Local adaptation of seed and seedling traits along a natural aridity gradient may both predict and constrain adaptive responses to climate change

Abstract

Premise: Variation in seed and seedling traits underlies how plants interact with their environment during establishment, a crucial life history stage. We quantified geneticbased variation in seed and seedling traits in populations of the annual plant Plantago patagonica across a natural aridity gradient, leveraging natural intraspecific variation to predict how populations might evolve in response to increasing aridity associated with climate change in the Southwestern U.S. Methods: We quantified seed size, seed size variation, germination timing, and specific leaf area in a greenhouse common garden, and related these traits to the climates of source populations. We then conducted a terminal drought experiment to determine which traits were most predictive of survival under early-season drought. Results: All traits showed evidence of clinal variation-seed size decreased, germination timing accelerated, and specific leaf area increased with increasing aridity. Populations with more variable historical precipitation regimes showed greater variation in seed size, suggestive of past selection shaping a diversified bet-hedging strategy mediated by seed size. Seedling height, achieved via larger seeds or earlier germination, was a significant predictor of survival under drought. Conclusions: We documented substantial interspecific trait variation as well as clinal variation in several important seed and seedling traits, yet these slopes were often opposite to predictions for how individual traits might confer drought tolerance. This work shows that plant populations may adapt to increasing aridity via correlated trait responses associated with alternative life history strategies, but that trade-offs might constrain adaptive responses in individual traits.

Resurrected seeds from herbarium specimens reveal rapid evolution of drought resistance in a selfing annual

“…Previous work in contemporary populations of P. patagonica has shown that seedlings with larger leaves survive terminal drought for longer than those with smaller leaves (Christie et al, 2022). Descendant populations of P. patagonica have shifted their resource allocation strategies towards greater vegetative investment at the cost of fecundity (Figure 3), as such a strategy may prioritize survival under increasingly arid conditions associated with prolonged drought in the region.…”

“…The species is an obligate inbreeder with cleistogamous flowers (Sharma et al, 1992). Among populations from the Colorado Plateau, seed and seedling traits show evidence of local adaptation across a natural aridity gradient (Christie et al, 2022), suggesting that abiotic selection has shaped trait variation.…”

Studies on the Germination and Emergence of Castor Seedlings

“…The hypothesis tested in this experiment was that the seed coat is impermeable to water, and a puncture on the seed coat will allow for water uptake without resistance. Castor seeds were incubated to germinate at temperatures of 16,19,22,25,28,31, and 34 °C. For each temperature, 70 castor seeds of the cultivar AKB 02 had the caruncle manually removed, and a small puncture was made in 35 seeds.…”

“…Many studies on other plant species have demonstrated the weak association between seed size and the time for germination and seedling emergence [31,32]. Corn (Zea mays) producers blame the variability in seed size for uneven seedling emergence [50]; however, while the effect of seed size is occasionally observed in the laboratory, it is not confirmed in field conditions.…”

“…This article reports a series of studies evaluating factors that were previously observed to influence the seed germination of castor and other plant species. The objective was to test the following hypotheses: (1) that castor seed germination is delayed because the castor seed coat is impermeable to water [17][18][19], (2) that the time for germination is influenced by temperature [20][21][22], (3) that the mechanical resistance of the seed coat is a mechanism to delay germination [23][24][25][26][27][28][29][30], (4) that the germination ability is influenced by the seed weight, volume, density, and seed coat thickness [7,15,16], (5) that castor seed germination is influenced by the hormone gibberellin [4,29], (6) that selection for fast germination changes the morphological characteristics of the seed in its descendants [7,31,32], and (7) that the time for germination can be reduced with a pre-germination treatment [3,17].…”