|Huxman, T. - UNIVERSITY OF ARIZONA|
|Barron-Gifford, G. - UNIVERSITY OF ARIZONA|
|Jenerette, G. - UNIVERSITY OF ARIZONA|
Submitted to: Trans American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2007
Publication Date: May 1, 2007
Citation: Huxman, T.E., Scott, R.L., Barron-Gifford, G., Jenerette, G.D. 2007. Ecohydrological Consequences of Shifts in Grass-to-Woody Plant Dominance in Water Limited Ecosystems. Eos Trans. AGU, 88(23), Jt. Assem. Suppl., Abstract B34A-03. Technical Abstract: An increase in the representation of woody plants in historic grasslands has been a wide-spread recent phenomena in the drylands of North America. The consequences of this vegetation change for ecosystem services are uncertain and likely related to how soil-plant interactions are influenced by precipitation. Here we compare ecosystem water and carbon dioxide fluxes, determined over four years by eddy covariance, for a grassland, a grassland-shrubland mosaic, and a fully developed woodland to evaluate the relationship between land surface cover and biosphere-atmosphere exchange. Since our system is located in a riparian system, it interacts with vegetation type to accentuate differences in soil water availability and helps us to disentangle with how different carbon cycling components are coupled to the hydrologic cycle. Compared to our grassland, our grassland-shrubland mosaic often uses a similar amount of water throughout a growing season (equivalent values of evapotranspiration), whereas it accumulated a similar amount of carbon from the atmosphere as our fully developed mesquite forest (resulting higher ecosystem water-use efficiency). This pattern depends on seasonal precipitation, where changes in the size-class distribution of rainfall events and season total differentially influence ecosystem respiration and photosynthesis, depending upon woody-plant abundance and woody-plant age. Interestingly the differences in vegetation type also change the relationship between soil carbon cycling and precipitation, where microsites with high resource availability become hot-spots of activity that are important in regulating ecosystem carbon balance. A careful understanding of the complexities of both the plant and soil compartment to vegetation change is important to predicting the consequences of vegetation change on biosphere-atmosphere material and energy exchange.