Trait dimensions of abiotic stress tolerance in woody plants of the Northern Hemisphere

Aim: Trade-offs among tolerances to different abiotic stressors limit polytolerance in woody plants. However, the general trait syndromes that underlie large-scale tolerance patterns of woody plants remain controversial. Here, we tested if the leading trait dimensions that define the global spectrum of plant form and function capture the underlying trait trade-offs limiting woody plant polytolerance.Location: Northern Hemisphere.Time Period: Present.Major Taxa Studied: Woody plants.Methods: We used a dataset of 779 species to link the trait dimensions defining the global spectrum of plant form and function with two dimensions summarizing tolerance syndromes to drought, shade, cold and waterlogging. Stress tolerance dimensions were a trade-off between drought and cold/waterlogging tolerance strategies, and a shade tolerance spectrum. Relationships among trait and stress tolerance dimensions were evaluated using general additive models separately for deciduous and evergreen angiosperms, and evergreen gymnosperms.Results: Drought-tolerant angiosperms showed greater specific stem density (SSD) and seed mass (SM), and lower specific leaf area (SLA) and leaf nitrogen content per mass (LN), compared to the cold/waterlogging-tolerant species. Shade-tolerant angiosperms displayed greater SSD and SM and lower SLA and LN compared to intolerant angiosperms. Highly contrasting trait adaptations also distinguished drought- (greater SSD, SM and lower SLA, LN) from shade-tolerant evergreen gymnosperms.Main Conclusions: The 'SSD-SM' and the 'SLA-LN' dimensions mainly distinguish cold or drought-tolerant woody angiosperms and shade- or drought-tolerant gymnosperms. Our results also support a conservative trait strategy for shade-tolerant compared to shade-intolerant species, with some differences between plant functional types probably due to contrasting leaf lifespans. Overall, our findings identify some leading functional constraints on polytolerance in woody plants and provide a framework to integrate additional trait dimensions to fully elucidate such constraints.