Characterization of hydrogen and oxygen isotope fractionation during root water uptake in winter wheat and summer maize

The experiments were conducted during the crop growing season from 2019 to 2020 at the Luancheng Agro-Eco-Experimental Station of the Chinese Academy of Sciences (37°53′ N, 114°41′ E). Winter wheat and summer maize were selected as the experimental subjects. The wheat pot experiment was set up with 2 cultivars (Jimai22 and Kenong8162), 4 irrigation treatments, 3 sampling times and 3 repetitions. Besides, rehydration experiments of soil, stems, roots and absorbent cotton (for bleeding sap) were conducted to reduce the uncertainty of the cryogenic vacuum distillation method. For sampling: (1) Wheat was sampled in three batches, at 12, 24 and 48 h after full watering. Soil, stem, bleeding sap and irrigation water were sampled in the wheat experiment. (2) Maize was sampled 24 h after full irrigation, and soil, stem, root and irrigation water samples were collected. (3) Three extra pots (without plants) were irrigated thoroughly and covered completely with plastic film as soil-only controls. Multiple successive soil samples were taken from each pot, 16 times for wheat over 72 h after flooding and 11 times for maize over 48 h. Water in the soil and plant samples was extracted by a CVD system (LI-2100, LICA, China). The water isotope analyses were performed by an isotopic ratio infrared spectroscopy system (IRIS, DLT-100; Los Gatos Research, USA).