Carbon Inputs from Miscanthus Displace Older Soil Organic Carbon Without Inducing Priming

Abstract

The carbon (C) dynamics of a bioenergy system are key to correctly defining its viability as a sustainable alternative to conventional fossil fuel energy sources. Recent studies have quantified the greenhouse gas mitigation potential of these bioenergy crops, often concluding that C sequestration in soils plays a primary role in offsetting emissions through energy generation. Miscanthus is a particularly promising bioenergy crop and research has shown that soil C stocks can increase by more than 2 t C ha −1 yr −1 . In this study, we use a stable isotope ( 13 C) technique to trace the inputs and outputs from soils below a commercial Miscanthus plantation in Lincolnshire, UK, over the first 7 years of growth after conversion from a conventional arable crop. Results suggest that an unchanging total topsoil (0-30 cm) C stock is caused by Miscanthus additions displacing older soil organic matter. Further, using a comparison between bare soil plots (no new Miscanthus inputs) and undisturbed Miscanthus controls, soil respiration was seen to be unaffected through priming by fresh inputs or rhizosphere. The temperature sensitivity of old soil C was also seen to be very similar with and without the presence of live root biomass. Total soil respiration from control plots was dominated by Miscanthus-derived emissions with autotrophic respiration alone accounting for ∼50 % of CO 2 . Although total soil C stocks did not change significantly over time, the Miscanthus-derived soil C accumulated at a rate of 860 kg C ha −1 yr −1 over the top 30 cm. Ultimately, the results from this study indicate that soil C stocks below Miscanthus plantations do not necessarily increase during the first 7 years.

Effect of Growing Miscanthus x giganteus on Soil Microbial Communities in Post-Military Soil

“…Activities of peroxidases can be attributed dominantly to soil fungi, and their increase reflects the increase of fungal PLFA. Unlike in the study of Robertson et al [35], soil respiration (Figure 3), referring to the overall activity of the microbial community and degradation of organic matter, increased significantly between first and second year. It may suggest the positive affect of plant growth on microbial activity, likely due to the secretion of root exudates [36].…”

AMiscanthusplantation can be carbon neutral without increasing soil carbon stocks

“…Given a 30% combustion efficiency and 129.2 t ha −1 yield (18 years at Lincolnshire), an increase of 1 t C ha −1 yr −1 in soils would offset 438 g CO 2 ‐eq kWh −1 on a life cycle basis (Eqn , GHG site fixed at −3.66 t CO 2 ‐eq ha −1 yr −1 ). An increase of 1 t C ha −1 yr −1 in the top 30 cm is not unrealistic; at this site, Miscanthus inputs were previously shown to add 0.86 t C ha −1 yr −1 to the top 30 cm (Robertson et al ., ) and Poeplau & Don () saw an average increase of 1.68 ± 0.7 t C ha −1 yr −1 from a range of Miscanthus crops across Europe. The unchanged topsoil C stocks reported here, therefore, have important consequences for whether it is deemed a preferable alternative to conventional fossil fuels.…”

“…Furthermore, despite relatively low yields and a lack of soil C sequestration, the crop studied here had a considerably lower GHG intensity than coal or natural gas when used for electricity generation. Additional research is required to elucidate why soil C stocks are not changing under this plantation (Zatta et al ., ; Robertson et al ., ) and future bioenergy sustainability studies should prioritize land use efficiency over GHG intensity comparisons. Nevertheless, this study demonstrates that even when yields are lower than many other sites due to climate or establishment issues, GHG benefits can still outweigh costs and contribute to climate change mitigation through the provision of low C renewable energy.…”

“…The land management prior to conversion to Miscanthus was a crop rotation of wheat and oilseed rape, with three years of wheat directly before conversion. Further site details can be found in Robertson et al ., .…”

N2O and CH4 emission from Miscanthus energy crop fields in the infertile Loess Plateau of China

“…Previous studies demonstrated that Miscanthus lutarioriparius , a C 4 endemic species in central China, can adapt to the semi-arid regions and produce high feedstock in North China [ 18 ]. Furthermore, growing this C 4 grass in the Loess Plateau has many environmental benefits, including soil and water conservation, carbon sequestration and soil restoration in the infertile and soil-eroded region [ 19 – 21 ]. Thus, bioenergy production in the large scale may bring a sustainable solution to this region [ 22 , 23 ].…”