PARENT SESSION
Oral Session #42: Decomposition.
Presiding: K. Gross
Tuesday, August 6. 1:00 PM to 4:45 PM. Apache Meeting Room, TCC.
Genetic variation in dominant riparian tree species affects leaf decomposition in streams: Within and among species contrasts.
LeRoy, Carri*,1, Moan, Jaina1, Whitham, Thomas1, Marks, Jane1, 1 Northern Arizona University, Flagstaff, AZ
ABSTRACT- Riparian zones in western US watersheds have large cottonwood hybrid zones. Stream-side vegetation at higher elevations is dominated by pure Narrowleaf cottonwood (Populus angustifolia) stands and lower elevations by Fremont cottonwood (Populus fremontii) stands connected by hybrid zones with F1 hybrids (P. fremontii x P. angustifolia), F1 x P. angustifolia backcrossed hybrids and both parental types. We placed leaves of each of the four cross types from common garden trees in mesh litterbags in Oak Creek, AZ to determine differences in decomposition rates. A concurrent study compared litter decomposition rates for five dominant native species, Arizona alder (Alnus oblongifolia), Arizona sycamore (Platanus wrightii), Fremont cottonwood (P. fremontii), Velvet ash (Fraxinus pennsylvanica var. velutina), and Gambel oak (Quercus gambelii). Native riparian tree species in Oak Creek have decomposition rates that range from 47.7%±0.813 SE (after 7 days) for quickly degraded species like Fremont cottonwood to 8.4%±0.544 SE (after 7 days) for slowly degraded species like oak. Despite this range, differences between species can be as small as 3.0% (alder vs. ash). Among the cottonwood cross types decomposition rates ranged from 40.7%±0.528 SE (after 7 days) for P. fremontii to 29.9%±0.528 SE (after 7 days) for P. angustifolia backcrossed hybrids. Not only was the range of decomposition rates across cross types greater than differences among species, but the difference between the two hybrid-types also exceeds species differences. The difference between F1 and backcross hybrids provides evidence for genetic control over in-stream decomposition rates. Prior studies have shown that species diversity has large impacts on litter quality and stream function. This study extends this by linking genetic diversity to ecosystem function.
KEY WORDS: Populus, genetic diversity, species diversity, aquatic decomposition