Stable water isotopes reveal modification of cereal water uptake strategies in agricultural co-cropping systems

Agricultural co-cropping is being evaluated in temperate environments as a potential nature-based solution to the changing climate. However, the understanding of underlying physiological processes in co-cropping and its potential to provide climate resilience in temperate agroecosystems remains limited. This study investigated water sources for plants in five distinct cereal-legume co-cropping systems and four of their corresponding cereal monocultures at four main growth stages, under contrasting temperate hydro-climatological conditions in Scotland. Stable water isotope compositions (δ 2 H and δ 18 O) for soil water and xylem water were established. Based on the isotope compositions, a Bayesian multi-source mixing model was used to explore proportional soil water uptake patterns for cereal crop plants. Cereals grown in monocultures in this environment took more than 60 % of their water from the upper topsoil (soil depth <5 cm) during the main growth stages, under both wet and dry conditions. However, cereals cultivated as co-crops with legumes modified their water uptake strategy through increased water acquisition from the lower topsoil (5 – 30 cm) compared to monocultures, independent of environmental conditions. These novel findings suggest that co-cropping systems could potentially provide climate resilience for temperate agricultural systems. The findings provide an evidence-base for sustainable water planning, drought preparation and environmental intervention policies. Water isotopic analyses (δ 2 H and δ 18 O) showed that cereal plants in monocultures mainly relied on upper topsoil for water, while co-cropping led to increased water uptake from lower topsoil. Arrow shows main source of plant water uptake. • Plant water uptake in temperate cereal mono- and co-cropping systems were investigated with isotopes. • Cereals in a temperate humid zone mostly depend on water from the upper topsoil. • Cereals in co-cropping showed enhanced water uptake from the lower topsoil compared to monocultures.