Abstract
Abstract. 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 (SFb), shrub stemflow equivalent water depth (SFd), 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 SFb, 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 SFb 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.
Highlights
Stemflow delivers precipitation to the plant root zone more efficiently via preferential root paths, worm paths and soil macropores, compared with throughfall, another important element of rainfall redistribution
Stemflow was measured at 36 rainfall events in this study, 18 events (209.8 mm) in 2014 and 18 events (205.3 mm) in 2015, which accounted for 32.7 and 46.2 % of total rainfall events, and 73.1 and 74.9 % of total precipitation amount during the experimental period of 2014 and 2015, respectively (Fig. 3)
Compared with S. psammophila, C. korshinskii produced a larger amount of stemflow more efficiently during different sized rains
Summary
Stemflow delivers precipitation to the plant root zone more efficiently via preferential root paths, worm paths and soil macropores, compared with throughfall, another important element of rainfall redistribution. The double-funnelling effects of stemflow and preferential flow create “hot spots” and “hot moments” by enhancing nutrient cycling rates at the surface soil matrix (Mcclain et al, 2003; Johnson and Lehmann, 2006; Sponseller, 2007), substantially contributing to the formation and maintenance of “fertile islands” (Whitford et al, 1997), “resource islands” (Reynolds et al, 1999) or “hydrologic islands” (Rango et al, 2006). Yuan et al.: Comparisons of stemflow and its bio-/abiotic influential factors
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