Document: DAR-3-63-35

Nitrogen limitation and ecosystem self-organization: The effects of spatial heterogeneity.

JENERETTE, G.D.* ^1,2, J.WU ² and N.B.GRIMM ¹

Arizona State University, Tempe, AZ 85287 U.S.A. ¹
Arizona State University West, Phoenix, AZ 85069, USA ²

Abstract:
Insufficient nitrogen resources limit the productivity of many terrestrial ecosystems. Why this occurs and is widespread is puzzling. If nitrogen is deficient, plants that form symbioses with nitrogen -fixing bacteria and are thus independent of nitrogen availability should be able to dominate the community. The dominance by nitrogen- fixing plants should in turn relieve nitrogen limitation. The process or processes responsible for this are not well understood, nor is it established if terrestrial nitrogen limitation is transitory or persistent over long time periods. Here we present and examine a new hypothesis, that the dynamic spatial structure of an ecosystem is itself sufficient to induce nitrogen limitation. To explore this hypothesis we generated a probabilistic cellular automata model of two vegetation functional types of vegetation, N-fixers and non-fixers. Vegetation dynamics were coupled to local nitrogen concentrations that fluctuated in response to the local vegetation present. The model ecosystem when initialized at low densities of randomly located vegetation, the model ecosystem allowed for the coexistence of both vegetation functional types at a state of permanent nitrogen limitation. Nitrogen limitation occurred through the generation of self-organized dynamic spatial heterogeneities of ecosystem components. While the importance of spatial patterning to community dynamics has been emphasized for community dynamics the relevance of these dynamics to biogeochemical cycling has not been adequately explored. These results support the hypothesis that spatial interactions can be important in both local and regional ecosystem functioning.

Keywords: self-organization, nitrogen limitation, cellular automata

This abstract is being presented at: 2:30 PM in session:
Oral Session #13: N Fixation and Biochemical Patterns.