Effects of drought and optimal soil moisture on soil respiration in a Norway spruce forest soil
O 1.4 in Funktion von Ökosystemen
15.04.2010, 09:15-09:30, H13
Extreme climatic events such as summer droughts and heavy rainfalls are predicted to occur more frequently in many parts of Central Europe. Changes in soil water are likely to affect soil respiration (Rs) as well as the origin of CO2 from different sources. In a mature Norway spruce stand at the Fichtelgebirge, we investigated the response of Rs to prolonged drought and to optimal soil moisture conditions. For this purpose, throughfall exclusion (TE) plots, irrigation plots (IR) and control plots (C) were established. To estimate the contribution of rhizospheric (Rr) and heterotrophic respiration (Rh) to total Rs we partitioned soil respiration using radiocarbon measurements. Additionally, we measured the vertical gradient of CO2 concentrations in the soil profile of every plot to quantify CO2 production in the soil. In the period of one year, Rs was reduced by 31 % in the TE-plots. A rewetting pulse as reported occasionally in the literature was not detected. In the IR-plots, soil respiration was 13 % greater than in the C-plots. Contribution of Rr to Rs was generally lower than contribution of Rh in all plots. However, in summer, contribution of Rr increased particularly in the TE-plots suggesting a lower sensitivity of the rhizosphere to drought. During the manipulation period, CO2 concentrations in the soil profiles of the TE-plots were significant lower than in the C-plots in all soil depths. In the IR-plots, CO2 concentrations were slightly greater in the upper mineral soil. Both observations suggest that CO2 production is lowered due to drought. However, lower CO2 concentrations in the soil can additionally result from increased gas diffusivity enhancing the exchange of soil air under drier conditions.
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