Tubular PMFC with oxygen reducing biocathode was applied in salt marsh and peat soil. Oxygen was passively supplied in the cathode via a silicone gas diffusion layer. Long term power generation with both biological anode and cathode in peat soil. Maximum long term power generation of 21 mW m−2 plant growth area was achieved. Salt marsh biocathode only started with pure O2 likely due to substrate crossover.