Evaluation of an optimal extraction method for measuring d-ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) in agricultural soils and its association with soil microbial CO2 assimilation

Assimilating atmospheric carbon (C) into terrestrial ecosystems is recognized as a primary measure to mitigate global warming. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) is the dominant enzyme by which terrestrial autotrophic bacteria and plants fix CO₂. To investigate the possibility of using RubisCO activity as an indicator of microbial CO₂ fixation potential, a valid and efficient method for extracting soil proteins is needed. We examined three methods commonly used for total soil protein extraction. A simple sonication method for extracting soil protein was more efficient than bead beating or freeze–thaw methods. Total soil protein, RubisCO activity, and microbial fixation of CO₂ in different agricultural soils were quantified in an incubation experiment using ¹⁴C-CO₂ as a tracer. The soil samples showed significant differences in protein content and RubisCO activity, defined as nmol CO₂ fixed g⁻¹ soil min⁻¹. RubisCO activities ranged from 10.68 to 68.07 nmol CO₂ kg⁻¹ soil min⁻¹, which were closely related to the abundance of cbbL genes (r = 0.900, P = 0.0140) and the rates of microbial CO₂ assimilation (r = 0.949, P = 0.0038). This suggests that RubisCO activity can be used as an indicator of soil microbial assimilation of atmospheric CO₂.     

Effects of land use and clay content on soil structure as measured by Fracture Surface Analysis

Soil clods were collected from the A horizons of six soils (3 Aqualfs and 3 Uderts) in the vicinity of Bayreuth in northern Bavaria. The soils had a range of clay contents and came from arable, meadow (pasture) and forest areas. The soils ranged in workability from easily workable to difficult to work. The clods, still moist as collected, were fractured into two parts by tensile stress and one part of each clod was embedded in polyester resin. The embedded clod parts were then sectioned to show profiles of the fracture surfaces. The profiles were digitized by a television scanner. Statistical measures of the roughness of the fracture surfaces were computed. Fracture surface roughness was strongly influenced by land use and soil clay content. Soil workability was related to fracture surface roughness and hence also to land use and soil clay content. Ease of soil working was mainly associated with the presence of soil structural features larger than 10 mm.     

三种农田土壤中氨氧化细菌amoA基因多样性比较分析

比较分析中国东部不同季风气候区中海伦黑土(HL)、封丘潮土(FQ)和鹰潭红壤(YT)3种土壤氨氧化细菌amoA基因多样性。采用非培养方法直接从土壤中提取微生物总DNA,用氨氧化细菌amoA基因特异引物扩增总DNA,构建了3种土壤amoA基因文库,并对文库进行限制性长度多态性(RFLP)分析。HL、FQ和YT的amoA基因文库克隆数量分别为49、50和48个,相应的RFLP类型数为10、10和14个OTUs,其中有4个OTUs为三种土壤共有;YT中氨氧化细菌amoA基因多样性指数最高,FQ最低;HL和FQ群落的相似为70%,HL与YT的相似度为50%,而FQ和YT之间仅为42%,说明氨氧化细菌具有地理分布的规律:17个amoA基因序列可以被聚成6个cluster,分属Nitrosospira和Nitrosomonas两个属。三种农田土壤中均存在丰富的氨氧化细菌,表明氨氧化细菌在农田土壤氮素循环中具有重要作用。     

NaOH‐extractable organic matter of andic soils from Galicia (NW Spain) under different land use regimes: a pyrolysis GC/MS study

The objective of this study was to determine to what extent the attenuation or loss of andic soil properties caused by land use change – from forest (FOR, average C content 118.2 ± 23.7 g kg^?1) to agricultural land (AGR, average C content 55.7 ± 16.7 g kg^?1) use – is reflected in soil organic matter (SOM) at the molecular level. For this, NaOH‐extractable SOM of A horizons from 17 soils developed on amphibolitic parent material in NW Spain was studied by pyrolysis gas chromatography spectrometry (Py‐GC/MS). We also included two buried andic A horizons (PAL, 2200 cal yr BP in age) on the same parent material, as a reference for the molecular composition of SOM from soils without recent litter additions. Organic matter of PAL soils had a composition largely different from that of superficial soils (FOR and AGR), with an important relative contribution of microbial polysaccharides and N‐compounds, and an absence of compounds that characterize fresh plant litter (e.g. lignins). In the superficial soils, the relative contribution of lignin‐derived compounds was greater in AGR than in FOR soils. Differences were also observed in the relative contribution of aliphatic compounds, FOR soils being enriched in this type of components compared with AGR soils. The results indicated that land use change from FOR to AGR, which was accompanied by a decrease in total SOM, resulted in an enrichment in primary SOM. The smaller relative abundance of primary SOM derivatives in andic FOR soils indicates that these compounds were quickly degraded in Andisols.     

Effects of nitrogen and intensive mixing on decomposition of C-labelled maize (Zea mays L.) residue in soils of different land use types

This study investigated the effects of mineral-N addition and intensive mixing (analogous to disturbance by plowing) on decomposition of ¹⁴C-labelled maize (Zea mays L.) residue and soil organic matter (SOM). Soils were collected from the upper 5 cm of three land use types at Edelweiler, Germany: plow tillage (PT), reduced tillage (RT), and grassland (GL). Soils were incubated for 112 days at 20 °C, with or without ¹⁴C-labelled maize residue (4 g DM kg⁻¹ soil), with or without nitrogen (100 mg N kg⁻¹ soil as NH₄NO₃) and with or without intensive mixing.

The effect of mineral-N on maize residue decomposition differed depending on the stage of decomposition and land use type. Nitrogen accelerated residue decomposition rates in the first 5 days in RT and GL soils, but not in PT soil, and decreased residue decomposition rate in all three land use types after 11 days. At the end of the incubation, N suppressed ¹⁴CO₂ efflux in RT and PT soils, but not in GL soil. Mineral-N did not increase SOM decomposition independently on the land use types.

Intensive mixing stimulated decomposition of both plant residue and SOM in all three land use types. However, effects were smaller in GL soil than in RT or PT soil, presumably because stronger soil aggregates in GL would have been less affected by mixing and allowed greater protection of SOM and plant residue against decomposition.     

The effect of starvation on the planarian Arthurdendyus triangulatus (Tricladida: Terricola) as measured by stable isotopes

Many studies of the population dynamics of the planarian Arthurdendyus triangulatus have been confounded because it has not been possible to define if small flatworms are adults that have been starved or young ones being recruited into the population. Body shrinkage is a process exhibited by planarians under nutritional stress. In birds and the few invertebrate species studied, starvation leads to a ¹⁵N-enrichment of body tissues (i.e. an increased δ ¹⁵N). Under laboratory conditions, the posterior parts of flatworms were removed at day 0 and frozen and compared isotopically with the anterior parts of flatworms, which were starved for 67, 108, 171 and 243 days. With one exception, δ ¹³C 108 days after starvation, the impact of starvation on A. triangulatus %N, %C and δ ¹³C was not significant statistically. In contrast, δ ¹⁵N increased significantly (to a maximum enrichment of 2.8‰ by day 243) on all sampling dates. This is supported by significant positive correlations between the changes in δ ¹⁵N between the anterior and posterior body parts and number of days after starvation (p≤0.05) and decrease in body weight (p≤0.01), respectively. Existing δ ¹⁵N data from field populations of animals show intra-population variability of around 5.0‰, greater than that noted as a result of starvation. Thus, as a single measure, it is unlikely that δ ¹⁵N can be used to accurately characterise the proportion of starved A. triangulatus within a field population.     

Effect of 7-year application of a nitrification inhibitor, dicyandiamide (DCD), on soil microbial biomass, protease and deaminase activities, and the abundance of bacteria and archaea in pasture soils

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO₃ ^?) leaching and nitrous oxide (N₂O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g^?1 soil) and biomass N (63 to 28 μg N g^?1), protease (361 to 694 μg tyrosine g^?1 soil h^?1) and deaminase (4.3 to 5.6 μg NH₄ ⁺ g^?1 soil h^?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?10⁹ to 2.77?×?10⁹ g^?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?10⁷ to 3.01?×?10⁸ g^?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.     

Relative saprophytic competence of Rhizobium japonicum strains in soils as determined by the quantitative fluorescent antibody technique (FA)

Experiments were conducted to estimate the saprophytic competence of four Rhizobium japonicum strains (110, 123, 532c, and 586) in a Rossmoyne silt loam (almost free of R. japonicum) and a Miamian silt loam (containing indigenous R. japonicum strains).All strains increased about 100-fold in sterilized Rossmoyne or Miamian soil during the first 2 weeks, and the population remained constant for 26 and 6 weeks respectively. Such results indicated that abiotic factors were not limiting Rhizobium populations in these soils under laboratory conditions. There was no inter-strain competition when strains were mixed and applied to either sterilized soil.All R. japonicum strains decreased about ten-fold but survived well in non-sterile Rossmoyne soil during 26 weeks incubation. But, all strains died at varying rates in non-sterile Miamian soil during a 6 week incubation. The most rapid decline occurred with strain 123, which decreased about 1000-fold during the first 5 days, while strain 586, decreased about 1000-fold during the first 10 days. The die-back of strain 123 was found to coincide with an increase in numbers of a parasitic microorganism which passed through a 0.45 μm pore-sized filter. A bacteriophage has been implicated, although Bdellovibrio cannot be ruled out completely. This parasitic microorganism is strain specific but does not lyse a field isolate of serogroup 123.     

Effect of land use on forest floor and soil of a Quercus suber L. forest in Gallura (Sardinia,Italy)

In order to determine the effect of land use on forest floor and soil, two adjacent sites with different land use were investigated in Gallura (northern Sardinia, Italy). One site is a Quercus suber L. forest mainly used for cork production and the other is an open Quercus suber L. forest where livestock is put out to graze. In each site one soil profile was studied to characterize the mineral soil, and five humus profiles were opened along a vegetation transect, were studied to characterize the forest floor. Samples of L, F and H horizons of the forest floor and of the A mineral horizons were collected and analysed for each profile. In the site mainly used for cork production well‐developed ectorganic (L, F and H) horizons are always present, with a total thickness ranging from 5·2 to 9·5 cm. Humus profile is of the Moder type, while mineral soils have an A–C profile, generally 50 cm deep. Organic matter content in the forest floor ranges from 1·76–3·72 kg m⁻² and nutrients content in the mineral soil is high. In the site used chiefly for grazing the ectorganic horizons are very poorly developed, with a total thickness ranging from 1–3 cm, except for some islands under the Quercus suber L. canopy where the total thickness may reach 5·3 cm. Humus profile is of the Mull type, but the used classification system seems not appropriate when the tree density is below a critical limit. Mineral soils have an A–C profile 20–25 cm deep. The organic matter content in the forest floor ranges from 0·45 to 1·84 kg m⁻², while nutrient content in the mineral soil maintains at high level, even higher than in the former case for C, N and Ca, probably in relation with higher supply of cattle excreta. Sheet erosion is evident in the site. It is concluded that cork production will maintain a sustainable forest floor development in cork–oak forest ecosystem, whereas cattle grazing, fires and ploughing in cork–oak forests may be considered to trigger off severe soil degradation processes. Copyright © 2000 John Wiley & Sons, Ltd.     

灭幼脲Ⅲ号防治马尾松毛虫效果及其松林昆虫多样性变化研究

湖南省宁乡县是3代类型的马尾松毛虫常灾区，1993年6月第1代应用25％灭幼脲Ⅲ号进行防治。防治后12代通过对灭幼脲＋溴氰菊酯（Ⅲ）和对照（CK）4种类型的松林内昆虫多样性调查表明，各处理区内灌木层物种数和个体数均高于树冠层，未施药对照区物种数高于其他3种处理区，溴氰菊酯施药区物种数最低；但各处理区树冠层和灌木层昆虫多样性指数无显著差异，灌木层昆虫物种多样性有待于进一步丰富；经过12代的持续控制后各处理区昆虫多样性水平已基本得到恢复。     

Naidid worms (Oligochaeta, Naididae) in paddy soils as affected by the application of legume mulch and/or tillage practice

Reproduction, intrinsic rate of natural increase and population density of naidid worms were investigated in submerged paddy fields and the laboratory. No tillage plus legume-mulching increased the population density of naidid worms. Soil treatments with neither tillage nor legume mulch, and tillage practice alone, did not increase the number of worms. Dero dorsalis Ferronnière was dominant in soil of the no-tillage treatment. In laboratory experiments, legume-mulching with the proper amount of dissolved O₂ accelerated asexual reproduction of D. dorsalis through zooid budding. For the legume and aeration treatment, (N_i+1-N_i) N_i^-1 values (where N_i and N_i+1 are the populations at times t=i and t=i+1) were plotted against N_i+1. Utilizing this linear relation, this data fitted the logistic curve (r²=0.885, P<0.05). Based on the linear relation, the intrinsic rate of natural increase (r), carrying capacity (K), and doubling time (T) were calculated as 0.2125 day^-1, 12,666 m^-2, and 3.26 days, respectively. The amounts of legumes applied were highly correlated with the population of D. dorsalis, indicating that the weight of legume is a limiting factor with respect to carrying capacity. A literature review indicated a significant correlation (P<0.01) between intrinsic rate of natural increase and maximum body length of naidids with temperature conversion of the growth rate. Sexually mature worms were rarely found in submerged paddy fields. Sexual reproduction seems to be adopted in response to soil desiccation after paddy field drainage.     

Effect of soil bacteria on the ability of polycyclic aromatic hydrocarbons (PAHs) removal by Trametes versicolor and Irpex lacteus from contaminated soil

The effect of bacteria represented by indigenous soil microflora or a mixture of soil bacteria Pseudomonas aeruginosa and Rhodococcus erythropolis on fungal growth, extracellular enzyme production and polycyclic aromatic hydrocarbons (PAHs) biodegradation efficiency in soil of white-rot fungi Trametes versicolor and Irpex lacteus was investigated. Both fungi were able to colonize soil. The growth yields measured by ergosterol were about two-fold in I. lacteus after 10 weeks. Laccase was produced in T. versicolor cultures in the presence or absence of bacteria but live bacteria reduced the laccase levels in soil about 5 times. Manganese-dependent peroxidase (MnP) was not detected in T. versicolor cultures. The amounts of MnP and laccase in I. lacteus cultures were not affected by the presence of bacteria. T. versicolor was more efficient in PAH removal for all PAHs tested although its capacity to colonize soil was lower. The removal rates of PAHs by T. versicolor in sterile soil were 1.5-fold, 5.8-fold and 1.8-fold for 2-3-ring, 4-ring and 5-6-ring PAHs, compared to I. lacteus, respectively. I. lacteus showed a low efficiency of removal of pyrene, benzo[a]anthracene and benzo[k]fluoranthene, compared to T. versicolor, whereas chrysene and benzo[b]fluoranthene were degraded by neither fungus. The main effect of the presence of the indigenous microflora or R. erythropolis and P. aeruginosa was a significant decrease of degradation of total PAHs by both T. versicolor and I. lacteus. Weak fungal/bacterial synergistic effects were observed in the case of removal of acenapthylene, benzo[a]pyrene, dibenzo[a,h]anthracene and benzo[g,h,i]perylene by I. lacteus and acenapthylene by T. versicolor. However, the bacterial effects were different in the two fungi. PAH abiotic losses represented 15 and 21% of the total PAHs after 5 and 10 weeks, respectively; naphthalene and acenaphthene were removed from the soil due to volatilization.     

Effect of biosolid application to Mollisol Chilean soils on the bioavailability of heavy metals (Cu,Cr, Ni,and Zn) as assessed by bioassays with sunflower (Helianthus annuus) and DGT measurements

Purpose

This study assessed the effect of biosolid application on the bioavailable fraction of some trace elements (Cu, Cr, Ni, and Zn) using a bioassay with sunflower (Helianthus annuus) and a chemical assay, diffusion gradient in thin films (DGT).

Materials and methods

Five surface soil samples (0–20 cm) were collected from an agricultural zone in Central Chile where biosolids are likely to be applied. Municipal biosolids were mixed with the soil at concentrations of 0, 30, 90, and 200 Mg ha^?1. The experiment to determine the bioavailability of metals in the soil using the bioassay was performed using sunflower. The DGT technique and Community Bureau of Reference (BCR) sequential extraction were used to determine the bioavailable fractions of the metals.

Results and discussion

The application of biosolids increased the phytoavailability of Zn, Ni, and Cr in most of the soils, as indicated by the increasing concentrations in sunflower plants as the biosolid application rate increased. In two of the soils, Codigua and Pelvín, this increase peaked at an application rate of 90 Mg ha^?1. Decreases in the bioavailable fractions of Zn, Ni, and Cr were observed with higher biosolid application rates. The bioavailability of metals was estimated through multiple linear regression models between the metals in the sunflower plants and the different chemical fractions of metals in the soils treated with different biosolid rates, which displayed a positive contribution of the labile (water soluble, carbonate, and exchangeable), oxide, and organic metal forms in the soil, particularly with respect to Ni and Zn at application rates of 30 and 90 Mg ha^?1. The bioavailable fraction of metals was determined in soils using the DGT technique. The effective concentration (C _E) results were compared with those in sunflower plants. The DGT technique could effectively predict the bioavailable fractions of Cr, Ni, and Zn in the Taqueral soil but only that of Zn in the Polpaico soil.

Conclusions

The application of biosolids significantly increased the labile fraction of most of the metals in the studied soils, particularly at the highest biosolid application rate. C _E increased as the concentration of biosolids increased for most of the metals. The effectiveness of the DGT technique for predicting the bioavailability of metals was dependent on the soil type and the metal. However, the C _E for soil Cu was not related to plant Cu for all soils studied.     

Carbon monoxide as an inhibitor of N2ase activity(C2H2) in control measurements of endogenous formation of ethylene by forest soils

Two problems with the recently suggested method to measure endogenous formation of C₂H₄ in an atmosphere enriched with C₂H₂ and CO in studies of N₂ase activity (C₂H₂) in forest soils were analysed, namely the effect of consumption of CO during incubation and the effect of water-saturated conditions.After an initial addition of 100 ml C₂H₂ and 20 ml CO 1^?1 to soil incubation vessels, CO was gradually consumed and followed by a recovery of N₂ase activity when the concentration of CO was lower than about 10 ml 1^?1. The shortest period within which this concentration was achieved was 1 day when incubating fresh soil cores at 15°C, and it was concluded that longer incubations should be avoided.The inhibition of N₂ase activity by CO was strongly suppressed when all soil pores were filled with water. Dissolved inorganic N (0.1% of dry mass soil) was much more efficient in inhibiting N₂ase activity under such conditions.     

Effect of aqueous extracts from vermicomposts on attacks by cucumber beetles (Acalymna vittatum) (Fabr.) on cucumbers and tobacco hornworm (Manduca sexta) (L.) on tomatoes

Vermicomposts are produced through interactions between earthworms and microorganisms in the breakdown of organic wastes. Aqueous extracts were prepared in commercial brewing equipment from vermicomposts produced from super-market food wastes. The ratio of vermicompost to water was one to five v:v, to produce a 20% aqueous solution which could be diluted to 5% and 10% concentrations. The effects of soil drenches applied at dilutions of 20%, 10%, and 5% vermicompost aqueous extracts, were compared with those of deionized water, in the suppression of cucumber beetles (Acalymna vittatum) attacking cucumbers and tobacco hornworms (Manduca sexta) attacking tomatoes, in greenhouse cage experiments. Tomatoes and cucumber seedlings were germinated and grown for 4 weeks in 25 cm diameter pots containing a soil-less growth medium - Metro-Mix 360 - and thinned to four plants per pot. They were placed under 0.2 mm mesh cages (40 cm×40 cm×40 cm), with one pot containing four plants in each treatment cage. At germination, plants were treated with soil drenches of 5%, 10%, or 20% vermicompost extract or a deionized water control to field capacity and thereafter at weekly intervals. A complete nutrient solution was applied weekly to all plants. In each experiment, eight cucumber beetles or eight tobacco hornworms were released onto the leaves of the appropriate plant species in each cage (four pests per test plant). All treatments were replicated four times per pest experiment, in a randomized complete block design. Numbers of pests were counted and damage rated (0-none to 5-total) on days 1, 3, 5, 7, 9, 11, 13 and 14 after the release of pests into the cages.All of the concentrations of vermicompost extracts significantly suppressed the establishment of and the damage caused by the two pests on the plants. The higher the rate of aqueous extract application the greater was the suppression of the pests. We concluded that the most likely cause for the unpalatability of the plants to pests was the uptake of soluble phenolic compounds from the vermicompost aqueous extracts into the plant tissues. These compounds are known to make plants unattractive to pests and to affect pest reproduction and survival rates.     

Removal of Remazol Red Rb by using Al (III) as Coagulant-Flocculant: Effect of Some Variables on Settling Velocity

This study addresses the research of the removal of a textile dye from aqueous solutions by using aluminum ions as coagulant-flocculant. A simulated textile wastewater was prepared from Remazol Red RB textile dye. The purpose of this study was to investigate the effects of temperature, pH, and concentrations of the cationic surfactant and electrolyte concentration on the settling velocity ofthe simulated textile wastewater. While investigating these factors, levels of variables were determined by considering the characteristicsof traditional textile wastewater like pH, temperature, and dye concentration. Although traditional coagulation-flocculation processesmake use of different aluminium salts as coagulant-flocculent, in this study, Al ions dissolved in pH and temperature of traditional textilewastewater were used. Furthermore, sludge volume index values (SVI) were determined and conductivity measurements carried out. The resultsshowed that, in the working range of these variables, the spectroscopic color measurement revealed 100% decolorization yieldof wastewater. In conclusion, researchers found that the optimum settling velocity conditions were as follows: low temperature (273K),surfactant concentration of 0.10 g L^-1, electrolyte concentration of 0.10 g L^-1, dye concentration of 0.025 g L^-1 and a pH of 10.05. Finally, by conducting experiments twice under the obtained optimum values, mean settling velocity was 0.014 m min^-1 and the mean sludge volume index 140 mL g^-1.     

外源Bt基因导入对棉花叶片维管束汁液的生化物质含量及烟粉虱种群增殖的影响

以转Bt基因棉花"国抗22"和常规棉亲本"泗棉3号"为试材,研究外源Bt基因导入对棉花叶片维管束汁液中营养物质和次生物质含量以及烟粉虱种群增殖的影响.结果表明,和"泗棉3号"相比,"国抗22"叶片维管束汁液中可溶性糖含量较低;单宁浓度苗期较低,但花铃期两个品种无明显差异;花铃期游离氨基酸总量无明显差异,但谷氨酸、脯氨酸、丙氨酸含量均明显高于"泗棉3号";在苗期和花铃期两品种棉花叶片维管束汁液中均未检测到棉酚.取食苗期和花铃期"国抗22"棉花的B型烟粉虱内禀增长率rm分别比取食"泗棉3号"对应生育期的高13.7%和20.2%.研究表明,外源Bt基因的导入影响转基因棉花中可溶性糖、游离氨基酸和其他抗生物质的合成,从而影响烟粉虱的种群发展.     

Effect of Zn binding to phytate and humic substances on its uptake by wheat (Triticum durum L.) as affected by carbonates and Fe oxides

Although complexation with soil organic matter may improve zinc (Zn) bioavailability to plants, the effect of Zn sorbent surface on the use of complexed Zn by plants remains unknown. The objective of this research was to elucidate how Zn complexation with humic substances (HS) and phytate affects the uptake of Zn by wheat plants depending on the main sorbent surface in growth media, i.e., carbonates and Fe oxides. To this end, two pot experiments were performed, one using Fe oxide-coated siliceous as the siliceous growth medium sand and the other using a mixture of calcareous sand and siliceous sand as the calcareous growth medium. Each experiment involved three Zn sources, Zn-HS complex, Zn phytate, and ZnSO₄. All sources were applied with surface irrigation at two Zn rates (0.25 and 2 mg kg^-1 growth medium). The Zn-HS complex significantly increased Zn uptake by plants in both media, relative to the other two Zn sources, but no significant difference was observed between Zn phytate and ZnSO₄. In the calcareous medium, Zn-HS complex and Zn phytate resulted in significantly higher dry biomass yields of wheat than ZnSO₄. In the siliceous medium, spike and shoot dry biomass yields with Zn-HS complex at the low rate and Zn phytate at both rates were not significantly different from those with ZnSO₄ at the high rate. After harvest, approximately 50% of the Zn applied as Zn-HS complex remained extractable by diethylenetriaminepentaacetic acid (DTPA), while this proportion was less than 20% for the other Zn sources. Thus, Zn-HS complex and Zn phytate are sources of available Zn for plants, and they are more effective than ZnSO₄ in increasing plant growth, particularly when carbonates are the main Zn sorbent surface.     

Toad on the road: Use of roads as dispersal corridors by cane toads (Bufo marinus) at an invasion front in tropical Australia

Determining the factors that influence the rate of spread of invasive species is an important goal for conservation biology. If invasive species utilize specific landscape features as dispersal corridors, control programs can target such corridors. Radio-telemetry was used to determine landscape level factors that influence dispersal of an introduced anuran species (the cane toad) at an invasion front in tropical Australia. Most radio-tracked toads moved along roads and cleared fencelines, avoiding heavily vegetated habitat; they typically sheltered overnight close to these open corridors, returning to the road each evening to recommence dispersal. Surveys of the compass orientation of dispersing toads on roads showed that most animals were oriented along the main axis of the road (and thus, travelling along the road) rather than moving across it. To test the hypothesis that use of roads enables toads to disperse more rapidly than would be possible across more thickly vegetated sites, locomotor performance of toads was quantified under field conditions. As predicted, toads rapidly slowed down in dense roadside vegetation but continued to move rapidly through open areas. These results suggest that simple habitat manipulations of roadside verges might help to reduce the rate of dispersal of cane toads across tropical Australia.     

Additive effects of copper and zinc on cadmium toxicity on phosphatase activities and ATP content of soil as estimated by the ecological dose (ED50)

The ecological dose (ED₅₀) of Cd on alkaline and acid phosphatase activity and the ATP content of three contrasting forest soils was measured with or without Cu and Zn to assess the additive toxic effects of these two metals. Soils polluted with Cu and/or Zn were treated with increasing Cd concentrations to give the following metal combinations: Cd, Cd+Cu, Cd+Zn and Cd+Cu+Zn. Alkaline and acid phosphatase activities and ATP content of the three soils were analysed 4 h, 7 and 28 days after the metal additions. The ED₅₀ values were obtained by interpolating the enzyme activities or ATP data with a kinetic model and the goodness of fit was satisfactory.Generally, the ED₅₀ values of both acid and alkaline phosphatase activities for Cd were lower (higher toxicity) with than without Cu and Zn and the effect of Cu and Zn was particularly adverse when these two metals were both added to soils. The alkaline phosphatase was more sensitive in the acid and neutral soil whereas the acid phosphatase was more sensitive in the alkaline soil. Both phosphatase activities and the ATP content were more sensitive in the sandy than in the finer textured soils. The ATP content was less sensitive to the additive effects. Increasing toxicity was observed during the incubation.Analysis of 1 M NH₄NO₃-extractable Cd, Cu and Zn revealed that Cd competed with Zn for the adsorption sites but not with Cu. However, the lower ED₅₀ values for Cd of the two phosphatase activities and of the ATP content in the presence of heavy metal combinations could be not explained by the heavy metal solubility data. It is concluded that the ED₅₀ may be a sensitive tool for assessing additve toxic effects to soil biochemical parameters.