Post-fire stimulation of soil biogenic emission of CO2 in a sandy soil of a Mediterranean shrubland.

Fire is a frequent perturbation in Mediterranean-type ecosystems, altering soil organic matter turnover. In a Mediterranean shrubland subjected to experimental fire, soil CO2 emissions were measured over an annual cycle in burned and unburned sites using static chambers. Some chemical–physical parameters affecting soil C turnover (soil nitrogen and organic carbon content, pH, soil temperature and water content) and some microbial indicators of soil C turnover, i.e. soil potential respiration, microbial carbon, metabolic quotient and coefficient of endogenous mineralisation, were also measured. A high spatial variability of CO2 effluxes was detected in control as well as in burned plots, with 8.9 and 16.6% respectively of ‘hot spots’ of gas emission; the ‘hot spots’ contributed 33% to the whole annual soil CO2 emission in control plots and 54.1% in the burned plots. No relationship between temperature and CO2 effluxes was found. In contrast, the data showed that soil water availability is the main climatic factor affecting field CO2 effluxes in the burned plots. Laboratory measurements under 55% of water-holding capacity showed a stimulating action of fire on soil organic matter mineralisation as indicated by coefficient of endogenous mineralisation, microbial carbon and metabolic quotient values.We concluded that fire could decrease the efficiency of soil microflora at conserving C.