Response of Potamogeton crispus root characteristics to sediment heterogeneity

Plant growth, biomass allocation, root distribution and plant nutrient content were investigated in the submerged macrophyte Potamogeton crispus growing in heterogeneous sediments. Three experimental sediments heterogeneous in nutrient content and phosphorus release capacity were used: sandy loam with low nutrient content (A), clay with intermediate nutrient content (B), and clay with high nutrient content (C). Biomass accumulation was significantly affected by the sediment type, and was highest in clay C (1.23 mg per plant dry weight) but lowest in sandy loam (0.69 mg per plant dry weight). The root:shoot ratios in treatments A, B and C were 0.30, 0.14 and 0.09, respectively. P. crispus allocated more biomass to roots in sandy loam compared with the other sediments. The average root numbers in sediments A, B and C were 16, 19 and 20, respectively, and the total root lengths in sediments A, B and C were 238.84, 200.36 and 187.21 cm, respectively. Almost 90% of the root biomass was distributed in the 0–15 cm depth in sediments B and C, compared with 64.53% in sediment A. The rank order of plant nitrogen and phosphorus concentrations in the sediment types was C > B > A. These results indicate that both sediment structure and nutrient availability influence the growth and distribution of the root system of P. crispus.     

Pollution characteristics of mercury (Hg) in surface sediments of major basins,China

To investigate the pollution status and potential pollution risk of mercury (Hg) in China, surface sediment samples were collected from eight hundred and eighty-one sites, including ten major basins (Songhua River Basin (SRB), Liao River Basin (LRB), Hai River Basin (HRB), Yellow River Basin (YRB), Huai River Basin (HuRB), Yangtze River Basin (YtRB), Pearl River Basin (PRB), Southeastern River Basin (SeRB), Southwestern River Basin (SwRB) and Northwestern River Basin (NwRB)). Results showed that Hg concentrations in sediments of ten basins in China ranged from 0.001 to 8.800 mg/kg, with average ± S.D. value of 0.274 ± 0.675 mg/kg, which was obviously higher than Chinese soil background value (0.038 mg/kg) and Chinese sediment background value (0.040 mg/kg). The mean Hg concentration of ten basins decreased in the order of HRB > YtRB > SRB > PRB > HuRB > SwRB > YRB > SeRB > LRB > NwRB. Moreover, it was found that the Hg concentrations in the sediments of LRB, YtRB, PRB, SeRB and SwRB were partly driven by their total organic carbon (TOC) contents, while the effect of pH on the distribution of Hg was not obvious. The Hg concentration data were also compared with those got in other periods (1994–2015) to obtain the general variation tendency of Hg level. It was recorded that Hg concentrations in HRB have remained on high levels for a long history, while Hg contamination situation in YRB after 2004 has potentially turned to be better. The results of pollution assessment by sediment quality assessment guidelines (SQGs), contamination factor (CF), geoaccumulation index (I_geo) and potential ecological risk (E_i) suggested that YRB and HRB were the most seriously polluted river basins among the ten basins. It is urgent of constructing SQGs in China to scientifically evaluate the Hg pollution in the future.     

Response in root morphology and nutrient contents of Myriophyllum spicatum to sediment type

Sediment may play an important role during the submerged macrophyte decline in the eutrophication progress. In order to investigate the response in root morphology and nutrient contents of submerged macrophytes Myriophyllum spicatum to sediment, five sediment types were treated and used (five types of sediment were used in the experiment: treatment 1 was nature sediment + sand, a 50:50 (v/v) mixture, treatment 2 was the studied sediment only, treatment 3 was sediment + nitrogen (N, NH₄Cl 400 mg kg^?1), treatment 4 was sediment + phosphorus (P, NaH₂PO₄ 300 mg kg^?1); treatment 5 was sediment + phosphorus (P, NaH₂PO₄ 600 mg kg^?1)). The results show that the root N content was only significantly affected by adding N in sediments and P was elevated by adding N and P. The root mass and its percentage increased at first, the peak values were reached at 35 d, and then decreased. The root growth was restrained by adding sand and N in sediments, root senescence process was delayed at the later experimental time by adding P in sediments. The increase of root volume showed a similar trend to that of root growth, except for plant with P addition where root volume remained high after 35 d. The root volume decreased while the main root number increased significantly by adding sand in sediments. The mean root length and main root diameter were reduced by adding P in sediments. The compatible sediment nutrient condition is necessary to restore submerged macrophytes in a degraded shallow lake ecosystem, and the effect of sediment on the root morphology and nutrient content is one of the important aspects restricting the restoration of submerged macrophytes.     

Distribution and enrichment of heavy metals among sediments,water body and plants in Hengshuihu Wetland of Northern China

In this study, a survey for the spatial distribution of heavy metals in Hengshuihu Wetland of China was conducted. Samples were collected from three compartments, water, sediment, and reed (Phragmites communis Trin), at different sites, and their contents of heavy metals, including mercury (Hg), arsenic (As), chromium (Cr), lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd), were analyzed. The results showed heavy metals in the sediments distributed in the Buffer Zone and Wangkou Sluice area at concentrations relatively higher than those in other areas, while concentrations in the Core Zone were lower. The heavy metal concentrations of water bodies in all areas, except those for Hg and Pb, were lower than the cutoff values for the first-grade water quality that was set as the highest standard to protect the national nature reserves. The heavy metal distributions among the three compartments were significantly different, with the following order: sediment > plant > water. In the reeds, accumulated amounts of different heavy metals varied in the following order: Hg > Zn > As > Cu > Cr. Concentrations of heavy metals only showed weak correlations between the water bodies and the sediments. Concentrations of heavy metals (except Hg and Cr) had no corrections between the sediments and the reeds. The distribution of mercury indicated that it enters the lake mainly from the atmosphere and outside water bodies. The concentrations of As, Hg, Cr, Cu and Zn in different parts of the reeds were detected and their abundances were ranked in the following order: root > leaf > stem.     

Experiment of emergent macrophytes growing in contaminated sludge: Implication for sediment purification and lake restoration

Three emergent macrophytes (Zizania latifolia (Turcz) Hand.-Mazz., Phragmites australis (Cav.) Trin. ex Steud. and Typha angustifolia Linn.) and three different sediments from Lake Dianchi of Yunnan province, China, were studied through orthogonal pot-planting experiment in order to compare the ability of the three emergent macrophytes in dealing with the contaminated sludge and to evaluate the possibility of purifying the sediment through aquatic plant rehabilitation. The results show that the number of sprouts and biomass of all the species growing in the sediment of site 3 were higher than those growing in the sediment of sites 1 and 2; the plants growing in the sediment of site 3 also exhibited the highest root activities; in each sediment, the sequence of root activity of the species was: Z. latifolia > P. australi > T. angustifolia; TP content in the sediments grown with different plants reduced significantly than those of control. These results indicated that these emergent plants were able to grow well in the contaminated sediment though it is black with a strong odor. Z. latifolia shows the highest root activity in the sediment of site 3, from which we can deduce that this plant should be the preferred pioneer species for purifying the sediment. According to their biomass and TN content and TP content, Z. latifolia, P. australi and T. angustifolia retained TN 16.6, 29.8, 12.8, and TP 2.2, 3.6, 3.9 g m^?2, respectively. Based on the climate of Dianchi valley, these plants can be harvested twice in a year. Thus, the amount of nutrient can be removed almost doubly. Therefore, the sludge can be purified through macrophytes restoration and not through sediment dredging, which was proved to be expensive and invalid in the large shallow lakes.     

Metal uptake by medicinal plant species grown in soils contaminated by a smelter

The hypothesis tested in this study was if medicinal plants could be grown as alternative crops in heavy metal polluted soils without contamination of the final marketable produce. Furthermore, medicinal crops may offer a phytoremediation option for mildly heavy metal polluted agricultural soils. The effect of metal-enriched soils was evaluated in five medicinal species (Bidens tripartita L., Leonurus cardiaca L., Marrubium vulgare L., Melissa officinalis L. and Origanum heracleoticum L.). Soils were sampled in the vicinities of the Non-Ferrous Metals Combine (Pb–Zn smelter) near Plovdiv, Bulgaria, from plots at 0.5 km (soil 1), 3 km (soil 2), 6 km (soil 3) and 9 km (control soil) from the smelter. Cadmium, Pb and Zn concentration in soil 1 were above the critical total (HNO₃-extractable) concentrations for these elements in soils. Generally, heavy metals in soil 1 decreased dry mater yields of the five species relative to the control. However, the essential oil content of M. vulgare, M. officinalis and O. heracleoticum was within the usual range for respective species and was not affected by the treatments. The overall metal uptake was in the order: B. tripartita > M. vulgare > O. heracleoticum > L. cardiaca > M. officinalis for Cd, L. cardiaca = M. vulgare > B. tripartita = M. officinalis = O. heracleoticum for Pb, L. cardiaca = M. vulgare > O. heracleoticum > B. tripartita = M. officinalis for Cu and B. tripartita > L. cardiaca = M. vulgare > M. officinalis = O. heracleoticum for Mn and Zn. Overall, metal concentration in plant parts was in the order: roots > leaves > flowers > stems for Cd, Pb and Cu, leaves > roots > flowers > stems for Mn and Zn. The concentration of Cd, Pb, Cu and Zn in plant tissue correlated to the exchangeable (EXCH) and the carbonate (CARB) bound fractions of metals in soil. Heavy metals caused disruptions of the plasma membrane of some root cortical cells and alterations in chloroplasts thylakoids in plants grown in soil 1. Metal content in teas prepared from the species was negligible, the essential oils were free of metals. Generally, the transfer factor (TF) was less than 1, indicating the tested species did not have a significant phytoextraction potential. This study demonstrated the three essential oil species M. vulgare, M. officinalis and O. heracleoticum can be grown as alternative high-value crops in metal polluted agricultural soils around the smelter and provide metal-free marketable produce.     

The drag and reconfiguration experienced by five macrophytes from a lowland river

Drag and flexibility of five macrophytes (fresh mass 3 g) collected from the same river were measured at velocities from 0 to 0.5 m s⁻¹ in a flume. Drag increased with increasing velocity for all five species examined. Sparganium emersum Rehmann, which has simple strap-like leaves experienced significantly less drag than the other, bushier species whilst there was no significant difference between the drag on Callitriche stagnalis Scop., Ranunculus penicillatus pseudofluitans (Syme) S.D. Webster, and Myriophyllum spicatum L. above 0.4 m s⁻¹. Potamogeton x zizii W.D.J. Koch ex Roth, which has large flat leaves, experienced significantly higher drag than all the other species. All the plants were very flexible but flexibility (as angle of bend) did not explain the drag experienced by the plants, e.g. S. emersum was the least flexible. The plants also changed shape and compressed (reconfigured) under increasing water velocity which reduced the rate at which drag increased. Reconfiguration capacity was assessed as E-values. There were no significant differences in E-values between species indicating that all the samples examined had a similar capacity to reconfigure. It is concluded that measurement of the drag experienced by plants is useful and may prove helpful in explaining the distribution of macrophytes in rivers.     

Metal uptake by medicinal plant species grown in soils contaminated by a smelter

The hypothesis tested in this study was if medicinal plants could be grown as alternative crops in heavy metal polluted soils without contamination of the final marketable produce. Furthermore, medicinal crops may offer a phytoremediation option for mildly heavy metal polluted agricultural soils. The effect of metal-enriched soils was evaluated in five medicinal species (Bidens tripartita L., Leonurus cardiaca L., Marrubium vulgare L., Melissa officinalis L. and Origanum heracleoticum L.). Soils were sampled in the vicinities of the Non-Ferrous Metals Combine (Pb–Zn smelter) near Plovdiv, Bulgaria, from plots at 0.5 km (soil 1), 3 km (soil 2), 6 km (soil 3) and 9 km (control soil) from the smelter. Cadmium, Pb and Zn concentration in soil 1 were above the critical total (HNO₃-extractable) concentrations for these elements in soils. Generally, heavy metals in soil 1 decreased dry mater yields of the five species relative to the control. However, the essential oil content of M. vulgare, M. officinalis and O. heracleoticum was within the usual range for respective species and was not affected by the treatments. The overall metal uptake was in the order: B. tripartita > M. vulgare > O. heracleoticum > L. cardiaca > M. officinalis for Cd, L. cardiaca = M. vulgare > B. tripartita = M. officinalis = O. heracleoticum for Pb, L. cardiaca = M. vulgare > O. heracleoticum > B. tripartita = M. officinalis for Cu and B. tripartita > L. cardiaca = M. vulgare > M. officinalis = O. heracleoticum for Mn and Zn. Overall, metal concentration in plant parts was in the order: roots > leaves > flowers > stems for Cd, Pb and Cu, leaves > roots > flowers > stems for Mn and Zn. The concentration of Cd, Pb, Cu and Zn in plant tissue correlated to the exchangeable (EXCH) and the carbonate (CARB) bound fractions of metals in soil. Heavy metals caused disruptions of the plasma membrane of some root cortical cells and alterations in chloroplasts thylakoids in plants grown in soil 1. Metal content in teas prepared from the species was negligible, the essential oils were free of metals. Generally, the transfer factor (TF) was less than 1, indicating the tested species did not have a significant phytoextraction potential. This study demonstrated the three essential oil species M. vulgare, M. officinalis and O. heracleoticum can be grown as alternative high-value crops in metal polluted agricultural soils around the smelter and provide metal-free marketable produce.     

Distribution and survival of faecal indicator bacteria in the sediments of the Bay of Vidy,Lake Geneva,Switzerland

The purpose of this study was to determine the concentrations and the horizontal distribution of faecal indicator bacteria (FIB) including Escherichia coli and Enterococcus sp. in the bottom sediments of the Bay of Vidy, City of Lausanne, Switzerland. A vertical distribution of FIB in sediments near the municipal wastewater treatment plant (WWTP) outlet was evaluated and their persistence in those sediments was monitored for a period of 90 days. High FIB levels were measured in the sediments sampled near the WWTP outlet pipe and the mouth of the Chamberonne River, at concentrations ranging between 10⁵ and 10⁷ CFU 100 g^?1. FIB levels at 10 cm depth in the sediments near the WWTP outlet pipe ranged between 10⁴ and 10⁵ CFU 100 g^?1, and were still detected in the top 6 cm after 90 days. Results of this study indicate that freshwater sediments of the Bay of Vidy constitute a reservoir of faecal indicator bacteria, which can persist in certain areas of the bay. Possible resuspension of FIB and pathogens may affect water quality and may increase health risks to sensitive populations during recreational activities. FIB survival in sediments for long periods is of considerable significance for the understanding of microbial pollution in water and for the management of risk at specific recreational coastal sites.     

Effects of phosphorus and nitrogen amendments on the growth of Egeria najas

The effect of nutrient addition on the growth of E. najas was evaluated in a dose response experiment using sand amended with phosphorus (P) and nitrogen (N), and in enrichment trials with N and P amendments to natural sediments. Plants, water and sediment came from lagoons of the Upper Paraná River Floodplain and from Itaipu Reservoir (Brazil). Relative growth rates (RGRs) of E. najas shoots, based on dry mass (DM), varied from 0.03 to 0.060 d⁻¹ for both nutrients. Root:shoot biomass ratios were related to sediment exchangeable P (r = −0.419; P = 0.03) and N (r = −0.54; P = 0.006), however root RGR was not related to sediment nutrient concentrations. When natural sediments were amended with N and P, neither shoot nor root RGRs differed among treatments for substrata from either the reservoir or the floodplain lagoons (P > 0.05). Comparison of nutrient concentrations measured in natural sediments collected from several sites in both the Upper Paraná River Floodplain (range 49–213 μg P g⁻¹ DM; 36–373 μg N g⁻¹ DM) and Itaipu Reservoir (range 43–402 μg P g⁻¹ DM; 7.9–238 μg N g⁻¹ DM) showed that sediment N and P from these systems usually exceeded minimum requirements necessary for E. najas growth, as measured in the dose response experiment. Together, these results indicate that E. najas, at least in early stages of development, responds to sediment nutrient amendments and relies upon bottom sediments to meet its N and P requirements and that for at least two Brazilian ecosystems, growth of this species is not limited by insufficient sediment N or P. Thus, reducing N and P in water is not enough to control E. najas growth in short time periods in these ecosystems.     

Increasing nitrogen depositions can reduce lichen viability and limit winter food for an endangered Chinese monkey

Increasing economic growth and industrial development in China is starting to impact even remote areas such as the Shennongjia nature reserve, where nitrogen pollution is becoming a major environmental threat. The epiphytic lichen flora is particularly rich in this area and is one of the components of this habitat most sensitive to nitrogen pollution. Since lichens represent an important food resource for the endangered monkey species Rhinopithecus roxellana, a reduction in lichen availability would have harmful consequences for the conservation of its habitat in the Shennongjia Mountains. To investigate the effects of increased nitrogen availability on the local lichen communities, so far scarcely considered, we conducted a one-year field experiment measuring growth, survival, and phosphomonoesterase activity of the widespread species Usnea luridorufa in response to nitrogen (up to 50 kg N ha⁻¹ year⁻¹ deposition) and phosphorus supply. Growth and survival of thalli and propagules of U. luridorufa decreased when treated with N deposition >12.05 kg N ha⁻¹ year⁻¹ and >2.14 kg N ha⁻¹ year⁻¹, respectively. The important role of phosphorus availability in relation to nitrogen supply was demonstrated by the increase in phosphomonoesterase activity with increasing nitrogen availability until a nitrogen toxicity threshold was reached. However, the high concentration of phosphorus in rainwater showed that phosphorus is not a limiting nutrient in the area.The results make a contribution to the knowledge of the negative effects of increased N deposition in the Shennongjia forest ecosystem.     

COMPARATIVE STUDIES ONXANTHORIA PARIETINA,A POLLUTION-RESISTANT LICHEN,ANDRAMALINA DURIAEI,A SENSITIVE SPECIES. I. EFFECTS OF AIR POLLUTION ON PHYSIOLOGICAL PROCESSES

Xanthoria parietinathalli were collected from a ‘ clean-air ’ location and from a polluted area.Ramalina duriaeithalli were collected from the same ‘ clean-air ’ location and some thalli were transplanted to air-polluted locations, whereR. duriaeino longer occurs. The effects of air contaminants on these two lichens were compared under controlled laboratory conditions and in field experiments. Air contaminants and exposure to bisulphite ions had little or no damaging effect onX. parietina, whereas severe damage was caused toR. duriaei, as judged by chlorophyll degradation, autofluorescence of photobionts, photosynthetic activity, membrane integrity and ATP content. The different responses presented confirm the sensitivity ofR. duriaeiand resistance ofX. parietinato air pollution.     

Cyanotoxin diversity and food web bioaccumulation in a reservoir with decreasing phosphorus concentrations and perennial cyanobacterial blooms

In a shallow multifunction dam reservoir, perennial water blooms formed by several toxin-producing cyanobacteria (Anabaena spp., Aphanizomenon spp., Planktothrix agardhii and Microcystis spp.) were observed. Over a seven-year period, concomitantly with a gradual decrease in phosphate and total phosphorus concentrations in the water and an increase in the DIN to DIP ratio, a reduced biomass of cyanobacteria was noted. Simultaneously, a twofold increase in cyanobacterial species richness was found. The concentration of intracellular anatoxin-a was positively correlated with the total cyanobacterial biomass, but the concentration of intracellular microcystins was significantly negatively correlated with the level of phosphorus in the water. Therefore, in a period with a very low (2.3–3.6) DIN:DIP ratio, intracellular ANTX prevailed in the reservoir, while in the following years (at DIN:DIP = 23–36) much higher MC levels were noted. The highest total concentrations (22.2 μg L⁻¹) of intracellular MCs (MC-LF > -LY > -LR > -LA = -LW) and ANTX (14.4 μg L⁻¹) were found in 2010. In the following year, eight MC iso-forms were detected (MC-LF > -LY > -LA > -LR > -LW > -WR > -YR > -RR). The number of MC variants was positively correlated with the increased contribution of Anabaena planctonica/A. affinis and Microcystis spp. to cyanobacteria biomass. The indigenous bentho-pelagic fish Abramis brama L. accumulated in their tissues relatively high amounts of both ANTX (e.g. 6.2–18.4 μg g⁻¹ FW of liver) and different variants of MCs (up to 4.4 μg g⁻¹ FW of liver). Cyanotoxin tissue contents decreased in the following order: gills > liver > muscles. These observed strong changes in the species structure of cyanobacteria assemblages, even at their considerably smaller biomass, appeared to be an undesirable phenomenon due to the predominance of the efficient MC and ANTX producers, such as Anabaena spp., which is easily digested by fish. The variability of the profile of cyanobacterial blooms that depends on nutrient fluctuations and may account for the diverse toxin accumulation and tissue distribution in freshwater ichthyofauna is noteworthy, especially in water bodies used for fishery.     

Fine-scale environmental heterogeneities of tidal creeks affect distribution of crab burrows in a Chinese salt marsh

Tidal creeks are an important structure of salt marshes in estuarine ecosystems, providing valuable ecosystem services to wildlife in the estuary. To determine the effects of environmental heterogeneities within tidal creeks on the features of crab burrows, we divided a typical creek section into four parts (i.e., microhabitats): bottom, slope, edge and flat, investigated the distribution of crab burrows and sediment properties on creek sections in the Yangtze River estuary, and compared the burrow distribution in tidal creeks with that in non-creek areas. Our results showed that from the creek bottom to flat soil water content declined (F_3, 60 = 93.8, p < 0.001), and the variations of other sediment physical and chemical properties associated with the change of soil water content were significant among the microhabitats on the creek sections (p < 0.001 for pH, conductivity, and grain size). No crab burrows were found at the creek bottom. The burrows on the slope were smaller in size (p < 0.001 for burrow opening diameter) while the density was higher than that at the edge and on the flat (F_2, 45 = 31.2, p < 0.001). Moreover, although the correlations between burrow distribution and sediment properties varied among the microhabitats on the creek sections, crabs generally selected relatively solid sediments to build their burrows. On the slope, there was a significantly negative relationship between burrow density and soil water content (r² = 0.53, p < 0.001). At the edge, the correlation between total burrow opening area and soil water content was significantly negative (r² = 0.44, p < 0.002). The density of small crab burrows (<10 mm) was greater, but that of large burrows (>10 mm) was lower in tidal creeks than in non-creek habitats. Therefore, sediment properties showed a gradual transition from hydrophytic to terrestrial environments on the creek section, which caused significant differences of burrow distribution among the microhabitats. The creeks of tidal salt marshes could affect ecological processes and functioning through affecting crab burrows.     

Short-time response in root morphology of Vallisneria natans to sediment type and water-column nutrient

Rooted submerged macrophytes can absorb significant amounts of nutrients from both sediment and water. We investigated root morphology of Vallisneria natans in mesocosm plastic bins, in response to three types of sediment (sandy loam, clay, and a 50:50 (v/v) mixture of the two sediments) and two levels of water-column nutrient (well water and nutrient medium). Compared to the plants grown in the clay or mixed sediments, root diameter decreased (0.39–0.41 versus 0.36–0.37 mm) but total root length per plant increased (0.87–1.27 versus 1.14–1.62 m) when grown in sandy loam. Increase of nutrient availability in water column led to decreased specific root length (306–339 versus 258–281 m g⁻¹). However, both sediment type and water-column nutrient had no impacts on root number (ranged from 19 to 24 number of roots per plant). Root weight ratio, root:leaf mass ratio and root:leaf length ratio generally decreased with enhanced nutrient availability in sediment or water. Plant growth was affected by sediment type alone (P < 0.05), rather than water-column nutrient (P > 0.05). However, plant N and P contents were significantly impacted by both sediment type (P ≤ 0.001) and water-column nutrient (P < 0.05). Increase of nutrient availability in sediment or water led to increased plant N (ranged from 2.47 to 4.77 mg g⁻¹) and P concentrations (ranged from 42.8 to 62.0 mg g⁻¹). These results indicate that considerable variation in root morphology of V. natans exists in response to the fertility of the sediment it is rooted in.     

Density and distribution of seeds in bottom sediments in Zostera marina beds in Ago Bay,central Japan

The density of Zostera marina L. seeds in bottom sediments was examined to study the reproductive patterns of the Z. marina population in Ago Bay, Mie Prefecture, central Japan.Seeds and seed coats were numerous in Tategami, where the annual type of Z. marina grows. In contrast, seeds were scarce in Hamajima, where the perennial type of Z. marina grows. Bottom sediment was sampled with sediment cores at Tategami in November 2004 and March 2005 to examine density and depth distribution of the seeds. Seeds were found as deep as 8 cm, but no deeper. On the other hand, empty seed coats were found as deep as 16 cm in both months. In the upper layers of the sediment to a depth of 8 cm, the average number of seed coats was 7960 ± 2997 m⁻² in November and 16,318 ± 2922 m⁻² in March. Deeper than 8 cm, the number of seed coats gradually decreased owing to decomposition, and none was found below 16 cm. We used the density of reproductive shoots and number of seeds per spadix in Tategami to estimate the fate of seeds and seed coats of the annual type of Z. marina in bottom sediments: out of the 6000 seeds m⁻² produced annually, 72% disappears from the stand and 28% is buried locally. The density and distribution of Z. marina seeds are among the most important factors in maintenance and propagation of the annual population at Tategami.     

Chloroplast evidence for the multiple origins of the hybrid Potamogeton × fluitans

Previous studies of Potamogeton × fluitans Roth. have supported the putative origin of this taxon as a result of hybridization between Potamogeton lucens L. and Potamogeton natans L. In the British Isles P. × fluitans is restricted to only a few sites, while both its parents are relatively common. Previous studies have shown that most of these hybrid populations are monomorphic, with the exception of the Moors River, in Hampshire and Dorset, where multiple genotypes have been identified. This is despite the fact that here the hybrid grows in the absence of one its parents, P. lucens. In this study, species-specific differences in the TrnL (UAA) chloroplast region, a maternally inherited marker, were used to identify the original seed-bearing parent of the hybrids within this river system. It was shown that both species have been maternal parents in the creation of this hybrid population.     

Structural indicators of richness and rarity of epiphytic lichens on Corylus avellana in two different forest types within a nature reserve in south-western Norway

Abstract:Epiphytic lichens (and some non-lichenized fungi) on 34 coppices (204 stems) ofCorylus avellana were investigated in a 140 ha study area in south-western Norway. A total of 65 species were recorded on a total bark area of 63 m². Corylus in broad-leaved deciduous forest supported more species of macrolichens, and fewer species of microlichens, than Corylus in pine forest. The macrolichen flora of the deciduous forest differed from that of the pine forest by having a rich flora of species belonging to the Lobarion alliance. OldCorylus coppices with tall stems (>8 m), large girth (>8 cm diameter at breast height) and a noticeable cover of macrolichens (>10% of bark area) supported the highest number of rare species, and overall, species of macrolichens. More than 50% cover of microlichens indicated richness and rarity of microlichens on Corylus.     

Growth and root distribution of Vallisneria natans in heterogeneous sediment environments

Plant growth, biomass allocation and root distribution were investigated in the submerged macrophyte Vallisneria natans growing in heterogeneous sediments. Experimentally heterogeneous sediment environments were constructed by randomly placing 4 cm of clay or sandy loam into the top (0–4 cm) or bottom (4–8 cm) layer within an experimental tray, providing two homogeneous and two heterogeneous treatments. Biomass accumulation was significantly affected by the experimental treatments: higher in the homogeneous sediment of clay (32 mg per plant) and the two heterogeneous treatments (about 27 mg per plant), but lower in the homogeneous sediment of sandy loam (15 mg per plant). Root: shoot ratio was also different among the four treatments. Compared with the treatments of clay in the top layer, plants allocated more biomass to roots at the treatments of sandy loam in the top layer. Heterogeneous sediments significantly affected root distribution pattern. Compared with the treatments of sandy loam in the bottom layer, root number (7–8 versus 13–14) and total root length (3.6–4.0 cm versus 29.5–40.0 cm) in the bottom layer were significantly higher in the treatments with clay in the bottom layer. These results indicate that both sediment structure and nutrient availability influence growth and root system distribution of V. natans.     

Cadmium distribution and its effects on molybdate-containing hydroxylases in Phragmites australis

The influence of cadmium (Cd) on physiological and biochemical parameters was studied to elucidate the mechanism of Cd resistance in Phragmites australis. Cadmium concentrations in roots, stems and leaves increased with exogenous Cd concentration, but Cd content in roots was much higher than in shoots. X-ray microanalysis was used to reveal compartments in which Cd accumulated in root cortex. Cadmium concentrations followed a gradient with the sequence: intercellular space > cell wall > vacuole > cytoplasm, indicating that most Cd was immobilized in the apoplast or sequestered into the vacuolar lumen. Sequential extraction of various Cd chelates revealed that more than half of extractable Cd was bound to proteins, whereas 26% was bound to organic acids. Cd-binding protein fractions were found in the roots after gel filtration chromatography, among which a polypeptide with an apparent molecular mass of 14 kDa bound Cd most avidly. One newly synthesized polypeptide of low molecular mass (1 kDa) appeared under Cd pollution, whereas a prominent fraction of 72 kDa disappeared. Four aldehyde oxidase (AO) isoenzyme activities increased significantly in roots under Cd pollution. Cd stress also enhanced xanthine dehydrogenase (XDH) activities in roots. Two AO polypeptides of different molecular sizes were detected in the roots by Western blot assay. The abundance of the 160 kDa subunit correlated with Cd stress, but the amount of the 90 kDa polypeptide did not change under Cd treatment. Enhanced abscisic acid (ABA) contents were observed in roots of P. australis exposed to Cd. The involvement of Cd distribution in plant tissues and subcellular compartments and of AO and XDH enzymatic activities in the acclimation mechanism of P. australis to Cd pollution is discussed herein.