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 CH4 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.