Food-chain transfer of zinc

This study examines the food-chain transfer of Zn from two plant species, Urtica 31 dioica (stinging nettle) and Acer pseudoplatanus (sycamore maple), into their corresponding 32 aphid species, Microlophium carnosum and Drepanosiphum platanoidis. The plants were 33 grown in a hydroponic system using solutions with increasing concentrations of Zn from 0.017 34 to 42 mg Zn/l, although U. dioica only survived in solution containing up to 18 mg Zn/l. 35 Above-ground tissue total and phloem concentrations in U. dioica and M. carnosum 36 concentrations increased with increasing Zn exposure (p<0.001). When U. dioica were 37 exposed to the 18 mg Zn/l solution the corresponding above-ground plant tissue, phloem and 38 M. carnosum concentrations were around 2100, 50 and 131 mg/kg respectively. Although Zn 39 concentrations in M. carnosum were lower than total plant concentrations bioaccumulation 40 was taking place as concentrations were greater than those in the phloem which represents 41 the Zn reservoir to which the aphids were exposed. Zn concentrations in A. pseudoplatanus 42 also increased with solution concentration from the control to the 9 mg Zn/l solution, after 43 which concentrations remained constant at around 160 mg/kg. Zn concentrations in both D. 44 platanoidis and the phloem tissue of A. pseudoplatanus were not affected by the Zn 45 concentration in the watering solution with concentrations of 6.2 and 375 mg/kg respectively 46 for exposure to solutions of 18 mg Zn/l and above. It appears that A. pseudoplatanus is able 47 to regulate Zn, whereas U. dioica is not resulting in increasing Zn exposure to the aphids on 48 the latter species. Despite this Zn concentrations in M. carnosum were around a third of 49 those in D. platanoidis, suggesting that the latter species may have naturally elevated Zn 50 concentrations. 51