CARBON FLOW THROUGH ROOT AND MICROBIAL RESPIRATION IN VINEYARDS AND ADJACENT OAK WOODLAND GRASSLAND COMMUNITIES

Principal Investigator:
David R. Smart
Asst. Professor, Dept. Viticulture & Enology
Asst. Plant Physiologist, Ag. Expt. Station
University of California
One Shields Avenue
Davis, CA 95616-8749

Duration of the Project: 2 years

Project Summary

Nearly all carbon lost from California soil is emitted in the form of CO₂ by soil respiration. Such respiration is the total of root respiration and heterotrophic microbial respiration. Root respiration functionally includes the loss of recently fixed photosynthate from roots and the rhizosphere, while microbial respiration includes growth and maintenance respiration by microorganisms involved in organic matter decomposition. Few measures of soil respiration exist for California's Mediterranean ecosystems, and fewer yet have examined the influence of land use changes or disturbance on soil respiration. None have estimated the contribution by root respiration. Recent estimates suggest root respiration may contribute as much as half of the CO₂ emitted from soils [1, 2]. The objectives of the following proposal are: 1) to monitor soil CO₂ emission from undisturbed oak woodland grasslands and adjacent lands converted to vineyards; 2) to partition CO₂ evolved into respiration derived from root plus rhizosphere respiration, soil organic matter oxidation, and litter decomposition. These studies complement a parallel investigation examining root population dynamics; therefore, will provide comprehensive information on carbon flow. Soil CO₂ respiration will be measured using both a dynamic flow system and a diffusive transport model based on the actual CO₂ concentration in the soil profile. Soil respiration will be partitioned into its major components using ¹³C abundances on CO₂ sampled from the soil profile, and on CO₂ trapped during dynamic flow measurements. Finally, the use of natural abundance measures to partition evolved CO₂ into root and microbial components will be confirmed using a long-term incubation of each soil under growth chamber conditions. This investigation addresses several key research priorities in the Kearney Foundation mission, including: 1. mechanisms affecting carbon storage and fluxes; 2. impacts of management on carbon storage and fluxes; and, 3. effects of soil carbon on nutrient cycling.