Quantification of dynamic soil–vegetation feedbacks following an isotopically labelled precipitation pulse

Abstract

Abstract. The presence of vegetation alters hydrological cycles of ecosystems. Complex plant-soil interactions govern the fate of precipitation input and water transitions through ecosystem compartments. Disentangling these interactions is a major challenge in the field of ecohydrology and a pivotal foundation for understanding the carbon cycle of semiarid ecosystems. Stable water isotopes can be used in this context as tracer to quantify water movement through soilvegetation-atmosphere interfaces.The aim of this study is to disentangle vegetation effects on soil water infiltration and distribution as well as dynamics of soil evaporation and grassland water use in a Mediterranean cork oak woodland during dry conditions. An irrigation experiment using δ 18 O labelled water was carried out in order to quantify distinct effects of tree and herbaceous vegetation on the infiltration and distribution of event water in the soil profile. Dynamic responses of soil and herbaceous vegetation fluxes to precipitation regarding event water use, water uptake depth plasticity, and contribution to ecosystem soil evaporation and transpiration were quantified.Total water loss to the atmosphere from bare soil was as high as from vegetated soil, utilizing large amounts of unproductive evaporation for transpiration, but infiltration rates decreased. No adjustments of main root water uptake depth to changes in water availability could be observed during the experiment. This forces understorey plants to compete with adjacent trees for water in deeper soil layers at the onset of summer. Thus, understorey plants are subjected to chronic water deficits faster, leading to premature senescence at the onset of drought. Despite this water competition, the presence of cork oak trees fosters infiltration and reduces evapotranspirative water losses from the understorey and the soil, both due to altered microclimatic conditions under crown shading. This study highlights complex soilplant-atmosphere and inter-species interactions controlling rain pulse transitions through a typical Mediterranean savannah ecosystem, disentangled by the use of stable water isotopes.

The Demographics of Water: A Review of Water Ages in the Critical Zone

“…For example, root water uptake is governed by root distribution and the hydraulic conductivity of the roots during wet periods, whereas the soil water potential is the main driver during dry periods ( Figure 5; Asbjornsen et al, 2008;Hallett et al, 2003;Song et al, 2014;Ellsworth & Sternberg, 2015;Zarebanadkouki et al, 2016). Only recently, due to technological developments have stable isotopes become commonly used in studying smallscale (10 0to 10 1 -cm scale; i.e., Volkmann, Haberer, et al, 2016;Volkmann, Kuhnhammer, et al, 2016, Rothfuss et al, 2015 or short-term (subdaily timescale; e.g., Volkmann, Haberer, et al, 2016;Piayda et al, 2017) root-water interactions.…”

A pool‐weighted perspective on the two‐water‐worlds hypothesis

“…Proportional RWU profiles were estimated using a multisource mixing model following Philips et al (2005) (see also Piayda et al, 2017). Briefly, the mean d 18 O and d 2 H isotopic compositions of xylem water (d X ) based on five independent measurements were compared with mathematic solutions for d X , assuming that current water sources for xylem water can only originate from the observed soil water sources (1, 5, 10, 20 and 30 cm; groundwater and precipitation).…”

Water fluxes mediated by vegetation: emerging isotopic insights at the soil and atmosphere interfaces

“…monthly sampling at most) or a short monitoring duration (i.e. Volkmann et al, 2016a;Piayda et al, 2017) of virtually all currently existing soil water isotope datasets in natural environments. To the best of our knowledge, the only currently existing dataset observing daily changes of soil water isotope profiles over a longer time period than a few days was conducted under controlled bare soil conditions in the laboratory (Rothfuss et al, 2015) and supports the hypothesis by Sprenger et al (2016b).…”

“…For example, contrasting responses were found in saplings of two competing tree species: one species (oak) adjusted uptake depth to the vertical water availability during prolonged drought but exhibited a retarded readjustment toward the rewetted topsoil within the first 28 h of a heavily labelled irrigation pulse (Volkmann et al, 2016a); by contrast, the competing species (beech) used water from all soil depths independent of the soil water status, enabling faster uptake of rainwater. For grassland species, no evidence for complementary water use was found in a community of different diversities (Bachmann et al, 2015), and the plasticity of water uptake seemed to be dependent on the timing within the growing season (Prechsl et al, 2015;Piayda et al, 2017). Furthermore, the response time of RWU and shifts in its distribution are influenced by climatic conditions, as it is strongly driven by overall canopy transpiration rate and hence vapour pressure deficit of the atmosphere, thus creating a feedback link within the soil-plant-atmosphere continuum.…”

“…trees vs grasses; see Kulmatiski et al, 2010). Similarly, infiltration of precipitation and subsequent utilization of event water is distinctively affected by plant forms, differing in root system traits (Volkmann et al, 2016a;Piayda et al, 2017).…”