Quantifying succulence: a rapid, physiologically meaningful metric of plant water storage

Abstract

Quantification of succulence should ideally convey information about physiological function and yet also be straightforward to measure. While important aspects of succulence and its physiological consequences may be quantified using parameters derived from pressure-volume (P-V) curves, this technique applied to succulent tissues is difficult, time consuming and generally not suitable for large comparative datasets. We performed P-V curves on leaves of 25 taxa from across Caryophyllales and compared the results with direct measures of saturated water content (SWCmeas), the ratio of water mass at full saturation to tissue dry mass, for the same taxa. SWCmeas was significantly related to relative capacitance, the most physiologically relevant parameter describing tissue succulence. We developed a linear model describing SWCmeas as a function of relative capacitance and leaf volume, which is also supported when accounting for the phylogenetic relationships among taxa. These results indicate that SWCmeas is a suitable proxy for tissue succulence, and that both cellular properties and variation in gross morphology contribute towards a plant's relative water storage capacity. Quantifying SWCmeas across many taxa showing variation in tissue succulence will provide a new avenue for exploring the evolutionary dynamics of this important ecological adaptation.

Making the best of the worst of times: traits underlying combined shade and drought tolerance of Ruscus aculeatus and Ruscus microglossum (Asparagaceae)

“…The 'succulence' of Ruscus phylloclades is distinctive relative to more typical succulent-leafed and succulent-stemmed species, which tend to have high leaf water content and capacitance values (Vendramini et al 2002;Ogburn and Edwards 2012). In contrast, in Ruscus species, the SWC was low relative to typical leaf succulent species, and for R. aculeatus, C ft fell within the range of typical evergreen leaves.…”

“…if only these were available. Sources of comparative data: leaf area ; LMA (Wright et al 2004); density (Niinemets 1999); LDMC (Vile 2005); and SWC (Vendramini et al 2002;Ogburn and Edwards 2012) …”

“…separation of mesophyll cell and water storage in space and their distinctions in anatomy) would contribute to high effectiveness of water storage, even if the bulk tissue overall had low SWC and capacitance. Indeed, across species there tends to be no relationship between the magnitude of SWC or capacitance and the degree of within-leaf tissue differentiation (Ogburn and Edwards 2012). Notably, such differentiation would contribute special advantages for supply of water, whether stomata are open or closed, as the large, thin-walled water storage cells with low solute concentration can yield their water to supply the evaporative load, while the photosynthetic tissues can maintain their volume according to their thicker walls and stronger solute concentration.…”

“…Such traits include a high water-use efficiency (Wright and Westoby 2003), as well as water storage tissue with high water storage capacitance associated with low bulk leaf modulus of elasticity, high relative water content at turgor loss point, and low cuticular conductance (Sack et al 2003a;Pasquet-Kok et al 2010;Ogburn and Edwards 2012). Traits potentially contributing to shade tolerance include low rates of maximum photosynthetic CO 2 assimilation per leaf area and per leaf mass, low light compensation point, low maximum rate of carboxylation, low maximum rate of electron transport, and more negative carbon isotope ratios (Walters and Reich 1999).…”

The Western Spring Beauties, Claytonia lanceolata (Montiaceae): A Review and Revised Taxonomy For California

“…Second and more substantially, the succulent nature of Claytonia poses a challenge to preserving diagnostic morphological characteristics in this group. Claytonia plants have relatively high saturated water content (Ogburn and Edwards 2012) which causes specimens to wilt quickly following removal from the ground. The fluids in Claytonia tissues cause newspaper and blotters used for collecting to stick to the plants, obliterating many morphological features during the drying process (T. Stoughton pers.…”