Grupo de Ecología de Invasiones, INIBIOMA, CONICET, Universidad Nacional del Comahue, Quintral 1250, San Carlos de Bariloche, CP 8400, Argentina.
Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington, Vermont, 05405, USA.
Ecology. 2020 May;101(5):e02997. doi: 10.1002/ecy.2997. Epub 2020 Mar 11.
Why some species become invasive while others do not remains an elusive question. It has been proposed that invasive species should depend less on mutualisms, because their spread would then be less constrained by the availability of mutualistic partners. We tested this idea with the genus Pinus, whose degree of invasiveness is known at the species level (being highly and negatively correlated with seed size), and which forms obligate mutualistic associations with ectomycorrhizal fungi (EMF). Mycorrhizal dependence is defined as the degree to which a plant needs the mycorrhizal fungi to show the maximum growth. In this regard, we use plant growth response to mycorrhizal fungi as a proxy for mycorrhizal dependence. We assessed the responsiveness of Pinus species to EMF using 1,206 contrasts published on 34 species, and matched these data with data on Pinus species invasiveness. Surprisingly, we found that species that are more invasive depend more on mutualisms (EMF). Seedling growth of species with smaller seeds benefited more from mutualisms, indicating a higher dependence. A higher reliance on EMF could be part of a strategy in which small-seeded species produce more seeds that can disperse further, and these species are likely to establish only if facilitated by mycorrhizal fungi. On the contrary, big-seeded species showed a lower dependence on EMF, which may be explained by their tolerance to stressful conditions during establishment. However, the limited dispersal of larger seeds may limit the spread of these species. We present strong evidence against a venerable belief in ecology that species that rely more on mutualisms are less prone to invade, and suggest that in certain circumstances greater reliance on mutualists can increase spread capacity.
为什么有些物种具有入侵性，而有些则没有，这仍然是一个难以捉摸的问题。有人提出，入侵物种应该较少依赖互惠共生关系，因为它们的传播就不会受到互惠共生伙伴的可用性的限制。我们用松属植物来检验这个想法，松属植物的入侵程度在种的水平上是已知的（与种子大小呈高度负相关），并且与外生菌根真菌（EMF）形成专性互利共生关系。菌根依赖性被定义为植物需要菌根真菌来表现出最大生长的程度。在这方面，我们将植物对菌根真菌的生长反应用作菌根依赖性的替代物。我们使用发表在 34 个物种上的 1,206 个对比来评估松属物种对 EMF 的响应性，并将这些数据与松属物种入侵性的数据相匹配。令人惊讶的是，我们发现更具入侵性的物种对互惠共生关系（EMF）的依赖程度更高。种子较小的物种的幼苗生长从互惠共生关系中获益更多，表明依赖性更高。对 EMF 的更高依赖可能是一种策略的一部分，即小种子物种产生更多可以更远传播的种子，并且这些物种只有在菌根真菌的帮助下才有可能建立。相反，大种子物种表现出对 EMF 的较低依赖，这可以用它们在建立过程中对压力条件的耐受性来解释。然而，较大种子的有限传播可能会限制这些物种的扩散。我们提供了有力的证据，反对生态学中一个古老的信念，即更多依赖互惠共生关系的物种不太可能入侵，并表明在某些情况下，对互惠共生者的更大依赖可以提高传播能力。
