Environmental and Experimental Botany 43 2000 55 – 71
Combination toxicology of metal-enriched soils: physiological responses of a Zn- and Cd-resistant ecotype of
Silene 6ulgaris on polymetallic soils
Wilfried H.O. Ernst , Hans J.M. Nelissen, Wilma M. Ten Bookum
Department of Ecology and Ecotoxicology of Plants, Faculty of Biology, Vrije Uni6ersiteit, De Boelelaan
1087
,
1081
HV Amsterdam, The Netherlands Received 2 July 1999; received in revised form 8 September 1999; accepted 10 September 1999
Abstract
Plants of an ecotype of Silene 6ulgaris Caryophyllaceae originating from a Cd-Pb-Zn mine at Plombie`re Belgium were grown on 15 polymetallic soils for a full life-cycle to investigate physiological responses which can help explain
previously reported disorders in plants. The degree of regulation of the metal concentration in the young seedlings was a very reliable indicator of the subsequent plant performance. Uptake of Zn could be regulated up to 200 nmol
water-soluble Zn g
− 1
dry soil without surpassing 7 mmol Zn g
− 1
dry leaf tissue supporting the hypothesis of a high regulating potential of Zn-resistant ecotypes. As soon as a certain ecotype-specific threshold was surpassed the Zn
concentration in all plant tissues strongly increased. The Cu concentration in roots and shoots had no threshold and showed the tendency to increase near linearly with the external Cu soil concentration. Similar behaviours were found
for Cd, Mn and Pb. The metal concentration of seeds was the lowest of all plant parts; nevertheless it increased linearly with increasing concentration of Fe and Zn in the soil. From visible symptoms the degree of chlorosis was
positively related with the concentration of Zn, but not with that of Cu, and interrelated with Fe availability. High cyanidin concentrations in leaves were not indicating a surplus of heavy metals, but deficiency in phosphorus and to
a lesser degree in nitrogen. Phytochelatins PCs were only present in measurable amounts in leaves of plants grown on soils rich in Cu; but PCs amounts in the early vegetative phase could not be related to vegetative and seed biomass
at the reproductive stage. Therefore, it is concluded that PCs are a less reliable indicator of metal toxicity during a full life-cycle than the metal concentration of young seedlings. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Chlorosis; Copper; Cyanidin; Lead; Mine soil; Phytochelatin; Seedling www.elsevier.comlocateenvexpbot
1. Introduction
Orogenic soils are the result of ore outcrops, mining, smelting, or refining activities with a co-
occurrence of several heavy metals and a high variation in the concentration of each metal
Corresponding author. Tel.: + 31-20-4447050; fax: + 31- 20-4447123.
E-mail address
:
wernstbio.vu.nl W.H.O. Ernst S0098-847200 - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 0 9 8 - 8 4 7 2 9 9 0 0 0 4 8 - 9
Ernst, 1974. A restricted number of plant species which have evolved metal resistance mechanisms
are able to colonize these polymetallic soils Ernst et al., 1992. In the analysis of the impact of metal
mixtures on plant performance, metal-resistant ecotypes can at least partly help to overcome the
disadvantage of sensitive plants on metal-contam- inated soils. In addition to many short-term ex-
periments with one metal Sanita´ di Toppi and Gabbrielli, 1999, only a few experiments on soils
artificially contaminated with one metal have been extended to a full life-cycle of plants Sheppard et
al., 1993. Metal-resistant plants offer an excellent opportunity to analyse the impact of complex
metal mixtures on the performance of plants dur- ing a full life-cycle. In addition, such plants can be
exposed to metal mixtures in a realistic environ- mental soil setting, i.e. with differences in pH,
organic matter, Ca content and other soil parame- ters because these plants are also adapted to low
levels of major nutrients in orogenic soils Ernst, 1974. The few studies on combination toxicology
of heavy metals analysed plants which were artifi- cially exposed to enhanced concentrations of these
elements in hydroponics for a short period Wal- lace and Abou-Zam Zam, 1989; Wallace and
Berry, 1989; Sharma et al., 1999. For our study we have selected the perennial herb Silene 6ulgaris
Caryophyllaceae being characteristic for many metal-enriched soils in Europe Ernst, 1974. In
contrast to many other metal-resistant plants, S.
6 ulgaris has nearly no symbiosis with arbuscular
mycorrhizal fungi Ernst et al., 1990; Pawlowska et al., 1996; Hildebrandt et al., 1999. Therefore
the roots are directly exposed to the metal concen- tration of the soil and changes of metal speciation
and benefits for the host by mycorrhizal fungi can be excluded Dueck et al., 1986; Hildebrandt et
al., 1999.
With regard to morphological and ecological parameters, we have shown that a Zn- and Cd-re-
sistant ecotype of S. 6ulgaris reacted quite differ- ent in the various phases of its life-cycle Ernst
and Nelissen, 1999. Here, we report on the phys- iological responses of this ecotype to an exposure
to combinations of the heavy metals Cd, Cu, Fe, Mn, Pb and Zn throughout a full life-cycle of the
Zn- and Cd-resistant plants Ernst and Nelissen, 1999. We tested the following hypotheses:
1. As soon as the metal concentration of the soil solution exceeds the Zn- and Cd-resistance of
the metal-resistant ecotype, disturbance of the nutrient uptake will occur, partly being visible
by discoloration.
2. The metal concentration in young seedlings is an indicator for the survival chance up to seed
maturity with a negative relationship between metal concentration and survival.
3. Due to low Cu concentration which diminishes the performance of this ecotype for Cu by
50, i.e. EC
50
Schat and Ten Bookum, 1992, Cu-enriched soils will strongly impair the
metabolism which will be expressed by an enhanced synthesis of phytochelatins PCs.
2. Materials and methods
