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Comunidades metanogênicas e metanotróficas em sedimentos de áreas alagáveis da Amazônia Oriental / Methanogens and methanotrophs communities in sediments of Eastern Amazonian wetlandsGontijo, Júlia Brandão 12 July 2017 (has links)
As áreas alagáveis naturais representam a mais importante fonte não-antropogênica de metano (CH4), com emissões estimadas entre 177 a 284 Tg ano-1, representando de 26 a 42% das emissões globais de CH4. A bacia do Rio Amazonas cobre uma grande porção dos trópicos úmidos, e a rede de drenagem deste rio excede a extensão de mais de um milhão de quilômetros quadrados. As grandes várzeas da bacia Amazônica são as maiores fontes naturais de CH4 desta região e estima-se que sua contribuição para as emissões totais de áreas alagadas no mundo seja na ordem de 5%. O CH4 produzido nas zonas anaeróbicas dos sedimentos por arquéias metanogênicas pode ser oxidado a CO2 pelos microrganismos metanotróficos. Com base na hipótese de que o fluxo de CH4 se altera sazonalmente em áreas alagáveis e que a microbiota presente está diretamente relacionada a esse processo, o presente estudo teve como objetivo geral avaliar a dinâmica dos genes funcionais envolvidos no ciclo do CH4 em épocas contrastantes, correlacionando com o fluxo do gás, variáveis ambientais e perfil taxonômico de Bacteria e Archaea em sedimentos de três áreas alagáveis e solo de floresta primária, da Amazônia Oriental (Belterra e Santarém-PA). Foram realizadas amostragem de gases, sedimentos e solo em duas épocas contrastantes (maio e outubro de 2016 - cheia e seca), para determinação da concentração de CH4 retido no sedimento durante a época cheia, cálculo do fluxo de CH4 durante a época seca, análises físico-químicas e extração de DNA dos sedimentos e solo para realização da qPCR dos genes funcionais mcrA e pmoA e dos genes marcadores filogenéticos 16S rRNA de Bacteria e Archaea, e sequenciamento do gene 16S rRNA de Bacteria e Archaea. A partir das amostragens de gases, foi possível observar que as áreas alagáveis possuem potencial de atuarem como fonte de CH4 durante a época cheia, e como fonte ou dreno de metano durante a época seca, confirmado pelas análises de qPCR, uma vez que a abundância do gene pmoA aumenta durante a época seca. Já no solo de floresta, o gene mcrA foi considerado como não detectado, portanto, a floresta pode ser considerada somente como potencial dreno de CH4. O estimador ACE e o índice Shannon mostraram que os sedimentos de áreas alagáveis possuem maior riqueza e diversidade de Bacteria e Archaea quando comparados ao solo de floresta. Todas as áreas apresentaram perfis taxonômicos do domínio Bacteria semelhantes, porém, a grande diferença entre as comunidades está relacionada ao domínio Archaea. A comunidade de arqueias no solo de floresta é majoritariamente composta por representantes do filo Thaumarchaeota. O solo de floresta apresentou baixa abundância dos filos potencialmente produtores de CH4, Bathyarchaeota e Euryarchaeota, e o contrário foi observado nas áreas alagáveis. Os dados gerados no presente estudo incentivam a continuidade de trabalhos relacionados ao ciclo do CH4 em áreas alagáveis da bacia Amazônica, incluindo investigações acerca do papel do filo Bathyarchaeota nessas áreas, principalmente em relação ao ciclo do CH4 / Natural wetlands represent the most important non-anthropogenic source of methane (CH4), with emissions estimated of 177-284 Tg year-1, accounting for 26-42% of global CH4 emissions. The Amazon basin covers a large portion of the humid tropics, and the drainage network of this river exceeds the extent of more than one million square kilometers. The wetlands of the Amazon basin are the largest natural sources of CH4 in this region and it is estimated that their contribution to the total emissions of wetlands in the world is around 5%. The CH4 produced in the anaerobic zones of the sediments by methanogenic archaea can be oxidized to CO2 by the methanotrophic microorganisms. Based on the hypothesis that methane flux changes seasonally in wetlands and its microbiota is directly related to this process, this research has the main objective to evaluate the dynamics of the functional genes involved in the CH4 cycle in contrasting seasons, correlating with the CH4 flux, environmental variables and taxonomic profile of Bacteria and Archaea in three wetlands and one primary forest of the Eastern Amazon (Belterra and Santarém-PA). The sampling of gas, sediments and soil was performed in May and October 2016 (wet and dry seasons) to determine the concentration of CH4 retained in the sediment in the wet season, measurement of CH4 flux in the dry season, physicochemical properties and molecular analysis (qPCR of the mcrA, pmoA functional genes and phylogenetic marker genes 16S rRNA of Bacteria and Archaea and sequencing of the 16S rRNA gene of Bacteria and Archaea). From gas samplings, it was possible to observe that wetlands have the potential to act as source of CH4 during the wet season, and as a source or drain of CH4 during the dry season, confirmed by qPCR analyzes, due the abundance increases of the pmoA gene during the dry season. In the forest soil, the mcrA gene was not detected, therefore, the forest could be considered only as CH4 drain potential. The ACE estimator and the Shannon index showed that the sediments of wetlands have higher richness and diversity of Bacteria and Archaea when compared to the forest soil. All areas presented similar taxonomic profiles of Bacteria, however, the main difference between the communities is related to the Archaea. The archaeal community in the forest soil is mostly composed of representatives of the phylum Thaumarchaeota. The forest soil presented low abundance of the phyla with potential CH4 producers, Bathyarchaeota and Euryarchaeota, however the opposite was observed in the wetlands. The data generated in the present study encourage the continuity of work related to the CH4 cycle in wetlands of the Amazon basin, including investigations about the role of the Bathyarchaeota phylum in these areas, especially in relation to the CH4 cycle
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Comunidades metanogênicas e metanotróficas em sedimentos de áreas alagáveis da Amazônia Oriental / Methanogens and methanotrophs communities in sediments of Eastern Amazonian wetlandsJúlia Brandão Gontijo 12 July 2017 (has links)
As áreas alagáveis naturais representam a mais importante fonte não-antropogênica de metano (CH4), com emissões estimadas entre 177 a 284 Tg ano-1, representando de 26 a 42% das emissões globais de CH4. A bacia do Rio Amazonas cobre uma grande porção dos trópicos úmidos, e a rede de drenagem deste rio excede a extensão de mais de um milhão de quilômetros quadrados. As grandes várzeas da bacia Amazônica são as maiores fontes naturais de CH4 desta região e estima-se que sua contribuição para as emissões totais de áreas alagadas no mundo seja na ordem de 5%. O CH4 produzido nas zonas anaeróbicas dos sedimentos por arquéias metanogênicas pode ser oxidado a CO2 pelos microrganismos metanotróficos. Com base na hipótese de que o fluxo de CH4 se altera sazonalmente em áreas alagáveis e que a microbiota presente está diretamente relacionada a esse processo, o presente estudo teve como objetivo geral avaliar a dinâmica dos genes funcionais envolvidos no ciclo do CH4 em épocas contrastantes, correlacionando com o fluxo do gás, variáveis ambientais e perfil taxonômico de Bacteria e Archaea em sedimentos de três áreas alagáveis e solo de floresta primária, da Amazônia Oriental (Belterra e Santarém-PA). Foram realizadas amostragem de gases, sedimentos e solo em duas épocas contrastantes (maio e outubro de 2016 - cheia e seca), para determinação da concentração de CH4 retido no sedimento durante a época cheia, cálculo do fluxo de CH4 durante a época seca, análises físico-químicas e extração de DNA dos sedimentos e solo para realização da qPCR dos genes funcionais mcrA e pmoA e dos genes marcadores filogenéticos 16S rRNA de Bacteria e Archaea, e sequenciamento do gene 16S rRNA de Bacteria e Archaea. A partir das amostragens de gases, foi possível observar que as áreas alagáveis possuem potencial de atuarem como fonte de CH4 durante a época cheia, e como fonte ou dreno de metano durante a época seca, confirmado pelas análises de qPCR, uma vez que a abundância do gene pmoA aumenta durante a época seca. Já no solo de floresta, o gene mcrA foi considerado como não detectado, portanto, a floresta pode ser considerada somente como potencial dreno de CH4. O estimador ACE e o índice Shannon mostraram que os sedimentos de áreas alagáveis possuem maior riqueza e diversidade de Bacteria e Archaea quando comparados ao solo de floresta. Todas as áreas apresentaram perfis taxonômicos do domínio Bacteria semelhantes, porém, a grande diferença entre as comunidades está relacionada ao domínio Archaea. A comunidade de arqueias no solo de floresta é majoritariamente composta por representantes do filo Thaumarchaeota. O solo de floresta apresentou baixa abundância dos filos potencialmente produtores de CH4, Bathyarchaeota e Euryarchaeota, e o contrário foi observado nas áreas alagáveis. Os dados gerados no presente estudo incentivam a continuidade de trabalhos relacionados ao ciclo do CH4 em áreas alagáveis da bacia Amazônica, incluindo investigações acerca do papel do filo Bathyarchaeota nessas áreas, principalmente em relação ao ciclo do CH4 / Natural wetlands represent the most important non-anthropogenic source of methane (CH4), with emissions estimated of 177-284 Tg year-1, accounting for 26-42% of global CH4 emissions. The Amazon basin covers a large portion of the humid tropics, and the drainage network of this river exceeds the extent of more than one million square kilometers. The wetlands of the Amazon basin are the largest natural sources of CH4 in this region and it is estimated that their contribution to the total emissions of wetlands in the world is around 5%. The CH4 produced in the anaerobic zones of the sediments by methanogenic archaea can be oxidized to CO2 by the methanotrophic microorganisms. Based on the hypothesis that methane flux changes seasonally in wetlands and its microbiota is directly related to this process, this research has the main objective to evaluate the dynamics of the functional genes involved in the CH4 cycle in contrasting seasons, correlating with the CH4 flux, environmental variables and taxonomic profile of Bacteria and Archaea in three wetlands and one primary forest of the Eastern Amazon (Belterra and Santarém-PA). The sampling of gas, sediments and soil was performed in May and October 2016 (wet and dry seasons) to determine the concentration of CH4 retained in the sediment in the wet season, measurement of CH4 flux in the dry season, physicochemical properties and molecular analysis (qPCR of the mcrA, pmoA functional genes and phylogenetic marker genes 16S rRNA of Bacteria and Archaea and sequencing of the 16S rRNA gene of Bacteria and Archaea). From gas samplings, it was possible to observe that wetlands have the potential to act as source of CH4 during the wet season, and as a source or drain of CH4 during the dry season, confirmed by qPCR analyzes, due the abundance increases of the pmoA gene during the dry season. In the forest soil, the mcrA gene was not detected, therefore, the forest could be considered only as CH4 drain potential. The ACE estimator and the Shannon index showed that the sediments of wetlands have higher richness and diversity of Bacteria and Archaea when compared to the forest soil. All areas presented similar taxonomic profiles of Bacteria, however, the main difference between the communities is related to the Archaea. The archaeal community in the forest soil is mostly composed of representatives of the phylum Thaumarchaeota. The forest soil presented low abundance of the phyla with potential CH4 producers, Bathyarchaeota and Euryarchaeota, however the opposite was observed in the wetlands. The data generated in the present study encourage the continuity of work related to the CH4 cycle in wetlands of the Amazon basin, including investigations about the role of the Bathyarchaeota phylum in these areas, especially in relation to the CH4 cycle
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Microbial perspectives of the methane cycle in permafrost ecosystems in the Eastern Siberian Arctic : implications for the global methane budgetWagner, Dirk January 2007 (has links)
The Arctic plays a key role in Earth’s climate system as global warming is predicted to be most pronounced at high latitudes and because one third of the global carbon pool is stored in ecosystems of the northern latitudes. In order to improve our understanding of the present and future carbon dynamics in climate sensitive permafrost ecosystems, the present study concentrates on investigations of microbial controls of methane fluxes, on the activity and structure of the involved microbial communities, and on their response to changing environmental conditions. For this purpose an integrated research strategy was applied, which connects trace gas flux measurements to soil ecological characterisation of permafrost habitats and molecular ecological analyses of microbial populations. Furthermore, methanogenic archaea isolated from Siberian permafrost have been used as potential keystone organisms for studying and assessing life under extreme living conditions.
Long-term studies on methane fluxes were carried out since 1998. These studies revealed considerable seasonal and spatial variations of methane emissions for the different landscape units ranging from 0 to 362 mg m-2 d-1. For the overall balance of methane emissions from the entire delta, the first land cover classification based on Landsat images was performed and applied for an upscaling of the methane flux data sets. The regionally weighted mean daily methane emissions of the Lena Delta (10 mg m-2 d-1) are only one fifth of the values calculated for other Arctic tundra environments. The calculated annual methane emission of the Lena Delta amounts to about 0.03 Tg. The low methane emission rates obtained in this study are the result of the used remotely sensed high-resolution data basis, which provides a more realistic estimation of the real methane emissions on a regional scale. Soil temperature and near soil surface atmospheric turbulence were identified as the driving parameters of methane emissions. A flux model based on these variables explained variations of the methane budget corresponding to continuous processes of microbial methane production and oxidation, and gas diffusion through soil and plants reasonably well. The results show that the Lena Delta contributes significantly to the global methane balance because of its extensive wetland areas.
The microbiological investigations showed that permafrost soils are colonized by high numbers of microorganisms. The total biomass is comparable to temperate soil ecosystems. Activities of methanogens and methanotrophs differed significantly in their rates and distribution patterns along both the vertical profiles and the different investigated soils. The methane production rates varied between 0.3 and 38.9 nmol h-1 g-1, while the methane oxidation ranged from 0.2 to 7.0 nmol h-1 g-1. Phylogenetic analyses of methanogenic communities revealed a distinct diversity of methanogens affiliated to Methanomicrobiaceae, Methanosarcinaceae and Methanosaetaceae, which partly form four specific permafrost clusters.
The results demonstrate the close relationship between methane fluxes and the fundamental microbiological processes in permafrost soils. The microorganisms do not only survive in their extreme habitat but also can be metabolic active under in situ conditions. It was shown that a slight increase of the temperature can lead to a substantial increase in methanogenic activity within perennially frozen deposits. In case of degradation, this would lead to an extensive expansion of the methane deposits with their subsequent impacts on total methane budget.
Further studies on the stress response of methanogenic archaea, especially Methanosarcina SMA-21, isolated from Siberian permafrost, revealed an unexpected resistance of the microorganisms against unfavourable living conditions. A better adaptation to environmental stress was observed at 4 °C compared to 28 °C. For the first time it could be demonstrated that methanogenic archaea from terrestrial permafrost even survived simulated Martian conditions. The results show that permafrost methanogens are more resistant than methanogens from non-permafrost environments under Mars-like climate conditions. Microorganisms comparable to methanogens from terrestrial permafrost can be seen as one of the most likely candidates for life on Mars due to their physiological potential and metabolic specificity. / Die Arktis spielt eine Schlüsselrolle im Klimasystem unserer Erde aus zweierlei Gründen. Zum einen wird vorausgesagt, dass die globale Erwärmung in den hohen Breiten am ausgeprägtesten sein wird. Zum anderen ist ein Drittel des globalen Kohlenstoffs in Ökosystemen der nördlichen Breiten gespeichert. Um ein besseres Verständnis der gegenwärtigen und zukünftigen Entwicklung der Kohlenstoffdynamik in klimaempfindlichen Permafrostökosystemen zu erlangen, konzentriert sich die vorliegende Arbeit auf Untersuchungen zur Kontrolle der Methanflüsse durch Mikroorganismen, auf die Aktivität und Struktur der beteiligten Mikroorganismen-gemeinschaften und auf ihre Reaktion auf sich ändernde Umweltbedingungen. Zu diesem Zweck wurde eine integrierte Forschungsstrategie entwickelt, die Spurengasmessungen mit boden- und molekularökologischen Untersuchungen der Mikroorganismengemeinschaften verknüpft.
Langzeitmessungen zu den Methanflüssen werden seit 1998 durchgeführt. Diese Untersuchungen zeigten beträchtliche saisonale und räumliche Schwankungen der Methanemissionen auf, die zwischen 0 und 362 mg m-2 d-1 für die untersuchten Landschaftseinheiten schwankten. Für die Bilanzierung der Methanemissionen für das gesamte Delta wurde erstmals eine Klassifikation der unterschiedlichen Landschaftseinheiten anhand von Landsat-Aufnahmen durchgeführt und für eine Hochrechnung der Methandaten genutzt. Die Mittelwerte der regional gewichteten täglichen Methanemissionen des Lenadeltas (10 mg m-2 d-1) sind nur ein Fünftel so hoch wie die berechneten Werte für andere arktische Tundren. Die errechnete jährliche Methanemission des Lenadeltas beträgt demnach ungefähr 0,03 Tg. Die geringen Methanemissionsraten dieser Studie können durch den bisher noch nicht realisierten integrativen Ansatz, der Langzeitmessungen und Landschafts-klassifizierungen beinhaltet, erklärt werden. Bodentemperatur und oberflächennahe atmosphärische Turbulenzen wurden als die antreibenden Größen der Methanfreisetzung identifiziert. Ein Modell, das auf diesen Variablen basiert, erklärt die Veränderungen der Methanflüsse gemäß der dynamischen mikrobiellen Prozesse und der Diffusion von Methan durch den Boden und die Pflanzen zutreffend. Die Ergebnisse zeigen, dass das Lenadelta erheblich zur globalen Methanemission aufgrund seiner weitreichenden Feuchtgebiete beiträgt.
Die mikrobiologischen Untersuchungen zeigten, dass Permafrostböden durch eine hohe Anzahl von Mikroorganismen besiedelt wird. Die Gesamtbiomasse ist dabei mit Bodenökosystemen gemäßigter Klimate vergleichbar. Die Stoffwechselaktivitäten von methanogenen Archaeen und methanotrophen Bakterien unterschieden sich erheblich in ihrer Rate und Verteilung im Tiefenprofil sowie zwischen den verschiedenen untersuchten Böden. Die Methanbildungsrate schwankte dabei zwischen 0,3 und 38,9 nmol h-1 g-1, während die Methanoxidation eine Rate von 0,2 bis 7,0 nmol h-1 g-1 aufwies. Phylogenetische Analysen der methanogenen Mikro-organismengemeinschaften zeigten eine ausgeprägte Diversität der methanogenen Archaeen auf. Die Umweltsequenzen bildeten vier spezifische Permafrostcluster aus, die den Gruppen Methanomicrobiaceae, Methanosarcinaceae und Methano-saetaceae zugeordnet werden konnten.
Die Ergebnisse zeigen, dass die Methanfreisetzung durch die zugrunde liegenden mikrobiologischen Prozesse im Permafrostboden gesteuert wird. Die beteiligten Mikroorganismen überleben nicht nur in ihrem extremen Habitat, sondern zeigten auch Stoffwechselaktivität unter in-situ-Bedingungen. Ferner konnte gezeigt werden, dass eine geringfügige Zunahme der Temperatur zu einer erheblichen Zunahme der Methanbildungsaktivität in den ständig gefrorenen Permafrostablagerungen führen kann. Im Falle der Permafrostdegradation würde dieses zu einer gesteigerten Freisetzung von Methan führen mit bisher unbekannten Auswirkungen auf das Gesamtbudget der Methanfreistzung aus arktischen Gebieten.
Weitere Untersuchungen zur Stresstoleranz von methanogenen Archaeen – insbesondere des neuen Permafrostisolates Methanosarcina SMA-21 - weisen eine unerwartete Widerstandsfähigkeit der Mikroorganismen gegenüber ungünstigen Lebensbedingungen auf. Eine bessere Anpassung an Umweltstress wurde bei 4°C im Vergleich zu 28°C beobachtet. Zum ersten Mal konnte gezeigt werden, dass methanogene Archaeen aus terrestrischem Permafrost unter simulierten Marsbedingungen unbeschadet überleben. Die Ergebnisse zeigen, dass methanogene Archaeen aus Permafrostböden resistenter gegenüber Umweltstress und Marsbedingungen sind als entsprechende Mikroorganismen aus Habitaten, die nicht durch Permafrost gekennzeichnet sind. Mikroorganismen, die den Archaeen aus terrestrischen Permafrosthabitaten ähneln, können als die wahrscheinlichsten Kandidaten für mögliches Leben auf dem Mars angesehen werden.
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QUANTIFYING CARBON FLUXES AND ISOTOPIC SIGNATURE CHANGES ACROSS GLOBAL TERRESTRIAL ECOSYSTEMSYoumi Oh (9179345) 29 July 2020 (has links)
<p>This thesis is a collection of three research
articles to quantify carbon fluxes and isotopic signature changes across global
terrestrial ecosystems. Chapter 2, the first article of this thesis, focuses on
the importance of an under-estimated methane soil sink for contemporary and
future methane budgets in the pan-Arctic region. Methane emissions from
organic-rich soils in the Arctic have been extensively studied due to their
potential to increase the atmospheric methane burden as permafrost thaws.
However, this methane source might have been overestimated without considering
high affinity methanotrophs (HAM, methane oxidizing bacteria) recently identified
in Arctic mineral soils. From this study, we find that HAM dynamics double the
upland methane sink (~5.5 TgCH<sub>4</sub>yr<sup>-1</sup>) north of 50°N in
simulations from 2000 to 2016 by integrating the dynamics of HAM and
methanogens into a biogeochemistry model that includes permafrost soil organic
carbon (SOC) dynamics. The increase is equivalent to at least half of the
difference in net methane emissions estimated between process-based models and
observation-based inversions, and the revised estimates better match site-level
and regional observations. The new model projects double wetland methane
emissions between 2017-2100 due to more accessible permafrost carbon. However,
most of the increase in wetland emissions is offset by a concordant increase in
the upland sink, leading to only an 18% increase in net methane emission (from
29 to 35 TgCH<sub>4</sub>yr<sup>-1</sup>). The projected net methane emissions
may decrease further due to different physiological responses between HAM and
methanogens in response to increasing temperature. This article was published
in <i>Nature Climate Change</i> in March
2020.</p>
<p>In Chapter 3, the second article of this
thesis, I develop and validate the first biogeochemistry model to simulate
carbon isotopic signatures (δ<sup>13</sup>C)
of methane emitted from global wetlands, and examined the importance of the wetland
carbon isotope map for studying the global methane cycle. I incorporated a carbon isotope-enabled module into an
extant biogeochemistry model to mechanistically simulate the spatial and
temporal variability of global wetland δ<sup>13</sup>C-CH<sub>4</sub>. The new
model explicitly considers isotopic fractionation during methane production,
oxidation, and transport processes. I estimate a mean global wetland δ<sup>13</sup>C-CH<sub>4</sub> of
-60.78‰ with its seasonal and inter-annual variability. I find that the new
model matches field chamber observations 35% better in terms of root mean
square estimates compared to an empirical static wetland δ<sup>13</sup>C-CH<sub>4</sub> map.
The model also reasonably reproduces the regional heterogeneity of wetland δ<sup>13</sup>C-CH<sub>4</sub> in
Alaska, consistent with vertical profiles of δ<sup>13</sup>C-CH<sub>4</sub>
from NOAA aircraft measurements. Furthermore, I show that the latitudinal
gradient of atmospheric δ<sup>13</sup>C-CH<sub>4</sub> simulated by a chemical
transport model using the new wetland δ<sup>13</sup>C-CH<sub>4</sub> map
reproduces the observed latitudinal gradient based on NOAA/INSTAAR global
flask-air measurements. I believe this study is the first process-based
biogeochemistry model to map the global distribution of wetland δ<sup>13</sup>C-CH<sub>4</sub>,
which will significantly help atmospheric chemistry transport models partition
global methane emissions. This article is in preparation for submission
to <i>Nature Geoscience</i>.</p>
<p>Chapter 4 of this thesis, the third
article, investigates the importance of leaf carbon allocation for seasonal
leaf carbon isotopic signature changes and water use efficiency in temperate
forests. Temperate deciduous trees remobilize stored carbon early in the
growing season to produce new leaves and xylem vessels. The use of remobilized
carbon for building leaf tissue dampens the link between environmental stomatal
response and inferred intrinsic water use efficiency (iWUE) using leaf carbon
isotopic signatures (δ<sup>13</sup>C). So far, few studies consider carbon
allocation processes in interpreting leaf δ<sup>13</sup>C signals. To
understand effects of carbon allocation on δ<sup>13</sup>C and iWUE estimates,
we analyzed and modeled the seasonal leaf δ<sup>13</sup>C of four temperate
deciduous species (<i>Acer saccharum, Liriodendron tulipifera, Sassafras
albidum, </i>and <i>Quercus alba</i>)
and compared the iWUE estimates from different methods, species, and drought
conditions. At the start of the growing season, leaf δ<sup>13</sup>C values
were more enriched, due to remobilized carbon during leaf-out. The bias towards
enriched leaf δ<sup>13</sup>C values explains the higher iWUE from leaf
isotopic methods compared with iWUE from leaf gas exchange measurements. I
further showed that the discrepancy of iWUE estimates between methods may be
species-specific and drought sensitive. The use of δ<sup>13</sup>C of plant
tissues as a proxy for stomatal response to
environmental processes, through iWUE, is complicated due to carbon
allocation and care must be taken when interpreting estimates to avoid proxy
bias. This
article is in review for publication in <i>New
Phytologist</i>.</p>
<p> </p>
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