The Impact of Plant Diversity on Carbon Storage Along the Gradient of Altitude in Alpine Grasslands of the Qinghai–Tibetan Plateau

Plant diversity plays an important role in shaping the carbon cycling of grassland ecosystems. However, differences in the diversity effect on aboveground and belowground carbon storage remains unclear at specific spatiotemporal scales. A transplant experiment was carried out along the gradient of altitude (4600–5200 m) in alpine grasslands of the Qinghai–Tibetan Plateau in the year 2017. Vegetation characteristics like species richness, vegetation cover and height were measured in the years 2020 and 2021. The plant diversity was described by species richness. Then, I calculated the vegetation biomass to quantify the aboveground carbon storage. The belowground carbon storage was represented by soil organic carbon. The results showed that the effect of species richness on belowground carbon storage was significantly positive (<i>p</i> < 0.05) at most altitudes for both years. However, the diversity effect on aboveground carbon storage was weak and inconsistent. The relationship between species richness and belowground carbon storage remained relatively stable over a period of two years. In contrast, the relationship altered greatly in terms of aboveground carbon storage in terms of inter-annual changes. Precipitation of growing seasons significantly impacted the species richness rather than aboveground carbon storage. Soil temperature was significantly associated with belowground carbon storage. These findings provide a new insight which will help us to assess the relationship between plant diversity and ecosystem functioning. They also allow us to understand how vegetation responds to climate change in high-altitudes areas.