EFFECT OF POT COLOR AND WHITE EXTERIOR POT ON RHAMNUS ALATERNUS DEVELOPMENT

To evaluate the influence of pot color on Rhamnus alaternus development, black and brown pots plus a combination of each with an exterior white pot (double pot) was evaluated (four treatments: black, brown, white-black and white-brown). The pots were set at an exterior plot, and the substrate temperature and soil matric potential (SMP) were registered hourly; leaching was registered weekly; growth (basal diameter, height, average shoots length), photosynthesis (Pn) and stomatal conductance (gs) were measured monthly while dry weight (aerial and root), leaf area and root distribution were determined at the end of the study. The results demonstrated that the treatments involving a white exterior pot reduced the average and maximum temperatures by 3 and 6°C respectively, although minimum temperatures were not affected. The soil matric potential (SMP) was lowest for the black pot during a few months in winter and particularly in spring, while the white-brown combination produced the lowest value in the following fall. These results could be related to greater average shoot lengths. Water leaching increased by 2% in the white exterior pot treatments, which indicates slightly lower water consumption. The total dry weight, height, Pn, g_s and leaf area were the same for all the treatments, which suggests that R. alaternus is not very sensitive to substrate heat and that the slight drop in temperature was not enough to produce great differences. However, the different pots affected biomass distribution. The base diameter of the black and brown pots was 17.1% smaller than the diameter of the external white pot. The brown pot alone produced shorter shoots than when in combination (33.4% shorter) and the black pot the smallest root dry weight. The roots had a greater presence in all the orientations when an exterior white pot was used except on the north side, where the difference was not significant. Roots were fewer on the south side in the black pot and on the south-west in the brown pot, the treatments with the white exterior pot showed the same result in this respect. Hence, the use of browns pot is recommended to obtain more compact plants (shorter shoots) probably due to a lower root distribution in south and west orientations.