Drought drives rapid shifts in tropical rainforest soil biogeochemistry and greenhouse gas emissions

O’Connell, Christine; Ruan, Leilei; Silver, Whendee L.

doi:10.1038/s41467-018-03352-3

Cited by 146 publications

(170 citation statements)

References 66 publications

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“…At TSP forest, soils in the groundwater discharge zone emit on average 7,000 μg CH 4 -C·m −2 ·hr −1 (Figure 3), which is within the range of global averages for wetland CH 4 emissions (Turetsky et al, 2014). However, this CH 4 emission is higher than the values reported for riparian soils in temperate (Itoh et al, 2009;Kaiser et al, 2018;Warner et al, 2018) and tropical forests (O'Connell et al, 2018). This may be related to the high groundwater tables during monsoonal summer at our site (Figure 2d).…”

Section: Journal Of Geophysical Research: Biogeosciencessupporting

confidence: 61%

Humid Subtropical Forests Constitute a Net Methane Source: A Catchment‐Scale Study

Zhu

Zhang

et al. 2019

JGR Biogeosciences

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Commonly, well‐drained forest soils are net methane (CH4) sinks, whereas poorly drained soils in groundwater discharge zones could contribute significant CH4 emissions. Climate change is projected to bring more summer precipitation extremes to subtropics, which may affect forest CH4 balance. Chinese forests often have a hilly topography with well‐drained hillslopes and pronounced groundwater discharge zones. Although different landscape elements are likely to have different source and sink functions for CH4, the climatic influence on CH4 budget at the catchment scale remains poorly studied. Here, we measured CH4 fluxes over three years along a topographic gradient in a subtropical forested catchment in SW China. CH4 fluxes exhibited a clear spatial pattern indicating moderate CH4 uptake or emission from the well‐drained soils on the hillslope (−5.8 to +1.0 kg CH4‐C·ha−1·year−1) and significant CH4 emission from the wetter soils in the groundwater discharge zone (94.3 to 479.5 kg CH4‐C·ha−1·year−1). Despite its small area contribution to the catchment (0.6%), the groundwater discharge zone emitted substantial amounts of CH4 in monsoonal summers, affecting the whole‐catchment budget. Hillslope soils showed weaker CH4 uptake or even turned into a small CH4 source under wet climatic conditions. Estimates of catchment‐scale CH4 budgets indicate that subtropical forest catchments can tip from a net CH4 sink in drier years to a net CH4 source in wetter years, highlighting the importance of interannual climate variabilities. Our findings suggest that subtropical forests under projected climate change could contribute a net CH4 source with consequences for the regional CH4 balance.

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Section: Journal Of Geophysical Research: Biogeosciencessupporting

confidence: 61%

Humid Subtropical Forests Constitute a Net Methane Source: A Catchment‐Scale Study

Zhu

Zhang

et al. 2019

JGR Biogeosciences

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“…Drought conditions during our study greatly decreased soil moisture and changed typical topographic patterns in soil moisture and O 2 availability across hillslopes at our research site. Several previous studies have found lower soil O 2 levels, higher soil moisture, and higher N gas fluxes in valley compared to ridge and slope locations at our experimental sites (O'Connell et al, 2018;Silver et al, 1999;Silver et al, 2013). However, at a site adjacent to ours during the drought, valley positions had the largest percentage increase in O 2 availability, with concentrations increasing from~5% prior to the drought to~15% in June (O'Connell et al, 2018).…”

Section: 1029/2018jg004851mentioning

confidence: 43%

“…However, at a site adjacent to ours during the drought, valley positions had the largest percentage increase in O 2 availability, with concentrations increasing from ~5% prior to the drought to ~15% in June (O'Connell et al, ). This shift put valley soils in the range of O 2 conditions typical of ridge and slope soils in this landscape (O'Connell et al, ; Silver et al, ). Our data show similarly anomalous soil moisture patterns across topographic positions.…”

Section: Discussionmentioning

confidence: 97%

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Effects of Changes in Nitrogen Availability on Nitrogen Gas Emissions in a Tropical Forest During a Drought

2019

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Atmospheric nitrogen (N) deposition in tropical forests may increase substantially in coming decades, stimulating a concomitant increase of soil N gas emissions. At the same time, climate change may increase the prevalence of drought, altering the processes that produce these gases (dominantly aerobic nitrification and anaerobic denitrification). This alteration is of particular concern if global changes increase the fraction of N gas released as nitrous oxide (N2O; a greenhouse gas) relative to dinitrogen (N2). To simulate the effects of atmospheric N deposition on the amount and species of soil N gas emissions, we installed fertilized ion exchange resin bags across a hillslope in the Luquillo Experimental Forest of Puerto Rico. Our experiment took place during a severe drought, providing opportunities to consider how N addition and dry soil conditions interact. After 2 months of fertilization, we measured denitrification potential using a denitrification enzyme assay, which utilizes anoxic incubations where N and carbon limitation are relieved and nitrification is inhibited. We also measured N2 and N2O emissions using a Nitrogen Free Air Recirculation Method (NFARM), which quantifies emissions from both nitrification and denitrification. Data from these two methods suggest that N inputs stimulated N2O emissions associated with aerobic nitrification. Our data suggest that soil drying during the drought decreased N2 emissions associated with anaerobic denitrification and changed the spatial patterns of emissions in the landscape. Together these results suggest that, at least during a drought, N inputs increase N2O emissions associated with nitrification, which may represent a positive feedback to climate change.

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“…In the dry season, the trend observed by Singh et al (1997) was reversed, with CH 4 consumption stimulated by additional moisture. The study described here was performed in a tropical wet forest more similar to a subtropical wet forest (O'Connell et al, 2018), than a dry tropical forest (Singh et al, 1997); however, in this site the drought experienced during the El Niño of 2015-2016 was an extreme negative precipitation anomaly, and the observed increased in methane consumption was dramatically different from all other dates studied.…”

Section: Journal Of Geophysical Research: Biogeosciencesmentioning

confidence: 98%

ENSO‐Influenced Drought Drives Methane Flux Dynamics in a Tropical Wet Forest Soil

et al. 2019

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Global atmospheric methane growth rates have wildly fluctuated over the past three decades, which may be driven by the proportion of tropical land surface saturated by water. The El Niño/Southern Oscillation Event (ENSO) cycle drives large‐scale climatic trends globally, with El Niño events typically bringing drier weather than La Niña. In a lowland tropical wet forest in Costa Rica, we measured methane flux bimonthly from March 2016 to June 2017 and using an automated chamber system. We observed a strong drying trend for several weeks during the El Niño in 2016, reducing soil moisture below normal levels. In contrast, soil conditions had high water content prior to the drought and during the moderate La Niña that followed. Soil moisture varied across the period studied and significantly impacted methane flux. Methane consumption was greater during the driest part of the El Niño period, while during La Niña and other time periods, soils had lower methane consumption. The mean methane flux observed was −0.022 mg CH4‐C m−2 hr−1, and methane was consumed at all timepoints, with lower consumption in saturated soils. Our data show that month studied, and the correlation between soil type and month significantly drove methane flux trends. Our data indicate that ENSO cycles may impact biogenic methane fluxes, mediated by soil moisture conditions. Climate projections for Central America show dryer conditions and increased El Niño frequency, further exacerbating predicted drought. These trends may lead to negative climate feedbacks, with drier conditions increasing soil methane consumption from the atmosphere.

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Drought drives rapid shifts in tropical rainforest soil biogeochemistry and greenhouse gas emissions

Cited by 146 publications

References 66 publications

Humid Subtropical Forests Constitute a Net Methane Source: A Catchment‐Scale Study

Humid Subtropical Forests Constitute a Net Methane Source: A Catchment‐Scale Study

Effects of Changes in Nitrogen Availability on Nitrogen Gas Emissions in a Tropical Forest During a Drought

ENSO‐Influenced Drought Drives Methane Flux Dynamics in a Tropical Wet Forest Soil

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