Leaf-cutter ants engineer large nitrous oxide hot spots in tropical forests

Though tropical forest ecosystems are among the largest natural sources of the potent greenhouse gas nitrous oxide (N 2 O), the spatial distribution of emissions across landscapes is often poorly resolved. Leaf cutter ants (LCA; Atta and Acromyrmex, Myrmicinae) are dominant herbivores throughout Central and South America, and influence multiple aspects of forest structure and function. In particular, their foraging creates spatial heterogeneity by concentrating large quantities of organic matter (including nitrogen, N) from the surrounding canopy into their colonies, and ultimately into colony refuse dumps. Here, we demonstrate that refuse piles created by LCA species Atta colombica in tropical rainforests of Costa Rica provide ideal conditions for extremely high rates of N 2 O production (high microbial biomass, potential denitrification enzyme activity, N content and anoxia) and may represent an unappreciated source of heterogeneity in tropical forest N 2 O emissions. Average instantaneous refuse pile N 2 O fluxes surpassed background emissions by more than three orders of magnitude (in some cases exceeding 80 000 µg N 2 O-N m −2 h −1 ) and generating fluxes comparable to or greater than those produced by engineered systems such as wastewater treatment tanks. Refuse-concentrating Atta species are ubiquitous in tropical forests, pastures and production ecosystems, and increase density strongly in response to disturbance. As such, LCA colonies may represent an unrecognized greenhouse gas point source throughout the Neotropics.

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Tropical Forests Natural History, Diversity, and Potentiality as Theatres of Human Adaptation and Negotiation

Tropical Forests in Prehistory, History, and Modernity ◽

10.1093/oso/9780198818496.003.0006 ◽

2019 ◽

Author(s):

Patrick Roberts

Keyword(s):

Tropical Forest ◽

Tropical Forests ◽

Homo Sapiens ◽

Terrestrial Ecosystems ◽

Black Pepper ◽

Wood Products ◽

Tropical Rainforests ◽

Cultural Significance ◽

Seasonally Dry ◽

Dry Tropical Forests

The above quote by the German poet, novelist, and painter Herman Hesse highlights the cultural significance of forests in nineteenth- and twentieth-century western culture as the ‘natural’ contrast to growing urban populations and industrial expansion. Hesse’s focus on the ‘ancient’ element of these environments is certainly valid in a tropical context, given that tropical forests are some of the oldest land-based environments on the planet, existing for over one thousand times longer than Homo sapiens (Upchurch and Wolf, 1987; Davis et al., 2005; Ghazoul and Shiel, 2010; Couvreur et al., 2011). This antiquity also makes them one of the richest and most diverse terrestrial ecosystems on the planet (Whitmore, 1998; Ghazoul and Shiel, 2010). Tropical rainforests, for example, contain over half of the world’s existing plant, animal, and insect species (Wilson, 1988). A significant portion of the developed world’s diet today originated in tropical forests—including staples such as squash and yams, spices such as black pepper, cinnamon, cloves, and sugar cane, and fruits including bananas, coconuts, avocados, mangoes, and tomatoes (Iriarte et al., 2007; Roberts et al., 2017a). Tropical forests also often provide ample freshwater for their inhabitants. However, despite popular perceptions of forests, and specifically tropical forests, as uniform, they are, in fact, highly variable across space and time. In tropical evergreen rainforests productivity is often primarily allocated to wood products, meaning that edible plants and animals for human subsistence have been considered lacking, or at least more difficult to extract, relative to more open tropical forest formations (Whitmore, 1998; Ghazoul and Shiel, 2010). Similarly, while evergreen tropical rainforests generally receive significant precipitation and freshwater, seasonally dry tropical forests are subject to sub-annual periods of aridity. Therefore, while archaeologists and anthropologists have tended to see ‘tropical forest’ as a uniform environmental block, it is important to explore the diversity within this category.

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Inter-specific variations in tree stem methane and nitrous oxide exchanges in a tropical rainforest

10.5194/egusphere-egu21-13260 ◽

2021 ◽

Author(s):

Warren Daniel ◽

Clément Stahl ◽

Benoît Burban ◽

Jean-Yves Goret ◽

Jocelyn Cazal ◽

...

Keyword(s):

Nitrous Oxide ◽

Tropical Forest ◽

Tropical Forests ◽

Wood Density ◽

Tree Species ◽

Pore Space ◽

Tree Size ◽

Tropical Tree ◽

Wet Season ◽

Ghg Fluxes

Tropical forests are the most productive terrestrial ecosystems, global centres of biodiversity and important participants in the global carbon and water cycles. The Amazon, which is the most extensive tropical forest, can contain more than 600 trees (diameter at breast height above 10 cm) and up to 200 tree species in only one hectare of forest. In upland forest, tropical soils are known to be a methane (CH4) sink and a weak source of nitrous oxide (N2O), which are both major greenhouse gases (GHG). Most of researches on GHG fluxes have been conducted on the soil compartment but recent works reported that tree stems of some tropical forests can be a substantial source of CH4 and, a to lesser extend of N2O. Tropical tree stems can act as conduits of soil-produced GHG but biophysical mechanisms controlling GHG fluxes and differences among tree species are not yet fully understood.In order to quantify CH4 and N2O fluxes of different tropical tree species, we took gas samples in 101 mature tree stems of twelve species with the manual chamber technique during the wet season 2020, in a French Guiana forest. Tree species were selected because of their abundance and their habitat preference. We chose trees belonging to two contrasted forest habitats, the hill-top and hill-bottom, which are respectively characterized by aerobic conditions and seasonal anaerobic conditions. Simultaneously with sampling GHG, we measured bark moisture and tree diameter. Four tree species were found in both habitats whereas the eight others were only present in one of these two habitats.Among the 101 tree stems, 78.6% were net sources of CH4 with a greater proportion in hill-bottom than hill-top. Overall, stem CH4 fluxes were significantly and positively correlated with the wood density (&#967;2 = 28.0; p < 0.01; N = 75) but neither with the habitat, bark moisture or tree size. We found a significant effect of the tree species on stem CH4 fluxes (F = 3.7, p < 0.001) but no interactions between the tree species and habitats.Among 43.0% of the stem N2O fluxes that were different from zero, half were from trees that were net sources of N2O mainly located in hill-top. Stem N2O fluxes are not significantly correlated with habitat, as also with the tree size, wood density or bark moisture. Unlike stem CH4 fluxes, tree species did not significantly influence stem N2O fluxes.Our study revealed that, in tropical forest, spatial variations in GHG fluxes would not only depend on soil water conditions, but also on tree species. Specific tree traits such as the wood density can favour stem CH4 emissions by providing more or less effective pore space for CH4 diffusion but seems to have a limited influence on stem N2O fluxes maybe because of the lower diffusive and ebullitive transport of N2O compared to CH4. Further investigation linking tree species traits and tree GHG fluxes are, however, necessary to elucidate the processes and mechanisms behind tree CH4 and N2O exchanges.

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Comparison of greenhouse gas fluxes from tropical forests and oil palm plantations on mineral soil

Biogeosciences ◽

10.5194/bg-18-1559-2021 ◽

2021 ◽

Vol 18 (5) ◽

pp. 1559-1575

Author(s):

Julia Drewer ◽

Melissa M. Leduning ◽

Robert I. Griffiths ◽

Tim Goodall ◽

Peter E. Levy ◽

...

Keyword(s):

Land Use ◽

Nitrous Oxide ◽

Soil Respiration ◽

Greenhouse Gas ◽

Tropical Forests ◽

Oil Palm ◽

Riparian Area ◽

Respiration Rates ◽

N2o Fluxes ◽

Ghg Fluxes

Abstract. In Southeast Asia, oil palm (OP) plantations have largely replaced tropical forests. The impact of this shift in land use on greenhouse gas (GHG) fluxes remains highly uncertain, mainly due to a relatively small pool of available data. The aim of this study is to quantify differences of nitrous oxide (N2O) and methane (CH4) fluxes as well as soil carbon dioxide (CO2) respiration rates from logged forests, oil palm plantations of different ages, and an adjacent small riparian area. Nitrous oxide fluxes are the focus of this study, as these emissions are expected to increase significantly due to the nitrogen (N) fertilizer application in the plantations. This study was conducted in the SAFE (Stability of Altered Forest Ecosystems) landscape in Malaysian Borneo (Sabah) with measurements every 2 months over a 2-year period. GHG fluxes were measured by static chambers together with key soil physicochemical parameters and microbial biodiversity. At all sites, N2O fluxes were spatially and temporally highly variable. On average the largest fluxes (incl. 95 % CI) were measured from OP plantations (45.1 (24.0–78.5) µg m−2 h−1 N2O-N), slightly smaller fluxes from the riparian area (29.4 (2.8–84.7) µg m−2 h−1 N2O-N), and the smallest fluxes from logged forests (16.0 (4.0–36.3) µg m−2 h−1 N2O-N). Methane fluxes were generally small (mean ± SD): −2.6 ± 17.2 µg CH4-C m−2 h−1 for OP and 1.3 ± 12.6 µg CH4-C m−2 h−1 for riparian, with the range of measured CH4 fluxes being largest in logged forests (2.2 ± 48.3 µg CH4-C m−2 h−1). Soil respiration rates were larger from riparian areas (157.7 ± 106 mg m−2 h−1 CO2-C) and logged forests (137.4 ± 95 mg m−2 h−1 CO2-C) than OP plantations (93.3 ± 70 mg m−2 h−1 CO2-C) as a result of larger amounts of decomposing leaf litter. Microbial communities were distinctly different between the different land-use types and sites. Bacterial communities were linked to soil pH, and fungal and eukaryotic communities were linked to land use. Despite measuring a large number of environmental parameters, mixed models could only explain up to 17 % of the variance of measured fluxes for N2O, 3 % of CH4, and 25 % of soil respiration. Scaling up measured N2O fluxes to Sabah using land areas for forest and OP resulted in emissions increasing from 7.6 Mt (95 % confidence interval, −3.0–22.3 Mt) yr−1 in 1973 to 11.4 Mt (0.2–28.6 Mt) yr−1 in 2015 due to the increasing area of forest converted to OP plantations over the last ∼ 40 years.

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Long-Term Nitrogen Addition Decreases Soil Carbon Mineralization in an N-Rich Primary Tropical Forest

Forests ◽

10.3390/f12060734 ◽

2021 ◽

Vol 12 (6) ◽

pp. 734

Author(s):

Xiankai Lu ◽

Qinggong Mao ◽

Zhuohang Wang ◽

Taiki Mori ◽

Jiangming Mo ◽

...

Keyword(s):

Microbial Biomass ◽

Organic Carbon ◽

Tropical Forest ◽

Soil Carbon ◽

Tropical Forests ◽

Carbon Mineralization ◽

N Deposition ◽

Soil Carbon Mineralization ◽

N Additions

Anthropogenic elevated nitrogen (N) deposition has an accelerated terrestrial N cycle, shaping soil carbon dynamics and storage through altering soil organic carbon mineralization processes. However, it remains unclear how long-term high N deposition affects soil carbon mineralization in tropical forests. To address this question, we established a long-term N deposition experiment in an N-rich lowland tropical forest of Southern China with N additions such as NH4NO3 of 0 (Control), 50 (Low-N), 100 (Medium-N) and 150 (High-N) kg N ha−1 yr−1, and laboratory incubation experiment, used to explore the response of soil carbon mineralization to the N additions therein. The results showed that 15 years of N additions significantly decreased soil carbon mineralization rates. During the incubation period from the 14th day to 56th day, the average decreases in soil CO2 emission rates were 18%, 33% and 47% in the low-N, medium-N and high-N treatments, respectively, compared with the Control. These negative effects were primarily aroused by the reduced soil microbial biomass and modified microbial functions (e.g., a decrease in bacteria relative abundance), which could be attributed to N-addition-induced soil acidification and potential phosphorus limitation in this forest. We further found that N additions greatly increased soil-dissolved organic carbon (DOC), and there were significantly negative relationships between microbial biomass and soil DOC, indicating that microbial consumption on soil-soluble carbon pool may decrease. These results suggests that long-term N deposition can increase soil carbon stability and benefit carbon sequestration through decreased carbon mineralization in N-rich tropical forests. This study can help us understand how microbes control soil carbon cycling and carbon sink in the tropics under both elevated N deposition and carbon dioxide in the future.

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Greenhouse gas emissions from the water–air interface of a grassland river: a case study of the Xilin River

Scientific Reports ◽

10.1038/s41598-021-81658-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Xue Hao ◽

Yu Ruihong ◽

Zhang Zhuangzhuang ◽

Qi Zhen ◽

Lu Xixi ◽

...

Keyword(s):

Carbon Dioxide ◽

Land Use ◽

Nitrous Oxide ◽

Greenhouse Gas Emissions ◽

Greenhouse Gas ◽

Ghg Emissions ◽

Nitrous Oxide Emissions ◽

Gas Emissions ◽

Sand Land ◽

Very High

AbstractGreenhouse gas (GHG) emissions from rivers and lakes have been shown to significantly contribute to global carbon and nitrogen cycling. In spatiotemporal-variable and human-impacted rivers in the grassland region, simultaneous carbon dioxide, methane and nitrous oxide emissions and their relationships under the different land use types are poorly documented. This research estimated greenhouse gas (CO2, CH4, N2O) emissions in the Xilin River of Inner Mongolia of China using direct measurements from 18 field campaigns under seven land use type (such as swamp, sand land, grassland, pond, reservoir, lake, waste water) conducted in 2018. The results showed that CO2 emissions were higher in June and August, mainly affected by pH and DO. Emissions of CH4 and N2O were higher in October, which were influenced by TN and TP. According to global warming potential, CO2 emissions accounted for 63.35% of the three GHG emissions, and CH4 and N2O emissions accounted for 35.98% and 0.66% in the Xilin river, respectively. Under the influence of different degrees of human-impact, the amount of CO2 emissions in the sand land type was very high, however, CH4 emissions and N2O emissions were very high in the artificial pond and the wastewater, respectively. For natural river, the greenhouse gas emissions from the reservoir and sand land were both low. The Xilin river was observed to be a source of carbon dioxide and methane, and the lake was a sink for nitrous oxide.

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Effects of strategic tillage on short-term erosion, nutrient loss in runoff and greenhouse gas emissions

Soil Research ◽

10.1071/sr16136 ◽

2017 ◽

Vol 55 (3) ◽

pp. 201 ◽

Cited By ~ 16

Author(s):

A. R. Melland ◽

D. L. Antille ◽

Y. P. Dang

Keyword(s):

Nitrous Oxide ◽

Greenhouse Gas ◽

Heavy Rainfall ◽

Ghg Emissions ◽

Nutrient Loss ◽

Nitrous Oxide Emissions ◽

Nutrient Losses ◽

Short Term ◽

Trade Offs ◽

Carbon Dioxide Co2

Occasional strategic tillage (ST) of long-term no-tillage (NT) soil to help control weeds may increase the risk of water, erosion and nutrient losses in runoff and of greenhouse gas (GHG) emissions compared with NT soil. The present study examined the short-term effect of ST on runoff and GHG emissions in NT soils under controlled-traffic farming regimes. A rainfall simulator was used to generate runoff from heavy rainfall (70mmh–1) on small plots of NT and ST on a Vertosol, Dermosol and Sodosol. Nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes from the Vertosol and Sodosol were measured before and after the rain using passive chambers. On the Sodosol and Dermosol there was 30% and 70% more runoff, respectively, from ST plots than from NT plots, however, volumes were similar between tillage treatments on the Vertosol. Erosion was highest after ST on the Sodosol (8.3tha–1 suspended sediment) and there were no treatment differences on the other soils. Total nitrogen (N) loads in runoff followed a similar pattern, with 10.2kgha–1 in runoff from the ST treatment on the Sodosol. Total phosphorus loads were higher after ST than NT on both the Sodosol (3.1 and 0.9kgha–1, respectively) and the Dermosol (1.0 and 0.3kgha–1, respectively). Dissolved nutrient forms comprised less than 13% of total losses. Nitrous oxide emissions were low from both NT and ST in these low-input systems. However, ST decreased CH4 absorption from both soils and almost doubled CO2 emissions from the Sodosol. Strategic tillage may increase the susceptibility of Sodosols and Dermosols to water, sediment and nutrient losses in runoff after heavy rainfall. The trade-offs between weed control, erosion and GHG emissions should be considered as part of any tillage strategy.

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Long-term greenhouse gas emissions from hydroelectric reservoirs in tropical forest regions

Global Biogeochemical Cycles ◽

10.1029/1998gb900015 ◽

1999 ◽

Vol 13 (2) ◽

pp. 503-517 ◽

Cited By ~ 81

Author(s):

Corinne Galy-Lacaux ◽

Robert Delmas ◽

Georges Kouadio ◽

Sandrine Richard ◽

Philippe Gosse

Keyword(s):

Tropical Forest ◽

Greenhouse Gas Emissions ◽

Greenhouse Gas ◽

Gas Emissions ◽

Hydroelectric Reservoirs ◽

Forest Regions

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Effects of nitrogen and phosphorus additions on nitrous oxide emission in a nitrogen-rich and two nitrogen-limited tropical forests

Biogeosciences ◽

10.5194/bg-13-3503-2016 ◽

2016 ◽

Vol 13 (11) ◽

pp. 3503-3517 ◽

Cited By ~ 8

Author(s):

Mianhai Zheng ◽

Tao Zhang ◽

Lei Liu ◽

Weixing Zhu ◽

Wei Zhang ◽

...

Keyword(s):

Nitrous Oxide ◽

Tropical Forests ◽

N2o Emission ◽

N Deposition ◽

Soil N ◽

N Addition ◽

Old Growth ◽

Old Growth Forest ◽

P Addition ◽

Stimulation Of

Abstract. Nitrogen (N) deposition is generally considered to increase soil nitrous oxide (N2O) emission in N-rich forests. In many tropical forests, however, elevated N deposition has caused soil N enrichment and further phosphorus (P) deficiency, and the interaction of N and P to control soil N2O emission remains poorly understood, particularly in forests with different soil N status. In this study, we examined the effects of N and P additions on soil N2O emission in an N-rich old-growth forest and two N-limited younger forests (a mixed and a pine forest) in southern China to test the following hypotheses: (1) soil N2O emission is the highest in old-growth forest due to the N-rich soil; (2) N addition increases N2O emission more in the old-growth forest than in the two younger forests; (3) P addition decreases N2O emission more in the old-growth forest than in the two younger forests; and (4) P addition alleviates the stimulation of N2O emission by N addition. The following four treatments were established in each forest: Control, N addition (150 kg N ha−1 yr−1), P addition (150 kg P ha−1 yr−1), and NP addition (150 kg N ha−1 yr−1 plus 150 kg P ha−1 yr−1). From February 2007 to October 2009, monthly quantification of soil N2O emission was performed using static chamber and gas chromatography techniques. Mean N2O emission was shown to be significantly higher in the old-growth forest (13.9 ± 0.7 µg N2O-N m−2 h−1) than in the mixed (9.9 ± 0.4 µg N2O-N m−2 h−1) or pine (10.8 ± 0.5 µg N2O-N m−2 h−1) forests, with no significant difference between the latter two. N addition significantly increased N2O emission in the old-growth forest but not in the two younger forests. However, both P and NP addition had no significant effect on N2O emission in all three forests, suggesting that P addition alleviated the stimulation of N2O emission by N addition in the old-growth forest. Although P fertilization may alleviate the stimulated effects of atmospheric N deposition on N2O emission in N-rich forests, this effect may only occur under high N deposition and/or long-term P addition, and we suggest future investigations to definitively assess this management strategy and the importance of P in regulating N cycles from regional to global scales.

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Herbaceous monocot plant form and function along a tropical rain-forest light gradient: a reversal of dicot strategy

Journal of Tropical Ecology ◽

10.1017/s0266467408005567 ◽

2009 ◽

Vol 25 (1) ◽

pp. 103-106 ◽

Cited By ~ 4

Author(s):

Nathan G. Swenson

Keyword(s):

Tropical Forests ◽

Environmental Gradients ◽

Plant Performance ◽

Seed Plants ◽

Form And Function ◽

Light Gradient ◽

Whole Plant ◽

Plant Form ◽

And Function ◽

High Degree

Whole plant form and function vary spectacularly across the seed plants. In recent years, plant evolutionary ecologists have begun to document this diversity on large geographic scales by analysing ‘functional traits’ that are indicative of whole plant performance across environmental gradients (Swenson & Enquist 2007, Wright et al. 2004). Despite the high degree of functional diversity in tropical forests, convergence in function does occur locally along successional or light gradients (Bazzaz & Pickett 1980, Swaine & Whitmore 1988).

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Degradation and forgone removals increase the carbon impact of intact forest loss by 626%

Science Advances ◽

10.1126/sciadv.aax2546 ◽

2019 ◽

Vol 5 (10) ◽

pp. eaax2546 ◽

Cited By ~ 19

Author(s):

Sean L. Maxwell ◽

Tom Evans ◽

James E. M. Watson ◽

Alexandra Morel ◽

Hedley Grantham ◽

...

Keyword(s):

Tropical Forest ◽

Tropical Forests ◽

Selective Logging ◽

Carbon Accounting ◽

Carbon Equivalent ◽

Forest Loss ◽

Climate Mitigation ◽

International Climate Policy ◽

Global Land ◽

International Climate

Intact tropical forests, free from substantial anthropogenic influence, store and sequester large amounts of atmospheric carbon but are currently neglected in international climate policy. We show that between 2000 and 2013, direct clearance of intact tropical forest areas accounted for 3.2% of gross carbon emissions from all deforestation across the pantropics. However, full carbon accounting requires the consideration of forgone carbon sequestration, selective logging, edge effects, and defaunation. When these factors were considered, the net carbon impact resulting from intact tropical forest loss between 2000 and 2013 increased by a factor of 6 (626%), from 0.34 (0.37 to 0.21) to 2.12 (2.85 to 1.00) petagrams of carbon (equivalent to approximately 2 years of global land use change emissions). The climate mitigation value of conserving the 549 million ha of tropical forest that remains intact is therefore significant but will soon dwindle if their rate of loss continues to accelerate.

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