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Can flooding-induced greenhouse gas emissions be mitigated by trait-based plant species choice?

Oram, Natalie J., van Groenigen, Jan Willem, Bodelier, Paul L.E., Brenzinger, Kristof, Cornelissen, Johannes H.C., De Deyn, Gerlinde B., Abalos, Diego
The Science of the total environment 2020 v.727 pp. 138476
Festuca arundinacea, Lolium perenne, Poa trivialis, Trifolium repens, biomass production, botanical composition, carbon dioxide, carbon nitrogen ratio, climate change, field experimentation, flooded conditions, global warming potential, grasses, grasslands, greenhouse experimentation, greenhouse gas emissions, greenhouse gases, legumes, methane, mineralization, nitrogen, nitrous oxide, plant communities, soil
Intensively managed grasslands are large sources of the potent greenhouse gas nitrous oxide (N₂O) and important regulators of methane (CH₄) consumption and production. The predicted increase in flooding frequency and severity due to climate change could increase N₂O emissions and shift grasslands from a net CH₄ sink to a source. Therefore, effective management strategies are critical for mitigating greenhouse gas emissions from flood-prone grasslands. We tested how repeated flooding affected the N₂O and CH₄ emissions from 11 different plant communities (Festuca arundinacea, Lolium perenne, Poa trivialis, and Trifolium repens in monoculture, 2- and 4-species mixtures), using intact soil cores from an 18-month old grassland field experiment in a 4-month greenhouse experiment. To elucidate potential underlying mechanisms, we related plant functional traits to cumulative N₂O and CH₄ emissions. We hypothesized that traits related with fast nitrogen uptake and growth would lower N₂O and CH₄ emissions in ambient (non-flooded) conditions, and that traits related to tissue toughness would lower N₂O and CH₄ emissions in flooded conditions. We found that flooding increased cumulative N₂O emissions by 97 fold and cumulative CH₄ emissions by 1.6 fold on average. Plant community composition mediated the flood-induced increase in N₂O emissions. In flooded conditions, increasing abundance of the grass F. arundinacea was related with lower N₂O emissions; whereas increases in abundance of the legume T. repens resulted in higher N₂O emissions. In non-flooded conditions, N₂O emissions were not clearly mediated by plant traits related with nitrogen uptake or biomass production. In flooded conditions, plant communities with high root carbon to nitrogen ratio were related with lower cumulative N₂O emissions, and a lower global warming potential (CO₂ equivalent of N₂O and CH₄). We conclude that plant functional traits related to slower decomposition and nitrogen mineralization could play a significant role in mitigating N₂O emissions in flooded grasslands.