Growth and biomass partitioning of Arbutus unedo, Laurus nobilis, Phillyrea angustifolia and Rhamnus alaternus seedlings under water deficit

Abstract

Water scarcity in the Mediterranean areas is very common and the selection of drought tolerant species is a priority for landscaping purposes in the Mediterranean areas. The objective of this study was to evaluate the effect of water deficit on growth and biomass partitioning of Arbutus unedo, Laurus nobilis, Phillyrea angustifolia and Rhamnus alaternus. Seventy-two seedlings per species were grown in the greenhouse in 4-liter pots and three water regimes were imposed starting on 6 April and until 9 June, 2010. One-third of the plants was well irrigated to maintain soil water content in the 25-35% range (CTR); a second group of plants was deficit-irrigated to maintain soil water content in the 15-25% range (MD); a third group was irrigated with a minimum amount of water to keep soil water content in the 5-15% range (SD). Toward the end of the deficit period, photosynthetic rates and stomatal conductances of all species were significantly reduced, especially under SD. By the end of April, reductions in stem elongation rate were evident in all species under SD, while stem diameter growth was affected only after mid May. By the end of the experiment, plant dry weight of all species was significantly reduced in both MD and SD treatments, with R. alaternus and L. nobilis showing greater reductions (61 and 57%, respectively) than P. angustifolia (36%) and A. unedo (21%). Water deficit generally reduced shoot:root ratios in P. angustifolia, whereas SD plants of A. unedo showed a reversed tendency mainly due to reduced allocation to roots. P. angustifolia seedlings generally exhibited the best performances even under SD, while R. alaternus and L. nobilis were severely affected by water deficit. A. unedo resulted relatively tolerant to water deficit (minor growth reductions) mainly due to its constitutional slow growth and small size.