Crops Grown in Mixtures Show Niche Partitioning in Spatial Water Uptake

More diverse plant communities generally produce more biomass than monocultures. This benefit of plant diversity is supposed to stem from resource partitioning of species in mixtures. Different plant species might use the resources spatially, temporally, or chemically in different ways. Along the same lines, for agricultural production crop mixtures outperform monocultures. Differences in vertical root distributions of crop species in mixtures could explain such higher yield. Here we used the stable isotopes of water and a Bayesian model to investigate the spatial water uptake patterns of six different crops species and how these patterns differ depending on the crop diversity. In addition, we calculated niche overlaps of water uptake as an indicator for belowground spatial niche partitioning, compared them among the different diversity levels, and linked them to productivity. The spatial water uptake pattern differed among crop species. The effect of crop diversity had a minor effect on water uptake but varied strongly depending on the crop species. Niche overlap in spatial water uptake was highest in monocultures and decreased strongly in mixtures. Furthermore, productivity in mixtures was higher compared to monoculture. Additionally, we showed that increased competition intensity leads to stronger changes in water uptake patterns. Synthesis. We found evidence for niche partitioning of spatial water uptake, and therefore complementary spatial root distribution, and higher productivity in crop mixtures compared to monocultures. Consequently, a more efficient use of soil resources in intercropping systems might explain their yield benefits.