Plant growth-promoting bacteria: a potential tool for arid mangrove reforestation

Although a few countries protect mangroves (USA, some states in Mexico), the systematic destruction of these ecosystems is increasing. Deforestation of mangrove communities is thought to be one of the major reasons for the decline in coastal fisheries of many tropical and subtropical countries. Although mangroves in the tropics can regenerate themselves or be restored using low-technology propagule planting, arid mangroves (areas having limited or no access to fresh water) can seldom regenerate, and if they do, it happens very slowly. To conserve arid tropical mangrove ecosystems, maintenance and restoration of the microbial communities is required. There is sufficient published evidence to propose a close microbe-nutrient-plant relationship that functions as a major mechanism for recycling and conserving essential nutrients in the mangrove ecosystem. The highly productive and diverse microbial community living in tropical and subtropical mangrove ecosystems continuously transforms dead vegetation into sources of nitrogen, phosphorus, and other nutrients that can later be used by the plants. In turn, plant-root exudates serve as a food source for the microorganisms living in the ecosystem, with other plant material serving a similar role for larger organisms, such as crabs and detritus-feeding fish. This speculative synthesis of recent work on growth-promoting bacteria proposes that mangrove rhizosphere bacteria be used as a tool to enhance reforestation with mangrove seedlings. This can be done by inoculating seedlings with plant-growth-promoting bacteria participating in one or more of the microbial cycles of the ecosystem.