Root-induced changes to soil water retention in permafrost regions of the Qinghai-Tibet Plateau, China

Abstract

Soil water retention plays a crucial role in regulating soil moisture dynamics, water circulation, plant growth, contaminant transport, and permafrost stability, and it is an issue of concern in water-limited ecosystems. However, our understanding of the relationship between plant roots and soil water retention is still relatively poor in the alpine grasslands of permafrost regions. To addresses this, our study evaluated the effect of plants on the soil water retention in permafrost regions of the Qinghai-Tibet Plateau. Three alpine grassland sites were identified and characterized as alpine wet meadow (AWM), alpine meadow (AM), and alpine steppe (AS). Root biomass, soil water retention, and soil physico-chemical properties were examined in the top 0–50 cm of active layer in the three experimental sites in the hinterland of the Qinghai-Tibet Plateau (QTP). Pedotransfer functions (PTFs) and Retention Curve program (RETC) were employed to illustrate how the plant roots affect soil water retention. Approximately 80, 65, and 60% of root biomass was distributed in the top 0–20 cm in the AWM, AM, and AS soil, respectively. Soil water retention was enhanced with the presence of plant roots; thereinto, the highest values of field capacity were found in AWM soil: on average, about 0.45 cm3 cm−3. Field capacity of AWM soil was almost twice as high as that of AM soil, and triple higher than that of AS soil. Correlation and regression analysis showed that root-induced changes to soil water retention were caused by altering the soil organic matter and soil structure. In addition, we evaluated the Retention Curve (RETC) program’s performance and found that the program underestimated soil water retention if the effects of plant roots were not considered. A lack of alpine plants is associated with a decline in soil physical conditions and soil water retention in permafrost regions, and the function of plant roots should be considered when predicting hydrological processes.