Root biomass and production of mangroves surrounding a karstic oligotrophic coastal lagoon

Abstract

Root production influences a range of belowground processes, such as soil accretion, carbon sequestration and nutrient acquisition. Here, we measured biomass and root production of mangroves surrounding a karstic oligotrophic lagoon that spans a nutrient and salinity gradient. We also measured forest structure and soil physicochemical conditions (salinity, bulk density, carbon, nitrogen (N) and phosphorus (P)) in order to determine factors associated with root production. We tested the following hypotheses: 1) root biomass and production increase at low soil P and N in order to maximize resource utilization, and 2) root biomass and production increase with high interstitial salinity. Root biomass (947 - 3040 g m-2) and production (0.46 - 1.85 g m-2 d-1) increased where soil P and interstitial salinity were relatively high. Thus, we rejected the first hypothesis and confirmed the second. The larger root fraction (5 - 20 mm) was the major contributor to root biomass and production. Our findings suggest that root production and thus capacity for belowground carbon storage in karstic regions, where P is often limiting, is greater where interstitial salinity and P are higher. This contrasts with past assessments indicating that P-deficiency stimulates root growth, suggesting wide variation in belowground responses in mangroves.