Co-application of Biochar and Arbuscular Mycorrhizal Fungi (AMF) for Mitigating Salinity Stress in Mangrove Seedlings

High salinity affects not only mangrove plants but also their surrounding ecosystem; thus, countermeasure action is inevitable. Therefore, the aim of this study was to mitigate salinity stress in mangroves through the co-application of biochar and AMF. Rhizophora apiculata, a true, pioneering, and salt-tolerant mangrove species, was selected as the model plant. The experiment was designed using a completely randomized factorial design. Six amendment treatments were set up in this experiment: (1) control (without addition of AMFs and biochar); (2) AMF (sole application of AMFs); (3) Bio1 (sole application of 1% w/w biochar); (4) Bio1 + AMF; (5) Bio10 (sole application of 10% w/w biochar); and (6) Bio10 + AMF. In order to examine the effect of salinity stress, two gradients of artificial seawater were conducted for each treatment: low salinity (5% v/v of seawater) and high salinity (60% v/v of seawater). The result showed that Bio10 + AMF was able to significantly increase the epicotyl height by 102% and 78% compared to control in low and high salinity, respectively. Moreover, in low salinity, the Bio10 + AMF increased 46.7% of fresh plant weight, but only 19.1% in high salinity. Application of Bio10 + AMF decreased 52.7% of malonaldehyde content compared to control, an indication of salinity stress alleviation. For mycorrhization, the addition of 1% and 10% biochar to AMF increased 45.3% and 49.3% of root colonization, respectively. In conclusion, the addition of biochar to AMF has significant potency to improve mangrove growth, alleviate salinity stress, and increase root mycorrhization.