Temperature Sensitivity Of CO2 Efflux Research Articles

Temperature sensitivity of CO2 efflux in soils from two alpine elevation levels with distinct bedrock types

Predicted increase in climate warming will affect soil organic carbon (SOC) dynamics in vulnerable cold alpine environments. In contrast to freeze and thaw cycles, less is known about the effects of temperature regimes in the range between 2 and 10 °C on SOC availability to soil microorganisms. For this reason, CO2 efflux, extracellular enzyme activities and microbial communities were measured in an incubation experiment with three temperature treatments: (T1) continuous 10 °C, (T2) cooled down to 2 °C, and (T3) rewarmed from 2 to 10 °C. Two forest soils at low elevation and two grassland soils at high elevation were taken from two sites with distinct bedrock types (limestone at Hochschwab, gneiss and schist at Rauris). The CO2 efflux did not differ significantly between the elevation levels at the two sites. In the continuous warm treatment T1, the relative decline in CO2 efflux was stronger in the two Rauris than in the two Hochschwab soils during the 0–123 days period. In the cooling treatment T2, the cumulative ΣCO2C efflux of the Hochschwab soils was lowered by 32% and that of the Rauris soils by only 19% compared with T1 during the 30–123 days period. In the rewarming treatment T3, the ΣCO2 efflux was on average 33% higher than that of treatment T1 during the 91–123 days period, ranging from +8% to +62%. Phospholipid fatty acid (PLFA) composition and extracellular enzyme activities were not markedly affected by incubation time or temperature treatments. The differences in bedrock properties had stronger effects on the ΣCO2 efflux, enzyme activities as well as total PLFA content and composition than elevation level or vegetation. Other, largely unknown factors control the rewarming effects on the mobilisation of a labile SOC pool.

Significance of soil respiration from biological activity in the degradation processes of different types of organic matter

Soil respiration is a major component of global carbon cycle. Therefore, it is crucial to understand the environmental controls on soil respiration for evaluating potential response of ecosystems to climate change. In a temperate deciduous forest (located in Northern-Hungary) we added or removed aboveground and belowground litter to determine total soil respiration. We investigated the relationship between total soil CO2 efflux, soil moisture, and soil temperature. Soil CO2 efflux was measured at each plot using soda-lime method. Temperature sensitivity of soil respiration (Q10) was monitored via measuring soil temperature on an hourly basis, while soil moisture was determined monthly. Soil respiration increased in control plots from the second year after implementing the treatment, but results showed fluctuations from one year to another. The effect of doubled litter was less significant than the effect of removal. Removed litter and root inputs caused substantial decrease in soil respiration. We found that temperature was more influential in the control of soil respiration than soil moisture. In plots with no litter Q10 varied in the largest interval. For treatment with doubled litter layer, temperature sensitivity of CO2 efflux did not change considerably. The effect of increasing soil temperature is more conspicuous to soil respiration in litter removal treatments since lack of litter causes greater irradiation. When exclusively leaf litter was considered, the effect of temperature on soil respiration was lower in treatments with added litter than with removed litter. Our results reveal that soil life is impacted by the absence of organic matter, rather than by an excess of organic matter. Results of CO2 emission from soils with different organic matter content can contribute to sustainable land use, considering the changed climatic factors caused by global climate change.

Diurnal evolution of the temperature sensitivity of CO2 efflux in permafrost soils under control and warm conditions.

Cryosols contain ~33% of the global soil organic carbon. Cryosol warming and permafrost degradation may enhance the CO2 release to the atmosphere through the microbial decomposition. Despite the large carbon pool, the permafrost carbon feedback on the climate remains uncertain. In this study, we aimed at better understanding the diurnal evolution of the temperature sensitivity of CO2 efflux in Cryosols. A Histic Cryosol and a Turbic Cryosol were instrumented in tussock tundra ecosystems near Salluit (Nunavik, Canada). Open top chambers were installed during summer 2011 and the ground temperature, the soil moisture and meteorological variables were recorded hourly while the ecosystem respiration was measured three times per day every second day with opaque and closed dynamic chambers in control and warm stations. Despite warmer conditions, the average CO2 efflux at the control stations at the Histic site (1.29±0.45μmolCO2m-2s-1) was lower than at the Turbic site (2.30±0.74μmolCO2m-2s-1). The increase in CO2 efflux with warming was greater in the Histic Cryosol (~39%) than in the Turbic Cryosol (~16%). Our study showed that the temperature sensitivity of the ecosystem respiration evolved during the day and decreased with the experimental warming. Both sites exhibited diurnal hysteresis loops between CO2 efflux and the soil surface temperature. The width of hysteresis loops increased with the solar radiation and decreased along the growing season. We developed simple linear models that took into account the diurnal evolution of the temperature sensitivity of CO2 efflux and we estimated the seasonal cumulative carbon release to the atmosphere. The calculation using solely diurnal measurements significantly differed from the seasonal carbon release modelled hourly. Our study highlighted that the time of the day when measurements are performed should be taken into account to accurately estimate the seasonal carbon release from tundra ecosystems.

Lasting effect of soil warming on organic matter decomposition depends on tillage practices

Global warming accelerates soil organic matter (SOM) decomposition with strong feedback to atmospheric CO2. Such an effect should be especially important for no-till agricultural practices, where SOM accumulates in the topsoil as compared with conventional tillage. We incubated soil samples (0–5 cm) at three temperature levels (15, 21 and 27 °C) from long-term till and no-till systems that were in situ warmed and non-warmed to assess the temperature sensitivity of CO2 efflux, labile organic carbon and extracellular enzyme activities. Thermal adaptation to prolonged warming was observed resulting in a lasting effect on SOM decomposition. On average, 26, 14 and 12% more CO2 was emitted at each incubation temperature from the warmed soils compared to the non-warmed soils. The Q10 value was lower for the warmed than the non-warmed soils. Soil microbial biomass C and dissolved organic C declined with warming. The activities of three extracellular enzymes, β-glucosidase, chitinase, and sulfatase, were higher under warming and no-till as compared to non-warmed and tilled soil. We concluded that the increased SOM decomposition due to the stimulation of microorganisms by warming was long-lasting. Predictions of C accumulation in the topsoil by no-till farming should be taken with caution, as this C pool is especially vulnerable to global warming.

CO2 flux estimation by different regression methods from an alpine meadow on the Qinghai-Tibetan Plateau

CO2 efflux was estimated using different regression methods in static chamber observation from an alpine meadow on the Qinghai-Tibetan Plateau. The CO2 efflux showed a seasonal pattern, with the maximun flux occurring in the middle of July. The temperature sensitivity of CO2 efflux (Q10) was 3.9, which was at the high end of the range of global values. CO2 emissions calculated by linear and nonlinear regression were significantly different (p < 0.05). Compared with the linear regression, CO2 emissions calculated by exponential regression and quadratic regression were 12.7% and 11.2% larger, respectively. However, there were no significant differences in temperature sensitivity values estimated by the three methods. In the entire growing season, the CO2 efflux estimated by linear regression may be underestimated by up to 25% compared to the real CO2 efflux. Consequently, great caution should be taken when using published flux data obtained by linear regression of static chamber observations to estimate the regional CO2 flux in alpine meadows on the Qinghai-Tibetan Plateau.