Effect of reed canary grass cultivation on greenhouse gas emission from peat soil at controlled rewetting

S. Karki,L. Elsgaard,P. E. Lærke

doi:10.5194/bg-12-595-2015

Abstract

Abstract. Cultivation of bioenergy crops in rewetted peatland (paludiculture) is considered as a possible land use option to mitigate greenhouse gas (GHG) emissions. However, bioenergy crops like reed canary grass (RCG) can have a complex influence on GHG fluxes. Here we determined the effect of RCG cultivation on GHG emission from peatland rewetted to various extents. Mesocosms were manipulated to three different ground water levels (GWLs), i.e. 0, −10 and −20 cm below the soil surface in a controlled semi-field facility. Emissions of CO2 (ecosystem respiration, ER), CH4 and N2O from mesocosms with RCG and bare soil were measured at weekly to fortnightly intervals with static chamber techniques for a period of 1 year. Cultivation of RCG increased both ER and CH4 emissions, but decreased the N2O emissions. The presence of RCG gave rise to 69, 75 and 85% of total ER at −20, −10 and 0 cm GWL, respectively. However, this difference was due to decreased soil respiration at the rising GWL as the plant-derived CO2 flux was similar at all three GWLs. For methane, 70–95% of the total emission was due to presence of RCG, with the highest contribution at −20 cm GWL. In contrast, cultivation of RCG decreased N2O emission by 33–86% with the major reductions at −10 and −20 cm GWL. In terms of global warming potential, the increase in CH4 emissions due to RCG cultivation was more than offset by the decrease in N2O emissions at −10 and −20 cm GWL; at 0 cm GWL the CH4 emissions was offset only by 23%. CO2 emissions from ER were obviously the dominant RCG-derived GHG flux, but above-ground biomass yields, and preliminary measurements of gross photosynthetic production, showed that ER could be more than balanced due to the photosynthetic uptake of CO2 by RCG. Our results support that RCG cultivation could be a good land use option in terms of mitigating GHG emission from rewetted peatlands, potentially turning these ecosystems into a sink of atmospheric CO2.

Highlights

Peatlands cover 3 % of the world’s area but contain 30 % of the soil organic carbon (Parish et al, 2008), signifying an important role in the global carbon cycle
In order to reduce the large emissions of CO2 from drained peatlands, extensive rewetting projects have been implemented in Europe and North America (Höper et al, 2008), and rewetted organic soils have been included in the guidelines for national greenhouse gas (GHG) inventories by the Intergovernmental Panel on Climate Change (IPCC, 2014)
The objective of the present study was to quantify the role of reed canary grass (RCG) cultivation on the resulting GHG emissions of CO2, N2O and CH4 from peat soils rewetted to various extents

Summary

Introduction

Peatlands cover 3 % of the world’s area but contain 30 % of the soil organic carbon (Parish et al, 2008), signifying an important role in the global carbon cycle. Agricultural use of wet and rewetted peatlands for crop growth (paludiculture) is considered as a possible land use option that may indirectly reduce the CO2 emissions by biomass production for energy purposes (Joosten et al, 2012; Günther et al, 2014). Reed canary grass (RCG) (Phalaris arundinacea) is one of the suitable biomass crops for paludiculture (Wichtmann and Tanneberger, 2011). It can be established from seeds as normal agricultural grass (Kandel et al, 2013b), but in some countries it is considered as an invasive species (Maurer et al, 2003). The plants thrive in wet soils due to aerenchyma tissues (Kercher and Zedler, 2004; Askaer et al, 2011) that transport oxygen to the roots in otherwise anaerobic

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