Patterns of population differentiation in early traits of development in Elymus glaucus

The role of intraspecific variation in plant species is an important component of plant community restoration. Despite its potential importance for restoration success, land managers and biologists often do not take this variation into account. However, prior studies demonstrate that distinct sub-populations adapted to a specific microhabitat often are observed in plant species. Although ecologists have known for decades that lack of adaptation to local conditions may interfere with the success of ecological restoration, there is a dearth of information about the occurrence and extent to which species commonly used in plant community restoration diverge among populations with respect to traits that may be adaptive. The objective of this study is to examine the degree to which Elymus glaucus, a California native bunchgrass widely used in restoration, exhibits population differentiation in early phenological traits. Two hypotheses were tested. The first hypothesis was that riparian and upland populations of E. glaucus exhibit local adaptation. The second hypothesis is that E. glaucus grown from local seed will outperform plants grown from commercial seed. To test these hypotheses, I compared time to germination, survival, growth rate, shoot length, root length, aboveground biomass and belowground biomass of local and commercial seed sources of E. glaucus under contrasting water regimes. Seeds of E. glaucus were collected from the Donald & Sylvia McLaughlin (McL) Natural Reserve in Lower Lake, CA from riparian and upland populations that are located ca. 6.25 miles apart. Commercial seeds were purchased from Hedgerow Farms in Winters, CA. A total of 180 seeds were used in the germination study, 60 from each of three sources: riparian, upland and commercial. Seeds were germinated on germination paper under moist conditions and time to germination was monitored daily for 3 months. Germinants were transferred to Cone-tainers filled with ca. 164 mL of soil collected from the McL reserve. Seedlings from each source type were randomly assigned to one of three watering regimes: high, medium, and dry. To estimate plant growth rate, the length of the tallest blade in each culm was measured weekly. Seedlings were harvested at four weeks, at which time seedling dry mass, root length and shoot length were recorded. Although no evidence of local adaptation was observed, results indicated population differentiation with respect to seed germination and shoot growth. Time to germination was significantly shorter for upland seeds compared to riparian or commercial seeds. In addition, the rate of shoot growth for upland plants was significantly higher than for riparian or commercial plants. Differences in germination and growth between seed sources indicate a potential intraspecific pattern of population divergence in early phenological stages of this plant species. Understanding patterns of plant population differentiation and its influence on early establishment of E. glaucus provides restoration ecologists and practitioners with information necessary to develop better seed sourcing strategies that may lead to more successful restoration efforts.