Influence of salinity on hydrogen isotope fractionation in Rhizophora mangroves from Micronesia

Abstract

Please cite this article as: Nemiah Ladd, S., Sachs, J.P., Influence of salinity on hydrogen isotope fractionation in Rhizophora mangroves from Micronesia, Geochimica et Cosmochimica Acta (2015), doi: http://dx. AbstractHydrogen isotope ratios ( 2 H/ 1 H or δ 2 H) 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 2 H fractionation in leaf lipids. To better understand and calibrate this effect, δ 2 H 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 δ 2 H and δ 18 O values of leaf water, xylem water and surface water. Net 2 H discrimination between surface water and taraxerol increased by 0.9 ± 0.2‰ per part per thousand (ppt -1 ) over a salinity range of 1-34 ppt. Xylem water was always depleted in 2 H relative to surface water, and the magnitude of this depletion increased with salinity, which is most likely due to a combination of greater 2 H discrimination by roots during water uptake and opportunistic use of freshwater.Changes in the 2 H 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 2 water enrichment is therefore unlikely to be responsible for increased 2 H/ 1 H 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.

Galápagos hydroclimate of the Common Era from paired microalgal and mangrove biomarker 2 H/ 1 H values

“…We separate convergence zone from El Niño-driven changes and observe substantial fluctuations even in the absence of perturbations as large as current anthropogenic forcing. it increases by 0.7-1.7‰ (13,16 Poza de las Diablas sediments were pink cyanobacterial deposits and contained few lithological changes between the sedimentwater interface and ∼340-cm depth (Fig. S2).…”

Plant water resource partitioning and isotopic fractionation during transpiration in a seasonally dry tropical climate

“…This is indicative of very limited evapotranspiration. Slightly depleted δ 2 H leaf values relative to δ 2 H xylem (i.e., small, negative ε l/x values) have previously been reported for some trees in Rhizophora mangroves (Ladd and Sachs, 2015). Ladd and Sachs (2015) ascribed this to the high ambient relative humidity, resulting in a small vapor pressure gradient across the leaf surface (see also Helliker and Ehleringer, 2000;Farquhar et al, 2007).…”

“…Slightly depleted δ 2 H leaf values relative to δ 2 H xylem (i.e., small, negative ε l/x values) have previously been reported for some trees in Rhizophora mangroves (Ladd and Sachs, 2015). Ladd and Sachs (2015) ascribed this to the high ambient relative humidity, resulting in a small vapor pressure gradient across the leaf surface (see also Helliker and Ehleringer, 2000;Farquhar et al, 2007). The atypical ε l/x values of the two Capparaceae in this study are possibly associated with their xerophytic traits, in particular the waxy appearance of the leaves in many species of this family (Elffers et al, 1964).…”

Fingerprinting Blue Carbon: Rationale and Tools to Determine the Source of Organic Carbon in Marine Depositional Environments

“…In addition, Duarte et al (2018) recently showed that Red Sea seagrass and macroalgae have distinct δ 2 H signatures and that the combination of δ 2 H and δ 13 C holds promise to discriminate these carbon sources in C org sediment stocks. Several factors such as photosynthesis, lipid content, isotopic discrimination during water uptake, biochemical and biophysical processes, and environmental seasonality allow differentiation of δ 2 H values in primary producers Ladd and Sachs, 2015;Adame et al, 2016).…”