nitrogen from soils to the atmosphere. The primary denitrifiers in most ecosystems are heterotrophic bacteria. Although, fungi are also known to transform nitrogen compounds, such as the production of N2O, but few studies have explored this process in soils. Aridland systems experience high temperatutres and low moisture conditions, favoring fungi in these environments. Thus, we explored the role of fungi and bacteria in denitrification of Sonoran Desert soils.

The California Current System is a coastal upwelling biome, as found along the eastern margins of all major ocean basins. These are among the more productive ecosystems in the world ocean. The California Current Ecosystem (CCE) LTER site (centered on 32.9° N, 120.3° W) is investigating nonlinear transitions in the California Current coastal pelagic ecosystem, with particular attention to long-term forcing by a secular warming trend, multi-decadal oscillations (e.g., PDO and NPGO), and ENSO in altering the structure and dynamics of the pelagic ecosystem.

Methane production in Siberian thaw lakes is estimated to be 3.8 Tg CH4 yr -1. When entered into global models, this estimate increases northern wetland CH4 emissions (<6-40 Tg CH4 yr -1) by 10-63% (Walter et al 2006). Methane release of this magnitude from Siberian and other northern lakes, such as those in Alaska, may be linked to the rich carbon resources available to sediment-dwelling methanogens.

Dynamic biogeochemical watershed models are the only practical approach that can predict concurrent exposure to multiple environmental factors and consider interactive effects between climate change, atmospheric deposition and CO2 fertilization effect. Therefore, they could be powerful tools to help to understand the long-term effects of climate change on ecosystems.

The Central Arizona–Phoenix Long-term Ecological Research (CAP LTER) project is based in the central Arizona and metropolitan Phoenix region, embedded in the Sonoran Desert. As the fifth-largest and, until recently, the fastest-growing city in the US, Phoenix is an excellent location for urban ecological research. Phoenix was established after the Civil War, initially one of several small towns surrounded by irrigated farmland. Continued agrarian expansion predated the explosive growth of housing in the second half of the 20th century.

Ecosystem processes in northern systems depend heavily on inputs of biologically fixed nitrogen (N) from A. tenuifolia, which contributes the majority of N accumulated during boreal forest succession. However because of the high phosphorus (P) demands of this plant, we hypothesize that N-fixation inputs are controlled by the ability of alder to assimilate P through associations with ectomycorrhizal fungi (EMF), which produce enzymes that mobilize organic and recalcitrant P forms.

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.