Veluci, Roberta M. * and Deborah A. Neher. University of Toledo, Toledo OH,
43606. Microbiotic Crust Communities: Nitrogen Fixation and Leaching within a
Temperate Oak Savannah.
Microbiotic crust is a biological soil crust composed of lichens, cyanobacteria,
green algae, mosses, and fungi. Although crusts are a dominant source of
nitrogen in arid ecosystems, this study is the first to examine their contribution to
nitrogen availability in xeric temperate habitats. The study site is located within
the Oak Openings Metropark of Northwest Ohio. Using an acetylene reduction
technique, we demonstrated that nitrogen fixation occurs in these crusts covering
sandy, low nitrogen soil. Based on video imaging analysis of crust surface cover,
proportion of moss cover explained more nitrogen fixation (p = 0.0003) than did
lichen, cyanobacteria or no cover (p  0.15). Fluorescent microscopy revealed
that moss surfaces are covered with cyanobacteria responsible for fixing
nitrogen. Nitrate and ammonium leaching from the crust layer were quantified
using Amberlite IRN-78 and IRN-77 resin bags inserted within intact soil cores at
4-cm depth. Leaching of nitrate (p = 0.07) but not ammonium increased with
precipitation. Neither extent nor composition of crust coverage affected leaching
of either ion (p > 0.15). Recovery efficiency of nitrate and ammonium ions from
resins was 33 and 70%, respectively, under optimal conditions. Automated
monitoring of microclimate in the surface 7-cm of soil suggests that moisture and
temperature fluctuations in soil are moderated under crust compared to bare soil
without crust. We conclude that biological crusts in northwestern Ohio enhance
nitrogen fixation and moderate soil microclimate but do not impact nitrogen
leaching.