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UVM Theses and Dissertations

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Format:
Print
Author:
Auch, Walter E.
Dept./Program:
Plant and Soil Science
Year:
2010
Degree:
PhD
Abstract:
Understanding whole-system biogeochemistry is imperative given NOx and SOx deposition, CO₂ fertilization, mineral weathering, and climate warming. Add to this the fact that 65% of the earth is allocated to biomass production and <20% wilderness. The fundamental question is whether plant productivity and organic soil inputs will "keep pace" with litter decay and heterotrophic respiration? The aim of this dissertation was to quantify, using analysis of variance and regression, these opposing forces and their interaction(s) in forests, grasslands, and agricultural lands. I examined global climatic and biochemical interactions between litter decomposition, plant productivity, and respiration on ecosystem cycling of carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and base cations (Be). I used deterministic ecosystem temperature responses to establish process and biome specific Ql0. This allowed an elementary and biologically feasible estimate of flux response and pool depletion or replenishment.
Terrestrial ecosystems are a net sink of 1.822 Teragrams (Tg) N yr⁻¹ accounting for 30 and 20% of the world's ecosystem P and S accrual (0.169 and 0.113 Tg yr⁻¹, respectively). On a mass basis the third most important element is calcium (Ca²) with accrual of 0.476 Tg Ca yr⁻¹. Terrestrial ecosystems sequester 0.574 Tg K⁺ + Mg2⁺ yr⁻¹. Increases in litter decay, specifically coarse woody debris (CWO), dissolved organic carbon (DOC) production, and soil heterotrophic respiration will outpace plant productivity with warming, resulting in a net decline in CNPS sequestration. Soil organic carbon (SOC) pools will decline by 348 MMT in tropical forests, 83 for arid lands, 143 for agricultural systems, and 67 MMT for grassland. Stable SOC production will decline substantially, while labile SOC will in some instances increase an order of magnitude in a warmer world.
These changes will be most pronounced at northern latitudes. Four distinct mechanisms are at work: i) increased soil respiration/decay (ISRD) + minimal increases in plant productivity, ii) ISRD + minimal increases in plant productivity + an already depauperate SOC pool, iii) ISRD + low plant productivity ceilings, and iv) ISRD + chronic biomass extraction, minimal/poorly timed replenlishment, mineral SOC exposure. Agricultural may offset their CO₂ footprint via biomass/manure conversion to fuels ~ 375-535 MB yr⁻¹. This translates to $36 trillion or 54% of the world's GDP. Results point to the importance of further understanding the plant-soil tradeoffs associated with climate change and CNPS-cycles. Certain agricultural inevitabilities may be offset by efficient and complete use ofpoorly utilized alternative fuels. Converting from fossil to renewable fuel sources will serve the fiduciary responsibility of the agronomic community and lessen their CO₂ footprint. This would ameliorate agriculture's influence on climate change and long-term C storage shifts proposed herein.