Accumulation of rare earths and circulation of cerium by mockernut hickory trees

Mockernut hickory (Carya tomentosa) trees accumulate the rare-earth elements in foliage in far greater concentrations than do other species on the same site (1350 ppm in ash, compared with less than 60 ppm by red maple, tulip tree, white oak, and black gum). Inoculation of hickory trees with, 144 Ce showed that this typical rare-earth element moves slowly through woody tissues, with only a small percentage of total-tree cerium lost annually by leaf abscission. Slow decomposition of hickory litter further limits losses of rare earths from the tree–soil system. These processes create centers of rare-earth concentration that perpetuate themselves, exemplifying the role of accumulator species in determining the distribution of elements within ecosystems.