Abstract
AbstractMiscanthus x giganteus's efficacy as an energy crop relies on maintaining low greenhouse gas (GHG) emissions. As demand for Miscanthus is expected to rise to meet bioenergy targets, fertilizers and composts may be employed to increase yields, but will also increase GHG emissions. Manipulation experiments are vital to investigate the consequences of any fertilizer additions, but there is currently no way to measure whole‐plant GHG fluxes from crops taller than 2.5 m, such as Miscanthus, at the experimental plot scale. We employed a unique combination of eddy covariance (EC), soil chambers and an entirely new automated chamber system, SkyBeam, to measure high frequency (ca. hourly) fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from a Miscanthus crop amended with green compost. Untreated controls were also monitored in a fully replicated experimental design. Net ecosystem exchange (NEE) of CO2 was partitioned into soil respiration (Rs), gross primary productivity (GPP) and ecosystem respiration, and the crop was harvested to determine the effect of compost on crop productivity. Compost increased NEE emissions by 100% (p < .05), which was the result of a 20% increase of Rs (p < .06) and a 32% reduction in GPP (p < .05) and biomass of 37% (p < .06). Methane fluxes were small and unaffected by compost addition. N2O emissions increased 34% under compost during an emission event; otherwise, fluxes were low and often negative, even under dry conditions. Diurnal variation in N2O fluxes, with uptake during the day and emission at night was observed. These fluxes displayed a negative relationship with soil temperature and a hitherto undescribed diurnal temperature hysteresis. We conclude that compost addition negatively affected the productivity and environmental effects of Miscanthus cultivation during the first year following application.
Highlights
To combat climate change, it may be necessary to use biomass to produce as much as a third of our future energy requirements (IPCC, 2014)
Previous work has shown that greenhouse gas (GHG) emissions, and especially N2O fluxes, from Miscanthus are much lower than conventional crop rotations (Drewer, Finch, Lloyd, Baggs, & Skiba, 2012), and this is key to its viability as a bioenergy crop (Whitaker et al, 2018)
Similar to eddy covariance (EC), SkyBeam Net ecosystem exchange (NEE) data were partitioned into ecosystem respiration (Reco) and gross primary productivity (GPP) following the method of Reichstein et al (2005)
Summary
It may be necessary to use biomass to produce as much as a third of our future energy requirements (IPCC, 2014). Previous investigations into the GHG emissions associated with Miscanthus production have generally relied on manual static chamber flux measurements (Drewer et al, 2012; Gauder, Butterbach‐Bahl, Graeff‐Honninger, Claupein, & Wiegel, 2012), with the greatest temporal resolution being biweekly (Oates et al, 2016). Circulating the headspace gas through multiple analysers allowed the quantification of fluxes of CO2, N2O and CH4 from a single chamber closure This new approach allowed monitoring of N2O, CO2 and CH4 from Miscanthus in near real‐time, to explore the extent to which episodic emissions of GHG occurred. The combination of techniques applied allowed investigation into the partitioning of carbon fluxes from NEE data to assess which elements of the C cycle would influence changes to the GHG balance following compost addition
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