Soil-Atmosphere CO Exchanges and Microbial Biogeochemistry of CO Transformations in a Brazilian Agricultural Ecosystem

Abstract

Although anthropogenic land use has major impacts on the exchange of soil and atmosphere gas in general, relatively little is known about its impacts on carbon monoxide. We compared soil-atmosphere CO exchanges as a function of land use, crop type, and tillage treatment on an experimental farm in Parãna, Brazil, that is representative of regionally important agricultural ecosystems. Our results showed that cultivated soils consumed CO at rates between 3 and 6 mg of CO m ؊2 day ؊1 , with no statistically significant effect of tillage method or crop. However, CO exchange for a pasture soil was near zero, and an unmanaged woodlot emitted CO at a rate of 9 mg of CO m ؊2 day ؊1 . Neither nitrite, aluminum sulfate, nor methyl fluoride additions affected CO consumption by tilled or untilled soils from soybean plots, indicating that CO oxidation did not depend on ammonia oxidizers and that CO oxidation patterns differed in part from patterns reported for forest soils. The apparent K m for CO uptake, 5 to 11 ppm, was similar to values reported for temperate forest soils; V max values, approximately 1 g of CO g (dry weight) ؊1 h ؊1 , were comparable for woodlot and cultivated soils in spite of the fact that the latter consumed CO under ambient conditions. Short-term (24-h) exposure to elevated levels of CO (10% CO) partially inhibited uptake at lower concentrations (i.e., 100 ppm), suggesting that the sensitivity to CO of microbial populations that are active in situ differs from that of known carboxydotrophs. Soil-free soybean and corn roots consumed CO when they were incubated with 100-ppm concentrations and produced CO when they were incubated with ambient concentrations. These results document for the first time a role for cultivated plant roots in the dynamics of CO in an agricultural ecosystem.Anthropogenic activity disturbs numerous elemental cycles and gas exchanges between the atmosphere and biosphere (42). Agriculture in particular impacts carbon, nitrogen, and phosphorous cycles, altering patterns of microbial activity and elemental distribution relative to what occurs in natural systems (see, e.g., references 16, 42, and 43). In addition, agriculture disturbs fluxes of methane, nitrous oxide, and nitric oxide (5,26,32,38,40,42,44). Each of these gases plays important roles in atmospheric radiative forcing and contributes significantly to greenhouse warming through various direct and indirect effects (15,37,45). Agriculture also affects carbon monoxide dynamics, though there remains some uncertainty about the nature and sign (positive or negative) of impacts (see, e.g., references 29 and 33).Changes in CO dynamics merit attention because CO largely determines the oxidative capacity of the troposphere by reacting rapidly with hydroxyl radicals (13, 37). Current best estimates suggest that global natural and anthropogenic sources contribute 2,600 Tg of CO year Ϫ1 to the atmosphere, with soils removing about 300 Tg year Ϫ1 (24). Therefore, soils play a role in atmospheric CO consumption similar to the role that th...

Molecular andCulture-Based Analyses of Aerobic Carbon Monoxide OxidizerDiversity†

“…Although all isolates oxidize CO at levels Ͻ 1%, high concentrations inhibit CO utilization for most of the strains used in this study. This is consistent with previous reports for a high-affinity soil isolate (14) and intact soil (22,27). Thus, it appears that two groups of CO oxidizers may be distinguished: a CO-tolerant group consisting of isolates that grow with high CO and a CO-sensitive group inhibited by concentrations higher than about 1%.…”

“…The physiological basis for the distinction between these groups is not yet apparent. However, the latter may be more significant in situ, judging on the basis of responses of soil to elevated CO levels (22,27).…”

Atmospheric CO and Hydrogen Uptake and CO Oxidizer Phylogeny for Miyake-jima, Japan Volcanic Deposits

“…SM, a forested site, emitted CO to the atmosphere, and thus represents an exception among the Miyake-jima samples, including, CL, a somewhat older forested site. CO emission by forested soils is not unusual however 15,16,19,26) , and SM emission rates are comparable to those reported for other forested soils 15,16,19,26) . The difference between net CO emission by SM and uptake by CL may be attributed to a greater litter layer and higher organic contents at the former; both of these variables have been associated previously with CO emission 15,26) .…”

Contributions of Atmospheric CO and Hydrogen Uptake to Microbial Dynamics on Recent Hawaiian Volcanic Deposits

“…A distinct decrease in CO uptake occurs for site II-C, however. This site, with a carbon content of about 20%, appears to behave similarly to continental forests, in which elevated abiological CO production linked to organic matter decreases net CO uptake from the atmosphere (19,30,31). Thus, recent Hawaiian volcanic deposits exhibit the full range of interactions between CO and organic matter dynamics.…”