Linking genetic variation in adaptive plant traits to climate in tetraploid and octoploid Basin Wildrye (Leymus cinereus (Scribn. & Merr.) A. Love) in the Western U.S.

Authors: Johnson, Richard; VANCE-BORLAND, KEN - The Conservation Planning Institute, Inc

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2016
Publication Date: 2/16/2016
Citation: Johnson, R.C., Vance-Borland, K. 2016. Linking genetic variation in adaptive plant traits to climate in tetraploid and octoploid Basin Wildrye (Leymus cinereus (Scribn. & Merr.) A. Love) in the Western U.S. PLoS One. 11(2):e0148982. https://doi.org/10.1371/journal.pone.0148982.
DOI: https://doi.org/10.1371/journal.pone.0148982

Interpretive Summary: A cycle of increasingly frequent fires and the spread of invasive weeds--aggravated by changing climate--is eroding the stability and functionality of rangeland plant communities in the intermountain Western U.S. Among the important rangeland species in the inter-mountain West is Basin wildrye, a large bunchgrass with an octoploid and tetraploid form. It is widely used for forage and cover by livestock and wildlife, and for soil stabilization, yet there are no studies of its genetic variation in relation to source climates, or guidelines for seed transfer of basin wildrye to ensure adaptation and genetic diversity during restoration. Research in common gardens revealed extensive genetic diversity in basin wildrye for plant adaptive traits among diverse wild populations of 57 octoploid and 52 tetraploid basin wildrye collected across the inter-mountain West. Octoploids had larger leaves, longer culms, and greater crown circumference than tetraploids but the numerical ranges of plant traits and their source climates overlapped between ploidy types. Consistent with drought escape mechanisms, earlier phenology in both ploidy types was associated with sources that had lower precipitation, more extreme high temperatures, higher moisture deficits, and lower relative humidity. Statistical models were developed that related genetic variation and source climates that combined both ploidy types. These were mapped using a geographic information system resulting in 15 seed zones to guide the choice of germplasm in restoration in the inter-mountain west. Of the 673258 km2 mapped, just three seed zones represented 58% of that area. The link between genetic variability and source climates suggested climate driven natural selection and evolution. We recommend the use of seed transfer zones to enhance basin wildrye adaptation and diversity for large scale restoration projects.

Technical Abstract: Basin wildrye (Leymus cinereus (Scribn. & Merr.) A. Love) is a large bunchgrass common in the intermountain Western U.S. with octoploid and tetraploid forms. In this study the interaction of adaptive plant traits with seed source climate is determined and seed movement guidelines developed for both ploidy types in the intermountain West. In common gardens at two sites over two years there were strong genetic differences in phenology, morphology, and production traits measured on diverse wild populations of 57 octoploid and 52 tetraploid basin wildrye (P<0.001). Octoploids had larger leaves, longer culms, and greater crown circumference than tetraploids but the numerical ranges of plant traits and their source climates overlapped between ploidy types. Consistent with drought escape mechanisms, earlier phenology in both ploidy types was associated with sources that had lower precipitation, more extreme high temperatures, higher moisture deficits, and lower relative humidity. In a single canonical correlation analysis using both ploidy types, 70% of the variation between plant traits and source climates was explained with the first two variates. Regression of canonical variates 1 and 2 with seed source climate variables produced models that explained 64% and 38% of the variation, respectively, and were used to map 15 seed zones covering 673258 km2. Three zones represented 58% of that area. Utilization of these seed zone will help ensure restoration with adaptive seed sources for both ploidy types. The link between genetic traits and seed source climates suggests climate driven natural selection and adaptive evolution in basin wildrye.