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The triangular space of abiotic stress tolerance in woody species: a unified trade-off model

Tolerance of abiotic stress in woody plants is known to be constrained by biological trade-offs between different forms of stress, shade and drought in particular. However, there is still considerable uncertainty about the relationship between tolerances, and the limits on tolerance combinations. Using the most extensive database available on tolerance of shade, drought, waterlogging and cold in woody species, we demonstrate that stress tolerance combinations can be summarized by two PCA dimensions defining a triangular stress tolerance space (STS). The first dimension reflects segregation between drought- and waterlogging-tolerant species. The second reflects shade tolerance, which is independent of the other tolerances. The shape of the STS was compared with theoretical surfaces generated from several prominent theories that assume different interdependence relationships between stress tolerances. This allowed us to define the limits of shade, drought, waterlogging and cold tolerance combinations across the 799 woody species in the database. The STS reconciles all major theories about trade-offs between abiotic stress tolerances. It provides a unified trade-off model and a set of coordinates that can be used to examine how other aspects of plant biology, such as plant functional traits, change within the limits of abiotic stress tolerance.