How does rising atmospheric CO2 affect marine organisms?

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Sphagnum Mosses: Could They Take the Heat of a Warmer World?
Gerdol, R. and Vicentini, R. 2011. Response to heat stress of populations of two Sphagnum species from alpine bogs at different altitudes. Environmental and Experimental Botany 74: 22-30.

The authors write that "Sphagnum mosses are a fundamental component of bog vegetation in northern regions, where these plants play a major role in controlling important ecosystem processes." However, they note that "as heat waves are expected [by some folks] to become increasingly intense and frequent, especially in cold territories," they felt it important to see if they could determine the ability of the mosses to survive such extreme weather events.

What was done
Scaling the south-eastern Alps of the Italian province of Bolzano, Gerdol and Vicentini collected cores of two Sphagnum species - S. fuscum and S. magellanicum - from three mountain heights above sea level: low (1090 m), intermediate (1780 m) and high (2100 m), which locations spanned, in their words, "almost the whole altitudinal range known for these species in mountainous regions of central-southern Europe." Then, back in the laboratory, they grew portions of the six cores for four days in a row at three 12-hour daytime temperature levels - ambient temperature (AT, 25°C), medium temperature (MT, 36°C) and hot temperature (HT, 43°C) - while they measured net CO2 exchange and chlorophyll a fluorescence, as well as plant tissue chemistry.

What was learned
The two Italian scientists report that normalized net CO2 exchange rates did not vary among species nor with altitude, and that net CO2 exchange rates in the plants experiencing the MT treatment declined during treatment but recovered noticeably six days after treatment stopped; and they say that despite receiving "severe damage," the plants experiencing the HT treatment also exhibited a capacity to recover six days after the conclusion of the temperature treatment.

What it means
Noting that their study suggests that "the two Sphagnum species possess moderate altitudinal plasticity to increased temperature," the ultimate conclusion of Gerdol and Vicentini, which they express in the final sentence of their paper, is that "heat waves, even stronger than ever recorded, will unlikely bring about die-off of Sphagnum mosses in bog ecosystems unless high temperatures are coupled with drought."

Reviewed 4 April 2012