Hydrological connectivity improves soil nutrients and root architecture at the soil profile scale in a wetland ecosystem.

Hydrological connectivity is an essential driver of the stability, structure, and function of wetland ecosystems. Small-scale hydrological connectivity restricts large-scale hydrological cycle processes. This study aimed to investigate the response of soil and root properties to hydrological connectivity at the soil profile scale. Tamarix chinensis, which is a typical plant of the Yellow River Delta wetland, was sampled for analysis. We investigated soil and root properties in the three study plots where T. chinensis distributed and compared them at different soil depths and under different hydrological connectivity conditions. We found that the soil organic carbon (SOC), soil organic matter (SOM), and soil total nitrogen (STN) were significantly higher in shallow soil (0-10 cm deep), and that root architecture parameters such as root length and width at soil depth of 0-10 cm were also significantly higher than at other soil depths. Both the soil nutrients and root architecture parameters were significantly influenced by hydrological connectivity. Specifically, SOC, SOM, and STN were significantly higher in regions of high hydrological connectivity than in regions of low hydrological connectivity. Additionally, root length, root surface area, root projected area, and root volume were markedly higher in regions of high hydrological connectivity. Furthermore, root length and width had significant positive correlations with both SOC and SOM in regions of high hydrological connectivity. Taken together, these results indicate that higher hydrological connectivity promotes soil nutrients and root architecture at the soil profile scale. In the process of wetland protection and restoration, we should not only pay attention to hydrological connectivity at a watershed scale, but also to improving hydrological connectivity at smaller scales so as to restore soil nutrients and promote plant growth.