Consequences of seed origin and biological invasion for early establishment of a North American grass species

Local, wild-collected seeds of native plants are recommended for use in ecological restoration to maintain patterns of adaptive variation. However, some environments are so drastically altered by exotic, invasive weeds that original environmental conditions may no longer exist. Under these circumstances, cultivated varieties selected for improved germination and vigor may have a competitive advantage at highly disturbed sites. This study investigated differences in early establishment and seedling performance between wild and cultivated seed sources of the native grass, Poa secunda, both with and without competition from the invasive exotic grass, Bromus tectorum. We measured seedling survival and above-ground biomass at two experimental sites in western Montana, and found that the source of seeds selected for restoration can influence establishment at the restoration site. Cultivars had an overall advantage when compared with local genotypes, supporting evidence of greater vigor among cultivated varieties of native species. This advantage, however, declined rapidly in the presence of B. tectorum and most accessions were not significantly different for growth and survival in competition plots. Only one cultivar had a consistent advantage despite a strong decline in its performance when competing with invasive plants. As a result, cultivated varieties did not meet expectations for greater establishment and persistence relative to local genotypes in the presence of invasive, exotic species. We recommend the use of representative local or regional wild seed sources in restoration to minimize commercial selection, and a mix of individual accessions (wild, or cultivated when necessary) in highly invaded settings to capture vigorous genotypes and increase the odds native plants will establish at restoration sites.

为维持适应性变异模式，生态修复工作推荐使用本地原生植物的野生采集种子。然而，部分生境已被外来入侵杂草彻底改变，原生环境条件或已不复存在。在此类情形下，为提升萌发率与生长活力选育的栽培品种，在受干扰程度极高的生境中或具备竞争优势。本研究针对原生禾草细早熟禾（Poa secunda）的野生与栽培种子源，在有无入侵外来禾草旱雀麦（Bromus tectorum）竞争的条件下，比较其早期定植与幼苗生长表现的差异。我们在蒙大拿州西部的两处试验站点测定了幼苗存活率与地上生物量，结果显示：用于修复项目的种子源会对修复位点的定植效果产生影响。相较于本地基因型，栽培品种整体表现更优，这印证了本土物种栽培品种具有更高活力的相关研究结论。但该优势在旱雀麦存在时会快速衰减，且在竞争样地中，多数种质的生长与存活率并无显著差异。仅有一种栽培品种在与入侵植物竞争时，尽管自身表现大幅下降，但仍保持了稳定的竞争优势。因此，在外来入侵植物存在的场景下，栽培品种相较于本地基因型并未展现出更优的定植与存续能力，未达到预期效果。我们建议在生态修复中采用具有代表性的本地或区域野生种子源，以降低商业选育带来的影响；在受入侵程度极高的区域，则可混合使用多种种质资源（野生种质，必要时辅以栽培种质），以筛选出高活力基因型，提升原生植物在修复位点的定植成功率。