HR: 18:05h
AN: B34A-08    [Abstracts]
TI: Linkages Between Biotic and Abiotic Belowground Processes in a Mojave Desert Ecosystem: Responses to Experimental Nitrogen and Water Additions
AU: * Verburg, P S
EM: Paul.Verburg@dri.edu
AF: Desert Research Institute, Division of Earth and Ecosystem Sciences, 2215 Raggio Parkway, Reno, NV 89512, United States
AU: Marion, G M
EM: Giles.Marion
AF: Desert Research Institute, Division of Earth and Ecosystem Sciences, 2215 Raggio Parkway, Reno, NV 89512, United States
AU: Young, A C
EM: Andrew.Young@dri.edu
AF: Desert Research Institute, Division of Earth and Ecosystem Sciences, 2215 Raggio Parkway, Reno, NV 89512, United States
AU: Glanzmann, I
EM: Isabelle.Glanzmann@dri.edu
AF: Desert Research Institute, Division of Earth and Ecosystem Sciences, 2215 Raggio Parkway, Reno, NV 89512, United States
AU: Stevenson, B
EM: StevensonB@landcareresearch.co.nz
AF: Desert Research Institute, Division of Earth and Ecosystem Sciences, 2215 Raggio Parkway, Reno, NV 89512, United States
AU: Arnone, J A
EM: Jay.Arnone@dri.edu
AF: Desert Research Institute, Division of Earth and Ecosystem Sciences, 2215 Raggio Parkway, Reno, NV 89512, United States
AU: Nowak, R S
EM: nowak@cabnr.unr.edu
AF: University of Nevada, Reno, Department of Natural Resources and Environmental Science, Mailstop 370, Reno, NV 89557, United States
AB: Fine roots play a critical role in nutrient acquisition and water uptake. Yet it is unclear how fine roots in arid environments respond to increased nitrogen deposition and rainfall, two important global change factors in arid lands in the southwestern United States. In addition it is unclear how changes in root activity may impact soil CO2 concentrations, an important parameter affecting carbonate dynamics. We measured fine root length density (RLD) and soil CO2 concentrations for two years in experimentally manipulated plots in a Mojave Desert ecosystem. The study was conducted at the Mojave Global Change Facility located at the Nevada Test Site 60 miles northwest of Las Vegas. The treatments included: 1) three 25 mm water additions during the summer, 2) one nitrogen addition in the fall equivalent to 40 kg per hectare per year, 3) a combined water and nitrogen addition and, 4) untreated controls. Root data were collected using minirhizotron imaging approximately every 90 days underneath shrubs and intershrub areas. Soil CO2 concentrations were collected at the same sampling times and locations at 10, 40 and 90 cm depth using gas wells. The RLD showed clear seasonal patterns with the fastest increase in RLD occurring between February and April. During the winter the increase in RLD was higher underneath shrubs than in intershrub areas but during the summer months increases in RLD were similar under shrubs and in intershrub areas. Water additions slightly increased root mortality during the summer but this increase in mortality was not large enough to cause consistent differences in RLD between control and irrigated plots. Nitrogen addition had no effect on root dynamics in any of the plots. In contrast to RLD, irrigation consistently increased soil CO2 concentrations at all depths during the summer even when roots were not actively growing anymore. We speculate that the increased mortality under irrigation causes increased heterotrophic respiration which may explain increases soil CO2 concentrations during the summer. These higher soil CO2 concentrations may result in increased carbonate dissolution especially in combination with increased soil moisture. Preliminary simulations using the CALGYP model indicate however that this increased dissolution will not result in changes in ecosystem C budgets since carbonates are likely to precipitate again deeper in the soil.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0486 Soils/pedology (1865)
DE: 1813 Eco-hydrology
SC: Biogeosciences [B]
MN: 2007 Joint Assembly