Print PageMany invasive plant species have been shown to alter ecosystem processes. In California’s grasslands, native species, naturalized invasives (invaded over 200 years ago) and recent invasives (in the process of dominating many sites) differ in their impacts on N cycling rates, but little is known about how the timing of soil N availability differs across the groups. We asked whether the timing of decomposition and nitrogen release matched the timing of plant N uptake across three typical grassland community types. Field plots were planted with three grassland community treatments: natives (annuals and perennials, grasses and legumes), naturalized invasives (annuals, grasses and legumes), and new invasives (annual grasses). We measured: Litter mass loss and N release, soil microbial biomass, nematode abundance and community composition, net N mineralization and nitrification, plant-available nitrogen (resin bags), and plant biomass and N content. These measurements were taken at 7 time-points during the 9-month growing season.
Results/Conclusions
Natives, naturalized exotics, and new invasives differ in their impacts on the nematode community, N availability, N cycling rates, the timing of litter mass loss, and timing of peak growth. In particular, early in the seasons when soils are dry, native plant communities have more nematodes than the other vegetation types (P = 0.022). Four months in to the 9-month growing season, litter from naturalized invasive communities had decomposed more (31.7% of mass lost) than litter from new invasives (26.7% of mass lost) (P = 0.052). Decomposition of natives is intermediate to the other two communities (29.95% of mass lost). Differences in the timing of nutrient cycling may maintain a community in an invaded state. However, managers may be able to exploit these differences in timing to competitively favor desirable grassland species.
