CO emissions from degrading plant matter: (I). Measurements

CO emissions from degrading deciduous leaf and grass matter have been investigated in laboratory and field measurements. CO emissions are induced both photochemically and thermally. Photochemical CO production can be described by a 2nd-order polynomial in light intensity and exhibits a hysteresis effect, not previously reported. Humid material showed higher CO emissions than dry material. A preliminary, relative action spectrum for the photochemically induced CO emissions is presented. Although UV irradiation caused most of the CO production, visible light also caused up to 40% of the emissions. We propose a cleavage of the cellulose chain as the important step prior to CO production. Thermal CO emissions from degrading plant material obey an Arrhenius type equation (presented for several species in this paper), but emissions are lower than those induced photochemically. During our field measurements on dry grasses in a South African savanna we found a strong influence of incident radiation intensity and temperature on measured CO fluxes. Solely photochemical CO production from the grasses is calculated by subtraction of soil fluxes and thermally induced grass CO emissions from the total CO emissions. CO emissions and hysteresis differ between the grasses investigated and may be interpreted by the grass’ colour and their architecture. Deposition of CO on the soils was much lower than CO emission from the dry grasses during daytime. Nighttime data show that possible thermal CO production from the grasses may partially compensate for CO deposition on the soils for several hours after sunset depending on temperature.