HR: 1340h
AN: V23A-1242    [Abstracts]
TI: Nutrient Sourcing of Ten Plant Species in the Southwest U.S. using Strontium Isotopes: Effects of Rooting Depth, Bedrock Type, and Landscape Age
AU: * Reynolds, A C
EM: areynold@email.arizona.edu
AF: University of Arizona Dept. of Geosciences, 1040 E Fourth St, Bldg. #77, Tucson, AZ 85721, United States
AU: Quade, J
EM: quadej@email.arizona.edu
AF: University of Arizona Dept. of Geosciences, 1040 E Fourth St, Bldg. #77, Tucson, AZ 85721, United States
AU: Betancourt, J L
EM: jlbetanc@usgs.gov
AF: U.S. Geological Survey, 1675 W Anklam Road, Tucson, AZ 85745, United States
AB: For decades, researchers have been examining chronosequences in Hawaii to quantify mineral weathering rates and tropical plant nutrient pools. Within El Malpais National Park, New Mexico, well-dated basalt flows allow for comparison of the Hawaiian data to a semi-arid ecosystem. We measured 87Sr/86Sr ratios in cellulose and bedrock to gauge tree, shrub, & grass (Pinus ponderosa, Pinus edulis, Juniperus monosperma, Juniperus scopulorum, Populus tremuloides, Chrysothamus nauseosus, Fallugia paradoxa, Rhus trilobata, Bouteloua gracilis, and Xanthoparmelia lineola (Berry) Hale) dependence on atmospheric dust as a nutrient source. Sampling sites varied by bedrock type (limestone, sandstone, granite, cinder and basalt) and by age (Quaternary to Precambrian) providing a wide and discrete range of 87Sr/86Sr ratios. Thus, we can pinpoint the roles landscape age (3 ka to greater than 200 ka) and bedrock recalcitrance play in mineral weathering versus eolian dust influence. This study suggests that dust dominates the nutrient cycle on younger landscapes (3 ka), shows a mixture of mineral weathering-dust inputs by 9 ka, and is rock-dominated by 120 ka. Rates of soil nutrient depletion vary in older, non-basalt landscapes (>250 ka), depending on the type the parent bedrock. For example, landscapes on Precambrian gneiss and Paleozoic limestone still show significant mineral contributions while the quartz-rich, carbonate-cemented Zuni Sandstone is almost completely eolian-dominated. Cellulose 87Sr/86Sr variation by plant species at a single site allows us to monitor plant rooting depths and interspecies competition for vital nutrients. Within semiarid ecosystems, nutrient concentrations exhibit both vertical and lateral heterogeneity. The reasons for this variation include vertical and lateral heterogeneity in soil moisture and foliar trapping of nutrient-rich dust followed by incorporation of the throughfall into the underlying soil. This study shows that throughfall does play a significant role for certain species (e.g. J. monosperma) but not for others. A species' ability to trap dust and its overall rooting depths both influence its nutrient intake.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Radiogenic isotope geochemistry
DE: 1051 Sedimentary geochemistry
DE: 1065 Major and trace element geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting