Stable oxygen isotope analysis of the water uptake mechanism via the roots in spring maize under the ridge-furrow rainwater harvesting system in a semi-arid region

Root water uptake plays an important role in plant growth and the water cycle in ecosystems, and it is greatly affected by the morphology and spatial distribution of the roots. The ridge-furrow rainwater harvesting system (RFRH) is an effective strategy in semi-arid regions, but the mechanism of spring maize root water uptake remains unclear. Therefore, we conducted a two-year experiment in a semi-arid region of northwestern China to study the soil water content (SWC), spring maize root morphology and spatial distribution, and water uptake in different root zones using the 18-oxygen stable isotope (818O) under RFRH. The root zones were investigated in three locations around a maize plant: (1) ridge (RF-R), (2) border of the ridge and furrow (RF-B), and (3) furrow (RF-F). The results showed that RFRH changed the symmetrical soil water distribution in the maize rows and significantly increased the SWC in RF-F, especially in the shallow soil profile (0-60 cm), which where the enhanced root growth in the shallower soil layers (0-40 cm) under RF-F and the roots reached deeper into the soil under RF-R. The roots reached deeper to absorb water as they developed vertically in the advanced of growth stage. The contributions of different soil layers to the total soil water uptake in the root zone exhibited a similar trend to the root proportion according to 818O analysis. In the filling stage, the maize roots under RF-R and RF-B acquired 64.1% and 65.8% of the water from the 40-60 cm layer in 2018, respectively, and 74.5% and 65.5% in 2019, whereas the amounts under RF-F were 49.9% and 27.6% from the 40-60 cm layer, and 30% and 53.9% from the 20-40 cm layer in 2018 and 2019. Thus, spring maize root water uptake was positively correlated with the root distribution, and the roots under the furrow absorbed more water from the shallower soil layers than the ridge, and less from the deeper soil layers than the ridge.