High Productivity Makes Mangroves Potentially Important Players in the Tropical Silicon Cycle

Abstract

Over the last two decades, recognition of the important role terrestrial plants play in regulating silicon (Si) cycling has emerged. Si improves plant fitness by protecting them from abiotic (e.g., desiccation) and biotic (e.g., fungal attack) stressors. Once incorporated into plant biomass this biogenic Si is more bio-available than the lithogenic material from which it was ultimately derived. Thus plants play a key function in regulating the amount and timing of Si availability in downstream ecosystems. Recent work has highlighted the importance of salt marshes in the temperate Si cycle. However, the role of their tropical counterparts, mangroves, has largely gone unexplored. Here we report foliar concentrations of plant Si (as %Si by dry weight) for four Caribbean mangrove species: Conocarpus erectus (buttonwood), Laguncularia racemosa (white mangrove), Avicennia germinans (black mangrove), and Rhizophora mangle (red mangrove). Overall, the median Si concentration was low (0.07%) and did not vary among plant part (e.g., foliage, twig, and propagule). There was also little variation in Si among species. Using literature values of aboveground net primary production, and the concentrations reported here, we estimate an aboveground mangrove Si uptake rate of 2–10 kg Si ha–1 year–1. These rates are on par with rates reported for temperate and boreal forests as well as low nutrient salt marshes, but lower than estimates for high nutrient salt marshes. Thus, despite the low Si concentrations observed in mangroves, their high productivity appears to make them a hot spot of Si cycling in tropical coastal systems.

Phylogeography of mangrove pit vipers (Viperidae, Trimeresurus erythrurus‐purpureomaculatus complex)

“…Obtaining a deeper understanding of the natural history, environmental constraints, physiology, population genetics, and ecological interactions between mangrove pit vipers and mangrove forests is crucial to the long‐term persistence and conservation of this species, especially in the face of rapid degradation and fragmentation of mangrove forests globally. Mangroves are one of the most productive ecosystems on the planet (Elizondo et al, 2021; Ribeiro et al, 2019), yet they are also being degraded at an unprecedented rate due to anthropogenic activities and climate change (Alongi, 2008; Carugati et al, 2018; Mukhopadhyay et al, 2015). Despite the relatively low plant diversity, mangroves harbour high levels of biodiversity that have yet to be fully appreciated (Yeo et al, 2021).…”

Marine macroalgae are an overlooked sink of silicon in coastal systems

“…We then converted dissolved SiO 2 concentrations of the digestate back to macroalgae percentage BSi by mass (Conley & Schelske, 2002). Finally, when reporting molar ratios of C : Si, we converted our BSi values to Si by multiplying by 0.47, the mass fraction of Si in the SiO 2 molecule (Elizondo et al ., 2021).…”

“…Across the marine landscape, from estuaries to the open ocean, biota take up silicon (Si) as monosilicic acid and deposit it into their tissues as biogenic silica (BSi). Along the coast, vegetated ecosystems, such as salt marshes and mangroves, sequester a significant amount of Si in their tissues and likely help regulate the availability of Si in surrounding waters (Carey & Fulweiler, 2014; Elizondo et al ., 2021). Si is also accumulated by sponges, euglyphid amoebae, radiolarians, silicoflagellates, and choanoflagellates, as well as a few coccolithophores, Prasinophyceae, and picocyanobacteria (Raven & Giordano, 2009; Gadd & Raven, 2010; Baines et al ., 2012).…”

Porewater exchange drives the dissolved silicate export across the wetland‐estuarine continuum

“…Water types DSi (mmol L -1 ) DSi : DIN DSi : DIP seawater during the submerged periods via the transport by roots and stem, and then stored them as the biogenic silica (BSi) (Raven, 2003;Yang and Zhang, 2018). A substantial reactive BSi can return to wetland sediments with litterfall, increasing DSi concentrations via mineralization and weathering (Cornelis et al, 2011;Elizondo et al, 2021). The monocots are recognized as the typical Siaccumulators due to the strong uptake of Si (Ma and Takahashi, 2002).…”

“…Silicon (Si, the second most abundant element in the earth's crust) is an important element for wetlands and marine ecosystems (Epstein, 1994;Ma and Takahashi, 2004). Many studies focused on Si concentrations, compositions and their variations in plants and sediments (de Bakker et al, 1999;Elizondo et al, 2021). However, the exportimport pattern of dissolved silicate (DSi) in mangrove wetlands was rarely studied.…”