Selection and nursery production of ornamental plants for landscaping and xerogardening in semi-arid environments

SummaryIn landscaping and xerogardening projects, under semi-arid conditions, appropriate plant selection and conditioning techniques used in the nursery during seedling production are crucial for the establishment, survival and subsequent growth of plants after transplanting. Selecting ornamental plants with appropriate morphological and physiological characteristics to improve nursery performance and tolerance of harsh environments is of vital importance. The use of native species of wild flora is of increasing interest because of their capacity to adapt to adverse local environmental conditions. However, the degree of adaptation to abiotic stresses varies considerably within a family, within a genus and even within a species. Morphological and anatomical adaptations in seedlings include reductions in shoot height and/or leaf area, rises in root-collar diameter and root growth potential and, often, a reduction in the shoot:root ratio. These occur as a result of hardening and acclimation processes (pre-conditioning) during the nursery period, and are correlated with the ability to withstand the shock of transplantation and to increase survival and plant growth following transplantation in xerogardens and semi-arid landscapes. In addition, there are physiological characteristics of seedlings related to osmotic adjustment and water-use efficiency, such as low stomatal conductance, leaf water potential, leaf turgor potential and relative water content. These provide seedlings with a considerable capacity to adapt to adverse conditions after transplantation into harsh environments. Suitable environmental conditions and cultivation techniques in the nursery are essential to produce sturdy seedlings, with the above-mentioned morphological and physiological characteristics. Deficit irrigation is the most commonly used pre-conditioning technique to produce high-quality seedlings. In addition, using large-sized containers and appropriate substrates, withholding N nutrition, inoculating arbuscular mycorrhizal fungi, applying plant growth retardants and mechanical conditioning methods (including brushing, and shoot- and/or root-pruning) are common. Varying microclimatic conditions (low temperature, low air humidity, enrichment with CO2, light intensity and photoperiod management) are also used to control growth to produce high-quality seedlings with the ability to withstand transplanting shock and be capable of rapid establishment and resumption of growth under xerogardening and semi-arid landscaping conditions.