Ecotypic variation in Elymus elymoides productivity and drought resistance traits across the western United States

Introduction: Understanding local adaptation to climate is critical for
managing ecosystems in the face of climate change. While there have been
many provenance studies in trees, less is known about local adaptation in
herbaceous species, including the perennial grasses that dominate arid and
semiarid rangeland ecosystems. Methods and Results: We used a
common-garden study to quantify variation in growth and drought-resistance
traits in 99 populations of Elymus elymoides from a broad geographic and
climatic range in the western United States. Ecotypes from drier sites
produced less biomass and smaller seeds, and had traits associated with
greater drought resistance: small leaves with low osmotic potential and
high integrated water use efficiency (δ13C). Seasonality also influenced
plant traits. Plants from regions with relatively warm, wet summers had
large seeds, large leaves, and low δ13C. Irrespective of climate, we also
observed tradeoffs between biomass production and drought resistance
traits. Discussion: Together, these results suggest that much of the
phenotypic variation among E. elymoides ecotypes represents local
adaptation to differences in the amount and timing of water availability.
In addition, ecotypes that grow rapidly may be less able to persist under
dry conditions. Land managers may be able to use this variation to improve
restoration success by seeding ecotypes with multiple drought resistance
traits in areas with lower precipitation. The future success of this
common rangeland species will likely depend on the use of tools such as
seed transfer zones to match local variation in growth and drought
resistance to predicted climatic conditions.