N2O and CO2 emissions from three different tropical forest sites in the wet tropics of Queensland, Australia

Klinikum Garmisch-Partenkirchen, Markt Garmisch-Partenkirchen, Bavaria, Germany
Soil Biology and Biochemistry (Impact Factor: 4.41). 07/2002; 34(7):975-987. DOI: 10.1016/S0038-0717(02)00031-7

ABSTRACT Three different tropical rain forest sites in Northeast Queensland, Australia, two in the Coastal Lowlands (Pin Gin Hill and Bellenden Ker) and one on the Atherton Tablelands (Kauri Creek), were investigated for the magnitude of N2O and CO2 emissions from soils during the wet and the dry season. At all sites, mean N2O emission rates were significantly higher during the wet season (Bellenden Ker: 242.0±7.4 μg N2O–N m−2 h−1, Pin Gin Hill: 140.8±5.1 μg N2O–N m−2 h−1, Kauri Creek: 80.8±3.3 μg N2O–N m−2 h−1) as compared to the dry season when N2O-emissions were markedly lower (<20 μg N2O–N m−2 h−1) due to limitations in soil moisture. During the wet season, mean N2O emission rates of the Coastal Lowland sites Bellenden Ker and Pin Gin Hill were approximately twofold higher as compared to N2O emission rates of the Atherton Tableland site Kauri Creek. These site differences were found to be due to differences in precipitation and soil moisture, the C-to-N ratio of the organic matter, soil pH and temperature. Site and seasonal differences in CO2-emissions were not as pronounced as for N2O-emissions. Mean CO2 emission rates at the different sites were in a range of 92.2±1.8 up to 137.3±4.5 mg C m−2 h−1. Correlation analysis revealed a strong dependency of N2O and CO2 emissions on changes in soil moisture, whereas changes in soil temperature did not significantly influence the magnitude of in situ N2O and CO2 emissions. N2O emissions were positively correlated to changes in water filled pore space (WFPS) up to a threshold of 50% WFPS at the Bellenden Ker and Kauri Creek sites and up to a threshold of 60% WFPS at the Pin Gin Hill site. CO2 emission rates were positively correlated to changes in WFPS at dry to moderate soil water contents during the dry season, but were negatively correlated to changes in WFPS during the wet season. Measurements of soil air N2O-concentrations at the different sites revealed the following sequence in magnitude: Bellenden Ker>Pin Gin Hill>Kauri Creek, which is the same as found for the N2O source strengths at these sites.

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    ABSTRACT: Upland humid tropical forest soils are often characterized by fluctuating redox dynamics that vary temporally and spatially across the landscape. An increase in the frequency and intensity of rainfall events with climate change is likely to affect soil redox reactions that control the production and emissions of greenhouse gases. We used a 24-day rainfall manipulation experiment to evaluate temporal and spatial trends of surface soil (0–20 cm) redox-active chemical species and greenhouse gas fluxes in the Luquillo Experimental Forest, Puerto Rico. Treatments consisted of a high rainfall simulation (60 mm day−1), a fluctuating rainfall regime, and a control. Water addition generated high temporal and spatial variation in soil moisture (0.3–0.6 m3 m−3), but had no significant effect on soil oxygen (O2) concentrations. Extractable nitrate (NO3−) concentrations decreased with daily water additions and reduced iron (Fe(II)) concentrations increased towards the end of the experiment. Overall, redox indicators displayed a weak, non-deterministic, nonlinear relationship with soil moisture. High concentrations of Fe(II) and manganese (Mn) were present even where moisture was relatively low, and net Mn reduction occurred in all plots including controls. Mean CO2 fluxes were best explained by soil C concentrations and a composite redox indicator, and not water addition. Several plots were CH4 sources irrespective of water addition, whereas other plots oscillated between weak CH4 sources and sinks. Fluxes of N2O were highest in control plots and were consistently low in water-addition plots. Together, these data suggest (1) a relative decoupling between soil moisture and redox processes at our spatial and temporal scales of measurement, (2) the co-occurrence of aerobic and anaerobic biogeochemical processes in well-drained surface soils, and (3) an absence of threshold effects from sustained precipitation on redox reactions over the scale of weeks. Our data suggest a need to re-evaluate representations of moisture in biogeochemical models.
    Ecosystems 06/2013; 16(4):576-589. DOI:10.1007/s10021-012-9631-2
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