To evaluate the potential utility of isotope ratios in plant materials as an archaeological proxy for past crop water status, relationships between water availability and stable isotope ratios in C₄ species must be established. This study quantified the isotopic values (δ¹³C and δ¹⁵N) of pearl millet (Pennisetum glaucum) seeds and leaves in response to varying degrees of water stress. Under greenhouse conditions, we exposed five strains of pearl millet to three different watering treatments. Pearl millet seed δ¹³C values (mean and SD = -13.9 ± 0.5‰, n = 48) and leaf δ¹³C values (mean and SD = -14.8 ± 0.7‰, n = 75) were positively correlated with water availability across 75 plants from five strains. The magnitude of the relationship for seeds (0.24 ± 0.04‰ per 0.1 m³ m⁻³ increase in soil moisture) and leaves (0.24 ± 0.06‰) was similar. The five strains showed differences in bulk carbon isotope ratios but had indistinguishable responses to water availability. Water availability had no discernible effect on δ¹⁵N in any of these strains. These results suggest that, while in some cases sensitive to water availability, the differences in the isotope ratios of pearl millet seeds and leaves across treatments were not of sufficient magnitude for reconstructing past crop water status without additional information.

为了评估植物材料中同位素比率作为过去作物水分状况的考古代理的潜在效用，必须建立C ₄物种中可用水量与稳定同位素比率之间的关系。本研究量化了珍珠粟（Pennisetum glaucum）种子和叶子在不同程度的水分胁迫下的同位素值（δ ¹³ C 和δ ¹⁵ N）。在温室条件下，我们将五株珍珠粟暴露于三种不同的浇水处理中。珍珠粟种子 δ ¹³ C 值（平均值和 SD = -13.9 ± 0.5‰，n = 48）和叶 δ ¹³C 值（平均值和 SD = -14.8 ± 0.7‰，n = 75）与来自 5 个菌株的 75 株植物的水可用性呈正相关。种子（土壤湿度每增加0.1 m ³ m ^-3增加0.24 ± 0.04‰ ）和叶子（0.24 ± 0.06‰）的关系幅度相似。这五种菌株在整体碳同位素比率方面表现出差异，但对可用水量的反应无法区分。在任何这些菌株中，水的可用性对 δ ¹⁵ N都没有明显的影响。这些结果表明，虽然在某些情况下对可用水量敏感，但不同处理的珍珠粟种子和叶子的同位素比率差异不足以在没有额外信息的情况下重建过去的作物水分状况。