PARENT SESSION
Oral Session #33: Biodiversity and Ecosystem Function: Nutrients, soils, microbes.
Presiding: K. Brown
Tuesday, August 6. 8:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.
Impacts of the nitrogen-fixing black locust on nitrogen-cycling in a pine-oak ecosystem .
Rice, Steven*,1, Westerman, Bryant1, Federici, Robert1, 1 Department of Biological Sciences, Union College, Schenectady, NY
ABSTRACT- We investigated the influence of the exotic, nitrogen-fixing black locust (Robinia pseudoacacia) on nitrogen cycling in a pitch pine (Pinus rigida) -scrub oak (Quercus ilicifolia, Q. prinoides) ecosystem. Six pine-oak stands were paired with adjacent 20-35 year old black locust stands. Soil nutrient contents, annual litterfall biomass and nitrogen, and growing season and annual soil nitrogen transformation rates were assessed at five subplots established within each stand (total subplot n = 60). Black locust soils had 1.3-3.2 times greater nitrogen concentrations relative to soils within pine-oak stands. Black locust soils also had elevated levels of P and Ca. In a series of four 20-21 d and one over-winter field incubations, rates of net nitrification and total net N-mineralization were measured. Net nitrification was 25-120 times greater in black locust than in pine-oak stands. Consequently, total N-mineralization rates were greatly enhanced in black locust stands (704-790 ug N g soil-1 yr-1 in black locust versus 56-141 ug N g soil-1 yr-1 pine-oak stands). High net N-mineralization rates in black locust stands were associated with an abundance of high nitrogen, low lignin leaf litter. On average, black locust stands returned 86 kg N ha-1 yr-1 in leaf litter compared with 19 kg N ha-1 yr-1 in pine-oak stands. Thus, black locust supplements nitrogen pools, increases nitrogen return in litterfall, and enhances soil nitrogen mineralization rates when it invades nutrient poor, pine-oak ecosystems.
KEY WORDS: black locust, invasive species, nitrogen cycling, nitrogen mineralization