Characteristics of water retention, nutrient storage, and biomass production across alpine grassland soils in the Qilian Mountains

Climate change has impaired the tightly-interlinked soil functions of grasslands, including water retention, biomass production, and carbon and nutrient storage. Limited knowledge of these functions' characteristics, influencing factors, and interrelationships hinders effective soil management. A field survey combined with regional data across alpine grasslands in the Qilian Mountains revealed that the soil water-holding capacity, measured by saturated water content, maximum water absorption, and field capacity, was strongest in alpine wet meadow (AWM), followed by alpine steppe (AS), alpine meadow (AM), and alpine meadow steppe (AMS), and lowest in alpine desert (AD). Soil bulk density and organic matter content (SOM) were key factors affecting water retention. The 0-50 cm storage of organic carbon and total nitrogen was the largest in AWM, about 2-3 times those in AD, with their concentrations significantly varied between soil layers, except for AWM. Conversely, total phosphorus and total potassium storage, with minimal concentration differences between layers, was highest in AD. Regression analysis showed that pH, soil water, and bulk density accounted for 24%-91% of organic carbon variance, and SOM explained over 98% of total nitrogen. Except for clay content, the effects of the mentioned factors on total potassium were mainly in surface layers (0-20 cm), whereas their effects on total phosphorus were smaller. Total biomass followed the pattern: AM>AWM > AMS > AS>AD. Aboveground biomass relied primarily on subsurface (20-50 cm) SOM and surface soil saturated water, while belowground biomass largely depended on subsurface total phosphorus and field capacity. Overall, soil functions exhibited gradient changes along the grassland sequence. Regional synergies suggest that soils in alpine meadows, the largest grassland type in the study area, can deliver multiple benefits concerning primary productivity and water-carbon storage. This study can provide insight for assessing soil functions of grasslands in areas affected by permafrost and seasonal frost.