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Aims: To investigate the relative contributions of pH, organic anions concentration, and phosphatase activity to rhizosphere soil phosphorus availability and crop phosphorus uptake in polycultures. Methods: A field experiment was conducted for three consecutive years in a split-plot design with main plots treated with two phosphorus levels and subplots treated with maize and alfalfa grown alone or intercropped. Results: Intercropped maize and alfalfa had 0.35 and 0.24 units lower rhizosphere pH, 28% and 30% higher total organic anions (TOA) concentration, and 21% and 41% greater acid phosphatase activity than those in monoculture. These changes in root exudates induced significant increases in rhizosphere phosphorus concentration of intercropped maize and alfalfa by 21% and 41%, and pH and TOA had greatest contributions, respectively. Rhizosphere phosphorus mobilization facilitated phosphorus uptake of intercropped maize, but this facilitation was offset by phosphorus uptake reduction due to decreased crown root surface area. Lateral root volume enhancement accounted for phosphorus uptake improvement of intercropped alfalfa by 86.6%, while rhizosphere phosphorus mobilization only had a 0.2% contribution. Conclusions: Rhizosphere pH and organic anions exhibit greater contributions than acid phosphatase activity in enhancing rhizosphere phosphorus availability. However, root surface area of maize and lateral root volume of alfalfa unveil greater influences on crop phosphorus uptake than rhizosphere pH and organic anions. [ABSTRACT FROM AUTHOR]

Aims: Mycorrhizae and root exudates have been considered the two important pathways for nitrogen (N) transfer from legume to non-legume plants. The present study aimed to investigate contribution of the relative importance of arbuscular mycorrhizal fungi and root exudates in short-term N transfer. Methods: A field experiment was conducted to explore N transfer from alfalfa to maize under two different N application levels using 15N leaf labeling. Results: N transfer amount ranged from 7 to 10 mg N plant−1 from alfalfa to maize and significantly decreased (by 11%–22%) with N fertilizer application. Intercropping of 4 rows of maize and 6 rows of alfalfa with 30 cm intra-row spacing (IMA43) was the optimal intercropping mode, which increased N transfer, total N uptake and yield by 18%, 15% and 11%, respectively. The relative importance of arbuscular mycorrhizal fungi and root exudates on N transfer was dependent on soil N availability. Under no N addition, hyphal length density (HLD) of rhizosphere soil explained the largest significant amount (50%) of the variability in N transfer and crop yield. However, root exudates explained 77% of the variability in N transfer and crop yields with N fertilizer application. Conclusions: Our findings highlighted that N transfer is reliant more on arbuscular mycorrhizal fungi than root exudates in N-deficient soil, whereas root exudates play a more important role in N-fertilized soil. [ABSTRACT FROM AUTHOR]

Belowground nitrogen (N) transfer from legumes to non-legumes provides an important N source for crop yield and N utilization. However, whether root contact facilitates N transfer and the extent to which N transfer contributes to crop productivity and N utilization have not been clarified. In our study, two-year rain shelter experiments were conducted to quantify the effect of root contact on N transfer in a maize/alfalfa intercropping system. N transfer occurred mainly one direction from alfalfa to maize during the growth period. Following the N0 treatment, the amount of N transfer from alfalfa to maize was 204.56 mg pot−1 with no root barrier and 165.13 mg pot−1 with a nylon net barrier, accounting for 4.72% and 4.48% of the total N accumulated in maize, respectively. Following the N1 treatment, the amount of N transfer from alfalfa to maize was 197.70 mg pot−1 with no root barrier and 139.04 mg pot−1 with a nylon net barrier, accounting for 3.64% and 2.36% of the total N accumulated in the maize, respectively. Furthermore, the amount of N transfer without no root barrier was 1.24–1.42 times higher than that with a nylon net barrier regardless of the level of N addition. Our results highlight the importance and the relevance of root contact for the enhancement of N transfer in a maize/alfalfa intercropping system. [ABSTRACT FROM AUTHOR]

The mechanisms underlying belowground processes in a perennial legume-dominated cereal/legume intercropping system were largely unknown. This study aimed to investigate whether alfalfa/maize intercropping can increase yield, phosphorus (P) uptake and utilization efficiency by influencing root morphology and distribution. Maize (Zea mays L.) and alfalfa (Medicago sativa L.) were grown in three different strip intercropping patterns and sole monocultures (monocultured maize, MM or monocultured alfalfa, MA), in field with or without P application from 2015 to 2018. Intercropping increased total yield by 68% compared with MM, and by 19% compared with MA; P uptake and P use efficiency of intercropping increased by 61% and 53% compared with the averaged monocultures, respectively, when considering all intercropping patterns and four-year results. This resulted in an enhanced land equivalent ratio (LER) based on yield and P uptake ranging from 1.13 to 1.62, with a higher LER observed under no P application. The intercropping pattern of four rows of maize and six rows of alfalfa with a row spacing of 30 cm had the greatest yield, leading to the highest LER among all the intercropping patterns. The positive complementary effect of intercropped alfalfa plays a crucial role in the observed advantages of maize/alfalfa intercropping. Intercropping increased alfalfa yield and P uptake. P uptake of alfalfa was positively correlated with the lateral root surface area. However, maize was at a competitive disadvantage under intercropping, the yield and P uptake was decreased compared to MM. P application increased total yield and P uptake averaged by 33% and 57%, respectively, compared to no P application. Phosphorus uptake efficiency was significantly higher under intercropping patterns (19.2%) compared to monocultures (9.0%) with P application. The complementary effect of intercropped alfalfa promoted the overall system yield and P uptake. The facilitative effects of maize/alfalfa intercropping were more pronounced in low P soils than with P application. The intercropping pattern of four rows of maize and six rows of alfalfa with a row spacing of 30 cm was recommended as the most productive cropping pattern. Maize/alfalfa intercropping are promising approaches to establishing productive and sustainable managed ecosystems, when designing a perennial legume-dominated cereal/legume intercropping system. [Display omitted] • Mechanisms underlying P uptake were studied at the root-soil interface in intercropping system. • Enhanced system yield and P uptake was due to complementary effect of intercropped alfalfa. • Superior water competition of alfalfa roots was critical to its enhanced yield and P uptake. • Four rows of maize alternated with six rows of alfalfa with a row spacing of 30 cm was recommended. • Appropriate maize/alfalfa intercropping help to establish productive and sustainable agroecosystems. [ABSTRACT FROM AUTHOR]