Soil quality improvement on Qinghai-Tibet Plateau induced by soil hydrothermal changes from 1980s to 2020s

• Soil quality on the Qinghai-Tibet Plateau improved significantly over the past four decades. • Alpine cushion vegetation showed the greatest increase in soil quality, followed by meadows. • Soil hydrothermal conditions were identified as key drivers of soil quality improvement. • Increased nitrogen limitation was observed, with varying factors across different ecosystems. The Qinghai-Tibet Plateau (QTP), as the world’s Third Pole, has experienced a sharp trend of warming and humidifying in recent decades within the context of global climate change. Under these circumstances, the soil nutrient cycling has been significantly modified. However, whether the soil quality had changed over recent decades on QTP remains unclear. In this study, we calculated, and drew high-resolution maps of the soil quality index (SQI) on QTP using soil property data in 1980s and 2020s. Results showed significantly an increasing trend of soil quality over the past four decades. The variation in trends of four typical ecosystems, more specifically, alpine cushion vegetation showing the most notable increase, followed by alpine meadow and alpine steppe, while forest & shrub exhibiting the smallest increase in soil quality. This implied that regions with more significant SQI changes correspond to stronger climate change. Through attribution analysis of 10 factors affecting the variation in SQI, including climate, soil hydrothermal, vegetation, and human activities, we found that the improvement in soil quality were predominantly driven by soil hydrothermal conditions. Additionally, we observed a pronounced increase in nitrogen limitation, with the factors contributing to this trend varying across different ecosystems. Our study emphasizes the warning of intensified nitrogen limitation, and, under the context of climate change, this phenomenon is likely to become increasingly severe in the future.