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CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Morishita, Tomoaki, Noguchi, Kyotaro, Kim, Yongwon, Matsuura, Yojiro
Soil science and plant nutrition 2015 v.61 no.1 pp. 98-105
Picea mariana, carbon dioxide, correlation, forest fires, forest soils, forests, greenhouse gases, greenhouses, highlands, methane, nitrous oxide, organic matter, soil temperature, soil water, Alaska
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.