The isotopic composition of xylem water (δX) is of considerable interest for plant source water studies. In‐situ monitored isotopic composition of transpired water (δT) could provide a nondestructive ...proxy for δX‐values. Using flow‐through leaf chambers, we monitored 2‐hourly δT‐dynamics in two tropical plant species, one canopy‐forming tree and one understory herbaceous species. In an enclosed rainforest (Biosphere 2), we observed δT‐dynamics in response to an experimental severe drought, followed by a 2H deep‐water pulse applied belowground before starting regular rain. We also sampled branches to obtain δX‐values from cryogenic vacuum extraction (CVE). Daily flux‐weighted δ18OT‐values were a good proxy for δ18OX‐values under well‐watered and drought conditions that matched the rainforest's water source. Transpiration‐derived δ18OX‐values were mostly lower than CVE‐derived values. Transpiration‐derived δ2HX‐values were relatively high compared to source water and consistently higher than CVE‐derived values during drought. Tracing the 2H deep‐water pulse in real‐time showed distinct water uptake and transport responses: a fast and strong contribution of deep water to canopy tree transpiration contrasting with a slow and limited contribution to understory species transpiration. Thus, the in‐situ transpiration method is a promising tool to capture rapid dynamics in plant water uptake and use by both woody and nonwoody species.
Summary Statement
Tracing the isotopic composition of transpiration (δT) in real‐time showed rapid dynamics in plant water uptake and use by woody and nonwoody species. Daily δ18OT‐values weighted by the transpiration flux are a good proxy for δ18O of xylem water.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Colonization of new ecological niches has triggered large adaptive radiations. Although some lineages have made use of such opportunities, not all do so. The factors causing this variation among ...lineages are largely unknown. Here, we show that deficiency in docosahexaenoic acid (DHA), an essential ω-3 fatty acid, can constrain freshwater colonization by marine fishes. Our genomic analyses revealed multiple independent duplications of the fatty acid desaturase gene
in stickleback lineages that subsequently colonized and radiated in freshwater habitats, but not in close relatives that failed to colonize. Transgenic manipulation of
in marine stickleback increased their ability to synthesize DHA and survive on DHA-deficient diets. Multiple freshwater ray-finned fishes also show a convergent increase in
copies, indicating its key role in freshwater colonization.
Severe droughts endanger ecosystem functioning worldwide. We investigated how drought affects carbon and water fluxes as well as soil-plant-atmosphere interactions by tracing
CO
and deep water
H
O ...label pulses and volatile organic compounds (VOCs) in an enclosed experimental rainforest. Ecosystem dynamics were driven by different plant functional group responses to drought. Drought-sensitive canopy trees dominated total fluxes but also exhibited the strongest response to topsoil drying. Although all canopy-forming trees had access to deep water, these reserves were spared until late in the drought. Belowground carbon transport was slowed, yet allocation of fresh carbon to VOCs remained high. Atmospheric VOC composition reflected increasing stress responses and dynamic soil-plant-atmosphere interactions, potentially affecting atmospheric chemistry and climate feedbacks. These interactions and distinct functional group strategies thus modulate drought impacts and ecosystem susceptibility to climate change.
Summary
Hydrogen isotope ratios of plant lipids are used for paleoclimate reconstruction, but are influenced by both source water and biosynthetic processes. Measuring 2H : 1H ratios of multiple ...compounds produced by different pathways could allow these effects to be separated, but hydrogen isotope fractionations during isoprenoid biosynthesis remain poorly constrained.
To investigate how hydrogen isotope fractionation during isoprenoid biosynthesis is influenced by molecular exchange between the cytosolic and plastidial production pathways, we paired position‐specific 13C‐pyruvate labeling with hydrogen isotope measurements of lipids in Pachira aquatica saplings.
We find that acetogenic compounds primarily incorporated carbon from 13C2‐pyruvate, whereas isoprenoids incorporated 13C1‐ and 13C2‐pyruvate equally. This indicates that cytosolic pyruvate is primarily introduced into plastidial isoprenoids via glyceraldehyde 3‐phosphate and that plastidial isoprenoid intermediates are incorporated into cytosolic isoprenoids. Probably as a result of the large differences in hydrogen isotope fractionation between plastidial and cytosolic isoprenoid pathways, sterols from P. aquatica are at least 50‰ less 2H‐enriched relative to phytol than sterols in other plants.
These results provide the first experimental evidence that incorporation of plastidial intermediates reduces 2H : 1H ratios of sterols. This suggests that relative offsets between the 2H : 1H ratios of sterols and phytol can trace exchange between the two isoprenoid synthesis pathways.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The hydrogen isotopic composition (δ2H) of lipid biomarkers has diverse applications in the fields of paleoclimatology, biogeochemistry, and microbial community dynamics. Large changes in hydrogen ...isotope fractionation have been observed among microbes with differing core metabolisms, while environmental factors including temperature and nutrient availability can affect isotope fractionation by photoautotrophs. Much effort has gone into studying these effects under laboratory conditions with single species cultures. Moving beyond controlled environments and quantifying the natural extent of these changes in freshwater lacustrine settings and identifying their causes is essential for robust application of δ2H values of common short-chain fatty acids as a proxy of net community metabolism and of phytoplankton-specific biomarkers as a paleohydrologic proxy. This work targets the effect of community dynamics, temperature, and productivity on 2H∕1H fractionation in lipid biomarkers through a comparative time series in two central Swiss lakes: eutrophic Lake Greifen and oligotrophic Lake Lucerne. Particulate organic matter was collected from surface waters at six time points throughout the spring and summer of 2015, and δ2H values of short-chain fatty acids, as well as chlorophyll-derived phytol and the diatom biomarker brassicasterol, were measured. We paired these measurements with in situ incubations conducted with NaH13CO3, which were used to calculate the production rates of individual lipids in lake surface water. As algal productivity increased from April to June, net discrimination against 2H in Lake Greifen increased by as much as 148 ‰ for individual fatty acids. During the same time period in Lake Lucerne, net discrimination against 2H increased by as much as 58 ‰ for individual fatty acids. A large portion of this signal is likely due to a greater proportion of heterotrophically derived fatty acids in the winter and early spring, which are displaced by more 2H-depleted fatty acids as phytoplankton productivity increases. Smaller increases in 2H discrimination for phytol and brassicasterol suggest that a portion of the signal is due to changes in net photoautotrophic 2H fractionation, which may be caused by increasing temperatures, a shift from maintenance to high growth, or changes in the community assemblage. The fractionation factors for brassicasterol were significantly different between the two lakes, suggesting that its hydrogen isotope composition may be more sensitive to nutrient regime than is the case for fatty acids or phytol.
Hydrogen isotope ratios (2H/1H or δ2H) of plant leaf waxes typically covary with those of precipitation, and are therefore used as a proxy for past hydrologic variability. Mangroves present an ...important exception to this relationship, as salinity can strongly influence 2H fractionation in leaf lipids. To better understand and calibrate this effect, δ2H values of taraxerol and n-alkanes were measured in the leaves of Rhizophora spp. (red mangroves) from three estuaries and four brackish lakes on the Micronesian islands of Pohnpei and Palau, and compared to the δ2H and δ18O values of leaf water, xylem water and surface water. Net 2H discrimination between surface water and taraxerol increased by 0.9±0.2‰ per part per thousand (ppt−1) over a salinity range of 1–34ppt. Xylem water was always depleted in 2H relative to surface water, and the magnitude of this depletion increased with salinity, which is most likely due to a combination of greater 2H discrimination by roots during water uptake and opportunistic use of freshwater. Changes in the 2H content of xylem water can account for up to 43% of the change in net taraxerol fractionation with salinity. Leaf water isotopes were minimally enriched relative to xylem water and there was not significant variability in leaf water enrichment with salinity, which is consistent with a Péclet-modified Craig–Gordon model of leaf water enrichment. As leaf water enrichment is therefore unlikely to be responsible for increased 2H/1H fractionation in mangrove leaf lipids at elevated salinities, the majority of this signal is most likely explained either by changes in biosynthetic fractionation in response to salt stress or by salinity influenced changes in the timing of water uptake and lipid synthesis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
► We measured D/H fractionation in mangrove leaf wax n-alkanes along an estuary. ► D/H fractionation in leaf waxes increases by ∼1.5‰ per salinity unit. ► This relationship is the opposite of that ...observed in phytoplankton. ► Complicates paleoclimate interpretation of leaf wax δD in regions with mangroves. ► Suggests that δD of a mangrove specific biomarker could be a paleosalinity proxy.
Hydrogen isotope ratios in lipids derived from mangroves have the potential to be used for paleohydrologic reconstructions and could serve as a much needed tool for establishing past climate variability in the tropics. We assessed the effect of salinity on the apparent fractionation factor, αa, between mangrove derived n-alkanes and their source water for Avicennia marina (gray mangrove) specimens collected along a 28PSU salinity gradient in the Brisbane River Estuary. Our results indicate that there is an inverse relationship between the apparent fractionation factor and salinity. This salinity effect is large enough to override variability in the isotopic composition of source water, which plays a dominant role in determining the hydrogen isotope ratio of leaf waxes in other vascular plants. We suggest that this relationship may be due to (i) increased discrimination against deuterium during water uptake at high salinity, (ii) increased production of compatible solutes from D enriched pyruvate at high salinity, resulting in more hydrogen from D depleted NADPH being incorporated in leaf waxes, and/or (iii) increased secretion of salty brine by leaves at high salinity, resulting in (iii.a) higher relative humidity at the leaf surface, and (iii.b) introducing the possibility that D depleted water of hydration is absorbed by the leaf. Our results indicate that hydrogen isotope ratios of mangrove lipid biomarkers can be developed as a paleosalinity indicator. They also imply that care must be taken when interpreting hydrogen isotopic variations in non-source specific higher plant lipids in sediments where both mangrove and non-mangrove plants contribute organic material.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Climate warming is causing rapid spatial expansion of ocean warm pools from equatorial latitudes towards the subtropics. Sedentary coral reef inhabitants in affected areas will thus be trapped in ...high temperature regimes, which may become the “new normal”. In this study, we used clownfish Amphiprion ocellaris as model organism to study reef fish mechanisms of thermal adaptation and determine how high temperature affects multiple lipid aspects that influence physiology and thermal tolerance. We exposed juvenile fish to two different experimental conditions, implemented over 28 days: average tropical water temperatures (26 °C, control) or average warm pool temperatures (30 °C). We then performed several analyses on fish muscle and liver tissues: i) total lipid content (%), ii) lipid peroxides, iii) fatty acid profiles, iv) lipid metabolic pathways, and v) weight as body condition metric. Results showed that lipid storage capacity in A. ocellaris was not affected by elevated temperature, even in the presence of lipid peroxides in both tissues assessed. Additionally, fatty acid profiles were unresponsive to elevated temperature, and lipid metabolic networks were consequently well conserved. Consistent with these results, we did not observe changes in fish weight at elevated temperature. There were, however, differences in fatty acid profiles between tissue types and over time. Liver showed enhanced α-linolenic and linoleic acid metabolism, which is an important pathway in stress response signaling and modulation on environmental changes. Temporal oscillations in fatty acid profiles are most likely related to intrinsic factors such as growth, which leads to the mobilization of energetic reserves between different tissues throughout time according to organism needs. Based on these results, we propose that the stability of fatty acid profiles and lipid metabolic pathways may be an important thermal adaptation feature of fish exposed to warming environments.
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•Effects of warm temperature on lipid profiles and pathways were tested in clownfish.•Muscle and liver were unresponsive to temperature change.•Lipid storage capacity was maintained, even with lipid peroxidation.•No change was detected in metabolic pathways at warm temperature.•Growth remained unchanged, suggesting ability to acclimate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The nutritional diversity of resources can affect the adaptive evolution of consumer metabolism and consumer diversification. The omega‐3 long‐chain polyunsaturated fatty acids eicosapentaenoic acid ...(EPA; 20:5n‐3) and docosahexaenoic acid (DHA; 22:6n‐3) have a high potential to affect consumer fitness, through their widespread effects on reproduction, growth and survival. However, few studies consider the evolution of fatty acid metabolism within an ecological context. In this review, we first document the extensive diversity in both primary producer and consumer fatty acid distributions amongst major ecosystems, between habitats and amongst species within habitats. We highlight some of the key nutritional contrasts that can shape behavioural and/or metabolic adaptation in consumers, discussing how consumers can evolve in response to the spatial, seasonal and community‐level variation of resource quality. We propose a hierarchical trait‐based approach for studying the evolution of consumers’ metabolic networks and review the evolutionary genetic mechanisms underpinning consumer adaptation to EPA and DHA distributions. In doing so, we consider how the metabolic traits of consumers are hierarchically structured, from cell membrane function to maternal investment, and have strongly environment‐dependent expression. Finally, we conclude with an outlook on how studying the metabolic adaptation of consumers within the context of nutritional landscapes can open up new opportunities for understanding evolutionary diversification.
Here, we review how the nutritional diversity of resources can affect the adaptive evolution of consumer metabolism and consumer diversification. We document the extensive diversity in fatty acid distributions amongst major ecosystems and habitats, highlighting some of the key nutritional contrasts that can shape behavioural and/or metabolic adaptation in consumers. We also propose a hierarchical trait‐based approach for studying the evolution of consumers’ metabolic networks and review the evolutionary genetic mechanisms underpinning consumer adaptation to fatty acid distributions.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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