Effects of seed source on seedling performance of Elymus multisetus (big squirreltail) in the Great Basin.

摘要

Widespread invasion by Bromus tectorum L. (cheatgrass) has drastically altered native plant communities in the Great Basin. Certain native perennials grasses appear to be more tolerant of cheatgrass invasion and are therefore considered promising species for restoration in cheatgrass-invaded areas, including big squirreltail (Elymus multisetus M.E. Jones). Native populations may also be evolving in response to cheatgrass invasion. Genetic studies have shown high levels of inter- and intra-population genetic variation for grass species native to the Great Basin, but there is still a large knowledge gap in how this genetic variation can impact and be impacted by restoration. The goal of this research was to investigate the effect of seed source on restoration seedling performance in the Great Basin using Elymus multisetus as a case study, addressing the following questions: Can seeds from local-wild sources establish with greater success than those from regional-farmed sources? Are squirreltail seedlings from cheatgrass invaded sources more competitive than seedlings from uninvaded sources? Is it possible to identify growth traits that are advantageous for seedlings in cheatgrass invaded areas?;To answer these questions we conducted two separate common garden experiments. Differences that persist in a common garden likely have a genetic basis and can evolve via natural selection. Our first experiment investigated the effect of seed source on field establishment of big squirreltail by comparing seedling performance of locally-collected seed and commercially-produced seed from Oregon, Idaho, and California at a recently-burned site on the Hallelujah Junction Wildlife Refuge, Bordertown, CA. Several phenological and growth traits varied significantly between source populations. Eighty-six percent of local seeds emerged, compared to 71%, 61% and 12% of seeds from Idaho, Oregon, and California, respectively. Local seeds emerged nine days earlier than other seeds sources on average. Through the first year, 7.6% of the local seedlings survived, followed by 5.2%, 4.8%, and 0.6% survival of Idaho, Oregon, and California seedlings, respectively. Though survivorship was highest for local seed, local seedlings produced 24% fewer leaves than the most productive seedlings from the Idaho seed source. These data would suggest that seed source is an important factor in seedling establishment and performance. If local seed can survive significantly better than regionally farmed seed, it may be both economically and ecologically beneficial to use seeds collected from relatively local sources in revegetation.;To examine the potential effect of cheatgrass invasion on the evolution of adaptive traits, our second experiment was conducted in a greenhouse and involved destructive harvesting of big squirreltail seedlings from invaded and uninvaded areas in order to measure both root and shoot growth traits. We determined if growth traits of plants from invaded areas displayed shifts consistent with evolution in response to cheatgrass invasion, measured genetic variation of potentially adaptive traits, and used a correlative approach to identify traits that may confer an advantage to native plants growing in cheatgrass invaded areas. Seedlings from invaded areas exhibited greater tolerance of competition and a greater ability to suppress cheatgrass than seedlings from adjacent uninvaded areas. Competitive ability was correlated with 10 day root:shoot ratio, root forks, and fine root length, but only 10 day root forks appear to be inherited and none have significantly shifted across invasion status. Additionally, we surveyed traits that varied between invaded and uninvaded areas. Invaded plants were smaller, allocated more biomass to roots, and produced a higher percentage of fine roots. Root traits, including early root growth, may be an important component of competitive ability in Elymus multisetus. The ability of native populations to evolve in response to invasion has significant implications for management and restoration of cheatgrass-invaded communities.