Are carbohydrate storage strategies of trees traceable by early–latewood carbon isotope differences?

Abstract

Key message Investigations of stable isotopes in earlyand latewood cellulose offer interesting insights to climate-driven adaptations of trees' carbon storage strategy during different phenological phases. Abstract We investigated d 13 C isotopic composition in both earlywood and latewood. The origin of the samples is an oak forest (Quercus petraea), situated in Switzerland. A comparison of isotope compositions between early-and latewood can help us to investigate and understand the processes of plant metabolism in more detail. The fact which we found excellent correlations (r 2 = 55 %) between early-and latewood for carbon isotopes strengthens the common knowledge that atmospheric CO 2 acts as the major carbon source for latewood but the earlywood strongly depends on the reserves from previous years (r 2 = 68 %), at least for oaks investigated in this study. In addition, that no correlation between late woods (r 2 = 0-5 %) was found, manifests the higher variability of direct assimilates. Furthermore, we examined the impacts of increasing air temperature and CO 2 concentration on carbohydrate fluxes in trees and we found remarkable differences between two time periods. In the period AD 1780-1825, the trees intensely used the young reserves while in the period AD 1960AD -1994, there is no clear preference of them. This suggests that in the latter period, a larger volume of reserves is available and that the new assimilated reserves (previous year) do not play the most important part, mainly due to the very favourable conditions induced by climate change, at the investigated site. In conclusion, a carbon isotope approach on early-and latewood samples is ideal to investigate isotope incorporation pathways of physiological processes. This will augment the interpretation of tree ring isotope records with respect to the assignments of their variations to specific biochemical processes within the tree, i.e. carbon allocation.

Disentangling seasonal and interannual legacies from inferred patterns of forest water and carbon cycling using tree‐ring stable isotopes

“…These residual correlations most likely reflect higher-frequency effects, such as the common utilization of stored carbohydrate pools or stored soil water pools within the same year. The common use of resources would introduce interseasonal lags in the influence of climate on observed patterns in iWUE, g s and A (Helle & Schleser, 2004;Kimak & Leuenberger, 2015;Kress et al, 2009;Labotka et al, 2016;Leavitt, 2010;Sargeant & Singer, 2016;Vaganov et al, 2009). The linear regression approach that we applied to the EW1 and LW time series was effective in distinguishing sites that show clear evidence of seasonal dependence of isotope ratios on climate.…”

“…One challenge, however, with climatic interpretation of isotope ratios in EW and LW, is that these ratios can reflect environmental input from multiple seasons and past years, consequently blurring the differences caused by specific seasonal climate regimes Helle & Schleser, 2004;Szejner et al, 2016;Vaganov et al, 2009). The cross-correlation between isotope ratios in EW and LW has been observed previously (Helle & Schleser, 2004;Kagawa, Sugimoto, & Maximov, 2006;Kimak & Leuenberger, 2015;Kress et al, 2009;Leavitt, 2002;Vaganov et al, 2009). This correlation can be attributed to external (e.g., persistent interannual climate trends) and internal (e.g., mixing of carbon and water pools) processes, and the assessment of the relative importance of these influences will provide insights into how to better read the seasonal and interannual alignment of climate-isotope relations.…”

An Overview on Isotopic Divergences – Causes for instability of Tree-Ring Isotopes and Climate Correlations

“…After budburst, photosynthesis directly produces carbohydrates. The proportion of direct assimilates increases progressively at the expense of reconverted stored material, until they are the only carbohydrate source for building new plant tissues and storing reserves, mainly as starch (Kimak and Leuenberger, 2015). Although evergreen conifers rely less on C reserves than deciduous trees, recent photosynthates supply their growth, but C fixed during previous years can also contribute (von Arx et al, 2017;Castagneri et al, 2018).…”

Tree ring dating using oxygen isotopes: a master chronology for central England

“…The early-or spring-wood of each ring was removed, as in oak this is formed prior to bud burst and comprises photosynthate from previous years (Switsur et al, 1995;Richardson et al, 2013;Kimak and Leuenberger, 2015;McCarroll et al, 2017). The lateor summer-wood for each year, which carries a clearer annual isotopic signal, was then manually subdivided as fine slivers (c. 40 μm thick), under magnification using a scalpel.…”