Oxygen and carbon isotope composition of parasitic plants and their hosts in southwestern Australia
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- Cernusak, L.A., Pate, J.S. & Farquhar, G.D. Oecologia (2004) 139: 199. doi:10.1007/s00442-004-1506-6
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We measured leaf dry matter δ18O and δ13C in parasitic plants and their hosts growing in southwestern Australia. Parasite/host pairs included two mistletoe species, three species of holoparasites, and five species of root hemiparasites. Among these parasite functional types, significant variation was observed in parasite/host isotopic differences for both δ18O (P<0.0001, n=65) and δ13C (P<0.0001, n=64). Mistletoes were depleted in both 18O and 13C compared to their hosts; parasite/host differences were −4.0‰ for δ18O (P<0.0001) and −1.9‰ for δ13C (P<0.0001). The lower δ18O in mistletoe leaf dry matter compared to their hosts is consistent with the frequently observed high transpiration rates of these parasites. Root hemiparasites were also depleted in 18O and 13C compared to their hosts, but not to the same extent as mistletoes; parasite/host differences were −1.0‰ for δ18O (P=0.04) and −1.2‰ for δ13C (P=0.0006). In contrast to mistletoes and root hemiparasites, holoparasites were enriched in both 18O and 13C compared to their hosts; parasite/host differences were +3.0‰ for δ18O (P<0.0001) and +1.5‰ for δ13C (P=0.02). The enrichment in 18O for holoparasite dry matter did not result from more enriched tissue water; holoparasite tissue water δ18O was less than host leaf water δ18O by a difference of −3.8‰ when sampled at midday (P=0.0003). Enrichment of holoparasites in 13C compared to their hosts is consistent with a generally observed pattern of enrichment in heterotrophic plant tissues. Results provide insights into the ecology of parasitic plants in southwestern Australia; additionally, they provide a context for the formulation of specific hypotheses aimed at elucidating mechanisms underlying isotopic variations among plants.