Intercropping with wheat leads to greater root weight density and larger below-ground space of irrigated maize at late growth stages

Intercropping two species at different growth stages is common in temperate and tropical areas. An apparent recovery of growth is observed in late-maturing species after early-maturing species have been harvested, but the mechanism remained unclear. This study tested the hypothesis that the roots of late-maturing species occupy greater below-ground space at later growth stages. The monolith method was employed to investigate the spatial and temporal distribution of maize grown alone (no interspecific interactions), maize intercropped with wheat (asymmetric interspecific facilitation before wheat harvesting), and maize intercropped with faba bean (symmetric interspecific facilitation) on August 8, September 2 and September 30, after harvesting of wheat (July 15) or faba bean (August 2). The results show that maize intercropped with wheat occupied more below-ground space at late growth stages than at early growth stages when the two crops grew at the same time, thus supporting our hypothesis. Furthermore, we also found that interspecific interactions during the co-growth stage of the two species led to a longer root life span in both maize intercropped with wheat and faba bean compared to the maize grown alone. The findings may partly explain the recovery of late-maturing species found in intercropping systems between two crop species with different growth stages and the complementary effect on the relationship between plant biodiversity and productivity.