222 D58. Recent Advances in Paleoclimatology and Paleoceanography

Wednesday, 7 November 2018
8:00 AM - 12:00 PM
Room 138-139

CAN CARBON ISOTOPE VALUES IN THE SEEDS OF A C4 PLANT (PEARL MILLET, PENNISETUM GLAUCUM) SERVE AS A PROXY FOR PAST WATER MANAGEMENT PRACTICES?

Paper number: 222-11
Program: Technical Sessions
Time: 10:30 AM – 10:45 AM

Authors

Abstract

Stable carbon isotope discrimination has been shown to correspond with water conditions during C3 plant growth and has therefore been developed into a proxy for past water management practices. Many important cereals grown in semiarid regions are however C4, and because C4 plants are less sensitive to environmental variables than C3 plants, the effects environmental variables have on their carbon isotope (δ13C) values have received comparatively less attention. We investigated the influence of water availability on pearl millet (Pennisetum glaucum) seed carbon isotope ratios by first examing the relationship between cumulative annual precipitation and δ13C values measured in USDA seeds grown outdoors at the Germplasm Introduction and Research Unit, Kingshill, St. Croix, United States Virgin Islands between 1994 and 2013. We observed that δ13C values were significantly positively related to cumulative annual precipitation, though over a fairly small range of δ13C values (< 2‰). We subsequently grew 75 millet plants from five regional accessions in the greenhouse at Washington University in St. Louis and subjected them to three different water treatments (maintained at average soil moisture levels of 0.43 m3/m3, 0.21 m3/m3, and 0.16 m3/m3, respectively). Pearl millet δ13C values were again significantly positively correlated with water availability; seeds were enriched in 13C by 0.23 ± 0.03‰ for each 0.1 m3/m3 increase in soil moisture. Sample origin (accession) was also a significant predictor of seed δ13C values. These results suggest that both environment (water availability) and genetics (accession) are responsible for variation in the isotopic values of pearl millet seeds. Because seed δ13C values differed by just 0.6‰ between the well-watered and draught treatments, it is unlikely that δ13C values in C4 plants are sensitive enough to serve as proxies for past water management practices, although isotope data may still be informative when combined with morphological information (e.g. seed size).

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-320520

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