Facilitation events were mostly reported in two modes of mutual promotion (+/+) and unilateral benefit (+/0) in cultivated plant populations, yet few investigations showed the third mode, i.e. +/-. We investigated the maize-faba bean intercropping system as the third mode which was little documented. Land equivalent ratio in intercropping system was significantly greater than in monocropping one, with faba bean as superior species (+), and maize as inferior species (-). For inferior species, interspecific competition restricted its substance remobilization and seed filling, and caused a relatively low pollen fertilization rate and high kernel abortion rate. This trend resulted from lower soil water availability in maize strip of intercropping system, and lower leaf chlorophyll content and photosynthetic rate in maize. Yield loss of inferior species provided mechanical explanation on the concurrent +/- facilitation. The findings enriched our understandings on asymmetric facilitation and the relationship between plant diversity and productivity in agroecosystems.

Nanoscale zero-valent iron (FeNPs) can affect plant growth and water uptake positively or negatively. Yet, its mechanism is still unclear, particularly for differentiate functional roles of FeNPs in plant-soil interaction. To address this issue, we first confirmed 1.0 and 1.5 g·kg-1 FeNPs as growth-promotion concentrations and 1.5 g·kg-1 as optimal one, while 2.0 g·kg-1 turned to restrict growth in maize seedlings, comparing with CK. When AM fungus (Funneliformis mosseae) was inoculated and cultured with FeNPs, 1.0 and 1.5 g·kg-1 FeNPs further evidently enhanced water uptake and biomass accumulation (P<0.05). ), as affected by the activated AMF colonization carrier. Contrarily, FeNPs turned to promote AMF colonization and development, achieving greater iron translocation efficiency in mycorrhiza (P < 0.05). Yet, 2.0 g·kg-1 FeNPs restricted AMF infection in roots, a negative effect. To investigate the mycorrhizal-FeNPs symbiosis, scanning electron microscopy was used to scan the extraradical hyphae, showing that hyphae intercepted excessive iron nanoparticles, alleviating the blockage of root surface apertures and ultimately restoring root activity. Therefore, dual effects of FeNPs on maize physiology were actively mediated by AMF via rhizosphere interactions. The findings provided new insights into safe and efficient utilization of nanomaterials in agro-ecosystems.