Warming and elevated CO2 promote rapid incorporation and degradation of plant-derived organic matter in an ombrotrophic peatland.

Nicholas O E Ofiti,Emily F Solly,Paul J Hanson,Guido L B Wiesenberg,Michael W I Schmidt,Avni Malhotra

doi:10.1111/gcb.15955

Nicholas O E Ofiti, Emily F Solly + Show 4 more

Open Access

https://doi.org/10.1111/gcb.15955

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Abstract

Rising temperatures have the potential to directly affect carbon cycling in peatlands by enhancing organic matter (OM) decomposition, contributing to the release of CO2 and CH4 to the atmosphere. In turn, increasing atmospheric CO2 concentration may stimulate photosynthesis, potentially increasing plant litter inputs belowground and transferring carbon from the atmosphere into terrestrial ecosystems. Key questions remain about the magnitude and rate of these interacting and opposing environmental change drivers. Here, we assess the incorporation and degradation of plant‐ and microbe‐derived OM in an ombrotrophic peatland after 4 years of whole‐ecosystem warming (+0, +2.25, +4.5, +6.75 and +9°C) and two years of elevated CO2 manipulation (500 ppm above ambient). We show that OM molecular composition was substantially altered in the aerobic acrotelm, highlighting the sensitivity of acrotelm carbon to rising temperatures and atmospheric CO2 concentration. While warming accelerated OM decomposition under ambient CO2, new carbon incorporation into peat increased in warming × elevated CO2 treatments for both plant‐ and microbe‐derived OM. Using the isotopic signature of the applied CO2 enrichment as a label for recently photosynthesized OM, our data demonstrate that new plant inputs have been rapidly incorporated into peat carbon. Our results suggest that under current hydrological conditions, rising temperatures and atmospheric CO2 levels will likely offset each other in boreal peatlands.

Highlights

More than one third of terrestrial soil carbon (C; 300–400 Pg C) is stored in boreal and subarctic peatlands, even though these ecosystems occupy less than 3% of the land surface (Bridgham et al, 2006; Gorham, 1991; Yu, 2012)
We evaluated the effects of temperature on peat organic carbon and nitrogen concentration and lipid biomarker by stepwise multiple linear regression analysis with temperature, elevated CO2, and elevated CO2 × temperature as possible factors
Peat organic carbon concentration increased with increasing depth, but there was no effect of temperature on the concentration in neither the ambient CO2 nor the elevated CO2 treatments

Summary

| INTRODUCTION

More than one third of terrestrial soil carbon (C; 300–400 Pg C) is stored in boreal and subarctic peatlands, even though these ecosystems occupy less than 3% of the land surface (Bridgham et al, 2006; Gorham, 1991; Yu, 2012). We further hypothesized that warming would accelerate peat decomposition through drying (Laine et al, 2019; Pinsonneault et al, 2016), and together with higher CO2 concentrations increase plant biomass inputs into OM (Malhotra et al, 2020; McPartland et al, 2019) To test these hypotheses, we employed molecular-level analyses (biomarkers) that quantify specific plant-and microbe-derived compounds (solvent extractable alkanes and fatty acids [FAs]). This combination of analyses allowed us to trace the allocation of carbon belowground during the experimental period

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION