Spatiotemporal variation in Coffea canephora leaf traits and iWUE in Congo Basin forests

Understanding how plant traits vary across space and time is critical for predicting responses to environmental change. This study analyzed 179 herbarium samples of Coffea canephora collected between 1900–60 and 2016–21 across the Congo Basin. Researchers measured morphological traits (specific leaf area [SLA], stomatal size [S], stomatal pore size [SPS], stomatal density [SD], maximum diffusive conductance [gcmax]) and physiological traits (δ¹³C, δ¹⁸O isotopes, intrinsic water-use efficiency [iWUE]). Results revealed significant spatiotemporal variation: SLA and stomatal size increased over the past century, while SPS, SD, gcmax, δ¹³C, and iWUE decreased. Morphological traits reflected long-term environmental adaptation, whereas physiological traits responded to short-term drivers such as atmospheric CO₂ and precipitation. Trait correlations highlighted functional trade-offs: SLA was negatively correlated with iWUE, while S, SD, and gcmax were positively associated. These findings suggest a decoupling between morphology and physiology that may constrain photosynthetic performance under future climate change. Herbarium-based multitrait approaches prove valuable for reconstructing long-term plant responses and climate sensitivity in tropical understorey species.

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