Leaf wounding or simulated herbivory in young N. attenuata plants reduces carbon delivery to roots and root tips

Main conclusion: InNicotiana attenuataseedlings, simulated herbivory by the specialistManduca sextadecreases root growth and partitioning of recent photoassimilates to roots in contrast to increased partitioning reported for older plants.

Root elongation rate in Nicotiana attenuata has been shown to decrease after leaf herbivory, despite reports of an increased proportion of recently mobilized photoassimilate being delivered towards the root system in many species after similar treatments. To study this apparent contradiction, we measured the distribution of recent photoassimilate within root tissues after wounding or simulated herbivory of N. attenuata leaves. We found no contradiction: herbivory reduced carbon delivery to root tips. However, the speed of phloem transport in both shoot and root, and the delivery of recently assimilated carbon to the entire root system, declined after wounding or simulated herbivory, in contrast with the often-reported increase in root partitioning. We conclude that the herbivory response in N. attenuata seedlings is to favor the shoot and not bunker carbon in the root system.