Young leaf protection in the shrub Leea glabra in south-west China: the role of extrafloral nectaries and ants

Field experiments on Leea glabra in its natural forest habitat of southern Yunnan, China were conducted to study the effects of artificial damage of young and old leaves on extrafloral nectaries (EFNs) secretion quantity and sugar concentration, as well as the effects on ant abundance on the plants following the damage treatments. We found there were no rapid changes in extrafloral nectar volume or nectar sugar concentration which would indicate an induced reaction following artificial damage. However, both cutting and punching of young leaves resulted in a significant increase (2–4-fold) of ants within 6 h after damage compared to undamaged controls. In another experiment, disks of fresh young L. glabra leaves that were pinned on young leaves of another L.glabra plant also resulted in a significant increase in the number of ants compared to treatment with paper disks, indicating that ants were most probably attracted by volatile organic compounds (VOCs) released from damaged young leaves. Furthermore, we found that portion of damaged leaf area of young leaves was significantly lower than that of old leaves and the concentration of tannins was significantly higher in young than in medium and old leaves. In conclusion, our results show that young leaves of L. glabra are protected against attacks by herbivores by multiple mechanisms, which include: (1) the activity of EFNs, which attract different ant species from the surrounding ground; (2) a mechanism induced by the damage of young leaves, which leads to rapidly increased ant recruitment and is most probably caused by the release of volatiles from damaged leaf and (3) a higher allocation of tannins in young than in older leaves.