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Bark beetle infestation induced changes in soil chemistry and biochemistry

Jiří Kaňa1, Hana Šantrůčková2, Karolina Tahovská2, Jiří Kopáček1
1 Biology Centre of the AS CR, v.v.i. Institute of Hydrobiology
2 University of South Bohemia in České Budějovice, Faculty of Science

O 2.12 in Environmental controls on fluxes and processes in ecosystems

17.07.2014, 15:50-16:10, H18

Bark beetle outbreaks cause important disturbances of forest ecosystems, affecting soil chemistry, microbial processes, and freshwater quality (Tahovská & al. 2010, Kaňa & al. 2013, Mikkelson & al. 2013).

We performed intensive soil sampling in 6-week intervals to evaluate changes in the chemistry and biochemistry of the uppermost soil horizons (litter and humus) in an unmanaged Norway spruce forest (National Park Bohemian Forest, Czech Republic) during 2008–2012 at a plot affected by tree dieback caused by a bark beetle infestation (in 2006) and at undisturbed control plot. Forest dieback and following elevated litter decomposition caused significant changes in soil biochemical processes and in element pools in the upper soil layers compared to the control plot, where only relatively small changes occurred.

Net ammonification rapidly increased from 2.1 to 3.8 mmol N m-2 d-1 during 2008–2010, then continuously decreased to 0.7 mmol N m-2 d-1 in 2012. Despite the increased NH4-N concentrations, net nitrification was even lower that at the control plot during 2008–2010, probably due to high DOC availability. Then, the average rates of net nitrification sharply increased from 0.08 mmol N m-2 d-1 up to 2 mmol N m-2 d-1 in 2012, reflecting parallel declines in soil DOC.

Pools of water-extractable inorganic N increased markedly in soils at the disturbed plot. The annual average NO3-N pools were 2.4 mmol m-2 in 2008–2009, then rapidly increased to 32 mmol m-2 in 2012. The pools of water-extractable NH4-N increased from 5 to 32 mmol m-2 between 2008 and 2010, and then decreased to 20 mmol m-2 in 2012. This indicated equal availability of both N forms for microbes until 2010, and then effective NH4-N consumption by nitrifiers in the later period.

Input of base cations (BC) from decomposing litter altered proportion of cations on soil sorption complex. While the pool of exchangeable BC increased by almost 75% (from ~1.1 to ~1.9 eq m-2), the pool of exchangeable acidity (sum of Al3+ and H+) proportionally decreased from ~2.0 to ~1.1 eq m-2. Base saturation of the upper soil horizons thus increased from 35% to 65%. An increase of exchangeable NH4-N in the uppermost soils (from 58 to 260 mmol m-2 during 2008–2010) also contributed to the reduced exchangeable acidity at the disturbed plot.

Soluble reactive P (SRP) pool increased approximately 20 times, from 0.3 in 2008 (a value similar to the control plot) to ~6 mmol m-2 in 2012. The bark beetle infestation thus significantly elevated P availability in the disturbed forest.

Changes similar to in soil chemistry were paralleled in composition of stream water draining the disturbed forest, with the most pronounced increases in concentrations of BC, Al3+, H+, NO3-, SRP, and DOC (Kopáček & al. 2013).

References:

Kaňa & al. 2013 Biogeochemistry 113:369–383

Kopáček & al. 2013 Silva Gabreta 19(3):105–137

Mikkelson & al. 2013 Biogeochemistry 115:1–21

Tahovská & al. 2010 Boreal Environment Research 15:553–564



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last modified 2014-06-19