Department of Botany, 1000 East University Ave, University of Wyoming, Laramie, WY 82070, USA
Department of Research, Conservation and Collections, Desert Botanical Garden, Phoenix, AZ, USA.
J Exp Bot. 2014 Jul;65(13):3405-13. doi: 10.1093/jxb/eru174. Epub 2014 Apr 23.
Columnar cacti occur naturally in many habitats and environments in the Americas but are conspicuously dominant in very dry desert regions. These majestic plants are widely regarded for their cultural, economic, and ecological value and, in many ecosystems, support highly diverse communities of pollinators, seed dispersers, and frugivores. Massive amounts of water and other resources stored in the succulent photosynthetic stems of these species confer a remarkable ability to grow and reproduce during intensely hot and dry periods. Yet many columnar cacti are potentially under severe threat from environmental global changes, including climate change and loss of habitat. Stems in columnar cacti and other cylindrical-stemmed cacti are morphologically diverse; stem volume-to-surface area ratio (V:S) across these taxa varies by almost two orders of magnitude. Intrinsic functional trade-offs are examined here across a broad range of V:S in species of columnar cacti. It is proposed that variation in photosynthetic gas exchange, growth, and response to stress is highly constrained by stem V:S, establishing a mechanistic framework for understanding the sensitivity of columnar cacti to climate change and drought. Specifically, species that develop stems with low V:S, and thus have little storage capacity, are expected to express high mass specific photosynthesis and growth rates under favourable conditions compared with species with high V:S. But the trade-off of having little storage capacity is that low V:S species are likely to be less tolerant of intense or long-duration drought compared with high V:S species. The application of stable isotope measurements of cactus spines as recorders of growth, water relations, and metabolic responses to the environment across species of columnar cacti that vary in V:S is also reviewed. Taken together, our approach provides a coherent theory and required set of observations needed for predicting the responses of columnar cacti to climate change.
柱状仙人掌广泛分布于美洲的多种生境和环境中，但在极干旱的沙漠地区尤为突出。这些雄伟的植物因其文化、经济和生态价值而广受赞誉，在许多生态系统中，它们为传粉者、种子传播者和食果者提供了高度多样化的群落。这些物种多汁的光合作用茎中储存着大量的水和其他资源，使它们在炎热和干燥的时期能够茁壮成长和繁殖。然而，许多柱状仙人掌可能受到环境全球变化的严重威胁，包括气候变化和栖息地丧失。柱状仙人掌和其他圆柱形茎仙人掌的茎在形态上多种多样；这些类群的茎体积与表面积比（V:S）相差近两个数量级。本文研究了广泛的 V:S 范围内柱状仙人掌物种之间的内在功能权衡。提出了光合作用气体交换、生长和对胁迫的反应的变化受到茎 V:S 的强烈限制，为理解柱状仙人掌对气候变化和干旱的敏感性建立了一个机制框架。具体来说，与 V:S 较高的物种相比，那些具有低 V:S 的物种形成的茎具有较小的储存能力，因此在有利条件下，预计具有较高的比质量光合作用和生长速率。但是，低 V:S 物种的储存能力较小，与 V:S 较高的物种相比，它们可能对强烈或长时间的干旱的耐受性较低。还回顾了利用稳定同位素测量仙人掌刺作为记录不同 V:S 的柱状仙人掌物种的生长、水分关系和代谢对环境响应的方法。总之，我们的方法提供了一种连贯的理论和所需的观测结果，用于预测柱状仙人掌对气候变化的反应。
