Microbiological parameters as indicators of soil organic carbon dynamics in relation to different land use management

Labile C fractions: microbial biomass C (MBC), K₂SO₄ extractable C ( textC_{textK 2 textSO 4} {text{C}}_{{{text{K}}_{ 2} {text{SO}}_{ 4} }} ) and the cumulated mineralized C in 21 days incubation at 28°C (C–CO_2(21d)), were compared as land use indicators in a calcareous soil under three different management systems: native Querqus ilex forest (under and outside tree cover), a Pinus halepensis plantation, and cropped land (with cereals). Microbial biomass and activity were found to be low and coincided with high carbonate contents. As indicators of land use, textC_{textK 2 textSO 4} {text{C}}_{{{text{K}}_{ 2} {text{SO}}_{ 4} }} and C–CO_2(21d) showed the same sensitivity as MBC. C–CO₂ emissions were measured in an incubation experiment in order to study C mineralization kinetics. The data for cumulative amounts of C–CO₂ released showed a good fit (R ² > 0.94) to the first-order kinetic model C _m = C _o(1 − e^−kt ). The kinetic parameters C _o and C _o k were affected by land use and especially by tree cover. Principal components analysis was applied to the data and the relationship among microbial metabolic quotient (qCO₂), labile C pools, and MBC revealed a decrease in efficiency of organic substrate utilization with an increase in availability and lability of the organic matter.