Abstract. Soil respiration is one of the largest terrestrial fluxes of carbon dioxide (CO 2 ) to the atmosphere. Hence, small changes in soil respiration rates could have large effects on atmospheric CO 2 . In order to assess CO 2 emissions from diverse European soils with different land-use types and climate (soil moisture and temperature), we conducted a laboratory incubation experiment.Emission measurements of CO 2 under controlled conditions were conducted using soil monoliths of nine sites from a European flux network (ÉCLAIRE). The sites are located all over Europe -from the United Kingdom in the west to Ukraine in the east, and from Italy in the south to Finland in the north -and can be separated according to four land-use types (forests, grasslands, arable lands and one peatland). Intact soil cores were incubated in the laboratory in a two-way factorial design, with temperature (5, 10, 15, 20 and 25 • C) and water-filled pore space (WFPS; 5, 20, 40, 60 and 80 %) as the independent variables, while CO 2 flux was the response variable. The latter was measured with an automated laboratory incubation measurement system.Land use generally had a substantial influence on carbon dioxide fluxes, with the order of CO 2 emission rates of the different land-use types being grassland > peatland > forest/arable land (P < 0.001). CO 2 efflux responded strongly to varying temperature and moisture content with optimum moisture contents for CO 2 emissions between 40 and 70 % WFPS and a positive relationship between CO 2 emissions and temperature. The relationship between temperature and CO 2 emissions could be well described by a Gaussian model. Q 10 values ranged between 0.86 and 10.85 and were negatively related to temperature for most of the moisture contents and sites investigated. At higher temperatures the effect of water and temperature on Q 10 was very low. In addition, under cold temperatures Q 10 varied with moisture contents, indicating a stronger prospective effect of rain events in cold areas on temperature sensitivity. At both coniferous forest sites we found a strong increase in the temperature sensitivity at a moisture range between 20 and 40 % WFPS.We developed a new approach to calculate moisture sensitivity (MS) of CO 2 efflux. MS was calculated as the slope of a polynomial function of second degree. Moisture sensitivities were highest under dry and wet conditions. In addition we found a positive relationship between MS of CO 2 efflux and temperature for both arable lands.
Abstract. Soil respiration is one of the largest terrestrial fluxes of carbon dioxide (CO2) to the atmosphere. Hence, small changes in soil respiration rates could have large effects on atmospheric CO2. In order to assess CO2 emissions from diverse European soils under different land-use and climate (soil moisture and temperature) we conducted a laboratory incubation experiment. Emission measurements of carbon dioxide under controlled conditions were conducted using soil monoliths of nine sites from the ÉCLAIRE flux network. Sites are located all over Europe; from the UK in the west to the Ukraine in the east; Italy in the south to Finland in the north and can be separated according to four land-uses (forests, grasslands, arable lands and one peatland). Intact soil cores were incubated in the laboratory at the temperatures 5, 10, 15, 20, and 25 °C in a two factorial design of five soil moisture levels (5, 20, 40, 60, 80 (100)% water filled pore space, WFPS), before analysed for CO2 fluxes with an automated laboratory incubation measurement system. Land-use generally had a substantial influence on carbon dioxide fluxes, with the order of CO2 emission rates of the different land-uses being grassland > peatland > forest/arable land (P < 0.001). CO2 efflux responded strongly to varying temperature and moisture content with optimum moisture contents for CO2 emissions between 40–70% WFPS and a positive relationship between CO2 emissions and temperature. The relationship between temperature and CO2 emissions could be well described by a Gaussian model. Q10 values ranged between 0.86–10.85 and were negatively related to temperature for most of the moisture contents and sites investigated. At higher temperatures the effect of water and temperature on Q10 was very low. In addition under cold temperatures Q10 varied with moisture contents indicating a stronger prospective effect of rain events in cold areas on temperature sensitivity. We found at both coniferous forest sites a strong increase of the temperature sensitivity at a moisture range between 20–40% WFPS. In our study moisture sensitivity (MS) of CO2 efflux was calculated as the slope of a polynomial function of second degree. Moisture sensitivities were highest under dry and wet conditions. In addition we found a positive relationship between MS of CO2 efflux and temperature for both arable lands.
The forest litter layer lies at the boundary between soil and atmosphere and is a major factor in biogeochemical cycles. While there are several studies on how the litter layer controls soil trace gas emissions, litter emissions itself are less well understood, and it is still unclear how important gases respond to changing temperature and moisture. In order to assess leaf litter gas exchange, we conducted laboratory incubation experiments in which the full set of climate relevant gases, i.e., carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and nitric oxide (NO) coming from deciduous and coniferous leaf litter were measured at five temperatures and seven moisture contents. In addition, we compared litter and soil from different origin in terms of temperature/moisture responses of gas fluxes and investigated possible interactions between the two climate factors. Deciduous litter emitted more CO2 (up to 335 mg CO2‐C kg−1 h−1) than coniferous litter, whereas coniferous litter released maximum amounts of NO (207 µg NO‐N kg−1 h−1). N2O was only emitted from litter under very moist and warm conditions (>70% wet weight, >10°C). CH4 emissions were close to zero. Temperature sensitivities of litter emissions were generally lower than for soil emissions. Nevertheless, wet and warm conditions always enhanced litter emissions, suggesting a strong feedback effect of the litter layer to predicted future climate change.
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