Inoculation of Arbuscular Mycorrhizal Fungi and Nitrogen-fixing Bacteria Affects Growth and Development of Melia dubia Seedlings Under Different Ni Concentrations

Two experiments were established in the screenhouse of the National Institute of Molecular Biology and Biotechnology, University of the Philippines Los Baños (BIOTECH-UPLB), to determine the effectiveness of new isolates of arbuscular mycorrhizal fungi (AMF) (NMYC) and nitrogen fixing bacteria (NNFB) from rhizosphere soil and roots of ferns and grasses growing in a more than three-decade barren copper mine tailing dumpsite in Barangay Capayang, Mogpog, Marinduque, on the growth and development of bagalunga (Melia dubia) belonging to the family Meliaceae. These were compared with those commercially available AMF inoculants (MYKOCAP® and MYKORICH®). The first experiment was established where seedlings were subjected to two factors (inoculation and nickel (Ni) level for a period of six months, following a Randomized Complete Block Design in four blocks with five treatments. The treatments were: control, MYKORICH®, MYKOCAP®, NewMYC (NMYC), and NewNFB (NNFB). Ni levels were: 0, 6, and 12mg kg-1 soil (coded as Ni-0, Ni-6 and Ni-12). Experiment 2 had similar inoculation treatment as Experiment 1 but the Ni rates were higher: 0, 3, and 6 g kg-1 soil (coded as Ni-0, Ni-3 and Ni-6). Results showed that in Experiment 1, the highest height and stem diameter increments were obtained in plants inoculated with MYKORICH® and grown in Ni-6. In Experiment 2, NMYC in Ni-0 produced the tallest height after six months whereas in Ni-6, MYKOCAP® gave the biggest stem diameter. The heaviest total biomass was obtained in MYKORICH® with Ni-6 and Ni-0 in Experiments 1 and 2, respectively. Moreover, in both trials, MYKOCAP® and MYKORICH®, exhibited highest root colonization and mycorrhiza spore counts, while isolates from the Cu mine dumpsite gave the highest NFB count. Inoculation with AMF including the isolates from the Cu mine site presented positive effect on growth and development of bagalunga seedlings grown in soil with Ni in the first experiment, and in soil without Ni in the second experiment. The study demonstrated better growth performance, soil microbial community, soil nutrient and heavy metal (HM) uptake due to inoculation with microbial biofertilizers including those Cu mine isolates. It is recommended that bagalunga be tested under field conditions specifically in Ni mined areas and determine the long-term impact of microbial inoculants on its growth and its capability as a bioremediation tree species.