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The Mehlich 3 method for the extraction of available micronutrients, such as copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn), is more advantageous compared to the diethylene triamine pentaacetic acid (DTPA) method, because it can also be used for the extraction of macronutrients. The aim of this study was to compare the Mehlich 3 and DTPA methods for 172 soils in Greece having different levels of pH and calcium carbonate. Single and multiple regression analyses were employed to evaluate the relationship between Mehlich 3 and DTPA tests. Mehlich 3 results correlated well with DTPA-extractable Cu and Zn, but the correlation was poor for DTPA-extractable Mn. Also, a high correlation was found between Mehlich 3 and DTPA-extractable Fe for calcareous soils (R2 = 0.89), while a moderate relationship was found for noncalcareous soils (R2 = 0.65), which was improved to 0.78 when the pH was taken into account in multiple regression analysis. [ABSTRACT FROM PUBLISHER]

The Mehlich 3 method for the determination of available phosphorus (P) is less laborious compared to the Olsen method and provides the advantage of multielement analysis. However, in Greece the Olsen P method is currently used because of its suitability for calcareous soils. The aims of this study were to compare (a) the Mehlich 3 and Olsen methods for 200 soils having different levels of pH and calcium carbonate and (b) Mehlich 3 colorimetric and Mehlich 3 inductively coupled plasma (ICP) analysis for 17 acidic and 23 alkaline soils. The correlation of Mehlich 3 P and Olsen P methods, excluding soils with pH less than 5 and soils with calcium carbonate levels from 10.3 to 48.3%, resulted in a linear slope of 0.24 and r2of 0.82, and thus for this range of soils the Mehlich 3 test provided a more reliable measurement of P compared to the Olsen method. This study confirms also previous results that show that Mehlich 3 ICP test measures more P compared to Mehlich 3 colorimetry. [ABSTRACT FROM PUBLISHER]

• Pomegranate cultivar (cv.) 'Grenada' was the most susceptible under all saline conditions. • Pomegranate cvs. 'Wonderful' and 'Ermioni' may be cultivated under saline conditions. • Concentrations of Ca and Mg in leaves significantly reduced under KCl and K 2 SO 4 salts. • The highest concentrations of KCl and K 2 SO 4 (75 mM) decreased the chlorophyll concentration. The present investigation assesses the behavior of three pomegranate cultivars (Punica granatum L.) ('Wonderful', 'Ermioni' and 'Grenada') under increased concentrations of three salts (NaCl, KCl and K 2 SO 4) after 150 days of growth in vivo conditions. The aim of this research was to study the nutrient accumulation and distribution in leaves and roots and its effects on total chlorophyll (a + b), carotenoids, photosynthetic rate and stomatal conductance of leaves. In general, high salt supply of KCl and K 2 SO 4 led to significant decline in Ca and Mg concentration in leaves in all cultivars. 'Grenada' found with the highest concentration of Mn in leaves under all salt treatments. Regarding the roots, 'Wonderful' had the highest Mg concentration at 25, 50 and 75 mM of KCl and K 2 SO 4 , while 'Ermioni' had the maximum Ca concentration in roots. Chlorophyll concentration was reduced by the effect of KCl and K 2 SO 4 salts in all cultivars. Furthermore, K 2 SO 4 salt significantly reduced carotenoid concentration in leaves in all cultivars, especially 'Wonderful' showed 63.36 % reduction. 'Grenada' had the lowest photosynthetic rate and K 2 SO 4 salt exerted a significant effect in all cultivars. Regarding stomatal conductance, 'Ermioni' had the highest values with KCl and K 2 SO 4 salt treatments, while 'Grenada' was the most affected cultivar by all salts and at all concentrations. Our findings show the considerable potential of exploiting saline soils to obtain pomegranate plants with higher level of salt tolerance. Furthermore, our results suggest that 'Wonderful' and 'Ermioni' pomegranate cultivars may be cultivated also under marginal saline conditions. [ABSTRACT FROM AUTHOR]

Imbalanced Ca/Mg and excess Ni (due to serpentine stress) are limiting factors for plant productivity. The purpose of this study was to investigate if growth, nutrient uptake, PSII activity, photosynthesis and antioxidant activity of pomegranate (Punica granatum L., cv. Granada) plants were affected by serpentine stress. Pomegranate plants were grown in soil substrates from parent material marl (control), serpentine and serpentinized peridotite. Plant height, leaf, stem, root and total plant dry weight, as well as foliar N, P, K, Ca, Zn, Cu, chlorophyll content, fluorescence parameters, photosynthetic rate, and internal water use efficiency (WUEi) were significantly lower for the plants grown in the serpentinized peridotite soil. In contrast, higher ferric reducing antioxidant power (FRAP), total phenolics and total flavonoid content (TFC) levels were found in the serpentinized peridotite soil. The insignificant differences between the marl and serpentine soils in plant growth, PSII activity, photosynthesis and nutrient uptake indicated that P. granatum could tolerate a mild (not with extremely high Ni) serpentine stress. However, P. granatum could not tolerate stress showing excess Mg and imbalanced Ca/Mg, as found for the serpentinized soil of our study. • Soils from marl, serpentine and serpentinized peridotite were used as substrates. • Most foliar nutrients were significantly lower in the serpentinized peridotite soil. • Photosynthesis was significantly lower in the serpentinized peridotite soil. • Chlorophyll and PSII activity were significantly lower in the serpentinized soil. • Increased levels of phenols, TFC and FRAP were found in the serpentinized soil. [ABSTRACT FROM AUTHOR]

Highlights • Soils from marl, serpentine and serpentinized peridotite were used as substrates. • Most foliar nutrients were significantly lower in the serpentinized soil. • Photosynthesis was significantly lower in the serpentinized peridotite soil. • Increased levels of phenols, TFC and FRAP were found in the serpentinized soil. • Differential tolerance to serpentine stress between 'Wonderful' and 'Acco' existed. Abstract It was investigated if differential genotypic tolerance of two pomegranate cultivars ('Wonderful' and 'Acco') to serpentine stress existed. For this purpose, pomegranate plants were grown outdoors, in three soil substrates (from parent material marl, serpentine and serpentinized peridotite). The results indicated that growth, most foliar nutrient concentrations, total chlorophyll content, chlorophyll fluorescence and photosynthetic rate, for both genotypes, were significantly lower in the serpentinized peridotite soil (severe stress). In contrast, higher levels of total phenolics, total flavonoid content (TFC) and FRAP, were found in the serpentinized soil. Lower tolerance index to stress in the serpentinized soil was found for the cultivar 'Acco', than for 'Wonderful'. Overall, the physiological and antioxidant response of 'Acco' was worse, than that of 'Wonderful', under serpentine stress. In conclusion, despite the lower Ni, Cr and Mg accumulation of 'Acco' (compared to 'Wonderful'), its lower tolerance indices in the serpentinized soil probably shows its higher tissue sensibility to serpentine stress. Thus, this genotype should not be preferred for cultivation in soils presenting high degree of serpentinization (excess Mg concentrations). In contrast, from the tolerance indices of both genotypes in the serpentine soil, it is concluded that a mild stress existed in this case. [ABSTRACT FROM AUTHOR]