Advances in the use of stable hydrogen isotopes of wood lignin methoxy groups as a proxy to determine plant source water and for climate variability

Stable hydrogen isotope values of tree-lignin methoxy groups (δ²H_LM) are increasingly used to reconstruct the stable hydrogen isotope composition of precipitation (δ²H_precip) and mean annual temperatures in mid-latitude regions. The climate reconstructions are typically derived considering an isotope fractionation of -200 mUr to -216 mUr between lignin methoxy groups and tree source water (Keppler et al. 2007, Anhäuser et al. 2017, Greule et al., 2021, Porter et al. 2022, Wieland et al. 2022). This empirical relationship was derived from different tree species collected along a European north-south transect at altitudes below 1000 m above sea level. However, the influence of various environmental and tree physiological factors on biochemical hydrogen isotope fractionation between lignin methoxy group and precipitation is still unknown.

In order to discuss the improvements and limitations of δ²H_LM values as a climate proxy at different spatial and temporal scales, we present several recent studies that show how environmental and tree physiological factors might influence δ²H_LM values. Our research involves various investigations, including the phylogenetic range by comparing 70 different tree species grown under similar climatic conditions, the influence of salinity by analysing different mangrove species from Australia, and finally the influence of altitude on δ²H_LM values with respect to variations in growing season and source water availability.