Effects of the Root System Architecture of Pinus taeda and Phyllostachys edulis on the Index of Hydrological Connectivity in Subtropical Forest Ecosystems

Abstract

The hydrological connectivity below the soil surface can influence the forest structure and function, especially soil and plant productivity. However, few studies have determined the changes in the hydrological connectivity below the soil surface with increasing soil depth and have quantified the effects of root systems on the hydrological connectivity in forest ecosystems. In this study, we evaluated the index of the hydrological connectivity (IHC) below the soil surface using a field dye tracing method and compared the difference in the index of hydrological connectivity in two subtropical forest stands (i.e., pine trees [SS] and bamboo [ZL]). We analyzed the interactions between the parameters of root system architecture and the index of hydrological connectivity. Back propagation (BP) neural networks were used to quantify which parameter can contribute the most relative importance to the changes of the IHC. The results revealed that the maximum value of the index of hydrological connectivity occurs at the soil surface, and it exhibits a non-linear decreasing trend with increasing soil depth. The parameters of root system architecture (root length, root projected area, root surface area, root volume, and root biomass) were rich in the top soil layers (0–20 cm) in the two sites. Those parameters were positively correlated with the IHC and the root length had the largest positive influence on the hydrological connectivity. Furthermore, we found that root system architecture with different root diameters had different degrees of influence on the index of hydrological connectivity. The very fine root systems (0 < D < 1 mm) had the greatest effect on the hydrological connectivity (p < 0.01). The results of this study provide more information for the assessment of the hydrological connectivity below the soil surface and a better understanding of the effects of root systems in soil hydrology within the rhizosphere.

The Impact of Vegetation Types on Soil Hydrological and Mechanical Properties in the Hilly Regions of Southern China: A Comparative Analysis

“…The dyeing area of CF was the largest, and the dyeing depth of CF was the deepest, but the distribution of the staining area was not uniform enough. This result was similar to the experimental results of Zhang et al [97]; the specific root length of coniferous forests was the smallest at 0.7, their root systems were thin, and their root length density was the largest at ≤2 mm in diameter. Preferential flow is the mechanism by which water bypasses a large portion of the matrix porous network along some preferred path, which may result in most of the permeate water passing through these pores at a significantly faster rate than the rest of the permeate water [98].…”

Assessment of hydrological connectivity characteristics of riparian zones and their correlation with root–soil composites at different bank heights of a first-class river in China

“…It is consistent with the results of dyeing area ratio, which confirms that the IHC is indeed a suitable indicator of hydrological connectivity. IHC in this study was similar to the results in the forest area, but differed from the values in the Yellow River Delta region (Zhang W. et al, 2022;. This may be due to the fact that the same D C with homogeneous and isolated dye-stained patches would lead to variable FD, which results in the changes of IHC.…”

“…IHC reflects the degree of overall hydrological connectivity and the contribution of patches (Zhang W. et al, 2022).…”

“…However, it is not only enough to use dye patterns as a qualitative picture to illustrate hydrological connectivity in soil, but also it can be used more effectively to quantify and compare flow processes in soil (Weiler and Flühler, 2003). The index of hydrological connectivity (IHC) below the soil surface obtained through field dye tracing experiments, allows the quantification of the hydrological connectivity within the soil and the evaluation of water flow and solute transport conditions and characteristics (Zhang W. et al, 2022). In the Yellow River Delta Wetland, the relationship between hydrological connectivity, root and wetland degradation based on IHC has been extensively studied (Zhang et al, 2021;.…”

“…In the Yellow River Delta Wetland, the relationship between hydrological connectivity, root and wetland degradation based on IHC has been extensively studied (Zhang et al, 2021;. The hydrological connectivity below the forest soil surface can also be presented by this index (Zhang W. et al, 2022). In the context of the combined effect of topography and vegetation, it is an interesting try to analyze hydrological connectivity on riparian zones based on dye-tracer technology.…”