Decreased Soil Cation Exchange Capacity Across Northern China's Grasslands Over the Last Three Decades

Cation exchange capacity (CEC) helps soils hold nutrients and buffer pH, making it vital for maintaining basic function of terrestrial ecosystems. However, little is known about the temporal dynamics of CEC over broad geographical scales. In this study, we used random forest method to compare historical CEC data from the 1980s with new data from the 2010s across northern China's grasslands. We found that topsoil CEC in the 2010s was significantly lower than in the 1980s, with an overall decline of about 14%. Topsoil CEC decreased significantly in alpine meadow, alpine steppe, meadow steppe, and typical steppe by 11%, 20%, 27%, and 9%, respectively. Desert steppe was the only ecosystem type that experienced no significant change. CEC was positively related to soil carbon content, silt content, and mean annual precipitation, suggesting that the decline was potentially associated with soil organic carbon loss, soil degradation, soil acidification, and extreme precipitation across northern China's grasslands since the 1980s. Overall, our results demonstrate topsoil CEC loss due to environmental changes, which may alter the vegetation community composition and its productivity and thus trigger grassland dynamics under a changing environment. Key Points Decreases in topsoil cation exchange capacity were observed across northern China's grasslands over the last three decades The decreases were detected on both the Tibetan Plateau and the Inner Mongolian Plateau, among various grassland types The decreases were attributed to soil carbon loss, soil desertification, soil acidification, and extreme precipitation