Atmospheric nitrogen deposition promotes carbon loss from peat bogs

Abstract

Peat bogs have historically represented exceptional carbon (C) sinks because of their extremely low decomposition rates and consequent accumulation of plant remnants as peat. Among the factors favoring that peat accumulation, a major role is played by the chemical quality of plant litter itself, which is poor in nutrients and characterized by polyphenols with a strong inhibitory effect on microbial breakdown. Because bogs receive their nutrient supply solely from atmospheric deposition, the global increase of atmospheric nitrogen (N) inputs as a consequence of human activities could potentially alter the litter chemistry with important, but still unknown, effects on their C balance. Here we present data showing the decomposition rates of recently formed litter peat samples collected in nine European countries under a natural gradient of atmospheric N deposition from Ϸ0.2 to 2 g⅐m ؊2 ⅐yr ؊1 . We found that enhanced decomposition rates for material accumulated under higher atmospheric N supplies resulted in higher carbon dioxide (CO2) emissions and dissolved organic carbon release. The increased N availability favored microbial decomposition (i) by removing N constraints on microbial metabolism and (ii) through a chemical amelioration of litter peat quality with a positive feedback on microbial enzymatic activity. Although some uncertainty remains about whether decay-resistant Sphagnum will continue to dominate litter peat, our data indicate that, even without such changes, increased N deposition poses a serious risk to our valuable peatland C sinks.decomposition ͉ global change ͉ litter peat ͉ CO2 P eatlands cover 2-3% of the land's surface, store approximately one-third of all soil carbon (C) (390-455 Pg), and currently act as sinks for atmospheric C (1, 2). The ability of peatlands to sequester atmospheric C resides in the long-term accumulation of partially decomposed organic matter (i.e., peat). Indeed, acidic water conditions, low soil temperature, frequent waterlogging, and low nutrient quality of plant litter impair decomposition of plant litter, favoring its accumulation (3). In peatlands exclusively fed by atmospheric deposition (i.e., bogs) (1), the accumulated peat is dominated by the remnants of the mosses of the genus Sphagnum, which produce a litter poor in nutrients and highly enriched in organochemical compounds such as uronic acids (4) and polyphenols (5) with a strong inhibitory effect on microbial activity and vascular plants (3). As such, Sphagnum plants form the bulk of living and dead biomass in bog ecosystems (3).Because of the strict dependence of bogs on atmospheric deposition as a source of nutrients (1), the increasing availability of biologically reactive nitrogen (N) from industrial and agricultural activities (6) could potentially alter the chemical quality of plant litter with consequent effects on the amount of C released during litter decomposition. Accordingly, an understanding of the mechanisms of bog soil C response to changing N availability is essential for assessing the capa...

Responses of peat carbon at different depths to simulated warming and oxidizing

“…In our study we failed to find any linear correlation between carbon export rate and soil characteristics like TC or C/N ratio. Lower quantity of soil N and higher soil C/N ratio could constrain soil microbial metabolism and carbon decomposition (Bragazza et al, 2006;Cleveland and Liptzin, 2007). The C/N ratio in our study was in the range of 12.36 to 35.39 among the whole depth.…”

Biogeochemical processes along a nutrient gradient in a tropical ombrotrophic peatland

“…As these enzymes are induced by the presence of substrate, this perhaps indicates a change in the carbon chemistry of the peat, although the increase in N-acetyl-b-glucosaminidase activity may indicate either an increased microbial investment in nitrogen acquisition (Olander and Vitousek 2000;Bragazza et al 2006) or increased fungal activity (Miller et al 1998) in the interior of the peatland. b-Xylanase is linked to more slowly decomposing material, but differences in its activity among sites were relatively small.…”

“…The activities of all hydrolytic enzymes investigated increased towards the centre of the peatland in parallel with the decline in nutrient concentrations, while the microbial biomass concentration per surface area declined. Enzymes involved in the cycling of phosphorus and nitrogen respond strongly to changes in the availability of these nutrients, both in mineral soils (Olander and Vitousek 2000;Allison et al 2007) and wetlands (e.g., Bragazza et al 2006;Rejmánková and Macek 2008;Penton and Newman 2008), indicating a shift in resources allocation to increased enzyme activity to maintain metabolic rates. Similar rates of phosphatase activity were also reported from Malaysian peat swamps (Jackson et al 2009).…”

Drained coastal peatlands: A potential nitrogen source to marine ecosystems under prolonged drought and heavy storm events—A microcosm experiment

“…Massive volumes of chemical nitrogen production via the HaberBosch process have been applied to the landscape following the industrial revolution, causing many natural ecosystems which previously acted as nitrogen sinks to become nitrogen sources to downstream waters after saturation (Aber, 1992;Bragazza et al, 2006;Lamers et al, 2000). Overloading of nitrogen is a leading cause of impairment of coastal marine ecosystems around the world (Boesch et al, 2001;Compton et al, 2011;Diaz and Rosenberg, 2008;Paerl and Piehler, 2008).…”