The soil may not be able to retain carbon dioxide as emissions increase

There is A figure of speech In the world of climate negation, raising carbon dioxide is good, in fact, because it helps plants grow. Leaving aside that saying that ignores all the harmful effects on life on Earth, there is another problem with tired speech.

A new study published in Nature on Wednesday suggests that while high concentrations of carbon dioxide in the atmosphere can stimulates plant growth, requires a huge tax another important source of carbon sequestration that is only those plants and trees: the earth.

Dirt is a vital part of the carbon cycle, but the impact of rising carbon dioxide on the soil is a notable gap in the literature. The authors of the new study decided to fill this gap. The study notes that there is a widely accepted assumption that carbon levels in the soil will increase as plants capture more carbon because when these plants die, they decompose and turn into soil. But there was not much evidence to support this.

“As a scientist, I was puzzled by how little I knew about the effects [estimated concentrations of carbon dioxide] about soil carbon stocks compared to plant traits, ”wrote Cesar Terrer, a colleague at Lawrence Livermore National Lab and a postdoctoral researcher at Stanford University who worked on the study.

For the study, Terrer and colleagues analyzed data from 108 previously published papers, focusing on soil carbon levels and plant growth amid rising carbon concentrations. They found that as carbon levels rise, so do the levels of organic matter in the soil. But contrary to what conventional wisdom would lead them to believe, researchers have found that an increase in soil biomass usually coincides with a decrease in soil carbon levels.

“We were expecting faster plant growth and more biomass to grow organic carbon in the soil as extra leaves and biomass fall to the forest floor,” wrote Rob Jackson, a professor of Earth system science at Stanford University. and the lead author of the study, in an email. “He didn’t, and that was the biggest surprise of our work.”

In fact, the authors found that the soil accumulated more carbon in experiments in which, even though the atmosphere had high carbon concentrations, plant growth continued at a steady pace, instead of growing rapidly.

The authors believe that they know why this happens: as plants grow faster, they need more nutrients, which they extract from the soil. To give plants access to more nutrients, soils must microbes such as bacteria and fungi grow faster. This requires them to increase their microbial respiration rate, which releases carbon into the atmosphere it might have remained otherwise on earth.

Not all ecosystems, the authors write, will behave the same in this regard. Based on their meta-analysis, the authors’ modeled to how much carbon will be absorbed by the soil of different landscapes as atmospheric carbon increases. They found that if carbon dioxide levels reach double pre-industrial levels, the rate of carbon consumption in forest soils will remain flat, but pasture soils will increase by 8%. This is probably the case, because in meadows, plants allocate more carbon from their roots than from the surface, and studied show that decaying roots tend to introduce more carbon into the soil than other parts of the plant. This suggests that world leaders should focus on restoration and efforts to conserve these ecosystems as a form of climate mitigation.

These discoveries are major implications for how climate scientists represent the amount of carbon that forests, grasslands and wetlands can sequester. As existing climate projections do not take into account the trade-off between carbon sequestration in soil and plants, it is likely to overestimate the terrestrial potential to absorb carbon and mitigate global warming. This means that we may not have as much freedom with carbon pollution as we thought.

“Forests and other land currently absorb a third of global carbon pollution, about 12 billion tons of carbon dioxide each year,” Jackson said. “We need to understand whether this valuable service will continue. ”