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Arizona State University (1997)

Carbon pools and fluxes along a semiarid gradient in northern Arizona

Conant, Richard Theodore

Titre : Carbon pools and fluxes along a semiarid gradient in northern Arizona

Auteur : Conant, Richard Theodore

Université de soutenance : Arizona State University

Grade : Doctor of Philosophy (PhD) 1997

An examination of the factors affecting carbon pools and fluxes was undertaken at five sites situated along an elevation gradient located in northern Arizona. Warm, dry conditions characterize the lowest site (mean annual temperature = 8.5$\sp\circ$C, mean annual precipitation = 320mm) ; conditions are cooler and more mesic at the highest site (5.5$\sp\circ$C, 530mm yr$\sp-1$). Carbon pools, including soil organic matter, L and H horizons, and above- and belowground biomass carbon pools were quantified at each of the five sites. Carbon outputs from the soil as soil respiration and inputs to the soil through litterfall were also quantified. Carbon storage pools increased with increasing elevation, corresponding to decreases in mean annual temperature and increasing mean annual precipitation. Total annual carbon efflux through soil respiration increased moving up the gradient ; soil respiration at the top site was 50% greater than at the bottom site. Seasonal patterns of soil respiration within each site were positively correlated to both precipitation and temperature. Soil respiration increases due to increasing temperature were constrained by soil moisture. Litterfall was greatest at the middle site, and differed substantially between canopies and interspaces. A soil swapping was initiated to examine sensitivity of soil processes to climate. Reconstructed soil columns with appropriate amounts of litter and duff were swapped between sites with temperature differentials of 1.5$\sp\circ$C and precipitation differentials of approximately 110 mm yr$\sp-1$. Soil respiration, extractable ammonium and nitrate, and soil moisture were measured monthly over the course of the 18 month incubation. Exchangeable cations, and soil pH were measured initially and following 12 months of incubation. Results supported conclusions based on earlier measurements of soil respiration, that climatic changes resulting in increases in temperature and decreases in precipitation will decrease carbon flux from soils in these semiarid systems. Patterns of change in soil respiration rate closely followed changes in soil moisture. Measured rates of soil respiration and litterfall both increased in response to El Nino. A soil respiration database examining regional and global response of soil respiration rates to El Nino events revealed that total global soil respiration may decrease by as much as 3 PgC yr$\sp-1$.

Mots clés : Ecology, ponderosa pine, pinyon-juniper, Biogeochemistry, Soil sciences, Earth sciences Biological sciences, Botany, climate change

Accès au document : Proquest Dissertations & Theses

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