Ozone‐induced changes in photosynthesis and photorespiration of hybrid poplar in relation to the developmental stage of the leaves

Abstract

Young poplar trees (Populus tremula Michx. x Populus alba L. clone INRA 717-1B4) were subjected to 120 ppb of ozone for 35 days in phytotronic chambers. Treated trees displayed precocious leaf senescence and visible symptoms of injury (dark brown/black upper surface stippling) exclusively observed on fully expanded leaves. In these leaves, ozone reduced parameters related to photochemistry (Chl content and maximum rate of photosynthetic electron transport) and photosynthetic CO(2) fixation [net CO(2) assimilation, Rubisco (ribulose-1,5-bisphosphate carboxylase oxygenase) activity and maximum velocity of Rubisco for carboxylation]. In fully expanded leaves, the rate of photorespiration as estimated from Chl fluorescence was markedly impaired by the ozone treatment together with the activity of photorespiratory enzymes (Rubisco and glycolate oxidase). Immunoblot analysis revealed a decrease in the content of serine hydroxymethyltransferase in treated mature leaves, while the content of the H subunit of the glycine decarboxylase complex was not modified. Leaves in the early period of expansion were exempt from visible symptoms of injury and remained unaffected as regards all measured parameters. Leaves reaching full expansion under ozone exposure showed potential responses of protection (stimulation of mitochondrial respiration and transitory stomatal closure). Our data underline the major role of leaf phenology in ozone sensitivity of photosynthetic processes and reveal a marked ozone-induced inhibition of photorespiration.

Jatropha curcasand Ricinus communisdisplay contrasting photosynthetic mechanisms in response to environmental conditions

“…Under drought conditions, the impairment of CO 2 assimilation causes an imbalance between the electron transport rate in the photosynthetic electron transport (PET) chain and the plant's capacity to utilize NADPH (reduced nicotinamide adenine dinucleotide phosphate) and ATP (adenosine tri-phosphate) in the Calvin cycle (Chaves et al, 2009). Under this CO 2 -limiting condition, photorespiration is proposed as an important alternative pathway for consuming the excess reducing equivalents from the photochemical reactions, avoiding photoinhibition (Bagard et al, 2008;Takahashi and Badger, 2011).…”

“…The estimation of the photorespiratory rate (P R ) was determined as described in Bagard et al (2008) from the measurements of gas exchange (P N and R d ) and chlorophyll a fluorescence-derived ETR parameter by the equation:…”

Elevated ozone negatively affects photosynthesis of current-year leaves but not previous-year leaves in evergreen Cyclobalanopsis glauca seedlings

“…At the canopy level, ambient O 3 concentrations caused reductions in both light-saturated photosynthesis rate (A sat ) and g s of the lower canopy that were about 30% more than those of the upper canopy in black poplar (Populus nigra L.) species (Novak et al, 2005). Young poplar trees also showed that reduced photosynthetic parameters related to chlorophyll content, maximum rate of photosynthetic electron transport and net photosynthetic assimilation appeared only on fully expanded leaves, but not on young and undeveloped leaves, which was partly attributed to differences in leaf anatomy between expanding and fully expanded leaves (Bagard et al, 2008). Similarly, for an evergreen broad-leaved species, Castanaopsis sieboldii, elevated O 3 significantly reduced the net photosynthetic rate of previous-year leaves but not that of expanding current-year leaves (Watanabe et al, 2008).…”

“…For hybrid poplar and Aspen, elevated O 3 concentrations altered the patterns of change in leaf area, photosynthetic rate and carbon gain with leaf position from root to apex and the older leaves were more sensitive to O 3 than younger leaves (Bagard et al, 2008;Greitner et al, 1994). At the canopy level, ambient O 3 concentrations caused reductions in both light-saturated photosynthesis rate (A sat ) and g s of the lower canopy that were about 30% more than those of the upper canopy in black poplar (Populus nigra L.) species (Novak et al, 2005).…”

“…Numerous experimental studies have demonstrated the detrimental effects of O 3 on tree species growth and physiological function, e.g. photosynthesis (Bagard et al, 2008;Feng et al, 2011;Schaub et al, 2005;Wittig et al, 2009;Zhang et al, 2010). The reduction in photosynthesis rate by O 3 could be attributed to stomatal closure, decreased chlorophyll content and electron transport rate, impaired carboxylation capacity and Rubisco content (Paoletti et al, 2009;Reich, 1983).…”