Collaborative Research: The Relationship of Climate to the Stable Isotopic Composition of Hackberry (Celtis) Endocarps:Modern Relationships & Paleoenvironmental Applications

拟议的综合研究的长期目标是利用黑莓(Celtis)内果皮的特殊成分，以同位素方法重建古环境。该项目将量化内果皮中有机和无机成分的稳定碳和氧同位素组成如何反映环境条件，以及遗传变异性如何影响这些关系。塞尔提斯果实的内果皮主要由文石组成，但也含有少量的有机C。高矿物含量可能是塞尔提斯内果皮是大平原新生代沉积物中常见且保存完好的植物残留物的原因之一。我们建议进行实验，以确定个别环境参数(光强、水势、温度、湿度)对不同植物成分的Delta C13和Delta O18值的影响，以及对Celtis内果皮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点的塞尔提斯果实、组织和气候数据来检验。我们将通过从美国农业部的一项涉及120多个种质来源的实验中采集一批塞尔提斯树的样本，建立气候和稳定同位素值之间的预测关系。这些实验在美国的12个地点进行，覆盖了整个南北温度范围以及东西向降雨量和大气缺水范围。成岩作用对同位素比率的影响，以及它对CELTIS在新生代古气候研究中的应用的影响，将通过短期实验来检验。如果这些研究证明令人鼓舞，我们将提交一份提案，开始该项目的第二阶段，在该阶段中，我们将收集大平原从全新世到渐新世的内果皮，并对其进行同位素分析。

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.