Plants and the Carbon Capture Question

Plants are complicated

The connections between life and climate on Earth go well beyond the Carbon Cycle. Image Credit: NASA/NASA Earth Science Enterprise

Planting trees, as everyone knows, is a good way to offset climate change. The more greenery on Earth, the better, since vegetation act as carbon sinks, essentially sucking up the excess CO2 and storing it in leaves, stems, and root systems.

But a recent paper published in the journal Nature Geoscience claims we have a long way to go towards understanding the biochemical processes in which plants interact with the climate. Simply looking at the carbon cycle involving plants is not enough, say the researchers led by the earth science department at Lund University in Sweden.

They outlined a number of other biochemical feedbacks worth considering and exploring in greater detail. Take ground level ozone (O3), for example. It’s produced during fossil fuel combustion and causes smog, which is toxic to pretty much all life forms, including plants. Ozone enters through the stomata and effectively destroys a leaf”s ability to produce chlorophyll. The researchers say that O3 toxicity could reduce the global land-carbon sink by 12 to 24 billion metric tons by the year 2100, depending on plant sensitivity.

Sphagnum decays in peat bogs.

That’s not all. Consider Nitrogen, that essential soil nutrient that boosts plant growth. Plants generally grow faster under warmer, higher CO2 concentrations in the atmosphere, but only if they have enough Nitrogen to keep them going. “The availability of Nitrogen, which is limited in many ecosystems, plays a critical role in controlling [net primary productivity,” the researchers write.

Although some models suggest that warming will enhance the amount of Nitrogen available to plants in the soil, generally the end result is still higher CO2 levels. No one has incorporated into models of climate feedbacks the impacts of nitrous oxides, which are emitted by microbe decomposition of the soil (and by human activities), despite their extreme potency as a greenhouse gas.

The impacts of biologically produced versions of volatile organic compounds and their generation of cooling aerosols has yet to be incorporated into experiments on how plants change in a warmer planet.

The researchers argue for incorporating more sophisticated models of all these biochemical processes into global warming scenarios. Just looking at CO2 as it relates to plants is not enough.

An emissions filter

A peat bog on Ben Lee, Skye Island, Scotland. Image Credit: Richard Dorrell

Peat bogs are an amazing carbon store. Up to a third of all the terrestrial carbon on Earth is captured by this kind of acidic wetland, a depository of dead plant material in northern ecosystems that are very biodiverse.

As the planet warms, a lot of that carbon is being released back into the atmosphere as methane, one of the more potent forms of greenhouse gases. The source: the anaerobic degradation of a kind of moss called Sphagnum.

But a new study published in the journal Nature Geoscience finds that rotting Sphagnum can be mitigated by a kind of bacteria called methanotrophs, which oxidize the gas and turn it into carbon dioxide, which is then available for the mosses to consume and grow.

The methanotrophs effectively act as a kind of “emissions filter,” the authors led by Radboud University Nijmegen in the Netherlands write. They did a worldwide survey of Sphagnum ecosystems to assess the distribution and activity of methanotrophs.

They found that increases in methane release, as a result of global temperature rise, could be counteracted by fostering this kind of Sphagnum -methanotrophs relationship.

The symbiotic exchange plays a role in carbon recycling in these waterlogged ecosystems. But that they could actually reduce methane emissions as well is something special.