# Dual Isotope Analysis Reveals Phylogenetic Patterns and Novel Insights Into Methoxy Group Synthesis of Structural Biomolecules in Leaf and Woody Plant Tissues

## TL;DR

This study uses isotope analysis to reveal how methoxy groups in plant tissues differ based on species and tissue type, offering new insights into plant biosynthesis and phylogenetic patterns.

## Contribution

The study identifies phylogenetic patterns in methoxy group isotopes and suggests distinct biosynthetic pathways in autotrophic and heterotrophic tissues.

## Key findings

- Phylogenetic patterns in δ2Hmeth and δ13Cmeth are stronger in leaves and distinguish angiosperms from gymnosperms.
- δ13Cmeth values are more negative in leaves than in twigs, indicating different methoxy precursor synthesis in tissues.
- Hydrogen isotope fractionation differs significantly between angiosperms and gymnosperms.

## Abstract

Stable carbon and hydrogen isotopes of wood methoxy groups (δ
2Hmeth, δ
13Cmeth), mainly sourced by structural biomolecules like lignin and pectin, provide important insights into climatic, hydrological and physiological conditions. This study systematically investigated species‐specific δ
2Hmeth and δ
13Cmeth variations in leaves and woody twigs of 65 different tree species grown in a common garden. Significant phylogenetic patterns were observed in δ
2Hmeth and δ
13Cmeth of both tissues, with stronger signals in leaves and the most pronounced differences between angiosperms and gymnosperms. δ
13Cmeth variations are likely explained by anatomical and physiological differences between seed types, while δ
2Hmeth variations were attributed to temporal differences in water uptake or isotope fractionation processes. Notably, δ
13Cmeth values were more negative in leaves than in twigs, while δ
2Hmeth values showed no tissue‐specific difference. This suggests that serine, a methoxy precursor, is differently synthesised in autotrophic than in heterotrophic tissues. Hydrogen isotope fractionation between xylem water and twig methoxy groups averaged at −197 mUr, with mean isotope fractionation of gymnosperms −209 mUr being significantly different to that of angiosperms −184 mUr. Weak relationships between δ
2Hmeth and δ
2H values of carbohydrates indicated that distinct signals are preserved within the two compounds. This study highlights the importance of phylogenetic considerations when using methoxy group isotopes as proxies and provides new insights into methoxy group biosynthesis.

Phylogenetic patterns were found in hydrogen and carbon isotopes of twig and leaf methoxy groups primarily at the seed type level. Strong offsets between leaves and twigs in carbon but not in hydrogen isotopes showed that methoxy groups are partly influenced by different precursors in plant tissues.