Both specific plant functional type loss and vegetation change influence litter metallic element release in an alpine treeline ecotone

Climate warming changes the plant community composition and biodiversity. Dominate species or plant functional types (PFTs) loss may influence alpine ecosystem processes, but much uncertainty remains. This study tested whether loss of specific PFTs and vegetation variation would impact the metallic element release of mixed litter in an alpine treeline ecotone. Six representative PFTs in the alpine ecosystem on the eastern Tibetan Plateau were selected. Litterbags were used to determine the release of potassium, calcium, magnesium, sodium, manganese, zinc, copper, iron, and aluminum from litter loss of specific PFTs after 669 days of decomposition in coniferous forest (CF) and alpine shrubland (AS). The results showed that potassium, sodium, magnesium, and copper were net released, while aluminum, iron, and manganese were accumulated after 669 days. Functional type mixtures promoted the release of potassium, sodium, aluminum, and zinc (synergistic effect), while inhibiting the release of calcium, magnesium, and iron (antagonistic effect). Further, loss of specific plant functional type significantly affected the aluminum and iron release rates and the relatively mixed effects of the potassium, aluminum, and iron release rates. The synergistic effects on potassium, sodium, and aluminum in AS were greater than those in CF, while the antagonistic effect of manganese release in AS was lower than that in CF. Therefore, increased altitude may further promote the synergistic effect of potassium, sodium, and aluminum release and alleviate the antagonistic effect of manganese in mixed litter. Finally, the initial stoichiometric ratios regulate the mixed effects of elemental release rates, with the nitrogen-related stoichiometric ratios playing the most important role. The regulation of elements release by stoichiometric ratios requires more in-depth and systematic studies, which will help us to understand the influence mechanism of decomposition more comprehensively.