Effects of climate change and anthropogenic activities on soil pH in grassland regions on the Tibetan Plateau

Although soil pH is an important indicator of soil quality, the effects of climate change and anthropogenic activities on soil pH remain controversial. Here, we quantified the potential soil pH at three depths (0–10, 10–20, and 20–30 cm) using annual temperature (AT), annual precipitation (AP) and annual radiation (ARad), and the actual soil pH at three depths using AT, AP, ARad and maximum normalized difference vegetation index based on random forest models over the grassland regions on the Tibetan Plateau in 2000–2020. Overall, climate change caused soil alkalinization at 0–10 cm, and soil acidification at 10–20 and 20–30 cm. Under climate change conditions, 36.84%, 29.87% and 23.71% regions showed soil alkalinization, whereas 45.52%, 44.49% and 21.43% regions showed soil acidification at 0–10, 10–20 and 20–30 cm, respectively. Climate change caused soil acidification in alpine meadows, but soil alkalinization in alpine steppes. The impacts of precipitation change on soil pH were not always greater than those of climate warming, depending on soil depth, and radiation change had some exclusive impacts on soil pH. Overall, anthropogenic activities caused soil alkalinization, but more than 1/10 regions showed soil acidification. Anthropogenic activities caused soil acidification in alpine meadows, but soil alkalinization in montane meadows at 10–20 cm. Therefore, the impacts of climate change and anthropogenic activities on soil pH did not always cause soil acidification or alkalization, but varied with grassland type and soil depth. Both climate change and anthropogenic activities reconstructed the spatial distribution pattern of soil pH. This study also cautioned that the impact of radiation change on soil pH should not be ignored.