Forest litter decomposition is considered as an essential ecosystem process affecting carbon and nutrient cycling in mountains. However, there exists high uncertainty in accurately estimating the contribution of litter decomposition to terrestrial ecosystems, largely due to the incomparability of different studies and the data limitation in microclimate and non-climatic factors at spatially matched scales. Here we used the tea bag index (TBI) as a standardized protocol to evaluate spatial variations in forest litter decomposition rate (k) and stabilization factor (S) across 10 mountains spanning a wide range of subtropical and tropical forests. Based on the coordinated experiment of 6,864 teabags in 568 sampling sites along elevations, we evaluated the importance of 10 environmental factors covering soil microclimate, edaphic properties, plant diversity, and topography on k and S by using model averaging and linear-mixed effects models. Of the 10 mountains, we found a consistently decreasing pattern of k and an increasing pattern for S along elevations. And the significant effect of k with elevation was mainly found in the western and northmost mountains, while the effect of S occurred in the western and southernmost mountains. For microclimate, there was a general importance of soil temperature (coef. = 0.48) and temperature variation in the growing season (coef. = 0.36) in k, and soil temperature (coef. = -0.46) and moisture variation on S (coef. = -0.36). The dominant role of soil microclimate was mainly found in western mountains with relatively cold environments. For non-climatic drivers, a significant effect of tree diversity on k and a negative correlation of edaphic and topography with S in the western and southern mountains were detected. These findings provide a general understanding of spatial variations of driving factors in forest litter decomposition and highlight a dominant control of soil microclimate in cold forests in high elevations and latitudes.

Mountainous regions can promote complex speciation scenarios, including hybridization leading to chloroplast capture, revealed by incongruent phylogenetic trees. Four allopatric Taxus lineages from the Hengduan Mountains, southwestern China, exhibit cytonuclear phylogenetic discordance. We use multi-omic data at the population level to investigate their historical speciation processes. Transcriptome data consistently showed that T. florinii and the Emei type, which are the focus of cytonuclear discordance, originated in the Late Miocene. Population genomic analysis based on ddRAD-seq data revealed limited contemporary inter-specific gene flow. However, neither taxon exhibited the mosaic nuclear genomes that usually characterized hybrids. Taxus florinii appears to have originated when a lineage of T. wallichiana captured the T. chinensis plastid type, whereas plastid introgression in the opposite direction generated the Emei Type. All four species have distinct ecological niches, and introgression might have contributed to, or even initiated, their ecological divergence. We propose that these speciation events represent very rare examples of chloroplast capture events despite the paternal cpDNA inheritance of Gymnosperms. These events might have been triggered by orogenic activities of the Hengduan Mountains and the intensification of the Asian monsoon in the late Miocene, and may represent a scenario more common in these mountains than presently known.