Plasticity of functional traits varies clinally along a rainfall gradient in Eucalyptus tricarpa.

Widespread species often occur across a range of climatic conditions, through a combination of local genetic adaptations and phenotypic plasticity. Species with greater phenotypic plasticity are likely to be better positioned to cope with rapid anthropogenic climate changes, while those displaying strong local adaptations might benefit from translocations to assist the movement of adaptive genes as the climate changes. Eucalyptus tricarpa occurs across a climatic gradient in south-eastern Australia, a region of increasing aridity, and we hypothesized that this species would display local adaptation to climate. We measured morphological and physiological traits reflecting climate responses in nine provenances from sites of 460 to 1040 mm annual rainfall, in their natural habitat and in common gardens near each end of the gradient. Local adaptation was evident in functional traits and differential growth rates in the common gardens. Some traits displayed complex combinations of plasticity and genetic divergence among provenances, including clinal variation in plasticity itself. Provenances from drier locations were more plastic in leaf thickness, whereas leaf size was more plastic in provenances from higher rainfall locations. Leaf density and stomatal physiology (as indicated by δ(13)C and δ(18)O) were highly and uniformly plastic. In addition to variation in mean trait values, genetic variation in trait plasticity may play a role in climate adaptation.

Wait or escape? Contrasting submergence tolerance strategies of Rorippa amphibia, Rorippa sylvestris and their hybrid.

BACKGROUND AND AIMS: Differential responses of closely related species to submergence can provide insight into the evolution and mechanisms of submergence tolerance. Several traits of two wetland species from habitats with contrasting flooding regimes, Rorippa amphibia and Rorippa sylvestris, as well as F(1) hybrid Rorippa × anceps were analysed to unravel mechanisms underlying submergence tolerance. METHODS: In the first submergence experiment (lasting 20 d) we analysed biomass, stem elongation and carbohydrate content. In the second submergence experiment (lasting 3 months) we analysed survival and the effect of re-establishment of air contact on biomass and carbohydrate content. In a separate experiment we analysed expression of two carbohydrate catabolism genes, ADH1 and SUS1, upon re-establishment of air contact following submergence. KEY RESULTS: All plants had low mortality even after 3 months of submergence. Rorippa sylvestris was characterized by 100 % survival and higher carbohydrate levels coupled with lower ADH1 gene expression as well as reduced growth compared with R. amphibia. Rorippa amphibia and the hybrid elongated their stems but this did not pay-off in higher survival when plants remained submerged. Only R. amphibia and the hybrid benefited in terms of increased biomass and carbohydrate accumulation upon re-establishing air contact. CONCLUSIONS: Results demonstrate contrasting 'escape' and 'quiescence' strategies between Rorippa species. Being a close relative of arabidopsis, Rorippa is an excellent model for future studies on the molecular mechanism(s) controlling these strategies.

Root hydraulic conductance and aquaporin abundance respond rapidly to partial root-zone drying events in a riparian Melaleuca species.

• Drying a portion of a root system (partial root-zone drying (PRD)) can induce partial stomatal closure, but this response is not always observed. We hypothesized that some of the variation in PRD response reflects adaptations to the native environment, where plants subjected to frequent PRD events may display a greater degree of root-level compensation. • Here, we examined PRD responses of Melaleuca argentea, a tree native to intermittent waterways in which PRD events are common. Seedlings were grown with part of their root system in soil and part in an aquatic compartment, mimicking conditions often observed in the field. • The aquatic roots initially provided two-thirds of total water uptake, but draining the aquatic compartment had no effect on stomatal conductance, so long as soil moisture remained c. 80% of field capacity. Water uptake from the soil compartment increased threefold within 24 h, with a corresponding transient threefold increase in root hydraulic conductance (L(p)), an increase in plasma membrane intrinsic protein 1 (PIP1) aquaporins at 24 h, and a decrease in PIP2 aquaporins by 48 h. • Our results demonstrate that PRD can induce rapid changes in L(p) and aquaporin expression in roots, which may play a role in short-term water uptake adjustments, particularly in species adapted to heterogeneous water availability.

Genomic Scans across Three Eucalypts Suggest that Adaptation to Aridity is a Genome-Wide Phenomenon.

Widespread species spanning strong environmental (e.g., climatic) gradients frequently display morphological and physiological adaptations to local conditions. Some adaptations are common to different species that occupy similar environments. However, the genomic architecture underlying such convergent traits may not be the same between species. Using genomic data from previous studies of three widespread eucalypt species that grow along rainfall gradients in southern Australia, our probabilistic approach provides evidence that adaptation to aridity is a genome-wide phenomenon, likely to involve multiple and diverse genes, gene families and regulatory regions that affect a multitude of complex genetic and biochemical processes.