Mangrove-microbe-soil relations

Abstract

The interactions of mangrove trees with soil and associated microorganisms are complex. Mangrove trees must cope with a harsh, waterlogged environment, being anchored in soils colonized by highly abundant, productive, and diverse microbial assemblages. The soil horizons are usually dominated by biogenic structures, usually crab burrows and deep tree roots, and are often pockmarked with cracks and fissures. These structures and their activities, coupled with drainage and recharge of interstitial water by tides, foster spatially complex patterns of organic matter decomposition within the forest floor. Except for biogenic structures, oxygen penetrates only a few millimeters into the soil, so anaerobic processes dominate early diagenesis. Sulfate reduction is often the major anoxic process, occurring to a soil depth of at least 1 m and relating to root uptake and exudation of dissolved materials. Recent evidence suggests that iron and manganese reduction may be important in close association with roots and crab activities. Mangrove soils are a source of microbially mediated gases, such as CO2, CH4, N2, and N20. The driving factor of plant-soil relations in mangrove forests is the high nutrient and water requirements needed to fuel high rates of tree photosynthesis. Close and highly efficient tree-microbe-soil interrelationships are a major factor in explaining why mangroves are highly productive forests in oligotrophic environments.