Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon, USA.
Pacific Northwest Research Station, Corvallis Forestry Sciences Lab, USDA Forest Service, Corvallis, Oregon, USA.
Ecology. 2022 Jul;103(7):e3697. doi: 10.1002/ecy.3697. Epub 2022 May 11.
Plant communities are predicted to be more resistant to invasion if they are highly productive, harbor species with similar functional traits to invaders, or support species with high competitive potential. However, the strength of competition may decrease with increasing abiotic stress if species more heavily invest in traits that confer stress tolerance over competitive ability, potentially influencing community trait-resistance relationships. Recent research examining how community traits influence invasion resistance has been predominantly focused on single vegetation types, and results between studies are often conflicting. Few studies have evaluated the extent to which abiotic factors and community traits interact to influence invasion along vegetation gradients. Here, we use an in situ seed addition experiment to examine how above- and below-ground plant traits and vegetation type interact to influence community resistance to invasion by a recently introduced annual grass, Ventenata dubia, along a productivity gradient in eastern Oregon, USA. To measure invasion resistance, we evaluated V. dubia biomass in seeded subplots with varying trait compositions across three vegetation types situated along a productivity gradient: scab-flats (sparsely vegetated dwarf-shrublands), low sage-steppe, and ephemeral wet meadows. Trait-resistance relationships were highly context dependent. In wet meadows (the most productive sites), resistance to invasion increased with increasing resident biomass and as community weighted mean trait values for specific leaf area, fine-to-total root volume, and height become more similar to V. dubia's trait values, although these relationships were relatively weak. We did not find evidence that neighboring species influenced invasion resistance in less productive vegetation types, in contrast to our expectations that facilitative interactions may increase with decreasing productivity as posited by the stress-gradient hypothesis. Unlike V. dubia, which heavily invaded all three vegetation types, introduced species with similar trait values, including Bromus tectorum, were not abundant throughout the study area demonstrating V. dubia's unique ability to take advantage of available resources. Our results illustrate how community traits and site productivity interact to influence community resistance to invasion and highlight that communities with lower overall biomass and few functionally similar species to V. dubia may be at the greatest risk for invasion.
如果植物群落具有较高的生产力、容纳与入侵种具有相似功能特征的物种，或者支持具有高竞争潜力的物种，那么它们预计将更能抵抗入侵。然而，如果物种更多地投资于赋予其对竞争能力的胁迫耐受性的特征，那么随着非生物胁迫的增加，竞争的强度可能会降低，这可能会影响群落特征对抵抗能力的关系。最近研究群落特征如何影响入侵抵抗的研究主要集中在单一植被类型上，而且研究结果之间往往存在冲突。很少有研究评估非生物因素和群落特征在多大程度上相互作用，从而影响沿植被梯度的入侵。在这里，我们使用原地种子添加实验来研究地上和地下植物特征以及植被类型如何相互作用，以影响美国俄勒冈州东部生产力梯度上由新近引入的一年生草本植物 Ventenata dubia 引起的群落对入侵的抵抗能力。为了衡量入侵抵抗能力，我们在三个植被类型的三个生产力梯度上的变异性状组成的播种小区中评估了 V. dubia 的生物量：疤痕洼地（稀疏植被矮灌木草原）、低山艾草草原和短暂湿地草原。特征抵抗关系高度依赖于上下文。在湿地草原（生产力最高的地点），随着驻留生物量的增加和群落加权平均特征值的变化，即比叶面积、细根与总根体积比和高度变得越来越类似于 V. dubia 的特征值，入侵抵抗能力增加，尽管这些关系相对较弱。我们没有发现证据表明在生产力较低的植被类型中，相邻物种会影响入侵抵抗能力，这与我们的预期相反，根据胁迫梯度假说，随着生产力的降低，促进相互作用可能会增加。与在所有三种植被类型中大量入侵的 V. dubia 不同，具有相似特征值的引入种，包括 Bromus tectorum，在整个研究区域并不丰富，这表明 V. dubia 具有独特的利用可用资源的能力。我们的结果说明了群落特征和站点生产力如何相互作用以影响群落对入侵的抵抗能力，并强调了生物量总体较低且与 V. dubia 功能相似的物种较少的群落可能面临最大的入侵风险。
