Soil organic matter may be more negatively affected by climate change than scientists previously thought. Plants, which send as much as 60 percent of their photosynthetically fixed carbon to their roots, can be affected by elevated carbon dioxide levels and then release altered secretions into the soil.
Lawrence Livermore scientists and colleagues said in the March 30 edition of Nature Climate Change that oxalic acid—a “common root secretion”—promotes the loss of carbon in the soil through the freeing of organic compounds from their associations with minerals.
Priming, the term for a “short-term” increase in microbial mineralization of soil carbon, can account for the loss of root secretion-induced soil carbon. Other studies have pointed to climate change as the reason for enhanced root secretions into soils of organic compounds. But recent studies show that increased root discharge may cause a loss of overall soil carbon.
“Our results provide new insights into the coupled biotic-abiotic mechanisms underlying the ‘priming’ phenomenon and challenge the assumption that mineral-associated carbon is protected from microbial cycling over millennial timescales,” said Jennifer Pett-Ridge, an LLNL scientist and co-author of the paper.
Pett-Ridge also mentioned that if root secretion rates continue to respond to climate change, as the scientists predict, the altered CO2 levels could increase metal and organic matter in the rooting zone, altering the soil.