TY - JOUR
T1 - A comment on the quantitative significance of aerobic methane release by plants
AU - Kirschbaum, Miko U.F.
AU - Bruhn, Dan
AU - Etheridge, David M.
AU - Evans, John R.
AU - Farquhar, Graham D.
AU - Gifford, Roger M.
AU - Paul, Keryn I.
AU - Winters, Anthony J.
PY - 2006
Y1 - 2006
N2 - A recent study by Keppler et al. (2006; Nature 439, 187-191) demonstrated CH4 emission from living and dead plant tissues under aerobic conditions. This work included some calculations to extrapolate the findings from the laboratory to the global scale and led various commentators to question the value of planting trees as a greenhouse mitigation option. The experimental work of Keppler et al. (2006) appears to be largely sound, although some concerns remain about the quantification of emission rates. However, whilst accepting their basic findings, we are critical of the method used for extrapolating results to a global scale. Using the same basic information, we present alternative calculations to estimate global aerobic plant CH4 emissions as 10-60 Mt CH4 year-1. This estimate is much smaller than the 62-236 Mt CH4 year-1 reported in the original study and can be more readily reconciled within the uncertainties in the established sources and sinks in the global CH4 budget. We also assessed their findings in terms of their possible relevance for planting trees as a greenhouse mitigation option. We conclude that consideration of aerobic CH4 emissions from plants would reduce the benefit of planting trees by between 0 and 4.4%. Hence, any offset from CH4 emission is small in comparison to the significant benefit from carbon sequestration. However, much critical information is still lacking about aerobic CH4 emission from plants. For example, we do not yet know the underlying mechanism for aerobic CH4 emission, how CH4 emissions change with light, temperature and the physiological state of leaves, whether emissions change over time under constant conditions, whether they are related to photosynthesis and how they relate to the chemical composition of biomass. Therefore, the present calculations must be seen as a preliminary attempt to assess the global significance from a basis of limited information and are likely to be revised as further information becomes available.
AB - A recent study by Keppler et al. (2006; Nature 439, 187-191) demonstrated CH4 emission from living and dead plant tissues under aerobic conditions. This work included some calculations to extrapolate the findings from the laboratory to the global scale and led various commentators to question the value of planting trees as a greenhouse mitigation option. The experimental work of Keppler et al. (2006) appears to be largely sound, although some concerns remain about the quantification of emission rates. However, whilst accepting their basic findings, we are critical of the method used for extrapolating results to a global scale. Using the same basic information, we present alternative calculations to estimate global aerobic plant CH4 emissions as 10-60 Mt CH4 year-1. This estimate is much smaller than the 62-236 Mt CH4 year-1 reported in the original study and can be more readily reconciled within the uncertainties in the established sources and sinks in the global CH4 budget. We also assessed their findings in terms of their possible relevance for planting trees as a greenhouse mitigation option. We conclude that consideration of aerobic CH4 emissions from plants would reduce the benefit of planting trees by between 0 and 4.4%. Hence, any offset from CH4 emission is small in comparison to the significant benefit from carbon sequestration. However, much critical information is still lacking about aerobic CH4 emission from plants. For example, we do not yet know the underlying mechanism for aerobic CH4 emission, how CH4 emissions change with light, temperature and the physiological state of leaves, whether emissions change over time under constant conditions, whether they are related to photosynthesis and how they relate to the chemical composition of biomass. Therefore, the present calculations must be seen as a preliminary attempt to assess the global significance from a basis of limited information and are likely to be revised as further information becomes available.
KW - Climate change
KW - Greenhouse gas
KW - Methane
KW - Plants
KW - Source
UR - http://www.scopus.com/inward/record.url?scp=33744964099&partnerID=8YFLogxK
U2 - 10.1071/FP06051
DO - 10.1071/FP06051
M3 - Article
SN - 1445-4408
VL - 33
SP - 521
EP - 530
JO - Functional Plant Biology
JF - Functional Plant Biology
IS - 6
ER -