PS 7-66
10 years exposure to elevated CO2 increases stomatal number of Pinus koraiensis and P. sylvestriformis needles
An increase in atmospheric CO2 concentration has affected many important physiological processes of plants. Investigations of a wide range of fossil plants and current evidence show that stomatal density decreased with rising CO2 concentrations. However, the mimic researches show that stomatal density for different plants grown in OTCs or FACE decrease, increase and even no detectable changes. Thus, the responses of stomatal density or number to elevated CO2 are highly species-specific and inconsistent. Here we report how elevated CO2 affect stomatal density and number of needles of Pinus koraiensis and P. sylvestriformis during 8 to 10 years’ exposure to elevated CO2. The OTCs were established at the Research Station of the Changbai Mountain Forest Ecosystem in NE China. Seeds of P. sylvestriformis and P. koraiensis were sown into the OTCs and were treated with ambient CO2 concentration of approx. 370 μmol mol-1 and elevated CO2 concentration of 500 μmol mol-1 CO2 since spring of 1999. In addition, gas exchange measurements of needles were also made in situ.
Results/Conclusions
Elevated CO2 increased stomatal density on P. sylvestriformis by 10.8% (13.5% on abaxial surface and 8.0% on adaxial surface) and the number of stomatal rows on P. koraiensis by 7.9% (5.0% in one-year-old needles and 10.7% in current-year needles). Increased stomatal density for P. sylvestriformis and number of stomatal rows for P. koraiensis indicate that elevated CO2 increases stomatal number in both tree species. Needle age significantly influenced stomatal density and number of stomatal rows in P. koraiensis but not in P. sylvestriformis. For both species, elevated CO2 did not significantly affect stomatal conductance but increased water use efficiency. The increase in stomatal number is not accompanied by significant changes in stomatal conductance at elevated CO2 for both tree species being exposed to elevated CO2 concentrations. The results indicate that there may be no direct relationship between stomatal conductance and stomatal numbers.