What was done
Two Australian mangrove species, differing in salt-tolerance and relative growth rates, were grown for 14 weeks in glasshouses with different combinations of atmospheric CO2 ( 340 and 700 ppm), relative humidity (43 and 86%), and salinity (25 and 75% of seawater) to determine the effects of these variables on their development and growth.  Of the two species utilized, Rhizophora stylosa has a slower relative growth rate than does Rhizophora apiculata, but it also has greater salt tolerance than does R. apiculata.

What was learned
Averaged across the entire experiment, elevated CO2 significantly increased rates of net photosynthesis in both mangrove species, but only when grown at the lower salinity level.  Interestingly, the percentage CO2-induced increase in photosynthesis was greater for R. stylosa, than it was for R. apiculata, which generally is faster growing than R. stylosa.

Although elevated CO2 did not significantly affect the relative growth rate of either species, the average relative growth rates of both species increased with atmospheric CO2 enrichment in the lower salt environment; and true to its characterization, R. apiculata displayed a greater CO2-induced growth stimulation than did R. stylosa, particularly at the lower relative humidity.

What it means
As the atmospheric CO2 concentration continues to rise, these two Australian mangrove species will likely display increases in both net photosynthesis and growth, particularly within their current geographical ranges under low salinity stress.  It is also conceivable that increasing amounts of atmospheric CO2 may enable R. apiculata to expand it's present range into areas of greater aridity, thus introducing greater species diversity into such regions.