Impact of freeze-thaw cycles on greenhouse gas emissions in marginally productive agricultural land under different perennial bioenergy crops.

Knowledge of freeze-thaw-induced carbon (C) and nitrogen (N) cycling and concomitant nitrous oxide (N 2 O) and carbon dioxide (CO 2 ) emissions in perennial bioenergy crops is crucial to understanding the contribution of these crops in mitigating climate change through reduced greenhouse gas (GHG) emissions. In this study, a 49-day laboratory incubation experiment was conducted to compare the impact of freeze-thaw cycles on N 2 O and CO 2 emissions in different perennial bioenergy crops [miscanthus (Miscanthus giganteus L.), switchgrass (Panicum virgatum L.), and willow (Salix miyabeana L.)] to a successional site and to understand the processes controlling the N 2 O and CO 2 emissions in these crops. The results showed that freeze-thaw cycles caused a decline in dissolved organic C (DOC) and dissolved inorganic N (DIN) concentrations but enhanced the dissolved organic N (DON) and nitrate (NO 3 - ). Although, freeze-thaw decreased water stable soil aggregates in all the bioenergy crops and successional site, this did not have any significant impact on N 2 O and CO 2 emissions, suggesting that the N 2 O and CO 2 emitted during the freeze-thaw cycles may have originated mostly from cellular materials released from lysis and death of microbial biomass rather than from soil aggregate disruption. Cumulative N 2 O emissions measured over the 49-day incubation period ranged from 148 mg N 2 O-N m -2 to 17 mg N 2 O-N m -2 and were highest in miscanthus followed by willow, switchgrass, and successional site. Cumulative CO 2 on the other hand was highest in the successional site than any of the bioenergy crops and ranged from 25,262 mg CO 2 -C m -2 to 15,403 mg CO 2 -C m -2 after the 49 days. Higher N 2 O emissions in the miscanthus and willow than switchgrass and successional site were attributed to accelerated N losses as N 2 O. Results from our study indicate that managing perennial bioenergy crops on low productive agricultural lands to reduce freeze-thaw related GHG emissions and climate change mitigation is dependent on the crop species grown.

Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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