CO₂ enrichment predisposes foliage of a eucalypt to freezing injury and reduces spring growth

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Seedlings of <jats:italic>Eucalyptus pauciflora</jats:italic>, were grown in open‐top chambers fumigated with ambient and elevated [CO<jats:sub>2</jats:sub>], and were divided into two populations using 10% light transmittance screens. The aim was to separate the effects of timing of light interception, temperature and [CO<jats:sub>2</jats:sub>] on plant growth. The orientation of the screens exposed plants to a similar total irradiance, but incident during either cold mornings (east‐facing) or warm afternoons (west‐facing). Following the first autumn freezing event elevated CO<jats:sub>2</jats:sub>‐grown plants had 10 times more necrotic leaf area than ambient CO<jats:sub>2</jats:sub> plants. West‐facing plants had significantly greater (25% more) leaf damage and lower photochemical efficiency (<jats:italic>F</jats:italic><jats:sub>v</jats:sub>/<jats:italic>F</jats:italic><jats:sub>m</jats:sub>) in comparison with east‐facing plants. Following a late spring freezing event east‐facing elevated CO<jats:sub>2</jats:sub> plants suffered a greater sustained loss in <jats:italic>F</jats:italic><jats:sub>v</jats:sub>/<jats:italic>F</jats:italic><jats:sub>m</jats:sub> than west‐facing elevated CO<jats:sub>2</jats:sub>‐ and ambient CO<jats:sub>2</jats:sub>‐grown plants. Stomatal conductance was lower under elevated CO<jats:sub>2</jats:sub> than ambient CO<jats:sub>2</jats:sub> except during late spring, with the highest leaf temperatures occurring in west‐facing plants under elevated CO<jats:sub>2</jats:sub>. These higher leaf temperatures apparently interfered with cold acclimation thereby enhancing frost damage and reducing the ability to take advantage of optimal growing conditions under elevated CO<jats:sub>2</jats:sub>.</jats:p>