Flooding effects on phosphorus dynamics in an Amazonian mangrove forest, Northern Brazil

Abstract

We examined porewater salinity, soil redox potential (Eh), soil extractable phosphate (extr.-P), leaf phosphorus (leaf-P) and plant growth in relation to inundation frequency (IF) and mangrove species distributions along a 600 m transect in the Braganca Peninsula, North Brazil. The forest species composition changed across the tidal zone with Avicennia germinans dominating (99.1%) the high intertidal (HI) zone where the IF was 41–67 d.y−1, Rhizophora mangle, Laguncularia racemosa and A. germinans co-occured in the mid intertidal (MI), and a mixed R. mangle (47.1%) - A, germinans (41.2%) stand occupied the low intertidal (LI) zone with an IF of 124–162 d.y−1. Low IF resulted in high Eh levels (200 mV) in the HI zone relative to the LI where Eh ranged from 0–100 mV. The IF showed a significant positive correlation with extr.-P (r = 0,89; p = 0.05) and a negative association with Eh (r = −0,75; p = 0.05). An ANCOVA confirmed that Eh and extr.P were influenced by flooding. Variations in these factors were reflected in patterns of P leaf tissue concentrations across the gradient; however, a MANCOVA showed that leaf-P was not related to tree height, tree volume or basal area. Water-logging conditions, porewater salinity, and P dynamics in the sediment appear to influence the forest structure. We suggest that P availability plays an important role in controling mangrove species distributions but not their growth.