Vol.:(0123456789) 1 3 Oecologia https://doi.org/10.1007/s00442-018-4158-7 PHYSIOLOGICAL ECOLOGY - ORIGINAL RESEARCH Can hydraulically redistributed water assist surrounding seedlings during summer drought? A. L. Muler 1  · E. J. B. van Etten 1  · W. D. Stock 1  · K. Howard 2  · R. H. Froend 1 Received: 12 June 2017 / Accepted: 1 May 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Plant interaction studies provide a good understanding of the roles of key species, which can assist restoration of natural ecosystems. Among the interactions, facilitation and competition are known to afect ecosystem structure and function. We investigated whether a deep-rooted species could positively afect surrounding seedlings through hydraulic redistribution during dry months. We conducted two experiments in which seedlings from two species were growing together or isolated from source plants (feld experiment) and where plants were isolated from source plants that were connected to or separated from a water table (glasshouse experiment). Survival, growth, water relations and soil water content were measured. We also applied δ 2 H enriched water adjacent to, or into, the roots of source plants to track water movement between plants. Soil water content was higher in shallow layers where source plants could interact with seedlings (feld) and when accessing water tables (glasshouse). Seedlings from all treatments had an increase in leaf δ 2 H. Seedlings of Banksia attenuata that were isolated from source plants had the highest survival, growth and stomatal conductance rates. Seedlings of Gompholo- bium tomentosum presented higher stomatal conductance rates when growing with source plants than when isolated from them during the frst months, but this relationship reversed towards the end of summer. These results suggest that source plants and seedlings competed, but the infuence of facilitation and competition might change during the year, at least for the shallow-rooted species. Therefore, competition for water and/or other limiting factors must be considered when planning ecological restoration in such areas. Keywords Facilitation · Competition · Water · Ecological restoration · Mediterranean-ecosystems Introduction Soil water availability during the dry summer represents a major environmental limitation (Di Castri 1973), particu- larly in Mediterranean-type ecosystems (MTEs) which have hot, dry summers and mild, wet winters (Aschmann 1973). MTEs support a high diversity of uniquely adapted plant species (Cowling et al. 1996) with a variety of functional responses to water use and carbon assimilation, including deep roots, specialized root morphology, efcient control of stomatal conductance, specialised hydraulic architecture and leaf physiology, and phenology attributes (Mitchell et al. 2008; Hernández et al. 2010; West et al. 2012; Vilagrosa et al. 2014; Skelton et al. 2015). However, MTEs are some of the most highly modifed ecosystems on the planet (Hobbs et al. 1995), and are predicted to be severely afected by the drier conditions projected by climate change modelling (Klausmeyer and Shaw 2009; IPCC 2014). Water stress is one of the main causes of seedling mortal- ity in MTEs (Lloret et al. 2005; Hallett et al. 2014; Rokich 2016), and this has resulted in the failure of many resto- ration projects (Mendoza et al. 2009; Vallejo et al. 2012). Therefore, knowledge of current plant water-use strategies has the potential to assist the design of restoration projects by identifying species that have traits that enable them to Communicated by Miquel A Gonzalez-Meler. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00442-018-4158-7) contains supplementary material, which is available to authorized users. * A. L. Muler analu.muler@gmail.com 1 Centre for Ecosystem Management, School of Science, Edith Cowan University, 270 Joondalup Drive, Joondalup, WA 6027, Australia 2 School of Veterinary and Life Sciences, Murdoch University, Perth 6150, Australia