PS 81-210
Global analysis of plasticity in turgor loss point, a key drought tolerance trait

Friday, August 15, 2014
Exhibit Hall, Sacramento Convention Center
Megan K. Bartlett, Ecology and Evolutionary Biology, Princeton University, Princeton, NJ
Ya Zhang, Xishuangbanna Tropical Botanical Gardens, China
Nissa Kreidler, Ecology and Evolutionary Biology Department, UCLA, Los Angeles, CA
Shanwen Sun, Xishuangbanna Tropical Botanical Garden, China
Rico Ardy, Ecology and Evolutionary Biology Department, UCLA, Los Angeles, CA
Kunfang Cao, Xishuangbanna Tropical Botanical Garden, Key Laboratory of Tropical Forest Ecology, Menglun, China
Lawren Sack, Ecology and Evolutionary Biology, UCLA, Los Angeles, CA
Background/Question/Methods

Many plant species face increasing drought under climate change. Plasticity in key physiology traits is expected to strongly influence species responses by widening their range of tolerable conditions. During drought, plants are well known to shift their turgor loss or “wilting” point (πtlp), by accumulating solutes in their leaf cells (i.e., “osmotic adjustment”), which allows plants to maintain gas exchange and photosynthesis under drier soil conditions. Plants also show shifts in their cell hydration at wilting point (RWCtlp), and the relative importance of πtlp and RWCtlp to drought tolerance has long been debated in the literature. Although plasticity in these traits (Δπtlp and ΔRWCtlp) has itself been considered a key drought tolerance trait for decades, there has been no synthesis of the importance of this plasticity to drought tolerance across species and ecosystems. We compiled a novel global database of seasonal changes in πtlp and RWCtlp for 283 species to address the following questions: 

1) For droughted plants, is the primary determinant of πtlp and RWCtlp the pre-drought values, or the plastic shift during drought?

2) How does plasticity in these traits vary across ecosystems, especially relative to ecosystem water supply?

3) Do crop species exhibit greater plasticity than wild species?

Results/Conclusions

Plasticity in πtlp was widely prevalent but moderate on average (-0.45 MPa), accounting for 15.7% of post-drought πtlp. The pre-drought πtlp was also a considerably stronger predictor of post-drought πtlp than was Δπtlp across wild species (r2  = 0.62, 0.34, respectively, both p < 0.001). However, for cultivars of certain crop species, Δπtlp accounted for major differences in post-drought πtlp. Overall, Δπtlp did not account for a significantly greater proportion of post-drought πtlp in crop than wild species. Conversely, RWCtlp did not exhibit significant seasonal differences for wild species (t-test, p = 0.16), although RWCtlp did become significantly lower for crop species (p = 0.01). For wild species, significantly more variation in Δπtlp occurred among species within ecosystems than at the ecosystem levels of study sites or biomes, and Δπtlp was not significantly different among biomes. Drier sites and biomes contained species with significantly more negative shifts in πtlp, although wet and dry season πtlp were considerably more strongly correlated with climate than Δπtlp. Thus, annual measurements of πtlp provide a reasonable simplification for characterizing drought tolerance across diverse species and communities, whereas plasticity in πtlp makes a minor contribution to drought tolerance.