Matzner Steven L, Konz Emily R, Marts Samantha A, Eversman Haley M, Kasuske Kyla M, Atkins Trinity L, Acharya Sneha, Matuck Lara C, Derynck Lillian M, Kreutzmann Sydney, Selberg Avery G, Glisar Kelli M, Capers Sydney A, Lind Victoria L, Olimb Sarah, Olson-Manning Carrie F
Department of Biology, Augustana University, Sioux Falls, SD, USA.
Physiol Plant. 2025 Jan-Feb;177(1):e70034. doi: 10.1111/ppl.70034.
Understanding factors that determine a species' geographical range is crucial for predicting climate-induced range shifts. Two milkweed species, Asclepias syriaca and Asclepias 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. speciosa did not exhibit greater drought tolerance, raising the question of how it survives in the more arid west. A reciprocal transplant study showed selection against A. syriaca in the western garden and that A. speciosa was better able to avoid seedling mortality. Focusing on seedling establishment, we found that A. speciosa exhibited 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 that A. speciosa avoids drought through faster deep-root growth and a slower wilting phenotype. Our study suggests that A. syriaca's range is limited by its drought tolerance, while A. speciosa employs a number of drought avoidance strategies to survive in more arid environments.
了解决定物种地理分布范围的因素对于预测气候导致的分布范围变化至关重要。两种马利筋属植物，即乳草和美丽马利筋，在北美洲沿着湿度梯度具有重叠的分布范围，并且是濒危帝王蝶幼虫的主要食物来源。随着湿度降低，长寿物种通常生长较慢且耐旱性更强，而许多一年生物种则表现出更快的生长策略。利用这种快 - 慢框架，我们评估了这两个姊妹物种的性状是否沿着快 - 慢生长连续体存在差异，以及是否可以解释它们的分布情况。我们在共同花园和温室实验中测量了叶片和根系功能性状。在表明耐旱性的关键指标（如生长、蒸腾作用和水势）方面，这两个物种几乎相同。与预期相反，美丽马利筋并未表现出更强的耐旱性，这就引发了它如何在更干旱的西部生存的问题。一项相互移栽研究表明，在西部花园中乳草受到了选择淘汰，而美丽马利筋更能避免幼苗死亡。专注于幼苗定植，我们发现美丽马利筋表现出更快的深根发育以及与较慢枯萎和延迟干旱诱导死亡相关的窄叶表型。我们的结果表明，美丽马利筋并非通过快 - 慢生长谱上的差异，而是通过更快的深根生长和较慢的枯萎表型来避免干旱。我们的研究表明，乳草的分布范围受到其耐旱性的限制，而美丽马利筋采用多种避旱策略在更干旱的环境中生存。
