Stemflow transports nutrient-enriched precipitation to the rhizosphere and functions as an efficient terrestrial flux in water-stressed ecosystems. However, its ecological significance has generally been underestimated because it is relatively limited in amount, and the biotic mechanisms that affect it have not been thoroughly studied at the leaf scale. This study was conducted during the 2014 and 2015 rainy seasons at the northern Loess Plateau of China. We measured the branch stemflow volume (SF_b), shrub stemflow equivalent water depth (SF_d), stemflow percentage of incident precipitation (SF %), stemflow productivity (SFP), funnelling ratio (FR), the meteorological characteristics and the plant traits of branches and leaves of C. korshinskii and S. psammophila. This study evaluated stemflow efficiency for the first time with the combined results of SFP and FR, and sought to determine the inter- and intra-specific differences of stemflow yield and efficiency between the two species, as well as the specific bio-/abiotic mechanisms that affected stemflow. The results indicated that C. korshinskii had a greater stemflow yield and efficiency at all precipitation levels than that of S. psammophila. The largest inter-specific difference generally occurred at the 5–10 mm branches during rains of ≤ 2 mm. Precipitation amount was the most influential meteorological characteristic that affected stemflow yield and efficiency in these two endemic shrub species. Branch angle was the most influential plant trait on FR. For SF_b, stem biomass and leaf biomass were the most influential plant traits for C. korshinskii and S. psammophila, respectively. For SFP of these two shrub species, leaf traits (the individual leaf area) and branch traits (branch size and biomass allocation pattern) had a great influence during lighter rains ≤ 10 mm and heavier rains > 15 mm, respectively. The lower precipitation threshold to start stemflow allowed C. korshinskii (0.9 mm vs. 2.1 mm for S. psammophila) to employ more rains to harvest water via stemflow. The beneficial leaf traits (e.g., leaf shape, arrangement, area, amount) might partly explain the greater stemflow production of C. korshinskii. Comparison of SF_b between the foliated and manually defoliated shrubs during the 2015 rainy season indicated that the newly exposed branch surface at the defoliated period and the resulting rainfall intercepting effects might be an important mechanism affecting stemflow in the dormant season.

Stemflow is important for recharging root-zone soil moisture in arid regions. Previous studies have generally focused on stemflow volume, efficiency and influential factors but have failed to depict stemflow processes and quantify their relations with rainfall characteristics within events, particularly for xerophytic shrubs. Here, we measured the stemflow volume, intensity, funneling ratio and time lags to rain at two dominant shrub species (Caragana korshinskii and Salix psammophila) and rainfall characteristics during 54 events at the semiarid Liudaogou catchment of the Loess Plateau, China, during the 2014–2015 rainy seasons. The funneling ratio was calculated as the ratio between stemflow and rainfall intensities at the inter- and intra-event scales. Our results indicated that the stemflow of C. korshinskii and S. psammophila, on average, started at 66.2 and 54.8 min, maximized 109.4 and 120.5 min after rain began, and ended 20.0 and 13.5 min after rain ceased. The two shrubs had shorter stemflow duration (3.8 and 3.4 h) and significantly larger stemflow intensities (517.5 and 367.3 mm h⁻¹) than those of rain (4.7 h and 4.5 mm h⁻¹). As branch size increased, both species shared the decreasing funneling ratios (97.7–163.7 and 44.2–212.0) and stemflow intensities (333.8–716.2 and 197.2–738.7 mm h⁻¹). Tested by the multiple correspondence analysis and stepwise regression, rainfall amount and duration controlled stemflow volume and duration, respectively, at the event scale by linear relations (p < 0.01). Rainfall intensity and raindrop momentum controlled stemflow intensity and time lags to rain for both species within the event by linear or power relationships (p < 0.01). Rainfall intensity was the key factor affecting stemflow process of C. korshinskii, whereas raindrop momentum had the greatest influence on stemflow process of S. psammophila. Therefore, rainfall characteristics had temporally dependent influences on corresponding stemflow variables, and the influence also depended on specific species.

Rainfall is known as the main water replenishment in dryland ecosystems, and rainfall partitioning by vegetation reshapes the spatial and temporal distribution patterns of rainwater entry into the soil. The dynamics of rainfall partitioning have been extensively studied at the inter-event scale, yet very few studies have explored its finer intra-event dynamics and the relating driving factors for shrubs. Here, we conducted a concurrent in-depth investigation of all rainfall partitioning components at inter- and intra-event scales for two typical xerophytic shrubs (Caragana korshinskii and Salix psammophila) in the Liudaogou catchment of the Loess Plateau, China. The event throughfall (TF), stemflow (SF), and interception loss (IC), and their temporal variations within the rainfall event, as well as the meteorological factors and vegetation characteristics, were systematically measured during the 2014–2015 rainy seasons. Our results showed that C. korshinskii had significantly higher SF percentage (9.2 %) and lower IC percentage (21.4 %) compared to S. psammophila (3.8 % and 29.5 %, respectively), but their TF percentages were not significantly different (69.4 % vs. 66.7 %). At the intra-event scale, TF and SF of S. psammophila were initiated (0.1 vs. 0.3 h and 0.7 vs. 0.8 h) and peaked (1.8 vs. 2.0 h and 2.1 vs. 2.2 h) more quickly, and TF of S. psammophila lasted longer (5.2 vs. 4.8 h) and delivered more intensely (4.3 vs. 3.8 mm h⁻¹), whereas SF of C. korshinskii lasted longer (4.6 vs. 4.1 h) and delivered more intensely (753.8 vs. 471.2 mm h⁻¹). For both shrubs, rainfall amount was the most significant factor influencing inter-event rainfall partitioning, and rainfall intensity and duration controlled the intra-event TF and SF variables. The C. korshinskii with larger branch angle, more small branches, and smaller canopy area, has an advantage over S. psammophila to produce SF more efficiently. The S. psammophila has lower canopy water storage capacity to generate and peak TF and SF earlier, and it has larger aboveground biomass and total canopy water storage of individual plants to produce higher IC compared to C. korshinskii. These findings contribute to the fine characterization of shrub-dominated ecohydrological processes, and improve the accuracy of water balance estimation in dryland ecosystems.