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,...

1. 入侵物种的影响强度甚至方向可能随入侵年限而改变。随着种群数量增加、个体体型增大以及生态变化累积，其影响可能会增强。

2. 我们采用年代序列法，表征了金雀花（Cytisus scoparius）入侵后土壤影响随时间的演变特征——这是一种广泛分布的固氮灌木，被认为会限制造林成功。在温室实验中，我们评估了外生菌根真菌（ectomycorrhizal fungi）丰度、花旗松（Douglas-fir）生长表现及叶片氮含量在3-31年入侵年代序列中的变化情况。每个年代序列样地均为造林失败且已被C. scoparius入侵的皆伐迹地。为了区分入侵本身与伴随干扰（即砍伐森林）的贡献，我们在每个年代序列样地中均纳入了入侵斑块和未入侵斑块的土壤样本。在一项补充性土壤调理实验中，...