Local climate adaptations in two ubiquitous Mojave Desert shrub species, Ambrosia dumosa and Larrea tridentata

Abstract

1. Widely distributed species are often locally adapted to climate gradients across their ranges. But little is known about the patterns of intraspecific adaptation in desert shrubs.2. We examined the questions of local adaptation in multiple populations of two common shrub species of the winter-wet Mojave Desert in North America in a multiple common garden experiment. Plants were raised in the greenhouse and transplanted at the age of 1 year. Ambrosia dumosa is a drought-deciduous low shrub and Larrea tridentata is an exceptionally long-lived evergreen. Over 4 years, we monitored growth, survivorship, leaf and reproductive cover and once measured leaf N content, δ 13 C and SLA. We hypothesized that populations of both species would be differentiated along a growth-survivorship trade-off according to homesite aridity.3. Both species exhibited previously undocumented population differences along gradients of winter precipitation and temperature. In general, populations from more winter-mesic regions had faster growth in more mesic gardens and lower survivorship in the most arid garden. Homesites with more variable summer precipitation had greater growth for A. dumosa populations, but lower growth for L. tridentata. Among L. tridentata populations, leaf cover correlated positively with growth and negatively with survival time. For A. dumosa populations, growth and survival could not be attributed to specific traits across gardens. However, larger transplants had generally lower growth rates and higher survival rates across gardens, except in the driest garden, where the population averages of intrinsic water use efficiency (iWUE) and stem growth rate were positively correlated. Synthesis.Two dominant species of the Mojave Desert adapted locally to variation in winter and summer precipitation and temperature. They did so in different ways, suggesting that L. tridentata mitigated the risk of hydraulic failure, while A. dumosa optimized carbon assimilation for growth.

What common‐garden experiments tell us about climate responses in plants

“…All four studies report significant trait correlations with climate provenance, equivalent to scenarios B and D developed here (Figure 1). This is also consistent with re- In the three studies from seasonally dry biomes, drought survival decreased, and growth potential increased with precipitation provenance, although not across all species examined and not in all common gardens (Custer et al, 2021;Johnson et al, 2020;Ramirez-Valiente & Robledo-Arnuncio, 2021). The studies from the Mediterranean Basin…”

“…In common-garden experiments, regeneration traits are reported chiefly for annual plants and short-lived perennials, but long-lived, woody perennials also have highly specialized germination requirements (Bowers et al, 2004;Gutierrez & Meserve, 2003;Meyer & Pendleton, 2005). Unfortunately, the practice of transplanting greenhouse-grown yearlings into common gardens (to ensure uniform establishment) often eliminates early responses to climate (for further discussion, see Custer et al, 2021;Ramirez-Valiente & Robledo-Arnuncio, 2021).…”

“…The four experimental studies in this special feature all use climate regression approaches, three of them in addition to variance partitioning. Three studies come from biomes with seasonal drought and significant geographic aridity gradients: Mediterranean woodlands (Ramirez-Valiente & Robledo-Arnuncio, 2021), the Mojave Desert of North America (Custer et al, 2021) and the North American prairie (Johnson et al, 2020). One study reports on experiments in the boreal forest of Canada and focuses on temperature gradients (Guo et al, 2020).…”

“…Ramirez-Valiente & Robledo-Arnuncio) and the Mojave Desert(Custer et al, 2021) additionally identify minimal winter temperature as having effects on key trait sets. In the Mediterranean, the variable is related to freezing tolerance (Ramirez-Valiente & Robledo-Arnuncio, 2021); in the Mojave Desert, winter temperature and precipitation have similar effects on traits, possibly mediated through their joint positive effect on soil water storage.…”

Context‐dependent concordance between physiological divergence and phenotypic selection in sister taxa with contrasting phenology and mating systems

“…The study of phenotypic divergence between, and phenotypic selection within, closely related taxa provides the opportunity to detect the processes contributing to evolutionary diversification and trait evolution (Hall and Willis, 2006; Anderson and Gezon, 2015; Teixido et al, 2019; Custer et al, 2021). Phenotypic divergence may be generated not only by adaptive evolutionary responses to short‐term or sustained differences between populations in the direction of natural selection, but also by plastic responses of populations to temporary or longstanding environmental conditions (which may or may not be adaptive) (Lucek et al, 2014; Frank et al, 2017; Rajkov et al, 2018).…”