Metla Project 3324

Pools and fluxes of carbon on mineral soils and peatlands

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Duration: 2001-2006   Keywords: decomposition, fine roots, greenhouse gas, litter, mineralisation, organic carbon, understorey
Research Programme: Pools and fluxes of carbon in Finnish forests and their socio-economic implications


The 5-year (2001-2005) research project, "Pools and fluxes of carbon on mineral soils and peatlands", is one of the three projects that form Metla's Research Programme "Pools and fluxes of carbon in Finnish forests and their socio-economic implications (HMS)".

The aim of the project is to determine and describe the carbon pools and fluxes in forest ecosystems on mineral soils and peatlands in Finland. In particular, we aim to determine:

Subproject 1: Pools and fluxes of carbon in mineral soils

Researchers: Heljä-Sisko Helmisaari (project leader), John Derome, Tatu Hokkanen, Marja Huotari, Mikko Kukkola, Antti-Jussi Lindroos, Päivi Merilä, Tiina Nieminen, Anna Saarsalmi, Aino Smolander, Michael Starr, Pekka Tamminen, Liisa Ukonmaanaho.

The general aim of the project is to combine empirical data from several completed and on-going projects within Metla related to carbon to provide a comprehensive and integrated account of the carbon status of forest ecosystems in Finland, to disseminate this information to policy makers, the public and to the scientific community in the form of reports, scientific journal articles and presentations, and to provide a sound empirical basis for the verification, calibration and evaluation carbon models.

In different sub-projects we will:


Subproject 1: Pools and fluxes of carbon in mineral soils

Two thirds of the soil carbon in upland soils in mineral soil
We have derived regression models based on parameters measured in the Finnish National Forest Inventory (VMI) (analysed data from 488 VMI 8 monitoring plots) for predicting soil organic carbon concentrations and amounts. The models were used as transfer functions for estimating the soil carbon concentrations and amounts for those VMI monitoring plots that have not been sampled for soil analyses. The models were also used to identify and evaluate the effects and importance of various factors on soil carbon. The analysed and calculated data was used to produce maps of carbon amounts in mineral forest soils in Finland.

Local site and soil factors- topography, soil thickness, distance to groundwater and soil texture- affect carbon amounts in upland soils. Amount of carbon in the organic layer seems to depend only on local factors, but carbon in the mineral soil is significantly explained also by the effective sum of temperature and elevation of the site. Amount of carbon in the organic layer is, on average, greatest in old conifer stands growing on medium fertile sites and on paludified sites, with a peat layer instead of normal mor layer.

Amount of carbon in the mineral soil seems to increase from north to south and on the other hand from near-sea-level sites to high elevated sites (see Fig.). Carbon amount in the mineral soils is the highest in fine-textured soils and on the most fertile sites. On the other hand, stoniness or shallowness of the soil due to bedrock clearly decrease the carbon amount in the mineral soil as they decrease the proportion of fine soil. Amount of carbon decreases quickly from soil surface to deeper layers (see Table). Read more (pdf)

Fine root litter production equals aboveground litterfall
Relationships between fine root biomass and stand and site factors were determined based on empirical studies in 25 Norway spruce and Scots pine stands in Finland. Fine root biomass of trees and understorey in Norway spruce stands varied between 2070 and 5520 kg/ha. Scots pine stands had a fine root biomass between 2300 and 4930 kg/ha. There were more fine roots in northern and/or infertile sites. Thus, when all fine roots in the stand (understorey belowground biomass and tree fine roots) were considered, there was a clear relation with fine root biomass and latitude as well as with the temperature sum for both Norway spruce and Scots pine stands . Commonly used variables describing stand structure (volume, basal area, number of stems, needle biomass) did not show notable correlations with fine root biomass at stand level. Thereagainst, on tree level the fine root biomass was quite strongly correlated with e.g. the needle mass and the basal area. The C content of tree and understorey fine and small roots (diameter < 5 mm) varied between 1860-5690 kgha -1. Read more (pdf)

Carbon fluxes in Scots pine litter in Finland can reliably be explained by climate and stand factors
The aim was to determine the aboveground annual litterfall amounts associated carbon inputs to the forest floor (data from c. 34 plots throughout Finland) and identify the most significant site, stand and climate factors affecting these inputs (e.g. tree species, site type, stand age, geographical location, stand characteristics, climate and weather) as well as and to develop multiple linear regression models that can be used to reliably predict litterfall production (LF needle and LF total) in the boreal zone using readily available variables. Unlike most other litterfall production studies, we used data for the actual sites and measured annual litterfall values.

Models for Scots pine using latitude and stand basal area (also dominant tree height in the case of LF needle) as predictive variables accounted for 82% of the variance in both LF needle and LF total. The standard error of the estimate (SE est) was 12.6 g m −2 for LF needle and 23.3 g m −2 for LF total. Latitude effectively described the climate at each stand but ignored the considerable within-stand variation in annual litterfall production. Using the annual values for the climate variables instead of latitude, 70% or more of the variation in both LF needle and LF total in MLR models could be explained.

These models are useful tools for predicting annual litterfall in mature Scots pine stands for use in soil organic and carbon models. The models for Norway spruce will be ready during 2006.

Latitude correlates with carbon input into forest soil in deposition
The DOC inputs into and outputs from humus and the upper mineral soil layer were determined using data available from some 13 stands in Finland. Latitude correlated with the carbon flux from canopy into forest soil both in Norway spruce and Scots pine stands. Carbon flux was greatest in southern Finland. The input of organic carbon in stand throughfall into forest soil varied between 20 and 57 kg/ha in Scots pine stands and between 33 and 85 kg/ha in Norway spruce stands. DOC leaching from the soil in percolation water was 0-42 kg/ha/v. Read more (pdf)

Dissolved organic carbon in throughfall, forest floor, and soil solutions was dominated by hydrophobic acids, which are relatively resistant to decay
The fractionation was made using adsorbtion/exchange resins that separates DOC into hydrophilic and hydrophobic acids, base and neutrals. The combined acids fraction, particularly hydrophobic acid (humic and fluvic acids) accounted 67 to 90 % of the DOC in the throughfall and forest floor leachate. The hydrophilic fraction has been shown to leach larger amounts from deciduous forest, coniferous forest is dominated by less easily decomposable acidic and hydrophobic compounds. The dominance of hydrophobic and acidic fractions in Valkea-Kotinen is particular indicated that spruce needles are an important source of these fractions.

Effects of afforestation on greenhouse gas emissions of organic soil croplands were determined Cultivated organic soil croplands are significant sources of CO 2 and N 2O and small sinks of CH 4. To quantify the soil GHG-fluxes of afforested organic soils, chamber measurements of soil CO 2, CH 4 and N 2O fluxes were made during years 2002 to 2005 on twelve afforested organic soil cropland sites and six afforested cutaway peatland sites in Finland. According to the results a fforestation of former organic soil croplands lowers considerably heterotrophic soil CO 2 emissions. The reduction of soil CO 2 efflux is due to the cessation of cultivation practices which accelerate the soil decomposition processes during the active agricultural phase. The N 2O emissions do not appear to change after afforestation of organic soil croplands. Neither do the fluxes of CH 4 change; after afforestation the areas remained small sinks of CH 4 . Since CO 2 emissions from soil do appear to decrease, the afforestation of organic croplands may decrease the greenhouse impact of these lands, especially when the increased sequestration of C into the growing tree stand is taken into consideration. Read more (pdf)

Subproject 3: Carbon accumulation rate in ombrotrophic peatlands near heavy metal emission sources

14 C bomb pulse and 210Pb methods allowed continuous age-dating of peat layers accumulated within the past 125 years
The carbon accumulation rate varied between the sites under different heavy metal load, and it could be related to different climatic parameters like annual precipitation. In addition some evidence of an influence of the local heavy metal exposure history on peat accumulation processes was provided.

In collaboration with the team of the Heidelberg University the benefits of the competence of both partners could be combined, like the Finnish knowledge of mire ecology and the long-term development work on peat age-dating carried out by the German colleagues. Read more

Project leader: Helmisaari, Heljä-Sisko

Other researchers: Alm, Jukka, JO (2002), Aro, Lasse, PA (2002-06), Badorek, Tiina (2006), Cernota, Mikulas (2003), Dahlin, Teija (2003), Derome, John, RO (2002-03,2006), Faubert, Patrick (2004), Hartman, Markus, VA (2002-06), Hokkanen, Tatu, VA (2002-06), Hytönen, Jyrki, KA (2002-06), Karsisto, Marjut, VA (2002-06), Kitunen, Veikko, ME (2002-03,2005-06), Lehtonen, Aleksi, VA (2005), Lindroos, Antti-Jussi, VA (2002-06), Luiro, Jukka, VA (2006), Makkonen, Kirsi (2002-04), Merilä, Päivi, PA (2003-04), Mäkiranta, Päivi (2003-05), Nieminen, Tiina, VA (2002-06), Penttilä, Timo, VA (2002-07), Potila, Hannamaria (2003-05), Saarsalmi, Anna, VA (2002-06), Salemaa, Maija, VA (2004-06), Silvan, Niko, PA (2005), Starr, Michael, VA (2002-04), Tamminen, Pekka, VA (2002-06), Tapanila, Tarja, ME (2005-06), Ukonmaanaho, Liisa, VA (2002-06), Wall, Antti, KA (2003-04,2006), Yli-Petäys, Mika (2002-03)

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Updated 12.06.2012