Elevated carbon dioxide and reduced salinity enhance mangrove seedling establishment in an artificial saltmarsh community
The global phenomenon of mangrove encroachment into saltmarshes has been observed across five continents. It has been proposed that this encroachment is driven in part by rising atmospheric CO2 concentration and reduced salinity in saltmarshes resulting from rising sea levels enhancing the establishment success of mangrove seedlings. However, this theory is yet to be empirically tested at the community-level. In this study, we examined the effect of CO2 and salinity on seedling growth of two mangrove species, Aegiceras corniculatum and Avicennia marina, grown individually and in a model saltmarsh community in a glasshouse experiment. We found that the shoot (210%) and root (91%) biomass of the saltmarsh species was significantly greater under elevated CO2. As a result, both mangrove species experienced a stronger competitive effect from the saltmarsh species under elevated CO2. Nevertheless, A. marina seedlings produced on average 48% more biomass under elevated CO2 when grown in competition with the saltmarsh species. The seedlings tended to allocate this additional biomass to growing taller suggesting they were light limited. In contrast, A. corniculatum growth did not significantly differ between CO2 treatments. However, it had on average 36% greater growth under seawater salinity compared to hypersaline conditions. Avicennia marina seedlings were not affected by salinity. From these results, we suggest that although CO2 and salinity are not universal drivers determining saltmarsh–mangrove boundaries, it is likely that rising atmospheric CO2 concentration and reduced salinity associated with sea level rise will enhance the establishment success of mangrove seedlings in saltmarshes, which may facilitate mangrove encroachment in the future.
KeywordsAegiceras corniculatum Avicennia marina Climate change Wetland Woody plant encroachment
We gratefully acknowledge the Plant Invasion and Restoration Ecology Laboratory (PIREL) of Macquarie University for their input throughout the experiment and Muhammad Masood for assistance in the glasshouses. A scientific license (SL101685) issued by the New South Wales Office of Environment and Heritage granted permission for the collection of mangrove propagules from the field.
Author contribution statement
AM and MRL conceived and designed the experiments. AM and IG performed the experiments. AM analysed the data. AM, IG and MRL wrote the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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