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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]

We hypothesized that soil phosphorus (P) utilization might be tightly associated with interspecific interactions. To clarify this issue, a maize-grass pea intercropping system was investigated in a rainfed field with P addition (P0 and P +), water (rain-fed and plastic film mulching) and isolation (root barrier and root intermingling) treatments. The data indicated that total net effect was higher than 0 under all the conditions, displaying facilitative effects of biodiversity on agroecosystem productivity. The dynamics of total land equivalent ratio demonstrated that the intensity of plant-plant facilitation became greater under P-deficient condition. Maize was the facilitated species consistently, while grass pea changed from facilitated species under low soil P and moisture to facilitator under high soil P and moisture. The driving mechanism was associated with soil acidification and microbial community promotion effect under P-deficient condition. Intercropped rhizosphere soil phosphatase activity was increased by 4.9–17.2%, and Olsen-P availability was evidently enhanced relative to monoculture. Interestingly, drought stress significantly enhanced this trend. Critically, root isolation confirmed that plant-plant facilitation was briefly driven by interspecific rhizosphere interactions. Conclusively, this study confirmed the context-dependent facilitation shift in agroecosystem and provided a novel insight into the importance of rhizosphere interaction on soil P availability and utilization. [Display omitted] • Plant-plant facilitation was observed in the maize-grass pea intercropping system. • The intensity of facilitation decreased from low to high P and water gradients. • P deficiency promotes rhizosphere phosphatase activity and acidification process. • Drought and P deficiency led to the optimal soil microbial biomass and activities. • Intercropped grass pea fostered soil P mineralization and resource use efficiency. [ABSTRACT FROM AUTHOR]

Note: P (phosphorus), W (water), + (positive or increase), – (negative or decrease). [Display omitted] • Plant facilitation was found in the intercropping system of maize and grass pea. • Facilitation shifted from +/+, +/0 to +/- from low to high water and P gradients. • In low P, rhizosphere soil acidification of grass pea fostered P mineralization. • Soil microbial biomass P was improved for higher productivity in +/+ facilitation. • Soil water and phosphorus availability altered interspecific facilitation model. Plant-plant facilitation is widely studied to increase productivity and resource utilization in cereal-legume intercropping system. However, physiological and ecological mechanisms driving interspecific interaction shift along the environmental gradients is largely unknown. To clarify this issue, we first tested plant-plant facilitation along with four phosphorus (P) gradients in maize-grass pea intercropping system. Results illustrated a progressive transition of seed yield-based facilitation from mutually facilitated (+/+) to maize facilitated but grass pea as facilitator (+/-) along with low to high P gradients. Secondly, above trend was evidently enhanced when combining with drought stress gradients, in which severe drought amplified facilitative effects, whereas the magnitude of facilitation was relatively weak under well-watered condition. Interestingly, biomass-based facilitation transition did not synchronize with seed-based one, in which occurred in a broader threshold range of water and P gradients. Specifically, total yield, biomass, N and P uptake increased by 0.5%, 4.1%, 1.8% and 2.9% under the sufficient P and water availability, whereas these indicators increased by 25.3%, 18.5%, 20.5% and 21.4% in P and water deficient soils. And the total net effect was positive under all the environmental conditions. Rhizosphere interaction plays a crucial role in facilitation judgment, and the driving mechanism was associated with soil acidification and microbial community promotion under P-deficient condition. Under low soil moisture and available P, soil acidification and lower rhizosphere soil pH of intercropped maize were observed. Rhizosphere phosphatase secretion were significantly activated in P-deficient soils and accelerated the mineralization of soil organophosphorus, and the microbial biomass P was improved for stronger facilitation. Taken together, our findings confirmed the P and water driven facilitation shift along with stress gradients and highlighted the roles of rhizosphere interaction in affecting species diversity advantage. In conclusion, our work provided a relatively full picture for plant facilitation evaluation and more accurate management regarding intercropping productivity. [ABSTRACT FROM AUTHOR]