Document: FAI-3-32-22

Size-dependent separation of two co-dominant woody species along an environmental gradient as related to differences in depth of water acquisition.

BARNES, F.J.* ¹, S.N.MARTENS ^1,2 and D.D.BRESHEARS ¹

Los Alamos National Laboratory, Los Alamos, NM, USA ¹
University of California Davis, Davis, CA, USA ²

Abstract:
Differences in the depth of soil-water acquisition are thought to be a major factor determining the distributions of plants in arid and semiarid environments, and these differences are likely to be size-dependent within a species or plant functional type. Canonical correspondence analysis of Pinus edulis (a pinyon) and Juniperus monosperma (a juniper) across 47 semiarid woodland sites in northern New Mexico, USA showed that the first axis was associated primarily with elevation, which relates to changes in the vertical distribution of water. The two species diverged along the first axis, with the amount of divergence between species increasing with size class. Temporal variation in predawn plant water potential of J. monosperma exceeded that of P. edulis for four sites along an elevational gradient, indicating that J. monosperma uses more shallow soil moisture than P. edulis. Seasonal mean of predawn plant water potential for each species was positively correlated with elevation, indicating that plant-available water increased with elevation, a result of precipitation which likely produces differences in the depth distributions of soil moisture. Collectively, these results indicate that size-species differences in the vertical distribution of roots largely determine their differences in population structure along the gradient. Hence, small differences in depth of water acquisition among woody plants can produce substantial divergence in population structure along gradients of soil water. These differences may be important to consider in predicting community dynamics in arid and semiarid ecosystems and assessing their responses to changes in land use and climate.

Keywords: pinyon, juniper, water use, canonical correspondence analysis, semiarid plant communities

This abstract is being presented at: 3:30 PM in session:
WATER RELATIONS