Aerobic methane emission from plants in the Inner Mongolia steppe

Traditionally, methane (CH₄) emission from terrestrial plants is thought to originate from belowground microbial metabolism under anaerobic conditions, with subsequent transport to the atmosphere through stems. However, a recent study reported aerobic CH₄ emission from plants by an unrecognized process, a result that has since been questioned. We investigated CH₄ emissions under aerobic conditions from aboveground tissues of 44 species indigenous to the temperate Inner Mongolia steppe. Ten herbaceous hydrophytes (wetland-adapted plants) were examined, two of which - Glyceria spiculosa and Scirpus yagara - emitted CH₄ from stems but not from detached leaves. Of 34 xerophytes (arid-adapted plants) examined, 7 out of 9 shrub species emitted CH₄ from detached leaves but not stems, whereas none of 25 herbaceous xerophytes emitted CH₄. The herbaceous hydrophyte, S. yagara, emitted highly ¹³C-depleted CH₄, suggesting a microbial origin. Achillea frigida exhibited the highest CH ₄ emission rates among the shrubs and continuously emitted relatively ¹³C-enriched CH₄ from detached leaves, indicating that CH₄ was derived directly from plant tissues under aerobic conditions. Because woody species are relatively rare in the Inner Mongolia steppe, aerobic, plant-derived CH₄ emission is probably negligible in this region. Our results may imply a larger role for aerobic CH₄ production in upland ecosystems dominated by woody species or in ecosystems where woody encroachment is occurring as a result of global change.