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Hydroxylated isoprenoid GDGTs (OH‐GDGTs) have emerged as a novel tool for reconstructing sea surface temperatures. However, when using marine OH‐GDGT calibration in lacustrine settings, it leads to a significant overestimation of temperatures, emphasizing the necessity for a thorough examination of OH‐GDGTs in lakes. Here, we investigated OH‐GDGT distributions in surface sediments from 65 lakes in West China and compiled published Asian lake and global marine OH‐GDGT data sets. Among all GDGT‐based indices, RI‐OH showed the strongest correlation with temperature across Asian lakes. The RI‐OH value was higher in lakes than in marine sediments, likely due to differences in the composition of Group 1.1a thaumarchaeotal species between the two settings. The first RI‐OH temperature calibration for lakes was developed and it addressed the issue of temperature overestimation when applied to both water column and sediment core, highlighting the potential of OH‐GDGTs as a new terrestrial paleothermometer. Plain Language Summary: Reconstruction of past terrestrial temperatures plays a crucial role in understanding modern global warming and projecting future climate patterns, yet reliable terrestrial temperature proxies remain limited. In this study, we present compelling evidence that the ring index of OH‐GDGTs, expressed as RI‐OH, is predominantly influenced by temperature in lacustrine settings, regardless of the wide range of physical and chemical characteristics of the lakes. We developed the first lacustrine RI‐OH‐temperature calibration and successfully applied it to a water column and a sediment core. These findings suggest that RI‐OH can be used as a novel paleothermometer in lacustrine settings. Key Points: OH‐GDGTs were first investigated in lacustrine settings along a wide temperature gradientTemperature was the most important factor affecting OH‐GDGT distributions in lacustrine settingsThe first calibration in lacustrine settings was established and successfully applied to a water column and a sediment core [ABSTRACT FROM AUTHOR]

Mangroves are unique ecosystems that harbor a wide variety of microbial communities including Archaea. Although Archaea have widely been reported to play important roles in biogeochemical cycles, the involvement of archaeal communities in mangrove ecosystems and nitrogen cycling remains largely underexplored. To bridge this gap, we investigated the distribution of archaeal communities and their functional genes involved in the nitrogen cycle in South China mangroves covering seven different geographical areas. Our results indicated that mangroves are an important reservoir of unclassified Archaea, and therefore these unique ecosystems could fuel important discoveries in the future. Moreover, total nitrogen, total carbon and nitrate concentrations were found to be critical drivers of archaeal community composition in these mangroves. Selective Archaea, particularly Crenarchaeota and Euryarchaeota, are the major contributors to nitrogen cycling in the mangroves, especially involved in nitrification. Taken together, our findings advance our understanding of Archaea-driven nitrogen cycling in mangrove ecosystems. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is an important process of the nitrogen cycle, and the anammox bacteria have been studied in a wide variety of environments. However, the distribution, diversity, and abundance of anammox bacteria in hot springs remain enigmatic. In this study, the anammox process was firstly investigated in hot springs of Conghua, China. Anammox-like bacterial sequences that closely affiliated to " Candidatus Brocadia," " Candidatus Kuenenia," " Candidatus Scalindua," " Candidatus Anammoxoglobus," and " Candidatus Jettenia" were detected. Several operational taxonomic units (OTUs) from this study shared low sequence identities to the 16S rRNA gene of the known anammox bacteria, suggesting that they might be representing putative novel anammox bacteria. A quantitative PCR analysis of anammox-specific 16S rRNA gene confirmed that the abundance of anammox bacteria ranged from 1.60 × 104 to 1.20 × 107 copies L–1. Nitrate was a key environmental factor defining the geographical distribution of the anammox bacterial community in the hot spring ecosystem. Dissolved inorganic carbon had a significant influence on anammox bacterial biodiversity. Our findings for the first time revealed that the diverse anammox bacteria, including putative novel anammox bacterial candidates, were present in Conghua hot spring, which extended the existence of anammox bacteria to the hot springs in China and expands our knowledge of the biogeography of anammox bacteria. This work filled up the research lacuna of anammox bacteria in Chinese hot spring habitat and would guide for enrichment strategies of anammox bacteria of Conghua hot springs. [ABSTRACT FROM AUTHOR]