Flora 205 (2010) 802–810 Contents lists available at ScienceDirect Flora journal homepage: www.elsevier.de/flora Mineral nutrition and heterotrophy in the water conservative holoparasite Hydnora Thunb. (Hydnoraceae) Jay F. Bolin a,∗ , Kushan U. Tennakoon b , Erika Maass c a Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, USA b Department of Biology, University of Brunei Darussalam, Jalan Tungku Link, Gadong BE 1410, Darussalam, Brunei c Department of Biological Sciences, University of Namibia, Windhoek, Namibia article info Article history: Received 30 August 2009 Accepted 20 December 2009 Keywords: Euphorbia Stable isotopes Transdermal water loss Parasitic plant Solute uptake abstract There are large gaps in our understanding of parasite–host nutrient relationships. Our goal was to evaluate transdermal water loss, parasite–host mineral relationships, and heterotrophy in the holoparasitic genus Hydnora. We estimated in situ transdermal water loss in Hydnora and measured nutrient profiles and  13 C and  15 N signatures for Hydnora and hosts in southern Africa and Madagascar. For comparison we also measured  13 C and  15 N for aerial hemiparasites at the same sites. Transdermal water loss in Hydnora ranged from 0.14 ± 0.02 to 0.38 ± 0.04 mg cm -2 h -1 and was comparable to transpiration rates for water conservative xerophytes. Concentrations of P and K were higher in Hydnora relative to CAM hosts; other mineral concentrations were significantly lower in the parasite or were not different.  13 C signatures of holoparasites and hemiparasites relative to their hosts reflected host metabolism and differences in com- mitment to heterotrophic C gain. Holoparasite  13 C values were significantly enriched (by 0.55‰ ± 0.23) compared to host shoot and depleted compared to host root tissues (by -0.97‰ ± 0.12). Holoparasite  13 C values were not significantly different compared to the estimated whole host  13 C value.  15 N val- ues for holoparasites and hemiparasites were significantly correlated with hosts. The water conservative nature of Hydnora spp. combined with parasite–host mineral nutrition profiles are suggestive of active processes of solute uptake. Stable isotope fractionation in host tissues dictated significant differences between parasite and host (shoot and root)  13 C signatures. The confirmation of complete heterotrophy and the lack of a confounding transpiration stream may make Hydnora a promising model organism for the examination of parasite solute uptake. © 2010 Elsevier GmbH. All rights reserved. 1. Introduction Parasitic plants derive all or part of their mineral and carbon requirements from their host plants. All parasitic plants share a specialized organ known as the haustorium, through which they mediate solute uptake from the host by a variety of mecha- nisms. Transpiration (mass flow/passive transport), osmotica, and active transport may all play important roles in solute and water uptake (Hibberd and Jeschke, 2001; Shen et al., 2006). The rel- ative importance of these modes of transport may depend on haustorial anatomy, the rate of parasite transpiration, and the mode of parasitism (from hemiparasitism to holoparasitism). Most hemiparasites, and particularly the well studied mistletoes, drive solute uptake primarily via greater transpiration rates than their respective hosts (Ehleringer et al., 1985). In contrast, holoparasites without the presence of extensive light gathering surfaces gener- ∗ Corresponding author. E-mail address: jbolin@odu.edu (J.F. Bolin). ally have drastically lower rates of transpiration relative to their hosts (Seel et al., 1992) but are still strong sinks for host derived solutes and water. Thus how do holoparasites, without the benefit of high transpi- ration, drive water and solute transport from the host? Hibberd and Jeschke (2001) state in their review of solute flux that the precise answer is still unclear, however progress has been made. Several studies have shown selective transport and processing of solute at or near the haustoria in hemiparasites using radiotrac- ers (ie. Govier et al., 1967) or analysis of xylem sap (e.g. Pate et al., 1994; Tennakoon and Pate, 1996; Tennakoon et al., 1997). Notably, in the hemiparasite Rhinanthus minor, haustorial anatomy influenced by host resistance strongly controlled the transport of solutes (Cameron and Seel, 2007). Integrated models of water and solute fluxes combined with sap analysis and other direct measure- ments have shown a trend of strong dependence on phloem borne nutrients in the holoparasites, Cuscuta (Jeschke et al., 1994) and Orobanche (Hibberd et al., 1999). Another starting point for understanding the role of osmotica in solute uptake are mineral relationships of parasite and host in gen- 0367-2530/$ – see front matter © 2010 Elsevier GmbH. All rights reserved. doi:10.1016/j.flora.2010.04.012