Effects of Altitude, Slope Aspect, and Soil Depth on Soil Properties and Herbaceous Root Distribution in Honghe Hani...

To elucidate the elevational differentiation patterns of soil physical properties and nutrient contents within the Yuanyang Hani Terrace system and to clarify their influence on the spatial distribution of vegetation root systems, we systematically collected soil and root samples across varying elevations, slope aspects, and soil depths. A combination of soil physicochemical analyses, root distribution quantification, correlation analysis, and principal component analysis (PCA) was employed. The results indicated that soil bulk density exhibited a unimodal trend along the elevation gradient, initially decreasing and then increasing, with the following order: high-elevation sunny slope > high-elevation shady slope > low-elevation sunny slope > low-elevation shady slope > mid-elevation sunny slope > mid-elevation shady slope. The lowest bulk density values (1.10-1.17 g cm^-3) were observed at mid-elevations, where porosity and infiltration rates reached their maxima (>54% and 1.31-1.34 mm min^-1, respectively), whereas the poorest conditions were found at high elevations. Shady slopes consistently outperformed sunny slopes, with the greatest aspect-induced divergence occurring at mid-elevations (bulk density difference: 0.079 g cm^-3). An anomalous combination of a sharp increase in bulk density (1.33 g cm^-3), alongside simultaneous peak porosity (54.74%) and infiltration rate (1.32 mm min^-1), was detected in the 20-40 cm layer, which was attributed to compaction-induced alterations in pore configuration while preserving preferential flow pathways. Most nutrient variables exhibited optimal levels at mid-elevations; however, total potassium and available phosphorus displayed maximal values at low elevations, likely related to chemical weathering intensity and plant uptake competition. Root systems were predominantly concentrated in the surface layer (0-20 cm), accounting for 87.88% of total root abundance, and showed significant positive correlations with soil moisture and porosity (r ≥ 0.89) and significant negative correlations with bulk density (r ≤ -0.97). The first principal component of PCA (explaining 73.4% of total variance) was dominated by moisture, porosity, and infiltration rate, whereas nutrient loadings were relatively low, indicating that physical hydrological processes constituted the primary drivers of environmental differentiation. Collectively, these findings elucidate the coordinated regulation of soil multi-attribute variations by elevation, slope aspect, and soil depth, thereby providing a theoretical basis for the sustainable management of terrace agroecosystems.