CARBON FRACTIONS AND STOCKS IN ORGANIC LAYERS IN BOREAL FOREST SOILS—IMPACTS OF CLIMATIC AND NUTRITIONAL CONDITIONS, ACTA UNIVERSITATIS OULUENSIS A Scientiae Rerum Naturalium 571
|Kustantaja:||Oulun yliopisto|| |
|Sijainti:||Print Tietotalo|| |
|Tekijät:||HILLI SARI || |
The SOM in boreal forests contains non-living heterogeneous components resulting frommicrobial and chemical transformations of organic debris from plant litter. The major componentsin the plant biomass all decompose at different rates and therefore, contribute variably to the stablestorages of soil C. The aims of the current thesis were 1) to explore how climate, soil fertility andinitial litter quality affect the decomposition rate of litter, 2) to study how the different carbonfractions found in the plant litter relate to the quality and quantity of SOM in forest soils, 3) todetermine whether the recalcitrant fraction of litter is derived from lignin and other polyphenolsor from lipophilic compounds and carbohydrates, and 4) to determine whether the litter originatingfrom different plant growth forms affects SOM formation in a similar way. The study wasconducted in six north boreal and six south boreal study sites, half of which were mesic and halfwere sub-xeric. The overall initial litter quality and decomposition rate of carbon fractions did notdiffer between the two fertility levels and climate regimes. Litter with high initial water-solubleextractives (WSE) and nitrogen (N) decomposed at a faster rate than litter with lower initial WSEand N concentration irrespective of the soil fertility or climate conditions. Althoughdecomposition rate varies among litter types, decomposition rate cannot explain differences inSOM quality or quantity between the northern and southern boreal forests. The organic matteraccumulation and relative proportion of acid-insoluble residue (AIR) in SOM was higher in southboreal sites both in sub-xeric and mesic sites. Detailed characterization of the AIR fraction usingpyrolysis-GC demonstrated that in the litter layer the concentration of AIR contains lignin andother insoluble polyphenols, but in the F and H layers, lignin-derived and chemically modifiedpolyphenolics and decomposition products of resin acids. Although the concentration of the AIRfraction varies among litter types, its composition varied very little among the litter types, andbetween a sub-xeric and a mesic site. The results of this study suggest that the differences in plantcommunity structure and quantitative differences in the litter input by various growth forms hasmore impact on OM accumulation than decomposition conditions in coniferous soils.