Nina Nikolic

Germanium-68 as an Adequate Tracer for Silicon Transport in Plants. Characterization of Silicon Uptake in Different Crop Species

A basic problem in silicon (Si) uptake studies in biology is the lack of an appropriate radioactive isotope. Radioactive germanium-68 (68Ge) has been used previously as a Si tracer in biological materials, but its suitability for the study of Si transport in higher plants is still untested. In this study, we investigated 68Ge-traced Si uptake by four crop species differing widely in uptake capacity for Si, including rice (Oryza sativa), barley (Hordeum vulgare), cucumber (Cucumis sativus), and tomato (Lycopersicon esculentum). Maintenance of a 68Ge:Si molar ratio that was similar in the plant tissues of all four plant species to that supplied in the nutrient solution over a wide range of Si concentrations demonstrated the absence of discrimination between 68Ge and Si. Further, using the 68Ge tracer, a typical Michaelis-Menten uptake kinetics for Si was found in rice, barley, and cucumber. Compared to rice, the relative proportion of root-to-shoot translocated Si was lower in barley and cucumber and especially in tomato (only 30%). Uptake and translocation of Si in rice, barley, and cucumber (Si accumulators) were strongly inhibited by 2,4-dinitrophenol and HgCl2, but in tomato, as a Si-excluding species, both inhibitors produced the opposite effect. In conclusion, our results suggest the use of the 68Ge tracer method as an appropriate choice for future studies of Si transport in plants. Our findings also indicate that the restriction of Si from symplast to apoplast in the cortex of Si excluders is a metabolically active process.

Phosphorus deficiency is the major limiting factor for wheat on alluvium polluted by the copper mine pyrite tailings: a black box approach

Failures of tailings dams have degraded large areas of agricultural alluvial soils worldwide, and concomitant soil pollution studies are abundant. Yet, the data on the actual effects of thereby imposed stresses on major crops are scarce. This work analyses the effect of pyrite tailings from a copper mine, deposited over crop fields by long-term flooding, on wheat (Triticum aestivum L.) under field conditions. The major previously reported polluting agents were Cu, As, Zn, Pb and acidity generated by sulphide oxidation. Flexible systematic sampling, based on visual symptoms in wheat, included transects through partially damaged fields (from calcareous to acid soils). Multivariate analysis of soil properties, leaf mineral composition and growth parameters revealed a consistent underlying soil gradient of decreasing available P and increasing Stot. Phosphorus was shown to have the highest unique contribution to predicting wheat yield, consistent correlation with growth and visual symptoms, and concentrations in the range of severe deficiency. In P deficient plants N deficiency, decrease of available micronutrients and increase of As occur irrespectively of their soil concentrations, and the competition with superior “pyrite” weeds increases. Different sorption of P and possible rhizotoxic effects of other pollutants imply that fertilization can hardly be a solution.

Land Degradation on Barren Hills: A Case Study in Northeast Vietnam

The term “barren hills” has been a keyword for land degradation in the uplands of Vietnam for over a decade. Nevertheless, the “barren” land is still not adequately ecologically characterized. In this work, we analyze land use-induced changes in vegetation and soil properties along a sequence of barren hills types formed on one physiotope. The study is undertaken in the Bac Kan province, one of the poorest upland regions where livestock plays an important role. A transition from an old-growth laurel forest to a sparse manmade grassland is characterized by a total of 177 species, rapid species turnover, and discrete dominants, and an overwhelming effect of disturbance history on both soil and vegetation patterning. Land degradation is most apparent in land use-induced maintenance of arrested successions, and the regeneration course is shifted towards drier formations. We hypothesize a conceptual model as an aid to understanding the process of early fallow differentiation in response to the patterned, fine-scale disturbances. The larger-scale implications of the observed trends in regeneration potentials deviation, and, in particular, the effect of water buffaloes in halting fallow successions, are discussed.

Silicon increases phosphorus (P) uptake by wheat under low P acid soil conditions

Background and aimsAlthough silicon (Si) is known to improve plant growth under low phosphorus (P) conditions, the in planta mechanisms responsible for this effect are still unknown. Here, we investigated the role of Si on P uptake along with the expression of Pi transporters in wheat (Triticum aestivum L.) grown in low P acid soil in comparison with P fertilization and liming.MethodsA combined approach was performed including analyses of rhizosphere soil, tissue P content, the expression of the root Pi transporter genes (TaPHT1.1 and TaPHT1.2), and the root exudation of citrate and malate.ResultsSupply of Si in a form of Na2SiO3 increased shoot P concentration to an adequate level in the range of P-fertilized plants. Silicon ameliorated low soil pH and high Al3+ comparable to the effect of liming. The in planta effect of Si on up-regulating the expression of TaPHT1.1 and TaPHT1.2 was several fold higher and consequently P uptake doubled compared to both P fertilization and liming. In addition, Si directly stimulated root Pi acquisition by prominently increasing both malate and citrate exudation rate.ConclusionsApplication of Si increased root exudation of organic acids that mobilize Pi in the rhizosphere and up-regulated Pi transporters in wheat roots.

Liming of anthropogenically acidified soil promotes phosphorus acquisition in the rhizosphere of wheat

We studied the effect of liming and P fertilization of extremely acid soil (accidently acidified by sulfidic mining waste) on P availability and the subsequent adaptive responses of wheat roots. The wheat plants were grown in rhizoboxes allowing precise sampling of rhizosphere and bulk soil for sequential extraction of P fractions and determination of exchangeable Al. Root exudates were collected by pieces of paper for electrophoresis and subjected to HPLC analysis. Expression of organic anions and Pi transporter genes was analyzed by a real-time quantitative PCR. The concomitant application of lime with P fertilization increased the concentrations of plant-available P fractions in both rhizosphere and bulk compartments. The applied soil amendments strongly affected plant growth, biomass partitioning and shoot P accumulation. Liming enhanced root exudation of citrate in P unfertilized plants, while the high malate efflux was maintained until both P deficiency and Al toxicity were eliminated by the amendments. We showed the importance of liming for recovering of P acquisition potential of wheat roots, which can be strongly impaired in acid soils. Our results clearly demonstrated that P-deficient roots not subjected to Al stress in the limed soil can maintain high efflux of malate and even increase efflux of citrate along with the enhanced expression of related anion transporters (TaMATE1 and TaALMT1).

Assembly processes under severe abiotic filtering: adaptation mechanisms of weed vegetation to the gradient of soil constraints.

Questions Effects of soil on vegetation patterns are commonly obscured by other environmental factors; clear and general relationships are difficult to find. How would community assembly processes be affected by a substantial change in soil characteristics when all other relevant factors are held constant? In particular, can we identify some functional adaptations which would underpin such soil-induced vegetation response? Location Eastern Serbia: fields partially damaged by long-term and large-scale fluvial deposition of sulphidic waste from a Cu mine; subcontinental/submediterranean climate. Methods We analysed the multivariate response of cereal weed assemblages (including biomass and foliar analyses) to a strong man-made soil gradient (from highly calcareous to highly acidic, nutrient-poor soils) over short distances (field scale). Results The soil gradient favoured a substitution of calcicoles by calcifuges, and an increase in abundance of pseudometallophytes, with preferences for Atlantic climate, broad geographical distribution, hemicryptophytic life form, adapted to low-nutrient and acidic soils, with lower concentrations of Ca, and very narrow range of Cu concentrations in leaves. The trends of abundance of the different ecological groups of indicator species along the soil gradient were systematically reflected in the maintenance of leaf P concentrations, and strong homeostasis in biomass N:P ratio. Conclusion Using annual weed vegetation at the field scale as a fairly simple model, we demonstrated links between gradients in soil properties (pH, nutrient availability) and floristic composition that are normally encountered over large geographic distances. We showed that leaf nutrient status, in particular the maintenance of leaf P concentrations and strong homeostasis of biomass N:P ratio, underpinned a clear functional response of vegetation to mineral stress. These findings can help to understand assembly processes leading to unusual, novel combinations of species which are typically observed as a consequence of strong environmental filtering, as for instance on sites affected by industrial activities.

The assessment of soil availability and wheat grain status of zinc and iron in Serbia: Implications for human nutrition.

The deficiency of zinc (Zn) and iron (Fe) is a global issue causing not only considerable yield losses of food crops but also serious health problems. We have analysed Zn and Fe concentrations in the grains of two bread wheat cultivars along native gradient of micronutrient availability throughout Serbia. Although only 13% of the soil samples were Zn deficient and none was Fe deficient, the levels of these micronutrients in grain were rather low (median values of 21 mg kg(-1) for Zn and 36 mg kg(-1) for Fe), and even less adequate in white flour. Moreover, excessive P fertilization of calcareous soils in the major wheat growing areas strongly correlated with lower grain concentration of Zn. Our results imply that a latent Zn deficiency in wheat grain poses a high risk for grain quality relevant to human health in Serbia, where wheat bread is a staple food.

Long-term passive restoration following fluvial deposition of sulphidic copper tailings: nature filters out the solutions

Despite the growing popularity of ecological restoration approach, data on primary succession on toxic post-mining substrates, under site environmental conditions which considerably differ from the surrounding environment, are still scarce. Here, we studied the spontaneous vegetation development on an unusual locality created by long-term and large-scale fluvial deposition of sulphidic tailings from a copper mine in a pronouncedly xerothermic, calcareous surrounding. We performed multivariate analyses of soil samples (20 physical and chemical parameters) and vegetation samples (floristic and structural parameters in three types of occurring forests), collected along the pollution gradients throughout the affected floodplain. The nature can cope with two types of imposed constraints: (a) excessive Cu concentrations and (b) very low pH, combined with nutrient deficiency. The former will still allow convergence to the original vegetation, while the latter will result in novel, depauperate assemblages of species typical for cooler and moister climate. Our results for the first time demonstrate that with the increasing severity of environmental filtering, the relative importance of the surrounding vegetation for primary succession strongly decreases.