[A-CG40] 陸域生態系の物質循環

[ACG40-P03] 沖縄島の亜熱帯常緑広葉樹林における土壌呼吸とその構成成分

*速水 眞誉¹、松本 一穂²、谷口 真吾²、大橋 瑞江³、高嶋 敦史² (1.琉球大学大学院農学研究科、2.琉球大学農学部、3.兵庫県立大学環境人間学部)

キーワード：土壌呼吸量、根呼吸量、微生物呼吸量、空間変動、亜熱帯常緑広葉樹林

We examined the factors controlling the spatial variation in the soil CO₂ efflux (soil respiration) in a subtropical mature evergreen broadleaf forest in northern Okinawa Island. At four locations with different soil respiration values (2.2, 2.5, 10.8, and 15.5 μmol m^-2 s^-1), we examined the flux components constituting soil respiration (i.e., root respiration and heterotrophic respiration originating from the surface litter and other belowground organic matter) in November 2016. To measure the first two, we sampled roots and the litter layer after measuring soil respiration, and then measured the flux from both in situ using a chamber with an infrared gas analyser. Then, we estimated the heterotrophic respiration from belowground organic matter by subtracting both of these from the total soil respiration. This showed that, at the two locations with the highest soil respiration, the heterotrophic respiration from belowground organic matter was large (7.5 and 10.6 μmol m^-2 s^-1) and accounted for 68–69% of the total soil respiration. In comparison, it was small at the two locations with low soil respiration. The root biomass and root respiration (0.7–4.3 μmol m^-2 s^-1) were positively correlated with the soil respiration. Although the biomass of the surface litter was positively correlated with soil respiration, the heterotrophic respiration originating from it was small (0.3–0.7 μmol m^-2 s^-1). A negative correlation between soil density and soil respiration was found. Based on the results, we postulated that the CO₂ flux from live roots, and especially from microbes consuming dead belowground organic matter supplied by litterfall, largely contributes to the spatial variability in the soil CO₂ efflux in this forest.