| Description |
Dischidia major, a succulent epiphyte abundant in the kerangas forests of . Malaysian Borneo, has evolved hollow, bulb-shaped ant leaves in which Philidris Shattuck and other ant species reside and deposit nitrogen-rich debris. The plants grow adventitious roots into the leaf cavities, presumably to absorb much-needed nutrients from this source. In addition, carbon dioxide respired by the ants may be absorbed through highly-concentrated stomata on the inner leaf surfaces. This enrichment of carbon may increase the plants' water use efficiency and alleviate drought stress. Ant associations may expand the realized niche of Dischidia by either enabling the species to invade hotter, drier habitats, or by proffering a competitive advantage over other epiphytic species. Although the mutualism between D. major and Philidris has been hypothesized for almost twenty years, no one has yet shown that the epiphytes actually receive a benefit from their ants; this was the purpose of our study. I used stable isotope techniques to trace the potential carbon path from Philidris to D. major. Because the carbon respired by ants is depleted in 13C, and ant-occupied leaves of D. major showed a significantly lower concentration of 13C than did vacant individuals growing under similar conditions, we concluded that Dischidia major is absorbing antrespired carbon. Models were developed to estimate the amount of antrespired carbon absorbed by each leaf studied and the internal C02 concentrations inside each leaf. I found that approximately 40% of leaf carbon originated from the ants, and air inside ant-occupied leaves could have contained almost twice as much carbon dioxide than the surrounding atmosphere. |
