PARENT SESSION
Oral Session #66: Invasions: Plants. Mechanisms, patterns, controls. Presiding: R. Mack.
Thursday, August 9, 2001. 1:00 PM to 4:45 PM. Hall of Ideas E.
Biomass and nitrogen allocation in an invasive annual grass and two native Mojave Desert annuals.
DeFALCO, LESLEY1,2, NOWAK, ROBERT2, 1 2
ABSTRACT- The invasive annual grass, Bromus madritensis ssp. rubens, is widespread throughout the Mojave Desert, yet we are only recently understanding how it establishes successfully in native plant communities. Previously we found that Bromus extracts soil water and N faster than native annuals. In this study we examined how greater resource acquisition in Bromus influences biomass, N allocation and fecundity compared to two native annual species Vulpia octoflora and Descurainia pinnata (grass and forb, respectively). While greater biomass and N allocation toward roots would increase the invasibility of Bromus in a variety of habitats, allocation of resources toward seed production would place Bromus at an advantage over native annuals in the seed bank. Total plant biomass was more than two times greater in Bromus compared to either Descurainia or Vulpia, yet total biomass was not different between the two native species. At low density, N fertilization favored shoot and root growth in Bromus , but seed biomass remained the same. Conversely, Descurainia and Vulpia had significant increases not only in root and shoots, but also seed biomass, irrespective of growth density. At high density, N fertilization increased shoot production of Bromus, but at a cost to seed and root biomass. Bromus' invasibility is more likely a consequence of resource extraction and less a result of it inundating the seed bank.
KEY WORDS: Invasive species, Mojave Desert, Bromus madritensis ssp. rubens