In leaves of the mangrove species Avicennia germinans (L.) L. grown in salinities from 0 to 40 ‰, fluorescence, gas exchange, and δ13C analyses were done. Predawn values of Fv/Fm were about 0.75 in all the treatments suggesting that leaves did not suffer chronic photoinhibition. Conversely, midday Fv/Fm values decreased to about 0.55-0.60 which indicated strong down-regulation of photosynthesis in all treatments. Maximum photosynthetic rate (Pmax) was 14.58 ± 0.22 µmol m-2 s-1 at 0 ‰ it decreased by 21 and 37 % in plants at salinities of 10 and 40 ‰, respectively. Stomatal conductance (gs) was profoundly responsive in comparison to Pmax which resulted in a high water use efficiency. This was further confirmed by δ13C values, which increased with salinity. From day 3, after salt was removed from the soil solution, Pmax and gs increased up to 13 and 30 %, respectively. However, the values were still considerably lower than those measured in plants grown without salt addition.
We consider the functional equation f(xf(x)) = ϕ(f(x)) where ϕ: J → J is a given increasing homeomorphism of an open interval J ⊂ (0, ∞) and f : (0, ∞) → J is an unknown continuous function. In a previous paper we proved that no continuous solution can cross the line y = p where p is a fixed point of ϕ, with a possible exception for p = 1. The range of any non-constant continuous solution is an interval whose end-points are fixed by ϕ and which contains in its interior no fixed point except for 1. We also gave a characterization of the class of continuous monotone solutions and proved a sufficient condition for any continuous function to be monotone. In the present paper we give a characterization of the equations (or equivalently, of the functions ϕ) which have all continuous solutions monotone. In particular, all continuous solutions are monotone if either (i) 1 is an end-point of J and J contains no fixed point of ϕ, or (ii) 1 ∈ J and J contains no fixed points different from 1.