Why are there no Arctic mangroves?

Mangrove plants are primarily found in tropical and sub-tropical tidal flats, and temperature appears to be critical to them, but it has not been clear why. Tomomi Inoue and colleagues have found that mangrove species require a warm temperature to ensure respiration rates sufficient for maintenance and growth, particularly in roots. The findings could help predict responses to the warming climate.

Inoue and colleagues examined two mangrove species, Bruguiera gymnorrhiza and Rhizophora stylosa. They grew the two species at four different temperatures (15, 20, 25 and 30 °C); they then measured growth parameters, chemical composition, and leaf and root O₂ respiration rates. 

The relative growth rates of both species increased with growth temperature due to changes in physiological parameters such as net assimilation rate and respiration rate rather than to changes in structural parameters such as leaf area ratio. 

Inoue and colleagues write: “We analysed the responses of growth parameters to growth temperature in the context of respiration cost for maintenance and growth in seedlings of two mangrove species and found that both species require a threshold temperature (12.2 °C in B. gymnorrhiza and 18.1 °C in R. stylosa) to ensure an O₂ respiration rate sufficient for their leaf and root maintenance and growth. The link between leaf and root growth parameters and O₂ respiration in the two mangrove species indicates that the underground temperature probably limits their growth under the low-temperature condition.”

“Our results suggest that the effects of global warming caused by climate change could differ between the two mangrove species. In the future, other factors controlling the warm habitat range of mangroves should be examined; for example, mangrove plants grow in tidal flats where salinity stress can affect respiratory cost for maintenance and growth.”

READ THE ARTICLE

Tomomi Inoue, Yasuaki Akaji, Ko Noguchi, Distinct responses of growth and respiration to growth temperatures in two mangrove species, Annals of Botany, Volume 129, Issue 1, 1 January 2022, Pages 15–28, https://doi.org/10.1093/aob/mcab117