Leaf traits and photosynthetic responses of Betula pendula saplings to a range of ground-level ozone concentrations at a range of nitrogen loads.
Ground-level ozone (O3) concentrations and atmospheric nitrogen (N) deposition rates have increased strongly since the 1950s. Rising ground-level O3concentrations and atmospheric N deposition both affect plant physiology and growth, however, impacts have often been studied in isolation rather than in combination. In addition, studies are often limited to a control treatment and one or two elevated levels of ozone and/or nitrogen supply. In the current study, three-year old Betula pendula saplings were exposed to seven different O3profiles (24h mean O3concentration of 36-68ppb in 2013, with peaks up to an average of 105ppb) in precision-controlled hemispherical glasshouses (solardomes) and four different N loads (10, 30, 50 or 70kgNha-1y-1) in 2012 and 2013. Here we report on the effects of enhanced O3concentrations and N load on leaf traits and gas exchange in leaves of varying age and developmental stage in 2013. The response of leaf traits to O3(but not N) vary with leaf developmental stage. For example, elevated O3did not affect the chlorophyll content of the youngest fully expanded leaf, but it reduced the chlorophyll content and photosynthetic parameters in aging leaves, relatively more so later than earlier in the growing season. Elevated O3enhanced the N content of senesced leaves prior to leaf fall, potentially affecting subsequent N cycling in the soil. Enhanced N generally stimulated the chlorophyll content and photosynthetic capacity. Whilst elevated O3reduced the light-saturated rate of photosynthesis (Asat) in aging leaves, it did not affect stomatal conductance (gs). This suggests that photosynthesis and gsare not closely coupled at elevated O3under-light saturating conditions. We did not observe any interactions between O3and N regarding photosynthetic parameters (Vc,max, Jmax, Asat), chlorophyll content, gs, N content in senesced leaves and leaf number. Hence, the sensitivity of these leaf traits to O3in young silver birch trees is neither reduced nor enhanced by N load.
Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK. Electronic address: hh@ceh.ac.uk.
Harry
H
Harmens
Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK. Electronic address: fhay@ceh.ac.uk.
Felicity
F
Hayes
Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK. Electronic address: katshar@ceh.ac.uk.
Katrina
K
Sharps
Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK. Electronic address: gmi@ceh.ac.uk.
Gina
G
Mills
Fundación CEAM, c/Charles R. Darwin 14, Parque Tecnológico, 46980 Paterna, Valencia, Spain. Electronic address: vicent@ceam.es.
Vicent
V
Calatayud
D029662:Betula / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism; D002980:Climate; D008027:Light; D009584:Nitrogen / Q000494:pharmacology*; D010126:Ozone / Q000494:pharmacology*; D010788:Photosynthesis / Q000187:drug effects* / Q000528:radiation effects; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D054046:Plant Stomata / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D019655:Quantitative Trait, Heritable; D012621:Seasons
D002734:Chlorophyll; D010126:Ozone; D009584:Nitrogen
Air pollution; Chlorophyll content; Leaf age; Nitrogen content; Photosynthetic capacity; Stomatal conductance