Background There are many species of forest stands and a well-developed root system in the Simian Mountains, Chongqing; however, this has led to the creation of a large amount of preferential root flow, generating more erosion and detrimental to the growth and development of the local vegetation. Therefore, this work is aimed to study the influence of root distribution on the saturated hydraulic conductivity of soil in Simian Mountain and to provide data support and scientific guidance for surface runoff mitigation and planting.

Methods Five kinds of typical stand types in there plantation forest were selected, and one in situ soil column containing root characteristics was taken every 20 cm in the 0-60 cm soil layer (three replicate groups were set up in each layer, 45 in situ soil columns in total) and brought back to the laboratory for root characteristics collection and constant head method to determine the saturated hydraulic conductivity of soil, and to investigate the influence of different stand types, soil depth and diameter class root system on the saturated hydraulic conductivity. The data were processed by origin ANOVA and correlation coefficient analysis.

Results 1) There were differences in root proportion among different stands, and the root proportion decreased with vertical depth. The percentage of roots in pure coniferous forest ≤5 mm was the highest, reaching 71.00%-98.67%. In coniferous mixed forest, roots with different diameters were evenly distributed. The root diameter distribution of coniferous and broad-leaved mixed forest showed the law that the root diameter increased with the vertical depth of soil layer. 2) With the increase of soil depth, the soil saturated hydraulic conductivity of each stand showed a decreasing trend, and it was significantly higher in 0-20 cm than other soil layers. The saturated hydraulic conductivity of soil was significantly different under different stand conditions with the same soil depth. In addition, the average K_s of different stands at the same depth was as follows: Theropencedrymion mixed forest > broadleat mixed forest > coniferous mixed forest > Cunninghamia Lanceolata pure forest > Pinus maweisong pure forest. 3) Among the five stands, the root diameter of > 1-3 mm has a strong correlation with soil saturated hydraulic conductivity, while the root diameter of ≤1 mm and >3 mm has a low correlation with soil saturated hydraulic conductivity.

Conclusions This study demonstrated the correlation between root systems of different diameter classes and soil saturated hydraulic conductivity in forest stands, the percentage of > 1-3 mm root systems showed negative correlation with soil saturated hydraulic conductivity, and the remaining diameter classes showed binary correlation with soil saturated hydraulic conductivity. It provides theoretical support for local stand planting and flash flood control.