Wolf Gruber

Genetic basis of Cd tolerance and hyperaccumulation in Arabidopsis halleri

The genetic basis of Cd tolerance and hyperaccumulation was investigated in Arabidopsis halleri. The study was conducted in hydroponic culture with a backcross progeny, derived from a cross between A. halleri and a non-tolerant and non-accumulating related species Arabidopsis lyrata ssp. petraea, as well as with the parents of the backcross. The backcross progeny segregates for both cadmium (Cd) tolerance and accumulation. The results support that (i) Cd tolerance may be governed by more than one major gene, (ii) Cd tolerance and Cd accumulation are independent characters, (iii) Cd and Zn tolerances co-segregate suggesting that they are under pleiotropic genetic control, at least to a certain degree, (iv) the same result was obtained for Cd and Zn accumulation.

Impacts of alien invasive plants on soil nutrients are correlated with initial site conditions in NW Europe.

Alien invasive plants are capable of modifying ecosystem function. However, it is difficult to make generalisations because impacts often appear to be species- and site-specific. In this study, we examined the impacts of seven highly invasive plant species in NW Europe (Fallopia japonica, Heracleum mantegazzianum, Impatiens glandulifera, Prunus serotina, Rosa rugosa, Senecio inaequidens, Solidago gigantea) on nutrient pools in the topsoil and the standing biomass. We tested if the impacts follow predictable patterns, across species and sites or, alternatively, if they are entirely idiosyncratic. To that end, we compared invaded and adjacent uninvaded plots in a total of 36 sites with widely divergent soil chemistry and vegetation composition. For all species, invaded plots had increased aboveground biomass and nutrient stocks in standing biomass compared to uninvaded vegetation. This suggests that enhanced nutrient uptake may be a key trait of highly invasive plant species. The magnitude and direction of the impact on topsoil chemical properties were strongly site-specific. A striking finding is that the direction of change in soil properties followed a predictable pattern. Thus, strong positive impacts (higher topsoil nutrient concentrations in invaded plots compared to uninvaded ones) were most often found in sites with initially low nutrient concentrations in the topsoil, while negative impacts were generally found under the opposite conditions. This pattern was significant for potassium, magnesium, phosphorus, manganese and nitrogen. The particular site-specific pattern in the impacts that we observed provides the first evidence that alien invasive species may contribute to a homogenisation of soil conditions in invaded landscapes.

Specific Interactions between Local Metallicolous Plants Improve the Phytostabilization of Mine Soils

At present, no efficient technique is available for cleaning up soils which are highly polluted by heavy metals. Limiting the movement of pollutants out of the contaminated area by creating a dense and persistent plant cover appears to be the more reasonable approach. In this context, phytostabilization is a technique that uses metallicolous plants to revegetate highly polluted soils. This paper presents the results of an experiment performed in situ using metallicolous ecotypes of four plant species native to the Mediterranean French region, and grown in different combinations at a polluted site over two years. The soils were highly polluted with zinc, cadmium and lead. The aim was to find the best species mixture in terms of cover, biomass and duration. The four species used were the biennial legume Anthyllis vulneraria, two perennial grasses, Festuca arvernensis and Koeleria vallesiana, and the perennial forb Armeria arenaria. Mixtures which included A. vulneraria, and especially when in combination with F. arvernensis, showed the highest values of cover and biomass. After flowering, the biennial individuals of A. vulneraria disappeared but subsequent germination and survival of seedlings occurred abundantly under the two grasses. Mixtures with A. arenaria showed the lowest values of cover and biomass. Soil nitrogen increased in the plots with A. vulneraria as well as the concentration of essential nutrients (N P K) in the aerial parts of the two grasses. In contrast, the concentration of metals (Zn Pb Cd) decreased in the aboveground biomass of the latter in the same plots. These results show that reciprocal facilitation effects can act in heavy metal polluted environments, and that phytostabilization efforts in the Mediterranean region can be improved by using mixtures including local metallicolous legume and grass species.

Invasion by Fallopia japonica increases topsoil mineral nutrient concentrations

ABSTRACT Fallopia japonica is one of the most troublesome alien invasive plants across temperate regions, with large negative impacts on plant species diversity. We examined its impacts on topsoil chemistry and nutrient stocks in standing biomass at 6 sites with contrasting resident plant communities in Belgium. Topsoil and biomass were sampled in invaded and closely adjacent uninvaded plots. Standing biomass and mineral nutrient concentrations in soil (ammonium acetate exchangeable cations and P, total C, and N) and plants were determined. Soil under F. japonica generally had higher exchangeable nutrient concentrations (Cu: +45%, K: +34%, Mg: +49%, Mn: +61%, P: +44%, Zn: +75%). Standing biomass was 3- to 13-fold higher depending on site. Despite lower nutrient concentrations in aboveground biomass, invaded stands had 3.2- to 5.4-fold larger nutrient stocks in aboveground biomass compared to the resident vegetation. We conclude that F. japonica enhances nutrient cycling rates and topsoil fertility, probably due to nutrient uplift. The impacts were greatest in sites with low nutrient concentrations in uninvaded plots, suggesting that F. japonica may contribute to soil homogenization in invaded landscapes.

Influence of logging traffic on the hydromorphic degradation of acid forest soils developed on loessic loam in middle Belgium

Modifications of soil physical parameters (bulk density, pore space pattern and clay dispersibility) induced by compaction in wheel-rutted areas due to mechanized forest exploitation was studied in loamy soils developed under beech stands in the loessic belt of middle Belgium. The consequences of surface waterlogging on pedological processes (especially the geochemical behaviour of iron and aluminium) were also investigated. The results show that rutted areas have: (1) a significant decrease of total porosity in the eluvial upper layers of the soil (0-30 cm depth), associated with an important lowering of the transmission pore volume and a decrease in macroporosity to about 6% of the total soil volume, i.e. to less than the current threshold value for root viability (10%); (2) a reduction of macropore space to about 9.5% in the lower illuvial horizons (30-50 cm depth); (3) a decrease of redox potential due to temporary waterlogging, inducing (a) the occurrence of reduced forms of iron, (b) a strong leaching of iron oxyhydroxides from the E(g) to the B(1g) horizon, (c) an increase of organically complexed iron forms in both the Es and B(tg) horizons, and (d) high solubility of Goethite and even of ferromagnesium minerals in the eluvial horizons; (4) an increase of clay dispersibility in both the E(g) and B(tg) horizons. These results provide clear evidence that on loessic materials soil compaction due to logging operations leads to rapid soil degradation through active hydromorphic processes.

Ring width and element concentrations in beech (Fagus sylvatica L.) from a periurban forest in central Belgium

The Foret de Soignes is a beech high forest located near Brussels (Belgium), established on a strongly acidic soil and subjected to atmospheric pollution and recreational pressure. We investigated variations in ring width and mineral element concentrations (N, P, K, Ca, Mg, Mn, Al) over the last 95 years in five 135-year-old trees, variations in ring width in four 40-year-old trees and tested associations with climatic parameters. Growth curves showed a striking increase in mean sensitivity in the last 20 years in the old trees but not in the young ones, starting with the 1976 summer drought. Mean sensitivity is a statistical measure of the mean relative variability between adjacent ring widths within a tree, which is correlated to susceptibility to climatic stress (Fritts, H.C., 1976. Tree Rings and Climate, Academic Press, London, 567pp). May rainfall and, to a lesser extent, soil water recharge (i.e. pooled rainfall from October to May) correlated significantly with ring width. However, two of the five growth depressions in the last 20 years could not readily be accounted for by adverse climatic conditions. Element concentration profiles were suggestive of a decrease in the availability of Mn, Mg and Ca, but no trend of increasing N was obvious. The possible causes of the recent increase in sensitivity of old beech trees are discussed in terms of interactions between ageing and extreme climatic events, aggravated by soil compaction due to logging traffic.

Metal accumulation and competitive ability in metallicolous and non-metallicolous Thlaspi caerulescens fed with different Zn salts

A non-metallicolous (NM) ecotype of Thlaspi caerulescens from Luxembourg and a metallicolous (M) ecotype from Prayon (E Belgium) are compared for growth and Zn, Mg and Ca accumulation in shoot in a pot experiment in six soil conditions with contrasting Zn availability. The soils were spiked with 2000 mg kg−1 Zn as monometallic salts of contrasting solubility. Both ecotypes were grown in pure and mixed culture in order to assess competitive ability. Both ecotypes had similar growth on all substrates except the one spiked with Zn-sulphate, where ecotype M grew better and had higher competitive ability than ecotype NM. Ecotype NM had higher Zn concentrations than M in all treatments and the difference varied with Zn availability, being largest with Zn-oxide (NM: 31 300 mg kg−1 Zn; M: 5900 mg kg−1 Zn). The results thus indicate that ecotype NM has constitutively higher Zn uptake capacity and may have a higher ability to obtain Zn from specific Zn salts. However, ecotype NM does not appear to be more efficient in obtaining Zn from little available forms. Mg concentration was also higher in ecotype NM. Zn mass per plant was higher in ecotype NM compared to ecotype M in all substrates except Zn-sulphate where the reverse was true. Accordingly, ecotype NM could prove to be a better phytoextractor of Zn for phytoremediation, except in substrates with low pH and high concentration of free Zn in the soil solution.

A phytogeochemical survey of the flora of ultramafic and adjacent normal soils in North Morocco

Variation in plant elemental composition (Ni, Ca, Mg, Mg/Ca ratio) in relation to soil composition was investigated in a poorly studied ultramafic area in the north of Morocco. A total of 142 leaf samples representing 36 species from 9 sites (5 ultramafic and 4 normal soils from adjacent areas) were analysed. The soil was richer in Mg and Ni and had a higher Mg/Ca ratio in the ultramafic sites than in the control sites, and these differences were qualitatively reflected in the average mineral composition of the plants. However, there were considerable differences in mineral composition among species within serpentinic sites, indicating that species with contrasting mineral nutrition strategies can cope with the mineral element imbalance characteristic of ultramafic soils. Particularly noteworthy was the finding that species with high requirements of Ca are not excluded from serpentinic soils. In view of their high responsiveness to soil nickel and magnesium concentration, Dittrichia viscosa and Lavandula dentata are proposed as bioindicators of these elements in the soil in the Rif area. By contrast, two local serpentine endemics, Halimium atriplicifolium and Notholaena marantae were excluders of nickel and magnesium.

Changes in humus microbiological activity induced by the substitution of the natural beech forest by Norway spruce in the Belgian Ardennes

Abstract Different microbiological methods, including determination of enzymatic activity and potential nitrogen availability, and microbial biomass estimation were used to evaluate soil modifications induced by the massive planting of Norway spruce on acid soils of the climatic deciduous forest of high Belgium. Investigations were made on the surface humic layers (holorganic and hemiorganic horizons) of ochreous brown earths (Dystrochrepts) in two neighbouring forest stands, a natural beech high-forest (Fagus sylvatica L.) and a 92-year-old spruce plantation (Picea abies (L.) Karst.). Results show that spruce monoculture has a significant depressive effect on soil microbiological activity, clearly shown by the lowering of microbial biomass and the decrease of both FDA hydrolytic activity and nitrogen potential availability.

The Effect of Seasonal Variations, Covariations with Minerals and Forage Value on Itchgrass’ Foliar Silicification from Sudanian Benin

Silica (SiO 2) in forage grasses has been found in reducing cell-wall digestibility. This study investigates whether: (i) the seasonal variability affects the silica and minerals accumulation and forage values of leaves of R. cochinchinensis and (ii) silica concentration is correlated with minerals and fodder value. In an itchgrass population selected in the W Biosphere Reserve, leaves were collected on 90 marked plants from May to October 2003 and 2004, at 15 days intervals except May, June and October. Some 300 g of fresh blades from the 3 rd most recently expanded leaves were oven dried and analyzed for dry mass, SiO 2, ash, N, Na, Ca, P, K, and Mg. Digestible Nitrogen Matter (DNM) and Fodder Energetic Value (FEV) were calculated using the Demarquilly formula. Apart from SiO 2, ash and forage value, data were log-transformed to restore homoscedasticity before statistical analyses. SiO 2 ranges from 5.69 % to 9.95 %, i.e. varying 1.4 fold between May and October, reaching 1.75 fold at mid-September. SiO 2 is positively related to Ca but negatively to K, P, N, DNM and FEV. The negative correlations suggest that SiO 2 concentration in R. cochinchinensis could be reduced with a significant increase in energy and accumulation of important nutrients such as N, P and K. Therefore, leaf silicification and nutritive value relationship should be conclusive in the case of itchgrass.