Data from: Foliar uptake of nitrogen from ant faecal droplets: an overlooked service to ant-plants

Nutrient supplies to plants from ants are well known from specialised myrmecophytic symbioses and from plants growing in soil close to ant nests. However, above-ground nutrient pathways may play a largely unrecognised role also in less specialised ant–plant interactions—the numerous facultative relationships, where ants forage on plants.
In a laboratory experiment, weaver ants (Oecophylla smaragdina) were confined to the canopies of coffee (Coffea arabica) seedlings, excluding any ant-to-plant transfer of nutrients via the soil strata. When ants were fed 15N-labelled glycine and subsequently deposited faecal droplets on the seedlings, coffee leaves showed increased levels of 15N and total nitrogen compared to control plants without ants. This was evident for both exposed leaves and leaves covered in plastic bags (i.e. not directly exposed to ants). Thus, nitrogen from ant excretions was absorbed through the coffee leaves, and subsequently, translocated within the plants and possibly leading to the observed higher shoot/root (wet weight) ratios observed on ant-plants compared to controls.
Synthesis. These results reveal an undescribed foliar uptake of ant-provided nutrients. If this is a general mechanism, a vast amount of ant–plant interactions involves fertilisation. Foliar fertilisation by ants may be an important steady benefit to plants, which has driven the evolution of ant–plant mutualisms in parallel with the well-recognised but probably more fluctuating benefit from herbivore protection. Given the world-wide abundance of plant canopies foraged by ants, this nutrient pathway may be of high ecological significance.

蚂蚁为植物提供养分的现象，早已在特化蚁生共生（myrmecophytic symbioses）体系，以及生长于蚁巢周边土壤的植物中得到广泛证实。然而，在特化程度更低的蚁植互作——即蚂蚁在植物上觅食的大量兼性共生关系——中，地上养分传递路径的作用却长期未被学界认知。

本研究通过室内控制实验，将织叶蚁（Oecophylla smaragdina）限定在阿拉伯咖啡（Coffea arabica）幼苗的冠层范围内，阻断了其通过土壤层向植物传递养分的可能路径。实验中，研究人员先为蚂蚁饲喂15N标记甘氨酸，待其在幼苗体表排泄粪便液滴后，检测发现相较于无蚁对照组，咖啡叶片的15N丰度与总氮含量均显著升高。这一现象在直接暴露于蚂蚁活动区域的叶片，以及用塑料袋密封（即未直接接触蚂蚁）的叶片中均有体现。由此可见，蚂蚁排泄物中的氮素可通过咖啡叶片被植物吸收，并在植株体内转运，这或许也解释了为何蚁植共生组的植株地上/地下（鲜重）比显著高于对照组。

综合分析：本研究结果揭示了一种此前未被报道的、植物通过叶面吸收蚂蚁来源养分的全新机制。若该机制具有普适性，则全球范围内大量蚁植互作体系均涉及养分补给过程。蚂蚁通过叶面为植物提供养分，可能是植物获得的一项稳定且重要的收益，这一收益与广为人知但波动幅度可能更大的植食动物防御收益共同推动了蚁植互利共生的演化。考虑到全球范围内蚂蚁觅食活动覆盖的植物冠层分布广泛，这种地上养分传递路径或许具有极高的生态意义。