The diazotrophic cyanobacterium Trichodesmium has been recognized as a potentially significant contributor to aerobic methane generation via several mechanisms including the utilization of methylphophonate (MPn) as a source of phosphorus. Currently, there is no information about how environmental factors regulate methane production by Trichodesmium. Here, we grew Trichodesmium IMS101 at five temperatures ranging from 16 to 31°C, and found that its methane production rates increased with rising temperatures to peak (1.028 ± 0.040 nmol CH4 μmol POC−1 day−1) at 27°C, and then declined. Its specific growth rate changed from 0.03 ± 0.01 d−1 to 0.34 ± 0.02 d−1, with the optimal growth temperature identified between 27 and 31°C. Within the tested temperature range the Q10 for the methane production rate was 4.6 ± 0.7, indicating a high sensitivity to thermal changes. In parallel, the methane production rates showed robust positive correlations with the assimilation rates of carbon, nitrogen, and phosphorus, resulting in the methane production quotients (molar ratio of carbon, nitrogen, or phosphorus assimilated to methane produced) of 227–494 for carbon, 40–128 for nitrogen, and 1.8–3.4 for phosphorus within the tested temperature range. Based on the experimental data, we estimated that the methane released from Trichodesmium can offset about 1% of its CO2 mitigation effects.
Trichodesmium , a nitrogen-fixing cyanobacterium, has recently been shown to release methane through utilization of the organic phosphorus methylphosphonate (MPn), which is commonly found in surface oceans. We demonstrated previously that methane production (MP) increased with rising temperatures and was positively correlated with assimilations of carbon and nitrogen under optimal light conditions. Here, we show that when grown under light-limitation, elevated temperatures within a range of 23 °C to 31 °C reduced growth by 67% and MP by 91%, with altered relationship of MP to assimilations of C, N and P. This indicates that light-limitation disrupted the synergy of MP with the C/N/P assimilations, highlighting that photosynthetic energy supply affects methane production to differential extents with increasing temperatures. Our results imply that Trichodesmium in deeper waters or exposed to low light conditions produces much less methane even under ocean warming scenarios.
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