Data from: Do impacts of an invasive nitrogen-fixing shrub on Douglas-fir and its ectomycorrhizal mutualism change over time following invasion?

1. Impacts of invasive species may change in magnitude and even direction with invasion age. Impacts could increase as the population increases, individuals grow in size, and ecological changes accumulate. 2. We used a chronosequence approach to characterize the development of soil impacts over time following the invasion of Cytisus scoparius, a widespread nitrogen-fixing shrub thought to limit reforestation success. In a greenhouse experiment, we evaluated how abundance of ectomycorrhizal fungi, Douglas-fir performance, and leaf nitrogen changed across a 3-31 year chronosequence of invasion. Each of the chronosequence sites were clearcuts where reforestation efforts were unsuccessful and where C. scoparius invaded. To estimate the contributions of the invasion separately from contributions of the accompanying disturbance, i.e. deforestation, we included soils from both invaded and uninvaded patches in each site of the chronosequence. In a complementary soil conditioning experiment, we examined the separate effects of host absence and invader presence on the mycorrhizal mutualism, leaf nitrogen, and seedling growth. 3. Ectomycorrhizal colonization was lower in invaded soil, but this effect did not intensify with time. Despite the suppression of the mutualism, Douglas-fir grew larger in invaded soils. This positive response is likely due to nitrogen fertilization, a conclusion supported by higher concentrations of leaf nitrogen of Douglas-fir grown in invaded soils. While leaf N concentration increased with invasion duration, Douglas-fir survival and growth did not. Synthesis. Our findings suggest that soil impacts of an invader can develop rapidly and can be surprisingly stable over time. In such systems, recently invaded areas may be as difficult to restore as long invaded areas, especially where ectomycorrhizal fungi are important drivers of reforestation success. More chronosequence studies or long time series are needed to evaluate whether this is a general pattern.1. 入侵物种的影响，其强度甚至方向都可能随入侵时长发生变化。随着入侵种群数量增加、个体体型增大以及生态变化不断累积，其影响效应可能会逐步增强。 2. 本研究采用年代序列法（chronosequence approach），以广泛分布的固氮灌木金雀花（Cytisus scoparius）为研究对象——该物种被认为会抑制造林成效，旨在刻画其入侵后土壤影响随时间的演变过程。在温室试验中，我们针对跨度3至31年的入侵年限序列，评估了外生菌根真菌（ectomycorrhizal fungi）丰度、花旗松（Douglas-fir）生长表现以及叶片氮含量的变化情况。所有年代序列样地均为造林失败且被金雀花入侵的皆伐迹地。为区分入侵本身的影响与伴随干扰（即森林砍伐（deforestation））的贡献，我们在每个年代序列样地中同时采集了入侵斑块与未入侵斑块的土壤样本。在补充性土壤驯化试验中，我们分别探究了宿主缺失与入侵者存在对菌根共生关系、叶片氮含量以及幼苗生长的独立影响。 3. 入侵土壤中的外生菌根定殖率更低，但该效应并未随时间推移而加剧。尽管共生关系受到抑制，生长在入侵土壤中的花旗松植株体型却更为高大。这种正向响应大概率源于氮素施肥效应，该结论得到了入侵土壤中培育的花旗松叶片氮浓度更高的支持。虽然叶片氮浓度随入侵时长增加而升高，但花旗松的存活率与生长量并未出现相应变化。 综合分析：本研究结果表明，入侵者对土壤的影响可快速形成，并在时间尺度上呈现出惊人的稳定性。在这类生态系统中，新近入侵区域与长期入侵区域的修复难度可能不相上下，尤其在外生菌根真菌是造林成效关键驱动因子的场景下。未来仍需开展更多年代序列研究或长期监测序列，以验证这一模式是否具有普遍性。