SOIL CONTAMINATION Applicability of Energy Crops for Metal Phytostabilization on Lands Moderately Contaminated with Copper, Nickel and Zinc J. Korzeniowska, E. Stanisławska-Glubiak, J. Igras Institute of Soil Science and Plant Cultivation - National Research Institute in Pulawy, Poland Department of Weed Science and Tillage Systems in Wroclaw, ul. Orzechowa 61, 50-540 Wroclaw, Poland, [email protected] Abstract A microplot experiment was conducted, using willow, reed canary grass and energy maize. Simulated soil contamination with Zn, Cu and Ni was used in the following combi- nations: control - no metals, Cu -50, Cu -100, Cu -200, Ni -40, Ni -80, Ni -160, Zn - -1 1 2 3 1 2 3 1 200, Zn 2-400, Zn 3-800 mg kg Willow was the most tolerant to Cu, Ni and Zn soil con- tamination and therefore can be used as a reclamation plant for moderately polluted land. Maize showed the most sensitivity to Ni, and reed canary grass to Zn excess in soil. Thus these species are not suitable for areas polluted with those metals respectively. The analysis of metal content in plant tissue reveled that Cu and Ni were accumulated in roots rather than in shoots. Zinc was accumulated in shoots in higher amount than Cu or Ni, especial- ly in willow. Key words: contamination, copper, nickel, zinc, energy plants, tolerance Introduction stems can be an obstacle to biomass combus- Recent years show increasing rate of tion for energy generation. interest in advantages of soil remediation with It is a beneficial solution to use energy plants (phytoremediation) as opposed to con- crops for phytostabilization. Cultivation of ventional methods. Among phytoremedia- these plants on contaminated land would tion techniques, two most popular ones can be serve a dual purpose: soil reclamation and bio- distinguished: phytoextraction and phytosta- mass production. For this purpose, it is impor- bilisation. Phytoextraction consists in extrac- tant to determine tolerance of energy crops to tion of metals from soil by plants, incorpora- excess heavy metals in soil and to analyze the tion of the extracted metals in plant tissues transfer of metals from roots to aerial parts. and their removal with the harvested plant The objective of this study has been to com- yield. This method, however, is applicable pare the resistance of willow, reed canary grass only when soil contamination is not so high as and maize to toxicity of Cu, Ni and Zn, and to reduce the crop's yield. The load of metals the ability of these crops to capture the ana- removed from soil depends on both their con- lyzed metals in roots, under conditions similar centration in plant tissues and the level of to field ones. crop's yield. The other method, phytostabilisa- tion, relies on using plants for reducing the Materials and Methods mobility and bioavailability of contaminants, A microplot experiment was conducted thus limiting their harmful effect on the envi- in four replicates on willow ( Salix viminalis ), ronment. Contaminated areas are cropped reed canary grass ( Phalaris arundinacea ) and with plants, whose roots mechanically bind maize ( Zea mays ) grown for biomass. In total, the contaminated soil while the root secre- 120 concrete-curbed microplots measuring tions stabilize the contaminants. Success of 1x1x1 m, were filled with Haplic Luvisols soil metal stabilization in the rhizosphere depends taken from a field, preserving the natural soil on the tolerance of plants to contamination horizons (pH in KCl 5.5; fraction <0.02 mm and ability of roots to accumulate the metals. 16%; Corg. 0.8%). Unlike phytoextraction, in phytostabilization In summer 2006 simulated soil contami- it is desirable that metals are captured by plant nation was achieved using Zn, Cu and Ni in the roots and not translocated to aerial tissues. form of sulphates according to the following Significant translocation of metals from roots design: the control - no metals, Cu 1 -50, Cu 2- to leaves, which can be carried by the wind, 100, Cu -200, Ni -40, Ni -80, Ni -160, Zn - 3 1 2 -1 3 1 can cause contaminants to spread. Moreover, 200, Zn 2-400, Zn 3-800 mg kg . Metal sul- excessive concentration of metals in twigs or phates were dissolved in water and applied over the microplots using a hand liquid sprayer. 15 th ICHMET 785 SOIL CONTAMINATION The test crops were sown (or planted) in dent at the lowest rate of the metal - 200 mg spring 2007, a year after the metals had been kg-1. The subsequent, higher doses caused a introduced to the soil. The microplots were 13, 17 and 59% yield loss. The zinc tolerance watered when rainfall was in deficit. The yield index decreased in the following order: willow was harvested in the second year of cultiva- > maize > reed canary grass. tion, in autumn 2008. At the same time, plant samples were taken for determination of Cu, Table 3. Tolerance index-average over 3 doses Ni and Zn. The plant material comprised aer- ial parts and roots of reed canary grass; ears, stems and roots of maize as well as leaves, twigs and roots of willow. Tolerance index of metals (metal resist- ance) was calculated according to the equa- tion: tolerance index = (yield treated/yield control) x 100. Metals in plant tissue were determined Our analysis of the yields and tolerance by the AAS method, having first dry ashed the indexes has demonstrated that willow was material in a muffle furnace and digested it in more tolerant than the other two crops to the hydrochloric acid. surface contamination of soil with metals, Differences between treatments were which seems to suggest that the plant is suit- analyzed by ANOVA and multiple compar- able for soil remediation. At the same time, isons of means using the Tukey significant dif- maize was the most sensitive plant to nickel ferences test at the 5% significance level. contamination whereas reed canary grass to zinc contamination of soil. Results and Discussion Concentration of metals in plant tissues Yields The lowest concentrations of metals in The three applied doses of Cu had no plant tissues were found in willow, and the negative effect on the yield of willow. Howev- highest ones - in reed canary grass (tab. 4, fig. er, the 100 mg Cu kg -1 rate led to a 13% yield 2). The difference was most evident in the case decrease of reed canary grass, and 200 mg Cu of roots. The concentration of Cu in willow kg -1 caused a 22% yield decrease of reed roots was two-fold, and that of Zn or Ni even canary grass and 53% of maize (fig. 1). Besides, 4-5 fold lower than in roots of the other two willow was characterized by the highest aver- crops. Analogously, twigs of willow had a age index of tolerance to copper, while maize lower level of metal concentrations than aerial had the lowest one (tab. 3). parts of reed canary grass and maize. There Willow and maize responded by a signif- was an exception, such as leaves of willow, in icant yield loss only to the highest dose of zinc which concentrations of Zn and Ni were com- - 800 mg kg -1 . In contrast, the toxic effect of parable to the ones determined in aerial tis- zinc on reed canary grass became already evi- sues of reed canary grass and maize. Figure 1. Plant yields in %: ∆ - willow twigs, o -top part of reed canary grass, x - stems+ears of maize. Letters in the tables refer to the significance of differences in the yields presented in the diagrams. Identical letters for a plant indicate no significant difference according to Tukey's test (P<0.05). 786 15 th ICHMET SOIL CONTAMINATION Table 4. Concentration in plat tissue in mg kg -1 - average over 3 doses Figure 2. Concentration of zinc, copper and nickel in plant tissue: + - roots, o - twigs or stems, x - leaves, . - whole top part, ∆ - ears. The aerial parts of the tested crops did helps to protect the photosynthetic appara- not accumulate excessive amounts of Cu, tus from excess amounts of metals, which whose concentration never exceeded 8 mg could interfere with the process of photosyn- kg -1 (fig. 2). Copper was accumulated in thesis (Landberg and Greger, 1996, Burzyns- roots, which contained on average 4.5-8.5- ki and Klobus, 2004). fold more of this element than the aerial Nickel, similarly to Cu, was gathered parts (tab. 5). The highest Cu concentration mainly in roots. The analyzed plants con- was found in grass roots (7-48 mg kg -1 ), and tained on average 3.8-22.4-fold more Ni in the lowest ones - in willow roots (4-18 mg roots than in aerial tissues (tab. 5). There kg -1 ) (fig. 2). In his study, McBride reports was an exception, such as willow leaves, that there is a strong barrier to the transloca- which contained comparable concentrations tion of Cu from roots to shoots (McBride and of Ni to those determined in roots (1-22 Martinez, 2000, McBride, 2001). When the compared to 1-27 mg kg -1 ) (fig. 2). The concentration of Cu and other metals is ele- observation that Ni is mainly accumulated vated, their transport from roots to shoots in roots is confirmed by Seregin et al. (2003) becomes limited so that the metals are accu- as well as Yang et al. (1997). mulated mainly in roots. This mechanism 15 th ICHMET 787 SOIL CONTAMINATION Table 5 . Relationship between concentration of metals in roots and in aerial part of plants. Accumulation of Zn in the analyzed crops All the tested plants accumulated copper was different from that of Cu and Ni.