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[ID: 261] Long-term nitrogen enrichment does not increase microbial phosphorus mobilization in a northern coniferous forest

PI: Benjamin Forsmark

Summary 1. Nitrogen (N) deposition can enhance carbon (C) capture and storage in northern coniferous forests but it may also enhance the demand for phosphorus (P). While it is well established that long-term N enrichment can decrease decomposition and enhance the accumulation of C in soils, it remains uncertain if a higher demand and acquisition of P influence soil C. 2. We studied microbial phosphorus mobilization and growth within a long-term N enrichment experiment in a Norway spruce forest, where N deposition was simulated by adding 0, 12.5, or 50 kg N ha-1 yr-1 for 21 yrs (n=12), by incubating microbial ingrowth cores with needles and humus with low and high P content, and with sand with and without mineral apatite P. 3. Long-term N enrichment had no effect on microbial P mobilization in needles and humus and did not enhance the positive effect that apatite had on fungal growth. However, it consistently strengthened the retention of C in the soil by decreasing decomposition of needle and humus, both with low and high P content, and by increasing fungal growth in sand-filled ingrowth cores. Further, we did not find any evidence that higher microbial P mobilization in response to N enrichment affected soil C storage. 4. These results show that long-term N enrichment in relatively young soils dominated by coniferous trees and ectomycorrhizal fungi can have relatively small impact on microbial P mobilization from organic sources and on the potential to mobilize P from minerals, and subsequently that elevated P demand due to N enrichment is unlikely to lead to a reduction in the soil C accumulation rate.

boreal forestcarbon sequestrationnitrogen depositiondecompositionsoil phosphorusapatiteectomycorrhizal fungi

[ID: 151] The impacts of long-term, high intensity N addition on soil organic matter accumulation in a boreal forest

PI: Shun Hasegawa

N addition is reported to influence decomposition of soil organic matters and potentially enhance carbon accumulation in boreal or temperate forests. Here, we investigate the effect of chronic N addition on boreal forests situated in norther Sweden with an aim of discerning the mechanisms altering the balance of accumulation and decomposition of soil organic matters. We will collect soil samples from the organic layer at Svartberget, Åheden, Rosinedal, Flakaliden and analyze molecular composition of soil organic matters as well as enzymatic activities responsible for C decomposition.

nitrogencarbonsoilorganic matterdecompositionmicrobeboreal forest

[ID: 148] The role of lignin for saprotrophic decomposition of plant litter and the genesis of soil organic matter in boreal soils

PI: Mats Öquist

A striking feature of soil organic matter (SOM) in the moor layer of boreal forests is that it contains 40-50% carbohydrate polymers, even in SOM that has been decomposed for decades to centuries. This is in contrast to all common conceptual decomposition models assuming aromatic and aliphatic polymers to constitute the fraction of recalcitrant SOM. We will elucidate if this accumulation of polymeric carbohydrates stems from protection by recalcitrant lignin or is a result of cellulose crystallinity. As model substrates we will use plant material of Populus genotypes differing both in lignin content and composition of the phenylpropanoid sub-units. We will also use 13C labelled cellulose with varying degree of crystallinity. The role of labile C substrates, according to the priming hypotheses, and N on decomposition will be explored. The decomposition of the substrates will be followed using 2D HSQC NMR identifying what molecular moieties in the lignocellulose complexes that are decomposed over time. 16S rRNA tracking and in depth metagenome characterization will give inferences about the emerging metabolic capabilities of the community and to trace the expression of the relevant hydrolytic genes over time and across treatments. The information derived from this detailed analysis will finally allow to systematically test the multi decadal-old hypothesis that currently shape our view of saprotrophic decomposition of plant litter in moor layers at early stages of SOM genesis.

lignincrystalline celluloseSoil organic matterdecomposition

[ID: 111] DRIP effect on organic matter decomposition

PI: Lenka Kuglerova

In this project we are looking on how do DRIPs (discrete riparian inflow points) affect decomposition of organic matter. We are using standardized assays of tea-bags and cotton strips to asses decomposition patters in riparian soils and in streams. 30 sites with a gradient of DRIP magnitude (from relatively dry sties to zero order stream channels) are used along streams C5-C6, C4, C8, C7, C10, C3, C1 (plus potential additions). The project is a collaboration with Umeå University and Griffith University, Australia.

decompositionstreamgroundwatertea-bagriparian soildriptemperaturecotton strip