sedaDNA and pollen disclose treeline advancing and plant diversity trajectory under recent climate warming in southwestern Hengduan Mountains, China

Abstract

The ongoing climate warming has been casting unprecedented impacts on alpine ecosystems within the Hengduan Mountain (HDM), a globally renowned biodiversity hotspot. However, current knowledge of how alpine vegetation and plant diversity are responding to recent climate warming remains inadequate. Here, we conducted pollen and sedimentary ancient DNA (sedaDNA) analyses on a short sediment core from Tiancai Lake, located in the southwestern HDM, to explore the vegetation and plant diversity changes over the past four centuries. The results manifested that the regional vegetation composition has undergone obvious changes during this period. Specifically, the ratio of broad-leaved to coniferous taxa (B/C), as well as palynological richness and diversity, exhibited significant correlations with the increasing mean annual temperature, implying that alpine species in the southwestern HDM have been subjecting to recent climate warming trends. The sedaDNA results further illustrated watershed-scale vegetation turnover, characterized mainly by the replacement of Rhododendron scrub by Abies forest and the upward migration of the alpine ecotone. The establishment of alpine coniferous forest around Tiancai Lake occurred about 1880 C.E. Additionally, the trajectories of plant diversity on watershed scale were highly resembled the mean annual temperature variations during post-industrial warming, indicating that the plant diversity around Tiancai Lake should be highly sensitive to and controlled by climate changes. Concurrently, warming-induced alpine habitat degradation may be imperiling plant diversity in the Tiancai Lake region, despite the upward trend in palynological diversity observed in the southwestern HDM.