BIOMINERALIZATION IN SEEDS - DEVELOPMENTAL-TRENDS IN ISOTOPIC SIGNATURES OF HACKBERRY

Experiments on hackberry (Celtis) fruits collected over the course of a growing season at two localities were undertaken to assess the isoto pic composition of the intricate mineral (CaCO3 and SiO2 . nH(2)O) and organic structure of hackberry endocarps. Hackberry fruits contain bi omineralized aragonite-rich endocarps and have been documented as foss ils in a variety of sites in North America and Eastern Europe ranging in age from historical to millions of years old, giving them potential as paleoclimate indicators. In the modern hackberries studied: three distinct stages of development were observed: stage 1 (0-55 days) show s a rapid increase in the whole mass of the hackberry drupe as basic c omponents differentiate; stage 2 (day 55-85) involves a short (30-day) period of slow growth overall; but is concurrent with a sharp rise in the mass of calcium carbonate mineral; stage 3 (day 85 to full maturi ty) involves a sharp increase in total mass due to mesocarp developmen t. Fruit tissues were found to have lon er delta(13)C values than stem tissues at both sites of collection; there was very little difference between the delta(18)O values in the endocarp carbonate at the two si tes. The most variable delta(13)C and delta(18)O values of endocarp we re observed in stage 1 development. After stage 2 begins, the delta(18 )O values in endocarp carbonate stabilized. The delta(13)C value of op al-occluded organic carbon appeared to be constant throughout the grow ing season. (C) 1998 Elsevier Science B.V.