Amounts of carbon mineralised and leached as DOC during decomposition of Norway spruce needles and fine roots

Abstract

a b s t r a c tChanges in climate or forest management practices leading to increased litter production will most likely cause increased leaching rates of dissolved organic carbon (DOC) from the O horizon. The rhizosphere is often assumed to have a large carbon flux associated with root turnover and exudation. However, little has been done to quantify the amount of DOC originating from root litter. We studied decomposition of fine root and needle litter of Norway spruce (Picea abies) through a combined incubation and leaching experiment in the laboratory using five different litter types: fresh needle litter, aged needles from the litter layer, fresh and dead roots from mineral soil samples, and seven-year-old roots from a previous litterbag study. After respiration measurements, the samples were percolated with artificial throughfall water and DOC and UV absorbance were measured in the leachate. Mineralisation of dissolved organic matter in the leachate and sorption of DOC to ferrihydrite were determined as a measure of DOC ability to be stabilised by iron (hydr)oxide surfaces.The mineralisation rate and DOC production rate of root samples were always lower than that of needle samples. However, root and needle derived dissolved organic matter (DOM) were similar in terms of aromaticity, as indicated by their specific UV absorbance, and ability to be sorbed by ferrihydrite. For sevenyear-old roots, a significantly higher fraction of carbon was lost as DOC (30%) than for younger roots (20%). Furthermore, DOM from old roots bound more strongly to ferrihydrite and is mineralised at a lower rate than DOC from younger roots, suggesting that roots at late stages of decomposition, although a small fraction of total litter, significantly contribute to carbon build-up in mineral soils. The slower decomposition rate of roots compared with needles must be taken into account when modelling litter decomposition.

Effects of phosphorus addition on soil microbial biomass and community composition in a subalpine spruce plantation

“…After all, C availability is usually considered to be the main limiting resource for soil microbial growth [6]. Fine root and floor litter have been found to be important sources of soil DOC [21]. Our field data showed that fine root biomass increased by 39% in the HP treatment compared to the control (Fig.…”

Gone or just out of sight? The apparent disappearance of aromatic litter components in soils

“…Data by Crow et al (2009) suggest that lignin concentrations of roots are in the range of those of leaf and needle litter. Root-derived DOM shows higher concentrations of aromatic compounds than DOM from foliar litter (Hansson et al, 2010;Uselman et al, 2012). Hansson et al (2010) showed that DOM production during root decomposition occurs in patterns that are similar to those of needle decomposition.…”

“…Hence, losses of lignin-derived C during litter decomposition can occur due to leaching of water-soluble products of an incomplete degradation or as CO 2 . Laboratory incubation tests on water-extractable organic matter from various plant and soil materials suggest that aromatic components are more resistant to mineralization than non-aromatic components (Pinney et al, 2000;Kalbitz et al, 2003a, b;Marschner and Kalbitz, 2003;Don and Kalbitz, 2005;McDowell et al, 2006;Hagedorn and Machwitz, 2007;Fellman et al, 2008;Hansson et al, 2010;Kothawala et al, 2012;Toosi et al, 2012). This suggests that leaching is an important factor in loss of lignin-derived matter during litter decomposition.…”

Experimental warming differentially affects microbial structure and activity in two contrasted moisture sites in a Sphagnum-dominated peatland

“…UV absorbance was then measured at 280 nm using a UV spectrophotometer. Finally, SUVA 280 was calculated as absorbance divided by WEOC concentration (Hansson et al, 2010) and is expressed as g of dry peat per mg C − 1 cm − 1 .…”