Tibetan lake sediments in NW China are sensitive recorders of climate change. However, many important plankton members do not leave any microscopic features in sedimentary records. Here we used ancient DNA preserved in Qinghai Lake sediments to reconstruct the temporal succession of plankton communities in the past 18,500 years. Our results showed that seven classes and sixteen genera of phytoplankton in the lake underwent major temporal changes, in correlation with known climatic events. Trebouxiophyceae and Eustigmatophyceae were predominant during the cold periods, whereas Chlorophyceae, Phaeophyceae, Xanthophyceae, Bacillariophyceae, and Cyanophyceae were abundant during the warm periods. The inferred changes in temperature, nutrients, precipitation, and salinity, as driven by the Westerlies and summer Monsoon strength, likely contributed to these observed temporal changes. Based on these correlations, we propose the phytoplankton index as a proxy to reconstruct the stadial versus interstadial climate change history in Qinghai Lake. This taxon-specific index is free of terrestrial contamination, sensitive to short-term climatic oscillations, and continuous in recording all climatic events in the lake. The validity of this index and its applicability to other lakes is demonstrated by its good correlations with multiple climate records of Qinghai Lake and another lake on the Tibetan Plateau, Kusai Lake.

Under the scenario of global warming, the response of greenhouse gas emissions from alpine wetlands remains unclear. In this study, fluxes of CO₂ and CH₄ were measured during daytime for the microtopographic features of hollows and hummocks in a wetland in the Tibetan Plateau under two elevated temperatures, increments of ∼1°C (T1 treatment) and ∼2°C (T2 treatment), during the growing season in 2019. The results showed that warming significantly increased the cumulative net ecosystem CO₂ exchanges (NEE) for both microtopographic features in the wetland compared to the control due to a combination of the increased gross primary production (GPP) with an increase in ecosystem respiration (ER). Similarly, warming also increased cumulative CH₄ emission significantly. The effect was stronger for T2 than that for T1 for all component fluxes (GPP, ER, NEE, and CH₄). Generally, NEE and CH₄ fluxes both rose at first and then decreased. NEE peaked at the end of July for both hollows and hummocks, while CH₄ emissions peaked in the middle of August. The cumulative CH₄ emissions from the hummocks were significantly higher than those of the hollows, and CH₄ emissions under illumination were significantly higher than those in darkness, which may be caused by the irradiation-sensitive vegetable internal convective gas transport system which diffuses CH₄ from the pedosphere. This study revealed that warming strengthened the function of the CO₂ sink but also increased CH₄ emissions from the alpine wetlands on the Qinghai–Tibet Plateau.

Geothermal hot springs, widely distributed on Earth, are important geological greenhouse gas sources which contribute large amounts of CO₂ emission to the atmosphere. Exploring microbial carbon fixation in these springs is vital to fully understand the carbon budget in these terrestrial aquatic systems. In this study, carbon fixation rate by photosynthetic mats was determined with a ¹³C‐labeling approach along a gradient of temperature (~69– ~75 °C) in a geothermal pool at Rehai Park in Tengchong, Yunnan Province, China. Light experiments were performed to determine carbon fixation rate by both photosynthesis and chemosynthesis, while dark experiments were performed by chemosynthesis. The results showed that the highest carbon fixation rate (4,637 μg C/g TOC/hr) was obtained in light at the lowest temperature (~69 °C) in the afternoon (1:00 to 6:00 p.m.), most of which (96.7%) was contributed by photosynthesis. The lowest carbon fixation rate (138 μg C/g TOC/hr) was measured at the highest temperature (~75 °C), where chemosynthesis dominated over photosynthesis in carbon fixation. At these rates, the photosynthetic mats would fix 80% of CO₂ emission during the daytime. At the end of daytime, the photosynthetic mats respired 34–70% of newly fixed organic carbon in 1 hr. Interestingly, both the carbon fixation rate and respiration rate decreased exponentially with increasing temperature, which may be ascribed to a temperature dependence of both microbial community composition and enzymatic activity. In summary, our study revealed that biological carbon fixation by photosynthetic mats is highly temperature dependent and significantly affects carbon cycling in hot springs.