CONICET | Buscador de Institutos y Recursos Humanos

Despite the economic importance of long-lived crop species in theMediterranean Basin and their expansion to new warmer regions, their potentialresponses to prolonged temperature increases have not been adequately addressed. Theobjectives of this study were to: 1) assess leaf gas exchange responses to prolongedelevated temperature in young olive trees; 2) evaluate some additional leaf traits such asstomatal density and size under these same conditions; and 3) determine whetherphotosynthetic acclimation to temperature was apparent. A field experiment with twotemperature levels was conducted using well-irrigated, potted olive trees (cvs.Arbequina, Coratina) grown in open top chambers during the summer and early fall intwo growing seasons. The temperature levels were a near-ambient control (T0) and aheated (T+) treatment (+4 °C). Maximum photosynthetic rate (Amax), stomatalconductance (gs), transpiration (E), and chlorophyll fluorescence were measured.Stomatal size and density and trichome density were also determined. The Amax, gs, andchlorophyll fluorescence were little affected by heating. However, leaf E was higher atT+ than T0 in the summer in both seasons due in large part to the moderate increase invapor pressure deficit that accompanied heating, and consequently water use efficiencywas reduced in heated leaves. When reciprocal temperature measurements wereconducted in mid-summer of the second season, Amax values of T0 and T+ leaves werehigher under the temperature level at which they grew than when measured at the othertemperature level, which suggests some thermal acclimation. Stomatal size and densitywere greater in T+ than in T0 grown leaves in some cases, which was consistent with agreater E in T+ leaves when measured at both temperature levels. These results suggestthat acclimation to long-term changes in temperature must be carefully considered tohelp determine how olive trees will be influenced by global warming.

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