Natural compensation mechanism of soil water infiltration through decayed roots in semi-arid vegetation species

In arid and semi-arid areas, unsuitable afforestation programs may cause soil water deficit and even, in some cases, deep-soil desiccation and the subsequent death of part of the vegetation. However, the benefits of preferential flow through decayed root channels for supplying water in the dried soil layers are rarely evaluated. This study examines the effects of root channels on soil water content (SWC) and infiltration (initial and steady-state) in two planted species with high drought tolerance, namely: Korshinsk peashrub (Caragana korshinskii Kom.), and red plum apricot (Armeniaca vulgaris Lam.), using bare land as control site and published data from alfalfa (Medicago sativa L.) plots to refine results analysis. The infiltration rates were measured using a double-ring infiltrometer in areas with alive and decayed roots; and methylene blue was used to trace the pathways of water flow. The highest SWC appeared in the Korshinsk peashrub land, whereas the alfalfa grassland had the lowest SWC; and the differences of SWC among treatments were significant at all soil layers. Korshinsk peashrub had the highest steady infiltration rates, which were about 23% and 83% higher than those rates measured in the fruit tree plantation and alfalfa grasslands, respectively. The steady infiltration rates were significantly and positively correlated with the average root diameter and area. Within the same species, the decayed root plots significantly increased the soil water infiltration capacity compared to the alive root plots. Considering the water scarcity conditions of the study area, the preferential flow formed through decomposed roots was conducive to soil water supplement, appearing as a natural compensation mechanism caused by dead vegetation. Our findings contribute to a better understanding of soil water infiltration during root decay of the plants in water-limited ecosystems, and how this dynamic replenishes soil moisture and alleviates soil desiccation.