Very fine roots contribute to improved soil water storage capacity in semi-arid wetlands in Northeast China

Wetland soil water storage affects the water cycle and maintains the stability of wetland ecosystems. Plant roots link soil and vegetation and play an important role in soil structure and function. However, our understanding of how roots control soil water storage in wetland ecosystems is relatively poor. This study compared and analyzed root traits and soil properties between different wetlands (Carex appendiculata, Calamagrostis angustifolia, and Phragmites australis) and bare land in the western Songnen Plain, Northeast China. We then comprehensively evaluated the soil water storage capacity under different vegetation types and identified the main root traits affecting soil water storage capacity. The results showed that different vegetation types presented different root distribution characteristics. Approximately 89.44%, 67.62%, and 82.67% of root biomass was distributed in the 0–20 cm soil layer in C. appendiculata, C. angustifolia, and P. australis wetlands, respectively. P. australis wetlands exhibited the lowest clay and silt contents, whereas the 0–40 cm soil layer exhibited the highest very fine sand, fine sand, and medium sand contents. C. angustifolia wetland showed the best soil water storage capacity, followed by C. appendiculata wetland, P. australis wetland, and bare land. Principal component analysis showed that the void ratio, bulk density, capillary porosity, organic matter content, medium sand content, silt content, very coarse sand content, and non-capillary porosity are major indicators for evaluating soil water storage capacity. Redundancy analysis showed that the volume of very fine roots is the most important root trait that affects the soil water storage capacity. This study provides practical guidelines for evaluating wetland ecosystem services and a theoretical basis for the restoration and reconstruction of degraded wetlands in semi-arid regions.