Who is "obstructing" forest carbon storage? It's the microorganisms in the soil!

Popular Science Times (intern Wang Yuke) Forests can store carbon, and rising carbon dioxide levels will stimulate forest growth. Recently, the international scientific journal Nature published a research paper titled "Microbial competition for phosphorus limits the response of mature forests to carbon dioxide", pointing out that soil microorganisms compete with plants for important nutrients, which may limit the ability of forests to remove carbon dioxide from the atmosphere.

Higher concentrations of carbon dioxide boost plant growth by stimulating photosynthesis, but the carbon dioxide fertilization effect can only boost plant growth to a certain point, and ultimately plant growth is limited by the nutrients available in the soil. In one-third to half of ecosystems, that limiting nutrient is phosphorus, says Christine Crews, a plant researcher at the University of Western Sydney in Australia. How the amount of available phosphorus changes as plants and soil microbes respond to rising carbon dioxide levels is a key unknown.

Over a six-year period, researchers collected data on changes in phosphorus levels in a mature forest in New South Wales, Australia. The experiment used long tubes suspended around trees to artificially increase carbon dioxide levels in the plot. Researchers had thought that this would stimulate soil microorganisms to recycle more phosphorus from dead and decaying matter, but the result was that plants released more carbon into the soil through their roots, and the amount of available phosphorus did not increase with the increase in carbon dioxide. This may be because microorganisms outcompeted plants in the process of competing with them for available phosphorus, resulting in microorganisms containing more than three times the amount of phosphorus contained in plants.

If the limiting nutrient, phosphorus, is widespread, forest responses to carbon dioxide fertilization may be lower than expected, Crews said. Some ecosystems may need added nutrients to reach their full carbon storage potential.