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Title: Polyploidy enhances the occupation of heterogeneous environments through hydraulic related trade-offs in Atriplex canescens (Chenopodiaceae)

item HAO, GUANG-YOU - Harvard University
item Lucero, Mary
item SANDERSON, STEWART - Us Forest Service (FS)
item ZACHARIAS, ELIZABETH - Harvard University
item HOLBROOK, N. MICHELE - Harvard University

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2012
Publication Date: 1/15/2013
Citation: Hao, G., Lucero, M.E., Sanderson, S.C., Zacharias, E.H., Holbrook, N. 2013. Polyploidy enhances the occupation of heterogeneous environments through hydraulic related trade-offs in Atriplex canescens (Chenopodiaceae). New Phytologist. 197:970-978.

Interpretive Summary: Introductions of shrub species carried out for arid land restoration are most likely to succeed when efforts are made to match the heterogeneity of the targeted environment with appropriate variants of the introduced shrubs. This requires knowledge of how intraspecies variations in factors such as ploidy level influence plant adaptation to environmental variants such as soil type or exposure to drought. In this study, plant ecophysiological traits related to water use and drought tolerance were examined in diploid, tetraploid and hexaploid cytotypes of fourwing saltbush (Atriplex canescens) to explore the relationship between ploidy level and environmental adaptation. Diploid cytotypes exhibited the highest hydraulic conductivity and the lowest resistance to drought induced hydraulic failure, suggesting that these cytotypes are best adapted to the arid, sandy soils in which they are found, where they can rapidly access and utilize water which is only briefly available following precipitation events. The need to grow rapidly during short resulting growing seasons, in order to stablize soil and nutrient resources present in mobile sand dunes, may outweigh the risk of drought induced hydraulic failure to which diploids are most susceptible. Tetraploid cytotypes represent intermediate forms with characteristics suited to the widest array of habitats and soil types. Hexaploid cytotypes exhibited the lowest hydraulic conductivity and the greatest resistance to drought-induced hydraulic failure, making them the most drought tolerant cytotype examined. Hexaploids were found in bottomlands characterized by heavy clay soils, where the need to adapt to chronic drought stress is less compromised by the need for rapid growth to stabilize resource supplies (clay bottomland soils resist erosion and bind nutrients) or by the need to rapidly utilize available water (clay bottomland soils collect and absorb water, so less is lost to drainage).

Technical Abstract: Plant hydraulic characteristics were studied in diploid, tetraploid and hexaploid cytotypes of Atriplex canescens (Chenopodiaceae) to investigate the potential physiological mechanism underlying the intraspecific habitat differentiation among plants of different ploidy levels. Populations of A. canescens from different habitats of the Chihuahuan Desert (New Mexico, USA) were analyzed using flow cytometry to determine ploidy levels. Traits related to xylem water transport efficiency and safety against drought-induced hydraulic failure were measured in both stems and leaves. At the stem level, cytotypes of higher ploidy levels showed consistently lower leaf-specific hydraulic conductivity but greater resistance to drought-induced loss of hydraulic conductivity. At the leaf level, comparisons in hydraulics between cytotypes did not show a consistent pattern, but exhibited high plasticity to proximal environmental conditions related to soil water availability. The results suggest that there is a trade-off between stem hydraulic efficiency an safety across ploidy levels, which underlies the intraspecific niche differentiation among different cytotypes of A. canescens. Polyploidization is likely an important mechanism in adaptation to the environmental heterogeneity related to water availability, and variation in water-related physiology found in the present study suggests a fundamental basis for the coexistence of different cytotypes in desert environments.