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.
"Disturbances to these vulnerable ecosystems will therefore likely lead to considerable changes in CO 2 exchanges with the atmosphere (Meir et al. 2008; Willis and Bhagwat 2009). The impact of warming on C fluxes in tropical rainforests has been explored in a range of studies (Kiese and Butterbach-Bahl 2002; Sotta et al. 2004; Saatchi et al. 2007; Cox et al. 2013). To estimate the impact of changing temperature and rainfall patterns on the C cycle of tropical rainforests in situ, several studies along altitudinal gradients have also been conducted (Girardin et al. 2010; Malhi et al. 2010; Moser et al. 2011). "
[Show abstract][Hide abstract] ABSTRACT: Tropical forests represent the largest store of terrestrial carbon (C) and are potentially vulnerable to climatic variations and human impact. However, the combined influence of temperature and precipitation on aboveground and belowground C cycling in tropical ecosystems is not well understood. To simulate the impact of climate (temperature and rainfall) on soil C heterotrophic respiration rates of moist tropical forests, we translocated soil cores among three elevations (100, 700 and 1540 m a.s.l.) representing a range in mean annual temperature of 10.9°C and in rainfall of 6840 mm. Initial soil C stocks in the top 30 cm along the gradient increased linearly with elevation from 6.13 kg C m–2 at 100 m a.s.l. to 10.66 kg C m–2 at 1540 m a.s.l. Respiration rates of translocated soil cores were measured every 3 weeks for 1 year and were fitted to different model functions taking into account soil temperature, soil moisture, mean annual temperature and total annual rainfall. Measured data coul
Soil Research 01/2015; 53(3-3):286-297. DOI:10.1071/SR14217 · 1.32 Impact Factor
"Erickson and others 2001; Kiese and Butterbach-Bahl 2002; Koehler and others 2009; Rowlings and others 2012), but N 2 O fluxes often display a Gaussian distribution across the entire range of potential soil moisture characterized by declines under very wet conditions (Kiese and Butterbach-Bahl 2002; Castellano and others 2010 "
[Show abstract][Hide abstract] 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.
"The annual soil CO 2 flux of 2.1 kg C m −2 yr −1 for the forest ecosystem, 1.1 kg C m −2 yr −1 for the sago ecosystem and 1.5 kg C m −2 yr −1 for the oil palm ecosystem (Table 3) were similar to those observed by other researchers (Davidson et al., 1998; Kiese and Butterbach-Bahl, 2002; Inubushi et al.). The soil CO 2 flux for the forest was among the highest reported in the literature (Raich and Schlesinger, 1992; Davidson et al., 2000; Inubushi et al., 2003). "
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