Adaptive phenology of desert and Mediterranean populations of annual plants grown with and without water stress

Abstract

The dynamics of vegetative and reproductive growth were compared in matched pairs of Mediteranean and desert populations of three unrelated annual species, Erucaria hispanica (L.) Druce, Brachypodium distachyon (L.) Beauv. and Bromus fasciculatus C. Presl., under high and low levels of water availability in a common-environment experiment. Plants of all desert populations showed earlier switches to reproductive development and to subsequent phenophases, and the transition to flowering occurred at smaller plant sizes. Water stress had no effect (E. hispanica) or slightly accelerated the transition to flowering in B. fasciculatus (by 1-2 days) and in B. distachyon (by 4-6 days). Plant senescence was strongly enhanced by water stress, and this enhancement was greater in desert populations than in corresponding Mediterranean ones. Duration of life cycle was greatly shortened by water stress in all three species. Desert and Mediterranean populations of the three species exhibited small differences in their relative response, i.e. phenotypic plasticity, to water stress for phenological and plant size parameters. In E. hispanica and B. fasciculatus the population x water regime interaction amounted to less than 3% of total variance. By contrast, the Mediterranean population of B. distachyon was much more plastic in its response to water stress than the desert population in its transition to plant senescence. Plants from the desert populations appeared to be adapted to shorter, more compact growth cycles, culminating in earlier dates of seed maturation and plant senescence. In addition, they showed larger phenotypic plasticity in the transition to plant senescence, which trait was enhanced or magnified by sustained or repeated lack of water. By contrast, plants from Mediterranean populations delayed switchover from one phenophase to the next, seeming thus to "bet" on more water being forthcoming.

Introduction beyond a species range: a relationship between population origin, adaptive potential and plant performance

“…Increasing aridity leads to shortening of growing season, and populations from arid habitats were found to flower earlier than in more mesic sites in many annual and perennial species (Aronson et al, 1992;Bennington and McGraw, 1995;Del Pozo et al, 2002;Eckhart et al, 2004;Franke et al, 2006;Hall and Willis, 2006;Volis, 2007). Selection for advance of flowering was found in several studies with experimentally induced drought stress (Stanton et al, 2000;Volis et al, 2004;Franks et al, 2007) and in a reciprocal transplant experiment with one desert and one Mediterranean site (Volis et al, .…”

Reconstructing the Origin of Helianthus deserticola: Survival and Selection on the Desert Floor

“…Small leaves and early flowering are both characteristic of desert annuals and are thought to be of adaptive significance. In general, small leaves can reduce water loss and prevent heat stress while early flowering enables seed production before the onset of strong summer drought (Givnish 1979;Fox 1989;Aronson et al 1992Aronson et al , 1993Smith et al 1997;Gibson 1998). Both of these traits were negatively transgressive in a previous greenhouse study, implying strong genetic control (Rosenthal et al 2002).…”

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

“…Experiments of this nature are carried out either in the field or under common garden or greenhouse conditions, where water availability has been shown to affect integral elements of population dynamics. In particular, additional precipitation increases germination [63,64], biomass [10] and fecundity [64], while precipitation deficit leads to a shortened life cycle, expedited flowering [65] and higher reproductive effort [30]. However, multi-species experiments have shown that these responses are not ubiquitous and, often, coexisting species do not respond at all to changes in water availability [10,30].…”