Gas chromatographic determination of flurprimidol in a submersed aquatic plant (Myriophyllum spicatum), soil,and water

Methods for the extraction and quantification of flurprimidol residues in Eurasian watermilfoil (Myriophyllum spicatum), soil, and water are described. The compound was detected and quantified by gas chromatography (GC) with a thermionic specific detector. Its identity was confirmed by gas chromatography-mass spectrometry (GCMS) with detection at m/e 40–320. Recoveries from samples spiked with flurprimidol at 10–10,000 ng ml^?1 or g^?1 averaged 86.8% for Eurasian watermilfoil shoots, 85.2% for roots, 79.3% for loam soil, and 93.3% for water. In a small-scale experiment under field conditions, approximately 88% of the applied flurprimidol dissipated in 4 weeks. The majority of recovered flurprimidol was found in the water and upper 5 cm soil layer. The half-life of the compound in water was 6.8–8 days during June/July 1989.     

Growth regulation of Eurasian watermilfoil with flurprimidol

Studies were conducted in 55-liter aquariums under controlled environment conditions to evaluate growth regulator effects of flurprimidol [-(1-methylethyl)--[4-(trifluoromethoxy) phenyl]-5-pyrimidinemethanol] on Eurasian watermilfoil (Myriophyllum spicatum L.). Treatments included flurprimidol concentrations ranging from 0 to 500 g L^-1, with exposure times varying from 0.25 to 28 days. Extending the flurprimidol contact time increased the growth inhibitory response. Flurprimidol-treated shoots were 14–64% shorter than untreated plants at 14 DAT (days after treatment). Growth inhibition persisted 56 DAT for plants exposed to 25 and 100 g L^-1 flurprimidol for 28 days or 200 g L^-1 flurprimidol for 10 days. Growth-inhibited plants accumulated starch in shoots and roots, whereas plants showing little or no growth suppression utilized available assimilate for growth. Treatments that most effectively suppressed shoot length accumulated up to 68% more total nonstructural carbohydrate compared with untreated plants. Shoot and root dry weight biomass were unaffected by flurprimidol.Abbreviations PGR(s) plant growth regulator(s) - TNC total non-structural carbohydrate - DAT days after treatment - PVC polyvinyl chloride - DW dry weight - BOD biological oxygen demand - DMSO dimethyl sulfoxide - LSD least significant difference     

Oviposition specificity and behavior of the watermilfoil specialist Euhrychiopsis lecontei

Eurasian watermilfoil (Myriophyllum spicatum L.) is a nuisance aquatic weed, exotic to North America. The freshwater weevil Euhrychiopsis lecontei (Dietz) is a potential control agent of Eurasian watermilfoil and is a fully submersed aquatic specialist herbivore. Its presumed original host is the native northern watermilfoil (Myriophyllum sibiricum Komarov). We conducted a set of oviposition experiments to reveal first and second oviposition preference of Euhrychiopsis lecontei when presented with seven macrophytes. We tested differences between source (lake) populations of weevils, differences in behavior between weevils reared on the exotic Eurasian watermilfoil and the native northern watermilfoil and between weevils in the presence and absence of their preferred hostplant. Oviposition assays confirmed that E. lecontei is a watermilfoil specialist. Out of the 207 females that laid eggs, only three oviposited on a non-watermilfoil plant, Megalodonta beckii. The weevils' degree of specificity was influenced by the watermilfoil species on which they were reared. Weevils reared on Eurasian watermilfoil tended to oviposit on Eurasian watermilfoil, spent more time on Eurasian watermilfoil than on other plants, and spent more time off plants and took longer to oviposit when Eurasian watermilfoil was removed. Weevils reared on northern watermilfoil did not exhibit a preference for either watermilfoil species in oviposition or in time allocation, although they oviposited on and spent significantly more time on watermilfoils than on other species. Rearing of the two populations on their complementary watermilfoil hostplant resulted in responses typical of the rearing plant, not the original host. These results show that although both weevil populations are watermilfoil specialists, Eurasian-reared weevils prefer Eurasian watermilfoil in general host attraction and oviposition, whereas northern-reared weevils do not. The results support the contention that E. lecontei may be a good biocontrol agent for Eurasian watermilfoil because of its high specificity. The results also suggest that the current host range expansion of the weevil to Eurasian watermilfoil has the potential to become a host shift due to the increased specificity. Herbivory in freshwater systems is not well studied, and the E. lecontei-M. spicatum relationship is a rare example of submersed freshwater specialist herbivore-host-plant interactions.     

In situ measurement of fine root water absorption in three temperate tree species—Temporal variability and control by soil and atmospheric factors

Miniature heat balance-sap flow gauges were used to measure water flows in small-diameter roots (3–4 mm) in the undisturbed soil of a mature beech–oak–spruce mixed stand. By relating sap flow to the surface area of all branch fine roots distal to the gauge, we were able to calculate real time water uptake rates per root surface area (J_s) for individual fine root systems of 0.5–1.0 m in length. Study aims were (i) to quantify root water uptake of mature trees under field conditions with respect to average rates, and diurnal and seasonal changes of J_s, and (ii) to investigate the relationship between uptake and soil moisture θ, atmospheric saturation deficit D, and radiation I. On most days, water uptake followed the diurnal course of D with a mid-day peak and low night flow. Neighbouring roots of the same species differed up to 10-fold in their daily totals of J_s (<100–2000 g m⁻² d⁻¹) indicating a large spatial heterogeneity in uptake. Beech, oak and spruce roots revealed different seasonal patterns of water uptake although they were extracting water from the same soil volume. Multiple regression analyses on the influence of D, I and θ on root water uptake showed that D was the single most influential environmental factor in beech and oak (variable selection in 77% and 79% of the investigated roots), whereas D was less important in spruce roots (50% variable selection). A comparison of root water uptake with synchronous leaf transpiration (porometer data) indicated that average water fluxes per surface area in the beech and oak trees were about 2.5 and 5.5 times smaller on the uptake side (roots) than on the loss side (leaves) given that all branch roots <2 mm were equally participating in uptake. Beech fine roots showed maximal uptake rates on mid-summer days in the range of 48–205 g m⁻² h⁻¹ (i.e. 0.7–3.2 mmol m⁻² s⁻¹), oak of 12–160 g m⁻² h⁻¹ (0.2–2.5 mmol m⁻² s⁻¹). Maximal transpiration rates ranged from 3 to 5 and from 5 to 6 mmol m⁻² s⁻¹ for sun canopy leaves of beech and oak, respectively. We conclude that instantaneous rates of root water uptake in beech, oak and spruce trees are above all controlled by atmospheric factors. The effects of different root conductivities, soil moisture, and soil hydraulic properties become increasingly important if time spans longer than a week are considered.     

Freeze or dehydrate: only two options for the survival of subzero temperatures in the arctic enchytraeid<Emphasis Type="Italic"> Fridericia ratzeli</Emphasis>

Hygrophilic soil animals, like enchytraeids, overwintering in frozen soil are unlikely to base their cold tolerance on supercooling of body fluids. It seems more likely that they will either freeze due to inoculative freezing, or dehydrate and adjust their body fluid melting point to ambient temperature as has been shown for earthworm cocoons and Collembola. In the present study we tested this hypothesis by exposing field-collected adult Fridericia ratzeli from Disko, West Greenland, to freezing temperatures under various moisture regimes. When cooled at –1 °C min^–1 under dry conditions F. ratzeli had a mean temperature of crystallisation (T_c) of –5.8 °C. However, when exposed to temperatures above standard T_c for 22 h, at –4 °C, most individuals (90%, n= 30) remained unfrozen. Slow cooling from –1 °C to –6 °C in vials where the air was in equilibrium with the vapour pressure of ice resulted in freezing in about 65% of the individuals. These individuals maintained a normal body water content of 2.7–3.0 mg mg^–1 dry weight and had body fluid melting points of about –0.5 °C with little or no change due to freezing. About 35% of the individuals dehydrated drastically to below 1.1 mg mg^–1 dry weight at –6 °C, and consequently had lowered their body fluid melting point to ca. –6 °C at this time. Survival was high in both frozen and dehydrated animals at –6 °C, about 60%. Approximately 25% of the animals (both frozen and dehydrated individuals) had elevated glucose concentrations, but the mean glucose concentration was not increased to any great extent in any group due to cold exposure. The desiccating potential of ice was simulated using aqueous NaCl solutions at 0 °C. Water loss and survival in this experiment were in good agreement with results from freezing experiments. The influence of soil moisture on survival and tendency to dehydrate was also evaluated. However, soil moisture ranging between 0.74 g g^–1 and 1.15 g g^–1 dry soil did not result in any significant differences in survival or frequency of dehydrated animals even though the apparent wetness and structure of the soil was clearly different in these moisture contents.Abbreviations DW dry weight - FW fresh weight - MP melting point - RH relative humidity - Tc crystallisation temperatures - WC water contentCommunicated by I.D. Hume     

Interactions between invasive Eurasian watermilfoil and native water stargrass in Cayuga Lake,NY, USA

Aims Eurasian watermilfoil (Myriophyllum spicatum L.) is a common invasive plant in American lakes and has many negative impacts on invaded ecosystems. Drastic decline of this plant at the northern end of Cayuga Lake in the New York State has occurred since the 1980s, with a much smaller magnitude of decline of Eurasian watermilfoil at the southern end (Johnson et al. 2000) During the same period, increases in the abundance of native plants, particularly water stargrass (Heteranthera dubia (Jacq.) MacMill.), have been observed (Johnson et al. (1998)) We aimed to investigate the mechanisms responsible for the decline of Eurasian watermilfoil and evaluate the responses of co-occurring plants at the two ends of Cayuga Lake over time. We hypothesized that plant interactions might have contributed to the drastic decline of Eurasian watermilfoil, particularly allelopathy by native water stargrass.Methods A lake survey was conducted to assess distribution and abundance of plant communities at the northern end and the southern end of Cayuga Lake. Additionally, two sets of greenhouse experiments were conducted to investigate the interactions between invasive Eurasian watermilfoil and native water stargrass. A competition experiment evaluated intra- versus inter-specific competition among plants grown together; an allelopathy experiment examined the responses of plants to each other's extracts.Important findings The lake survey showed that water stargrass was extremely abundant at the northern end, whereas Eurasian watermilfoil was sparse at the northern end but one of the most common species at the southern end. The survey also revealed that water stargrass was more abundant than Eurasian watermilfoil at sites where the two species coexisted in the lake. Results from greenhouse experiments revealed no effects of Eurasian watermilfoil on water stargrass growth. However, Eurasian watermilfoil biomass was reduced by 46% when treated with high concentration of water stargrass extracts. This is likely due to osmotic effects rather than allelopathic effects of water stargrass. We proposed several possible reasons for the drastic decline of Eurasian watermilfoil and the increase in water stargrass abundance at the northern end of Cayuga Lake, including space competition, nutrients, substrates, wind exposure and water clarity in addition to insect herbivory and mechanic harvesting.     

Physical control of Eurasian watermilfoil in an oligotrophic lake

The introduction of Eurasian watermilfoil (Myriophyllum spicatum) into oligotrophic waters of high water clarity in temperate zones of North America has produced growth in excess of 6 m depth and yearly biomass approaching 1000 g m^–2 dry weight. From its initial observation in Lake George, New York, USA in 1985, by 1993 milfoil had spread to 106 discrete locations within the lake. A 7-year study of one site having no management showed milfoil to grow expansively, suppressing native plant species from 20 in 1987 to 6 in 1993 with the average number of species m^–2 quadrat declining from 5.5 in 1987 to less than 2 in 1993. Management of milfoil by means of hand harvesting, suction harvesting and benthic barrier has reduced the number of unmanaged sites from 106 in 1993 to 11. One year post-treatment at sites utilizing suction harvesting, showed a greater number of native species at all sites than pretreatment with a substantial reduction in milfoil biomass. At sites where benthic barrier was removed 1–2 years after installation, milfoil had recolonized 44% of grid squares within 30 days. Ninety days after barrier removal 74% of grid squares contained milfoil and one year later 71% of the grids supported milfoil. During the first year following mat removal, the average number of species m^–2 peaked at 4.7 and stabilized at 4.5 during the second year. Hand harvesting by SCUBA in areas of limited milfoil growth (new sites of infestation and sites of former treatment) was found to reduce the number of milfoil plants present in subsequent years. Hand harvesting did not eliminate milfoil at any of the sites and regrowth/colonization necessitated reharvesting every 3 or more years. Results of evaluations of physical plant management techniques indicate that (1) an integrated program utilizing different techniques based on plant density reduced the growth of milfoil and (2) long term commitment to aquatic plant management is necessary since none of the techniques employed singly were found to eliminate milfoil.     

Seasonal changes in the contribution of root respiration to total soil respiration in a cool-temperate deciduous forest

A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (R _trench) and in a control plot (R _control) were measured from May 2000 to September 2001 by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (R _D) was estimated by using a root-bag method to correct the soil respiration measured from the trenched plots for the additional decaying root biomass. The soil respiration rates in the control plot increased from May (240–320 mg CO₂ m^–2 h^–1) to August (840–1150 mg CO₂ m^–2 h^–1) and then decreased during autumn (200–650 mg CO₂ m^–2 h^–1). The soil respiration rates in the trenched plot showed a similar pattern of seasonal change, but the rates were lower than in the control plot except during the 2 months following the trenching. Root respiration rate (R _r) and heterotrophic respiration rate (R _h) were estimated from R _control, R _trench, and R _D. We estimated that the contribution of R _r to total soil respiration in the growing season ranged from 27 to 71%. There was a significant relationship between R _h and soil temperature, whereas R _r had no significant correlation with soil temperature. The results suggest that the factors controlling the seasonal change of respiration differ between the two components of soil respiration, R _r and R _h.     

Water chemistry and nutrient budgets in an undisturbed evergreen rainforest of southern Chile

In a pristine evergreen rainforest of Nothofagus betuloides, located at the Cordillera de los Andes in southern Chile (41 °S), concentrations and fluxes of nutrients in bulk precipitation, cloud water, throughfall water, stemflow water, soil infiltration and percolation water and runoff water were measured. The main objectives of this study were to investigate canopy-soil-atmosphere interactions and to calculate input-output budgets. From May 1999 till April 2000, the experimental watershed received 8121 mm water (86% incident precipitation, 14% cloud water), of which the canopy intercepted 16%. Runoff water volume amounted 9527 mm. Bulk deposition of inorganic (DIN) and organic (DON) nitrogen amounted 3.6 kg ha^–1 year^–1 and 8.2 kg ha^–1 year^–1 respectively. Occult deposition (clouds + fog) contributes for 40% to the atmospheric nitrogen input (bulk + occult deposition) of the forest. An important part of the atmospheric ammonium deposition is retained within the canopy or converted to nitrate or organic nitrogen by epiphytic bacteria or lichens. Also the export of inorganic (0.9 kg ha^–1 year^–1) and organic (5.2 kg ha^–1 year^–1) nitrogen via runoff is lower than the input to the forest floor via throughfall and stemflow water (3.2 kg DIN ha–1 year^–1 and 5.6 kg DON ha^–1 year^–1). The low concentrations of NO ₃ ^– and NH ₄ ⁺ under the rooting depth suggest an effective biological immobilization by vegetation and soil microflora. Dry deposition and foliar leaching of base cations (K⁺, Ca²⁺, Mg²⁺) was estimated using a canopy budget model. Bulk deposition accounted for about 50% of the total atmospheric input. Calculated dry and occult deposition are both of equal value (about 25%). Foliar leaching of K⁺, Ca²⁺, and Mg²⁺ accounted for 45%, 38% and 6% of throughfall deposition respectively. On an annual basis, the experimental watershed was a net source for Na⁺, Ca²⁺ and Mg²⁺.     

Effects of milfoil weevils and weather on the control of Eurasian watermilfoil

We examined the response of Eurasian watermilfoil (Myriophyllum spicatum) coverage on Manistee Lake, Michigan (U.S.A.) in the presence of milfoil weevils (Euhrychiopsis lecontei). Among 150 sites, milfoil presence declined from 2008 levels of 34 (23%) sites to 2 (1%) sites by 2015 coincident with cumulative stocking of 259,500 weevils from 2007 to 2014. Severe winter temperatures also were associated with milfoil declines. Each 1°C decline in average low temperature during the preceding winter was associated with 3.4 (95% CI 0.8–6.1) fewer sites with milfoil. Impacts of weevil herbivory on watermilfoil may be accentuated by severe winter temperatures. Lake managers should, when possible, integrate weather conditions with weevil stocking regimes to control Eurasian watermilfoil.     

Nitrogen mineralization in heathland ecosystems dominated by different plant species

Net N mineralization rates were measured in heathlands still dominated by ericaceous dwarf shrubs (Calluna vulgaris or Erica tetralix) and in heathlands that have become dominated by grasses (Molinia caerulea or Deschampsia flexuosa). Net N mineralization was measuredin situ by sequential soil incubations during the year. In the wet area (gravimetric soil moisture content 74–130%), the net N mineralization rates were 4.4 g N m^–2 yr^–1 in the Erica soil and 7.8 g N m^–2 yr^–1 in the Molinia soil. The net nitrification rate was negligibly slow in either soil. In the dry area (gravimetric soil moisture content 7–38%), net N mineralization rates were 6.2 g N M-2 yr^–1 in the Calluna soil, 10.9 g N m^–2 yr^–1 in the Molinia soil and 12.6 g N m^–2 yr^–1 in the Deschampsia soil. The Calluna soil was consistently drier throughout the year, which may partly explain its slower mineralization rate. Net nitrification was 0.3 g N m^–2 yr^–1 in the Calluna soil, 3.6 g N m^–2 yr^–1 in the Molinia soil and 5.4 g N m^–2 yr^–1 in the Deschampsia soil. The net nitrification rate increased proportionally with the net N mineralization rate suggesting ammonium availability may control nitrification rates in these soils. In the dry area, the faster net N mineralization rates in sites dominated by grasses than in the site dominated by Calluna may be explained by the greater amounts of organic N in the soil of sites dominated by grasses. In both areas, however, the net amount of N mineralized per gram total soil N was greater in sites dominated by Molinia or Deschampsia than in sites dominated by Calluna or Erica. This suggests that in heathlands invaded by grasses the quality of the soil organic matter may be increased resulting in more rapid rates of soil N cycling.     

Species distribution models for invasive Eurasian watermilfoil highlight the importance of data quality and limitations of discrimination accuracy metrics

AimAvailability of uniformly collected presence, absence, and abundance data remains a key challenge in species distribution modeling (SDM). For invasive species, abundance and impacts are highly variable across landscapes, and quality occurrence and abundance data are critical for predicting locations at high risk for invasion and impacts, respectively. We leverage a large aquatic vegetation dataset comprising point‐level survey data that includes information on the invasive plant Myriophyllum spicatum (Eurasian watermilfoil) to: (a) develop SDMs to predict invasion and impact from environmental variables based on presence–absence, presence‐only, and abundance data, and (b) compare evaluation metrics based on functional and discrimination accuracy for presence–absence and presence‐only SDMs.LocationMinnesota, USA.MethodsEurasian watermilfoil presence–absence and abundance information were gathered from 468 surveyed lakes, and 801 unsurveyed lakes were leveraged as pseudoabsences for presence‐only models. A Random Forest algorithm was used to model the distribution and abundance of Eurasian watermilfoil as a function of lake‐specific predictors, both with and without a spatial autocovariate. Occurrence‐based SDMs were evaluated using conventional discrimination accuracy metrics and functional accuracy metrics assessing correlation between predicted suitability and observed abundance.ResultsWater temperature degree days and maximum lake depth were two leading predictors influencing both invasion risk and abundance, but they were relatively less important for predicting abundance than other water quality measures. Road density was a strong predictor of Eurasian watermilfoil invasion risk but not abundance. Model evaluations highlighted significant differences: Presence–absence models had high functional accuracy despite low discrimination accuracy, whereas presence‐only models showed the opposite pattern.Main conclusionComplementing presence–absence data with abundance information offers a richer understanding of invasive Eurasian watermilfoil''s ecological niche and enables evaluation of the model''s functional accuracy. Conventional discrimination accuracy measures were misleading when models were developed using pseudoabsences. We thus caution against the overuse of presence‐only models and suggest directing more effort toward systematic monitoring programs that yield high‐quality data.     

Processes affecting the response of sulfate concentrations to clearcutting in a northern hardwood forest, Catskill Mountains, New York, U.S.A.

The effects of disturbance on the biogeochemical processes that affect the sulfur (S) cycle in forested ecosystems are important, but have been studied in only a few locations. In this investigation, the mechanisms that caused large decreases in stream SO ₄ ^2– concentrations after clearcutting a small forested catchment in the Catskill Mountains of southeastern New York in 1997 were identified through an examination of pH and SO ₄ ^2– concentrations in soil solutions, bulk deposition of SO ₄ ^2– in throughfall collectors, adsorbed SO ₄ ^2– concentrations in buried soil bags, and spatial variations in SO ₄ ^2– concentrations in shallow groundwater. The load of SO ₄ ^2– –S in stream water during the first 2 years after clearcutting was about 2 kg ha^–1 year^–1 less than the background value of 8–10 kg ha^–1 year^–1. The 10 and 19% decrease in net throughfall flux of SO ₄ ^2– –S during the 2nd and 3rd year after the clearcut, respectively, reflects reduced dry deposition of S after removal of the canopy, but this decrease accounts for 0 and 43%, respectively, of the decrease in SO ₄ ^2– load in streamflow for these 2 years. The pH of B-horizon soil water decreased from 4.5 to 4.0 within 8 months after the clearcut, and SO ₄ ^2– concentrations decreased from 45 µmol L^–1 to less than 20 µmol L^–1 during this time. A strong correlation between SO ₄ ^2– concentrations and pH values (r ² = 0.71, p < 0.01) in B-horizon soil water during the post-harvest period (1997–1999) reflects increased SO ₄ ^2– adsorption in response to soil acidification. Sulfate concentrations in groundwater from 21 spatially distributed wells were inversely related to a topographic index that served as a surrogate for soil wetness; thus, providing additional evidence that SO ₄ ^2– adsorption was the dominant cause of the decreased SO ₄ ^2– concentrations in the stream after clearcutting. These results are consistent with those from a 1985 whole-tree harvest at the Hubbard Brook Experimental Forest in New Hampshire in which increased SO ₄ ^2– adsorption resulting from decreased soil pH was the primary cause of decreased SO ₄ ^2– concentrations in stream water.     

Foliar and root absorption of Na+ and Cl− in maize and barley: Implications for salt tolerance screening and the use of saline sprinkler irrigation

Above-canopy sprinkler irrigation with saline water favours the absorption of salts by wetted leaves and this can cause a yield reduction additional to that which occurs in salt-affected soils. Outdoor pot experiments with both sprinkler and drip irrigation systems were conducted to determine foliar ion accumulation and performance of maize and barley plants exposed to four treatments: nonsaline control (C), salt applied only to the soil (S), salt applied only to the foliage (F) and salt applied to both the soil and to the foliage (F+S). The EC of the saline solution employed for maize in 1993 was 4.2 dS m^–1 (30 mM NaCl and 2.8 mM CaCl₂) and for barley in 1994, 9.6 dS m^–1 (47 mM NaCl and 23.5 mM CaCl₂). The soil surface of all pots was covered so that in the F treatment the soil was not salinized by the saline sprinkling and drip irrigation supplied nutrients in either fresh (treatments C and F) or saline water (treatments S and F+S).Saline sprinkling increased leaf sap Na⁺ concentrations much more than did soil salinity, especially in maize, even though the saline sprinkling was given only two or three times per week for 30 min, whereas the roots of plants grown in saline soil were continuously exposed to salinity. By contrast, leaf sap Cl^– concentrations were increased similarly by saline sprinkling and soil salinity in maize, and more by saline sprinkling than saline soil in barley. It is concluded that barley leaves, and to a greater extent maize leaves, lack the ability to selectively exclude Na⁺ when sprinkler irrigated with saline water. Moreover, maize leaves selectively absorbed Na⁺ over Cl^– whereas barley leaves showed no selectivity. When foliar and root absorption processes were operating together (F+S treatment) maize and barley leaves accumulated 11–14% less Na⁺ and Cl^– than the sum of individual absorption processes (treatment F plus treatment S) indicating a slight interaction between the absorption processes. Vegetative biomass at maturity and cumulative plant water use were significantly reduced by saline sprinkling. In maize, reductions in biomass and plant water use relative to the control were of similar magnitude for plants exposed only to saline sprinkling, or only to soil salinity; whereas in barley, saline sprinkling was more detrimental than was soil salinity. We suggest that crops that are salt tolerant because they possess root systems which efficiently restrict Na⁺ and Cl^– transport to the shoot, may not exhibit the same tolerance in sprinkler systems which wet the foliage with saline water. ei]T J Flowers     

Bronchial response to breathing dry gas at 3.7 MPa ambient pressure

In diving, pulmonary mechanical function is limited by the increased density of the gas breathed. Breathing cold and dry gas may cause an additional increase in airways resistance. We have measured forced vital capacity, forced expired volume in 1 s (FEV₁) and forced midexpiratory flow rate (FEF_25%–75%) before and after breathing dry or humid gas at 29–32°C during a standardized exercise intensity on a cycle ergometer at an ambient pressure of 3.7 MPa. The atmosphere was a helium and oxygen mixture with a density of 6.8 kg · m^–3. Six professional saturation divers aged 26–37 years participated in the study. There were no significant differences in convective respiratory heat loss between the exposures. The mean evaporative heat loss was 67 W (range 59–89) breathing dry gas and 37 W (range 32–43) breathing humid gas, corresponding to water losses of 1.7 g · min^–1 (range 1.5–2.2) and 0.9 g · min^–1 (range 0.8–1.1), respectively. There was a significant reduction in FEV₁ of 4.6 (SD 3.6)% (P<0.05), and in FEF_25%–75% of 5.8 (SD 4.7)% (P<0.05) after breathing dry gas. There were no changes after breathing humid gas. By warming and humidifying the gas breathed in deep saturation diving bronchoconstriction may be prevented.     

Determination of 1-aminocyclopropane-1-carboxylic acid (ACC) in leaf tissue and xylem sap using capillary column gas chromatography and a nitrogen/phosphorus detector

The Lizada and Yang method, commonly used for analyzing 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of the plant hormone ethylene, is subject to interference and lacks internal standards. The use of combined gas chromatography-mass spectrometry (GC-MS) overcomes these shortcomings but the method is expensive and unavailable to many laboratories. We describe an alternative physico-chemical method using a capillary column gas chromatograph fitted with a standard nitrogen/phosphorus detector. After forming the N-benzoyl n-propyl derivative, measurements of ACC concentrations in extracts of leaves and in xylem sap of tomato plants using the nitrogen/phosphorus detector were within 10% of those obtained by GC-MS. Concentrations in plants grown in well-drained soil were approximately 0.16 nmol g^–1 fresh weight (leaves) and 0.04–0.01 mmol m^–3 (sap). Flooding the soil for 48–72 h increased these values approximately 9-fold.     

Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

Summary Vesicular-arbuscular mycorrhizal fungi (VAM) are known to increase plant growth in saline soils. Previous studies, however, have not distinguished whether this growth response is due to enhanced P uptake or a direct mechanism of increased plant salt tolerance by VAM. In a glasshouse experiment onions (Allium cepa L.) were grown in sterilized, low-P sandy loam soil amended with 0, 0.8, 1.6 mmol P kg^–1 soil with and without mycorrhizal inoculum. Pots were irrigated with saline waters having conductivities of 1.0, 2.8, 4.3, and 5.9 dS m^–1. Onion colonized withGlomus deserticola (Trappe, Bloss, and Menge) increased growth from 394% to 100% over non-inoculated control plants when soil P was low ( 0.2 mmol kg^–1 NaHCO₃-extractable P) at soil saturation extract salinities from 1.1 dS m^–1 to 8.8 dS m^–1. When 0.8 and 1.6 mM P was added no dry weight differences due to VAM were observed, however, K and P concentrations were higher in VAM plants in saline treatments.Glomus fasciculatum (Gerdeman and Trappe) andGlomus mosseae (Nicol. and Gerd.) isolates increased growth of VAM tomato 44% to 193% in non-sterilized, saline soil (10 dS m^–1 saturation extract) despite having little effect on growth in less saline conditions when soil P was low. Higher tomato water potentials, along with improved K nutrition by VAM in onion, indicate mechanisms other than increased P nutrition may be important for VAM plants growing under saline stress. These effects appear to be secondary to the effects of VAM on P uptake.     

The role of <Emphasis Type="Italic">Calamagrostis</Emphasis> communities in preventing soil acidification and base cation losses in a deforested mountain area affected by acid deposition

The effects of grass growth and N deposition on the leaching of nutrients from forest soil were studied in a lysimeter experiment performed in the Moravian-Silesian Beskydy Mts. (the Czech Republic). It was assumed that the grass sward formed on sites deforested due to forest decline would improve the soil environment. Lysimeters with growing acidophilous grasses (Calamagrostis arundinacea and C. villosa), common on clear-cut areas, and with unplanted bare forest soil were installed in the deforested area affected by air pollution. Wet bulk deposition of sulphur in SO₄^2– corresponded to 21.6–40.1 kg ha^–1 and nitrogen in NH₄⁺ and NO₃^– to 8.9–17.4 kg N ha^–1, with a rain water pH of 4.39–4.59 and conductivity of 18.6–36.4 S cm^–1 during the growing seasons 1997–1999. In addition, the lysimeters were treated with 50 kg N ha^–1 yr^–1 as ammonium nitrate during the 3 years of the experiment. Rapid growth of planted grasses resulted in a very fast formation of both above- and below-ground biomass and a large accumulation of nitrogen in the tissue of growing grasses. The greatest differences in N accumulation in aboveground biomass were observed at the end of the third growing season; in C. villosa and C. arundinacea, respectively, 2.66 and 3.44 g N m^–2 after addition of nitrogen and 1.34 and 2.39 g N m^–2 in control. Greater amounts of nitrogen were assessed in below-ground plant parts (9.93–12.97 g N m^–2 in C. villosa and 4.29–4.39 g N m^–2 in C. arundinacea). During the second and third year of experiment, the following effects were the most pronounced: the presence of growing grasses resulted in a decrease of both the acidity and conductivity of lysimetric water and in a lower amount of leached nitrogen, especially of nitrates. Leaching of base cations (Ca²⁺ and Mg²⁺) was two to three times lower than from bare soil without grasses. An excess of labile Al³⁺ was substantially eliminated in treatments with grasses. Enhanced N input increased significantly the acidity and losses of nutrients only in unplanted lysimeters. The leaching of N from treatments with grasses (3.9–5.6 kg N ha^–1) was 31–46% of the amount of N in wet deposition. However, the amount of leached N (4.2–6.0 kg N ha^–1) after N application was only 7.1–8.9% of total N input. After a short three year period, the features of soil with planted grasses indicated a slight improvement: higher pH values and Ca²⁺ and Mg²⁺ contents. The ability of these grass stands to reduce the excess nitrogen in soil is the principal mechanism modifying the negative impact on sites deforested by acid depositions. Thus it is suggested that grass sward formation partly eliminates negative processes associated with soil acidification and has a positive effect on the reduction of nutrient losses from the soil.     

Bioenergetics and thermal physiology of American water shrews (<Emphasis Type="Italic">Sorex palustris</Emphasis>)

Rates of O₂ consumption and CO₂ production, telemetered body temperature (T_b) and activity level were recorded from adult and subadult water shrews (Sorex palustris) over an air temperature (T_a) range of 3–32°C. Digesta passage rate trials were conducted before metabolic testing to estimate the minimum fasting time required for water shrews to achieve a postabsorptive state. Of the 228 metabolic trials conducted on 15 water shrews, 146 (64%) were discarded because the criteria for inactivity were not met. Abdominal T_b of S. palustris was independent of T_a and averaged 38.64±0.07°C. The thermoneutral zone extended from 21.2°C to at least 32°C. Our estimate of the basal metabolic rate for resting, postabsorptive water shrews (96.88±2.93 J g^–1 h^–1 or 4.84±0.14 ml O₂ g^–1 h^–1) was three times the mass-predicted value, while their minimum thermal conductance in air (0.282±0.013 ml O₂ g^–1 h^–1) concurred with allometric predictions. The mean digesta throughput time of water shrews fed mealworms (Tenebrio molitor) or ground meat was 50–55 min. The digestibility coefficients for metabolizable energy (ME) of water shrews fed stickleback minnows (Culaea inconstans) and dragonfly nymphs (Anax spp. and Libellula spp.) were 85.4±1.3% and 82.8±1.1%, respectively. The average metabolic rate (AMR) calculated from the gas exchange of six water shrews at 19–22°C (208.0±17.0 J g^–1 h^–1) was nearly identical to the estimate of energy intake (202.9±12.9 J g^–1 h^–1) measured for these same animals during digestibility trials (20°C). Based on 24-h activity trials and our derived ME coefficients, the minimum daily energy requirement of an adult (14.4 g) water shrew at T_a = 20°C is 54.0 kJ, or the energetic equivalent of 14.7 stickleback minnows.     

Soil properties and turf growth on a sandy soil amended with fly ash

Field lysimeters of a sandy soil were amended to a depth of 100 mm with four rates (0, 5, 10 and 20%, wt/wt) of fly ash, and effects on soil water content, nutrient leaching, turf growth and nutrition, and uptake of trace elements by turf were assessed. Measurements were taken for 70 days for lysimeters either planted with rhizomes of Cynodon dactylon(L.) Pers., cv. `Wintergreen', or left bare. When irrigated daily, soil water content increased progressively with increasing rates of fly ash and leachate volumes were decreased by 17–52% for lysimeters containing fly ash amended soil. Fertiliser was applied equivalent to 28.4 g N m<sup>–2</sup> and 10.3 g P m<sup>–2</sup> for the entire 70 days (including pre-plant application). Macronutrient concentrations in leaf tissue were within levels regarded as sufficient. Total dry mass (root plus shoot) decreased when fertiliser application rates were reduced by 25%, irrespective of fly ash treatment. In `bare' lysimeters containing fly ash amended soil, cumulative leaching of NO₃ ^–, NH₄ ⁺and P were 0.32–0.88 of the values in non-amended soil. When planted with turf, leaching of those nutrients was minimal (equivalent to 3% of total N applied) and leaching loses did not differ among fly ash rates. Extractable soil P levels were increased 2.5–4.5-fold in the fly ash amended zone, compared with non-amended soil. Root mass in the top 100 mm was 1.2–1.5-fold larger for turf in fly ash amended soil, compared to non-amended soil. The Se concentrations were higher in leaf tissue grown in fly ash amended soil (being at most 0.63 g g^–1), but there was no effect of fly ash amended soil on As, Ba, B, Cd, Co, Cr, Cu, Pb, Hg, Mn, Ni, Ag or Zn in leaf tissues. Thus, fly ash amendment may be a suitable management option for turf culture on sandy soils, since fly ash improved soil water holding capacity and root growth in the amended zone.