Methane Cycling in Arid Soils: Methanotrophic Microbiomes and Associations with Plants

Committee Members

• Dr. Marina G. Kalyuzhnaya, Chair, SDSU
• Dr. Elizabeth R. Waters, SDSU
• Dr. Nicholas Barber, SDSU
• Dr. Eric E. Allen, UCSD
• Dr. Jack Gilbert, UCSD

Abstract

This work takes the first steps towards linking symbiotic associations of microbes to desert plants with global methane cycling. Drylands occupy 37.1% of the Earth’s terrestrial surface and are increasingly being converted into agricultural fields. Sustainable and productive use of arid land requires a better understanding of the functional traits of microbes inhabiting native arid environments.

To improve our knowledge of native arid ecosystem functioning, we performed preliminary studies with soil samples collected from Anza-Borrego Desert State Park. The following discoveries were made: 1) Metagenomic data identified the methanotrophic bacteria Methylocaldum sp. as the predominant genus within the methanotrophic community in vegetated and unvegetated soil of the Anza-Borrego desert. 2) The consumption rate of atmospheric methane positively correlated with the presence of vegetation; 3) Genome annotations of methanotrophs from the rhizosphere of desert plants highlight several functions that can contribute to interactions with plants; 4) Methanotrophs have the potential to improve plant survival during drought stress.

Based on these data we propose that in arid environments plants facilitate methane transport to the ground and cooperate with methane-consuming microbes to capture methane efficiently evolved in deeper soil layers and atmospheric methane (i.e. reverse chimney), which is then metabolized to provide supplemental resources for survival in water-limiting conditions.

The results suggest that the plant-methanotroph associations represent an overlooked sink of atmospheric methane in dryland ecosystems. We show that supplementation with native Methylocaldum isolates from the Anza-Borrego Desert can potentially improve crop drought tolerance (e.g. Sorghum).

Furthermore, this work provides essential evidence that targeted engineering of association between crops and methanotrophs in dryland soils can enhance atmospheric methane sink, ultimately influencing the global climate.