Responses of Leaf Processes in a Sensitive Birch (Betula pendulaRoth) Clone to Ozone Combined with Drought

Abstract

Saplings of an ozone sensitive clone of birch (Betula pendula Roth, KL-5-M) were well-watered or exposed to mild drought-stress combined with ambient or elevated (1n5ithe ambient) ozone for 11 weeks in open-field conditions in central Finland. Stomatal response, visible injury, chlorophyll and nutrient content, and changes in cellular anatomy and plant growth were studied. Drought stress alone, in ambient ozone, reduced stomatal density and stomatal conductance. Drought stress and ozone effects were additive, reducing total leaf number, foliage area and starch formation in mesophyll cells. Drought stress and ozone effects were additive, increasing the N concentration in the leaves, the thickness of the upper epidermal cell wall, the number of pectinaceous projections of mesophyll cell walls, and the vacuolar tannin-like depositions and phenolic droplets, regarded as signs of activated stress defence mechanisms. The increase in specific foliage mass, cytoplasmic lipids (younger leaves), and a condensed appearance of the upper epidermal mucilaginous layer were caused by both drought and ozone, but were not additive. The results show that combined drought stress contributed to birch responses to 1n5icurrent ambient ozone concentrations, corresponding to critical-level ozone exposure. The only beneficial effect of drought stress was the slight reduction of visible leaf symptoms induced by ozone in autumnal leaves.# 1998 Annals of Botany Company

Moderate drought did not affect the effectiveness of ethylenediurea (EDU) in protecting Populus cathayana from ambient ozone

“…It can be concluded that the protection of EDU against O 3 was not affected by moderate drought. Similar results with no significant interaction between O 3 and drought were also found in tree species such as Betula pendula, Picea abies (Pearson and Mansfield, 1994;Karlsson et al, 2002), but O 3 damage enhanced by less severe drought was also observed compared to that of well-watered plants (Pääkkönen et al, 1998). Actually, the interaction of O 3 and drought is very complex and determined by many aspects, such as species, the sequence, degree, and duration of both factors.…”

“…From existing studies, possible interactions between O 3 and drought have been determined to be antagonistic, additive, or synergistic (Pearson and Mansfield, 1994;Wieser and Havranek, 1995;Pääkkönen et al, 1998;Pollastrini et al, 2014;Tingey and Hogsett, 1985). Drought usually induces the closure of stomata, thus reducing the stomatal O 3 flux into the apoplast, whereas EDU is retained in the apoplast only (Pasqualini et al, 2016).…”

Ecophysiological Responses of Northern Birch Forests to the Changing Atmospheric CO2 and O3 Concentrations

“…Although N concentration in green leaf is not affected by O 3 so much Shimizu and Feng, 2007;Karlsson et al, 2003;Oksanen and Rousi, 2001;Saleem et al, 2001;Oksanen and Saleem, 1999;Pääkkönen et al, 1998), N concentration in leaf litter (fallen leaves) increased by O 3 treatment, suggesting the impaired capacity of trans-locating N from senescent leaves to tree body (Uddling et al, 2005). This may lead increased N loss at the whole tree level.…”

“…High O 3 damages chloroplasts (Prozherina et al, 2003;Pääkkönen et al, 1998) and reduces the photosynthetic rate (Mäenpää et al, 2011;Shimizu and Feng, 2007;Uddling et al, 2005;Shavnin et al, 1999). This can be reflected in changes in chlorophyll fluorescence that reveals O 3 stress in photosynthetic pathways (Mao et al, 2012;Wittmann et al, 2007;Shavnin et al, 1999).…”

“…Although Oksanen (2003) exceptionally reported that O 3 treatment had increased stomatal conductance, this could be attributed to increased stomatal density, which is common response to O 3 (Oksanen, 2005;Paoletti and Grulke, 2005;Pääkkönen et al, 1998;. Increase in stomatal density may be reflected in smaller leaf size under elevated O 3 (Oksanen, 2003(Oksanen, , 2001Oksanen and Saleem, 2001;Pääkkönen et al, 1998), for the ratio of guard cells (equal to stomata) to epidermal cells on leaf is unaffected by O 3 (Prozherina et al, 2003). In terms of the reason why stomatal conductance does not increase despite increased density of stomata under elevated O 3 , the effectiveness of low stomatal aperture against O 3 stress, or impaired photosynthetic pathway by O 3 seems to be a good answer (Paoletti and Grulke, 2005).…”