Stem CH4 fluxes and related microbial communities from dead and live trees in subtropical forests
摘要
CH4 fluxes have been measured for live tree stems within forests. However, the CH4 flux of standing dead trees in subtropical forests remains unclear. Using static sealed chamber technology, we determined CH4 fluxes from standing dead and live tree stems of Lithocarpus glaber with two different tree heights (0.5 m and 1.0 m) in subtropical China from January 2022 to December 2023. We measured CH4 fluxes and the corresponding environmental variables and analyzed their relationships. Heartwood wood samples were also analyzed to identify potential microbe communities and functional groups associated with CH4 fluxes. The annual tree stem CH4 flux from standing dead trees was significantly greater (0.07945 g CH4 m−2 yr−1) than that from live trees (0.06815 g CH4 m−2 yr−1) at 0.5 m from the ground. The CH4 fluxes of tree stems from the two stem types (dead vs. live) and two tree heights (0.5 vs. 1.0 m from the ground) were significantly related to temperature, with their effects further enhanced by increasing temperature. The main methanogenic pathways were methylotrophic methanogenesis and CO2 reduction in live tree stem heartwood but CO2 reduction in standing dead tree stem heartwood. Furthermore, three methanotrophic genera were identified in standing dead and live tree stems at tree heights of 0.5 and 1 m: Methylocystis, Methylobacterium, and Paracoccus. Our study revealed interannual variations in CH4 fluxes in standing dead and live tree stems, suggesting the importance of long-term continuous monitoring. The coexistence of methanotrophs and methanogens within standing dead and live trees emphasizes the necessity of future research on microbe mechanisms and their associated driver factors underlying dead and live stem CH4 exchange in response to global change.