Effects of carbon dioxide on the searching behaviour of the root-feeding clover weevil Sitona lepidus (Coleoptera: Curculionidae).

The respiratory emission of CO2 from roots is frequently proposed as an attractant that allows soil-dwelling insects to locate host plant roots, but this role has recently become less certain. CO2 is emitted from many sources other than roots, so does not necessarily indicate the presence of host plants, and because of the high density of roots in the upper soil layers, spatial gradients may not always be perceptible by soil-dwelling insects. The role of CO2 in host location was investigated using the clover root weevil Sitona lepidus Gyllenhall and its host plant white clover (Trifolium repens L.) as a model system. Rhizochamber experiments showed that CO2 concentrations were approximately 1000 ppm around the roots of white clover, but significantly decreased with increasing distance from roots. In behavioural experiments, no evidence was found for any attraction by S. lepidus larvae to point emissions of CO2, regardless of emission rates. Fewer than 15% of larvae were attracted to point emissions of CO2, compared with a control response of 17%. However, fractal analysis of movement paths in constant CO2 concentrations demonstrated that searching by S. lepidus larvae significantly intensified when they experienced CO2 concentrations similar to those found around the roots of white clover (i.e. 1000 ppm). It is suggested that respiratory emissions of CO2 may act as a 'search trigger' for S. lepidus, whereby it induces larvae to search a smaller area more intensively, in order to detect location cues that are more specific to their host plant.

Effects of dung and urine amendments on the isotopic content of N(2)O released from grasslands.

The temporal and diurnal changes in nitrous oxide (N(2)O) fluxes were measured between 29(th) September and 2(nd) November 1999 from urine and dung patches from cattle deposited on grazed grassland. The delta(15)N and delta(18)O values of the N(2)O emitted from soil from both treatments were examined on four occasions during this period. The diurnal fluxes of N(2)O were measured by a chamber technique that provides hourly measurement of N(2)O fluxes. The (15)N and (18)O analysis of N(2)O were determined by isotope ratio mass spectrometry. N(2)O fluxes from the excreta patches were large, with peak emissions up to 1893 ng N m(-2) s(-1) occurring after heavy precipitation, measured one month after the treatment applications. Emissions from the urine patches were significantly greater than from the dung. The results showed that excretal patches are an important source of atmospheric N(2)O. The flux pattern showed a strong diurnal variation with maximum fluxes generally occurring in late afternoon or early morning, and generally not in phase with the soil temperature changes. The isotopic content of (15)N and (18)O in the N(2)O showed a similar trend to that of the N(2)O flux. The (15)N and (18)O values of the N(2)O emitted from the soil indicated that denitrification was the major process involved. After heavy precipitation on the 6(th) October, the larger delta(15)N and delta(18)O values suggested a consumption of the N(2)O by total denitrification.

Ammonia emission factors for N fertilizers applied to two contrasting grassland soils.

Ammonia volatilization from nitrogen (N) fertilizer applied throughout the year to two soil types was measured using a system of small wind tunnels. Losses from urea ranged from 12 to 46% of the applied N. Small losses, averaging <1%, were measured from ammonium nitrate (AN) and calcium nitrate applications. Factors influencing these losses are discussed. Using these results and those from other workers, emission factors for urea and AN applications to grassland in the UK were determined as 23.0 and 1.6% of the applied N, respectively. Emission factors for these fertilizers when applied to arable land were estimated as 11.8 and 0.8%, respectively. The emission factor for all other applied N (as straight and compound fertilizers) was assumed to be similar to that for AN. Calculations showed that fertilizer applications to agricultural land in the UK contributes 34 kt NH3-N per year, equivalent to 17% of the total annual NH3 emission.

The measurement of methane losses from grazing animals.

A detailed description is given of the construction, operation and calibration of a system designed to measure methane emissions from sheep grazing in the field under as near natural conditions as possible. Results from four preliminary studies show that emission of methane averaged 14 g day(-1) per animal, equivalent to 5.1 kg year(-1) per animal. These rates, although lower than some estimates, confirm that methane emission from sheep forms a significant proportion of the total methane emissions currently attributed to UK agriculture.

Measurements of ammonia emission from grazed grassland.

Some of the factors influencing NH(3) emission from grazed grassland were examined. The large day-to-day variation in rates of loss were only partially explained by variation in the measured environmental factors (wind speed, soil and air temperature, soil moisture status, relative humidity, rainfall and potential evapotranspiration). Of the measured variables, wind speed had the largest effect but the best multiple linear regression model of daily NH(3) loss had an adjusted R(2) value of only 0.406. The mechanisms controlling NH(3) flux were therefore unclear. There were marked diurnal rhythms in NH(3) loss and the concentration gradients above the sward were strongest during the period which included the 3 h each side of midday. This pattern of NH(3) release has important implications in relation to atmospheric mixing processes and chemical reactions. A comparison of two means of determining NH(3) concentrations, i.e. a bubbler collection system or denuder tubes, indicated that different forms were collected which could be related to the environmental conditions. Such differences and effects should be considered when models are developed to describe the behaviour of nitrogenous and other species in the atmosphere.

Human lymphocyte motility: normal characteristics and anomalous behavior of chronic lymphocytic leukemia cells.

The characteristics of human lymphocyte motility and its relationship to the redistribution of surface membrane antigens (capping) are poorly defined. Since chronic lymphocytic leukemia (CLL) cells cap poorly when compared with normal human lymphocytes, this study was undertaken to compare the motility of these two cell types. A modification of the Boyden chamber system was employed to quantify lymphocyte motility by placing lymphocyte suspensions on 8-mum convoluted-pore nitrocellulose filters and measuring the depth of migration of the cells into the filter at 37 degrees C. After 3 hr of incubation, CLL cells migrated significantly less into the filter than normal cells. Incubation in the presence of sodium azide or at 4 degrees C abolished all motility, indicating the active nature of the process. The relative motility of individual CLL patients' cells correlated best with the proportion of abnormal cells present as determined by surface receptor assays. The possibility that decreased cell motility in CLL was a reflection of enrichment by a "bone marrow-derived" (B cell) population was eliminated by the finding that normal B cells purified by gradient separation of rosetted cells migrated faster than normal T cells and considerably faster than CLL cells. Motility of normal and CLL lymphocytes was decreased by cytochalasin B and increased by colchicine, vincristine, and vinblastine. Thus, human lymphocyte motility appears to be dependent on microfilament integrity but not to require the colchicine-sensitive cytoskeleton. The decreased motility of CLL cells is the result of an intrinsic cell abnormality, but this finding cannot fully explain the decreased capping, since in human lymphocytes the latter is not prevented by an inhibitor of motility.