Plant leaf wax biomarkers capture gradients in hydrogen isotopes of precipitation from the Andes and Amazon

Abstract

Plant leaf waxes have been found to record the hydrogen isotopic composition of precipitation and are thus used to reconstruct past climate. To assess how faithfully they record hydrological signals, we characterize leaf wax hydrogen isotopic compositions in forest canopy trees across a highly biodiverse, 3 km elevation range on the eastern flank of the Andes. We sampled the dominant tree species and assessed their relative abundance in the tree community. For each tree we collected xylem and leaf samples for analysis of plant water and plant leaf wax hydrogen isotopic compositions. In total, 176 individuals were sampled across 32 species and 5 forest plots that span the gradient. We find both xylem water and leaf wax δD values of individuals correlate (R 2 = 0.8 and R 2 = 0.3 respectively) with the isotopic composition of precipitation (with an elevation gradient of −21‰ km −1). Minimal leaf water enrichment means that leaf waxes are straightforward recorders of the isotopic composition of precipitation in wet climates. For these tropical forests we find the average fractionation between source water and leaf wax for C 29 nalkanes, −129 ± 2‰ (s.e.m., n = 136), to be indistinguishable from that of temperate moist forests. For C 28 n-alkanoic acids the average fractionation is −121 ± 3‰ (s.e.m., n = 102). Sampling guided by community assembly within forest plots shows that integrated plant leaf wax hydrogen isotopic compositions faithfully record the gradient of isotopes in precipitation with elevation (R 2 = 0.97 for n-alkanes and 0.60 for n-alkanoic acids). This calibration study supports the use of leaf waxes as recorders of the isotopic composition of precipitation in lowland tropical rainforest, tropical montane cloud forests and their sedimentary archives.

The effect of 18O‐labelled water vapour on the oxygen isotope ratio of water and assimilates in plants at high humidity

“…). Our findings contribute to observed isotopic gradients and patchiness in leaf water isotopes and may also be important for studies using twig xylem water as an indicator for δ 18 O of source water (Gan et al ., ; Evaristo et al ., ; Feakins et al ., ).…”

Evaluation of bacterial glycerol dialkyl glycerol tetraether and <sup>2</sup>H–<sup>18</sup>O biomarker proxies along a central European topsoil transect

“…8). Likewise, the ε bio values reported in the literature for 2 H of nalkanes can be off from −160 ‰ by tens of per mille (Feakins and Sessions, 2010;Tipple et al, 2015;Feakins et al, 2016;Freimuth et al, 2017). The degree to which hydrogen originates from NADPH rather than leaf water is important, because NADPH is more negative (Schmidt et al, 2003).…”

Mixing as a driver of temporal variations in river hydrochemistry: 1. Insights from conservative tracers in the Andes‐Amazon transition

“…Detailed information about the climatic conditions [ Espinoza et al ., ; Feakins et al ., ], hydrology [ Clark et al ., ], and lithology [ Torres et al ., ] of this river system is available in previously published work. Briefly, the catchment is heterogeneous with respect to temperature (mean annual temperature between 5 and 25°C) [ Lambs et al ., ; Feakins et al ., ] and precipitation (mean annual precipitation between 2 and 5 m ) [ Lambs et al ., ; Feakins et al ., ] due to its the large elevation range (Figure ). The headwaters of the catchment are underlain by Paleozoic sedimentary and metasedimentary rocks, Mesozoic sedimentary rocks, and minor igneous intrusions.…”