Factors controlling drought resistance in grapevine ( Vitis vinifera , chardonnay): application of a new micro CT method to assess functional embolism resistance

Premise Quantifying resistance to embolism in woody plants is important for understanding their drought response. Methods to accurately quantify resistance to embolism continue to be debated. Methods We used a new micro CT ‐based approach that quantifies embolized conduits and also analyzes conductive conduits by using an x‐ray‐dense, iodine‐rich tracer that moves though the vascular system and can easily be observed in micro CT images. Many previous micro CT studies assumed that all conduits were initially conductive, which may not be the case if there are developing or occluded conduits. We compared micro CT results to a standard benchtop dehydration method and a centrifuge method. During dehydration, we measured gas exchange and quantified water potential at mortality. Results Our micro CT curves agreed with previously published micro CT curves from the same greenhouse‐grown cultivar. We found a significant difference in embolism estimates if we assumed that all water‐filled conduits were functional rather than only those containing tracer. Embolism estimates from micro CT differed from both the benchtop and centrifuge methods. The benchtop and centrifuge methods did not differ from one another. Conclusions The new micro CT method presented here is valuable in sampling species that may contain nonconductive conduits. Disagreement between micro CT and two other methods was likely due to differences in the ways they quantify embolism. Micro CT assess the theoretical effect of embolism, whereas benchtop and centrifuge methods directly measure hydraulic conductivity. The theoretical approach does not fully account for the resistances of flow through a complex 3D vascular network.