Changes in CH4 production during different stages of litter decomposition under inundation and N addition

Abstract

Purpose:

Our aim was to examine linkages between mass loss, chemical transformation and CH4 production during decomposition of leaf litters submerged under water. We hypothesised that (i) labile leaf litters would fuel a rapid, high rate of methane (CH4) production and that recalcitrant litters would fuel long-lasting but lower emissions, (ii) leaf litters experiencing a greater alteration to chemical properties would stimulate increased CH4 production and (iii) nitrogen (N) addition would increase CH4 emissions.

Materials and methods:

Litters from six plant species were collected from a riparian ecosystem adjacent to Wyaralong Dam, located in Queensland, Australia, i.e., Lophostemon confertus, Cynodon dactylon, Heteropogon contortus, Chamaecrista rotundifolia, Chrysocephalum apiculatum and Imperata cylindrica. We evaluated the rate of mass loss and CH4 emissions for 122 days of incubation in inundated microcosms with and without N addition. We quantified the chemical changes in the decomposing litters with 13C-cross polarization and magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectrum.

Results and discussion:

The inundation treatment of plant litters significantly affected decomposition rates. All litters decomposed in either inundated or aerobic microcosms were quite distinct with regard to the NMR spectra of their initial litters. N addition altered the NMR spectra under both inundation and aerobic conditions. The N treatment only marginally influenced the decomposition rates of I. cylindrica and C. apiculatum litters. The diurnal patterns of CH4 production in the H. contortus, C. rotundifolia and C. apiculatum litters under inundation incubation could be expressed as one-humped curves, with the peak value dependent on litter species and N treatment. N addition stimulated CH4 emission by C. rotundifolia and C. apiculatum litters and inhibited CH4 emission from microcosms containing the litters of the three gramineous species, i.e., I. cylindrica, C. dactylon and H. contortus.

Conclusions:

Our results provide evidence that labile leaf litters could fuel a rapid, high rate of CH4 production and that recalcitrant litters fuelled a lower CH4 emission. We did not find that leaf litters with altered chemical properties stimulated increased CH4 production. We also found that N addition was able to increase CH4 emissions, but this effect was dependent on the litter species.