A synthesis of local adaptation to climate through reciprocal common gardens

Abstract

1. Contrasts of differences within plant species and ecotypes are often best examined in ecology, evolution and genetics through provenance and biogeographical comparisons. Climate adaptation studies in plants are no exception and benefit from experiments that use these sets of factors. Reciprocal common gardensare a tool used to test for local adaptation in species to different contexts including climate. 3. A synthesis of common gardens and intraspecific tests for climate adaptation was used to compile over 200 studies that explored the relative efficacy of this tool and the ecology of change. Exclusion criteria were applied to review this literature and to compile specific tests that explicitly examined climate, plants and reciprocity in gardens for a total of 70 independent instances. 4. A meta-analysis was used to test for consistency and significance of detecting ecotypes for the different categories of traits tested and by the transplanting of seeds or seedlings. 5. This meta-analysis provides clear evidence for plant adaptation to climate change because all significant effect size estimates were positive, relatively large, and both seed and seedling transplants demonstrated consistent evidence for local adaptation. Emergence and germination responses from seed transplant experiments and relative growth and biomass differences from seedling transplants provided particularly strong support. 6. Synthesis. Reciprocal common gardens were a highly effective experimental design to test for ecotypic differentiation and for climate adaptation. Nonetheless, we propose that future studies clearly define whether ecotypes are being explicitly tested in common garden experiments to enable evidence syntheses and discovery, and we highlight the need for reciprocal climatic gardens to clearly test for continued capacity for local adaptation in response to divergent climate selection processes in many plant species.

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

“…Given the potentially high levels of uncertainty inherent to individual common garden studies, meta‐analysis is a logical next step for examining the overall evidence for local adaptation across experiments. In this special feature, Lortie and Hierro (2021) report on a meta‐analysis refined to reciprocal common‐garden experiments. The effect size and metric of local adaptation was operationalized as the standardized mean difference between sympatric (genotypes at home) and allopatric (genotypes away from home) G × E interaction terms.…”

“…The fast-slow trait continuum is a conceptual framework that arrays plant taxa by their tradeoff between resource-acquisitive and -conservative traits, but it is unclear if or how this macroecological pattern relates to eco-evolutionary processes, including growth, sur- In that respect, Lortie and Hierro's (2021) meta-analysis provides a glimpse into the importance of recruitment traits by showing that germination and emergence produce the largest overall effect size for local adaptation (compared to e.g., growth and survival). This suggests that common garden studies must pay greater attention to the earliest life history stages, i.e., regeneration niches (Grubb, 1977;Schwinning & Kelly, 2013).…”

“…Given the potentially high levels of uncertainty inherent to individual common garden studies, meta-analysis is a logical next step for examining the overall evidence for local adaptation across experiments. In this special feature, Lortie and Hierro (2021) report on a meta-analysis refined to reciprocal common-garden experiments.…”

“…At last, there is further unrealized potential for comparing and synthesizing the outcomes of many common‐garden experiments, so that we can begin to develop a generalized conceptual framework for plant response to climate change (Huxman et al, 2021; Lortie & Hierro, 2021; Ramirez‐Valiente & Robledo‐Arnuncio, 2021). Publications based on common garden studies sharply increased in the first decade of this century, and this trend will likely continue as scientists across the world prioritize climate change preparedness (Strassburg et al, 2020; Turney et al, 2020).…”

“…These dynamics along stress gradients may be universal among members of similar niches, and even in long-lived species should be observable in juvenile stages(Kelly et al, 2008). To date, competitive arenas, such as those described byJohnson et al (2020) are not routinely implemented in common garden experiments, a lost opportunity for testing foundational theories of trait evolution and community assembly.At last, there is further unrealized potential for comparing and synthesizing the outcomes of many common-garden experiments, so that we can begin to develop a generalized conceptual framework for plant response to climate change(Huxman et al, 2021;Lortie & Hierro, 2021;Ramirez-Valiente & Robledo-Arnuncio, 2021).Publications based on common garden studies sharply increased inthe first decade of this century, and this trend will likely continue as scientists across the world prioritize climate change preparedness(Strassburg et al, 2020;Turney et al, 2020). Data integration will benefit from more standardized research techniques, including a set of priority traits, guidelines for garden selection, and reporting standards that facilitate quantitative synthesis.…”