Beneath every meadow, an invisible economy determines whether carbon remains buried or rises into the air. A study of 33 grassland soils across Chile has found that the chemical character of organic matter — particularly its abundance of simple, energy-rich compounds — governs how vigorously soil microbes grow and breathe. The discovery that microbial growth does not simply follow energy availability challenges long-held assumptions and opens a more precise path toward predicting how soils will behave as the climate shifts.