We review observational, experimental, and model results on how plants respond to extreme climatic conditions induced by changing climatic variability. Distinguishing between impacts of changing mean climatic conditions and changing climatic variability on terrestrial ecosystems is generally underrated in current studies. The goals of our review are thus (1) to identify plant processes that are vulnerable to changes in the variability of climatic variables rather than to changes in their mean, and (2) to depict/evaluate available study designs to quantify responses of plants to changing climatic variability. We find that phenology is largely affected by changing mean climate but also that impacts of climatic variability are much less studied, although potentially damaging. We note that plant water relations seem to be very vulnerable to extremes driven by changes in temperature and precipitation and that heat-waves and flooding have stronger impacts on physiological processes than changing mean climate. Moreover, interacting phenological and physiological processes are likely to further complicate plant responses to changing climatic variability. Phenological and physiological processes and their interactions culminate in even more sophisticated responses to changing mean climate and climatic variability at the species and community level. Generally, observational studies are well suited to study plant responses to changing mean climate, but less suitable to gain a mechanistic understanding of plant responses to climatic variability. Experiments seem best suited to simulate extreme events. In models, temporal resolution and model structure are crucial to capture plant responses to changing climatic variability. We highlight that a combination of experimental, observational, and/or modeling studies have the potential to overcome important caveats of the respective individual approaches.

A possible alternative to minimize the effects of salt and drought stress is the introduction of species tolerating these conditions with a good adaptability in terms of quantitative and qualitative yield. So quinoa (Chenopodium quinoa Willd.) cultivar Titicaca was grown in an open field trial in 2009 and 2010 to investigate the effects of salt and drought stress on quantitative and qualitative aspects of the yield. Treatments irrigated with well water (Q100, Q50 and Q25) and corresponding treatments irrigated with saline water (Q100S, Q50S and Q25S) with an electrical conductivity (ECw) of 22 dS m−1 were compared. Salt and drought stress in both years did not cause significant yield reduction, while the highest level of saline water resulted in higher mean seed weight and as a consequence the increase in fibre and total saponin content in quinoa seeds.

Chenopodium quinoa Willd. or ‘quinoa’ is a plant having many uses as a food. Importantly, it offers an alternative to normal cereals in coeliac diets because its seeds are gluten‐free. For this reason, it is worthwhile to determine the properties of quinoa and to evaluate the suitability of this crop for the south of Italy. At the CNR‐ISAFoM’s experimental station in Vitulazio (CE), a 2‐year (2006–2007) field trial under rain‐fed conditions was carried out to compare the two quinoa genotypes: KVLQ520Y (KV) and Regalona Baer (RB). Comparison was also made between two sowing dates for KV. The results showed that April was the best sowing time for quinoa in our typical Mediterranean region. Of the two genotypes, RB recorded better growth and productivity, apparently being more tolerant to abiotic stress (high temperatures associated with water stress). Chemical analyses reveal the potential of quinoa seed as a valuable ingredient in the preparation of cereal foods having improved nutritional characteristics.

Leaf chlorophyll content provides valuable information about physiological status of plants; it is directly linked to photosynthetic potential and primary production. In vitro assessment by wet chemical extraction is the standard method for leaf chlorophyll determination. This measurement is expensive, laborious, and time consuming. Over the years alternative methods, rapid and non-destructive, have been explored. The aim of this work was to evaluate the applicability of a fast and non-invasive field method for estimation of chlorophyll content in quinoa and amaranth leaves based on RGB components analysis of digital images acquired with a standard SLR camera. Digital images of leaves from different genotypes of quinoa and amaranth were acquired directly in the field. Mean values of each RGB component were evaluated via image analysis software and correlated to leaf chlorophyll provided by standard laboratory procedure. Single and multiple regression models using RGB color components as independent variables have been tested and validated. The performance of the proposed method was compared to that of the widely used non-destructive SPAD method. Sensitivity of the best regression models for different genotypes of quinoa and amaranth was also checked. Color data acquisition of the leaves in the field with a digital camera was quick, more effective, and lower cost than SPAD. The proposed RGB models provided better correlation (highest R (2)) and prediction (lowest RMSEP) of the true value of foliar chlorophyll content and had a lower amount of noise in the whole range of chlorophyll studied compared with SPAD and other leaf image processing based models when applied to quinoa and amaranth.

Quinoa is a native Andean crop for domestic consumption and market sale, widely investigated due to its nutritional composition and gluten-free seeds. Leaf water potential (Ψ leaf ) and its components and stomatal conductance (g s ) of quinoa, cultivar Titicaca, were investigated in Southern Italy, in field trials (2009 and 2010). This alternative crop was subjected to irrigation treatments, with the restitution of 100 %, 50 % and 25 % of the water necessary to replenish field capacity, with well water (100 W, 50 W, 25 W) and saline water (100 WS, 50 WS, 25 WS) with an electrical conductivity (EC w ) of 22 dS m À1 . As water and salt stress developed and Ψ leaf decreased, the leaf osmotic potential (Ψ p ) declined (below À2.05 MPa) to maintain turgor. Stomatal conductance decreased with the reduction in Ψ leaf (with a steep drop at Ψ leaf between À0.8 and 1.2 MPa) and Ψ p (with a steep drop at Ψ p between À1.2 and À1.4 MPa). Salt and drought stress, in both years, did not affect markedly the relationship between water potential components, RWC and g s . Leaf water potentials and g s were inversely related to water limitation and soil salinity experimentally imposed, showing exponential (Ψ leaf and turgor pressure, Ψ p , vs. g s ) or linear (Ψ leaf and Ψ p vs. SWC) functions. At the end of the experiment, salt-irrigated plants showed a severe drop in Ψ leaf (below À2 MPa), resulting in stomatal closure through interactive effects of soil water availability and salt excess to control the loss of turgor in leaves. The effects of salinity and drought resulted in strict dependencies between RWC and water potential components, showing that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under stress, resulting in osmotic adjustment at turgor loss. The extent of osmotic adjustment associated with drought was not reflected in Ψ p at full turgor. As soil was drying, the association between Ψ leaf and SWC reflected the ability of quinoa to explore soil volume to continue extracting available water from the soil. However, leaf ABA content did not vary under concomitant salinity and drought stress conditions in 2009, while differing between 100 W and 100 WS in 2010. Quinoa showed good resistance to water and salt stress through stomatal responses and osmotic adjustments that played a role in the maintenance of a leaf turgor favourable to plant growth and preserved crop yield in cropping systems similar to those of Southern Italy.Andean crop for domestic consumption and for market sale, which has been widely investigated (e.g. Jacobsen 2011) mainly due to its nutritional composition (Ruales

The climate of Mediterranean region will become drier and hotter, with increased problems of soil salinity. A possible alternative to minimize the effects of climate change is to introduce species with better tolerance to salt and drought stresses. One of the options is quinoa (Chenopodium quinoa Willd.), which was grown in field trials in several Mediterranean countries, to study the effects of drought and salinity on yield and other characters. Drought stress during the vegetative growth stage leads to deep root development, and without stress conditions for the rest of the growing season allowed the plant to be able to optimize its photosynthesis and carbon translocation. Stress during seed filling recorded the lowest yields. The influence of organic matter on yield was more important under deficit irrigation than under full irrigation. The interaction between relative water content and leaf water potential indicated that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under drought. In all climatic conditions, drought and use of irrigation water with salinity up to 30 dS m À1 caused slightly reduced yield as compared to full irrigation with fresh water. Highest values of water conductivity resulted in higher seed weight, and as a consequence, an increase in fibre and total saponin content, and a small decrease in free phenolic compounds in quinoa seeds. The yield increase in quinoa accessions was less at the highest level of nitrogen application, that is, 200 mg kg À1 soil, compared with other levels of nitrogen application, that is, 50, 100 and 150 mg kg À1 soil.

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