The effect of plantation forests on the global carbon balance is controversially discussed in recent times. As soil respiration is a decisive component in the carbon exchange between terrestrial ecosystems and atmosphere, effects of forest management measures (e.g. thinning) in the context of driving parameters of soil CO2 efflux is a key issue in optimizing carbon friendly land management. In the present study, we report the effects of thinning, soil temperature and soil moisture, and biotic parameters on soil CO2 efflux rate. Soil CO2 efflux was measured by using an Infrared Gas Analyzer. We selected thinned and un-thinned stands within six years old Cupressus lusitanica plantation forest. Soil respiration rate ranged from 1.47 to 6.92 µmol m-2s-1 (thinned) and 1.31 to 5.20 µmol m-2s-1 (control stand). Generally higher soil respiration rates were measured during wet than in dry season. Seasonal variability of soil CO2 efflux was significantly (p<0.05) correlated with soil moisture, but poorly correlated with soil temperature. Soil respiration increased with increasing soil moisture and reached maximum at 31% but after this threshold it start to decline. In general, soil CO2 efflux rate in the first and second year after thinning was 24% and 14% higher in the thinned stand. Increased soil temperature at the thinned stand contributed minor to the larger soil CO2 efflux, the more important reason appeared to be the trees’ direct response. Higher fine root production together with larger microbial concentrations representing different groups infers a higher autotrophic respiration by roots and associated mycorrhizal fungi as well as by heterotrophic respiration. Despite the higher CO2 losses with soil respiration, the organic C and total N concentrations in soil rather tended to increase, indicating higher organic matter input to soil at the thinned stand.
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