Pulse disturbances to the colonization of hard-substrates and in situ determination of copper using diffusive gradients in thin-films (DGT): quantifying dose and response in the field

Studies conducted in Port Philip Bay, Victoria, Australia are described that examined the effect of experimentally elevated copper concentrations on the recruitment of epifauna to settlement plates. Simultaneous measurement of the copper concentration using diffusive gradients in thin films (DGT) allowed direct comparisons to be made between the labile copper concentration measured at the settlement surface, and the biological effects observed. Copper concentrations created by the field dosing technique were between 20-30 micrograms l-1 for the first 2 d, but then dropped considerably for the following 4 d (3 micrograms l-1), and were indistinguishable from background for the final 7 d. The first 2 d of a copper pulse reduced the recruitment of barnacles, ascidians, serpulid worms, an encrusting bryozoan, and didemnid ascidians. The impacts occurred despite the copper pulse being much less than published LC50 values for similar species. The impacts were no longer obvious by day 7 or 14, having been obscured by either high mortality of early settlers, or large settlement events that took place after day 2. Thus the greatest impact of the pollution event occurred during the period of highest toxicant concentration. The value of this study lies in the correlation of toxicity effects with bio-available metal concentrations under realistic (natural, in situ) conditions.     

Effects of ageing on bioavailability of selenium in soils assessed by diffusive gradients in thin-films and sequential extraction

Plant and Soil - Santalum acuminatum (quandong) is a root hemi-parasite with a very wide distribution across southern Australia. Despite its very wide distribution, along the Jurien Bay...     

Intraspecific differences in physiological response of 20 wheat cultivars to enhanced ultraviolet-B radiation under field conditions

Field studies were conducted to determine the potential for alterations in physiology and the intraspecific variation in sensitivity of 20 wheat (Triticum aestivum) cultivars to enhanced ultraviolet-B (UV-B, 280-315 nm) radiation. The supplemental UV-B radiation was 5 kJ m(-2), simulating a depletion of 20% stratospheric ozone. Out of 20 wheat cultivars (from South China, North China and Mexico) tested, 13 showed significant changes in total chlorophyll content. In most of these sensitive species, chlorophyll a content was strongly reduced, and chlorophyll b content decreased in a lesser extent, leading to a decrease in chlorophyll a/b ratio. However, some species had an increased chlorophyll a/b ratio under enhanced UV-B. The effect of UV-B on flavonoid content also showed intraspecific differences, a significant increase for one cultivar, decreases in 12 cultivars and no effect on the other seven cultivars. Superoxide dismutase (SOD) activity of five cultivars was significantly increased, and that of six cultivars significantly decreased. Membrane permeability of 12 cultivars significantly increased, while only that of Dali 905 was significantly decreased. Malonaldehyde (MDA) contents of eight cultivars were increased significantly, while that of three cultivars was significantly decreased. Although large intraspecific differences were found for the different parameters measured, there was no clear correlation between them under UV-B radiation.     

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

Plant and Soil - Although silicon (Si) is known to improve plant growth under low phosphorus (P) conditions, the in planta mechanisms responsible for this effect are still unknown. Here, we...     

Comparison of application methods for suppressing the pecan weevil (Coleoptera: Curculionidae) with Beauveria bassiana under field conditions

The pecan weevil, Curculio caryae (Horn), is a key pest of pecans. The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin is pathogenic to C. caryae. One approach to managing C. caryae may be application of B. bassiana directed toward adult weevils as they emerge from the soil to attack nuts in the tree canopy. Our objective was to compare different application methods for suppression of C. caryae adults. Treatments included direct application of B. bassiana (GHA strain) to soil under the tree canopy, soil application followed by cultivation, soil application in conjunction with a cover crop (Sudan grass), direct application to the tree trunk, and application to the trunk with an UV radiation-protecting adjuvant. The study was conducted in a pecan orchard in Byron, GA, in 2005 and 2006. Naturally emerging C. caryae adults, caught after crawling to the trunk, were transported to the laboratory to determine percentage mortality and signs of mycosis. When averaged over the 15-d sampling period, weevil mortality and signs of mycosis were greater in all treatments than in the nontreated control in 2005 and 2006; >75% average mortality was observed with the trunk application both years and in the trunk application with UV protection in 2005. Results indicated trunk applications can produce superior efficacy relative to ground application, particularly if the ground application is followed by cultivation. Efficacy in the cover crop treatment, however, did not differ from other application approaches. Future research should focus on elucidating the causes for treatment differences we observed and the extent to which B. bassiana-induced C. caryae mortality reduces crop damage.     

Efficacy of Beauveria bassiana (Hyphomycetes) for control of Russian wheat aphid (Homoptera: Aphididae) on resistant wheat under field conditions

The Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae) is considered the most important pest of wheat produced under dryland field conditions in South Africa. As part of an integrated pest management strategy, the entomopathogenic hyphomycete Beauveria bassiana (Balsamo) Vuillemin was evaluated in combination with antibiotic host plant resistance under dryland field conditions during 1998 and 1999. A commercial formulation, Mycotrol® ES, was applied at a rate of 2.4 L (5×10¹³ conidia) per hectare +0.1% organosilicone surfactant. During both years, two applications were administered, i.e., on growth stages 31 (first node detectable) and 39 (early flag leaf). An additional treatment, application at growth stage 39 only, was included during 1999. Over the duration of the 1998 trial, ca. 65% fewer aphids were observed on treated plots compared with controls. A similar level of population reduction was observed during the 1999 trial; however, treatment effects were only briefly evident due to a rapid field-wide decline in aphid populations caused by adverse (cool, wet) weather conditions. The early application (GS 31) resulted in some level of control only during 1998. It was hypothesized that this phenomenon was the result of greater exposure to the spray applications and/or greater secondary pick-up of fungal inoculum by the aphids due to the higher level of aphid activity observed on the cultivar employed during that year. In this regard, migration of D. noxia onto the flag leaves should be further investigated as a behavioural trait for possible exploitation when considering the use of a mycoinsecticide.     

Maintenance of phosphorus removal in an EBPR system under permanent aerobic conditions using propionate

Enhanced biological phosphorus removal (EBPR) is an efficient and sustainable technology to remove phosphorus from wastewater preventing eutrophication in natural waters. It is widely accepted that EBPR requires an optimal anaerobic hydraulic retention time to obtain stable P-removal from wastewater. Thus, it is suggested that deterioration of the EBPR efficiency regularly observed in full-scale wastewater treatment plants (WWTPs) is normally caused by an excessive aeration of activated sludge that increments the amount of oxygen recycled to the anaerobic reactor and consequently, the anaerobic conditions are not totally preserved. Furthermore, it has been reported a progressive decrease in P-removal capacity in an EBPR lab-scale system enriched with acetate as the sole carbon source under permanent aerobic conditions. Hence, to evaluate the stability of P-removal with a different carbon source, an EBPR-SBR was operated with propionate under permanent aerobic conditions. As a result, net P-removal was successfully accomplished in the SBR without any anaerobic phase during 46 days of aerobic operation. Moreover, the system was shifted after this period to the standard anaerobic–aerobic conditions and reliable P-removal was maintained. FISH (fluorescence in situ hybridisation) analysis showed a significant presence of Accumulibacter (70, 50 and 72%, in different periods) and the absence of Competibacter. The results indicate that using propionate as carbon source it is possible to maintain in a long term an enriched culture of phosphorus accumulating organisms (PAO) able to remove phosphorus under permanent aerobic conditions.     

Effect of water stress on the boron response of wheat genotypes under low boron field conditions

Sterility has emerged as a widespread problem for wheat (Triticum aestivum) production in South and South-east Asia. Whilst boron (B) deficiency is commonly associated with sterility in wheat, the expression of sterility is complicated in rainfed conditions by a number of environmental factors including water stress. A field experiment was conducted to examine the effect of water stress on B response of wheat genotypes on a low B soil (0.087 mg B kg-1soil) at Chiang Mai, Thailand (18°45 N, 99° E) during the dry season from November to March. The experiment consisted of three factors arranged in a split-split plot design with two levels of irrigation: water stress (I–) and full irrigation (I+) in main plots, two levels of B: 0 kg (B0) and 1 kg B ha-1 (B+) as borax in sub plots and four wheat genotypes: SW 41, BL 1022, UP 262 and Sonora 64 in sub–sub plots. Water stress was applied by discontinuing irrigation in I– treatments after the double ridge stage. In all genotypes, above ground biomass was decreased by I–, but not by B deficiency. Significant B×genotype interactions were detected for reproductive growth. SW 41 and BL 1022 strongly responded to added B with relief from B deficiency symptoms at anthesis and improved grain set index (GSI), grains ear-1, ears with grain and grain yield at maturity. By contrast, Sonora 64 could set grain well at B0 and did not show any response to added B with respect to these parameters. Grains ear-1 of SW 41 and BL 1022 was not affected by full irrigation at B0, but were significantly increased when fully irrigated with added B. In all genotypes, B concentration of the flag leaf and the ear at booting and at anthesis was significantly higher in B+, but was not affected by irrigation. Boron × irrigation interactions detected in this study indicate the possibility of the influence of water stress on the severity of wheat sterility in South and South-east Asia.     

在控制条件下云南松幼苗根系对低磷胁迫的响应

磷是控制生命过程的重要元素,植物在生长过程中需要大量的磷,低磷常导致一些植物发生适应性变化。云南松(PinusyunnanensisFranch.)以云南高原为起源和分布中心,其对低磷土壤环境表现出了很强的适应能力,广泛分布并正常生长于贫瘠的低磷红壤上,研究云南松对低磷环境的适应机制,对人类探索高效利用有限的磷素资源的方法具有现实意义。本实验通过对不同磷处理水平下培养的云南松幼苗根系生物量和根冠比等的研究,分析了云南松幼苗根系对低磷胁迫的响应。实验所用云南松种子采集自云南省通海县秀山森林公园内的健壮云南松林。结果表明:当磷浓度下降到0.5mmol/L时,云南松幼苗主根长度开始随磷浓度的降低而增加,根冠比随磷浓度的降低而增大,而侧根发生数没有随磷浓度的降低而显示出显著的增减规律,根系生物量也没有随磷浓度的降低而呈现出有规律的增减,根系生物量始终保持在一定的水平。进一步的分析表明:低磷胁迫下,云南松幼苗保证了物质分配对根的优先地位,以维持其根的生物量在一定水平,进而维持整个生命;云南松幼苗主要是靠主根长度的增加而不是靠侧根数量的增加来适应低磷环境。     

Silicification patterns in wheat leaves related to ontogeny and soil silicon availability under field conditions

Plant and Soil - Silicon (Si) accumulation is an important strategy for plant defense against biotic and abiotic stress. Solid amorphous silica (ASi) deposits have been found to protect plants...     

Aerobic fitness and sympatho-adrenal response to short-term psycho-emotional stress under field conditions

A possible relationship between aerobic fitness (AF), measured by maximal cycle ergometry (CE) and sympatho-adrenal response to acute, short lasting psycho-emotional stress was investigated by monitoring heart rate (f _c) and excretion of catecholamines. The activation of the sympatho-adrenal system was characterised by the noradrenaline : adrenaline ratio. A group of 11 healthy men [22.8 (SD 2.52) years] lived under identical environmental conditions; their mean maximal oxygen uptake ( ) was 47.1 (SD 3.9) ml · min^–1 · kg^–1. After the physiological and psychological laboratory tests had been completed thef _c of the subjects was monitored continuously during the guerilla slide and parachute jump by night, two emotionally stressful military tasks. Maximalf _c (f _{c, max}) attained during these events was 84.5% and 83% off _{c, max} during CE (f _{c, max, CE}), respectively. A significant relationship (r=–0.92,P<0.0002) betweenf _{c, max} reached during the stressful tasks and was found only for the guerilla slide, which was preceded by physical strain, sleep deprivation and energy deficit. One subject with some prior experience in parachuting showed the lowestf _c response and the lowest sympatho-adrenal activation in both events, independent of the degree of AF. In conclusion, AF was found to influence the sympatho-adrenal and fc response to acute, short-lasting emotional stress when the stressful event was aggravated by preceding physical strain, the magnitude of the stress response depending largely on individual experience and effective mechanisms for coping with specific stimuli.     

磷肥施用方式及类型对冬小麦产量和磷素吸收的影响

采用田间微区试验研究不同磷肥施用方式和种类对冬小麦生长和当季磷素吸收的影响.磷肥种类为磷酸二氢钙(MCP)和磷酸氢二铵(DAP),施用方式包括表面撒施,种子正下方5 cm条施,种子下方5 cm、偏3 cm条施,种子下方5 cm、偏10 cm条施,种子正下方20%土体混施5种.结果表明: 种子正下方5 cm条施对小麦的增产效果最高,其中磷酸二氢钙的产量达到7.63 t·hm^-2,磷酸氢二铵的产量达到7.99 t·hm^-2,分别较农民习惯撒施方式增产10.3%和10.7%.在5种施磷方式中,偏10 cm条施的小麦产量最低(6.60～6.77 t·hm^-2).种子正下方5 cm条施和20%土体混施处理的小麦总吸磷量均处于较高水平(34.4～35.6 kg·hm^-2),偏10 cm条施在小麦各生长阶段的吸磷量均显著低于其他施磷方式,但磷酸氢二铵偏10 cm条施的小麦总吸磷量较磷酸二氢钙高11.9%.表明将磷肥近距离集中施用于种子附近为该地区较为合理的施磷方式,在偏远距离条施下磷酸氢二铵对小麦的磷素吸收利用效果优于磷酸二氢钙.     

Ecophysiological response of dune species to experimental burial under field and controlled conditions

Field, greenhouse, and growth chamber experiments were conducted to determine the effects of different burial treatments on photosynthesis (carbon dioxide exchange rate), chlorophyll-a fluorescence, leaf area, biomass, leaf thickness, total chlorophyll content and chlorophyll a/b ratio of ten sand dune species: Agropyron psammophilum, Cakile edentula, Cirsium pitcheri, Corispermum hyssopifolium, Elymus canadensis, Oenothera biennis, Panicum virgatum, Strophostyles helvola, Tusilago farfara, and Xanthium strumarium. Although there were significant differences between species, all of them exhibited stimulation in growth following burial in sand. Generally, buried plants of these species showed an increase in biomass, photosynthetic efficiency, and chlorophyll-a fluorescence because of higher energy content in their roots, rhizomes, and underground stems. The main reasons for the stimulation in growth were an increase in leaf area, leaf thickness, and root biomass. The total chlorophyll content of leaves of buried plants of A. psammophilum, E. canadensis, and P. virgatum was higher than controls, but there were no significant differences for Cirsium pitcheri, O. biennis, and S. helvola. The similarities and differences exhibited by the test species in their responses to burial would be ecologically adaptive to survive the harsh environmental conditions of foredunes. All species showed a clear compensatory response following recovery from the burial episode and surpassed control by enhancing the vital physiological, morphological and growth functions.     

Stomata response to changes in temperature and humidity in wheat cultivars grown under contrasting climatic conditions

Stomatal response to changes in temperature and humidity was studied in wheat (Triticum aestivum L.) cv. Iren’ cultivated under conditions of high water supply and cv. Kazakhstanskaya 10, which is relatively drought tolerant. Experiments were performed under both laboratory and field conditions. It was demonstrated that stomata of cv. Kazakhstanskaya 10 plants closed rapidly with reducing humidity (the response of the first type), whereas, in cv. Iren’, this response was less expressed and, under conditions of a high water content in soil, stomatal conductance could increase in response to reduced humidity (the response of the second type). At an increased stomatal conductance and transpiration, water content in cv. Iren’ plants was maintained due to the increase in hydraulic conductance and water inflow from the roots. A possible role of the first-type response (rapid stomata closure) for growth maintenance under drought and of the second-type response (a parallel increase in the stomatal and hydraulic conductance) for providing of rapid growth and high productivity under sufficient water supply is discussed. A possibility to use the type of stomata behavior for cultivar assessment is considered.     

Seasonal mycorrhizal colonization of winter wheat and its effect on wheat growth under dryland field conditions

 A field experiment was conducted to determine the seasonal patterns of arbuscular mycorrhiza (AM) in a dryland winter wheat (Triticum aestivum L.) system and to determine wheat growth and P uptake responses to inoculation with mycorrhizal fungus. Broadcast-incorporated treatments included (1) no inoculation with mycorrhizal fungus, with and without P fertilizer, and (2) mycorrhizal fungal inoculation at a rate of 5000 spores of Glomus intraradices (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination of dry matter, grain yield and yield components, and N and P uptake. No AM infection was evident during the fall months following seeding, which was characterized by low soil temperature, while during the spring, the AM increased gradually. Increases in wheat grain yields by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization but not by fungal inoculation. At harvest, enhanced AM increased P uptake regardless of whether or not fertilizer P was added. The AM symbiosis increased with rising soil temperatures in the spring, in time to enhance late-season P accumulation and grain production. Accepted: 15 July 1998     

Resistance of wheat lines to Rhopalosiphum padi (Hemiptera: Aphididae) under laboratory conditions

Bird cherry-oat aphid, Rhopalosiphum padi (L.), a polyphagous species with a nearly worldwide distribution, is an important pest of wheat as well as the main vector of barley yellow dwarf virus. We evaluated the resistance categories of eight wheat lines including antibiosis, antixenosis, and tolerance against R. padi under laboratory conditions. The wheat lines tested were ERWYT 88-8, ERWYT 87-6, and ERWYT 87-4 (resistant); ERWYT 87-1, ERWYT 87-20, and ERWYT 88-11 (susceptible); ERWYT 88-12 and ERWYT 88-13 (intermediate). In the antibiosis experiment, R. padi produced fewest progeny on ERWYT 88-8, ERWYT 87-6, and ERWYT 87-4 in reproduction period. In the antixenosis test, R. padi performed best on ERWYT 87-1, ERWYT 87-20, and ERWYT 88-11. Fewer apterous aphids selected ERWYT 88-8, ERWYT 87-4, and ERWYT 87-6 lines indicating antixenosis of these lines to R. padi. In tolerance experiments, however growth parameters differed between treated and untreated seedlings of wheat lines with 10 aphids per day infestation during 21-d period, but not among eight wheat lines. The plant resistance index values were greatest for ERWYT 88-8 (9.71), followed by ERWYT 87-4 (7.04) and ERWYT 87-6 (4.76). ERWYT 88-8, ERWYT 87-6, and ERWYT 87-4 may be important sources of R. padi resistance for small grain breeding and integrated pest management programs.     

Movement of Tribolium castaneum (Coleoptera: Tenebrionidae) adults in response to temperature gradients in vertical and horizontal wheat and corn columns

The movement and redistribution of adult Tribolium castaneum (Herbst) in stored grain provide important information for detection of insect pests and for simulations of their distribution in grain bins. Movement and redistribution of T. castaneum adults in 1 or 6 d and in wheat or corn were determined in a 100 by 100 by 1000-mm acrylic box with a 10 degrees C/m temperature gradient (from 20 to 30 degrees C) or at a uniform temperature (20, 25, and 30 degrees C). In a vertical corn column with a uniform temperature, approximately 15 and 25% of adults moved to the top or bottom section in 6 d, respectively; and < 30% of adults were recovered in 1-d movement in the middle two sections where insects were initially introduced. In a horizontal or vertical wheat column, > 90% of the adults were recovered in the two middle sections where insects were introduced after 6 d. Adults responded to the temperature gradient and preferred the warmer areas in both wheat and corn. The slower movement in wheat is probably caused by the small granular space in bulk wheat than in bulk corn.     

Plant leaf area expansion and assimilate production in wheat (Triticum aestivum L.) growing under low phosphorus conditions

Under phosphorus deficiency reductions in plant leaf area have been attributed to both direct effects of P on the individual leaf expansion rate and to a reduced availability of assimilates for leaf growth. In this work we use experimental and simulation techniques to identify and quantify these processes in wheat plants growing under P-deficient conditions. In a glasshouse experiment we studied the effects of soil P addition (0–138 kg P₂O₅ ha^-1) on tillering, leaf emergence, leaf expansion, plant growth, and leaf photosynthesis of wheat plants (cv. INTA Oasis) that were not water stressed. Plants were grown in pots containing a P-deficient (3 mg P g^-1 soil) sandy soil. Sowing and pots were arranged to simulate a crop stand of 173 plants m^-2. Experimental results were integrated in a simulation model to study the relative importance of each process in determining the plant leaf area during vegetative stages of wheat. Phosphorus deficiency significantly reduced plant leaf area and dry weight production. Under P-deficient conditions the phyllochron (PHY) was increased up to a 32%, compared to that of high-P plants. In low-P plants the rate of individual leaf area expansion during the quasi-linear phase of leaf expansion (LER) was significantly reduced. The effect of P deficiency on LER was the main determinant of the final size of the individual leaves. In recently expanded leaves phosphorus deficiency reduced the photosynthesis rate per unit leaf area at high radiation (AMAX), up to 57%. Relative values of AMAX showed an hyperbolic relationship with leaf P% saturating at 0.27%. Relative values of the tillering rate showed an hyperbolic relationship with the shoot P% saturating at values above 0.38%. The value of LER was not related to the concentration of P in leaves or shoots. A morphogenetic model of leaf area development and growth was developed to quantify the effect of assimilate supply at canopy level on total leaf area expansion, and to study the sensitivity of different model variables to changes in model parameters. Simulation results indicated that under mild P stress conditions up to 80% of the observed reduction in plant leaf area was due to the effects of P deficiency on leaf emergence and tillering. Under extreme P-deficient conditions the simulation model failed to explain the experimental results indicating that other factors not taken into account by the model, i.e. direct effects of P on leaf expansion, must have been active. Possible mechanisms of action of the direct effects of P on individual leaf expansion are discussed in this work.