Climate Change – it’s in the Soil, it’s in the Leaves

Reading the leaves

We know there’s a relationship between rising levels of CO2 and warmer temperatures. That, of course, is the crux of global warming science and plays an important part in the models that predict future climate change. But looking at the past can be just as informative.

A group of Penn State-led geoscientists and ecologists are shedding light on the matter by looking at the ecological conditions that lead to types of carbon in plants leaves. In a paper published in March 2010 in Proceedings of the National Academy of Science, the team reported a study involving 3,000 modern plants from diverse environments. They looked at two naturally-occurring carbon isotopes — carbon 12 and carbon 13 — in plant leaves to get a better sense of the environmental conditions in which they were growing.

It turns out not just atmospheric carbon impacts these isotope levels, but also water availability and the plant type — deciduous or evergreen. Why does this matter? Sounds a bit roundabout, but the more we know about how plants accumulate different kinds of carbon, the better we can study fossilized plant remains and infer past environmental/climate conditions … the more we can then understand the future climate.

“What we hope is that by using this approach, we are going to get a better value for the carbon isotope ratio in the atmosphere, which you then plug into your model and get a better estimate for climate sensitivity,” said Kevin Mueller, a Penn State researcher.

The group writes about the limitations of studying the recent past:

Human perturbation of the global carbon cycle is potentially far greater in rate and magnitude than variations in the recent past, pushing predictions of future climate beyond the calibration range of models based on modern and near-modern observations.

Permafrost on northeastern Spitsbergen, Svalbard, Norway. Image Credit: Olafur Ingolfsson

A longer term, “geologic” view of CO2 levels and ecological patterns is what’s needed.

Soil Critters

We’ve heard a lot about methane bubbling out of the Arctic permafrost. But just as much concern over soil carbon emissions is factoring into global warming prediction models.

The idea is that higher temperatures activate the gazillions of microbes in the soil, and they hungrily chomp their way through plant debris and the like, in the process creating enzymes that respirate lots of carbon molecules into the atmosphere.

It turns out that the interplay between climate and microbes is a little more complicated than previously thought. A study published this month in Nature Geoscience showed that microbes release lots of carbon initially in response to atmospheric warming, but can overheat and taper off over time. Under higher temperatures, their “carbon-use efficiency,” a measurement standard the scientists are using to establish how well the microbes process carbon, can be affected by changes to their physiological systems. As microbe growth decreases, so does their production of carbon-releasing enzymes, according to new research.

In short, the microbes have just not adapted to the extra heat. “When we developed a model based on the actual biology of soil microbes, we found that soil carbon may not be lost to the atmosphere as the climate warms,” said Steve Allison of UC Irvine and a lead author in the study, who developed a computer model to test how efficiently microbes were decomposing soil carbon after several years of experimental warming.

But that doesn’t mean that microbes won’t adapt to the higher temperatures over time, or that some new heat-insensitive species might take over and continue the breakdown of carbon. Also, the response could change in differing ecosystems. The researchers started out in Massachusetts but have begun collecting samples in Alaska, California, Maine, and Costa Rica to study.

It’s easy to overlook the teeny critters that give life to soil. But their goings-about is critical to climate science and to a warming world.