Short-Term Disappearance of Foliar Litter in Three Species Before and After a Hurricane1

Litter disappearance was examined before (1989) and after (1990) Hurricane Hugo in the Luquillo Experimental Forest, Puerto Rico using mesh litterbags containing abscised Cyrilla racemiflont or Dacryodes excelsa leaves or fresh Prestoea montana leaves. Biomass and nitrogen dynamics were compared among: (i) species; (ii) mid- and high elevation forest types; (iii) riparian and upland sites; and (iv) pre- and post-hurricane disturbed environments. Biomass disappearance was compared using multiple regression and negative exponential models in which the slopes were estimates of the decomposition rates subsequent to apparent leaching losses and the y-intercepts were indices of initial mass losses (leaching). Cyrilla racemiflora leaves with low nitrogen (0.39%) and high lignin (22.1%) content decayed at a low rate and immobilized available nitrogen. Dacryodes excelsa leaves had moderate nitrogen (0.67%) and lignin (16.6%) content, decayed at moderate rates, and maintained the initial nitrogen mass. Prestoea montana foliage had high nitrogen (1.76%) and moderate lignin (16.7%) content and rapidly lost both mass and nitrogen. There were no significant differences in litter disappearance and nitrogen dynamics among forest types and slope positions. Initial mass loss of C. racemiflora leaves was lower in 1990 but the subsequent decomposition rate did not change. Initial mass losses and the overall decomposition rates were lower in 1990 than in 1989 for Dacryodes excelsa. Dacryodes excelsa and C. racemiflora litter immobilized nitrogen in 1990 but released 10-15 percent of their initial nitrogen in 1989, whereas P. montana released nitrogen in both years (25-40%). Observed differences in litter disappearance rates between years may have been due to differences in the timing of precipitation. Foliar litter inputs during post-hurricane recovery of vegetation in Puerto Rico may serve to immobilize and conserve site nitrogen.     

A culture unit system for the study of responses of mycorrhizal and non-mycorrhizal seedling to treatments

The time-dependence of Mn accumulation was confirmed in potato foliage (Solanum tuberosum. L.cv. Norland) grown in solution culture. Older leaves grown at 0.61 mM Mn had substantially higher Mn concentrations than younger leaves and stem samples. Levels of Mn in older leaves increased steadily from 4000 µg g^–1 at one week to 8–10,000 µg g^–1 at 6 weeks, but were relatively constant in the emerging leaves. Even foliage grown at low Mn levels (0.01 mM Mn) had 4 fold gradients in Mn concentration from younger (40 µg g^–1) to older leaves (180 µg g^–1).At 0.61 mM Mn, concentrations of 3–4000 µg g^–1 in the youngest fully-developed leaves did not bring about any decline in yield, and levels of up to 5000 µg g^–1 occurred in individual potato leaves before Mn toxicity symptoms were observed. Potato foliage grown at the high Mn had similar leaf numbers, but showed an increased stem length and smaller leaves than foliage grown at 0.01 mM Mn. In particular, the leaf area of the middle and lower leaf fractions were affected by the high Mn level.The ability of rapidly growing plants to withstand high concentrations of Mn is discussed in relation to the pattern of dry matter and Mn accumulation shown by potato foliage.     

Digestion and metabolism of a natural foliar diet (Eucalyptus punctata) by an arboreal marsupial, the koala (Phascolarctos cinereus)

Summary Digestion and energy metabolism in an arboreal marsupial, the koalaPhascolarctos cinereus, fed mature foliage from a common food tree, the grey gumEucalyptus punctata, were investigated. Six feeding (balance) experiments, at various times of year, and one slaughter experiment were performed and average daily oxygen consumption was measured.The average apparent digestibilities of dietary constituents were: dry matter 54%; total cell-contents 69%; available carbohydrate 92%; crude lipid 43%; total nitrogen 45%; total phenolics 91%; total cell walls 25%; hemicellulose 24%; acid-detergent fibre 25%; cellulose 31%; lignin 19%.Average digestible and metabolizable energy intakes were 0.50 and 0.43 MJ kg^–0.75 d^–1 respectively of which only 0.28 MJ kg^–0.75 d^–1 was expended in oxidative metabolism. The digestible energy intake required for maintenance was estimated to be 0.33 MJ kg^–0.75 d^–1, which is lower than that of eutherian and of other marsupial herbivores. The principal sources of metabolizable energy were non-structural carbohydrate and lipid.It is postulated that the ability of koalas to utilizeEucalyptus foliage as a sole source of nutrients is facilitated by their low requirement for energy and their ability to maximize intake of non cell-wall constituents.E. punctata foliage has a high digestible energy content compared with the foliage of many other trees and this may be a factor in its selection by koalas.Abbreviations DMI dry matter intake - DMD dry matter digestibility - DE digestible energy - ME metabolizable energy     

Solasodine production in transformed organ cultures (roots and shoots) of Solanum eleagnifolium Cav.

Summary Transformed organ cultures of Solanum eleagnifolium Cav. (roots and shoots) were obtained by infection with different Agrobacterium species (A. rhizogenes and A. tumefaciens). The growth index and the solasodine productivity of both kinds of cultures were determinated for several clones. Transformed roots (clone 5) shows a Growth Index of 39.07 and a solasodine yield of 1.90 ± 0.08 mg g^-1DW . Solasodine content in clone 5 of transformed roots (1.9 ± 0.08 mg g^-1 DW) is similar to those obtained by hormonal manipulation (1.00 – 1.68 mg g^-1DW) but higher than those found in shoots and leaves of the wild-grown plant (0.3–0.4 mg g^-1DW).     

Production of ajmalicine and ajmaline in hairy root cultures of Rauvolfia micrantha Hook f., a rare and endemic medicinal plant

Hairy roots of Rauvolfia micrantha were induced from hypocotyl explants of 2–3 weeks old aseptic seedlings using Agrobacterium rhizogenes ATCC 15834. Hairy roots grown in half-strength Murashige & Skoog (MS) medium with 0.2 mg indole 3-butyric acid l^–1 and 0.1 mg -naphthaleneacetic acid l^–1 produced more ajmaline (0.01 mg g^–1 dry wt) and ajmalicine (0.006 mg g^–1 dry wt) than roots grown in auxin-free medium. Ajmaline (0.003 mg g^–1 dry wt) and ajmalicine (0.0007 mg g^–1 dry wt) were also produced in normal root cultures. This is the first report of production of ajmaline and ajmalicine in hairy root cultures of Rauvolfia micrantha.     

Impact of picolinic acid on the chromium accumulation in fodder radish and komatsuna

Effects of picolinic acid (2-pyridinecarboxylic acid) and chromium(III) picolinate was studied on the chromium (Cr) accumulation of fodder radish (Raphanus sativus L. convar. oleiformis Pers., cv. Leveles olajretek) and komatsuna (Brassica campestris L. subsp. napus f. et Thoms. var. komatsuna Makino, cv. Kuromaru ) grown in a pot experiment. Control cultures, grown in an uncontaminated soil (UCS; humous sand with pH_KCl 7.48, sand texture with 12.4% clay+silt content, organic carbon 0.56%, CaCO₃ 2.2%, CEC 6.2 cmol_c kg^–1, Cr 10.6 mg kg^–1), accumulated low amounts of chromium (less than 5.4 g g^–1) in their roots or shoots. When this UCS was artificially contaminated with 100 mg kg^–1 Cr (CrCl₃) later picolinic acid treatment promoted the translocation of chromium into the shoots of both species. In fodder radish shoots Cr concentration reached 30.4 g g^–1 and in komatsuna shoots 44.5 g g^–1. Application of ethylene diamine tetra-acetic acid (EDTA) to this Cr contaminated soil had similar effect to picolinic acid. When the UCS was amended with leather factory sewage sediment (which resulted in 853 mg kg^–1 Cr in soil), Cr mobilization was observed only after repeated soil picolinic acid applications. From a galvanic mud contaminated soil (brown forest soil with pH_KCl 6.77, loamy sand texture with 26.6% clay+silt content, organic carbon 1.23%, CaCO₃ 0.7%, CEC 24.5 cmol_c kg^–1, Cd 5.0 mg kg^–1, Cr 135 mg kg^–1, and Zn 360 mg kg^–1) the rate of Cr mobilization was negligible, only a slight increase was observed in Cr concentration of fodder radish shoots after repeated picolinic acid treatments of soil. Presumably picolinic acid forms a water soluble complex (chromium(III) picolinate) with Cr in the soil, which promotes translocation of this element (and also Cu) into the shoots of plants. The rate of complex formation may be related to the binding forms and/or concentration of Cr in soil and also to soil characteristics (i.e. pH, CEC), since the rate of Cr translocation was the following: artificially contaminated soil > leather factory sewage sediment amended soil > galvanic mud contaminated soil. Four times repeated 10 mg kg^–1 chromium(III) picolinate application to UCS multiplied the transport of chromium to shoots, as compared to single 10 mg kg^–1 CrCl₃ treatment. This also suggests that chromium(III) picolinate is forming in the picolinic acid treated Cr-contaminated soils, and plants more readily accumulates and translocates organically bound Cr than ionic Cr. Picolinic acid promotes Cr translocation in soil-plant system. This could be useful in phytoextraction (phytoremediation) of Cr contaminated soils or in the production of Cr enriched foodstuffs.     

Stimulation of artemisinin production in Artemisia annua hairy roots by the elicitor from the endophytic Colletotrichum sp.

Artemisinin content in hairy roots of Artemisia annua was increased from 0.8 mg g^–1 dry wt to 1 mg g^–1 dry wt by using elicitor treatment of mycelial extracts from the endophytic fungus Colletotrichum sp. The increase of artemisinin was dependent on the growth stage of hairy roots as well as on the dose of the elicitor applied. When hairy roots of 23-day-old cultures (later growth phase) were exposed to the elicitor at 0.4 mg total sugar ml^–1 for 4 days, the maximum production of artemisinin reached to 13 mg l^–1, a 44% increase over the control. This is the first report on the stimulation of artemisinin production in hairy roots by the elicitor from an endophytic fungus of A. annua.     

<Emphasis Type="Italic">Cannabis sativa</Emphasis> L. growing on heavy metal contaminated soil: growth,cadmium uptake and photosynthesis

The effects of different cadmium concentrations [17 mg(Cd) kg⁻¹(soil) and 72 mg(Cd) kg^{− 1}(soil)] on Cannabis sativa L. growth and photosynthesis were examined. Hemp roots showed a high tolerance to Cd, i.e. more than 800 mg(Cd) kg⁻¹(d.m.) in roots had no major effect on hemp growth, whereas in leaves and stems concentrations of 50 – 100 mg(Cd) kg⁻¹(d.m.) had a strong effect on plant viability and vitality. For control of heavy metal uptake and xylem loading in hemp roots, the soil pH plays a central role. Photosynthetic performance and regulation of light energy consumption were analysed using chlorophyll fluorescence analysis. Seasonal changes in photosynthetic performance were visible in control plants and plants growing on soil with 17 mg(Cd) kg⁻¹(soil). Energy distribution in photosystem 2 is regulated in low and high energy phases that allow optimal use of light and protect photosystem 2 from overexcitation, respectively. Photosynthesis and energy dissipation were negatively influenced by 72 mg(Cd) kg⁻¹(soil). Cd had detrimental effects on chlorophyll synthesis, water splitting apparatus, reaction centre, antenna and energy distribution of PS 2. Under moderate cadmium concentrations, i.e. 17 mg(Cd) kg⁻¹(soil), hemp could preserve growth as well as the photosynthesis apparatus, and long-term acclimation to chronically Cd stress occurred.     

Digestion and metabolism of high-tanninEucalyptus foliage by the brushtail possum (Trichosurus vulpecula) (Marsupialia: Phalangeridae)

Summary The digestion and metabolism ofEucalyptus melliodora foliage was studied in captive brushtail possums (Trichosurus vulpecula). The foliage was low in nitrogen and silica but high in lignified fibre and phenolics compared with diets consumed by most other herbivores. The high lignin content was suggested as the main cause of the low digestibility ofE. melliodora cell walls (24%); microscopic observations of plant fragments in the caecum and faeces revealed few bacteria attached to lignified tissues. The conversion of digestible energy (0.34 MJ·kg^–0.75·d^–1) to metabolizable energy (0.26 MJ·kg^–0.75·d^–1) was low compared to most other herbivores, probably because of excretion of metabolites of leaf essential oils and phenolics in the urine. When the inhibitory effect of leaf tannins on fibre digestion was blocked by supplementing the animals with polyethylene glycol (PEG), intake of dry matter, metabolizable energy and digestible fibre increased. These effects were attributed to the reversal by PEG of tanninmicrobial enzyme complexes. It was concluded that the gut-filling effect of a bulk of indigestible fibre is a major reason why the brushtail possum does not feed exclusively onEucalyptus foliage in the wild.Abbreviations ADF acid-detergent fibre - AL acid-lignin - DE digestible energy - DM dry matter - ME metabolizable energy - NDF neutral-detergent fibre - PEG polyethylene glycol     

Digestion and energy metabolism in a small arboreal marsupial,the Greater Glider (Petauroides volans), fed high-terpeneEucalyptus foliage

Summary The digestion and metabolism ofEucalyptus radiata foliage was studied in a small (1–1.5 kg) arboreal marsupial, the greater glider (Petauroides volans). Mean dry matter intake was 44 g·kg^–0.75·d^–1 and mean cell wall digestibility was 34%; these values fall within the range of other marsupials fedEucalyptus foliage. Digestible energy content ofE. radiata was high compared to other eucalypts because of the high content and digestibility of essential oils. However, excretion of essential oils and their metabolites in the urine meant that greater gliders retained only 55% of their digestible energy intakes (0.61 MJ · kg^–0.75· d^–1) as metabolizable energy (ME). Low ME intakes were not offset by low standard metabolic rates (2.39 W · kg^–0.75), but the efficiency with which ME substituted for tissue energy was high (94%), so that greater gliders were able to maintain energy balance and body mass onE. radiata foliage.Abbreviations ME metabolizable energy - DE digestible energy - RQ respiratory quotient - FHP fasting heat production     

Effects of air pressure oscillation amplitude on oxygen transfer rate and biomass productivity in a solid-state fermenter

The modified sulfite oxidation method was adapted for estimation of the overall oxygen transfer rate in a pressure oscillating, solid-state fermenter. At 4.5 atm and 30 °C, the oxygen transfer rate reached 717 mmol kg^–1 initial dry matter h^–1 in this system against 37 mmol kg^–1 initial dry matter h^–1 in a static tray fermenter. At 30 °C and 3 atm, Azotobacter vinelandii grew on wheat straw and reached 4.7×10¹⁰ c.f.u. g^–1 substrate dry matter after 36 h, while only 8.2×10⁹ c.f.u. g^–1 substrate dry matter was obtained in a static tray system.     

Zinc phytotoxicity to oilseed rape grown on zinc-loaded substrates consisting of Fe oxide-coated and calcite sand

The risk of zinc (Zn) phytotoxicity in soils has increased in various regions following application of different anthropogenic materials. In order to assess the relative efficiency of Fe oxide and calcite in sorbing Zn and hence alleviating Zn phytotoxicity, we grew oilseed rape for 28 days in pots containing Zn-loaded model substrates consisting of Fe oxide (ferrihydrite)-coated sand (FOCS, 0.2–0.5 mm, 0.3 m² ferrihydrite g^–1 sand) and calcium carbonate (calcite) sand (CCS, 0.2–0.5 mm, 0.3 m² calcite g^–1 sand). Five substrates containing 5, 10, 20, 40, and 80% FOCS and supplied with ZnSO₄ at a rate of 30, 100, 300, and 1000 mg Zn kg^–1 were used in the cropping experiment and in an in vitro study of Zn desorption for 62 days. Plants exhibited good growth and a similar dry matter yield (DMY) at the 30 and 100 mg Zn kg^–1 rates. On the other hand, DMY was markedly reduced at the 300 and, especially, at the 1000 mg Zn kg^–1 rate, particularly for the substrates with the higher FOCS proportions. Symptoms of phytotoxicity (viz. chlorosis, purple colouration due to P deficiency) were apparent at such rates and were accompanied by high Zn concentrations in both shoot (average values >1000 and >1500 mg Zn kg^–1 dry matter for the 300 and 1000 mg Zn kg^–1 rate, respectively) and root (average values >2500 and >6000 mg Zn kg^–1 dry matter for the 300 and 1000 mg Zn kg^–1 rate, respectively). Total Zn uptake was maximal at 300 mg Zn kg^–1. The results of water extractable Zn in the substrate after cropping and the dissolved Zn concentrations measured in substrate–water systems (desorption experiment) suggest that, on a surface area basis, calcite is more effective than Fe oxide to retain Zn and thus alleviate phytotoxicity at high Zn loadings. However, the Zn-sorption capacity of the Fe oxide cannot be neglected, particularly at low Zn loadings, where Fe oxide seems to exhibit a higher affinity for Zn – but not a higher Zn-sorption capacity – than does calcite.     

Effects of soil cadmium on Pinus sylvestris L. seedlings

The effects of Cd on the growth and distribution of Cd and mineral nutrients within plant tissues were investigated for Pinus sylvestris L. seedlings grown in mineral forest soil with increasing levels of Cd addition (0–100 mg kg^–1). Approximately 20% of added Cd was found to be extractable from sandy loam forest soil. Root growth was less affected by Cd than shoot growth, which showed a significant reduction in the 100 mg Cd kg^–1 treatment. Cadmium accumulated in roots up to 325 mg kg^–1. Decreased concentrations of K in needles and Ca in stems with increasing Cd levels suggest a disturbance of mineral nutrition as a result of Cd addition.     

Astragaloside IV and polysaccharide production by hairy roots of Astragalus membranaceus in bioreactors

Hairy roots of Astragalus membranaceus were grown in bioreactors up to 30 l for 20 d. Cultures from a 30 l airlift bioreactor gave 11.5 g l dry wt with 1.4 mg g^–1 astragaloside IV, similar to cultures from 250 ml and 1 l flasks, but greater than yields from a 10 l bioreactor (dry wt 9.4 g l^–1, astragaloside IV 0.9 mg g^–1). Polysaccharide yields were similar amongst the different bioreactors (range 25–32 mg g^–1). The active constituent content of the cells approached that of plant extracts, indicating that large scale hairy root cultures of A. membranaceus has the potential to provide an alternative to plant crops without compromising yield or pharmacological potential.     

Relative Importance of Bacteria and Fungi in a Tropical Headwater Stream: Leaf Decomposition and Invertebrate Feeding Preference

Bacteria and fungi provide critical links between leaf detritus and higher trophic levels in forested headwater food webs, but these links in tropical streams are not well understood. We compared the roles of bacteria and fungi in the leaf decomposition process and determining feeding preference for two species of freshwater shrimp found in the Luquillo Experimental Forest, Puerto Rico, using experimental microcosms. We first tested the effects of four treatments on decomposition rates for leaves from two common riparian species, Cecropia scheberiana (Moraceae) and Dacryodes excelsa (Burseraceae), in laboratory microcosms. Treatments were designed to alter the microbial community by minimizing the presence of bacteria or fungi. The fastest decay rate was the control treatment for D. excelsa where both bacteria and fungi were present (k = −0.0073 day⁻¹) compared to the next fastest rate of k = −0.0063 day⁻¹ for the bacterial-conditioned D. excelsa leaves. The fastest decay rate for C. scheberiana was also the control treatment (k = −0.0035 day⁻¹), while the next fastest rate was for fungal-conditioned leaves (k = −0.0029 day⁻¹). The nonadditive effect for leaf decomposition rates observed in the control treatments where both fungi and bacteria were present indicate that bacteria and fungi perform different functions in processing leaf litter. Additionally, leaf types differed in microbial colonization patterns. We next tested feeding preference for leaf type and microbe treatment in microcosms using two species of freshwater shrimp: Xiphocaris elongata, a shredder, and Atya lanipes, a scraper/filterer. To estimate feeding preferences of individual shrimp, we measured change in leaf surface area and the amount of particles generated during 5-day trials in 16 different two-choice combinations. X. elongata preferred D. excelsa over C. scheberiana, and leaves with microbial conditioning over leaves without conditioning. There was no clear preference for fungal-conditioned leaves over bacterial-conditioned leaves. This lack of preference for which microbes were responsible for the conditioning demonstrates the importance of both bacterial and fungal resources in these tropical stream food web studies.     

Heavy metal and PCB contamination of Bryozoan colonies in the River Meuse (Belgium)

In the Meuse River (Liège area, Belgium), large amounts of three species of Bryozoans, Fredericella sultana (BLUM.), Plumatella emarginata ALL. and Plumatella fungosa (PALL.) occur. They cover 3 to 40% of the bank walls and their biomass ranges from 12 to 293 g m^–2 (dry weight). In the heated waters of a nuclear power plant (Tihange) and of industries lined up along the river, colony development occurs 3 to 4 weeks earlier than at an upstream station. The heavy metal content of living colonies ranges from 4 to 21 mg kg^–1 Cd, 45 to 182 mg kg^–1 Cu, 803 to 2232 mg kg^–1 Zn, 150 to 483 mg kg^–1 Pb and 21 to 138 mg kg^–1 Cr (DW). The mean concentration of PCBs was 925 µg kg^–1 (DW). Heavy metal and PCB concentrations in the sediments were close to those of colonies, suggesting that most of the pollutants found in the Bryozoans is in fact in the sediment trapped by the colonies.     

The ability of white-rot fungi to degrade the endocrine-disrupting compound nonylphenol

Phanerochaete chrysosporium, Pleurotus ostreatus, Trametes versicolor and Bjerkandera sp. BOL13 were tested for their ability to degrade the endocrine-disrupting compound nonylphenol at an initial concentration of 100 mg l^–1. The highest removals were achieved with T. versicolor and Bjerkandera sp. BOL13, which were able to degrade 97 mg l^–1 and 99 mg l^–1 of nonylphenol in 25 days of incubation, respectively. Nonylphenol removal was associated with the production of laccase by T. versicolor, but the levels of laccase, manganese peroxidase and lignin peroxidase produced by Bjerkandera sp. BOL13 were very low. At 14°C, T. versicolor and Bjerkandera sp. BOL13 sustained the removal of 88 mg l^–1 and 79 mg l^–1 of nonylphenol, respectively. No pollutant removal was recorded at 4°C, although both fungi could grow at this temperature in the absence of nonylphenol. A microtoxicity assay showed that the fungi produced compounds that were toxic to Vibrio fischerii; and thus a reduction in toxicity could not be correlated with nonylphenol metabolism. T. versicolor and Bjerkandera sp. BOL13 were capable of colonizing soil artificially contaminated with 430 mg kg^–1 of nonylphenol. Only 1.3±0.1% of nonylphenol remained in the soil after 5 weeks of incubation.     

Effects of host plant and cucurbitacin on growth of larval Diabrotica undecimpunctata howardi

The effects of host plant and dietary cucurbitacin on the growth of larval southern corn rootworm (SCR), Diabrotica undecimpunctata howardi Barber (Chrysomelidae: Luperini), were investigated. SCR were reared on four hosts: corn, Zea mays; peanuts, Arachis hypogaea; and two squash varieties, Cucurbita pepo cv. Ambassador (containing cucurbitacin D (0.08 mg g^–1 fr.wt.) = bitter), and C. pepo cv. Early Yellow Crookneck (lacking cucurbitacin = non-bitter). Larval growth was significantly greater on corn and peanuts than on either squash variety. After four weeks, adults had emerged from corn and peanut plants, while squash-reared larvae had not yet entered the pupal stage. There was no difference in larval growth on the two varieties of squash. Primary metabolite measurements showed no nutritional differences between the two squash varieties. Artificial diet experiments were used to test the effect of three concentrations of cucurbitacin D (0.0, 0.1, and 0.6 mg g^–1 diet) on growth of larval SCR. Larvae reared on diet containing 0.6 mg g^–1 cucurbitacin weighed significantly less than larvae reared on diet containing 0.1 mg g^–1 or no cucurbitacin after 10 d. No significant difference in growth was measured between the 0.1 mg g^–1 diet and the 0.0 mg g^–1 diet. Results are discussed relative to theories about the relationship between diabroticites and cucurbitacins.     

Ecophysiological characterization of carnivorous plant roots: Oxygen fluxes,respiration, and water exudation

Various ecophysiological investigations on carnivorous plants in wet soils are presented. Radial oxygen loss from roots of Droseraceae to an anoxic medium was relatively low 0.02 – 0.07 mol(O₂) m^{– 2} s^–1 in the apical zone, while values of about one order of magnitude greater were found in both Sarracenia rubra roots and Genlisea violacea traps. Aerobic respiration rates were in the range of 1.6 – 5.6 mol kg^–1 (f.m.) s^–1 for apical root segments of seven carnivorous plant species and 0.4 – 1.1 mol kg^–1 (f.m.) s^–1 for Genlisea traps. The rate of anaerobic fermentation in roots of two Drosera species was only 5 – 14 % of the aerobic respiration. Neither 0.2 mM NaN₃ nor 0.5 mM KCN influenced respiration rate of roots and traps. In all species, the proportion of cyanide-resistant respiration was high and amounted to 65 – 89 % of the total value. Mean rates of water exudation from excised roots of 12 species ranged between 0.4 – 336 mm 3 kg^–1 (f.m.) s^–1 with the highest values being found in the Droseraceae. Exudation from roots was insensitive to respiration inhibitors. No significant difference was found between exudation rates from roots growing in situ in anoxic soil and those kept in an aerated aquatic medium. Carnivorous plant roots appear to be physiologically very active and well adapted to endure permanent soil anoxia.     

Lead tolerance of Betula and Salix in the mining area of Mechernich/Germany

Natural populations of woody perennials on lead-mining sites in the Mechernich area of the Eifel Mountains were investigated with respect to soil factors determining the degree and type of heavy metal tolerance. Salix caprea L. (Goat Willow) grew on soils with up to 17000 mg kg^–1 total lead (ca. 4000 mg kg^–1 ammonium acetate-exchangeable Pb). Betula pendula Roth (Silver Birch) was found on soils containing as much as 29000 mg kg^–1 total lead (7000 mg kg^–1 ammonium acetate-exchangeable Pb). Other woody perennials, with the exception of the dwarf shrub Calluna vulgaris, were not found in the contaminated area even though they did occur in the immediate vicinity. The two lead-tolerant tree species did not form mixed populations.Because of a significantly lower Pb/Ca ratio in Salix soils (2.2) compared with Betula soils (7.4), a calcium-dependent mechanism of lead tolerance is suggested for Salix, but not for Betula.The Betula population could be divided into two groups, each showing a highly significant correlation between root-lead content and exchangeable lead amounts in the soil, but with different levels of lead uptake. The only soil factor distinguishing the two groups was found to be the level of soluble phosphate. A distinctly low level of soil phosphate correlated with a high lead concentration in roots of the one group (30000 mg Pb kg^–1 DW), whereas high phosphate amounts corresponded with a much lower lead concentration in roots of the other (12000 mg Pb kg^–1 DW^–1). Since the correlation between lead in the soil and in plants was similar for the two groups, it is concluded that the type of lead tolerance in Betula is determined by the status of plant phosphate nutrition, rather than by simple phosphate precipitation in the soil.A comparison of growth between different populations of Betula seedlings on homogenized soils from the mining area revealed the Mechaernich population to be a distinct ecotype with respect to lead tolerance. The control population obtained from a non-contaminated area exhibited a lower degree of lead tolerance coupled with a two-step strategy of adaptation to lead.