Methane production in plants a defensive strategy

As we have discussed the methane production from plants with Keppler et al 2006,and further refinement from Nobel Laureate Paul Crutzen and who estimated the global production at 8%.

The possibility of plant methane production as a defense mechanism was in the 2008 UNEP report on ozone,UNEP. (2008). Environmental effects of ozone depletion and its interactions with climate change: Progress report, 2008. Photochemical & Photobiological Sciences.

A further paper examines the causal mechanism.

Physical injury stimulates aerobic methane emissions from terrestrial plants

Z.-P. Wang1, J. Gulledge2,3, J.-Q. Zheng1, W. Liu1, L.-H. Li1, and X.-G. Han1

Abstract. Physical injury is common in terrestrial plants as a result of grazing, harvesting, trampling, and extreme weather events. Previous studies demonstrated enhanced emission of non-microbial CH4 under aerobic conditions from plant tissues when they were exposed to increasing UV radiation and temperature. Since physical injury is also a form of environmental stress, we sought to determine whether it would also affect CH4 emissions from plants. Physical injury (cutting) stimulated CH4 emission from fresh twigs of Artemisia species under aerobic conditions. More cutting resulted in more CH4 emissions. Hypoxia also enhanced CH4 emission from both uncut and cut Artemisia frigida twigs. Physical injury typically results in cell wall degradation, which may either stimulate formation of reactive oxygen species (ROS) or decrease scavenging of them. Increased ROS activity might explain increased CH4 emission in response to physical injury and other forms of stress. There were significant differences in CH4 emissions among 10 species of Artemisia, with some species emitting no detectable CH4 under any circumstances. Consequently, CH4 emissions may be species-dependent and therefore difficult to estimate in nature based on total plant biomass. Our results and those of previous studies suggest that a variety of environmental stresses stimulate CH4 emission from a wide variety of plant species. Global change processes, including climate change, depletion of stratospheric ozone, increasing ground-level ozone, spread of plant pests, and land-use changes, could cause more stress in plants on a global scale, potentially stimulating more CH4 emission globally.

http://www.biogeosciences.net/6/615/2009/bg-6-615-2009.html

We can also correlate this with intense solar activity such as flares in solar cycle 23 as the above CH4 "spikes show" and as a defensive response to increased uvb.