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Abstract Droughts are predicted to become more frequent and intense in many tropical regions, which may cause shifts in plant community composition. Especially in diverse tropical communities, understanding how traits mediate demographic responses to drought can help provide insight into the effects of climate change on these ecosystems. To understand tropical tree responses to reduced soil moisture, we grew seedlings of eight species across an experimental soil moisture gradient at the Luquillo Experimental Forest, Puerto Rico. We quantified survival and growth over an 8‐month period and characterized demographic responses in terms of tolerance to low soil moisture—defined as survival and growth rates under low soil moisture conditions—and sensitivity to variation in soil moisture—defined as more pronounced changes in demographic rates across the observed range of soil moisture. We then compared demographic responses with interspecific variation in a suite of 11 (root, stem, and leaf) functional traits, measured on individuals that survived the experiment. Lower soil moisture was associated with reduced survival and growth but traits mediated species‐specific responses. Species with relatively conservative traits (e.g., high leaf mass per area), had higher survival at low soil moisture whereas species with more extensive root systems were more sensitive to soil moisture, in that they exhibited more pronounced changes in growth across the experimental soil moisture gradient. Our results suggest that increasing drought will favor species with more conservative traits that confer greater survival in low soil moisture conditions.
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This content will become publicly available on December 26, 2025
Differences in drought avoidance rather than differences in the fast versus slow growth spectrum explain distributions of two Asclepias species
Abstract Understanding factors that determine a species' geographical range is crucial for predicting climate‐induced range shifts. Two milkweed species,Asclepias syriacaandAsclepias speciosa, have overlapping ranges along a moisture gradient in North America and are primary food sources for endangered monarch caterpillars. With decreasing moisture, long‐lived species often exhibit slower growth and greater drought tolerance, while many annual species exhibit faster growth strategies. Using this fast‐slow framework, we assessed whether traits of these two sister species differ along a fast‐slow growth continuum and could explain their distributions. We measured leaf and root functional traits in common gardens and greenhouse experiments. In key measures indicative of drought tolerance (e.g., growth, transpiration, and water potentials), the species were nearly identical. Contrary to expectations,A. speciosadid not exhibit greater drought tolerance, raising the question of how it survives in the more arid west. A reciprocal transplant study showed selection againstA. syriacain the western garden and thatA. speciosawas better able to avoid seedling mortality. Focusing on seedling establishment, we found thatA. speciosaexhibited faster deep‐root development and a narrow leaf phenotype associated with slower wilting and delayed drought‐induced mortality. Rather than differences on the fast‐slow growth spectrum, our results indicate thatA. speciosaavoids drought through faster deep‐root growth and a slower wilting phenotype. Our study suggests thatA. syriaca'srange is limited by its drought tolerance, while A. speciosaemploys a number of drought avoidance strategies to survive in more arid environments.
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- Award ID(s):
- 2238209
- PAR ID:
- 10562198
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Physiologia Plantarum
- Volume:
- 177
- Issue:
- 1
- ISSN:
- 0031-9317
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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