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Post-thinning soil organic matter evolution and soil CO2 effluxes in temperate radiata pine plantations: impacts of moderate thinning regimes on the forest C cycle

Fernandez, Irene, Álvarez-González, Juan Gabriel, Carrasco, Beatríz, Ruíz-González, Ana Daría, Cabaneiro, Ana
Canadian journal of forest research = 2012 v.42 no.11 pp. 1953-1964
Pinus radiata, biodegradability, carbon dioxide, carbon sequestration, carbon sinks, climate change, forest ecosystems, forest soils, forests, greenhouse gas emissions, mineralization, nuclear magnetic resonance spectroscopy, plantations, seasonal variation, soil heating, soil organic matter, soil respiration, soil sampling
Forest ecosystems can act as C sinks, thus absorbing a high percentage of atmospheric CO₂. Appropriate silvicultural regimes can therefore be applied as useful tools in climate change mitigation strategies. The present study analyzed the temporal changes in the effects of thinning on soil organic matter (SOM) dynamics and on soil CO₂ emissions in radiata pine (Pinus radiata D. Don) forests. Soil C effluxes were monitored over a period of 2 years in thinned and unthinned plots. In addition, soil samples from the plots were analyzed by solid-state ¹³C-NMR to determine the post-thinning SOM composition and fresh soil samples were incubated under laboratory conditions to determine their biodegradability. The results indicate that the potential soil C mineralization largely depends on the proportion of alkyl-C and N-alkyl-C functional groups in the SOM and on the microbial accessibility of the recalcitrant organic pool. Soil CO₂ effluxes varied widely between seasons and increased exponentially with soil heating. Thinning led to decreased soil respiration and attenuation of the seasonal fluctuations. These effects were observed for up to 20 months after thinning, although they disappeared thereafter. Thus, moderate thinning caused enduring changes to the SOM composition and appeared to have temporary effects on the C storage capacity of forest soils, which is a critical aspect under the current climatic change scenario.