Complex controls on nitrous oxide flux across a large-elevation gradient in the tropical Peruvian Andes

Torsten Diem, Nicholas Jackson Morley, Adan Julian Ccahuana, Lidia Priscila Hauraca Quispe, Elizabeth Baggs, Patrick Meir, Mark Lee Andrew Richards, Peter Smith, Yit Arn Teh

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Abstract

Current bottom–up process models suggest that montane tropical ecosystems are weak atmospheric sources of N2O, although recent empirical studies from the southern Peruvian Andes have challenged this idea. Here we report N2O flux from combined field and laboratory experiments that investigated the process-based controls on N2O flux from montane ecosystems across a large-elevation gradient (600–3700 m a.s.l.) in the southern Peruvian Andes. Nitrous oxide flux and environmental variables were quantified in four major habitats (premontane forest, lower montane forest, upper montane forest and montane grassland) at monthly intervals over a 30-month period from January 2011 to June 2013. The role of soil moisture content in regulating N2O flux was investigated through a manipulative, laboratory-based 15N-tracer experiment. The role of substrate availability (labile organic matter, NO3−) in regulating N2O flux was examined through a field-based litter-fall manipulation experiment and a laboratory-based 15N–NO3− addition study, respectively. Ecosystems in this region were net atmospheric sources of N2O, with an unweighted mean flux of 0.27 ± 0.07 mg N–N2O m−2 d−1. Weighted extrapolations, which accounted for differences in land surface area among habitats and variations in flux between seasons, predicted a mean annual flux of 1.27 ± 0.33 kg N2O–N ha−1 yr−1. Nitrous oxide flux was greatest from premontane forest, with an unweighted mean flux of 0.75 ± 0.18 mg N–N2O m−2 d−1, translating to a weighted annual flux of 0.66 ± 0.16 kg N2O–N ha−1 yr−1. In contrast, N2O flux was significantly lower in other habitats. The unweighted mean fluxes for lower montane forest, montane grasslands, and upper montane forest were 0.46 ± 0.24 mg N–N2O m−2 d−1, 0.07 ± 0.08 mg N–N2O m−2 d−1, and 0.04 ± 0.07 mg N–N2O m−2 d−1, respectively. This corresponds to weighted annual fluxes of 0.52 ± 0.27 kg N2O–N ha−1 yr−1, 0.05 ± 0.06 kg N2O–N ha−1 yr−1, and 0.04 ± 0.07 kg N2O–N ha−1 yr−1, respectively. Nitrous oxide flux showed weak seasonal variation across the region; only lower montane forest showed significantly higher N2O flux during the dry season compared to wet season. Manipulation of soil moisture content in the laboratory indicated that N2O flux was significantly influenced by changes in water-filled pore space (WFPS). The relationship between N2O flux and WFPS was complex and non-linear, diverging from theoretical predictions of how WFPS relates to N2O flux. Nitrification made a negligible contribution to N2O flux, irrespective of soil moisture content, indicating that nitrate reduction was the dominant source of N2O. Analysis of the pooled data indicated that N2O flux was greatest at 90 and 50 % WFPS, and lowest at 70 and 30 % WFPS. This trend in N2O flux suggests a complex relationship between WFPS and nitrate-reducing processes (i.e. denitrification, dissimilatory nitrate reduction to ammonium). Changes in labile organic matter inputs, through the manipulation of leaf litter-fall, did not alter N2O flux. Comprehensive analysis of field and laboratory data demonstrated that variations in NO3− availability strongly constrained N2O flux. Habitat – a proxy for NO3− availability under field conditions – was the best predictor for N2O flux, with N-rich habitats (premontane forest, lower montane forest) showing significantly higher N2O flux than N-poor habitats (upper montane forest, montane grassland). Yet, N2O flux did not respond to short-term changes in NO3− concentration.
Original languageEnglish
Pages (from-to)5077-5097
Number of pages21
JournalBiogeosciences
Volume14
Issue number22
DOIs
Publication statusPublished - 15 Nov 2017

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montane forest
nitrous oxide
pore space
habitat
moisture content
soil moisture
grassland
litterfall
montane forests
nitrate
water
organic matter
ecosystem
leaf litter
wet season
nitrification
dry season
denitrification
land surface
soil water content

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Diem, T., Morley, N. J., Ccahuana, A. J., Hauraca Quispe, L. P., Baggs, E., Meir, P., ... Teh, Y. A. (2017). Complex controls on nitrous oxide flux across a large-elevation gradient in the tropical Peruvian Andes. Biogeosciences, 14(22), 5077-5097. https://doi.org/10.5194/bg-14-5077-2017

Complex controls on nitrous oxide flux across a large-elevation gradient in the tropical Peruvian Andes. / Diem, Torsten; Morley, Nicholas Jackson; Ccahuana, Adan Julian; Hauraca Quispe, Lidia Priscila; Baggs, Elizabeth; Meir, Patrick; Richards, Mark Lee Andrew; Smith, Peter; Teh, Yit Arn.

In: Biogeosciences, Vol. 14, No. 22, 15.11.2017, p. 5077-5097.

Research output: Contribution to journalArticle

Diem, T, Morley, NJ, Ccahuana, AJ, Hauraca Quispe, LP, Baggs, E, Meir, P, Richards, MLA, Smith, P & Teh, YA 2017, 'Complex controls on nitrous oxide flux across a large-elevation gradient in the tropical Peruvian Andes' Biogeosciences, vol. 14, no. 22, pp. 5077-5097. https://doi.org/10.5194/bg-14-5077-2017
Diem T, Morley NJ, Ccahuana AJ, Hauraca Quispe LP, Baggs E, Meir P et al. Complex controls on nitrous oxide flux across a large-elevation gradient in the tropical Peruvian Andes. Biogeosciences. 2017 Nov 15;14(22):5077-5097. https://doi.org/10.5194/bg-14-5077-2017
Diem, Torsten ; Morley, Nicholas Jackson ; Ccahuana, Adan Julian ; Hauraca Quispe, Lidia Priscila ; Baggs, Elizabeth ; Meir, Patrick ; Richards, Mark Lee Andrew ; Smith, Peter ; Teh, Yit Arn. / Complex controls on nitrous oxide flux across a large-elevation gradient in the tropical Peruvian Andes. In: Biogeosciences. 2017 ; Vol. 14, No. 22. pp. 5077-5097.
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title = "Complex controls on nitrous oxide flux across a large-elevation gradient in the tropical Peruvian Andes",
abstract = "Current bottom–up process models suggest that montane tropical ecosystems are weak atmospheric sources of N2O, although recent empirical studies from the southern Peruvian Andes have challenged this idea. Here we report N2O flux from combined field and laboratory experiments that investigated the process-based controls on N2O flux from montane ecosystems across a large-elevation gradient (600–3700 m a.s.l.) in the southern Peruvian Andes. Nitrous oxide flux and environmental variables were quantified in four major habitats (premontane forest, lower montane forest, upper montane forest and montane grassland) at monthly intervals over a 30-month period from January 2011 to June 2013. The role of soil moisture content in regulating N2O flux was investigated through a manipulative, laboratory-based 15N-tracer experiment. The role of substrate availability (labile organic matter, NO3−) in regulating N2O flux was examined through a field-based litter-fall manipulation experiment and a laboratory-based 15N–NO3− addition study, respectively. Ecosystems in this region were net atmospheric sources of N2O, with an unweighted mean flux of 0.27 ± 0.07 mg N–N2O m−2 d−1. Weighted extrapolations, which accounted for differences in land surface area among habitats and variations in flux between seasons, predicted a mean annual flux of 1.27 ± 0.33 kg N2O–N ha−1 yr−1. Nitrous oxide flux was greatest from premontane forest, with an unweighted mean flux of 0.75 ± 0.18 mg N–N2O m−2 d−1, translating to a weighted annual flux of 0.66 ± 0.16 kg N2O–N ha−1 yr−1. In contrast, N2O flux was significantly lower in other habitats. The unweighted mean fluxes for lower montane forest, montane grasslands, and upper montane forest were 0.46 ± 0.24 mg N–N2O m−2 d−1, 0.07 ± 0.08 mg N–N2O m−2 d−1, and 0.04 ± 0.07 mg N–N2O m−2 d−1, respectively. This corresponds to weighted annual fluxes of 0.52 ± 0.27 kg N2O–N ha−1 yr−1, 0.05 ± 0.06 kg N2O–N ha−1 yr−1, and 0.04 ± 0.07 kg N2O–N ha−1 yr−1, respectively. Nitrous oxide flux showed weak seasonal variation across the region; only lower montane forest showed significantly higher N2O flux during the dry season compared to wet season. Manipulation of soil moisture content in the laboratory indicated that N2O flux was significantly influenced by changes in water-filled pore space (WFPS). The relationship between N2O flux and WFPS was complex and non-linear, diverging from theoretical predictions of how WFPS relates to N2O flux. Nitrification made a negligible contribution to N2O flux, irrespective of soil moisture content, indicating that nitrate reduction was the dominant source of N2O. Analysis of the pooled data indicated that N2O flux was greatest at 90 and 50 {\%} WFPS, and lowest at 70 and 30 {\%} WFPS. This trend in N2O flux suggests a complex relationship between WFPS and nitrate-reducing processes (i.e. denitrification, dissimilatory nitrate reduction to ammonium). Changes in labile organic matter inputs, through the manipulation of leaf litter-fall, did not alter N2O flux. Comprehensive analysis of field and laboratory data demonstrated that variations in NO3− availability strongly constrained N2O flux. Habitat – a proxy for NO3− availability under field conditions – was the best predictor for N2O flux, with N-rich habitats (premontane forest, lower montane forest) showing significantly higher N2O flux than N-poor habitats (upper montane forest, montane grassland). Yet, N2O flux did not respond to short-term changes in NO3− concentration.",
author = "Torsten Diem and Morley, {Nicholas Jackson} and Ccahuana, {Adan Julian} and {Hauraca Quispe}, {Lidia Priscila} and Elizabeth Baggs and Patrick Meir and Richards, {Mark Lee Andrew} and Peter Smith and Teh, {Yit Arn}",
note = "Acknowledgements The authors would like to acknowledge the agencies that funded this research; the UK Natural Environment Research Council (NERC; joint grant references NE/H006583, NE/H007849 and NE/H006753). Patrick Meir was supported by an Australian Research Council Fellowship (FT110100457). Javie Eduardo Silva Espejo, Walter Huaraca Huasco and the ABIDA NGO provided critical fieldwork and logistical support. Angus Calder (University of St.Andrews) and Vicky Munro (University of Aberdeen) provided invaluable laboratory support. Thanks to Adrian Tejedor from the Amazon Conservation Association, who provided assistance with site access and site selection at Hacienda Villa Carmen. This publication is a contribution from the Scottish Alliance for Geoscience, Environment and Society (http://www.sages.ac.uk).",
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language = "English",
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pages = "5077--5097",
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TY - JOUR

T1 - Complex controls on nitrous oxide flux across a large-elevation gradient in the tropical Peruvian Andes

AU - Diem, Torsten

AU - Morley, Nicholas Jackson

AU - Ccahuana, Adan Julian

AU - Hauraca Quispe, Lidia Priscila

AU - Baggs, Elizabeth

AU - Meir, Patrick

AU - Richards, Mark Lee Andrew

AU - Smith, Peter

AU - Teh, Yit Arn

N1 - Acknowledgements The authors would like to acknowledge the agencies that funded this research; the UK Natural Environment Research Council (NERC; joint grant references NE/H006583, NE/H007849 and NE/H006753). Patrick Meir was supported by an Australian Research Council Fellowship (FT110100457). Javie Eduardo Silva Espejo, Walter Huaraca Huasco and the ABIDA NGO provided critical fieldwork and logistical support. Angus Calder (University of St.Andrews) and Vicky Munro (University of Aberdeen) provided invaluable laboratory support. Thanks to Adrian Tejedor from the Amazon Conservation Association, who provided assistance with site access and site selection at Hacienda Villa Carmen. This publication is a contribution from the Scottish Alliance for Geoscience, Environment and Society (http://www.sages.ac.uk).

PY - 2017/11/15

Y1 - 2017/11/15

N2 - Current bottom–up process models suggest that montane tropical ecosystems are weak atmospheric sources of N2O, although recent empirical studies from the southern Peruvian Andes have challenged this idea. Here we report N2O flux from combined field and laboratory experiments that investigated the process-based controls on N2O flux from montane ecosystems across a large-elevation gradient (600–3700 m a.s.l.) in the southern Peruvian Andes. Nitrous oxide flux and environmental variables were quantified in four major habitats (premontane forest, lower montane forest, upper montane forest and montane grassland) at monthly intervals over a 30-month period from January 2011 to June 2013. The role of soil moisture content in regulating N2O flux was investigated through a manipulative, laboratory-based 15N-tracer experiment. The role of substrate availability (labile organic matter, NO3−) in regulating N2O flux was examined through a field-based litter-fall manipulation experiment and a laboratory-based 15N–NO3− addition study, respectively. Ecosystems in this region were net atmospheric sources of N2O, with an unweighted mean flux of 0.27 ± 0.07 mg N–N2O m−2 d−1. Weighted extrapolations, which accounted for differences in land surface area among habitats and variations in flux between seasons, predicted a mean annual flux of 1.27 ± 0.33 kg N2O–N ha−1 yr−1. Nitrous oxide flux was greatest from premontane forest, with an unweighted mean flux of 0.75 ± 0.18 mg N–N2O m−2 d−1, translating to a weighted annual flux of 0.66 ± 0.16 kg N2O–N ha−1 yr−1. In contrast, N2O flux was significantly lower in other habitats. The unweighted mean fluxes for lower montane forest, montane grasslands, and upper montane forest were 0.46 ± 0.24 mg N–N2O m−2 d−1, 0.07 ± 0.08 mg N–N2O m−2 d−1, and 0.04 ± 0.07 mg N–N2O m−2 d−1, respectively. This corresponds to weighted annual fluxes of 0.52 ± 0.27 kg N2O–N ha−1 yr−1, 0.05 ± 0.06 kg N2O–N ha−1 yr−1, and 0.04 ± 0.07 kg N2O–N ha−1 yr−1, respectively. Nitrous oxide flux showed weak seasonal variation across the region; only lower montane forest showed significantly higher N2O flux during the dry season compared to wet season. Manipulation of soil moisture content in the laboratory indicated that N2O flux was significantly influenced by changes in water-filled pore space (WFPS). The relationship between N2O flux and WFPS was complex and non-linear, diverging from theoretical predictions of how WFPS relates to N2O flux. Nitrification made a negligible contribution to N2O flux, irrespective of soil moisture content, indicating that nitrate reduction was the dominant source of N2O. Analysis of the pooled data indicated that N2O flux was greatest at 90 and 50 % WFPS, and lowest at 70 and 30 % WFPS. This trend in N2O flux suggests a complex relationship between WFPS and nitrate-reducing processes (i.e. denitrification, dissimilatory nitrate reduction to ammonium). Changes in labile organic matter inputs, through the manipulation of leaf litter-fall, did not alter N2O flux. Comprehensive analysis of field and laboratory data demonstrated that variations in NO3− availability strongly constrained N2O flux. Habitat – a proxy for NO3− availability under field conditions – was the best predictor for N2O flux, with N-rich habitats (premontane forest, lower montane forest) showing significantly higher N2O flux than N-poor habitats (upper montane forest, montane grassland). Yet, N2O flux did not respond to short-term changes in NO3− concentration.

AB - Current bottom–up process models suggest that montane tropical ecosystems are weak atmospheric sources of N2O, although recent empirical studies from the southern Peruvian Andes have challenged this idea. Here we report N2O flux from combined field and laboratory experiments that investigated the process-based controls on N2O flux from montane ecosystems across a large-elevation gradient (600–3700 m a.s.l.) in the southern Peruvian Andes. Nitrous oxide flux and environmental variables were quantified in four major habitats (premontane forest, lower montane forest, upper montane forest and montane grassland) at monthly intervals over a 30-month period from January 2011 to June 2013. The role of soil moisture content in regulating N2O flux was investigated through a manipulative, laboratory-based 15N-tracer experiment. The role of substrate availability (labile organic matter, NO3−) in regulating N2O flux was examined through a field-based litter-fall manipulation experiment and a laboratory-based 15N–NO3− addition study, respectively. Ecosystems in this region were net atmospheric sources of N2O, with an unweighted mean flux of 0.27 ± 0.07 mg N–N2O m−2 d−1. Weighted extrapolations, which accounted for differences in land surface area among habitats and variations in flux between seasons, predicted a mean annual flux of 1.27 ± 0.33 kg N2O–N ha−1 yr−1. Nitrous oxide flux was greatest from premontane forest, with an unweighted mean flux of 0.75 ± 0.18 mg N–N2O m−2 d−1, translating to a weighted annual flux of 0.66 ± 0.16 kg N2O–N ha−1 yr−1. In contrast, N2O flux was significantly lower in other habitats. The unweighted mean fluxes for lower montane forest, montane grasslands, and upper montane forest were 0.46 ± 0.24 mg N–N2O m−2 d−1, 0.07 ± 0.08 mg N–N2O m−2 d−1, and 0.04 ± 0.07 mg N–N2O m−2 d−1, respectively. This corresponds to weighted annual fluxes of 0.52 ± 0.27 kg N2O–N ha−1 yr−1, 0.05 ± 0.06 kg N2O–N ha−1 yr−1, and 0.04 ± 0.07 kg N2O–N ha−1 yr−1, respectively. Nitrous oxide flux showed weak seasonal variation across the region; only lower montane forest showed significantly higher N2O flux during the dry season compared to wet season. Manipulation of soil moisture content in the laboratory indicated that N2O flux was significantly influenced by changes in water-filled pore space (WFPS). The relationship between N2O flux and WFPS was complex and non-linear, diverging from theoretical predictions of how WFPS relates to N2O flux. Nitrification made a negligible contribution to N2O flux, irrespective of soil moisture content, indicating that nitrate reduction was the dominant source of N2O. Analysis of the pooled data indicated that N2O flux was greatest at 90 and 50 % WFPS, and lowest at 70 and 30 % WFPS. This trend in N2O flux suggests a complex relationship between WFPS and nitrate-reducing processes (i.e. denitrification, dissimilatory nitrate reduction to ammonium). Changes in labile organic matter inputs, through the manipulation of leaf litter-fall, did not alter N2O flux. Comprehensive analysis of field and laboratory data demonstrated that variations in NO3− availability strongly constrained N2O flux. Habitat – a proxy for NO3− availability under field conditions – was the best predictor for N2O flux, with N-rich habitats (premontane forest, lower montane forest) showing significantly higher N2O flux than N-poor habitats (upper montane forest, montane grassland). Yet, N2O flux did not respond to short-term changes in NO3− concentration.

U2 - 10.5194/bg-14-5077-2017

DO - 10.5194/bg-14-5077-2017

M3 - Article

VL - 14

SP - 5077

EP - 5097

JO - Biogeosciences

JF - Biogeosciences

SN - 1726-4170

IS - 22

ER -