Leaf water δD and δ<sup>18</sup>O enrichment process and influencing factors in spring maize (Zea mays) grown in the middle reaches of Heihe River Basin

Abstract

Aims The stable isotope fractionation of plant water is an important part for the water cycle in the soil-plant-atmosphere continuum. There is a lack of control mechanisms research of leaf water isotope ratio (δl,b) enrichment based on the field conditions. Because it is tough to get the measured 18 O isotope ratio (δ 18 O l,b) and deuterium (D) isotope ratio (δDl,b) of leaf water (collective name δl,b). Therefore most previous research focuses on model building used the limited number of δl,b. Leaf water δDl,b and δ 18 O l,b enrichment (collective name Δl,b) is usually represented as the difference of the leaf water isotope ratio (δl,b) and the plant source water isotope ratio (δDx and δ 18 O x,collective name δx), that is Δl,b = δl,b - δx. Methods A field experiment with spring maize (Zea mays) was conducted in the middle reaches of Heihe River Basin to investigate the characteristics of leaf water δ 18 O and δD enrichment and their abiotic control mechanisms on seasonal and daily scales. Leaf and stem samples were collected and analyzed according to different time scales, and the δ 18 O and δD of atmospheric water vapor (collective name δv) were determined based on the in situ and continuous water vapor isotope ratio measurement system at the same time. Important findings The results showed that: δl,b and Δl,b of leaf water varied little during the experimental sea- son while largely at daily scale, which enrichment was found at the daytime but depletion at night. Atmospheric water vapor isotope ratio (δv) and relative humidity were main factors to D on both seasonal and daily scales; for 18 O, only relative humidity was the key control factor on both seasonal and daily scales. Differences of D and 18 O came from the equilibrium fractionation because equilibrium fractionation factor for D was over 8 times than for