Article pubs.acs.org/JAFC
Accumulation and Translocation of Essential and Nonessential Elements by Tomato Plants (Solanum lycopersicum) Cultivated in Open-Air Plots under Organic or Conventional Farming Techniques Olaia Liñero,*,†,‡,§ Maite Cidad,†,‡,§ Jose Antonio Carrero,† Christophe Nguyen,‡,§ and Alberto de Diego† †
Department of Analytical Chemistry, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), P.O. Box 644, 48080 Bilbao, Basque Country, Spain ‡ INRA, UMR 1391 ISPA, 71 Avenue Edouard Bourlaux, F-33140 Villenave d’Ornon, France § Bordeaux Sciences Agro, UMR 1391 ISPA, F-33170 Gradignan, France S Supporting Information *
ABSTRACT: A 5-month experiment was performed to study the accumulation of several inorganic elements in tomato plants cultivated using organic or synthetic fertilizer. Plants were harvested in triplicate at six sampling dates during their life cycle. Statistical and chemometric analysis of data indicated the sequestration of toxic elements and of Na, Zn, Fe, and Co in roots, while the rest of the elements, including Cd, were mainly translocated to aboveground organs. A general decreasing trend in element concentrations with time was observed for most of them. A negative correlation between some element concentrations and ripening stage of fruits was identified. Conventionally grown plants seemed to accumulate more Cd and Tl in their tissues, while organic ones were richer in some nutrients. However, there was no clear effect of the fertilizer used (organic vs synthetic) on the elemental composition of fruits. KEYWORDS: tomato plants (Solanum lycopersicum), nutrients, toxic elements, organic fertilizer, synthetic fertilizer
1. INTRODUCTION During the last decades, more and more concern has been focused on the optimization of agricultural techniques all over the world, with the aim of improving the nutritional value of crops and reducing their toxic content. The accumulation of essential and nonessential elements in plants depends on several factors, such as the agricultural technique used, the soil properties, the type of plant, the harvesting time, and the environmental conditions, among others.1,2 Conventional practices that use chemical fertilizers, insecticides, and pesticides have been partially substituted by other more environmentally friendly organic techniques. It has been reported that the use of organic farming techniques reduces the entrance of toxic trace elements in the food chain.3−5 Some essential nutrients, such as micronutrients, are incorporated into plants through absorption by root membrane transport proteins, such as NRAMP (natural resistance associated macrophage protein), ZIP (zinc-regulated transporter, iron-regulated transporter protein), YSL (yellow-stripelike), and ATPases.6−8 However, some undesirable ions can also be accumulated in plant tissues due to the lack of specificity of these membrane transporters, which results in the contamination of the food chain with subsequent risk for human health. This problem has already been described, for example, for Cd in tomato plants.9 Tomatoes (Solanum lycopersicum) are one of the mostconsumed vegetables worldwide, representing a significant part of the human diet. Their nutritional properties (major source of antioxidant compounds, such as carotenoids and phenols, with low levels of fat, calories, and cholesterol) make them beneficial © XXXX American Chemical Society
for human health, by reducing the risks of cardiovascular disease and certain types of cancer, specially cancers of the prostate, lung, and stomach.10 Several studies have been recently carried out to compare the accumulation of minerals in tomato tissues when using organic or conventional farming techniques. Recently, Kelly and Bateman11 found significant differences in the concentrations of Mn, Ca, Cu, and Zn in tomato fruits produced in the United Kingdom using different farming techniques. Other authors, however, reached the opposite conclusion working with tomato fruits obtained in a local market.12 On the other hand, the elemental composition of plant tissues is known to vary during the growth stages of the crop, depending on the age of the plant and on the translocation or remobilization of elements between organs.13 Due to the inconsistencies existing in the literature and the lack of controlled field experiments to investigate the effect that the farming technique has on the accumulation and translocation of chemical elements in tomato plants, we decided to perform a 5-month experiment in which the whole vegetative cycle of tomato plants was monitored in two open-air plots, one of them treated with organic fertilizers and the other one with synthetic ones. The objective of the work was to investigate the effect of the farming technique and the harvesting time on the accumulation of essential and nonessential elements in different parts of the plant. Received: August 7, 2015 Revised: October 7, 2015 Accepted: October 12, 2015
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DOI: 10.1021/acs.jafc.5b03878 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry
the fourth one was used to estimate the water content of the different plant parts. During the first, third, and fifth sampling campaigns and 2 weeks after the sixth sampling campaign, soils were also collected at the root zone of the first two sampled plants. All samples were preserved in prelabeled zip bags and kept in portable coolers at low temperature during their transportation to the laboratory. Once in the lab, samples were stored in dark at 4 °C until pretreatment, which was carried out on the day of sampling. Meteorological data registered from the C051 meteorological station (43°1.9271′ N, 3°0.237′ W) of the Basque Meteorological Agency17 were collected during the whole experiment. The parameters registered were the daily values of temperature (maximum, minimum, and mean values, °C), wind velocity (mean and maximum values, km h−1), precipitation (mm), relative humidity (%), and total solar irradiation (W m−2). Cumulative growing degree days (GDD, °C) were used as thermal time to establish the growth stage of the crop during the 139 days of the experiment. The GDDs were calculated according to eq 1, where Tbase (10 °C) is the base temperature of the considered plant and Tmax and Tmin are, respectively, the maximum and minimum daily temperature.
2. MATERIALS AND METHODS 2.1. Implementation of the Plots and Agricultural Treatments. The experiment was carried out in an open-air garden located in Beotegi, a rural area of the Basque Country (43°5.370′ N, 3°4.590′ W), Spain, at 370 m over the sea level with no greenhouse protection. Two plots of 15 m2, separated each other by 35 m, were selected in the garden. Four soil samples were collected at each plot in February 2013, 4 months before plantation, for soil characterization. Soils were randomly selected and collected from 15 to 30 cm depth, using a garden spade and removing padding and roots. Twenty-five tomato seedlings (S. lycopersicum var. Jack) with two to four leaves obtained from a local producer (Camino Sociedad Civil, Llodio, Spain) were transplanted in each plot on June 5, 2013. Several certified agricultural products were applied in the garden. In the plot intended for conventional practice, 0.25 kg m−2 of a synthetic chemical fertilizer (NPK 15-15-15 (15), Fertiberia, S.A.) was applied once 25 days before plantation, which corresponds to a dose of 563 g of total N, P2O5, and K2O. An insecticide (Epik 20 SG; Sipcam Jardiń S.L.) and a fungicide (Galben M.; Sipcam Jardiń S.L.) were added (200 mL m−2 in total) 7 and 36 days after plantation as phytosanitary treatment to minimize pest attacks. The plot intended for organic practice was supplied with an organic fertilizer (natural horse manure, Abonos Naturales Hermanos Aguado, S.L.; product approved and certified by CAEE as ecological product; C qualification) in two phases, 10 and 2 days before plantation, using a total of 6.48 kg m−2, which corresponds to a dose of 4471 g of total N, 389 g of P2O5, and 875 g of K2O. A total of 0.67 g m−2 of powdered copper sulfate ́ (Desarrollo Quimico Industrial, S.A.; product approved and certified by SHC for organic farming) was sprinkled on the aerial parts of the tomato plants 7 and 36 days after plantation to ensure the absence of typical fungi found in tomato cultivars, such as mildew. In the periphery of the organic plot, protective plants (Tagetes patula) were planted as natural repellent to avoid pests and insect attacks. Both plots were maintained until October 2013. During the cultivation, a vegetative pruning in an axis was performed, removing the auxiliary buds so as to favor the vigor of the plants and to improve fruit growth and quality. 2.2. Characterization of Soils. Soils collected in February 2013 were submitted to several physicochemical analyses to determine the content of organic matter (OM), organic carbon (OC), total calcium carbonate (CaCO3), and total nitrogen (N) in the samples, as well as their pH, cation exchange capacity (CEC), and texture. Samples were air-dried in a laminar-flow chamber. All the analyses were performed on the fraction
