Effects of experimental defoliation on resource allocation using integrated physiological units in the andromonoecious Camptotheca acuminata

• Defoliation of IPUs affected photosynthetic abilities of the remaining leaves.
• Defoliation had different influences on male and female reproductive traits.
• The effects of 100% defoliation were more significant than those of 50% defoliation.
• The secondary and tertiary capitulum positions suffered greater effects than those in the primary position.
• The reduction of available resources caused a trade-off between the male and female functions and resource limitation and architectural effects together determined the sex allocation of C. acuminata.

The resource allocation of individual plants is a relatively complex process. Trade-off exists between vegetative growth and reproduction, male and female characteristics in monoecious plant. Camptotheca acuminata Decne. (Nyssaceae) is a perennial woody plant that annually forms short shoots that contain an apex cyme consisting of four to six capitula and four to eight (usually six) alternate leaves. We regard these short shoots as integrated physiological units (IPUs). Three levels of defoliation treatments were applied to the IPUs: 100%, 50% and 0% (control). The results showed that in the primary capitula the male input (pollen production) decreased and the change of female function (pistil weight) was not statistically significant. In contrast, the secondary capitula exhibited a plastic shift toward maleness and stopped producing pistils but increased pollen production. Due to the inherent inflorescence structures and flowering time sequence of the cymes, the effects of defoliating different capitulum positions were diverse, and the secondary and tertiary capitula suffered greater effects than those in the primary position. Moreover, the effects of 100% defoliation were more significant than those of 50% defoliation. Furthermore, no new leaves were produced within the IPUs after defoliation, but the photosynthetic capacities of the remaining leaves were enhanced. The results of this study revealed that defoliation on IPUs had different impacts on the reproductive and vegetative traits, and caused a trade-off between male and female functions in C. acuminata. These findings indicated that defoliation on IPUs can help to explain sex allocation in the andromonoecious C. acuminata, and resource limitations further intensify intra-inflorescense sex allocation.