There's a lot of confusion about nitrogen.

Increasing levels of nitrogen deposition associated with industry and agriculture can drive soils toward a toxic level of acidification, reducing plant growth and polluting surface waters, according to a new study published online in Nature Geoscience.

The study, conducted in the Tatra Mountains of Slovakia by the University of Colorado, University of Montana, Slovak Academy of Sciences, and the U.S. Geological Survey, shows what can happen when nitrogen deposition in any part of the world increases to certain levels – levels similar to those projected to occur in parts of Europe by 2050, according to some global change models.

On the basis of these results, the authors warn that the high levels of nitrogen deposited in Europe and North America over the past half century already may have left many soils susceptible to this new stage of acidification. The results of this further acidification, wrote the authors, are highly reduced soil fertility and leaching of acids and toxic metals into surface waters.

Acid soils are the norm, especially in mountainous terrain since the soils are often granitic - derived from weathered granite rocks. Trees can make it worse since organic matter is acidic, and some trees rely on this to stifle competitors of their seedlings. But soils can be too acid even for trees, so this sounds like it might be a legitimate concern except . . .

Automated pumps maintained the gaseous concentration at about 550 parts per million in the forest, roughly the atmospheric level of CO2 expected in 2050 and beyond. . .

The 10-year experiment in Oak Ridge showed that higher levels of carbon dioxide enhanced productivity of sweetgum trees - at least for a while. Absorption of carbon dioxide and conversion to wood, leaves, roots and sugars took place at an increased rate.

"This is important because if forests across the Earth absorb carbon from the atmosphere a bit faster, the carbon dioxide from fossil fuel combustions won't build up quite as fast, and the greenhouse effect causing climate change will be slowed," Norby said, emphasizing that the change won't be stopped.

The increased productivity occurred mostly below ground, the scientist said. Instead of making more wood in the trunk, the trees enriched with carbon dioxide made more roots, he said. These fine roots only live for about a year and then deposit their carbon into the soil, he said.

"Although these results all sound like good news," Norby said, "recent results suggest that the responses might not be sustained indefinitely because there is not enough nitrogen in the forest soil."

The first study worried about excess nitrogen and the second worried about insufficient nitrogen. It's nice that trees suck CO2 from the air and store in underground (rather than as leaves which recycle back to the air quickly) but is that enough to dispell the nitrogen fud? Well, that's not the only benefit.

While scientists have long known that nitrogen-rich foliage is more efficient at pulling carbon dioxide out of the atmosphere, this new discovery suggests that nitrogen plays an important additional role in the Earth's climate system that has never before been considered. Specifically, trees with high levels of foliar nitrogen have a two-fold effect on climate by simultaneously absorbing more CO2 and reflecting more solar radiation than their low-nitrogen counterparts. . .

"Bits and pieces of evidence for this have been around for years but nobody put them together before because it's a question we hadn't even thought to ask," Ollinger says. "Scientists have long been aware of the importance of albedo, but no one suspected that the albedo of forests might be influenced by nitrogen. And because most of the effect is in the infra-red region of the sun's spectrum, beyond that which human eyes can detect, the pattern isn't immediately obvious."

The newly discovered link between foliar nitrogen and canopy albedo adds an interesting new twist to the understanding of the climate system and raises intriguing questions about the underlying nature of ecosystem–climate interactions.

Changes in climate, air pollution, land use, and species composition can all influence nitrogen levels in foliage, and all of these may be part of a climate feedback mechanism that climate models have not yet examined.

There seems to be a hole in scholarship and research methodology big enough to fly a jumbo jet through. The researchers seem to lack basic understanding of natural systems. Perhaps they are so specialized that they don't have a grasp of how the system as a whole functions. If so, that also reflects poorly on the education system.

But, acidic soils truly are a problem in many places, and most everything makes the problem worse. Life is acidic for the most part. Plant roots exude acids. Animal dung is acidic. Decomposing organic matter of all sorts is acidic. Nitrates are acidic and they fall to the earth in rain even when there is no industrial pollution. Mother Nature's best is acidic.

There are two great sources of base materials that can neutralize those acids: sea shells and ashes. Over the millenia huge deposits of fossil sea shells - especially those of tiny ocean plankton - built up on sea beds and some later rose above the waves as the earth's crust shifted and heaved. The white cliffs of Dover are a good example. The floor of the southern San Joaquin valley is another. Ashes - used for eons to make soap out of animal fat - occur naturally but are also produced in abundance by industry, especially power plants that burn biomass. Best of all is biochar produced by heating biomass without free oxygen so that it doesn't burn. It's essentially charcoal, but when produced with precise temperature control the properties of the char can be fine tuned. It has a pretty high PH (often near 12, very base).

Will forests balance themselves by sucking CO2 from the air and nitrogen from the soil, while reflecting more sunlight to space, and in so doing help manage the soil, atmosphere and planetary albedo? That might be an interesting study. Knowing if intervention is actually needed is useful, and knowing the various ways to usefully intervene is as well. I'd like to see better educated scientists. Maybe teams with diverse skills as well as heuristics are required, at least for review of experimental design prior to funding.

Update: Related studies

How human activity is also lowering carbon dioxide in the atmosphere

This broad study analyzed the carbon balance across a network of forest sites that represent nitrogen deposition in most of Western Europe and the continental United States. Until now, it has been difficult to separate the effects of nitrogen deposition on forests from the many other variables that affect their carbon release or sequestration – things like forest age, logging, wildfires, disease or insect epidemics, or other causes. This study attempted to do that, and found that the net carbon sequestration by temperate and boreal forests was overwhelmingly determined by nitrogen inputs. . .

“The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests, either directly through forest management or indirectly through nitrogen deposition,” the study authors said.

Cyanobacteria And The Nitrogen Factor In Long Term Forest Productivity

In pristine boreal ecosystems, most new nitrogen enters the forest through cyanobacteria living on the shoots of feather mosses, which grows in dense cushions on the forest floor. . .

Nitrogen fixation is an energy demanding process. Thus, when mosses are exposed to high concentrations of bioavailable nitrogen, the cyanobacteria will consume this resident nitrogen rather than expending energy on fixing new nitrogen. Thus the nitrogen content of canopy throughfall acts as a regulator of newly fixed nitrogen into these boreal forests. . .

These findings are important from a global standpoint, because feather mosses (and associated cyanobacteria) are the primary source of biologically fixed nitrogen in the boreal forest biome. The dominating feathermoss Pleurozium schreberi is also found in arctic and temperate biomes and thus may be the widest distributed individual nitrogen-fixing plant species on Earth. Understanding feed back mechanisms among dominating organisms that regulate fundamental ecosystem processes are integral to our ability to predict long term outcomes of global carbon dynamics.

I might add that from the bumpkin perspective this is old hat. Every pasture manager deals with the trade offs.