Reconstructing relative humidity from plant δ18O and δD as deuterium deviations from the global meteoric water line. Issue 5 (1st July 2014)

• Record Type: Journal Article
• Authors: Voelker, Steven L.; Brooks, J. Renée; Meinzer, Frederick C.; Roden, John; Pazdur, Anna; Pawelczyk, Slawomira; Hartsough, Peter; Snyder, Keirith; Plavcová, Lenka; Šantrůček, Jiří
• Is Part Of: Ecological applications. Volume 24:Issue 5(2014)
• Page Start: 960
• Page End: 975
• Publication Date: 2014-07-01
• Subjects: cellulose -- δD -- δ18O -- deuterium-excess -- leaf vapor pressure -- leaf water -- relative humidity -- water isotopes; Ecology -- Periodicals; Environmental protection -- Periodicals; Biology, Economic -- Periodicals; 577.05
• DOI: 10.1890/13-0988.1
• Languages: English
• ISSNs: 1051-0761

Abstract

Abstract : Cellulose δ 18 O and δD can provide insights on climates and hydrological cycling in the distant past and how these factors differ spatially. However, most studies of plant cellulose have used only one isotope, most commonly δ 18 O, resulting in difficulties partitioning variation in δ 18 O of precipitation vs. evaporative conditions that affect leaf water isotopic enrichment. Moreover, observations of pronounced diurnal differences from conventional steady‐state model predictions of leaf water isotopic fractionation have cast some doubt on single isotope modeling approaches for separating precipitation and evaporation drivers of cellulose δ 18 O or δD. We explore a dual isotope approach akin to the concept of deuterium‐excess ( d ), to establish deuterium deviations from the global meteoric water line in leaf water (Δ d l ) as driven by relative humidity (RH). To demonstrate this concept, we survey studies of leaf water δ 18 O and δD in hardwood vs. conifer trees. We then apply the concept to cellulose δ 18 O and δD using a mechanistic model of cellulose δ 18 O and δD to reconstruct deuterium deviations from the global meteoric water line (Δ d c ) in Quercus macrocarpa, Q. robur, and Pseudotsuga menziesii . For each species, Δ d c showed strong correlations with RH across sites. Δ d c agreed well with steady‐state predictions for Q. macrocarpa, while for Q. robur, the relationship with RH was steeper than expected. The slope of Δ d c vs. RH of P. menziesii was also close to steady‐state predictions, but Δ d c were more enriched than predicted. This is in agreement with our leaf water survey showing conifer Δ d l was more enriched than predicted. Our data reveal that applications of this method should be appropriate for reconstructing RH from cellulose δ 18 O and δD after accounting for differences between hardwoods and conifers. Hence, Δ d c should be useful for understanding variability in RH associated with past climatic cycles, across regional climates, or across complex terrain where climate modeling is challenging. Furthermore, Δ d c and inferred RH values should help in constraining variation in source water δ 18 O.