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

在每年的干旱时期，索诺兰沙漠的野生动物依靠大型蓄水仙人掌和其他多肉植物提供的资源。例如，在一年中最干旱的时期，巨型仙人掌的花朵和果实为许多昆虫、鸟类和哺乳动物提供水、营养和能量。壁虎的生长和繁殖对气候变率和变化极为敏感，对其依赖的群落具有潜在的重要影响。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，并利用在仙人掌刺的同位素组成记录的信息进行繁殖。在水胁迫下，树刺中氧和碳稳定同位素比值的变化记录了水分吸收和蒸发的模式以及光合过程的变化。由于仙人掌生长的尖端产生了刺，并在植物上保留了长达100年或更长时间，因此任何仙人掌植物都有可能获得长期，高分辨率的水平衡和光合压力记录。使用放射性碳（14C）测年技术验证了脊柱的年龄。这个新项目将建立精确的年代，高分辨率的同位素记录，这些记录来自于在亚利桑那州不同气候梯度的仙人掌植物的整个生命周期中生长和保存的刺。该项目假设：1)刺的氧同位素比值记录了仙人掌植物的水源和水量以及蒸发条件的变化；2)碳同位素比值反映水分胁迫对光合作用的影响。将刺的年分解同位素记录与过去50 ~ 80年的生长速率、花/果产量和气候记录进行比较，将揭示刺对局部和区域环境变化的响应。除了两名博士后外，该提案还将资助本科生的原创研究。该项目将为现有的K-12外展项目开发一个关于仙人掌与水关系的课程单元。

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.