Data from: Below-ground processes control the success of an invasive seaweed

1. Whilst the successful establishment and spread of invasive species can
be determined by above ground processes, results are often equivocal.
Emergent research, mostly from terrestrial ecosystems, demonstrates that
below-ground processes (nutrient cycling, chemical properties) under
microbial control can mediate interactions between native and invasive
plants. Because microbes can control similar sediment properties in marine
ecosystem that influence plant fitness, we argue that below-ground
properties should also exert strong control interactions between native
and invasive marine macrophytes. 2. We coupled surveys of microbial
communities and chemistry of sediments collected from an invasive alga
(Caulerpa cylindracea), a native competitor (the seagrass Posidonia
oceanica) and unvegetated sediments with a large field experiment, in
which we manipulated the presence/absence of the canopies of both species
to determine the effects of above- and below-ground processes on the
success of C. cylindracea. 3. P. oceanica and C. cylindracea sediments
have microbial communities and predicted metabolic process that reflect
aerobic and anaerobic conditions, respectively. Moreover, the nutritional
quantity of organic matter was higher, but quality was lower in C.
cylindracea sediments compared to the two native habitats. The growth of
C. cylindracea fragments was equally low in the presence or absence of a
P. oceanica canopy, whereas the growth of C. cylindracea was higher in the
canopy removed vs. present treatment, possibly because, in the absence of
a C. cylindracea canopy, fragments are released from intra-specific
competition for resources. 4. Synthesis: Sediment/soil processes are
increasingly recognised as important drivers of the success and hence
impacts of invasive plants. We extended this theory to marine ecosystems
and suggest biotic resistance to invasion may not always be attributable
to intact canopies, but may also result from indirect effects of native
macrophytes on sediment quality and microbial processes. This information
may, in part, resolve why above-ground interactions don’t always explain
invasive plant success and thus can be used to develop better informed
management strategies.

1. 尽管入侵物种（invasive species）的成功定殖与扩散常可通过地上过程（above-ground processes）进行解析，但相关研究结论往往尚无定论。现有新兴研究多基于陆地生态系统，证实受微生物调控（microbial control）的地下过程——包括养分循环（nutrient cycling）与沉积物化学性质——可介导本土与入侵植物间的相互作用。鉴于微生物可在海洋生态系统（marine ecosystem）中调控类似的沉积物属性，进而影响植物适合度（plant fitness），我们认为地下属性同样可对本土与入侵大型海洋植物（marine macrophytes）间的相互作用产生强烈调控效应。2. 本研究将针对入侵藻类（Caulerpa cylindracea）、本土竞争者波西多尼亚海草（Posidonia oceanica）及无植被沉积物（unvegetated sediments）的微生物群落与沉积物化学特征调查，与一项大型野外实验（field experiment）相结合：实验中我们操控两个物种的冠层（canopy）的有无，以明确地上与地下过程对圆柱鞘藻（C. cylindracea）入侵成功的影响。3. 波西多尼亚海草生境沉积物与圆柱鞘藻生境沉积物的微生物群落及预测代谢过程，分别对应好氧条件（aerobic conditions）与厌氧条件（anaerobic conditions）。此外，相较于两种本土生境，圆柱鞘藻生境沉积物中的有机质（organic matter）营养总量更高，但营养质量更低。在有无波西多尼亚海草冠层的处理中，圆柱鞘藻片段的生长速率均处于较低水平；而在移除冠层的处理组中，圆柱鞘藻的生长速率显著高于保留冠层组，这可能是因为当不存在圆柱鞘藻冠层时，片段可摆脱资源获取方面的种内竞争（intra-specific competition）。4. 综合与结论：沉积物/土壤过程作为入侵植物成功定殖及其生态影响的重要驱动因子，正日益受到学界认可。我们将这一理论拓展至海洋生态系统，并提出：对入侵的生物抗性（biotic resistance）并非总能归因于完整冠层，也可能源自本土大型海洋植物对沉积物质量及微生物过程的间接效应。该研究结果可部分解释为何地上相互作用并非总能阐释入侵植物的成功定殖，进而可为制定更具科学依据的管理策略提供支撑。