Characteristics of Caragana korshinskii and Hippophae rhamnoides stemflow and their significance in soil moisture enhancement in Loess Plateau, China

Stemflow of xerophytic shrubs represents a significant component of water replenishment to the soil-root system and influences water utilization of plant roots at the stand scale, especially in water-scarce semi-arid ecosystems. The stemflow of two semi-arid shrubs (Caragana korshinskii and Hippophae rhamnoides) and its effect on soil moisture enhancement were evaluated during the growing season of 2011 in the semi-arid loess region of China. The results indicated that stemflow averaged 12.3% and 8.4% of the bulk precipitation for C. korshinskii and H. rhamnoides, respectively. Individual stemflow increased in a linear function with increasing rainfall depth. The relationship between funneling ratios and rainfall suggested that there existed a rainfall depth threshold of 11 mm for both C. korshinskii and H. rhamnoides. Averaged funneling ratios were 156.6 +/- 57.1 and 49.5 +/- 30.8 for C. korshinskii and H. rhamnoides, respectively, indicating that the canopy architecture of the two shrubs was an effective funnel to channel stemflow to the root area, and C. korshinskii showed a greater potential to use stemflow water in the semi-arid conditions. For individual rainfall events, the wetting front depths were approximately 2 times deeper in the rooting zone around the stems than in the bare area outside canopy for both C. korshinskii and H. rhamnoides. Correspondingly, soil water content was also significantly higher in the root area around the shrub stem than in the area outside the shrub canopy. This confirms that shrub stemflow conserved in the deep soil layers may be an available moisture source for plant growth under semi-arid conditions.