Catastrophic hydraulic failure and tipping points in plants

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 are caused by soil drying and/or cavitation-induced xylem embolism. Xylem embolism and plant hydraulic failure share several analogies to 'catastrophe theory' in dynamical systems. These catastrophes are often represented in the physiological and ecological literature as tipping points when control variables exogenous (e.g., soil water potential) or endogenous (e.g., leaf water potential) to the plant are allowed to vary on time scales much longer than time scales associated with cavitation events. Here, plant hydraulics viewed from the perspective of catastrophes at multiple spatial scales is considered with attention to bubble expansion within a xylem conduit, 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 fine scales such as pit membranes and cell-wall mechanics, intermediate scales such as xylem network properties and at larger scales such as soil-tree hydraulic pathways are discussed. Understudied areas in plant hydraulics are also flagged where progress is urgently needed.

Declining tree growth resilience mediates subsequent forest mortality in the US Mountain West

“…Processes include reduced hydraulic conductance and increased vulnerability to embolism, reduced carbon assimilation, and shifting C allocation away from resin and defense molecule production, which may compromise tree vulnerability to subsequent biotic and abiotic perturbations (McDowell, 2011; Raffa et al, 2008; Rissanen et al, 2020). At the forest scale, the processes that underlie loss of resilience likely destabilize the system and increase the likelihood that future perturbations may lead forests to transition to an alternate stable state (Hammond, 2020; Johnson et al, 2022).…”

Agrivoltaics in Color: Going From Light Spectra to Biomass

“…where n is a scaling exponent that depends on whether the plant is shade tolerant (the preferred crop type for AV) or not (see Figure 1), B o is a reference biomass for which L = L o is known and is usually set by the early seedling stage (set here at t = 0). With this representation, the VBE reduces to an autonomous first-order dynamical system given by (Johnson et al, 2022)…”

“…The primary one is to naively assume an allometric relation between B ( t ) and L ( t ) given by (Mrad et al., 2020; Niklas, 1994; Perry, 1984; Richards, 1959) $$$\frac{L}{{L}_{o}}={\left(\frac{B}{{B}_{o}}\right)}^{n},$$$ where n is a scaling exponent that depends on whether the plant is shade tolerant (the preferred crop type for AV) or not (see Figure 1), B o is a reference biomass for which L = L o is known and is usually set by the early seedling stage (set here at t = 0). With this representation, the VBE reduces to an autonomous first‐order dynamical system given by (Johnson et al., 2022) $$$\frac{dB}{dt}=F(B)={A}_{c}{P}_{g}{L}_{o}{\left(\frac{B}{{B}_{o}}\right)}^{n}-{k}_{m}B={k}_{m}B\left[\alpha {\left(\frac{B}{{B}_{o}}\right)}^{n-1}-1\right],\hspace*{.5em}\phantom{\rule{0ex}{0ex}}\alpha =\left(\frac{{L}_{o}}{{k}_{m}}\frac{{A}_{c}{P}_{g}}{{B}_{o}}\right).$$$ Von Bartalenffy labeled the first term describing F ( B ) as anabolism (biosynthesis potential) to allow for an n that differs from the commonly assumed 2/3 value (initially proposed by Galileo). The VBE also allows for supra‐exponential growth ( n > 1), which is at times observed in some systems such as cities (Bettencourt et al., 2007).…”

“…In fact, B e ,2 exhibits what is termed finite‐time singularity (Johansen & Sornette, 2001; Parolari et al., 2015; Von Foerster et al., 1960)—meaning it attains an infinite value in finite time. Thus, varying n leads to a so‐called transcritical bifurcation at the critical point n = 1 (Johnson et al., 2022; Strogatz, 1994). The time scale τ e associated with the attainment of B e ,2 can also be derived for n < 1 and is given by $${\tau }_{e}^{-1}=\left\vert {k}_{m}(n-1)\right\vert $$.…”

Effects of foliar and root silicon application on mitigating water deficit stress in young Eucalyptus urophylla plants

“…The effects of water de cit have been well documented (Li et al 2020;Misra et al 2020;Patmi et al 2020); they mainly affect cell elongation and division, inhibiting plant growth at different stages. This growth reduction is partly due to a decrease in stomatal conductance to prevent cavitation and hydraulic failure, leading to a sharp drop in transpiration and CO 2 assimilation (Johnson et al 2022). Water restriction can also affect the contents of photosynthetic pigments, soluble and storage carbohydrates, proteins, and amino acids (Patmi et al 2020), and negatively impact other photosynthetic traits, such as the quantum yield (F v /F 0 ) and the maximum quantum e ciency of photosystem II photochemistry (Tripathi et al 2015;Li et al 2020).…”