In the Mediterranean, annual mean precipitation has continuously decreased
over the last three years (by ca 36% in Barcelona), and the decrease
has been dramatic during the summer (by ca 78 and
64% during July and August, respectively). The impact of increased
drought on the photosynthetic capacity of Mediterranean vegetation is
currently unknown. In this study, two native Mediterranean plants
[rosemary (Rosmarinus officinalis L.) and lavender
(Lavandula stoechas L.)] were grown outdoors and
subjected to two water regimes (50 mm month–1
during the summer, or no supplementary water at all). Rosemary and lavender
plants watered with 50 mm month–1 during the
summer had higher relative leaf water content and water potential than
non-watered plants. Changes in water status were accompanied by large
decreases in parameters of gas exchange [i.e. the light-saturated rate of
CO2 assimilation, the maximum velocity of
ribulose-1,5-bisphosphate (RuBP) carboxylation by Rubisco and the capacity for
RuBP] and of modulated chlorophyll fluorescence (i.e. the relative
quantum efficiency of PSII photochemistry and the efficiency of energy capture
by open PSII reaction centres) during the summer, but no differences were
found in any photosynthetic parameters for leaves subjected to the two water
regimes. The drought-induced decreases in the relative quantum efficiency of
PSII photochemistry in rosemary and lavender plants were attributable to
‘downregulation’ of electron transport. Photodamage to PSII in the
field appeared to be a later effect of drought in these plants.
Photorespiration was not a major mechanism protecting the photosynthetic
apparatus of these plants from photodamage in the field. After the autumn
rainfall, photosynthetic capacity fully recovered. We conclude that rosemary
and lavender are well adapted to drought, and that an increase in water
deficit is unlikely to have a significant impact on the photosynthetic
capacity of leaves.
Microplastics and copper effects on the neotropical teleost Prochilodus lineatus: Is there any interaction?