Plant growth of Atriplex portulacoides affected by irrigation amount and substrate type in an extensive green roof system

Abstract

Extensive green roofs in coastal areas planted with halophytes can contribute to the species preservation of local salt marshes that are being destroyed and threatened by urban development and enhance the local landscape character of coastal areas. Additional, benefits of halophytes include drought tolerance and the ability to withstand saline conditions in coastal areas. Herein the plant growth of A. portulacoides a native Mediterranean halophyte established on an extensive green roof system that received the effects of two irrigation water amounts (100% ET0 and 75% ET0) defined by substrate hydraulic properties and three substrate types are presented. The duration of the experiment was 285 days. The substrates contained soil (S), pumice (Pum), pure sphagnum peat (P) and/or grape marc compost (C) in different volume ratios (15S:70Pum:15P, 15S:70Pum:15C and 15S:70Pum:7.5C:7.5P). The height, shoot canopy diameter, growth index, and ground cover percentage of plants were measured at regular intervals, and at the end of the experiment, both shoot and root dry weights were also measured. It was found that irrespective of substrate type, plant growth of A. portulacoides was healthy and similar in size for both irrigation treatments therefore with an aim to conserve water, the use of the 75% ET0 irrigation treatment is proposed. The use of grape marc compost in the substrate (15S:70Pum:15C) is also proposed as it improved the substrate's nutrient content increasing most of the measured plant growth parameters of A. portulacoides. The use of grape marc compost as an alternative organic material to peat in green roof substrates would also contribute to the preservation of wetlands.