Growth and photosynthetic responses of four landscape shrub species to elevated ozone

Abstract

Attention should be paid to ozone (O 3) sensitivity of greening plant since ground-level O 3 concentrations are increasing especially in urban and suburban area. We studied the ecophysiological responses to elevated O 3 of four shrub species [Euonymus bungeanus Maxim. (EB), Photinia × fraseri (PF), Chionanthus retusus Lindl. & Paxt. (CR) and Cornus alba L. (CA)], which are often used for garden greening in China. Saplings of those species were exposed to high O 3 concentration (70 nmol mol -1, 7 h d -1 for 65 d) in open-top growth chambers. Responses to O 3 were assessed by gas exchanges, chlorophyll (Chl) fluorescence and dry mass. We found that elevated O 3 significantly decreased lightsaturated net photosynthetic rate (P Nsat), transpiration rate (E) and stomatal conductance (g s). The ratio of intercellular CO 2 to ambient CO 2 concentration (C i/C a) did not reduce under O 3 fumigation which suggested that the O 3-induced depressions of P Nsat under O 3 fumigation were probably due to limitation of mesophyll processes rather than stomatal limitation. High O 3 exposure also significantly depressed the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (F v/F m) which meant the O3-induced photoinhibition. Both root dry mass and root/shoot ratios were significantly decreased under ozone fumigation, but the total mass was unchanged. The responses of gas exchange such as P Nsat in these four shrubs to O 3 exposure were species-specific. Highest loss of P Nsat was observed in EB (-49.6%), while the CR had the lowest loss (-36.5%). Moreover, the O 3-exposed CR showed similar g s as CF, reflecting that its O 3 flux might be unchanged under elevated O 3 environment. Ozone drastically decreased actual quantum yield of PSII (Φ PSII) and electron transport rate (ETR) in EB while increased Φ PSII and ETR in CR. Furthermore, the relative losses in P Nsat positively correlated with the relative decreases in Φ PSII and ETR which indicated that the impairment of photosynthesis was probably affected by the light reaction process. The light reaction of EB was impaired most seriously but that of CR was not damaged. All results indicated that EB was probably the most sensitive shrub species to O 3 while CR the most tolerant one. Therefore, CR might be an ideal choice for greening in ozone-polluted areas. © 2012 Springer Science+Business Media B.V.