Håkan Asp

INFLUENCE OF LEAD AND CADMIUM ON GROWTH, HEAVY METAL UPTAKE, AND NUTRIENT CONCENTRATION OF THREE LETTUCE CULTIVARS GROWN IN HYDROPONIC CULTURE

The uptake of cadmium and lead by three lettuce (Lactuca sativa L.) cultivars was studied in water culture experiment. Different amounts of cadmium (Cd) and leaf (Pb) were added to the nutrient solution (0; 0.05 μM Cd; 0.5 μM Cd; 0.05 μM Pb; 0.5 μM Pb; 0.5 μM Cd together with 0.5 μM Pb). Fresh and dry matter yield of leaves and roots were significantly reduced by the presence of 0.5 μM Cd and 0.5 μM Cd together with 0.5 μM Pb. The higher the Cd or Pb concentration in solution the more Cd and Pb accumulated in the plants. Most of the accumulated heavy metals were located in the roots. The combination of Cd and Pb in the nutrient solution had an additive effect on most investigated parameters. The presence of lead alone, almost in all cases, did not effect the concentration of macro- and microelements. Cadmium in concentration 0.5 μM Cd and Cd together with Pb caused a significant increase of the Ca and Cu contents in shoot content of Pb. Roxette accumulated the least Pb in the roots at 0.5 μM Pb whereas Pia the least when both Cd and Pb were present in the solution.

Cadmium and copper interactions on the accumulation and distribution of Cd and Cu in birch (Betula pendula Roth) seedlings

The effect of different external cadmium (Cd) and copper (Cu) regimes on the concentration of Cd and Cu in roots and shoots of birch (Betula pendula Roth.) seedlings was investigated. The seedlings were grown for 12 days in a weak nutrient solution (containing all essential nutrient elements including 0.025 µM Cu) at pH 4.2 with combinations of additional 0–2 µM CdCl2 and 0–2 µM CuCl2. Root and shoot concentrations of Cu were decreased by Cd in all treatments which included 0.1–2 µM of additional Cu in the treatment solution. When no extra Cu was added, only the shoot concentration of Cu was decreased by Cd whereas the root concentration was not affected. The shoot concentration of Cd was decreased by 0.5 and 2 µM of additional Cu in the treatment solution. The root concentration of Cd was decreased by Cu only when the concentration of additional Cu in the treatment solution was equal to or exceeded the concentration of Cd.

Fine-root morphology and uptake of 32P and 35S in a Norway spruce (Picea abies (L.) Karst.) stand subjected to various nutrient and water supplies

An investigation of fine (< 1 mm in diameter) and small (1–2 mm in diameter) roots in the organic soil layer was carried out in a Norway spruce forest stand with different treatments of water and nutrients, including control (C); ammonium sulphate application (NS); nitrogen-free fertilization (V); irrigation with liquid fertilization (a complete nutrient solution) (IF); NS followed by artificial drought (ND); V followed by artificial drought (VD). In order to evaluate the vitality and function of the fine roots, the following approaches were used: i) classification of fine roots, based on morphological characteristics; ii) nutrient uptake bioassay, using 32P-phosphate and 35S-sulphate; iii) nutrient concentration in fine roots and its relation to nutrient uptake. The NS treatment showed effects on the fine and small roots, with a decrease in amount of living roots, and a decrease in the total amount of fine and small roots. The VD treatment resulted in increased amounts of living small roots, while the ND treatment showed the opposite, as compared with the V and NS treatments, respectively. The uptake of P was negatively related to the P supply, with a higher P uptake for C and NS fine roots than for IF and V fine roots. The specific root length (SRL, m g-1 DW) decreased for NS fine roots and increased for IF fine roots, indicating a further increase in uptake for NS roots and a decreased uptake for IF roots if calculated on a root length basis. So far, the NS and IF treatments maintain a considerable increase in above-ground biomass with a significantly reduced root biomass and standing crop.

INFLUENCE OF NITROGEN SUPPLY ON CADMIUM ACCUMULATION IN POTATO TUBERS

The effect of different levels and forms of nitrogen (N) fertilizer on cadmium (Cd) concentrations in potato (Solanum tuberosum L.) tubers, a large component of the northern European diet, was investigated with the aim of decreasing the Cd content. A high and a low Cd-accumulating cultivar were used in two field trials and a pot experiment. The N fertilizers tested were balanced N- phosphorus (P)- potassium (K) 11-5-18 + micronutrients, alkaline calcium nitrate and acidic ammonium sulfate at levels of 60, 160, and 240 kg N ha−1 at planting or (for the higher N doses) split between two or three occasions. The Cd concentration in tubers of both cultivars decreased when increasing the N fertilizer from 60 to 160 or 240 kg N ha−1, indicating that Cd uptake and translocation are not positively correlated to the growth rate of the potato plant. A strong positive linear correlation was found between the Cd concentration in leaves at 77 days after planting and the Cd concentration in tubers at harvest, irrespective of N treatment, although the Cd concentration was three-fold higher in the leaves. The genetic variation in leaf and tuber Cd accumulation was consistent, regardless of the form of N fertilizer used. Ammonium sulfate decreased soil pH and increased tuber Cd concentration in both cultivars compared with NPK fertilizer, possibly due to increased amounts of plant-available Cd arising from the pH decrease after ammonium sulfate application. The tuber Cd concentration in the low Cd-accumulating cultivar increased when fertilized with calcium nitrate, an effect attributed to Cd availability being influenced by the increased Ca2+ concentration.

Effects of pH and nitrogen on cadmium uptake in potato

This study investigated the effects of pH and nitrogen form and concentration on cadmium (Cd) uptake by potato (Solanum tuberosum L.) grown in hydroponic culture. Potato plants grown in a pH-buffered nutrient solution for 10 d were exposed for 24 h to 25 nM CdCl2 labelled with 109Cd. Plants showed a significantly higher Cd uptake and accumulation at pH 6.5 than at pH 4.5 and 5.5. Nitrogen supplied as nitrate (NO3−) generally resulted in a higher Cd uptake and accumulation than N supplied as ammonium (NH4+). This effect was most pronounced at pH 6.5. The N concentration increasing from 6.5 to 26 mM resulted in a decreased Cd influx when either NO3− or NH4+ was used. Cd translocation to the shoot was increased when NO3− was used as the sole N source. In conclusion, pH had a strong influence on Cd uptake by roots and N form is especially important for Cd translocation within the potato plant.

Physiological effects of cadmium and UV-B radiation in phytochelatin-deficient Arabidopsis thaliana, cad1-3

Plants are most often exposed to multiple environmental stress, rather than single stress phenomena. Therefore, the aim of this study was to investigate plant response to two potential stress factors. We also wished to determine whether one of the stress factors would be dominant, and to assess the outcome in terms of the importance for plant survival. Arabidopsis thaliana L. plants were subjected to both enhanced levels of cadmium (Cd) and ultraviolet-B (UV-B, 280–315 nm) radiation. Wild type plants and a phytochelatin (PC)-deficient mutant, cad1-3, were used. To assess the contribution of Cd and/or UV-B to plant stress, chlorophyll fluorescence, oxygen (O 2 ) evolution, pigment content and Cd and nutrient content were measured. Cadmium inhibited O2 evolution at irradiances above growth light in both wild type and cad1-3. In the latter, photochemical yield (Φp ) was lowered by Cd, and was accompanied by a decreased and light-independent non-photochemical quenching (NPQ), whereas UV-B radiation did not influence these parameters when applied alone. In combination with Cd, UV-B radiation resulted in no detectable change as compared with results with only Cd exposure. The effect of Cd on the content of essential nutrients was analysed by inductively coupled plasma emission (ICP), which showed that Cd and zinc (Zn) were significantly lower in both the root and shoot of cad1-3, compared with the wild type. In roots, the content of potassium (K), magnesium (Mg) and sulfur (S) was significantly lower in cad1-3 than in wild type, whereas Cd or Cd + UV resulted in higher calcium (Ca) amounts in cad1-3. Compared with Cd alone, the Cd p UV treatment reduced the content of Ca in wild type roots. Supplemental UV-B radiation decreased the content of Mg and S; otherwise Cd was the stronger stress factor, generally overriding the sometimes stimulatory effect of the UV-B radiation.

Effect of microalgal treatments on pesticides in water

ABSTRACT The effect of the microalgae Chlorella vulgaris on a wide range of different pesticides in water was studied. Treatments included short-term exposure (1 h) to living and dead microalgal biomass and long-term exposure (4 days) to actively growing microalgae. The initial pesticide concentration was 63.5 ± 3.9 µg L−1. There was no significant overall reduction of pesticides after short-term exposure. A significant reduction of the total amount of pesticides was achieved after the long-term exposure to growing microalgae (final concentration 29.7 ± 1.0 µg L−1) compared with the long-term control (37.0 ± 1.2 µg L−1). The concentrations of 10 pesticides out of 38 tested were significantly lowered in the long-term algal treatment. A high impact of abiotic factors such as sunlight and aeration for pesticide reduction was observed when the initial control (63.5 ± 3.9 µg L−1) and the long-term control (37.0 ± 1.2 µg L−1) were compared. The results suggest that water treatment using microalgae, natural inhabitants of polluted surface waters, could be further explored not only for removal of inorganic nutrients but also for removal of organic pollutants in water.

Potato yield response to foliar application of phosphorus as affected by soil moisture and available soil phosphorus

Abstract Foliar application of phosphorus (P) may be a supplementary treatment to sustain adequate P-status of potato (Solanum tuberosum L.). However, the prediction of the potential benefits of foliar P supply is difficult, since several factors, such as weather conditions and plant P-status influence the effects. We determined the impact of soil moisture and soil P-supply on the responsiveness to foliar P-application under controlled environmental conditions. Plant dry matter yields, P-accumulation and phosphorus use efficiency (PUE) with or without foliar application were determined at five soil P-levels in combination with two soil moisture levels. The results suggest that water status is of importance for the responsiveness to foliar P-application and may be related to diffusion of P through the leaf cells, which require a good water status. The PUE was significantly improved with irrigation while adding P to the soil decreased the PUE.

Biofilm Formation by Chlorella vulgaris is Affected by Light Quality

Abstract Formation of biofilm on surfaces is a common feature in aquatic environments. Major groups of inhabitants in conditions where light is present are photoautotrophic microorganisms, such as cyanobacteria and microalgae. This study examined the effect of light quality on growth and biofilm formation of the microalgal species Chlorella vulgaris. Dense biofilm formation and aggregated growth of cells were observed in treatments exposed to blue, purple and white light. Less dense biofilm formation and solitary growth of cells were observed in treatments exposed to red, yellow or green light. Microalgal biofilms are of high importance in many respects, not least from an economic perspective. One example is the intense efforts undertaken to control biofilm formation on technical surfaces such as ship hulls. The present study suggests that light quality plays a role in biofilm formation and that blue-light receptors may be involved.

Adding benefit to wetlands – Valorization of harvested common reed through mushroom production

Wetlands have been successfully implemented as water purification systems for removal of plant nutrients and can play a significant role in nutrient recycling, depending on use of the harvested biomass. In a constructed wetland in southern Sweden examined in this study, assimilation of plant nutrients in wetland biomass corresponded to 234 kg/ha nitrogen, 22.8 kg/ha phosphorus, and 158 kg/ha potassium in the study year (2016). The harvested biomass, composed exclusively of common reed, was evaluated as a substrate for production of oyster mushrooms, one of the most widely produced edible mushrooms in the world. The biological efficiency of the substrate was 138 ± 10%, corresponding to production of 1.4 kg mushrooms (fresh weight) based on 1 kg reed (dry weight). The fruiting bodies had high quality, with total protein concentration 18.3 ± 2.8% and very low levels of contaminating heavy metals. Thus, nutrient assimilation in wetland biomass not only decreases the risk of eutrophication in recipient waters, but can be utilized for direct production of high-quality food. The biomass remaining after mushroom production, composed of mycelium and partly degraded wetland biomass, has potential for use in ruminant feed, i.e., as roughage.