Background and aims

Plant-soil feedbacks may determine the long-term success of introduced species. Here we examined plant-soil feedbacks of a globally invasive shrub, Cytisus scoparius (hereafter Cytisus), which associates with multiple guilds of microbial mutualists and dominates harvested Douglas-fir forests in the Pacific Northwest.

Methods

We studied Cytisus root nodulation, mycorrhizal colonization, and growth in two greenhouse experiments. First, we compared invaded to uninvaded field soils. Then we did a soil conditioning experiment with Cytisus (in both invaded and uninvaded field soil) compared to soil conditioned by Douglas-fir.

Results

Cytisus grown in invaded soils had 67% more root nodules and 72% more AMF colonization than uninvaded soil. Conditioning uninvaded soil with Cytisus increased root nodules by 14% and mycorrhizal colonization by 55%, compared to Douglas-fir conditioned soil. Despite the increased abundance of mutualists, Cytisus grown in Cytisus-conditioned soils were 41% smaller than in uninvaded soil.

Conclusions

Cytisus increased the abundance of its microbial mutualists in soils, but overall plant-soil feedback was still negative, likely driven by soilborne pathogens, nutrient depletion, and/ or reduced benefits of mutualists. Our results do not support the idea that the high densities reached by Cytisus in its invaded range are caused by positive plant-soil feedbacks.

中文翻译：

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尽管增强了有益土壤微生物的数量，但广泛的固氮入侵者仍遭受负面的土壤反馈

背景和目标

植物土壤的反馈可能决定引入物种的长期成功。在这里，我们研究了一种全球侵入性灌木Cytisus scoparius（以下称Cytisus）的植物土壤反馈，该灌木与多种微生物互惠协会相关，并在西北太平洋地区以道格拉斯冷杉森林为主。

方法

我们在两个温室实验中研究了猕猴桃的根瘤，菌根定植和生长。首先，我们比较了入侵土壤和未入侵土壤。然后，我们与使用花旗松（Douglas-fir）处理过的土壤相比，对Cytisus（在入侵和未入侵的田间土壤中）进行了土壤处理实验。

结果

金雀儿属在侵入土壤上种植有更多的67％根瘤和72％以上AMF定植比未侵入土壤。与花旗松处理过的土壤相比，使用Cytisus处理未侵染的土壤可使根瘤增加14％，菌根定植增加55％。尽管共有人的数量增加了，但在经过Cytisus处理的土壤中生长的Cytisus比未侵染的土壤小41％。

结论

Cytisus增加了土壤中微生物共生体的丰度，但植物土壤的总体反馈仍然为负，这可能是由土壤传播的病原体，营养物质耗竭和/或共生体收益降低所驱动。我们的结果不支持这样的想法，即Cytisus在其入侵范围内达到的高密度是由植物土壤的积极反馈引起的。