Soil net methane uptake rates in response to short-term litter input change in a coniferous forest ecosystem of central China

The uptake of CH4 by well-drained soil plays a vital role in mitigating the atmospheric CH4, but the impacts of shift in plant litter input on uptake of CH4 and the underlying mechanism are not fully understood. Here, we conducted in situ measurements of soil CH4 flux rates monthly throughout the year after the short-term litter input manipulations (i.e. Detritus Input and Removal Treatment-DIRT: control, CK; double litter, DL; no litter, NL; no roots, NR; and no aboveground litter and no roots, NRNL) in a coniferous forest (Platycladus orientalis (Linn.) Franco) ecosystem in subtropical China. The associated microclimates, soil properties and microbial PLFAs were also measured. Our results showed that soils acted as CH4 sink in all litter manipulation treatments, and the CH4 sink capacity significantly differed under litter manipulation treatments. Based on annual average values, net CH4 uptake rates decreased by 37.7 +/- 4.9% and 41.7 +/- 5.8% in the NL and NRNL treatments (i.e. litter layer removal), respectively, compared to the CK treatment. Thus, the net CH4 uptake induced by litter layer approximately accounted for 37.7 +/- 4.9% of the total net CH4 uptake rate. The net CH4 uptake rate was not significantly influenced by the root exclusion (NR) treatment. In contrast, the effect of litter addition on net CH4 uptake rate was strongly depended on soil water content. During the dry season, litter addition did not significantly affect net CH4 uptake rate. In contrast, during the wet season, the net CH 4 uptake rate decreased by 47.1 +/- 4.9% in the DL treatment compared to the CK treatment. There was no significant difference in net CH4 uptake rate between dry and wet season under other litter input manipulation treatments. The net CH4 uptake rate was positively correlated with the abundance of methanotrophic bacteria across all litter input manipulation treatments, whereas the significant negative relationship between net CH4 uptake rate and water filled pore space (WFPS) was only found in the DL treatment. Overall, our results suggest that aboveground organic layer (i.e. litter) is more important in regulating the soils acting as atmospheric CH4 sink than roots, while the regulating function primarily depends on soil dry/wet conditions and the abundance of methanotrophic bacteria.