Soil organic matter biochemistry and potential susceptibility to climatic change across the forest‐tundra ecotone in the Fennoscandian mountains

Abstract

We studied soil organic carbon (C) chemistry at the mountain birch forest-tundra ecotone in three regions of the Fennoscandian mountain range with comparable vegetation cover but contrasting degrees of continentality and latitude. The aim of the study was to identify functional compound classes and their relationships to decomposition and spatial variation across the ecotone and latitudinal gradient. Solid-state 13C nuclear magnetic resonance (CPMAS 13C NMR) was used to identify seven functional groups of soil organic C: alkyls, N-alkyls, 0-alkyls, acetals, aromatics, phenolics and carboxyls. N-alkyls, 0-alkyls and acetals are generally considered labile substrates for a large number of saprotrophic fungi and bacteria, whilst phenolics and aromatics are mainly decomposed by lignolytic organisms and contribute to the formation of soil organic matter together with aliphatic alkyls and carboxyls. All soils contained a similar proportional distribution of functional groups, although relatively high amounts of N-alkyls, 0-alkyls and acetals were present in comparison to earlier published studies, suggesting that large amounts of soil C were potentially vulnerable to microbial degradation. Soil organic matter composition was different at the most southerly site (Dovrefjell, Norway), compared with the two more northerly sites (Abisko, Sweden, and Joatka, Norway), with higher concentrations of aromatics and phenolics, as well as pronounced differences in alkyl concentrations between forest and tundra soils. Clear differences between mountain birch forest and tundra heath soil was noted, with generally higher concentrations of labile carbon present in tundra soils. We conclude that, although mesic soils around the forest-tundra ecotone in Fennoscandia are a potential source of C to the atmosphere in a changing environment, the response is likely to vary between comparable ecosystems in relation to latitude and continentality as well as soil properties especially soil nitrogen content and pH.

Long term effects of reduced fertilizer rates on millet yields and soil properties in the West-African Sahel

“…3, peak 6), compared to all other treatments, indicating alkyl-N may build up as amides and pyrrolics break down. Alkyl-N may be low when amides are highest because amides must break down to form alkyl-N (Sjorgersten et al 2003). Another important observation is that the alkyl-N peaks for R2F0M2 and R2F1M2, the treatments highest in organic matter as well as amides, are shifted to the left (Fig.…”

Organic matter chemistry controls greenhouse gas emissions from permafrost peatlands

“…Spectra were referenced externally to solid adamantane 304 (resonance at  = 38.5 ppm) to provide a chemical shift scale relative to neat TMS 305 (Morcombe and Zilm 2003). After processing, the spectra were integrated over chemical shift 306 ranges corresponding to the major organic functional groups (Sjögersten et al, 2003). 307…”

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“…Again, a large portion of carbohydrates are likely derived from dead and living marine microbial cells [Simpson et al, 2007a]. In addition, it has been reported that O-alkyl and acetyl carbon (anomeric carbon constituents) can serve as substrates for bacteria in sediment organic matter and increased microbial activity can result in the synthesis of new carbohydrates, initially increasing the labile SOM concentration [Sjögersten et al, 2003]. Over time, the catabolism of O-alkyl carbon by microbes leads to a net alkyl carbon accumulation by the synthesis of new alkyl carbon structures which may help explain some of the alkyl carbon observed at the lowest depth outside and at 2, 4 and 6 mbsf inside the pockmark [Baldock et al, 1990].…”