wAbstract
@The effect of nitrogen addition, through deposition or fertilization,
on ecosystem processes responsible for storing and releasing greenhouse
gasses (GHG) CO2, CH4
and N2O are poorly understood. We measured
the effects of winter application of 200 kg N ha-1
to a near-end-of-rotation coastal Douglas-fir stand on soil CH4 and N2O fluxes, soil and
bole respiration (Rs and Rb,
respectively), and soil CH4 and N2O
concentrations. Fertilization resulted in a significant decrease
in CH4 uptake and changed a small uptake
of N2O to significant emissions. Based on
the average reduction of 2 Κmol m-2 h-1
CH4 uptake with N fertilization, from an
average of 4 Κmol m-2 h-1 with no N fertilization,
the approximate first-year annual reduction was estimated to be
2.8 kg CH4 ha-1. In comparison,
net annual increase in N2O emissions with
N fertilization was 17.6 kg N2O ha-1.
Calculations showed that fertilizer-induced net GHG emissions
due to the reduction in CH4 uptake and the
increase in N2O emissions was 0.07 and 5.3
t CO2 ha-1 equivalents (CO2_Eqv), respectively, indicating that the reduction
in CH4 uptake was much less important than
the increase in N2O emissions. Contrary to
expectation, the annual loss of 17.6 kg N2O
ha-1 arising from this winter application of N was
slightly higher than the 15.7 kg N2O ha-1
loss following spring application of N in the previous year. N
fertilization also resulted in small increase in soil respiration,
confirming our previous results. Temporal dynamics of Rb
matched those of soil respiration and N2O
fluxes. Fertilization resulted in a small but persistent increase
in Rb over the first 4-5 months. While soil
temperature was the main control of soil N2O
and CO2 fluxes as well as Rb,
CH4 uptake was better correlated to soil
water content, i.e., soil gas diffusivity and gas exchange with
the atmosphere.
Keywords: Nitrogen fertilization; Greenhouse gas emissions; Forest-floor
methane uptake; Nitrous oxide; Soil respiration; Bole respirationx
1. Introduction
2. Materials and methods
3. Results
4. Discussion
5. Conclusions
Acknowledgements
References