Effects of maize/soybean intercropping on nitrogen mineralization and fungal communities in soil

Aims\r\nMicroorganisms in intercropping systems accelerate nitrogen (N) cycling in soil and supply N for crops compared to monoculture. However, whether fungi increase the organic N mineralization under intercropping systems compared to soils with sole crops remains unknown. We hypothesized that the fungal-mediated N mineralization in intercropping under low N conditions increases soil N mineralization because fungi decompose complex organic substances by secreting extracellular enzymes.\r\n\r\nMethods\r\nSoil was sampled in a 13-year field experiment with monocultures of maize and soybean as well as maize/soybean intercropping without N input (N0) or with 180 kg N ha−1 input (N180). The net N mineralization and the enzymes (urease and protease) as well as fungal community structure were analyzed in soil during vegetation season to assess the role of fungi in N mineralization in intercropping systems.\r\n\r\nResults\r\nIntercropping increased the net N mineralization in soil by 1.6 times compared to monocultured maize while the fungi did not correlate with N mineralization under N0. The redundancy analysis showed that the soil chemical properties and enzyme activities explained 68% of the total variation of fungal communities. The net mineralized N amount increased with the relative abundance of Glomeromycota under N180 (p = 0.04).\r\n\r\nConclusion\r\nMaize/soybean intercropping exploited more N from the soil organic matter pool under low soil N conditions without the role of soil fungal communities, but the activities of phylum Glomeromycota can increase net N mineralization under high soil N conditions. This study provides evidence of N mineralization driven by fungi in intercropping at high N input.