Nutrient and Water Relations of the Mistletoe Phoradendron leucarpum (Viscaceae): How Tightly are they Integrated?

Abstract

Tissue mineral concentrations of calcium, copper, iron, magnesium, manganese, nitrogen, phosphorus, potassium, sodium, and zinc, and long-term water-use efficiency (as estimated by δ13C±) were measured in the mistletoe Phoradendron leucarpum and its hosts to investigate the relationship between nutrient concentrations and water economies of the parasite and hosts. The mistletoe had mineral concentrations 0.97 to 2.88 times greater than the hosts. Mean long-term mistletoe water-use efficiency (-27.89±) was comparable to mean long-term host water-use efficiency (-27.69±) and generally greater than the water-use efficiency reported for most mistletoe species. Differences between mistletoe and host water-use efficiency ranged from +0.65 to -0.75± and were more similar to mistletoes found growing on nitrogen-fixing host species as reported in other studies. Mistletoe nutrient concentrations, in particular nitrogen, were not related to changes in mistletoe water-use efficiencies. Nutrient: calcium ratios indicated that mistletoes acquire nutrients in excess of that which can be delivered by the host xylem. These data are discussed relative to the passive vs. active theories of nutrient uptake.