A stage‐based study of drought response in Cryptantha flava (Boraginaceae): gas exchange, water use efficiency, and whole plant performance

Abstract

Models of global climate change predict an increase in the frequency of major droughts, yet we know little about the consequences of drought for the demography of natural populations. This study examined a population of the semi-desert perennial Cryptantha flava (Boraginaceae) to determine how plants of different developmental stages respond to drought through changes in leaf gas exchange, leaf water potential, water use efficiency, growth, and reproduction. In two of the four years, drought was applied using rainout shelters, and a severe natural drought occurred in another. Small, presumably younger, plants sometimes had lower rates of maximum photosynthesis, lower leaf water potentials, and lower instantaneous or integrated water-use efficiency than large plants. Small plants also had higher relative growth rates and lower reproductive effort. Large plants with evidence of shrinkage from a previously larger size often produced less growth and reproduction than large healthy plants, suggesting a decline in plant vigor with age. Drought depressed gas exchange and leaf water potentials equally in all plant stages. Thus, leaf-level physiological attributes provide no clues for why drought reduces growth more strongly in large plants. The results point to several additional avenues of research relevant to understanding stage-dependent or age-dependent plant performance under drought conditions.

Growth and essential oil yield of rose‐scented geranium (Pelargonium capitatum×P. radens‘Rose’) as affected by withholding irrigation at different times during regrowth

“…This probably resulted in slow plant growth (smaller LAI), and also hastened senescence of older leaves. in agreement with the current results, studies conducted on Cryptantha flava revealed that larger plants were more sensitive to drought stress than smaller plants (Casper et al 2006). …”

Carbon gain and hydraulic limits on water use differ between size classes of Larrea tridentata

“…Our data on gas exchange and twig growth suggest that small and large plants both responded to drought by limiting transpiration rates and reducing aboveground growth, as was also reported for Cryptantha flava (Casper et al, 2006). Reductions in canopy size in response to drought have been observed previously in L. tridentata growing near our field site (Allen et al, 2008).…”

“…2a and b) were observed in conjunction with elevated transpiration. Increased growth in association with higher rates of water use has also been reported in the woody desert shrub Chrysothamnus nauseosus (Donovan and Ehleringer, 1991, though this was not the case in the drought adapted species Cryptantha flava (Casper et al, 2006) for which higher transpiration rates in small plants did not translate into increased growth.…”

“…Higher transpiration rates and lower water use efficiency among small compared to large individuals has been observed in species as varied as annuals (Casper et al, 2006), arid-land shrubs (Brown and Archer, 1990;Ehleringer, 1991, 1992;Mediavilla and Escudero, 2004), and trees (reviewed in Ryan et al, 2006). Higher transpiration rates could allow small plants to maximize carbon uptake during brief pulses of water availability, favoring establishment (Cohen, 1970).…”

A demographic approach to study effects of climate change in desert plants

“…A recent comparative study has shown a positive correlation between individual plant shrinkage and survival [52], but the importance of this phenomenon for population dynamics has often been overlooked. Plant shrinkage or dieback of shrub canopies is common during drought events [37,53,54], and negative size changes may occur over time even when severe drought is not apparent [31,39,55]. Sometimes the entire plant canopy dies, so dormant and dead plants are not immediately distinguishable [37].…”