The Root-Soil Water Relationship Is Spatially Anisotropic in Shrub-Encroached Grassland in North China: Evidence from GPR Investigation

Abstract

To analyze the root-soil water relationship at the stand level, we integrated ground-penetrating radar (GPR), which characterized the distribution of lateral coarse roots (>2 mm in diameter) of shrubs (Caragana microphylla Lam.), with soil core sampling, which mapped soil water content (SWC) distribution. GPR surveys and soil sampling were carried out in two plots (Plot 1 in 2017 and Plot 2 in 2018) with the same size (30 × 30 m2) in the sandy soil of the semi-arid shrubland in northern China. First, the survey area was divided into five depth intervals, i.e., 0–20, 20–40, 40–60, 60–80, and 80–100 cm. Each depth interval was then divided into three zones in the horizontal direction, including root-rich canopy-covered area, root-rich canopy-free area, and root-poor area, to indicate different surface distances to the canopy. The generalized additive models (GAMs) were used to analyze the correlation between root distribution density and SWC after the spatial autocorrelation of each variable was eliminated. Results showed that the root-soil water relationship varies between the vertical and horizontal directions. Vertically, more roots are distributed in soil with high SWC and fewer roots in soil with low SWC. Namely, root distribution density is positively correlated with SWC in the vertical direction. Horizontally, the root-soil water relationship is, however, more complex. In the canopy-free area of Plot 1, the root-soil water relationship was significant (p < 0.05) and negatively correlated in the middle two depth intervals (20–40 cm and 40–60 cm). In the same two depth intervals in the canopy-free area of Plot 2, the root-soil water relationship was also significant (p < 0.01) but non-monotonic correlated, that is, with the root distribution density increasing, the mean SWC decreased first and then increased. Moreover, we discussed possible mechanisms, e.g., root water uptake, 3D root distribution, preferential flow along roots, and different growing stages, which might lead to the spatially anisotropic relationship between root distribution and SWC at the stand level. This study demonstrates the advantages of GPR in ecohydrology studies at the field scale that is challenging for traditional methods. Results reported here complement existing knowledge about the root-soil water relationship in semi-arid environments and shed new insights on modeling the complex ecohydrological processes in the root zone.

Linking horizontal crosshole GPR variability with root image information for maize crops

“…In contrast, using crosshole GPR allows a direct link from the EM wave velocity to ε r (for more details, see Klotzsche et al, 2018). In recent years, surface GPR has been used to investigate the soil-plant continuum with large root systems such as tree roots (reviewed in L. Guo et al, 2013 andRodríguez-Robles et al, 2017) and shrub roots (e.g., Cui et al, 2021;Liu et al, 2020Liu et al, , 2019Parsekian et al, 2012). Although some studies investigated the possibility of estimating agricultural root systems (Delgado et al, 2017;Klotzsche, Lärm, et al, 2019;Liu et al, 2017;Wijewardana & Galagedara, 2010;Galagedara et al, 2002Galagedara et al, , 2003, the detection and mapping of finer root systems found in crops are still challenging using surface GPR.…”

The Effect of Thickness of Covering Soil on Soil Water Retention and Crop Growth in Land Reclamation Filled with Fly Ash: Evidence from GPR and UAV Investigation

“…Author Copy to enhance the visibility of the fly ash-soil critical layer [28]. Since the GPR data contain background noise, which is mainly caused by the horizontal frequency band created by the antenna-ground interaction, multiple underground reflections, and high-frequency spike events, we conducted background removal processing [29]. Following this step, band-pass filtering was used to eliminate the high-frequency and lowfrequency noise.…”

Preliminary Application of Ground-Penetrating Radar for Reconstruction of Root System Architecture in Moso Bamboo

“…In addition, the total biomass and To date, non-invasive geophysical techniques have led to some progress in the study of coarse roots in the field [27,28]. Ground-penetrating radar (GPR) is a well-established, nondestructive geophysical technique used widely for in-situ detection of coarse roots [29][30][31][32][33][34][35][36]. However, GPR cannot estimate topological relationships between root points.…”