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，早已在特化的蚁栖植物共生（myrmecophytic symbioses）以及蚁巢周边土壤中生长的植物中被广泛证实。然而，在特化程度更低的蚁-植物互作——即蚂蚁在植物上觅食的各类兼性共生关系中，地上养分传递途径的作用却长期未被充分认知。
本研究通过室内实验，将织叶蚁（Oecophylla smaragdina）限定在小粒咖啡（Coffea arabica）幼苗的冠层范围内，排除了经由土壤层发生的蚂蚁-植物养分传递途径。实验中，先以15N标记的甘氨酸（15N-labelled glycine）饲喂织叶蚁，待其在幼苗上排泄粪便液滴后，检测发现相较于无蚁对照植株，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的叶片以及以塑料袋隔绝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，并在植株体内进行转运，这或许也解释了为何蚁植共生植株相较于对照植株，其地上/地下（鲜重）比更高。
综合分析表明，本研究揭示了一种此前未被报道的、蚂蚁来源养分的叶片吸收途径。若该机制具有普遍性，则绝大多数蚁-植物互作过程均涉及养分供给。蚂蚁通过叶面为植物施肥，或许是植物获得的一项重要且稳定的收益，这与学界早已认知、但波动程度可能更高的植食动物防护收益一同，推动了蚁-植物互利共生关系的演化。鉴于全球范围内蚂蚁觅食的植物冠层分布广泛，这一养分传递途径可能具有极高的生态学意义。