Solar Photochemical Emission of CO 2 From Leaf Litter: Sources and Significance to C Loss
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Solar Photochemical Emission of CO2 From Leaf Litter: Sources and Significance to C Loss Thomas A. Day*
and Michael S. Bliss
School of Life Sciences, Arizona State University, Tempe, Arizona, USA
ABSTRACT Although photodegradation can be a significant mechanism of plant litter decay in drylands, the abiotic photochemical emission component of this process is not well characterized. We measured the temperature response of abiotic photochemical emission of CO2 from 12 litter types under midday sunlight in the Sonoran Desert, assessed what litter traits predicted emission rates, and estimated its significance to litter C loss. Emission rates increased exponentially with temperature (Q10= 1.75) and declined as litter decayed. Rates varied substantially among litter types. Microbial respiration rates of litter explained the most variation in emission rates at lower temperature (78% at 45 C), suggesting that compounds amenable to microbial consumption were major precursors of emission. In contrast, wax concentrations explained the most variation at high temperature (76% at 70 C), implying that precursors shifted with temperature. Photochemical emission of initial litter at 55 C was a strong predictor of the mass loss of litter in full sunlight over 34 months in the field, explaining 67% of the
variation among litter types. We estimate that photochemical emission of CO2 was responsible for 10% of all C lost from litter in sunlight over 34 months and accounted for 39% of the greater C lost from litter in sunlight compared to litter that did not receive sunlight in the UV to blue wavelength bands. Hence, abiotic photodegradation via photochemical emission appeared to be a significant pathway for C loss from sunlit litter. The substantial exponential increase in photochemical emission with temperature illustrates that temperature needs to be considered in assessments of abiotic photodegradation and implies this process will be greatest in systems where litter is exposed to high solar irradiance in conjunction with high temperatures. Key words: Carbon dioxide; Decay; Drylands; Litter decomposition; Photochemical emission; Photodegradation; Solar radiation; Sonoran Desert; UV radiation; Waxes.
HIGHLIGHTS Received 7 May 2019; accepted 30 November 2019 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-019-00473-8) contains supplementary material, which is available to authorized users. Author Contributions TAD conceived and designed the study, wrote the paper and contributed to the data analysis. MSB performed the research and contributed to the design, data analysis and writing. *Corresponding author; e-mail: [email protected]
Photochemical emission rates increased exponentially with temperature Microbial respiration and wax concentration were strong predictors of emission rates Photochemical emission accounted for 10% of the C lost over 34 months, corresponding to 39% of the greater C lost from sunlit litter
T. A. Day, M. S. Bliss
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