Characteristics of nitrogen distribution and its response to microecosystem changes in green infrastructure with different woody plants

Abstract

With the acceleration of urbanization, N pollution in rainfall runoff has become the primary cause of eutrophication. In order to control N pollution in rainfall runoff, green infrastructure (GI) has been widely implemented. However, little is known about the process through which plants, especially woody plants, affect N distribution and the microecosystem in GI. Limited information suggests that woody plants mainly affect N distribution and alter the microecosystem through the influence of their roots. Therefore, laboratory tests were conducted to investigate the roles of the taproot plant Sophora japonica and the fibrous root plant Malus baccata and the resultant changes at the microecosystem level regarding N removal in a column-scale GI. After one year of growth, analysis of the morphological traits of the roots revealed that the average root length and diameter of S. japonica were approximately 2.3 and 1.8 times greater than those of M. baccata, respectively. An investigation of microbial diversity revealed that in comparison to the control GI system without plants, the GI systems with S. japonica and M. baccata hosted 45.68% and 59.88% more Actinobacteria, respectively. Further, the soil urease (S-UE) activities in the GI systems with S. japonica and M. baccata were 13.6% and 98.8% higher than that in the control, respectively, and the soil acid protease (S-ALPT) activities were 20.5% and 25.4% higher than that in the control, respectively. Compared to the control and the S. japonica GI system, the NH₃-N content in the soil of the M. baccata GI was 94.4% and 15.2% lower, respectively, and the NO₃-N content was 57.3% and 12.7% lower, respectively. The M. baccata GI system had the lowest NH₃-N and NO₃-N contents because it was most abundant in Actinobacteria and Arthrobacter and had the highest S-UE and S-ALPT activities. The results may be useful for improving N removal in GI containing different woody plants, and by extension for improving control of N pollution from rainfall runoff.

Keywords: Ammonia; Enzyme; Microorganism; Nitrate; Rainwater; Roots.