Mechanism of the improvement effect by biochar and AM fungi on the availability of soil nutrients in coal mining area

Objectives The soil of mining area is infertile and lack of available nutrients, biochar and arbuscular mycorrhizal (AM) fungi play critical roles in driving soil nutrient cycling processes, and improving plant resistance to environmental stress and nutrient utilization. Therefore, this study evaluated the synergy of biochar and AM fungi, in order to find a better measurement for ecological restoration and the efficient agriculture production in mining areas.

Methods A pot experiment was conducted to investigate the effects of biochar amendment and AM inoculation on maize (Zea mays) growth and nutrient uptake, and soil nutrient contents in heavy metal pollution soil. The soil used for the pot experiment was collected from the “Jiangchun” mining area in Xin’an, Luoyang City, Henan Province. Maize cultivar of Hongdan 897 was used as test materials in Henan University of Science and Technology. There were 4 treatments: without biochar or AM inoculation, base application of biochar 20 g/kg, AM inoculation 20 g/kg, wheat-straw biochar and AM inoculation together, denoted as CK, B, M and BM, respectively. Pots were randomly arranged in the greenhouse with eight replicates per treatment. After two months of growth, maize was harvested, dry weight was measured, nutrients and antioxidant enzyme activities were analyzed, and the content of soil nutrients was determined.

Results The results showed that biochar or AM inoculation alone or their combination significantly increased maize growth and improved net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), leaf color value (SPAD value), and antioxidant enzymatic activities (P < 0.05). AM fungi inoculation played a better role in promoting maize growth, physiological biochemistry characteristics and phosphorus (P) absorption than biochar, while biochar amendment alone was more effective in improving soil pH and potassium (K) absorption in maize. Amending soil with biochar and AM inoculation together produced the largest increase in maize growth and soil improvement with 176.67%, 45.84% increase of biomass of root and shoot, 84.22% greater of total root length, 35.42%, 56.44%, 88.31% and 22.77% higher of P_n, T_r, G_s and SPAD value in maize leaves respectively. The combined treatment also had a synergistic effect on inducing the root AM fungi colonization rates with 234.20% increase compared with CK, the mycelium density could reach 4.37 m/g, and the total glomalin (TG) and easy extraction glomalin (EEG) could reach 4.32 and 1.60 g/kg, respectively. In addition, biochar amendment and AM inoculation together increased the contents of organic matter, alkaline hydrolysis nitrogen, available phosphorus and readily available potassium by 24.23%, 43.26%, 98.63% and 33.93%, respectively.

Conclusions On the whole, biochar and AM inoculation alone or their combination all improved maize growth, nutrient uptake, and the availability of soil nutrients. The combined treatment of biochar and AM fungi showed the best effect on maize growth, nutrient uptake, showing promising measurement for ecological restoration and efficient agriculture production in mining areas.