Embolism spreading varies depending on contrasting leaf vein networks and herbivory treatments

Background/Question/Methods

During drought, plant veins (xylem) risk forming air bubbles (embolisms), that can expand rapidly and block the transport of water and nutrients. Differences in venation patterns could represent variances of safety mechanisms for resource transport, resistance to damage, and mechanical support. Local spreading of embolisms could also occur when xylem-feeding insects damage veins. The presence of vein loops, however, may provide redundant pathways that allow water to continue to flow after damage from drought or herbivores. We asked (1) whether the distance and vulnerability of embolism spreading in response to (simulated) herbivory vary among species depending on their venation architecture, i.e. looping versus branching, and (2) how embolism spreading varied with vessel size. We simulated three herbivory treatments: control, and two groups where we punched a hole in the midrib vein or the lamina. We chose two tree species with contrasting vein patterns, Combretum erythrofyllum with branched veins (pinnate) and Acer rubrum with looping veins (palmate). We used the “Optical Vulnerability Method” to reveal how embolisms traveled throughout the veins of sampled leaves. We used FIJI to analyze the leaf scans to detect embolism events. We also created maps that depict how embolisms traveled throughout the veins over time.

Results/Conclusions

We found differences between the treatments. The lamina treatment of both species showed similar patterns of embolizing later than the other treatments, with a steeper slope representing rapid spread of the embolism. The Combretum embolized later in time than Acer and reached 100% cavitated pixels quicker. We found a similar path of embolized veins between the treatments and species, with the midrib embolizing first, then secondary, then tertiary. Tertiary veins embolizing after the midrib and primary veins suggests that the veins were not completely blocked from water transporting through throughout the leaf. These results indicate the two species’ leaves responded differently to our herbivory treatments, indicating possible variances in resistance to damage and transport of water and nutrients.