No evidence that modification of soil microbiota by woody invader facilitates subsequent invasion by herbaceous species

Abstract

en

Many terrestrial ecosystems are co-invaded by multiple exotic species. The “invasional meltdown” hypothesis predicts that an initial invasive species will facilitate secondary invasions. In the plant kingdom, the potential underlying mechanisms of this hypothesis may be that modification of the soil properties by the initial invaders benefits for the subsequent exotic species invasion. In this study, we analyzed the composition of soil microbial communities and soil chemical properties from sites invaded by woody Rhus typhina, as well as uninvaded sites, to assess the impact of R. typhina invasion. Furthermore, we conducted a greenhouse experiment with multiple native–invasive pairs of herbaceous species to test whether R. typhina invasion facilitates subsequent exotic herb invasion. Our results showed that R. typhina invasion significantly altered the composition of soil fungal communities, especially pathogenic, endophytic, and arbuscular mycorrhizal fungi. However, this change in microbial composition led to neither direction nor magnitude changes in negative plant–soil feedback effects on both native and invasive species. This indicates that initial R. typhina invasion does not facilitate subsequent herb invasion, which does not support the “invasional meltdown” hypothesis. Additionally, R. typhina invasion significantly decreased soil total nitrogen and organic carbon contents, which may explain the significantly lower biomass of herbaceous roots grown in invaded soils compared with uninvaded soils. Alternately, although invasive herb growth was significantly more inhibited by soil microbiota compared with native herb growth, such inhibition cannot completely eliminate the risk of exotic herb invasion because of their innate growth advantages. Therefore, microbial biocontrol agents for plant invasion management should be combined with another approach to suppress the innate growth advantages of exotic species.

外来入侵木本植物对土壤微生物群的改变并未促进外来草本植物入侵

zh

许多陆地生态系统正遭受到多种外来物种的共同入侵。“入侵崩溃”假说认为:一个外来种成功入侵之后, 会促进其他外来种后续的入侵, 进而放大入侵的危害。对植物入侵而言，这一假说的潜在机制可能是初始入侵者改变了土壤特征、特别是微生物群落组成，从而有利于后续的外来植物入侵。该研究收集了来自被外来木本植物火炬树(Rhus typhina)入侵及相邻的未被其入侵的生境的土壤样品，分析了土壤微生物群落组成与化学性质差异，并进一步通过一个多物种对的温室实验检验这些土壤性质的改变是否会促进外来草本植物的后续入侵。结果显示:火炬树入侵显著改变了土壤真菌群落的组成——特别是病原菌、内生菌和丛枝菌根真菌。土壤微生物的存在会同时抑制外来入侵植物与本地植物的生长，即存在负反馈效应。然而，这种土壤负反馈效应的方向与强度并未因为火炬树入侵引起的土壤微生物组成的变化而改变，暗示火炬树的成功入侵并不能促进外来草本植物的后续入侵，即研究结果不支持“入侵崩溃”假说。此外，火炬树入侵显著降低了土壤总氮和有机碳含量，因此在火炬树入侵生境土壤中生长的草本植物产生了更少的根系生物量。另外，不管是来自火炬树入侵生境还是邻近非入侵生境的土壤，其微生物的存在对外来草本植物生长的抑制效应显著强于本地草本植物。但是，这种不对称抑制效应并不能消除外来草本植物由于其先天的生长优势带来的入侵风险。因此，在使用微生物控制剂进行外来植物入侵防控时需考虑结合其他手段，进一步抑制外来入侵植物的先天生长优势。