黑河中游春玉米叶片水δD和δ^(18)O的富集过程和影响因素

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

植物水的稳定同位素分馏过程是水在土壤-植物-大气连续体中循环的重要环节。以往研究由于叶片水18O同位素比值(δ^(18)O l,b)和氘(D)同位素比值(δDl,b)(合称δl,b)实测数量少只能作为模型验证数据,导致δl,b富集机制研究多集中于模型研究,缺乏基于野外试验条件的δl,b富集的控制机制研究。叶片水δDl,b和δ^(18)O l,b的富集程度(ΔDl,b和Δ18O l,b,合称Δl,b)通常表示为δl,b与茎秆水D同位素比值(δDx)和18O同位素比值(δ^(18)Ox)(合称δx)之差,即Δl,b=δl,b–δx。该研究以黑河中游沙漠绿洲春玉米(Zea mays)生态系统为研究对象,重点采集和分析了季节和日尺度δl,b和δx数据,配套开展了大气水汽δ^(18)O和δD(合称δv)等辅助变量的原位连续观测,探讨了季节和日尺度上的δl,b富集特征及其影响因素。结果表明:叶片水δl,b和Δl,b的季节变化趋势不明显,而受蒸腾作用影响表现出白天富集夜间贫化的单峰日变化特征。对于D来说,无论季节尺度上还是日尺度上,大气水汽δv和相对湿度是δDl,b和ΔDl,b的主要环境控制因素;而对于18O来说,无论季节尺度上还是日尺度上,相对湿度是δ^(18)O l,b和Δ18O l,b的主要环境控制因素。由于D和18O在热力学平衡分馏上有约8倍差异,直接分析叶片水ΔDl,b和Δ18Ol,b与影响因素的差异性,有助于理解叶片水δD和δ^(18)O富集过程以及对模型发展有一定的指导意义。

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 18O isotope ratio （δ18O 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 δ18O 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 δ18O 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 δ18O 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 δ18O 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 18O, only relative humidity was the key control factor on both seasonal and daily scales. Differences of D and 18O came from the equilibrium fractionation because equilibrium fractionation factor for D was over 8 times than for＆amp;nbsp;18O. The analysis of these differences help us distinguish the environmental factors of leaf water enrichment for D （ΔDl,b） from leaf water enrichment for 18O （Δ18Ol,b）, and improve our understanding of leaf water enrichment process and develop the related models as well.