Larch Cellulose Shows Significantly Depleted Hydrogen Isotope Values With Respect to Evergreen Conifers in Contrast to Oxygen and Carbon Isotopes

Abstract

The analysis of the stable isotope of the tree-ring cellulose is an important tool for paleo climatic investigations. Long tree-ring chronologies consist predominantly of oaks and conifers in Europe, including larch trees (Larix decidua) and cembran pines (Pinus cembra) that form very long tree ring chronologies in the Alps and grow at the treeline, where tree growth is mainly determined by temperature variations. We analyzed δ13C, δ18O and δ2H isotopes in the cellulose extracted from tree-rings of wood samples collected at high altitude in the Swiss and Tyrol Alps, covering the whole Holocene period. We found that larch cellulose was remarkably more depleted in deuterium than that of cembran pine, with mean δ2H values of −113.4 ± 9.7‰ for larch and of −65.4 ± 11.3‰ for cembran pine. To verify if these depleted values were specific to larch or a property of the deciduous conifers, we extended the analysis to samples from various living conifer species collected at the Bern Botanical Garden. The results showed that not only the larch, but also all the samples of the deciduous larch family had a cellulose composition that was highly depleted in δ2H with regard to the other evergreen conifers including cembran pine, a difference that we attribute to a faster metabolism of the deciduous conifers. The δ18O values were not statistically different among the species, in agreement with the hypothesis that they are primary signals of the source water. While the δ13C values were slightly more depleted for larch than for cembran pine, likely due to metabolic differences of the two species. We conclude that the deciduous larch conifers have specific metabolic hydrogen fractionations and that the larch unique signature of δ2H is useful to recognize it from other conifers in subfossil wood samples collected for paleoclimatic studies. For climate information the absolute δ2H values of larch should be considered carefully and separate from other species.

Investigating Masking Effects of Age Trends on the Correlations among Tree Ring Proxies

“…The generally high correlation values in all different scenarios between the water isotopes of larch are consistent with the earlier assumption that this deciduous conifer has a lower post-photosynthetic fractionation due to the lower exchange of glucose with the surrounding water after photosynthesis, which preserves most of the leaf water signature [37]. Instead, the cembran pine correlations between water isotopes have lower values and are more influenced by the age, with a generally lower correlation in the juvenile phase.…”

“…The initial analysis was the non-detrend scenario that showed a moderate but significant correlation between TRW and water isotopes (negative for δD, positive for δ 18 O) only in the youngest age classes, with similar behaviors and values in larch and in cembran pine. This indicates that these trends are not species-specific (Figure 2) and possibly respond to the same causes, even if the δD age-related trends are species-specific [37]. The observation that TRW vs. δ 18 O correlates significantly only in the juvenile period may partially explains previous contradictory reports [18,21,[23][24][25]34] since their tree ages were not given and different configurations of data were used; mostly detrended TRW and non-detrended isotope values.…”

A high‐temperature water vapor equilibration method to determine non‐exchangeable hydrogen isotope ratios of sugar, starch and cellulose

“…We assume that δ 2 H ne of NSC are susceptible to diel or seasonal changes in environmental conditions such as temperature and light intensity due to their short turnover time (Fernandez et al, 2017 ; Gibon et al, 2004 ). The variability in 2 H‐fractionation between different species might also be important if multiple tree species are used during the establishment of tree‐ring isotope chronologies in dendroclimatological studies (Arosio, Ziehmer‐Wenz, Nicolussi, Schlüchter, & Leuenberger, 2020 ).…”

Cambial-age related correlations of stable isotopes and tree-ring widths in wood samples of tree-line conifers

“…The particularity of δD in larch cellulose is described before (Arosio et al 2020b), but without understanding what specific metabolic step is involved, and how this can change in relation to metabolism.…”