Tuesday, November 14, 2006 - 3:00 PM

Injections of 13C-Acetic Acid Vapor and 15N-Ammonia Gas into Soil to Track the Fate of Nutrients Without Dsturbing Soil Water Status: Applications in an Investigation of Hydraulic Redistribution Under Artemisia tridentata.

Patrick Herron1, Carson Holt2, John Stark3, and Zoe Cardon1. (1) EEB Dept, Univ of Connecticut, 75 N. Eagleville Rd, Storrs, CT 06269, (2) Dept of Biology, Utah State Univ, 5305 Old Main Hill, Logan, UT 84322-5305, (3) Utah State University, Dept. of Biology Utah State Univ., 5305 Old Main Hill, Logan, UT 84322-5305

In order to investigate how hydraulic redistribution influences gross and net N cycling rates in soil, microbial growth efficiencies, and plant uptake of N, it is necessary to provide labeled 15N- and 13C-labeled substrates without delivering them to soil with water. We developed techniques using 13C-acetic acid and 15N-ammonia, injected in vapor form into the soil, to track C and N cycling, immobilization, and mineralization without perturbing soil water status. Results indicate acetic acid vapor injected into calcareous soils is used by microbes for growth, with microbial growth efficiencies of approximately 45-50% depending on soil water potential. We applied these techniques in a split-pot greenhouse experiment with Artemisia tridentata; plants were rooted in a top soil container, with roots growing through to a second, separate bottom container where water supply could be controlled. Hydraulic redistribution treatment plants were watered in the bottom container in the evening, and plants in the control treatment were watered in the bottom container in the morning. Plants watered in the morning demonstrated markedly reduced redistribution of water from bottom to top pots in comparison to plants watered in evening. Soil water potential in the upper pot was tracked using thermocouple psychrometers; we aimed to keep average soil water potential in the two treatments similar. We used 13C-acetic acid and 15N-ammonia, injected in the vapor form into the soil, to track carbon and nitrogen cycling in the soil as influenced by hydraulic redistribution.