Abstract
Current vegetation modeling strategies use broad categorizations of plants to estimate transpiration and biomass functions. A significant source of model error stems from vegetation categorizations that are mostly taxonomical with no basis in plant hydraulic strategy and response to changing environmental conditions. Here, we compile hydraulic traits from 355 species around the world to determine trait covariations in order to represent hydraulic strategies. Simple and stepwise regression analyses demonstrate the interconnectedness of multiple vegetative hydraulic traits, specifically, traits defining hydraulic conductivity and vulnerability to embolism with wood density and isohydricity. Drought sensitivity is strongly (Adjusted R2 = 0.52, p < 0.02) predicted by a stepwise linear model combining rooting depth, wood density, and isohydricity. Drought tolerance increased with increasing wood density and anisohydric response, but with decreasing rooting depth. The unexpected response to rooting depth may be due to other tradeoffs within the hydraulic system. Rooting depth was able to be predicted from sapwood specific conductivity and the water potential at 50% loss of conductivity. Interestingly, the influences of biome or growth form do not increase the accuracy of the drought tolerance model and were able to be omitted. Multiple regression analysis revealed 3D trait spaces and tradeoff axes along which species’ hydraulic strategies can be analyzed. These numerical trait spaces can reduce the necessary input to and parameterization of plant hydraulics modules, while increasing the physical representativeness of such simulations.
Highlights
IntroductionFollowing Ackerly, et al [1] plant functional traits (‘traits’ from here onward) are defined as characteristics of a species or broader group of plants which have significant influence on performance at all stages of life: development, growth, and survival
The traits included in this study are biome classification, the unitless shape parameter of xylem vulnerability curve (a), conduit density, mean annual precipitation (MAP, mm), mean annual temperature (MAT, C), Ψ50 (MPa), drought tolerance, rooting depth (m), sapwood specific conductivity (Kmax, kg m−1 s−1 MPa−1 ), growth form, leaf permanence, wood density (g cm−3 ), and isohydricity (σ, as defined by Martinez-Vilalta, et al [58]) (Table 1)
Our results demonstrate the interconnectedness of multiple hydraulic traits, and traits surrounding hydraulic conductivity and vulnerability to embolism with wood density and isohydricity
Summary
Following Ackerly, et al [1] plant functional traits (‘traits’ from here onward) are defined as characteristics of a species or broader group of plants which have significant influence on performance at all stages of life: development, growth, and survival. Traits that have evolved within the lifespan of an individual are considered to be plastic responses to environmental conditions and are known as “plastic traits”. Innate traits that differentiate species or larger subdivisions of flora are hereditary and are considered to be “adaptive traits” [1]. Adaptations divide plant life into a host of Forests 2018, 9, 446; doi:10.3390/f9080446 www.mdpi.com/journal/forests. Forests 2018, 9, 446 different resource-use and survival categories. Plants adopt different survival strategies through suites of traits in which define how an individual responds to water, sunlight, nutrients and other stimuli
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