How Elevated CO2 Shifts Root Water Uptake Pattern of Crop? Lessons from Climate Chamber Experiments and Isotopic Tracing Technique

Abstract

Root water uptake plays an important role in water transport and carbon cycle among Groundwater–Soil–Plant–Atmosphere–Continuum. The acclimation of crops under elevated carbon dioxide concentrations (eCO2) depends greatly on their capability to exploit soil water resources. Quantifying root water uptake and its relationship with crop growth under eCO2 remains challenging. This study observed maize growth subjected to current CO2 (400 ppm) and eCO2 (700 ppm) treatments via a device combined with a climate chamber and weighing lysimeters. Root water uptake patterns were determined based on the isotopic tracing technique. The main water uptake depth shifted from 0−20 cm under current treatment to 20−40 cm under eCO2 at the seedling growth stage. Maize took up 22.7% and 15.4% more soil water from a main uptake depth of 40−80 cm at jointing and tasseling stages in response to eCO2, respectively. More soil water (8.0%) was absorbed from the 80−140 cm layer at the filling stage under eCO2. Soil water contributions at the main uptake depth during seedling stage were negatively associated with leaf transpiration rate (Tr), net photosynthetic rate (Pn), and leaf area index (LAI) under both treatments, whereas significant positive correlations in the 40−80 cm layer under current treatment shifted to the 80−140 cm layer by eCO2. Deep soil water benefited to improve Tr, Pn and LAI under both treatments. No significant correlation between soil water contributions in each layer and leaf water use efficiency was induced by eCO2. This study enhanced our knowledge of crop water use acclimation to future eCO2 and provides insights into agricultural water management.