Effect of temperature and moisture on rates of carbon mineralization in a Mediterranean oak forest soil under controlled and field conditions

We examined the relationship between carbon mineralization (C-min), moisture and temperature in a Mediterranean forest soil under controlled and field conditions. We studied the following. 1 The temperature sensitivity at three soil depths: soil samples were incubated at 4, 10, 20 and 30 degrees C at optimal water content of 60% of water holding capacity (WHC). Values of C-min of the top layer were more than 12 times faster than those measured in deeper layers. We found a temperature sensitivity factor (Q(10)) of 3.3, 2.7 and 2.2 for the 0-5 cm, 5-10 cm and 10-20 cm layers, respectively. 2 The relationship between C-min, moisture and temperature (top layer). The sensitivity of C-min to fluctuating moisture depended on temperature. However, the Q(10) was not significantly affected by soil moisture. We fitted a multiple polynomial model that predicted C-min as a multiplicative function of temperature and moisture (R-2 > 0.99). 3 The response of C-min of soil to rewetting after 1 and 24 hours. In all cases, the response was rapid. The soil incubated at 60% WHC or less responded positively to a sudden increase in water content, with the largest increase in the 20% WHC treatment. The model predicted C-min in the field well when rewetting effects were taken into account (R-2 > 0.81). These results indicate that sudden changes in soil moisture can lead to increased carbon mineralization during the dry summer. It is necessary to include such responses in models as they may represent a substantial loss of carbon in the overall carbon balance of Mediterranean ecosystems.