The Relationship of Climate to the Stable Isotopic Com- position of Hackberry (Celtis) Endocarps: A Potential Means of Paleoenvironmental Reconstruction in the Great Plains

综合研究的长期目标是利用hackberries （Celtis）内腕果的特殊成分进行同位素方法的古环境重建。该项目将量化内鲤鱼中有机和无机组分的稳定C和O同位素组成如何反映环境条件，以及遗传变异如何影响这些关系。Celtis果实的内腕果主要由文石组成，但也含有少量的有机c。高矿物质含量可能是Celtis内腕果在大平原新生代沉积物中常见且保存完好的植物遗迹的原因之一。我们拟通过实验确定不同环境参数（光强、水势、温度、湿度）对不同植物组分δ c13和δ o18值的影响，以及对内carps中有机质和碳酸盐同位素组成的影响。目前内果皮同位素比率与区域气候的关系将通过收集美国许多地方的凯乐蒂斯果实、组织和气候数据来检验。我们将建立气候和稳定同位素值之间的预测关系，通过从美国农业部涉及120多个种质资源的实验中取样凯尔蒂斯树的一个子集。这些在美国12个地点进行的实验跨越了整个南北温度范围以及东西降雨量和大气水分亏缺范围。成岩作用对同位素比率的影响及其对在新生代古气候研究中使用Celtis的意义将通过短期实验进行检验。如果这些研究被证明是令人鼓舞的，我们将提交一份提案，开始项目的第二阶段，我们将收集和同位素分析大平原全新世到渐新世沉积物中的内腕足。

The long-term goal of the proposed integrated research is to exploit the peculiar composition of hackberry (Celtis) endocarps for an isotopic approach to paleoenvironmental reconstructions. This project will quantify how the stable C and O isotopic composition of organic and inorganic components in the endocarps reflect environmental conditions and how genetic variability affects these relationships. Endocarps of Celtis fruit mainly consist of aragonite, but also contain smaller amounts of organic C. The high mineral content may be one reason why Celtis endocarps are a common, and well-preserved, plant remnant in Cenozoic sediments of the Great Plains. We propose to conduct experiments to determine the effect of individual environmental parameters (light intensity, water potential, temperature, humidity) on the delta C 13 and delta O 18 values of various plant components and on the isotopic composition of organic matter and carbonate in Celtis endocarps. The present relationship of endocarp isotope ratios to regional climate will be examined by collecting Celtis fruit, tissue, and climate data, from many locations in the United States. We will establish predictive relationships between climate and stable isotope values by sampling a subset of Celtis trees from a USDA experiment involving more than 120 sources of germplasm. These experiments at 12 sites in the United States span the entire north-south temperature range as well as the east-west rainfall and atmospheric water deficit ranges. The effects of diagenesis on the isotope ratios, and its implications for the use of Celtis in Cenozoic paleoclimatic studies, will be examined via short-term experiments. Should these studies prove encouraging, we will then submit a proposal to begin a second phase of the project in which we will collect, and isotopically analyze, endocarps from Holocene to Oligocene sediments of the Great Plains.