Photosynthetic and leaf respiration activity of Malcolmia littorea (L.) R. Br. in response to air temperature

Plant traits of Malcolmia littorea growing at the Botanic Garden of Rome and transplanted from the wild population developing along the Latium coast (Italy) were analyzed. The highest photosynthetic rates [P(N), 22.5 +/- 0.5 mu mol(CO(2)) m(-2) s(-1)], associated to the highest chlorophyll content (Chl, 60 +/- 5 SPAD units), and respiration rates [R, 11.1 +/- 0.2 mu mol(CO(2)) m(-2) s(-1)] were reached in spring, when mean air temperature (T(m)) was in the range 17 degrees C to 23 degrees C. PN, Chl, and R decreased by 86, 38, and 59% in summer when mean maximum air temperature (T(max)) was 30.3 +/- 2.6 degrees C. Leaf water potential decreased by 34% in summer compared to the spring value, and it was associated to a relative water content (RWC) of 74 +/- 4%, and to a water-use efficiency (WUE) of 2.15 +/- 0.81 mol(CO(2)) mmol(-1)(H(2)O). Moreover, also low air temperatures determined a significant P(N) and R decreases (by 52 and 40% compared to the maximum, respectively). Responsiveness of gross photosynthetic rate (P(g)) to R was higher than that to P(N) as underlined by the slope of the regression line between the two variables. The results underlined a low tolerance to both high- and low air temperatures of M. littorea. The selected key traits (R, WUE, Chl) by the discriminant analysis might be used to monitor the M. littorea wild population in the long time. The ex situ cultivated plants could be propagated and used to increase the individuals number of the wild population.