Compound-Specific Carbon Isotopes and Concentrations of Carbohydrates and Organic Acids as Indicators of Tree Decline in Mountain Pine

Abstract

Abstract:We investigated seasonal variations in δ 13 C values and concentrations of carbohydrates and organic acids in needles of declining and healthy mountain pine (Pinus mugo ssp. uncinata (DC.) Domin) trees from the Swiss National Park (SNP), using compound-specific isotopes analysis (CSIA). Our goal was to study the impact of climatic drivers on the individual compounds and understand the reasons of partial tree declines in relation to healthy mountain pine trees under seasonal weather patterns. We found that temperature is the main climatic driver determining the seasonal carbon dynamics at the needle level. Lower seasonal δ 13 C variability and lower concentration levels of sucrose in needles suggest less photosynthetic activity and sink carbon demand in declining compared to healthy mountain pine trees. Higher concentration levels of hexose (glucose and fructose) can play a reserve function for surviving mechanisms of mountain pine trees. Seasonal patterns of organic acid (malate and citrate) suggest an increasing investment in maintenance and repair mechanisms. The seasonal course of carbohydrates and organic acids can therefore be considered an indicator for a modified carbon metabolism within the leaves and possibly within the other tree tissues, partially explaining the decline of mountain pine trees.

Estimating intra-seasonal photosynthetic discrimination and water use efficiency using δ13C of leaf sucrose in Scots pine

“…The iWUE, VPD, and T signals in δ 13 C WSC were also dampened in the current study ( Figs 4 , 5B ), as has been reported for mature mountain pine ( Churakova et al , 2018 ). This result is in contrast to the report by Brugnoli et al (1988) that carbon isotope discrimination in WSC (‘soluble sugars’ therein) correlated strongly with c i / c a .…”

Drivers of intra‐seasonal δ13C signal in tree‐rings of Pinus sylvestris as indicated by compound‐specific and laser ablation isotope analysis

“…CSIA studies on larch in Siberia (Rinne, Saurer, Kirdyanov, Bryukhanova, et al, 2015; Rinne, Saurer, Kirdyanov, Loader, et al, 2015) proposed that the generally reported 13 C‐enrichment of sink organs relative to leaves is in large parts caused by the high abundance of 13 C‐depleted pinitol in leaves and the INV acid induced 13 C‐enrichment of leaf sucrose relative to hexoses (Gilbert et al, 2011; Mauve et al, 2009). However, the role of INV acid associated fractionation is inconsistent between the published studies: the level of 13 C‐enrichment of sucrose over hexose is variable (e.g., Sidorova et al, 2018), even within a growing season (Rinne, Saurer, Kirdyanov, Bryukhanova, et al, 2015), or not detectable (the present study). This inconsistency may indicate species‐specific differences (Dominguez & Niittylä, 2021), tree health status (Sidorova et al, 2018) or differences in the activity level of INV acid (Rinne, Saurer, Kirdyanov, Loader, et al 2015).…”

“…At leaf level, compound‐specific isotope analysis (CSIA) has been applied in a few studies on WSCs of conifers, to examine how environmental signals are recorded and post‐photosynthetically modified in δ 13 C values of individual assimilates during a growing season (Rinne, Saurer, Kirdyanov, Bryukhanova, et al, 2015; Sidorova et al, 2018, 2019; Tang, Schiestl‐Aalto, Lehmann, et al, 2022). In Rinne, Saurer, Kirdyanov, Loader, et al (2015) the intra‐seasonal records of needle δ 13 C Suc (δ 13 C Suc_ Needle ) were further compared to high spatial resolution δ 13 C Ring profiles, to examine the reasons behind the widely reported 13 C‐enrichment of sink organs relative to leaves (Gessler, Brandes, et al, 2009; Gleixner et al, 1993) and evaluate the quality of seasonal climate information stored in larch ( L. gmelinii ) trees.…”

Updating the dual C and O isotope—Gas‐exchange model: A concept to understand plant responses to the environment and its implications for tree rings

“…However, starch‐related 13 C fractionations can be very small (Maunoury‐Danger et al, 2009) and their significance can vary among species and are under debate (Bögelein et al, 2019, Lehmann et al, 2019). Moreover, δ 13 C differences among individual sugars in leaf and phloem have been observed (Churakova et al, 2018; Rinne et al, 2015), with sucrose being often the most 13 C‐enriched soluble sugar. The 13 C fractionations have been related to the invertase reaction (Mauve et al, 2009).…”