Reduced winter precipitation decreases microbial growth efficiency and alters soil organic carbon composition in California grassland (microbiomejournal.biomedcentral.com)

• Reduced winter precipitation decreased microbial growth and mortality rates by one to two orders of magnitude.
• Despite similar CO2 emissions, this led to lower community growth efficiency (CGE).
• Soil organic carbon shifted from necromass-derived to plant-derived compounds.
• High CGE was linked to increased biosynthesis and necromass degradation; low CGE to stress-related metabolism.

"A field experiment in a California Mediterranean grassland subjected to 50% reduced winter precipitation for one growing season. Six months later, after summer dry-down, soils were rewetted. Microbial growth and mortality rates dropped by ~1 and ~2 orders of magnitude, respectively, compared to normal precipitation controls, despite similar CO2 efflux. This resulted in decreased community growth efficiency (CGE). Soil organic carbon shifted from microbial necromass-like compounds (lipids, amino sugars, proteins) to more oxidized plant-derived compounds (lignins, tannins). Metatranscriptomics revealed that at high CGE, microbes invested in biosynthesis and necromass degradation; at low CGE, they invested more in carbohydrate metabolism and lipid turnover, consistent with stress maintenance."