Tree carbon allocation is a dynamic process that depends on the tree’s environment, but we know relatively little about how biotic interactions influence these dynamics. In central Kenya, the loss of vertebrate herbivores and the savanna’s invasion by the ant Pheidole megacephala are disrupting mutualisms between the foundational tree Acacia (Vachellia) drepanolobium and its native ant defenders. Here, we piloted a ¹³Carbon (C) pulse-labeling method to investigate the influence of these biotic interactions on C allocation to ant partners by adult trees in situ. Trees withstood experimental conditions and took up sufficient labeled ¹³CO₂ for ¹³C to be detected in various C sinks, including ant mutualists. The δ¹³C in ants collected shortly after labeling suggested that trees exposed to herbivores allocated relatively more newly assimilated C to native ant defenders. Our results demonstrate the viability of the pulse-labeling method and suggest that C allocation to ant partners depends on the biotic context of the tree, but further investigation with replication is needed to characterize such differences in relation to invasion and herbivore loss.

树木碳分配是一个动态过程，取决于树木的环境，但我们对生物相互作用如何影响这些动态知之甚少。在肯尼亚中部，脊椎动物食草动物的消失以及大头蚁Pheidole megacephala的入侵，正在破坏基础树金合欢树( Vachellia ) drepanolobium与其本土蚂蚁防御者之间的共生关系。在这里，我们试行了¹³碳 (C) 脉冲标记方法，以研究这些生物相互作用对成年树原位向蚂蚁伙伴分配碳的影响。树木经受住了实验条件并吸收了足够的标记¹³ CO ₂ ¹³在各种碳汇中检测到碳，包括蚂蚁互利共生体。标记后不久收集的蚂蚁体内的δ ¹³ C 表明，暴露于食草动物的树木将相对更多新同化的 C 分配给本地蚂蚁防御者。我们的结果证明了脉冲标记方法的可行性，并表明对蚂蚁伙伴的碳分配取决于树的生物环境，但需要进一步的复制研究来表征与入侵和食草动物损失相关的这种差异。