The effect of clear cutting on podzolisation and soil carbon dynamics in boreal forests (Middle Taiga zone, Russia).
Articolo
Data di Pubblicazione:
2012
Abstract:
Boreal forests are one of the most important terrestrial carbon sink, and a large portion of C is allocated in soil
for long-term storage. However forest harvesting may quickly affect soil carbon stocks and dynamics, especially
where organic substances drive the soil-forming processes, such as in Podzols. To evaluate the effects
of clear cutting on carbon dynamics and podzolisation process over a short time period, a pristine boreal forest
(Komi Republic, Russian Federation) and a recently clear cut site (5 year-old) were selected. Soils are polygenic:
podzolisation occurs within the clay-depleted eluvial horizon, formed by a previous lessivage process. Because
podzolisation can start only after the eluvial horizon has reached a sort of threshold, bisequal soils allow to individuate
comparable pedogenic conditions prior to anthropogenic disturbances.
After harvesting, C storage tended to increase in the upper part of the soil profile (organic layer and podzolic
sequum) from 2.2 to 5.0 kgm−2. The abundance of woody materials on the forest floor together with an increase
in soil water saturation, discernible by the vegetation survey and iron fractionation, prevented litter degradation
and allowed organic matter accumulation at the soil surface. Fulvic acids (FA) in the organic layer of
the pristine site showed a low incorporation of polysaccharide and proteinaceous moieties, confirming a higher
degradation of the humified fraction than at the clear cut site. The lack of disturbances allowed a selection of FA
with the more oxidised and mobile fractions accumulating in the deeper horizons, as currently observed in
Podzols. Almost no differences were instead found in the chemical composition of FA along the profile from
the clear cut site. A larger portion of FA showed the tendency to migrate through the profile after clear cutting
even below the Bhs horizon (C-fulvic acid/C-humic acid >1) with a marked increase in the FA-carbon
stocks with respect to the pristine forest soil (0.66 and 0.30 kg m−2 down to 30 cm, respectively).
Clear cutting also affected Al and Fe dynamics. The reducing conditions acted upon soil mineral surfaces
and enhanced Fe mobilisation probably both in the ionic form and complexed with organic matter. The
Al dynamics was instead more related to short term transformations of the layer silicate phases. Traces
of a poorly crystalline chlorite were detectable in the Bhs in the pristine forest, but at the clear site only
hydroxy-interlayered vermiculite was present. The high amounts of organic acids that migrated through the
Bhs after clear cutting may have partially complexed the Al from pedogenic chlorite, giving rise to hydroxyinterlayered
behaviour, as normally occurs in Podzol eluvial horizons from where the organic Al-complexes migrate.
Our findings suggested that if this trend proceeds further the whole podzolic sequum may migrate downwards.
This may have important implication on C budget, as organic carbon will be transferred deeper in the soil profile
limiting its losses at least over a short time period.
Tipologia CRIS:
03A-Articolo su Rivista
Elenco autori:
Falsone G.; Celi L.; Caimi A.; Simonov G.; Bonifacio E.
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