Environmental controls over methane emissions from bromeliad phytotelmata: The role of phosphorus and nitrogen availability, temperature, and water content

Tank bromeliads are common epiphytic plants throughout neotropical forests that store significant amounts of water in phytotelmata (tanks) formed by highly modified leafs. Methanogenic archaea in these tanks have recently been identified as a significant source of atmospheric methane. We address the effects of environmental drivers (temperature, tank water content, sodium phosphate [P], and urea [N] addition) on methane production in anaerobically incubated bromeliad slurry and emissions from intact bromeliad tanks in montane Ecuador. N addition ≥ 1 mg g^-1 had a significantly positive effect on headspace methane concentrations in incubation jars while P addition did not affect methane production at any dosage (≤ 1 mg g^-1). Tank bromeliads (Tillandsia complanata) cultivated in situ showed significantly increased effluxes of methane in response to the addition of 26 mg N addition per tank but not to lower dosage of N or any dosage of P (≤ 5.2 mg plant ^-1). There was no significant interaction between N and P addition. The brevity of the stimulatory effect of N addition on plant methane effluxes (1-2 days) points at N competition by other microorganisms or bromeliads. Methane efflux from plants closely followed within-day temperature fluctuations over 24 h cycles, yet the dependency of temperature was not exponential as typical for terrestrial wetlands but instead linear. In simulated drought, methane emission from bromeliad tanks was maintained with minimum amounts of water and regained after a short lag phase of approximately 24 h. Our results suggest that methanogens in bromeliads are primarily limited by N and that direct effects of global change (increasing temperature and seasonality, remote fertilization) on bromeliad methane emissions are of moderate scale.