Leaf trait adaptations of xylem-tapping mistletoes and their hosts in sites of contrasting aridity
Background and aims
Xylem-tapping mistletoes may experience relaxed selective pressure to use water efficiently during photosynthesis because of lower per-unit costs for water acquisition than experienced by host plants. As a result, we hypothesised that mistletoes would exhibit parallel but dampened leaf-level adaptations and responses to aridity, compared to those seen in hosts.
Photosynthetic traits, leaf dark respiration, nutrient concentrations and specific leaf area (SLA) were measured on 42 mistletoe-host species-pairs sampled from five sites in Australia and Brazil that vary widely in aridity.
Mistletoes exhibited similar trait-shifts to hosts in relation to site aridity. In both groups, arid-site species showed stronger control over stomatal water loss, larger drawdown of CO2 during photosynthesis (lower ci: ca), higher leaf N and P concentrations per unit leaf area, and lower SLA. Nevertheless, mistletoes were profligate water users compared to their hosts and showed substantially less efficient use of water during photosynthesis. On average, mistletoes showed twice higher leaf dark respiration rates at a given photosynthetic capacity, suggesting relatively higher leaf maintenance costs for these parasitic plants.
Despite fundamental differences in lifestyle and in photosynthetic traits, mistletoes exhibit trait responses and adaptations to site aridity in parallel and to approximately the same extent as their hosts.
KeywordsPhotosynthesis Leaf nutrient concentration Dark respiration Loranthaceae Hemi-parasite Water use efficiency
MCS was supported by a scholarship from ‘Conselho Nacional do desenvolvimento Cientifico e Tecnologico’ (CNPq) and by Macquarie University. IJW acknowledges support from the Australian Research Council. We acknowledge Australian National Parks offices, RECOR/IBGE, Lindsay Hutley and Augusto Cesar Franco for logistic support. We thank New South Wales and South Australia National Parks and Wildlife Services (license numbers SL100326 and M26025-1, respectively) for permits. We also thank Izabelly Sant’Ana, Allyson Eller, Julieta Garcia-Russell, Julia Cooke and Fabricius Domingos for the valuable help in the field.
MCS and IJW conceived and designed the study. MCS conducted fieldwork, performed statistical analyses, and wrote the manuscript with help from IJW.
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