CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska
2015
Morishita, Tomoaki | Noguchi, Kyōtarō | Kim, Yongwon | Matsuura, Yojiro
Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO ₂), methane (CH ₄) and nitrous oxide (N ₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO ₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO ₂ flux was highest at PB (128 ± 85 mg CO ₂-C m ⁻² h ⁻¹) and lowest at SB1 (47 ± 19 mg CO ₂-C m ⁻² h ⁻¹) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO ₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO ₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH ₄ uptake rate was highest at SB1 [–91 ± 21 μg CH ₄-C m ⁻² h ⁻¹] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH ₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N ₂O flux was highest [3.6 ± 4.7 μg N ₂O-N m ⁻² h ⁻¹] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.
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