A meta-analysis on effects of root development on soil hydraulic properties

Root development can alter the structure of soil and its hydraulic properties, which in turn can affect runoff generation processes. Although some experimental studies have examined the relationships between root characteristics and soil hydraulic properties under certain conditions, the general patterns of the effects of root development on soil hydraulic properties under different conditions remain unclear. With an aim of examining the change patterns and factors influencing soil hydraulic properties induced by root development, we conducted a literature review and subsequent meta-analysis based on the evaluated literature data. Our findings revealed that root development significantly increased soil infiltration rates [average infiltration rate (AIR), 80.1%; initial infiltration rate (IIR), 81.8%; and steady infiltration rate (SIR), 144.9%], and saturated hydraulic conductivity (K-sat) by 46.3%. Among the selected indexes, only the non-capillary porosity showed moderate correlation with AIR and IIR (R-2 = 0.6-0.65), and root length density showed a low correlation with soil infiltration rates (R-2 = 0.2-0.3). In forestland, the increase in SIR was 5.6 times that of grassland; furthermore, SIR in soil associated with plants more than 5 years old was 3-fold higher than that observed in 1-5-year-old plants. Based on our analyses, we established that the identification of a general pattern in the relationship between root characteristics and soil hydraulic properties could not be achieved owing to the diverse influences of different conditions. For example, increases in soil infiltration rates and K-sat were found to be higher in loam soils and in soils with plants bearing a larger number of tap roots. Nevertheless, it can be implied that infiltration rates and K-sat gradually increase with plant age, and that root systems generally exert the most pronounced effect on infiltration rates in spring and summer. Accordingly, we recommend that future experimental research should focus on the effects of mot systems under specific conditions, and that datasets based on observations recorded under multiple conditions should be compiled to establish general patterns based on the corresponding relationships under specific conditions. The information thus obtained would accordingly provide a basis for conducting further in-depth studies examining soil water movement and terrestrial hydrological cycle.