Phenological sensitivitgy of Bromus tectorum genotypes to current and source environments

Authors: VAHSEN, MEGAN - Utah State University; MAXELL, TOBY - Us Geological Survey; Blumenthal, Dana; GAMBA, DIANA - Pennsylvania State University; GERMINO, MATT - Us Geological Survey; HOOTEN, MEVIN - University Of Texas; LASKY, JESSE - Pennsylvania State University; LEGER, ELIZABETH - University Of Nevada; PIRTEL, NIKKI - Utah State University; Porensky, Lauren; VAN EE, JUSTIN - Colorado State University; Copeland, Stella; ENSING, DAVID - Agriculture And Agri-Food Canada; ADLER, PETER - Utah State University

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plants respond to short-term (i.e., within-generation) changes in their current environment via plasticity, and long-term (i.e., between-generation) trends in the environment via evolutionary change. However, the relative importance of plant responses to short- and long-term changes are still not yet well-understood. We conducted a replicated common garden experiment using 92 genotypes of Bromus tectorum (cheatgrass) collected across the Western United States and British Columbia, Canada to assess the role of current and source environments in explaining variation in first flowering phenology. Replicates of each genotype were planted in low or high density and low or high temperature (four treatments total) across four common garden locations in Idaho and Wyoming. Plants growing in warm conditions, and genotypes collected from hot and dry climates flowered consistently earlier than those growing in cool conditions or collected from or cool and wet climates. Flowering date was particularly sensitive to a plant’s current environment. These results help predict how plants will respond to rapid environmental change. Understanding the sensitivity of B. tectorum flowering time to climate will help land managers improve the timing of efforts to control this invasive grass.

Technical Abstract: Plants can shift their traits in response to both short-term (i.e., within-generation) changes in their current environment via plasticity, and long-term (i.e., between-generation) trends in the environment via evolutionary change. However, the relative importance of plant responses to short- and long-term changes in the environment are still not yet well-understood. Phenological traits can serve as harbingers for plant responses to environmental change, and there is evidence that they respond to both shifts in their current environment (evidence for plasticity) and source environment (evidence for local adaptation). Here, we conducted a replicated common garden experiment using 92 genotypes of Bromus tectorum (cheatgrass) collected across the Western United States and British Columbia, Canada to assess the role of current and source environments in explaining variation in first flowering phenology. Replicates of each genotype were planted in two densities (low density = 100 seeds / 1 m2, high density = 100 seeds / 0.04 m2) under two different temperature treatments (low temperature, white gravel; high temperature, black gravel) in a factorial design, replicated across four common garden locations in Idaho and Wyoming. We tested for the effect of current environment (i.e., density treatment, temperature treatment, common garden location), source environment (i.e., climate of genotype source location), and their interaction on each plant’s day of first flowering (n = 7973). The date of first flowering was strongly influenced by both a plant’s current and source environment, but there was minimal evidence of interactions between environment types. Genotype identity strongly explained first flowering date, which was largely explained by its source climate: genotypes from hot and dry climates flowered consistently earlier than those from cool and wet climates. Characterizing the phenological sensitivities (i.e., D day of year / D temperature) of current and source climates post-hoc suggested that the date of first flowering is more sensitive to shifts in the current climate compared to changes in the source climate. These results add to a growing body of work seeking to resolve the mechanisms by which plants will respond to rapid environmental change over the next few decades.