Collaborative Research: An Isotopic Record of Response to Climate Change in Spines of Saguaro Cactus

索诺兰沙漠的野生动物物种在一年一度的干旱期间依赖于大型储水仙人掌和其他多肉植物提供的资源。例如，巨型仙人掌的花朵和果实在一年中最干燥的时期为许多昆虫、鸟类和哺乳动物提供水分、营养和能量。美洲斑羚的生长和繁殖对气候变异性和变化极其敏感，可能会对依赖的社区产生重要影响。该项目开发了一种新的方法来评估气候波动、生长、胁迫反应和繁殖，使用在斑羚脊椎的同位素组成中记录的信息。Saguaro刺中氧和碳稳定同位素比率的变化记录了水分吸收和蒸发的模式，以及与水分胁迫相关的光合作用过程的变化。因为刺是在仙人掌生长的顶端产生的，并在植物上保留了长达100年或更长时间，所以对任何一种仙人掌植物来说，都有可能获得关于水分平衡和光合作用压力的长期、高分辨率记录。脊椎的年龄是用放射性碳(14C)测年技术来验证的。这一新项目将从亚利桑那州气候梯度上种植和保留的藏红花植物的整个生命周期中建立精确的年代和高分辨率的同位素记录。该项目假设：1)脊椎的氧同位素比率记录了西瓜属植物水分的来源和数量以及蒸发条件的变化；2)碳同位素比率反映了水分胁迫对光合作用的影响。将脊椎每年分辨的同位素记录与过去50到80年的生长速度、花卉/水果产量和气候记录进行比较，将揭示Saguaro对当地和地区环境变化的反应。除了两名博士后外，该提案还将为原创的本科生研究提供资金。该项目将为现有的K-12外联方案开发一个关于仙人掌-水关系的课程单元。

Wildlife species in the Sonoran Desert depend on resources supplied by large, water-storing cactuses and other succulents during periods of annual drought. The flowers and fruits of the giant saguaro cactus, for instance, provide water, nutrients and energy to numerous insects, birds and mammals during the driest periods of the year. Growth and reproduction of saguaro are extremely sensitive to climate variability and change, with potentially important impacts on dependent communities. This project develops a novel approach for assessing climate fluctuations, growth, stress responses, and reproduction of saguaro using information recorded in the isotope composition of saguaro spines. Variation in the oxygen and carbon stable isotope ratios in saguaro spines records patterns of water uptake and evaporation and changes in photosynthetic processes associated with water stress. Because spines are produced at the growing tip of the cactus and retained on the plant for up to 100 or more years, a long-term, high-resolution record of water balance and photosynthetic stress is potentially available for any saguaro plant. The age of spines is verified using radiocarbon (14C) dating techniques. This new project will construct precisely dated, high resolution isotope records from spines grown and retained throughout the life of saguaro plants across climate gradients in Arizona. The project hypothesizes that that 1) oxygen isotope ratios of spines record the source and amount of water to saguaro plants and variation in evaporative conditions; and 2) carbon isotope ratios reflect water stress effects on photosynthesis. Comparison of annually-resolved isotope records from spines with growth rates, flower/fruit production, and climate records covering the last 50 to 80 years will reveal saguaro's response to local and regional environmental variation. In addition to two post-doctoral students, the proposal will fund original undergraduate research. The project will develop a curriculum unit on cactus-water relations for an existing K-12 outreach program.