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Non-stomatal limitation to photosynthesis in Cinnamomum camphora seedings exposed to elevated O3.

Niu J, Feng Z, Zhang W, Zhao P, Wang X - PLoS ONE (2014)

Bottom Line: Ozone (O3) is the most phytotoxic air pollutant for global forests, with decreased photosynthesis widely regarded as one of its most common effects.The actual photochemical efficiency of photosystem II (PSII) in saturated light (Fv'/Fm') was also significantly decreased by E-O3, as was the effective quantum yield of PSII photochemistry (ΦPSII).Although neither the stomatal conductance (gs) nor the intercellular CO2 concentration (Ci) was decreased by E-O3, PN/gs was significantly reduced.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, Guangdong, China.

ABSTRACT
Ozone (O3) is the most phytotoxic air pollutant for global forests, with decreased photosynthesis widely regarded as one of its most common effects. However, controversy exists concerning the mechanism that underlies the depressing effects of O3 on CO2 assimilation. In the present study, seedlings of Cinnamomum camphora, a subtropical evergreen tree species that has rarely been studied, were exposed to ambient air (AA), ambient air plus 60 [ppb] O3 (AA+60), or ambient air plus 120 [ppb] O3 (AA+120) in open-top chambers (OTCs) for 2 years. Photosynthetic CO2 exchange and chlorophyll a fluorescence were investigated in the second growing season (2010). We aim to determine whether stomatal or non-stomatal limitation is responsible for the photosynthesis reduction and to explore the potential implications for forest ecosystem functions. Results indicate that elevated O3 (E-O3) reduced the net photosynthetic rates (PN) by 6.0-32.2%, with significant differences between AA+60 and AA+120 and across the four measurement campaigns (MCs). The actual photochemical efficiency of photosystem II (PSII) in saturated light (Fv'/Fm') was also significantly decreased by E-O3, as was the effective quantum yield of PSII photochemistry (ΦPSII). Moreover, E-O3 significantly and negatively impacted the maximum rates of carboxylation (Vcmax) and electron transport (Jmax). Although neither the stomatal conductance (gs) nor the intercellular CO2 concentration (Ci) was decreased by E-O3, PN/gs was significantly reduced. Therefore, the observed reduction in PN in the present study should not be attributed to the unavailability of CO2 due to stomatal limitation, but rather to the O3-induced damage to Ribulose-1,5-bisphosphate carboxylase/oxygenase and the photochemical apparatus. This suggests that the down-regulation of stomatal conductance could fail to occur, and the biochemical processes in protoplasts would become more susceptible to injuries under long-term O3 exposure, which may have important consequences for forest carbon and water budget.

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Effects of elevated O3 on the maximum rates of carboxylation (Vcmax) and electron transport (Jmax).Vertical bars represent average levels and distinct letters indicate significant differences among O3 regimes (n = 4) (AA: ambient air; AA+60: ambient air plus 60 [ppb] O3; AA+120: ambient air plus 120 [ppb] O3).
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pone-0098572-g002: Effects of elevated O3 on the maximum rates of carboxylation (Vcmax) and electron transport (Jmax).Vertical bars represent average levels and distinct letters indicate significant differences among O3 regimes (n = 4) (AA: ambient air; AA+60: ambient air plus 60 [ppb] O3; AA+120: ambient air plus 120 [ppb] O3).

Mentions: Vcmax was significantly decreased by AA+60 and AA+120 on 24 September, but only by AA+120 on 22 July (Figure 2b). Both AA+60 and AA+120 exerted significantly negative effects on Jmax (Figure 2a) across the two MCs. The difference in Jmax between AA+60 and AA+120 was statistically significant on 22 July, but not on 24 September (Figure 2a). Jmax varied significantly, while Vcmax maintained the same levels across the two MCs (Table 2). Jmax/Vcmax was not significantly affected by E-O3 in the present study (Figure 2c).


Non-stomatal limitation to photosynthesis in Cinnamomum camphora seedings exposed to elevated O3.

Niu J, Feng Z, Zhang W, Zhao P, Wang X - PLoS ONE (2014)

Effects of elevated O3 on the maximum rates of carboxylation (Vcmax) and electron transport (Jmax).Vertical bars represent average levels and distinct letters indicate significant differences among O3 regimes (n = 4) (AA: ambient air; AA+60: ambient air plus 60 [ppb] O3; AA+120: ambient air plus 120 [ppb] O3).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4043779&req=5

pone-0098572-g002: Effects of elevated O3 on the maximum rates of carboxylation (Vcmax) and electron transport (Jmax).Vertical bars represent average levels and distinct letters indicate significant differences among O3 regimes (n = 4) (AA: ambient air; AA+60: ambient air plus 60 [ppb] O3; AA+120: ambient air plus 120 [ppb] O3).
Mentions: Vcmax was significantly decreased by AA+60 and AA+120 on 24 September, but only by AA+120 on 22 July (Figure 2b). Both AA+60 and AA+120 exerted significantly negative effects on Jmax (Figure 2a) across the two MCs. The difference in Jmax between AA+60 and AA+120 was statistically significant on 22 July, but not on 24 September (Figure 2a). Jmax varied significantly, while Vcmax maintained the same levels across the two MCs (Table 2). Jmax/Vcmax was not significantly affected by E-O3 in the present study (Figure 2c).

Bottom Line: Ozone (O3) is the most phytotoxic air pollutant for global forests, with decreased photosynthesis widely regarded as one of its most common effects.The actual photochemical efficiency of photosystem II (PSII) in saturated light (Fv'/Fm') was also significantly decreased by E-O3, as was the effective quantum yield of PSII photochemistry (ΦPSII).Although neither the stomatal conductance (gs) nor the intercellular CO2 concentration (Ci) was decreased by E-O3, PN/gs was significantly reduced.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, Guangdong, China.

ABSTRACT
Ozone (O3) is the most phytotoxic air pollutant for global forests, with decreased photosynthesis widely regarded as one of its most common effects. However, controversy exists concerning the mechanism that underlies the depressing effects of O3 on CO2 assimilation. In the present study, seedlings of Cinnamomum camphora, a subtropical evergreen tree species that has rarely been studied, were exposed to ambient air (AA), ambient air plus 60 [ppb] O3 (AA+60), or ambient air plus 120 [ppb] O3 (AA+120) in open-top chambers (OTCs) for 2 years. Photosynthetic CO2 exchange and chlorophyll a fluorescence were investigated in the second growing season (2010). We aim to determine whether stomatal or non-stomatal limitation is responsible for the photosynthesis reduction and to explore the potential implications for forest ecosystem functions. Results indicate that elevated O3 (E-O3) reduced the net photosynthetic rates (PN) by 6.0-32.2%, with significant differences between AA+60 and AA+120 and across the four measurement campaigns (MCs). The actual photochemical efficiency of photosystem II (PSII) in saturated light (Fv'/Fm') was also significantly decreased by E-O3, as was the effective quantum yield of PSII photochemistry (ΦPSII). Moreover, E-O3 significantly and negatively impacted the maximum rates of carboxylation (Vcmax) and electron transport (Jmax). Although neither the stomatal conductance (gs) nor the intercellular CO2 concentration (Ci) was decreased by E-O3, PN/gs was significantly reduced. Therefore, the observed reduction in PN in the present study should not be attributed to the unavailability of CO2 due to stomatal limitation, but rather to the O3-induced damage to Ribulose-1,5-bisphosphate carboxylase/oxygenase and the photochemical apparatus. This suggests that the down-regulation of stomatal conductance could fail to occur, and the biochemical processes in protoplasts would become more susceptible to injuries under long-term O3 exposure, which may have important consequences for forest carbon and water budget.

Show MeSH
Related in: MedlinePlus