Assessing soil quality in association with frozen ground in the source areas of the Yangtze and Yellow Rivers, Qinghai-Tibet Plateau

Abstract

Frozen-ground environments represent one of the most fragile ecosystems in the source areas of the Yangtze and Yellow Rivers (SAYYR), characterized by persistently low temperatures and slow decomposition of soil organic matter, which sustains substantial soil organic carbon reserves. As climate warming intensifies, ecological stressors in the SAYYR increasingly threaten soil conditions. However, research on soil quality within the SAYYR remains scarce. This study systematically assessed soil quality through vegetation and soil surveys and analyses across 12 sites in the SAYYR. A soil quality index (SQI) was calculated using a selected minimum dataset comprising total nitrogen (TN), total phosphorus (TP), total kilocalorie (TK), available phosphorus (AP), available kilocalorie (AK), and total dissolved salt (TDS). Results revealed that the CLQ site, abundant in organic matter, exhibited the largest average SQI at 0.59, while the CMEH site located in seasonally frozen ground recorded the lowest value (0.26), highlighting the influence of frozen soil types on soil quality. The regional average SQI in the SAYYR was 0.44, indicating moderate soil quality. Diagnostic modeling identified TN as the primary constraint on soil quality in the SAYYR, with an average obstacle rate of 22.4%. Further analysis showed that fractional vegetation coverage and aboveground biomass were key determinants of soil quality in the SAYYR. The interaction between fractional vegetation coverage and mean annual ground temperature explained 58% of soil quality variability, the highest among tested factors. Additionally, the interactions of altitude with vegetation cover and vegetation cover with aboveground biomass accounted for 47.6% and 45.1% of variability, respectively. Results underscored the necessity of integrating vegetation characteristics, altitude, and frozen-ground thermal conditions to interpret soil quality variations in the SAYYR. This study provided valuable scientific insights and theoretical foundations for guiding ecological conservation, climate adaptation, and frozen-ground preservation in the SAYYR.