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Contributed Talk

Session: : Physiological Ecology 4

COS 201-5 - Global carbon stable isotope ecology of plant leaves

Wednesday, August 9, 2023
2:30 PM – 2:45 PM PDT
Location: E142
Abstract: Plant carbon stable isotope composition varies by photosynthetic type, species ecophysiology, and with environmental variation. Variation in plant tissue δ13C has been repeatedly explored using rich datasets. Several studies have also investigated δ13C from an evolutionary perspective. These studies have included phylogeny either in very general categorizations (e.g., gymnosperms versus angiosperms) or have focused primarily within lineages (e.g., Gymnosperms). In order to represent a wide range of seed plants with global coverage, we used a large combination of previously published and newly available leaf δ13C datasets. The resulting isotope data span Angiosperms and Gymnosperms, include various vegetation growth forms from forbs and grasses to trees, and are globally distributed. We conducted an analysis of δ13C using a Boosted Regression Tree approach with common climatic variables (e.g., Mean Annual Precipitation (MAP), Vapor Pressure Deficit (VPD), Mean Annual Temperature, Potential Evapotranspiration, Seasonality), biome type, altitude, growth form, leaf habit, and evolutionary lineage as predictors. Finally, we performed phylogenetically-controlled regression analysis within specific lineages to explore unique drivers of δ13C within clades.

Across a broad sample of plants we found that evolutionary lineage was a critical predictor of leaf δ13C. When compared to previous studies that did not include evolutionary information (e.g., family, phylogeny), we found that a different suite of predictor variables were most important for explaining carbon stable isotope ecology. Evolutionary lineage became the overall most important predictor. Notably, the role of MAP as a control for δ13C values was greatly reduced compared to previous studies. Instead, biome differences and VPD (especially in Pinaceae) emerged as more important than reported in past studies that did not include evolution. We find similar reorganization of the importance of environmental drivers within lineages as well, although results depend on lineage. Because our results show that the nature of δ13C variation depends on evolutionary lineage, we suggest that phylogeny may be a source of error when estimating δ13C from empirical climate-based equations. This finding is similar to previous work focused primarily on Gymnosperms which report that δ13C-climate relationships are poorly explained by leaf-level responses to MAP. Instead they suggest that δ13C can better be described by species with constant fractionation that sort ecologically. Our work suggests the need for lineage and species-specific calibrations for proxy studies using δ13C as an indicator of climate.