Groundwater enhances above‐ground growth in mangroves

Abstract

Groundwater flow through coastal wetlands plays an important role in the maintenance of productivity of intertidal ecosystems. Groundwater can reduce salinity and increase nutrient availability which can enhance plant growth and alter plant biomass allocation patterns. Here, we used stable isotopes of oxygen and hydrogen to assess how groundwater influences below‐ground and above‐ground growth in the widespread mangrove species Avicennia marina. We found source water within tree stems varied seasonally, with non‐saline water use higher in the wet season when rainwater availability was highest compared to the dry season. Stems with higher proportional contribution of non‐saline water had increased above‐ground growth but no effect on below‐ground growth. Below‐ground growth was however influenced by nutrient availability across the intertidal zone which was higher in the high‐ compared to the low‐intertidal zone. Synthesis. This study shows that mangroves use non‐saline groundwater and rainwater when available rather than saline water sources. Groundwater flows into the intertidal stimulates organic matter accumulation in above‐ground biomass suggesting the availability of non‐saline water sources, such as groundwater and rainfall, are important for the growth and productivity of mangrove forests.

Daily salinity fluctuation alleviates salt stress on seedlings of the mangroveBruguiera gymnorhiza

“…Spatially, mangroves can use a variety of FW resources (Bazihizina, Barrett‐Lennard, & Colmer, ; Lambs et al, ; Nguyen et al, ; Reef & Lovelock, ; Semeniuk, ). A few researches have confirmed that mangroves can utilize seasonal FW (Gabler et al, ; Hayes et al, ; Santini, Reef, Lockington, & Lovelock, ). In our study, B. gymnorhiza seedlings under daily FS treatments were able to absorb enough Na + and Cl − ions to perform proper osmotic adjustment in their roots when re‐subjected to periodical saline habitats, and they also absorbed enough water to avoid excessively high salt concentrations when their roots come into contact with periodical FW.…”

“…This view is corroborated by higher leaf succulence detected under the FS treatment (Figure b). A few field studies have shown that adding FW (as precipitation or fresh groundwater) could increase primary productivity of mangrove forests via reductions in soil salinity (Gabler et al, ; Hayes et al, ; Osland et al, ; Santini et al, ). Our results are consistent with those findings.…”

Foliar water uptake by coastal wetland plants: A novel water acquisition mechanism in arid and humid subtropical mangroves

“…41‰ and 25.08 ± 0.03‰ respectively. From previous research(Hayes et al, 2019), we estimated mangrove isotopic leaf values (pre-treatment) would range between 0 and −30‰ for δD and between 0 and −6‰ for δ 18 O. Thus, after application with our labelled mist water, if leaves accumulated labelled mist water following foliar mist exposure, we would expect internal leaf water values of δD to become more depleted and δ 18 O to become more enriched.…”

Stable isotopes track the ecological and biogeochemical legacy of mass mangrove forest dieback in the Gulf of Carpentaria, Australia

“…As elements such as carbon (C), nitrogen (N) and sulfur (S) circulate in the biosphere, stable isotopic compositions of 13 C/ 12 C, 15 N/ 14 N and 34 S/ 32 S change in predictable ways due to mixing and fractionation, giving insights into sources and cycling of these elements (Fry 2006). SIA has been widely used in mangrove ecosystem studies to better understand food web interactions (Bouillon et al, 2008;Larsen et al, 2012;Bui and Lee, 2014;Abrantes et al, 2015), mangrove nutrient uptake (McKee et al, 2002), mangrove water use (Santini et al, 2015;Hayes et al, 2019), cycling of C (Maher et al, 2013a;Maher et al, 2017;Sasmito et al, 2020), N (Fry and Cormier, 2011), S (Raven et al 2019), and greenhouse gas emissions (Maher et al, 2013b).…”