Biochar and nitrogen fertilizer increase Glomus synergism and abundance and promote Trifolium pratense growth while inhibiting pollutant accumulation

Abstract

We examined the effects of nitrate nitrogen fertilizer (N), biochar (BC) and arbuscular mycorrhizal fungi (AMF) on Trifolium pratense mycorrhizal colonization, dry mass, nutrient and pollutant accumulation and soil AMF community, aiming to determine a potential approach that is beneficial to clover growth and AMF community under contaminated environment. Result showed that soil pH increased from 6.88 to 7.01 in the presence of N in combination BC treatments. Compared to control, N in combination BC treatments significantly decreased DTPA-Zn, Pb, Cd, As and Cu concentrations, and the average reduction for DTPA-Zn, Pb, Cd, As and Cu concentration by 53.2, 52.5, 48.8, 44.5 and 45.5%, respectively. Root colonization, shoot and root dry masses were increased when receiving both N and BC. On average, the shoot P, Zn, Pb, Cd and As levels were reduced by 39.7, 62.4, 86.7, 84.6 and 87.8% when receiving both N and BC and simultaneously the root Cd and Zn concentrations were reduced by 64.9 and 55.8%, respectively. DTPA-extractable Cd, Zn and Pb were positively correlated to shoot Zn, Pb and Cd concentrations as well as root Zn and Cd concentrations but negatively correlated with pH. Moreover, Glomus species were the soil major AMF present with all treatments. The combination N and BC treatments increased Glomus abundance but did not affect overall AMF diversity. Soil pH, DTPA-Cd, Zn, Pb and Cu had greater effect on AMF community structure as assessed by redundancy analysis (RDA). Glomus abundance was positively related to pH, root colonization, shoot and root dry mass and negatively related to DTPA-Cd, Zn, Pb and Cu. A network analysis indicated that BC and N addition promoted synergistic interactions among Glomus species. Our results demonstrated that the N in combination BC treatments can promote plant growth while decreasing pollutant accumulation in shoot and root, and the N and BC addition can increase Glomus abundance and their synergistic interactions under multi-contaminated soil.