Just How Does Nitrogen Drive Change in Plant Communities?

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Nitrogen enrichment can dramatically change the existing environment for plants and typically leads to increased productivity, decresed diversity, and shifts plant community composition. But what mechanisms are responsible for these changes? Researchers designed a multi-site experiment to find out, experimentally manipulating each of three possible drivers across mesocosms of three ecosystem types (tall grass prairie, alpine tundra, and desert grassland).

Chronic Nitrogen Deposition Restructures Soil Fungal Communities

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New analyses demonstrate that long-term nitrogen enrichment substantially changes the community composition of soil fungi in a temperate hardwood forest. The mix of fungal taxa that emerges appears to be better able to tolerate high nitrogen but less able to break down the lignin in organic matter, which contributes to an overall accumulation of soil carbon.

Growing Grass: A Story of Nitrogen, Phosphorus, and Leaf Size

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Ecologists know that nitrogen, phosphorus and leaf area play key roles in the productivity of plant communities. But how tightly are they tied together? And are those relationships sustained over different types of landscapes? A recent study of tallgrass prairie communities, building on a previous study of arctic tundra, found leaf area index (LAI) to be strongly correlated to both total foliar nitrogen and total foliar phosphorus in several plant functional types (grass, forb, woody, and sedge) and grazing treatments (cattle, bison, and ungrazed).

Coastal Everglades in the Cold: Mapping Ecological Sensitivity

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How sensitive are coastal ecosystems to sharp changes in temperature? Using a detailed spatial analysis in the Florida Everglades, researchers found that cold snaps reduced ecosystem productivity most dramatically in areas with low water levels that were located away from the coast. With more extreme weather events predicted in the future, knowing the likely effects of low temperature events on subtropical wetlands systems can inform management of these important ecosystems.

Finding the Hidden Phytoplankton Blooms

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In stratified lakes, a large portion of phytoplankton biomass is found—not at the surface, where sampling is easiest—but somewhere down the water column, in what is known as a subsurface chlorophyll maximum (SSCM). Researchers in Global Lake Ecological Observatory Network (GLEON) compared automated high-frequency chlorophyll fluorescence (ChlF) profiles with surface samples and discrete depth profiles. In 7 of the 11 lakes studied, automated sampling captured the presence of SSCM’s that would have been missed by conventional sampling.

What (and when) is the point-of-no-return?

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How-and when-do ecosystems change character? Are those shifts reversible? And what signs might precede them? Such questions are hard enough to answer in a single place. One might think that incorporating different kinds of ecosystems would only complicate the problem. But a group of scientists in the Long-Term Ecological Research Network is finding a remarkably consistent pattern by combining models and data across several long-term ecological experiments.

Climate variability predicted to affect outcome of exotic grass invasion

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Novel ecosystems can emerge through many kinds of changes, including changes in mean climate, species invasions, and increased or decreased variability. Researchers at Jordana Basin LTER have highlighted the role of interannual climate variability in changing the outcome when an exotic grass species invades dry shrubland. Using a process-based model, they predicted three outcomes, depending on the degree of variability and timing relative to invasion.

Arctic Communities See Access Challenges Ahead

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Climate-change is predicted to have a larger impact on Arctic regions than on temperate ecosystems. As a result, rural communities relying on local wild resources, or subsistence harvesting, are vulnerable to climate-change-induced environmental trends affecting the availability of fish, waterfowl, and other key resources.

Cold Air Drainage Flows Subsidize Montane Valley Ecosystem Productivity

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Landscape ecologists and nature-lovers are well aware of the way that valleys collect deeper, moister soils than neighboring hill slopes and crests. Now, researchers at Coweeta LTER have have found that cool air, sliding downslope from higher elevations and pooling in mountain valleys, subsidizes productivity in a different way. The cold air drainage was most prevalent at night and in the evenings, so it had little effect on photosynthesis, but reduced plant and soil respiration by about 8 percent. Overall, the authors estimate it boosted annual net carbon uptake by about 15 percent.

Genetic Differences May Help Corals Adapt to Changing Conditions

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Individuals—even individuals of the same species—don’t always respond to a stimulus in the same way. Studying calcification in a key coral species, Acropora pulchra, researchers at the Moorea Coral Reef LTER found greater variety in the corals’ response to temperature than to high levels of CO2 in seawater. Since individual variation is the raw material of evolution, the contrast suggests it may be easier for this coral species to adapt to rising temperatures than to increased ocean acidification.