Juan Barceló

Arsenic and heavy metal contamination of soil and vegetation around a copper mine in Northern Peru

Abstract At present, very little information is available on either the environmental impact or the biogeochemistry of mine sites in Latin America. Here we present preliminary results on contamination of soils and plants around a copper mine in the Andes of Northern Peru. Plants and soils were sampled at six sites ranging from low (S1) to high phytotoxicity (S6); samples were analysed for concentrations of As and heavy metals. Stepwise multiple regression analysis was used in order to determine the soil factors that significantly influenced As and metal availability. High As and Cu concentrations in soil extracts (ammonium acetate-EDTA), in addition to low pH and high Al availability, seem to be the most important soil factors that limit plant performance around the mice. A high organic matter content favoured Cu and Al extractability. Nevertheless, phytotoxicity was more intense at sites with low organic matter concentrations. Unusually high concentrations of As and metal concentrations were detected in leaves of some species (e.g. in Bidens cynapiifolia up to 1430 μg/g dry wt. As, 437 Zn, 620 Cu, 6510 Al and 5.7% Fe) while others (e.g. Eriochloa ramosa) more effectively restricted metal transport to the shoots. These plant species seem interesting for future investigations on both metal tolerance mechanisms and revegetation of contaminated soils at the numerous mine sites located at high altitudes in equatorial regions.

Zinc hyperaccumulation in Thlaspi caerulescens. II. Influence on organic acids

Abstract The influence of different zinc (Zn) concentrations (1.5 to 1500 μM) on organic acid levels in roots and shoots of the Zn‐hyperaccumulator plant Thlaspi caerulescens was investigated. In shoots, malate was the most abundant organic acid (164 to 248 μmol/g f.w.), followed by citrate, succinate, and oxalate. A significant correlation between soluble Zn and both malate and oxalate was observed in shoots, but not in roots. In shoots, a significant correlation between inorganic cation equivalents and organic acid anion equivalents was found. These observations and the finding, that organic acid concentrations were high even under suboptimal Zn supply (1.5 μM) suggest that in T. caerulescens the high organic acid concentration in shoots is a constitutive property. The variation of the organic acid concentrations seem to be a consequence of the cation‐anion balance rather than a specific Zn tolerance mechanism. The constitutively high organic acid concentration may be responsible for the high Zn and iro...

Phosphorus Efficiency and Root Exudates in Two Contrasting Tropical Maize Varieties

ABSTRACT Nutrient solution culture and quartz sand amended with or without rock phosphate, were used to compare the short-term responses to phosphorus (P) deficiency of two contrasting maize hybrids, L3x228-3 (P-efficient) and HS 2841x5046 (P-inefficient). In solution-grown seedlings, the rapid P deficiency-induced enhancement of root growth and of the root/shoot ratio was a sign of P deficiency stress rather than of P efficiency. In sand culture, uptake of P from sparingly soluble rock phosphate was higher in P-efficient plants than in P-inefficient maize. In the variety L3-228-3, P efficiency seemed due to enhanced P acquisition rather than to an enhanced P use efficiency. In sand, but not in solution culture, higher citrate concentrations were detected in the rhizosphere of P-efficient than of P-inefficient maize. Quartz sand amended with rock phosphate was a better substrate than nutrient solution for revealing the varietal differences in P acquisition efficiency in short-term experiments.

Callose production as indicator of aluminum toxicity in bean cultivars

Abstract The response of seven cultivars of beans to aluminum (Al) stress was assessed by using root elongation rate and callose accumulation in 5 mm root tips as early markers of injury. Bean seedlings were grown in acid nutrient solution (pH 4.5) and exposed to 0, 20, and 50 μM Al for 24 h. Root elongation was recorded at frequent intervals and callose accumulation was determined spectrofluorometrically. Based on the root elongation rate, Strike and Contender were Al‐sensitive and F‐15 and Superba were the most Al‐tolerant cultivars. The cultivars Hilds maxi, Hinrichs riesen, and Saxa showed an intermediate behavior. Callose synthesis positively correlated with internal Al concentration and negatively correlated with root elongation rate. Both callose accumulation and root elongation rate were useful in classifying the bean cultivars for aluminum tolerance, but root elongation rate was a more sensitive parameter. Root callose deposition can serve as an early marker for Al toxicity and tolerance in beans.

Constitutive and aluminium-induced patterns of phenolic compounds in two maize varieties differing in aluminium tolerance.

Aluminium tolerance in maize is mainly due to more efficient Al exclusion. Nonetheless, even in tolerant varieties Al can gain access into the cells. Detoxification by binding to strong organic ligands should therefore play a role also in plants with high Al exclusion capacity. To test this hypothesis in this study the concentrations of soluble, free and bound, phenolics were analyzed in roots of two maize varieties differing in Al tolerance. Exposure for 24 h to 50 microM Al in nutrient solution strongly inhibited root elongation in the sensitive variety 16 x 36, but not in the Al-tolerant variety Cateto. Cateto accumulated about half the concentration of Al in roots than 16 x 36 (analysis performed after root desorption with citrate). Roots of Al-tolerant Cateto contained higher concentrations of caffeic acid, catechol and catechin than roots of the sensitive variety. Exposure to Al induced the accumulation of taxifolin in roots of both varieties. However, Al-tolerant Cateto accumulated about twice the concentration than Al-sensitive 16 x 36 of this pentahydroxyfavonol. The molar ratio for phenolics with catecholate groups to Al was about unity in roots of Cateto, while in those of 16 x 36 the ratio was ten times lower. Both the fact that these phenolics are strong ligands for Al and their high antioxidant and antiradical activity suggest that these compounds may provide protection against the Al fraction that is able to surpass the exclusion mechanisms operating in the tolerant maize variety.