Linking phosphorus and potassium deficiency to microbial methane cycling in rice
paddies
Abstract. Phosphorus (P) and potassium (K) availability in soil are crucial for the growth and development of resident microorganisms, which in turn modulate local and global carbon emissions from the terrestrial biosphere. Carbon dioxide and methane are key climate active soil emissions, the latter being 25 times more active than CO2 on a per unit basis and its biological production regulated by the balance of activities of key production (methanogenic) and consumption (methanotrophic) taxa. Here, we assessed whether deficiencies in P and K modulated the activities of methanogens, methanotrophs, or both in long term (20 yr) experimental systems undergoing limitation in either one or both nutrients. Biogeochemical measures of methane production, in tandem with mcrA (methanogen) and pmoA (methanotroph) activity under nutrient limitation demonstrated that P deficiency significantly reduced methane flux rates, whereas K deficiency did not. Under P deficiency, methanotroph transcript copy number significantly increased in tandem with a decrease in methanogen transcript activity, suggesting that P deficiency reduced CH4 emissions via reduced methane production in tandem with an increased methane consumption potential. Assessments of community structures based upon transcript or gene abundance indicated transcriptional activities were more sensitive to P and K deficiency than DNA copy number, with phosphorus deficiency inducing greater shifts in the active methanotroph community than for potassium deficiency. In contrast, both phosphorus and potassium deficiencies exhibited similar community structures of active methanogens at the mRNA level, suggesting that methane emissions from paddy soils under nutrient limitation are regulated at the transcriptional level and not the methanogen/methanotroph population size.
