Data from: N/P imbalance as a key driver for the invasion of oligothrophic dune systems by a woody legume

Oligotrophic ecosystems, previously considered to be more resilient to invasive plants, are now recognised to be highly vulnerable to invasions. In these systems, woody legumes show belowground ecosystem engineering characteristics that enable invasion, however, the underlying processes are not well understood. Using a Portuguese primary dune ecosystem as an oligotrophic model system, belowground biomass pools, turnover rates and stoichiometry of a native (Stauracanthus spectabilis) and an invasive legume (Acacia longifolia) were compared and related to changes in the foliage of the surrounding native (Corema album) vegetation. We hypothesized that the invasive legume requires less phosphorus per unit of biomass produced and exhibits an enhanced nutrient turnover compared to the native vegetation, which could drive invasion by inducing a systemic N/P imbalance. Compared with the native legumes, A. longifolia plants had larger canopies, higher SOM levels and lower tissue P concentrations. These attributes were strongly related to legume influence as measured by increased foliar N content and less depleted δ15N signatures in the surrounding C. album vegetation. Furthermore, higher root N concentration and increased nutrient turnover in the rhizosphere of the invader were associated with depleted foliar P in C. album. Our results emphasize that while A. longifolia itself maintains an efficient phosphorus use in biomass production, at the same time it exerts a strong impact on the N/P balance of the native system. Moreover, this study highlights the engineering of a belowground structure of roots and rhizosphere as a crucial driver for invasion, due to its central role in nutrient turnover. These findings provide new evidence that, under nutrient-limited conditions, considering co-limitation and nutrient cycling in oligotrophic systems is essential to understand the engineering character of invasive woody legumes.

寡营养生态系统（oligotrophic ecosystem）此前被学界认为对入侵植物具有更强的抗入侵能力，如今却被证实极易遭受生物入侵。在这类生态系统中，木本豆科植物具备可促进入侵发生的地下生态系统工程特性，但其背后的核心调控机制仍未得到充分阐明。本研究以葡萄牙原生沙丘生态系统作为寡营养模型系统，对比了本土豆科植物（Stauracanthus spectabilis）与入侵豆科植物（Acacia longifolia）的地下生物量库（belowground biomass pool）、养分周转速率（turnover rate）及化学计量比（stoichiometry），并将相关指标与周边原生植被（Corema album）的叶片特征变化进行关联分析。我们提出假说：相较于本土植被，入侵豆科植物每单位生物量合成所需的磷元素更少，且养分周转速率更高，这可能通过诱发系统性氮磷失衡来推动生物入侵进程。与本土豆科植物相比，长叶相思树（Acacia longifolia）具有更大的冠幅、更高的土壤有机质（Soil Organic Matter, SOM）含量以及更低的组织磷浓度。这些特征与豆科植物的调控效应显著相关，具体表现为周边Corema album植被的叶片氮含量升高，且其δ¹⁵N同位素特征的耗竭程度减弱。此外，入侵植物根际（rhizosphere）区域较高的根氮浓度与加速的养分周转过程，与Corema album植被叶片磷含量的耗竭显著相关。本研究结果表明，尽管长叶相思树自身在生物量合成过程中具备高效的磷利用策略，但同时也对本土生态系统的氮磷平衡产生了强烈干扰。此外，本研究强调，根系与根际的地下结构工程化作用，因其在养分周转中的核心地位，成为推动生物入侵的关键驱动因素。本研究结果为养分限制条件下的寡营养生态系统中，需同时考虑共同限制效应与养分循环过程，才能深入解析入侵木本豆科植物的工程化特性，提供了新的实证依据。