Shrub Sciences Laboratory, Rocky Mountain Research Station, United States Department of Agriculture Forest Service, 735 North 500 East, Provo, UT, 84606, USA,
Oecologia. 2014 Apr;174(4):1401-13. doi: 10.1007/s00442-013-2868-4. Epub 2014 Jan 8.
Invasive plants exhibit both direct and indirect negative effects on recruitment of natives following invasion. We examined indirect effects of the invader Bromus tectorum (cheatgrass) on seed fates of two native grass species, Elymus elymoides and Pseudoroegneria spicata, by removing B. tectorum and by adding inoculum of the shared seed pathogen Pyrenophora semeniperda in factorial experiments at xeric and mesic field sites. We also included a supplemental watering treatment to increase emergence and also the potential for pathogen escape. We recorded emergence and survival of native seedlings and also determined the fate of unemerged seeds. At the xeric site, Pyrenophora-caused mortality was high (34%), and effects of other pathogens and failed emergence of germinants were smaller. Cheatgrass removal negatively affected both emergence (35 vs. 25%) and spring survival (69 vs. 42%). Pyrenophora-caused seed mortality increased with inoculum augmentation for both species (22 vs. 47% overall), but emergence was negatively impacted only for P. spicata (20 vs. 34%). At the mesic site, Pyrenophora-caused mortality was low (6%). Cheatgrass removal doubled emergence (26 vs. 14%). Seed mortality increased significantly with inoculum augmentation for P. spicata (12 vs. 5%) but not E. elymoides, while emergence was not significantly affected in either species. A large fraction of seeds produced germinants that failed to emerge (37%), while another large fraction (35%) was killed by other pathogens. We conclude that facilitation by cheatgrass at the xeric site but interference at the mesic site was probably mediated through litter effects that could be ameliorative or suppressive. Apparent competition between cheatgrass and native grasses could occur through Pyrenophora, especially in a xeric environment, but effects were weak or absent at emergence. This was probably because Pyrenophora attacks the same slow-germinating fraction that is subject to pre-emergence mortality from other causes, including attack by other pathogens such as Fusarium.
入侵植物对入侵后本地植物的繁殖具有直接和间接的负面影响。我们通过在干旱和湿润野外地点进行的去除 B. tectorum 和添加共享种子病原体 P. semeniperda 接种体的因子实验，研究了入侵物种 B. tectorum 对两种本地草种 Elymus elymoides 和 Pseudoroegneria spicata 的种子命运的间接影响。我们还包括补充浇水处理以增加萌发率和病原体逃逸的可能性。我们记录了本地幼苗的萌发和存活率，也确定了未萌发种子的命运。在干旱地点，由 P. 引起的死亡率很高（34%），而其他病原体的影响和发芽失败的可能性较小。去除 B. tectorum 对两种物种的萌发（35%对 25%）和春季存活率（69%对 42%）都有负面影响。P. 引起的种子死亡率随着接种体的增加而增加（两种物种总体上为 22%对 47%），但仅对 P. spicata 的萌发有负面影响（20%对 34%）。在湿润地点，由 P. 引起的死亡率较低（6%）。去除 B. tectorum 使萌发率增加一倍（26%对 14%）。P. spicata 的种子死亡率随着接种体的增加而显著增加（12%对 5%），但对 E. elymoides 没有显著影响，而在两种物种中，萌发率都没有受到显著影响。大量产生发芽幼苗的种子未能萌发（37%），而另一大部分（35%）被其他病原体杀死。我们得出结论，在干旱地点，B. tectorum 的促进作用和在湿润地点的干扰作用可能是通过凋落物的影响介导的，这种影响可能是缓解性的或抑制性的。B. tectorum 和本地草种之间的竞争可能通过 P. 发生，特别是在干旱环境中，但在萌发时影响较弱或不存在。这可能是因为 P. 攻击同一缓慢萌发的部分，这些部分容易受到其他原因引起的萌发前死亡率的影响，包括来自其他病原体如 Fusarium 的攻击。
