Differential accumulation of nutrient elements in some New Zealand mistletoes and their hosts

It has been generally assumed that differential accumulation of mineral nutrients, leading to greater accumulation of elements in mistletoe tissues, is associated with greater transpiration in the mistletoe than in the host. Only a few investigations have measured both tissue element concentrations and transpiration, or transpiration-related parameters such as carbon isotope ratios (δ¹³C). Seasonal means for foliar concentrations of Ca, Mg, K, Na, P, N, transpiration and δ¹³C were obtained from ten mistletoe-host pairs, nine involving the mistletoe Ileostylus micranthus and one with Tupeia antarctica. Annual means of transpiration and δ¹³C were similar in mistletoes and hosts, but hosts showed greater variation in both transpiration and δ¹³C than mistletoes. Foliar concentrations of Ca and Mg in mistletoes were similar to those of their hosts, N concentrations were less, and foliar concentrations of K, Na and P were greater in mistletoes than in their hosts. Ratios of foliar concentrations of Ca, Mg and P in mistletoes to those in their hosts (M/H) were greatest when host transpiration was low, when host δ¹³C was least negative, and when the difference between mistletoe and host δ¹³C was most negative. The lack of a phloem connection between host and mistletoe, combined with circulation of elements in the host phloem and their transfer into the host xylem, provides a mechanism that explains the accumulation of phloem-mobile elements in the mistletoe.