Carbon mineralization dynamics in soils after wildfires in two Galician forests

Abstract

The carbon mineralization dynamics of two Humic Cambisols, developed over granite, one under Pinus sylvestris L. (1740 m a.s.l.) and the other under Pinus pinaster Aiton (140 m a.s.l.), were determined in samples of 0±5 and 5±10 cm depth collected after high intensity wild®res. Burnt and unburnt soils were sampled ®ve times over 2 yr after the wild®res to determine changes in C concentration and in potential mineralization activity of the soil organic matter. Soil samples from the same forests unaected by the ®res were used as controls. In both soils the ®re resulted in a substantial decrease in the soil carbon concentration. Immediately after the ®re, the C mineralization was decreased in the surface layer; however, the percentage of total C mineralized increased in both layers. The evolution of these variables over time depended on the soil and on the layer considered. During the ®rst months after the burning the C mineralization presented values lower than those of the control in both layers of the soil located at higher altitude (M) and in the surface layer of the other soil (R), but values higher than those of the control in the subsurface layer of soil R. For the same period, the C mineralization coecient in the surface layer was similar to (M) or lower than (R) that of the corresponding control, whereas in the subsurface layer it was maintained above that of the control in both soils. Two years after the ®re, the total C concentration had been recovered in the surface layer of both soils whereas in the subsurface layers its value was still 15±19% lower than that of the same layer in the corresponding control. At the same time, the C mineralization and the percentage of the total C mineralized in the surface layer of the burnt soils were lower than those in the corresponding unburnt soils. In the subsurface layer, soil M exhibited values of these two mineralization indices higher than those of the control, whereas soil R presented values lower than those of the control from 1 yr after the ®re. The cumulative CO 2 -C evolved by the samples during each incubation ®ts two kinetic models: a simple and a double exponential ®rst order equation. In most cases the coecient of determination (R 2 ) was higher for the double exponential model. The ®re aected the kinetic parameters; the eect was ephemeral on the labile C pool, which increased its content (C 0 ) and its mineralization rate (k ), but more persistent on the recalcitrant fraction, which shows a long-term decrease of its instantaneous mineralization rate (h ). According to principal components analysis, the variability of the samples studied is mainly due to dierences on their organic matter quality and, in a smaller proportion, to dierences in organic matter concentration. The eect of ®re on these factors, which was more pronounced in the soil with the initially higher C concentration, persisted during the 2 yr study. #

Soil gross N transformation rates after a wildfire and straw mulch application for burned soil emergency stabilisation

“…Wildfires modify quantitatively and qualitatively the soil C and N pools (Castro et al 2006;Certini et al 2011;Fernández et al 1997Fernández et al , 1999 that are the energy source for heterotrophs and the substrate for N transformations, respectively. Although weak relations have also been reported (Gómez-Rey et al 2012), the soil C and N pools are considered to be important controlling factors of gross N transformations (Booth et al 2005;Lang et al 2010;Magill and Aber 2000), with which they showed moderate to strong correlations in our plots.…”

Effects of site preparation treatments before afforestation on soil carbon release

“…The effect of controlled burning on soil C release is more complex than that of brush clearing. Compared to brush clearing, controlled burning can affect soil C release not only during the burning process but also during the post-burning period (Fernández et al, 1999). During the burning process, 60-80% of the surface organic materials are burned out and revert to the atmosphere as CO 2 (González-Pérez et al, 2004), leading to a remarkable decrease in soil C stock (Guo et al, 2006).…”

Response of respiration and nutrient availability to drying and rewetting in soil from a semi-arid woodland depends on vegetation patch and a recent wildfire

“…Semi-arid woodlands are frequently exposed to fire, which changes not only vegetation structure and communities but also soil properties such as reducing soil organic matter content and increasing recalcitrance of the remaining organic matter (Fernandez et al, 1999;Hatten and Zabowski, 2009). These changes in soil organic matter content and recalcitrance could also influence the response of respiration to drying and rewetting.…”