PARENT SESSION
Oral Session #21: Nutrient cycling: Nitrogen.
Presiding: S. Hart
Monday, August 5. 1:00 PM to 3:45 PM. Grand Ballroom Central, Radisson.

Predicting the effects of community composition on nitrogen dynamics in a coastal California grassland.

Corbin, Jeffrey^*,1, D'Antonio, Carla^1,2, Bouchier, Todd¹, ¹ University of California, Berkeley, Berkeley² USDA-ARS, Reno, Nevada

ABSTRACT- To test whether the effects of community composition on nitrogen cycling rates in a coastal California grassland can be predicted based on plant traits, we established experimental communities dominated by three different groups of species: non-native annual grasses, non-native perennial grasses, and native perennial grasses. These species differ in such plant traits as phenology, growth rates, and allocation to above- and below-ground tissue. Leaf C:N ratio did not differ between the three groups of species, though the rates of nitrogen loss from litter was higher in annual grasses than the other two groups. Over three years of growth, above- and below-ground productivity was higher in the two perennial-dominated treatments than in the annual-dominated treatment. Levels of extractable inorganic nitrogen and nitrogen leaching losses varied predictably according to differences in phenology: in the fall, nitrate levels were significantly higher in annual treatments and corresponded to high rates of nitrogen leaching losses. Despite the greater loss of nitrogen from annual litter, rates of net nitrogen mineralization and net nitrification were highest in native-dominated plots and lowest in annual-dominated plots. CO₂ respiration rates were better predictors of nitrogen cycling rates, indicating that indirect effects of plant composition, such as microbial activity and biomass, may be required to predict soil nitrogen dynamics.

KEY WORDS: nitrogen cycling, species effects, native perennial bunchgrasses, California grassland