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Effects of Elevated CO2 and Nutrients on the Growth of Mangroves

Paper Reviewed
Reef, R., Slot, M., Motro, U., Motro, M., Motro, Y., Adame, M.F., Garcia, M., Aranda, J., Lovelock, C.E. and Winter, K. 2016. The effects of CO2 and nutrient fertilization on the growth and temperature response of the mangrove Avicennia germinans. Photosynthesis Research 129: 159-170.

Introducing their significant study, Reef et al. (2016) describe how they collected Avicennia germinans propagules in July of 2014 at Galeta Point, Panama, and transferred them to the Santa Cruz Experimental Field Facility of the Smithsonian Tropical Research Institute, where they were planted in individual 1.6-L tree pots filled with a mixture of local clay-textured topsoil and sand, after which the plants "were randomly assigned to one of two well-ventilated, naturally-illuminated glasshouses receiving full sunlight, one with similar to ambient (ca. 400 ppm) CO2 concentrations and one with an elevated (800 ppm) CO2 concentration."

The seedlings thus produced were watered twice weekly with a 300-ml salt solution and either a low- or high-nutrient (five times greater) solution. And after three months of subsequent growth, they report that "photosynthetic temperature response curves were assessed for four randomly selected plants from each of the four treatments over the period of a week." So what did the ten researchers learn from their study?

First of all, they report that they found (1,2) "large synergistic gains in both growth (42%) and photosynthesis (115%) when seedlings grown under elevated CO2 were supplied with elevated nutrient concentrations relative to their ambient growing conditions," that (3) "under low-nutrient conditions and elevated CO2, root volume was more than double that of seedlings grown under ambient CO2 levels," and that (4) "elevated CO2 significantly increased the temperature optimum for photosynthesis by ca. 4°C."

As further justification for what they observed, Reef et al. note, in concluding, that (5) "for a congenitor in the Pacific Ocean (A. marina), there is evidence that primary production has already been influenced by elevated CO2," citing the findings of Reef and Lovelock (2014), which were also of a significant positive nature. And in light of these complementary findings, they conclude that because "increased nutrient loading in coastal areas is widespread," that (6-8) "synergistic interactions with elevated CO2 are likely to result in overall increases in mangrove biomass, carbon sequestration and below-ground carbon storage."

Reef, R. and Lovelock, C.E. 2014. Historical analysis of mangrove leaf traits throughout the 19th and 20th centuries reveals differential responses to increases in atmospheric CO2. Global Ecology and Biogeography 23: 1209-1214.

Posted 15 November 2016