Field testing a 13C labeling method in an East African ant-plant

Tree carbon allocation is a dynamic process that depends on the tree's environment, but we know relatively little about how biotic interactions influece 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 founational tree Acacia drepanolobium and its native ant defenders. Here we piloted a 13Carbon (C) pulse-labeling mathod to investigate the influece of these biotic interactions on C allocation strategies 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 13C 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 the 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.

Methods
Biological samples were collected at Ol Pejeta Conservancy by Grabriella Mizell, John Mosiany, and John Lemboi. Samples were analyzed for 13C content at the University of California, Davis Stable Isotope Facility.  Gabriella Mizell and Elizabth Pringle conducted data analyses at the University of Nevada, Reno. No other processing was done beyond transformations and manipulations outlined in the data files, R script, and associated article.