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Background and Aims: Selection effect (SE) and complementarity effect (CE) are often considered as two key indicators to mediate the positive diversity-productivity relationship in the maize-legume intercropping system, as intercropping generally enables crops to use the available resources more efficiently than monoculture. Yet, it is unclear whether soil moisture drives the SE and CE transformation, plant-plant interaction, and accordingly affect the productivity. Methods: A two-year field experiment was conducted to explore the impacts of soil water status (with and without plastic mulching) on interspecific interaction and productivity and its key mechanism in the maize-faba bean intercropping system. Results: Low soil moisture reduced the net effect (NE) and land equivalent ratio (LER) with evident yield loss (NE < 0 and LER = 1.05), whereas the improved soil moisture reversed this trend and resulted in overyielding (NE > 0 and LER = 1.13). Regardless of soil moisture, faba bean was the dominant species and maize was the inferior one. Low soil moisture promoted the contribution of SE to productivity (P < 0.05). In contrast, high moisture turned to lower the competition intensity of faba bean against maize and accordingly promote the transformation of biodiversity effect from SE to CE. The main mechanism was that the water competition imposed by faba bean strips on maize ones decreased the NE through reducing photosynthetic rate and water use efficiency of maize. Conclusion: The adaptive transitions of interspecific relationship and the biodiversity effect were driven by soil water availability. This novel phenomenon should be emphasized in the crop diversity management of intercropping system in the rainfed region. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) play a vital role in mediating rhizosphere interactions and plant growth, especially in resource-constrained soils. However, few studies have documented the effects of AMF on plant–plant interaction patterns and resource use efficiency along stress gradients. In this study, a growth environment-controlled experiment was carried out to evaluate the effects of AMF inoculation on maize-grass pea intercropping along three phosphorus (P) and two water gradients. The data indicated that soil water and P availability determined the plant interspecific interaction pattern, and that interaction was strongly mediated by AMF inoculation. Grass pea and maize were mutually facilitated under low P and water conditions and transitioned to a new pattern, i.e., that maize was facilitated but grass pea was neutral role or facilitator with increasing resource availability. The facilitative effect was particularly significant under P- and water-deficient conditions. Moreover, the transition of the plant–plant interaction pattern was mechanically driven by improving rhizospheric phosphatase activities by 5.08–20.02 %, rhizospheric acidification and enhanced microbial activities under resource deficit conditions. Critically, AMF inoculation was observed to significantly improve rhizospheric soil P availability and microbial biomass (p < 0.05); however, it enhanced the complementary utilization of P and water and weakened interspecific competition under high-resource conditions. Therefore, AMF inoculation positively transformed the plant–plant interaction pattern along resource gradients for higher P, nitrogen and water use efficiency. This study validates the context-dependent interspecific interaction and the role of AMF in optimizing resource use in a nutrient-impoverished intercropping system. Illustrating the effect of AMF inoculation on plant growth and plant–plant interaction in maize-grass pea intercropping system. [Display omitted] • Plant diversity increased rhizosphere microbial activity and phosphatase secretion. • AMF inoculation enhanced facilitation intensity with increasing stress conditions. • AMF lowered interspecific competition intensity for higher resource use efficiency. [ABSTRACT FROM AUTHOR]

Intercropping, the simultaneous production of two or more crops on the same field, offers opportunities for sustainable agricultural intensification by providing higher yield per unit of land than monoculture. However, intercropping is largely ignored when evaluating regional carbon (C) cycle and ecosystem service function. We hypothesized that interspecific interactions in intercropping systems might induce changes in rhizosphere soil properties and accordingly affect carbon emission. To test the hypothesis, three intercropping systems including maize-soybean (2 M:4 S, 2-row maize: 4-row soybean), wheat-soybean (4 W:4 S), and maize-wheat (2 M:4 W) were established to explore the effects of interspecific interactions on land equivalent ratio (LER), C emission and soil properties in a typical semiarid rainfed site from 2019 to 2020. The results showed that interspecific facilitation (LER>1 and RII>0) was observed when soybean was intercropped with maize and wheat. On average, soil C emission was substantially increased by 10.6%, compared with their respective monocultures. Particularly, the intercropping with soybean not only alleviated N deficiency in the rhizosphere of maize or wheat, but also improved water use efficiency (WUE) of maize or wheat via complementary effect. Moreover, facilitating process evidently promoted the input of dissolved organic carbon (DOC) and easily oxidized organic carbon (EOOC) in rhizosphere soils (P < 0.05). This resulted in greater microbial activities, N mineralization rate, and inorganic N supply in the maize and wheat strips. However, the belowground competition from the intercropped wheat significantly lowered soil moisture and inorganic N content in maize strips. Also, soil labile C input (DOC and EOOC) and microbial activities were declined, while carbon emission was evidently lowered by 7.4%. Interestingly, the trade-off between grain yield production and carbon emission showed that interspecific facilitation promoted the yield per unit of carbon emission, indicating higher carbon emission efficiency. Yet, interspecific competition led to an opposite trend. The findings enhanced the understandings on carbon emission efficiency and its potential management strategy regarding crop diversity and green production in semiarid agroecosystems. [Display omitted] • Soybean intercropped with cereal promoted crop yield, showing plant facilitation. • Plant facilitation was resulted from water complementary use and N enrichment. • Increased labile carbon input and microbial activities enhanced carbon emission. • Yet, wheat-maize mixture showed an opposite trend due to interspecific competition. • Soybean-led rhizosphere interaction promoted carbon production efficiency & yield. [ABSTRACT FROM AUTHOR]