Stable Nitrogen Isotopic Changes in Winter Wheat (Triticum aestivum L.) Induced by its Growth Temperature

The nitrogen dynamics of plants can be quantified using the variation in their δ¹⁵N level. This reveals details of plant physiological characteristics and the relationship between plants and their growth conditions. To better understand plant nitrogen dynamics and the effects of external temperature changes on their nitrogen isotopic composition, we investigated the δ¹⁵N characteristics in Triticum aestivum and its mother soils during the plant's life cycle. We found that under field conditions, the plant's leaves and roots δ¹⁵N significantly changed. The δ¹⁵N values in Triticum aestivum changed from -1.6‰ to -8.1‰ for leaves and from -2.0‰ to -8.8‰ for roots, respectively. δ15N values for both, the leaves and roots were positively correlated with temperature. However, the foliar δ¹⁵N corresponded more strongly to air temperature, while the root δ¹⁵N corresponded to soil temperature. δ¹⁵N values of leaf and root both changed around 0.2‰ in response to a 1 degree change in temperature. Plant roots or shoot material cannot reflect the whole plant δ¹⁵N values due to a considerable difference between the δ¹⁵N values of root and leaf. However, the variations in leaf and root δ¹⁵N provide useful proxies to trace seasonal plant nitrogen cycles.