Leaf water ¹⁸O and ²H enrichment along vertical canopy profiles in a broadleaved and a conifer forest tree

Abstract

Distinguishing meteorological and plant-mediated drivers of leaf water isotopic enrichment is prerequisite for ecological interpretations of stable hydrogen and oxygen isotopes in plant tissue. We measured input and leaf water δ H and δ O as well as micrometeorological and leaf morpho-physiological variables along a vertical gradient in a mature angiosperm (European beech) and gymnosperm (Douglas fir) tree. We used these variables and different enrichment models to quantify the influence of Péclet and non-steady state effects and of the biophysical drivers on leaf water enrichment. The two-pool model accurately described the diurnal variation of leaf water enrichment. The estimated unenriched water fraction was linked to leaf dry matter content across the canopy heights. Non-steady state effects and reduced stomatal conductance caused a higher enrichment of Douglas fir compared to beech leaf water. A dynamic effect analyses revealed that the light-induced vertical gradients of stomatal conductance and leaf temperature outbalanced each other in their effects on evaporative enrichment. We conclude that neither vertical canopy gradients nor the Péclet effect is important for estimates and interpretation of isotopic leaf water enrichment in hypostomatous trees. Contrarily, species-specific non-steady state effects and leaf temperatures as well as the water vapour isotope composition need careful consideration.

Spatial variation in throughfall, soil, and plant water isotopes in a temperate forest

“…The relationships between δ 18 O and δ 2 H of water isotopes in precipitation, throughfall, soil, and plants are presented in Figure 2 and Δ 2 H leaf-branch ) than did P. abies (t test; p < 0.001). The unique canopy structure of each species may lead to differences in biophysical conditions (e.g., the ratio of ambient air vapour pressure to leaf intracellular vapour pressure) that would explain the differences in leaf water enrichment (Bögelein et al, 2017).…”

“…Tracing stable isotopes of water ( 18 O/ 16 O and 2 H/H) through the soil–plant–atmosphere continuum has been essential for addressing many ecohydrological questions. Recent applications include studies of the transit times and flow paths of water in soils (Sprenger, Seeger, & Blume, ), the depth of plant root water uptake (Goldsmith et al, ), leaf physiological response to climate (Bögelein, Thomas, & Kahmen, ), the relative roles of evaporation versus transpiration in returning water to the atmosphere (Jasechko et al, ), and the reconstruction of past climate conditions (Saurer et al, ).…”

Investigating old‐growth ponderosa pine physiology using tree‐rings, δ13C, δ18O, and a process‐based model

“…, Bögelein et al. ). This is partly because contributions of each Peclet effect component are challenging to disentangle, especially the effective path length ( L ), an elusive component of the Peclet effect that is not directly measurable (Song et al.…”

The 18O‐signal transfer from water vapour to leaf water and assimilates varies among plant species and growth forms

“…However, recent studies demonstrate strong daily and seasonal variations in δ 18 O V on the basis of local, regional, and global hydrological processes that affect atmospheric weather conditions (Huang & Wen, 2014;Lee, Smith, & Williams, 2006;Tremoy et al, 2012;Yu, Tian, Ma, Xu, & Qu, 2015). This causes δ 18 O V to often be decoupled from δ 18 O S (Bögelein, Thomas, & Kahmen, 2017;Lai et al, 2008). As a consequence, δ 18 O V and δ 18 O S do not covary in their influence on δ 18 O LW , and disentangling the relative importance of these two water sources on δ 18 O LW and thus on δ 18 O of plant material is therefore critical (Helliker, 2014;Helliker & Griffiths, 2007;Roden & Ehleringer, 1999).…”