sustainability Review Halophyte Common Ice Plants: A Future Solution to Arable Land Salinization Danilo Loconsole 1,* , Bernardo Murillo-Amador 2 , Giuseppe Cristiano 1 and Barbara De Lucia 1 1 Department of Agro-Environmental and Territorial Science (DISAAT), University of Bari, “Aldo Moro”, Italy Via Amendola 165/A, 70120 Bari, Italy; [email protected] (G.C.); [email protected] (B.D.L.) 2 Centro de Investigaciones Biológicas del Noroeste (CIBNOR), S.C. La Paz, Baja California Sur 23096, Mexico; [email protected] * Correspondence: [email protected] Received: 10 September 2019; Accepted: 18 October 2019; Published: 1 November 2019 Abstract: The problems associated with the salinization of soils and water bodies and the increasing competition for scarce freshwater resources are increasing. Current attempts to adapt to these conditions through sustainable agriculture involves searching for new highly salt-tolerant crops, and wild species that have potential as saline crops are particularly suitable. The common ice plant (Mesembryanthemum crystallinum L.) is an edible halophyte member of the Aizoaceae family, which switches from C3 photosynthesis to crassulacean acid metabolism (CAM) when exposed to salinity or water stress. The aim of this review was to examine the potential of using the ice plant in both the wild and as a crop, and to describe its ecology and morphology, environmental and agronomic requirements, and physiology. The antioxidant properties and mineral composition of the ice plant are also beneficial to human health and have been extensively examined. Keywords: Mesembryanthemum crystallinum; functional foods; sustainability 1. Introduction Climate change, the lack of global water resources, and the increase of saline and dry conditions have negatively affected arable lands. By 2050, it is estimated that crop production must increase by 70% to 100% to meet global food demand [1]. As the actual trend is a 1% to 1.5% annual yield increase for major crops, guaranteeing sustainable agriculture in the future is a challenge [2]. Technological progress and the improvement of cultivation techniques are among the key factors determining wellness in contemporary populations, and have led to extensive population growth in recent decades. Increased soil use due to the growth in production has led to a loss of fertility and the phenomena of salinization and desertification, which render soils unsuitable for cultivation. In particular, salinity induces constraints in plants that are associated with a reduction in their primary production, leaf expansion, and biomass losses. Sustainability in terms of water resource preservation, food availability for poor populations, and a reduction in production inputs is thus a major challenge for researchers. The adoption of tolerant species and good agronomic practices, and the reduction of resource waste are, thus, significant research topics. Seawater and coastal lands represent potentially cultivable areas, but they are useless for conventional agriculture. Halophytes are an exception, as they are highly productive under saline conditions [3]. Saline agriculture with halophyte crops could be one solution to the problems of fresh water resource depletion and the increase of salinized soil areas, as they allow for the cultivation of marginal areas and can enable coastal and salt lands to be productive [4]. Halophytic cash crops can be domesticated through conventional breeding programs and thus improve their productivity and salt tolerance [5]. Sustainability 2019, 11, 6076; doi:10.3390/su11216076 www.mdpi.com/journal/sustainability Sustainability 2019, 11, 6076 2 of 16 Sustainability 2019, 11, x FOR PEER REVIEW 2 of 15 Halophytes are species that are able to complete their life cycles in environments where the concentrationHalophytes of sodium are species chloride that is are greater able to than complete 200 mM their [6 ].life They cycles are in characterized environments bywhere anatomical the changesconcentration such as inof thesodium bladder chloride cells is andgreater the than salt 200 glands, mM [6]. through They are which characterized the excretion by anatomical of excessive sodiumchanges occurs such [7]. as The in the leaves bladder of halophytes cells and the can salt be glands, used as through human which food the (i.e., excretionChenopodium of excessive quinoa [8]), sodium occurs [7]. The leaves of halophytes can be used as human food (i.e., Chenopodium quinoa [8]), for fodder (i.e., Atriplex spp. [9]), or as oil seeds (i.e., Salicornia bigelovii [10]). They can also be sources for fodder (i.e., Atriplex spp. [9]), or as oil seeds (i.e., Salicornia bigelovii [10]). They can also be sources of secondary metabolites [11] with potential economic value [12]. Wild halophyte domestication of secondary metabolites [11] with potential economic value [12]. Wild halophyte domestication is an is anapproach approach that that should should therefore therefore be considered. be considered. Menzel Menzel and Lieth and [13] Lieth produced [13] produced a list of over a list 2600 of over 2600halophyte halophyte species species that that differ diff erin intheir their degree degree of oftolerance tolerance to salinity. to salinity. Some Some belong belong to the to group the group "obligatory"obligatory halophytes", halophytes", which which require require saline saline environmentsenvironments for for optimal optimal growth, growth, such such as the as common the common ice plantice plant (Mesembryanthemum (Mesembryanthemum crystallinum crystallinum L.).L.). The aim aim of of this this review review was was to assess to assess the potential the potential of of adaptingadapting the wildthe wild ice ice plant plant as as a crop,a crop, describing describing its ecology ecology and and morphology, morphology, its environmental its environmental and and agronomicagronomic requirements, requirements, and and its its physiology. physiology. In addition,In addition, the the ice ice plant’s plant’s antioxidant antioxidant properties properties and and mineralmineral composition composition were were examined, examined, as it as it is is a food crop that can be highly beneficial to human health. a food crop that can be highly beneficial to human health. 2. Wild Plant 2. Wild Plant 2.1. Origin and Diffusion 2.1. Origin and Diffusion M. crystallinum L. (2n = 18) (Figure 1) is an annual succulent belonging to the Aizoaceae family M.and crystallinum is native to L.South (2n =and18) East (Figure Africa,1) isthe an Sinai, annual and succulent southern belongingEurope (Spain) to the [4,14,15].Aizoaceae It isfamily also and is nativenaturalized to South in and Mediterranean East Africa, coastal the Sinai, areas, and the southernU.S., Australia, Europe Mexico, (Spain) Chile, [4,14 and,15 the]. It Caribbean is also naturalized [16– in Mediterranean19]. In Italy it can coastal be found areas, in theApulia U.S., (Vieste), Australia, Sicily, Mexico, Sardinia, Chile, Lazio, and Campania, the Caribbean Liguria, [ 16and–19 Tuscany]. In Italy it can be[20,21]. found in Apulia (Vieste), Sicily, Sardinia, Lazio, Campania, Liguria, and Tuscany [20,21]. FigureFigure 1. 1.Young Young Mesemrbyanthemum Mesemrbyanthemum crystallinum crystallinum plant. plant. 2.2. Ecology2.2. Ecology and and Morphology Morphology The commonThe common ice ice plant plant is typicallyis typically distributed distributed on coastal coastal sand sand dunes, dunes, saline saline flats, flats, inland inland saline saline areas,areas, and and roadsides. roadsides. It It is is tolerant tolerant to to lowlow temperaturestemperatures and and accumulations accumulations of salt of salton the on top the soil, top soil, whichwhich excludes excludes other other species species from from growing growing [[22,22,2323].]. The The seeds seeds survive survive hot hot dry dry summers summers and can and can germinategerminate after after short short periods periods of of rain rain [22 [22,24–26].,24–26]. Th Thee plant plant is is typically typically heliophile heliophile and andmegatherm megatherm [27]. [27]. It can grow in sandy and loamy soils that are well-drained, and even nutritionally poor and saline. Sustainability 2019, 11, 6076 3 of 16 It cannotSustainability grow 2019 in the, 11, x shade FOR PEER and REVIEW prefers dry or moist soil. Its suitable temperature range is from3 of 15 12 to 30 ◦C, and it can be killed by frost [26]. It can grow in sandy and loamy soils that are well-drained, and even nutritionally poor and saline. It It is covered with bladder cells (vesicles) (Figure2), which are appressed during the juvenile phase, cannot grow in the shade and prefers dry or moist soil. Its suitable temperature range is from 12 to that give30 °C, it and a shiny it can appearance, be killed by frost from [26]. which it derives the name common ice plant [22,28]. Its growth form is prostrateIt is covered and with its height bladder ranges cells between(vesicles) 10–15(Figure cm. 2), which The leaves are appressed are large during oval or the paddle juvenile shaped withphase, a rosette that form,give it anda shiny are appearance, light green from (3–5 which5–10 it derives cm) during the name the common juvenile ice period plant [22,28]. and then Its turn × darkgrowth green andform becomesis prostrate thicker and its andheight smaller ranges inbetween the adult 10–15 phase cm. The [28 leaves,29] (Figure are large3). oval The or flowerspaddle are hermaphrodite,shaped withwhite a rosette or slightlyform, and pink, are light and green are 7–30 (3–5 mm x 5– in10 diameter.cm) during They the juvenile have five period calyx and lobes, then about 30 staminodes,turn dark green and a whitend becomes stigmas, thicker and and the bladdersmaller in cells the adult of the phase receptacle [28,29]are (Figure particularly 3). The flowers prominent. The iceareplant hermaphrodite, flowers year-round, white or slightly but mainly pink, and from are spring 7–30 mm to summer.in diameter. The They flowers have openfive calyx in the lobes, morning about 30 staminodes, and white stigmas, and the bladder cells of the receptacle are and close at night, and are insect pollinated [27].