Abstract
Water inside plants forms a continuous chain from water in soils to the
water evaporating from leaf surfaces. Failures in this chain result in
reduced transpiration and photosynthesis and these failures are caused
by soil drying and/or cavitation-induced xylem embolism. Xylem embolism
and plant hydraulic failure share a number of analogies to “catastrophe
theory” in dynamical systems. These catastrophes are often represented
in the physiological and ecological literature as tipping points or
alternative stable states when control variables exogenous (e.g. soil
water potential) or endogenous (e.g. leaf water potential) to the plant
are allowed to slowly vary. Here, plant hydraulics viewed from the
perspective of catastrophes at multiple spatial scales is considered
with attention to bubble expansion (i.e. cavitation), organ-scale
vulnerability to embolism, and whole-plant biomass as a proxy for
transpiration and hydraulic function. The hydraulic safety-efficiency
tradeoff, hydraulic segmentation and maximum plant transpiration are
examined using this framework. Underlying mechanisms for hydraulic
failure at very fine scales such as pit membranes, intermediate scales
such as xylem network properties and at larger scales such as soil-tree
hydraulic pathways are discussed. Lacunarity areas in plant hydraulics
are also flagged where progress is urgently needed.