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Interactive Feedbacks of Climate, Mineralogy, and Microbial Communities on Soil Carbon: A Deep Soil Warming Experiment

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Title:Interactive Feedbacks of Climate, Mineralogy, and Microbial Communities on Soil Carbon: A Deep Soil Warming Experiment
Authors:McGrath, Casey
Contributors:Crow, Susan (advisor)
Natural Resources and Environmental Management (department)
Keywords:Soil sciences
Environmental science
Environmental management
climate change
show 4 moredeep soil warming
soil carbon
tropical soils
show less
Date Issued:2019
Publisher:University of Hawaiʻi at Mānoa
Abstract:Climate change conversely is the largest issue facing humanity today. Natural systems exist that could potentially sequester large reservoirs of carbon (C) from the atmosphere and aid in the preservation of global ecosystems while long term solutions to destructive human behavior are enacted into policy. Soils are one such system with high potential to drawdown carbon and reduce atmospheric greenhouse gas concentration. This benefit may only occur if the mechanisms for stabilizing and storing carbon are not overwhelmed by the interactive effects of rapid warming on multiple soil processes. Volcanic ash derived Andisols, with a high concentration of poorly and non-crystalline minerals, have a strong affinity to stabilize C and offer a unique study system to test hypotheses about mineral control on carbon stabilization and protection from disturbance losses (Giardina et al. 2014; Crow et al., 2015). Andisols unique affinity to C may hold the key in utilizing an understudied, but critical carbon sequestration management tool within the global C cycle.
Interactive feedbacks of climate, mineralogy, and microbial communities on the soil C balance will determine the net soil C balance under a changing environment. In Hawaiian Andisols organo-mineral associations are strong soil C-protection mechanisms leading to large soil C stocks. Existing evidence from non-Andic soils suggests that increased soil temperature escalates microbial activity in the soil and consequently soil respiration rates throughout the soil profile, implying declining C stocks if metabolic losses outweigh input gains. However, how the intensive warming predicted with climate change by 2100 will impact C cycling and storage in Andisols is unknown. On a 200 m² hillslope of a wet montane Andisol, soil was heated using a randomized design that allowed for a temperature gradient of ambient to +4°C across sampling depths (20, 40, 60, 80, and 100 cm). After a year of deep soil warming during which soil respiration and flux throughout the soil profile was measured, the warming response ranged from 0.89 to 17,000 mg CO2 m-3 hr-1 across the gradient of temperature and depth. Generalized additive modeling (GAM), indicated that overall, the amount of C released from the soil did not significantly increase in response to warming at depth. GAM also confirmed the hypothesis that poorly and non-crystalline minerals (hydroxylamine hydrochloride extractable Al + 0.5Fe, and the active Fe ratio), derived from the volcanic ash parent material, was the primary driver of the lack of CO2 response. Another significant driver limiting the CO2 response was ∆pH (pHKCl - pHH2O), with possible positive net colloid charges stabilizing organic matter. Bacterial and fungal diversity measured by high-throughput sequencing at 20 and 40cm were significantly more diverse than those at 60, 80 and 100cm. The significant relationship of mean CO2 produced in response to warming and poorly and non-crystalline minerals suggests the strong organo-mineral protection mechanisms found in Hawaiian Andisols could be considered as a C management tool.
Pages/Duration:151 pages
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Natural Resources and Environmental Managament

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