Stomatal and non‐stomatal limitation to photosynthesis in two trembling aspen (Populus tremuloides Michx.) clones exposed to elevated CO₂ and/or O₃

Abstract

Leaf gas exchange parameters and the content of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) in the leaves of two 2‐year‐old aspen (Populus tremuloides Michx.) clones (no. 216, ozone tolerant and no. 259, ozone sensitive) were determined to estimate the relative stomatal and mesophyll limitations to photosynthesis and to determine how these limitations were altered by exposure to elevated CO2 and/or O3. The plants were exposed either to ambient air (control), elevated CO2 (560 p.p.m.) elevated O3 (55 p.p.b.) or a mixture of elevated CO2 and O3 in a free air CO2 enrichment (FACE) facility located near Rhinelander, Wisconsin, USA. Light‐saturated photosynthesis and stomatal conductance were measured in all leaves of the current terminal and of two lateral branches (one from the upper and one from the lower canopy) to detect possible age‐related variation in relative stomatal limitation (leaf age is described as a function of leaf plastochron index). Photosynthesis was increased by elevated CO2 and decreased by O3 at both control and elevated CO2. The relative stomatal limitation to photosynthesis (ls) was in both clones about 10% under control and elevated O3. Exposure to elevated CO2 + O3 in both clones and to elevated CO2 in clone 259, decreased ls even further – to about 5%. The corresponding changes in Rubisco content and the stability of Ci/Ca ratio suggest that the changes in photosynthesis in response to elevated CO2 and O3 were primarily triggered by altered mesophyll processes in the two aspen clones of contrasting O3 tolerance. The changes in stomatal conductance seem to be a secondary response, maintaining stable Ci under the given treatment, that indicates close coupling between stomatal and mesophyll processes.

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

“…Cinnamonum campora (Feng et al, 2011), Viburnum lantana (Calatayud et al, 2010), poplar (Bohler et al, 2010), aspen (Noormets et al, 2001) and beech (Bortier et al, 2008). Also, Fv 0 /Fm 0 and F PSII but not qP were significantly reduced by E-O 3 , suggesting that E-O 3 increased light energy dissipation of the antenna pigment, thus leading to a reduction in the efficiency of excitation energy captured by the open PSII reaction center, but no change on the proportion of open PSII reaction center.…”

Photosynthetic behaviour during the leaf ontogeny of rubber tree clones[Hevea brasiliensis (Wild. ex. Adr. de Juss.) Muell. Arg.], in Lavras, MG

“…In the present wok, even when the photosynthetic apparatus was completely formed, the clones presented, in stage D, values of Fv / Fm ratio somewhat lower than (Figure 4c) that ones showed in other publications, which may be associated with the influences of low temperatures and dry period during the experimental evaluations. Noormets et al (2001) investigated the behavior of young, newly mature, mature and old leaves, during the development of Populus tremuloides Michx. Clones.…”

Trocas gasosas e injúrias foliares visíveis em plantas jovens de Astronium graveolens Jacq. fumigadas com ozônio

“…proporcional em Ci, uma vez que A foi reduzida em 45% e Ci aumentou apenas 5%. Isso foi verificado por Noormets et al (2001) em Populus tremuloides, Guidi et al (2001) em Populus × euramericana e por Pellegrini et al (2011) em Liriodendrum tupilifera que concluíram que a fotossíntese nessas espécies era limitada principalmente pela redução da capacidade de assimilação das células do mesofilo, com a Rubisco (ribulose-1,5-bifosfato carboxilase/ oxigenase) sendo um dos primeiros alvos dos subprodutos do O 3 . Segundo Heath (2008), o aumento da resistência mesofílica é causado pelas espécies ativas de oxigênio que degradam a Rubisco e reduzem sua síntese, diminuindo sua atividade e quantidade e, consequentemente, a assimilação do carbono.…”