Studies of Absorption of 32P, 59FE, and 45CA by Water-Milfoil (Myriophyllum Exalbescens Fernald)

A method was developed for determining uptake and translocation of mineral elements by intact submersed aquatic vascular plants in laboratory and field studies. Autoradiographs and radioactivity measurements provided direct evidence that 32P, 59Fe, and 45Ca were absorbed by the roots of Myriophyllum exalbescens and translocated to the shoot tissues. Similar evidence was obtained for absorption of 32P by the shoots and translocation to the roots. Data from experiments designed to compare the effect of substrate type (sand or muck) and the presence or absence of light showed no significant difference in the amounts of 32P absorbed by roots. Translocation of 59Fe from root to shoot tissues occurred mainly when plants were rooted in muck. 45Ca translocation from roots to shoots was greatest for plants rooted in sand and maintained in the light. 32P was generally distributed throughout Myriophyllum as revealed by autoradiography, with some accumulation occurring at the nodal and building regions. 59Fe and 45Ca were not translocated as readily but some accumulation of each occurred in the stem. 32P absorbed by the roots of Myriophyllum was translocated to the shoot system and released to the surrounding water. Experimental evidence showed that injury to submersed hydrophytes can result in additional release of phosphate to the water. The rate of release is increased as a result of physical damage to the shoot. This provides an additional pathway for the cycling of phosphorus in freshwater environments.