Mycorrhiza (2014) 24:209–217 DOI 10.1007/s00572-013-0532-9
ORIGINAL PAPER
Nickel tolerance of serpentine and non-serpentine Knautia arvensis plants as affected by arbuscular mycorrhizal symbiosis Pavla Doubková & Radka Sudová
Received: 28 June 2013 / Accepted: 25 September 2013 / Published online: 18 October 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract Serpentine soils have naturally elevated concentrations of certain heavy metals, including nickel. This study addressed the role of plant origin (serpentine vs. nonserpentine) and symbiosis with arbuscular mycorrhizal fungi (AMF) in plant Ni tolerance. A semi-hydroponic experiment involving three levels of Ni and serpentine and non-serpentine AMF isolates and populations of a model plant species (Knautia arvensis) revealed considerable negative effects of elevated Ni availability on both plant and fungal performance. Plant growth response to Ni was independent of edaphic origin; however, higher Ni tolerance of serpentine plants was indicated by a smaller decline in the concentrations of photosynthetic pigments and restricted root-to-shoot Ni translocation. Serpentine plants also retained relatively more Mg in their roots, resulting in a higher shoot Ca/Mg ratio. AMF inoculation, especially with the non-serpentine isolate, further aggravated Ni toxicity to host plants. Therefore, AMF do not appear to be involved in Ni tolerance of serpentine K. arvensis plants. Keywords Arbuscular mycorrhizal fungi . Calcium . Magnesium . Nickel toxicity . Semi-hydroponics . Tolerance index
Electronic supplementary material The online version of this article (doi:10.1007/s00572-013-0532-9) contains supplementary material, which is available to authorized users. P. Doubková : R. Sudová Institute of Botany, Academy of Sciences of the Czech Republic, 252 43 Průhonice, Czech Republic P. Doubková (*) Department of Experimental Plant Biology, Faculty of Science, Charles University in Prague, 128 44 Prague 2, Czech Republic e-mail: [email protected]
Introduction Although serpentine soils represent a highly variable group in terms of their chemical composition, they share several characteristic features such as low calcium-to-magnesium ratio, elevated and potentially phytotoxic concentrations of heavy metals (especially nickel, cobalt, chromium or manganese) and often general macronutrient deficiency (for reviews, see, e.g. Kazakou et al. 2008; O’Dell and Rajakaruna 2011). Among heavy metals typical of serpentine soils, Ni is of particular importance due to its high plant-available concentrations, considerable plant toxicity and relatively high rate of root-to-shoot translocation (Seregin and Kozhevnikova 2006; Kazakou et al. 2008). Although Ni ranks among essential micronutrients, the amount required for normal plant growth is very low (Marschner 2002; Chen et al. 2009). The toxicity of Ni generally consists of interference with other essential metal ions and induction of oxidative stress, resulting in restricted cell division and expansion, disruption of photosynthesis, inhibition of root growth and branching, leaf chlorosis, necrosis and wilting, modification in uptake of other cations, etc. (Chen et al. 2009; Nagajyoti et al. 2010). Plants inhabiting serpentine habitats have adopted different mechanisms of avoidance or tolerance of elevated heavy metal availability such as exclusion, compartmentalisation in certain tissues, tolerance to toxic effects or even hyperaccumulation (Kazakou et al. 2008; O’Dell and Rajakaruna 2011). With regard to Ni, hyperaccumulation (i.e. shoot concentration higher than 1,000 mg Ni kg−1 of dry biomass) is probably the most studied strategy. Nevertheless, the majority of plant species inhabiting serpentine soils are rather tolerant to elevated Ni availability, or they limit Ni uptake and translocation to the aboveground biomass (Kazakou et al. 2008; O’Dell and Rajakaruna 2011), which also applies to our model species, Knautia arvensis (Doubková et al. 2012). Previous studies comparing the response of non-hyperaccumulating serpentine
210
and non-serpentine plants to high Ni availability (see, e.g. Nagy and Proctor 1997; Taylor and Levy 2002; Nyberg Berglund et al. 2003) produced highly diverse results, likely related to different soil Ni concentrations at the sites of plant origin. In general, a considerable role in plant adaptation to adverse soil conditions belongs to arbuscular mycorrhizal fungi (AMF) from the phylum Glomeromycota that enter into a symbiosis with roots of most vascular plants (Smith and Read 2008). The involvement of these obligatory symbiotic fungi in plant nutrient uptake and drought stress alleviation in serpentine soils has been previously documented, though the extent of AMF-mediated benefits seems to depend on particular soil– plant–AMF combinations (e.g. Castelli and Casper 2003; Ji et al. 2010; Doubková et al. 2012, 2013). Considering specifically the AMF interaction with Ni, it has received relatively little attention compared with other heavy metals such as cadmium, zinc or lead. Both positive and negative effects of AMF inoculation on plant Ni tolerance have been documented in this respect, often associated with an AMF-mediated decrease (Vivas et al. 2006; Orlowska et al. 2011; Amir et al. 2013) or increase (Turnau and Mesjasz-Przybylowicz 2003; Lagrange et al. 2011) in Ni uptake. A series of pot experiments involving serpentine and nonserpentine populations of K. arvensis, and their native AMF and soils, has recently provided ambiguous results concerning AMF involvement in plant Ni uptake and translocation (Doubková et al. 2011, 2012, 2013). In the present study, a semi-hydroponic system was adopted enabling to separate Ni toxicity from the other aspects of serpentine soil chemistry. The following hypotheses were addressed: (1) K. arvensis population and AMF isolate of serpentine origin will show a higher tolerance to elevated Ni concentrations than their nonserpentine counterparts; (2) with rising Ni concentration in solution, the extent of mycorrhizal growth promotion will increase for plants inoculated with serpentine AMF; and (3) plant Ni uptake and translocation will be affected both by plant origin and AMF inoculation, with the serpentine plant– AMF complex showing the most effective barrier to root-toshoot Ni translocation.
Material and methods
Mycorrhiza (2014) 24:209–217
hydroponic solution. The experiment was conducted in a greenhouse under natural sunlight and supplementary 12-h artificial illumination (metal halide lamps, 400 W, Philips HPI-T Plus). The experiment consisted of 18 treatments resulting from a combination of (1) two K. arvensis populations (serpentine and non-serpentine), (2) three AMF inoculation treatments (non-inoculated plants, plants inoculated with a serpentine AMF isolate and plants inoculated with a non-serpentine AMF isolate) and (3) three Ni concentrations in the hydroponic solution (0, 50 and 100 μM Ni). Each treatment involved six replicates (i.e. 108 plants in total were grown in 18 flower boxes), with three individuals of both plant populations being combined in the same flower box. Plant material Field scabious, K. arvensis (L.) J. M. Coult. (Dipsacaceae), is a perennial rosette-forming herb, entering into symbiosis with AMF (Doubková et al. 2011) and encompassing both serpentine and non-serpentine populations in Central Europe (Kaplan 1998; Kolář et al. 2009). The present semihydroponic study involved two K. arvensis populations from the Czech Republic. The serpentine population (referred to as S) originating from a semi-dry meadow in W Bohemia (Křížky, 50°03′54.2″N, 12°45′03.6″E) thrives naturally in soil with a DTPA-extractable Ni concentration of ~260 mg kg−1 and a Ca/Mg ratio of 0.8. In contrast, the non-serpentine population (NS) from a dry meadow in SW Bohemia (Chanovice, 49°24′39.0″N, 13°43′55.5″E) grows in soil with a low DTPA-extractable Ni concentration (100 C>50>100 C>50>100 50>100 C>50=100 C>50>100 50ns
↓s ↓s ns> nm=s
ns ns ns ns ns ns
0.7 ns 23.6*** 3.7 ns 1.2 ns 75.4*** 7.1**
↓S ↑S ↑S ↓S ↓S
↑S
↓S ↑S
0.5 7.0 0.7 0.5 0.5 1.7
ns ns ns ns ns ns
For significant effects of single factors, the direction of change is indicated by arrows and mathematical symbols (e.g. ↑S denotes higher values for S population than NS population; C>50=100 denotes higher values in control than in both 50 and 100 μM Ni solution). df error=75.The data in columns represent F values with significance level ns non-significant effect ***P
ORIGINAL PAPER
Nickel tolerance of serpentine and non-serpentine Knautia arvensis plants as affected by arbuscular mycorrhizal symbiosis Pavla Doubková & Radka Sudová
Received: 28 June 2013 / Accepted: 25 September 2013 / Published online: 18 October 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract Serpentine soils have naturally elevated concentrations of certain heavy metals, including nickel. This study addressed the role of plant origin (serpentine vs. nonserpentine) and symbiosis with arbuscular mycorrhizal fungi (AMF) in plant Ni tolerance. A semi-hydroponic experiment involving three levels of Ni and serpentine and non-serpentine AMF isolates and populations of a model plant species (Knautia arvensis) revealed considerable negative effects of elevated Ni availability on both plant and fungal performance. Plant growth response to Ni was independent of edaphic origin; however, higher Ni tolerance of serpentine plants was indicated by a smaller decline in the concentrations of photosynthetic pigments and restricted root-to-shoot Ni translocation. Serpentine plants also retained relatively more Mg in their roots, resulting in a higher shoot Ca/Mg ratio. AMF inoculation, especially with the non-serpentine isolate, further aggravated Ni toxicity to host plants. Therefore, AMF do not appear to be involved in Ni tolerance of serpentine K. arvensis plants. Keywords Arbuscular mycorrhizal fungi . Calcium . Magnesium . Nickel toxicity . Semi-hydroponics . Tolerance index
Electronic supplementary material The online version of this article (doi:10.1007/s00572-013-0532-9) contains supplementary material, which is available to authorized users. P. Doubková : R. Sudová Institute of Botany, Academy of Sciences of the Czech Republic, 252 43 Průhonice, Czech Republic P. Doubková (*) Department of Experimental Plant Biology, Faculty of Science, Charles University in Prague, 128 44 Prague 2, Czech Republic e-mail: [email protected]
Introduction Although serpentine soils represent a highly variable group in terms of their chemical composition, they share several characteristic features such as low calcium-to-magnesium ratio, elevated and potentially phytotoxic concentrations of heavy metals (especially nickel, cobalt, chromium or manganese) and often general macronutrient deficiency (for reviews, see, e.g. Kazakou et al. 2008; O’Dell and Rajakaruna 2011). Among heavy metals typical of serpentine soils, Ni is of particular importance due to its high plant-available concentrations, considerable plant toxicity and relatively high rate of root-to-shoot translocation (Seregin and Kozhevnikova 2006; Kazakou et al. 2008). Although Ni ranks among essential micronutrients, the amount required for normal plant growth is very low (Marschner 2002; Chen et al. 2009). The toxicity of Ni generally consists of interference with other essential metal ions and induction of oxidative stress, resulting in restricted cell division and expansion, disruption of photosynthesis, inhibition of root growth and branching, leaf chlorosis, necrosis and wilting, modification in uptake of other cations, etc. (Chen et al. 2009; Nagajyoti et al. 2010). Plants inhabiting serpentine habitats have adopted different mechanisms of avoidance or tolerance of elevated heavy metal availability such as exclusion, compartmentalisation in certain tissues, tolerance to toxic effects or even hyperaccumulation (Kazakou et al. 2008; O’Dell and Rajakaruna 2011). With regard to Ni, hyperaccumulation (i.e. shoot concentration higher than 1,000 mg Ni kg−1 of dry biomass) is probably the most studied strategy. Nevertheless, the majority of plant species inhabiting serpentine soils are rather tolerant to elevated Ni availability, or they limit Ni uptake and translocation to the aboveground biomass (Kazakou et al. 2008; O’Dell and Rajakaruna 2011), which also applies to our model species, Knautia arvensis (Doubková et al. 2012). Previous studies comparing the response of non-hyperaccumulating serpentine
210
and non-serpentine plants to high Ni availability (see, e.g. Nagy and Proctor 1997; Taylor and Levy 2002; Nyberg Berglund et al. 2003) produced highly diverse results, likely related to different soil Ni concentrations at the sites of plant origin. In general, a considerable role in plant adaptation to adverse soil conditions belongs to arbuscular mycorrhizal fungi (AMF) from the phylum Glomeromycota that enter into a symbiosis with roots of most vascular plants (Smith and Read 2008). The involvement of these obligatory symbiotic fungi in plant nutrient uptake and drought stress alleviation in serpentine soils has been previously documented, though the extent of AMF-mediated benefits seems to depend on particular soil– plant–AMF combinations (e.g. Castelli and Casper 2003; Ji et al. 2010; Doubková et al. 2012, 2013). Considering specifically the AMF interaction with Ni, it has received relatively little attention compared with other heavy metals such as cadmium, zinc or lead. Both positive and negative effects of AMF inoculation on plant Ni tolerance have been documented in this respect, often associated with an AMF-mediated decrease (Vivas et al. 2006; Orlowska et al. 2011; Amir et al. 2013) or increase (Turnau and Mesjasz-Przybylowicz 2003; Lagrange et al. 2011) in Ni uptake. A series of pot experiments involving serpentine and nonserpentine populations of K. arvensis, and their native AMF and soils, has recently provided ambiguous results concerning AMF involvement in plant Ni uptake and translocation (Doubková et al. 2011, 2012, 2013). In the present study, a semi-hydroponic system was adopted enabling to separate Ni toxicity from the other aspects of serpentine soil chemistry. The following hypotheses were addressed: (1) K. arvensis population and AMF isolate of serpentine origin will show a higher tolerance to elevated Ni concentrations than their nonserpentine counterparts; (2) with rising Ni concentration in solution, the extent of mycorrhizal growth promotion will increase for plants inoculated with serpentine AMF; and (3) plant Ni uptake and translocation will be affected both by plant origin and AMF inoculation, with the serpentine plant– AMF complex showing the most effective barrier to root-toshoot Ni translocation.
Material and methods
Mycorrhiza (2014) 24:209–217
hydroponic solution. The experiment was conducted in a greenhouse under natural sunlight and supplementary 12-h artificial illumination (metal halide lamps, 400 W, Philips HPI-T Plus). The experiment consisted of 18 treatments resulting from a combination of (1) two K. arvensis populations (serpentine and non-serpentine), (2) three AMF inoculation treatments (non-inoculated plants, plants inoculated with a serpentine AMF isolate and plants inoculated with a non-serpentine AMF isolate) and (3) three Ni concentrations in the hydroponic solution (0, 50 and 100 μM Ni). Each treatment involved six replicates (i.e. 108 plants in total were grown in 18 flower boxes), with three individuals of both plant populations being combined in the same flower box. Plant material Field scabious, K. arvensis (L.) J. M. Coult. (Dipsacaceae), is a perennial rosette-forming herb, entering into symbiosis with AMF (Doubková et al. 2011) and encompassing both serpentine and non-serpentine populations in Central Europe (Kaplan 1998; Kolář et al. 2009). The present semihydroponic study involved two K. arvensis populations from the Czech Republic. The serpentine population (referred to as S) originating from a semi-dry meadow in W Bohemia (Křížky, 50°03′54.2″N, 12°45′03.6″E) thrives naturally in soil with a DTPA-extractable Ni concentration of ~260 mg kg−1 and a Ca/Mg ratio of 0.8. In contrast, the non-serpentine population (NS) from a dry meadow in SW Bohemia (Chanovice, 49°24′39.0″N, 13°43′55.5″E) grows in soil with a low DTPA-extractable Ni concentration (100 C>50>100 C>50>100 50>100 C>50=100 C>50>100 50ns
↓s ↓s ns> nm=s
ns ns ns ns ns ns
0.7 ns 23.6*** 3.7 ns 1.2 ns 75.4*** 7.1**
↓S ↑S ↑S ↓S ↓S
↑S
↓S ↑S
0.5 7.0 0.7 0.5 0.5 1.7
ns ns ns ns ns ns
For significant effects of single factors, the direction of change is indicated by arrows and mathematical symbols (e.g. ↑S denotes higher values for S population than NS population; C>50=100 denotes higher values in control than in both 50 and 100 μM Ni solution). df error=75.The data in columns represent F values with significance level ns non-significant effect ***P
