CHANGES IN TISSUE NITROGEN AND PHOSPHORUS AND FOLIAR FREE AMINO-ACIDSIN AUTUMN OLIVE, BLACK LOCUST, AMERICAN SYCAMORE, AND HONEY LOCUST DURING AUTUMN

Changes in tissue nitrogen, phosphorus, and foliar free amino acids of four temperate woody deciduous plants (autumn olive (Elaeagnus umbell ata Thunb.), black locust (Robinia pseudoacacia L.), American sycamore (Platanus occidentalis L.), and honey locust (Gleditsia triacanthos L .)) were determined during the autumns of 1987 and 1988 on two physica lly and nutritionally distinct sites in central Illinois, United State s. The dinitrogen-fixing species, actinorhizal autumn olive (Frankia n odulated) and leguminous black locust (Rhizobium nodulated), resorbed a greater proportion of phosphorus than nitrogen from leaves prior to autumnal leaf abscission in comparison with the nonfixing American syc amore and honey locust. The net autumnal changes in nitrogen or phosph orus of each species did not differ with site in most cases. Free amin o acid contents of leaves tended to decline as leaves senesced during the drier autumn of 1987; however, during the autumn of 1988 foliar fr ee amino acid contents tended to increase as the season progressed, wi th abscised leaves having the greatest contents. Root bark seemed to b e a major sink for phosphorus during autumn in the dinitrogen-fixing s pecies, while all of the species investigated showed significant autum nal increases in twig-bark concentrations of nitrogen.