In the coming decades, non-conventional water sources (e.g., marginal quality waters, saline-sodic drainage waters, wastewaters) will become an important component of agricultural water supplies as a result of global increasing water demand, the impacts of extreme climate events, and climate change (Qadir et al., 2007), especially in water-scarce areas. The Mediterranean region is one of the driest agricultural areas on earth (Jacobsen et al., 2012). Therefore, a shift toward water-saving strategies (e.g., crop irrigation with non-conventional waters) is necessary to meet agricultural water requirements and to alleviate present and future demand on freshwater sources. Generally, non-conventional water sources in water-scarce regions contain moderate to high salt content, which could increase soil salinity and potentially impair plant growth.
As a general effect, salinity reduces plant growth rate, thus resulting in lower crop yields (Shannon and Grieve, 1999). As discussed by Munns (2002), this reduction occurs over time in two phases: the initial growth reduction phase is quick and is induced by the salt surrounding the plant roots, which impairs water uptake as a result of osmotic effect; the second phase takes more time to develop and results from the excessive ion accumulation in the shoots and the inability to tolerate these accumulated ions. This growth reduction may also arise because of potential nutritional imbalances induced by salinity. For instance, Na is considered to be the primary cause of ion-specific damage for some plant species (Tester and Davenport, 2003) and may impair other ions uptake, especially K, which is essential for plant life (Maathuis and Amtmann, 1999). Thereby, traits like tissue mineral concentration or nutrient uptake of salt-stressed plants can contribute to identify and clarify potential reductions in biomass production and/or quality (Grattan and Grieve, 1999). To obtain valuable crop yields, it is advisable to study and select crop species that are able to grow under salt stress.
Cardoon (Cynara cardunculus L.) is a versatile plant adapted to Mediterranean conditions but limited information about its growth under salt stress is available. Cardoon, known as cynara for industrial applications, has a widespread spectrum of potential applications (liquid biofuel, paper pulp production, green forage, and pharmacological source of active compounds) (Fernández et al., 2006) with growing interest focused in the use of its high epigeal biomass yields (mainly heads and stalk) for energy purposes (Piscioneri et al., 2000; Raccuia and Melilli, 2007). However, studies on the effect of salinity on cynara growth have been limited to the vegetative period (germination stage and leaf development stage) and solely under soilless conditions (Benlloch-González et al., 2005; Colla et al., 2012; Raccuia et al., 2004). Soil plays an important role in plant nutrient availability because the concentration and composition of solutes in the soil solution control the activity of the nutrient ions, especially phosphorus (P), K, and micronutrients (Grattan and Grieve, 1992). Hence, there are still uncertainties regarding cynara growth under salt stress, mainly concerning the impact on cynara reproductive organs (stalk, caulicle leaves, and heads) and the influence of soil as a growing substrate.
The aims of the present study were to characterize the effect of saline irrigation (NaCl-dominated waters) on cynara growth and mineral nutrition in two natural Mediterranean soils. For these purposes, morphological parameters, tissue mineral concentration, and aboveground biomass mineral content of cynara plants irrigated with saline waters were examined. Additionally, the effect of saline irrigation on cynara applications is discussed as a result of its importance for potential growers.
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