Nitrogen dynamics and Microbial Adaptations in High-Latitude soils under Decadal Warming

Soils at high latitudes are experiencing significant warming due to climate change, raising concerns about potential disruptions in nitrogen (N) and carbon (C) cycling. This study investigates the decadal effects of soil warming on microbial N transformations in an Icelandic grassland. To this purpose, a geothermal gradient was utilized, where soil temperatures varied naturally from +0ºC to +12.3°C, simulating enhanced warming effects. Seasonal sampling of N pools and rates of gross N transformations—including amino acid, ammonia, and nitrate consumption and production—provided insights into microbial responses to prolonged warming. Warming accelerated the turnover of amino acids, driven by increased rates of microbial production and consumption, but did not affect net protein depolymerization. Ammonia consumption rates increased with temperature, although production rates remained constant. Additionally, total soil N content decreased substantially after five years of warming but remained stable between 5 and 10 years of warming. These findings suggest that N losses induced by warming occurred primarily within the first five years, stabilizing in a new equilibrium without further N losses. The enhanced microbial C limitation in warmed soils likely compelled microorganisms to rely more on the turnover of organic N pools as a dual source of both C and N to meet their heightened metabolic demands, thus preventing further N losses.  Overall, these findings challenge the assumption of progressive N depletion under warming conditions and highlight the role of microbial physiological adaptations in maintaining soil N availability despite increased metabolic demands.