STELTZER, HEIDEMARIE* AND WILLIAM D. BOWMAN. Environmental, Population and Organismic Biology, University of Colorado, Campus Box 334, Boulder, CO 80309-0334. - Influence of plant species on community structure through the control of spatial heterogeneity in nitrogen cycling in alpine tundra.
Nitrogen availability is an important control of productivity and
species composition in the alpine. Plant species can control the
spatial variability in N availability, by influencing rates of litter
decomposition and mineralization. As a result, plant species can
affect the spatial variability in species composition, which can be
demonstrated through the spatial cross-correlation of the relative
abundances of dominant species to species diversity. In alpine
tundra, soil beneath patches dominated by either of two abundant,
codominant, species differ seven fold in net N mineralization rates,
which is greater than variation associated with differences in soil
microclimate. Three plant traits, phenolic:N ratio, C:N ratio, and
fine root production vary between these two species. Variation in
these traits accounts for 33% of the variability in soil N
transformation rates among patches where one species or the other is
dominant. Experimental results indicate that the phenolic:N ratio is
a stronger control of N mineralized from litter than the C:N ratio.
The spatial variability in the relative abundances of dominant
species, which determine N availability by controlling quality of
carbon inputs, thus has the potential to influence the spatial
variability of other community characteristics such as plant and
microbial species diversity.
Key words: Acomastylis rossii, community structure, Deschampsia caespitosa, nitrogen cycling, spatial heterogeneity, species effects