Sedimentary recorded nitrogen-transforming microbes reflect climate fluctuations in a glacial lake on the Qinghai-Tibetan Plateau over a millennium timescale

We used sedimentary ancient DNA (sedaDNA) to reveal the temporal dynamics of the microbial community responsible for nitrogen (N) transformation within Lake Gyaring located on Qinghai-Tibetan Plateau over the past 1400 years. Our results revealed that the change points of microbial composition linked to N-transforming reactions occurred at ∼769 CE, ∼1286 CE, and ∼1850 CE, preceding the corresponding recorded climatic stages—the beginning of the Medieval Warm Period, the transition between the Medieval Warm Period and Little Ice Age, and the transition between the Little Ice Age and the Current Warm Period, respectively—by approximately 0–30 years. The dominant genus Spirochaeta and Anaeromyxobacter participating in N₂ fixation and dissimilatory nitrate reduction to ammonium (DNRA) underwent a sharp decrease, while the prevalent components Iamia, Chitinophaga, Nitrospira, and Nitrosospira involved in NH₄⁺ assimilation, ammonification, and nitrification exerted an increase shift at ∼1300 CE. These variations closely matched evident decreases in total nitrogen (TN) content, total organic carbon (TOC) content, and the organic carbon to nitrogen (C:N) ratio, as well as a noticeable increase in TP content at ∼1300 CE. Partial least square path modeling revealed that those nutrient variations induced by climate fluctuations were the predominant driver for the microbial community succession with respect to N transformation. The prevailing community structure across distinct climate periods mainly arose from preferences of the microbial taxa for nutrient loading.