Earlier Field Experiments Research Articles

How did amber get its aquatic insects? Water-seeking polarotactic insects trapped by tree resin

ABSTRACT Amber contains numerous well-preserved adult aquatic insects (e.g., aquatic beetles – Coleoptera, water bugs – Heteroptera, dragonflies – Odonata, caddisflies – Trichoptera, mayflies – Ephemeroptera, stone flies – Plecoptera). Since amber is fossilised resin of terrestrial conifer trees, it is an enigma how aquatic insects have ended up in the resin. Based on field studies in a Hungarian forest along a freshwater creek we suggest that tree resin traps water-seeking flying polarotactic aquatic insects because of its property to polarise reflected light. The sticky tree resin was modelled by a water-proof, transparent, colourless insect-monitoring glue laid on vertical and horizontal fallen tree trunks next to the creek. Adults of various polarotactic aquatic insect species were trapped only by the horizontal sticky trunk. In earlier field experiments we showed that these insects find water by means of the horizontal polarisation of water-reflected light, and therefore are attracted to and land on all surfaces which reflect horizontally polarised light. Using imaging polarimetry, we revealed the criterion of polarisation-based trapping by resiny tree trunks. According to our observations, flying aquatic insects can be trapped by sticky (resiny) regions of fallen tree trunks that reflect horizontally polarised light and thus attract polarotactic species. The resin continues to flow out of the trees even when fallen over or fractured in a storm. Our findings support and complement an earlier hypothesis, according to which amber-preserved adult aquatic insects have been trapped by resiny bark when they dispersed over land.

Drought Tolerance of European Barley (Hordeum Vulgare L.) Varieties

Abstract Drought is one of the major abiotic stresses that frequently causes severe loss in crop yield worldwide. Laboratory predictors of field drought tolerance could significantly increase the effectiveness of existing plant breeding programs. In earlier field experiments, drought tolerance of 22 cultivated barley varieties has already been quantified. In order to develop laboratory markers of drought sensitivity, field drought tolerance data were correlated with parameters obtained in laboratory tests. Root and shoot length and weight were measured on control and PEG-treated (a simple laboratory drought model) seedlings. Significant correlations were found among root growth, shoot weight in laboratory stress conditions and field drought tolerance. Interestingly, a negative correlation was found between root length of the untreated seedlings and drought tolerance. Laboratory Drought Tolerance Index (DTI) was introduced as the linear combination of those laboratory parameters which were correlated with field drought tolerance. DTI showed good predictive value (r = 0.57, p < 0.05) for drought tolerance in field experiments and we suggest it for preselection of drought tolerant barley breeding lines and for the characterization of drought tolerance in general.

Soil CO2 venting as one of the mechanisms for tolerance of Zn deficiency by rice in flooded soils

We sought to explain rice (Oryza sativa) genotype differences in tolerance of zinc (Zn) deficiency in flooded paddy soils and the counter-intuitive observation, made in earlier field experiments, that Zn uptake per plant increases with increasing planting density. We grew tolerant and intolerant genotypes in a Zn-deficient flooded soil at high and low planting densities and found (a) plant Zn concentrations and growth increased with planting density and more so in the tolerant genotype, whereas the concentrations of other nutrients decreased, indicating a specific effect on Zn uptake; (b) the effects of planting density and genotype on Zn uptake could only be explained if the plants induced changes in the soil to make Zn more soluble; and (c) the genotype and planting density effects were both associated with decreases in dissolved CO2 in the rhizosphere soil solution and resulting increases in pH. We suggest that the increases in pH caused solubilization of soil Zn by dissolution of alkali-soluble, Zn-complexing organic ligands from soil organic matter. We conclude that differences in venting of soil CO2 through root aerenchyma were responsible for the genotype and planting density effects.

Short-distance attraction of saproxylic Heteroptera to olfactory cues

As dead wood is ephemeral, saproxylic insect species must be able to effectively locate new resources via, e.g. olfactory cues. 2. Although saproxylic flat bugs feed on fungal mycelia, published evidence points to their use of dead wood-specific volatile cues rather than fungal-specific cues for long-distance orientation towards new habitat patches. 3. To evaluate which olfactory cues saproxylic flat bugs use for short-distance orientation, we tested the attraction of Aradus obtectus (Vasarhelyi) to fresh wood, fungal mycelia and fungal fruiting bodies using an olfactometer. 4. Aradus obtectus individuals were attracted only to fungal mycelia but not to wood or fungal fruiting bodies. 5. Our results and those of our earlier field experiment testing long-distance attraction (Seibold et al., 2014) together suggest that A. obtectus uses cues emit- ted by dead wood to locate potential resources over long distances, but relies on olfactory cues emitted by mycelia of its host species to locate suitable short- range microhabitats.

Effects of deer and mice on seedling survival in a temperate mixed forest of Japan

To detect the magnitude of indirect positive effects of deer and mice on seedling survival of some woody species in a Japanese temperate forest, we analyzed the data from an earlier field experiment using a hierarchical Bayesian approach. The forest studied was inhabited by sika deer ( Cervus nippon) and mice ( Apodemus spp.), and the floor was covered with dwarf bamboo, Sasa nipponica, which negatively affected tree seedlings and was in turn negatively affected by deer and mice. The field experiment was designed as the combination of exclusion or removal of these factors: deer, mice and dwarf bamboo. A hierarchical Bayesian model was constructed and the parameters were estimated by the Markov chain Monte Carlo method. The model successfully showed the indirect positive effects of deer and mice, which improved the survival rate of five cohorts of the seedlings of three tree species by ameliorating the direct negative effect of dwarf bamboo. The cohorts studied were formed by the seedlings of Abies homolepis that emerged in 1997 and 2002, those of Fraxinus lanuginosa f. serrata that emerged in 1998 and 2002, and those of Fagus crenata that emerged in 1999. The positive indirect effect was especially large in F. crenata, which is known to be severely affected by dwarf bamboo. The total effect of deer was shown to be positive for all cohorts except the A. homolepis cohort that emerged in 1997, at which time the dwarf bamboo had not yet fully recovered from the browsing pressure of deer. The total effect of mice was shown to be positive for all of the cohorts. We conclude that these positive effects were due to the large negative effect of dwarf bamboo on the seedlings.

Long-term ground penetrating radar monitoring of a small volume DNAPL release in a natural groundwater flow field

An earlier field experiment at Canadian Forces Base Borden by Brewster and Annan [Geophysics 59 (1994) 1211] clearly demonstrated the capability of ground penetrating radar (GPR) reflection profiling to detect and monitor the formation of DNAPL layers in the subsurface. Their experiment involved a large volume release (770 L) of tetrachloroethylene into a portion of the sand aquifer that was hydraulically isolated from groundwater flow by sheet pile walls. In this study, we evaluated the ability of GPR profiling to detect and monitor much smaller volume releases (50 L). No subsurface confining structure was used in this experiment; hence, the DNAPL impacted zone was subjected to the natural groundwater flow regime. This condition allowed us to geophysically monitor the DNAPL mass loss over a 66 month period. Reflectivity variations on the GPR profiles were used to infer the presence and evolution of the solvent layers. GPR imaging found significant reflectivity increases due to solvent layer formation during the two week period immediately after the release. These results demonstrated the capacity of GPR profiling for the detection and monitoring of lesser volume DNAPL releases that are more representative of small-scale industrial spills. The GPR imaged solvent layers subsequently reduced in both areal extent and reflectivity after 29 months and almost completely disappeared by the end of the 66 month monitoring period. Total DNAPL mass estimates based on GPR profiling data indicated that the solvent mass was reduced to 34%–36% of its maximum value after 29 months; only 4%–9% of the solvent mass remained in the study area after 66 months. These results are consistent with independent hydrogeological estimates of remaining DNAPL mass based on the downgradient monitoring of the dissolved solvent phase. Hence, we have concluded that the long-term GPR reflectivity changes of the DNAPL layers are likely the result from the dissolution of chlorinated solvents residing in those layers. The long-term monitoring results demonstrated that GPR profiling is a promising non-invasive method for use at DNAPL contaminated sites in sandy aquifers where temporal information about immiscible contaminant mass depletion due to either natural flow or remediation is needed. However, our results also indicated that the GPR signature of older DNAPL impacted zones may not differ greatly from the uncontaminated background if significant mass reduction due to dissolution has occurred.

Use of a Modified N-Expert System for Vegetable Production in the Beijing Region

A series of field experiments were conducted over a three-year period to test a modified N-Expert system (the decision support system for nitrogen recommendations) with different irrigation regimes for a rotation of amaranth (Amaranthus tricolor L.), spinach (Spinacia oleracea L.), and cauliflower (Brassica oleracea L.). Local commercial fertilizer practice based on farmer surveys was selected as the control, and irrigation treatments followed conventional practice with a balanced irrigation schedule. Some parameters, notably target yields and net mineralization rates, were modified according to local conditions, and most were referenced from the database of the N-Expert system in the first cultivation year of the rotation. Parameters were tested in earlier field experiments and were fine-tuned in later experiments. No significant yield reduction occurred below conventional nitrogen (N) practice using the recommended N treatment (N2) with different water treatments, except for irrigation treatments between 60% and 90% of PESW (plant extractable soil water: the difference between field capacity and wilting point) in 2000 and conventional irrigation practice in 2001 for cauliflower. There was a significant decrease in residual Nmin at harvest in treatments using the modified N-Expert recommendation system compared with conventional N practice. This indicates that there is considerable potential for use of the N recommendation system for sustainable vegetable production in the North China Plain.

Comparative allozyme and microsatellite population structure in a narrow endemic plant species, Centaurea corymbosa Pourret (Asteraceae).

Centaurea corymbosa Pourret (Asteraceae) is a narrow endemic species known only from six populations located in a 3-km2 area in the south of France. Earlier field experiments have suggested that pollen and seed dispersal were highly restricted within and among populations. Consistent with the field results, populations were highly differentiated for five allozyme loci and among-population variation fitted an isolation-by-distance model. In the present study, we investigated the genetic structure of C. corymbosa using six microsatellite loci. As with allozymes, microsatellites revealed no within-population structure and a large differentiation among populations. However, allozyme loci were less powerful than microsatellites in detecting the extent of gene flow assessed by assignment tests. The patterns of structuration greatly varied among loci for both types of marker; we suggest that differences in single-locus pattern could mainly be an effect of stochastic variation for allozymes and an effect of variation in mutation rate for microsatellites. In contrast to the multilocus results, the two most polymorphic microsatellite loci did not show any isolation-by-distance pattern. Our results suggest that highly variable loci might not always be the best suited markers to quantify levels of gene flow among populations.

Flexible niche partitioning via a foraging mode shift: a proposed mechanism for coexistence in stream‐dwelling charrs

Summary1. Foraging behaviour, diet and interference competition were examined for two morphologically similar charrs,Salvelinus malma(Dolly Varden) andS. leucomaenis(white‐spotted charr), under varying food resource conditions over four summers in a Japanese mountain stream. Data were used to test predictions from a mechanistic model of resource partitioning developed from an earlier field experiment.2. The charrs adopted one of two distinct foraging modes, ambushing drifting invertebrates from relatively fixed foraging positions or actively searching for benthic prey over large areas. The proportion of benthos foragers increased markedly when drifting prey declined, and was much greater inS. malmathanS. leucomaeniswhen drift was lean, upholding predictions made from our earlier experiment.3. For drift foragers of both species, frequency of foraging attempts decreased as drift rate declined, and aggressive encounters increased. In contrast, for benthos foragers of both species the frequency of foraging attempts was essentially constant across the range of benthos biomass measured, and aggressive encounters remained low.4. Salvelinus leucomaenisate larger drifting prey thanS. malma, even though the former charr were smaller. In contrast,S. malmaforaged on benthic prey at a higher rate thanS. leucomaenis, although there was no difference in prey mass. Thus, the optimal point to shift to benthic foraging is at a higher drift threshold forS. malmathanS. leucomaenis, most probably due to differences in jaw morphology. Moreover, because dominance for favourable drift foraging positions was based on size alone,S. malmashifted to benthos foraging at a larger size thanS. leucomaenis, as predicted by a simple model.5. Charr consumed distinct prey types according to their foraging mode. Drift foragers primarily ate terrestrial invertebrates, whereas benthos foragers ate mainly chironomid larvae. Consequently, diet overlap was high when drift was abundant and both species were drift foragers, but declined as drift declined andS. malmashifted to benthos foraging. Therefore, species‐specific differences in foraging mode shifts across the resource gradient explained the flexible resource partitioning we observed, and probably account for the coexistence of these congeneric charrs in zones of sympatry in northern Japan.

Growth and yield responses of Pakistan rice ( Oryza sativa L.) cultivars to O 3 and NO 2

Two separate experiments were undertaken to determine Pakistan rice ( Oryza sativa L.) cultivar responses to air pollution, and specifically to test whether O 3 was the pollutant likely to have caused the large effects of filtration on rice yield found in earlier field experiments in Pakistan. In the first experiment (Exp 1), cv. IRRI-6 was exposed to ozone (O 3) at a mean concentration of 43 nl l −1 (8 h day −1) for 133 days until final harvest, covering both the vegetative and reproductive stages of growth. Results showed a significant reduction in total grain weight per plant. In the second experiment (Exp 2), fumigation of two rice cultivars with O 3 at 40−42 nl l −1 (8 h day −1) and nitrogen dioxide (NO 2) at 21–23 nl l −1 (24 h day −1), both singly and in combination, was carried out for 42 days during the vegetative stage of growth to determine if the presence of low concentrations of NO 2 might influence the responses of both cultivars to O 3. Results showed O 3 to be more phytotoxic than NO 2 at the concentrations used. No significant O 3×NO 2 interactions were found at the time of harvest, but O 3 significantly reduced the photosynthetic capacity and biomass of both cultivars. Results of both experiments are compared with those reported for an open-top chamber filtration experiment carried out in Pakistan using the same two rice cultivars. Grain yield of cv. IRRI-6 was decreased in the closed chamber experiment by 57%, compared to a 37% decrease in the open-top chamber experiment; different yield components were affected in the open-top and closed chamber experiments which may be the result of differences in environmental conditions between the two studies. The results suggest that O 3 may have significant effects on rice yield in Pakistan and indicate that Pakistan rice cultivars have a high sensitivity to O 3.

Varietal differences in perennial ryegrass for nitrogen use efficiency in leaf growth following defoliation: performance in flowing solution culture and its relationship to yield under simulated grazing in the field

Varietal differences in rates of NO3 uptake and remobilization of nitrogen (N) during a cycle of severe defoliation and regrowth were assessed in perennial ryegrass (Lolium perenne L.) varieties Ba11778, Aberelan, Talbot and Gator. Plants were grown in flowing solution culture for 34 days, prior to a 30 d treatment period, including 21 d of regrowth. Net uptake of NO3 was measured continuously from solutions maintained automatically at 10 mmol m-3NO3.15 N-labelled NO3 3 was supplied to the plants in situ for either 21 h immediately prior to defoliation, or for 7-11 days afterwards, to measure remobilization of N from roots and stubble into the regrowing leaves. The four varieties differed only slightly in total dry matter production over 30 d, but varied substantially in post-defoliation specific growth rate by the leaf fraction. Gator was the lowest ( 0.11 g g-1 d-1), Ba11778 the highest ( 0.15 g g-1 d-1) and Aberelan and Talbot intermediate in leaf regrowth rate. Varieties did not vary significantly in shoot: root dry weight ratio, but the rate of NO3 uptake per unit of leaf fresh weight during regrowth was 27% lower in Ba11778 than in Gator. Leaves of Ba11778 and Aberelan had a lower organic N concentration in the dry matter at the end of the regrowth period than Talbot, which, in turn, had a lower concentration than Gator. Varieties differed in amount of leaf dry matter produced per unit of N absorbed by the plants after defoliation, the values (g g-1 N) being Ba11778 (22.6 ), Aberelan (20.7), Talbot (18.3) and Gator (16.7). More N was remobilized from the roots than from the stubble after defoliation. There were no significant differences among varieties in the amount and rate of N remobilization following defoliation. In earlier field experiments employing frequent cutting to simulate grazing, Ba11778 and Aberelan yielded at least 10% more dry matter annually than Talbot which, in turn, outyielded the amenity variety Gator by a similar amount. Thus the present results are consistent with the hypothesis that the efficiency of N use in leaf growth is an important factor determining genetic variation in productivity under frequent defoliation in the field when the herbage produced consists primarily of leaf.

Estimates of area-averaged turbulent energy fluxes in a convectively driven boundary layer using aircraft measurements

During the field campaign of EFEDA II several aircraft measurements were performed in order to evaluate area mean values of turbulent energy fluxes over a relatively flat terrain in a desertification threatened area in Spain. Since earlier field experiments indicated differences between airborne measurements and surface observations, we tried to close the gap by carefully analysing the turbulence measurements. In order to evaluate the influence of the temporal variation of the convective boundary layer, the rise of the inversion, derived from simultaneously performed radiosonde ascents, was taken into account. By estimating the linear approximated fields of the meteorological parameters, it was possible to calculate the mean values of these quantities as well as the temporal and spatial derivatives, which are necessary for the evaluation of the advective terms of the energy budget. In this way is possible to examine the terms of the conservation equations in a supplementary way.

How Trichogramma parasitoids use moth sex pheromones as kairomones: orientation behaviour in a wind tunnel

Abstract The orientation behaviour of Trichogramma egg parasitoids (T.evanescens Westwood and T.pretiosum Riley) in response to the sex pheromone of their noctuid hosts {Mamestra brassicae L. and Heliothis tea (Boddie)) was investigated in a wind tunnel. Wasps were released on platforms which served as models of leaves, and were exposed to overhead light and an air stream that was either clean or loaded with host sex pheromone. The wasps exhibited: upwind anemotaxis, which was not affected by odour; odour‐modulated positive phototaxis; and odour‐induced inverse orthokinesis. Compared with clean air, residence times, walking times and path lengths on a platform were higher in pheromone‐loaded air than in clean air. In pheromone‐loaded air, walking velocity was reduced. During locomotion on a horizontal platform, net movement was upwind, regardless of the presence or absence of pheromone in the air. On a platform inclined at 45o, anemotaxis appeared offset by positive phototaxis. If wasps were released on top of a glass rod above a platform, host sex pheromone caused wasps to land shortly after take‐off. These results are used to explain higher rates of parasitism of moth eggs in pheromone‐treated plots in earlier field experiments.

Laboratory studies of radar sea spikes at low grazing angles

We report on measurements of low grazing angle radar sea spikes in a laboratory wave tank. Using an X band radar with 10‐cm range resolution and multiple‐range bin capability, the sea spikes were observed to have a horizontal/vertical polarization ratio much larger than unity. This is similar to observations in earlier field experiments, but is in contrast to a ratio of unity recently observed for moderate grazing angles (Jessup et al., 1990). Our experiment was designed to validate the low grazing field results and to establish design criteria for spatial‐temporal measurement instrumentation; single‐point measurements currently used as surface truth cannot provide water surface profiles needed for modeling of radar scatter from deterministic surface features. Surface scattering features were generated using a paddle‐generated wave, combined with wind waves for a series of wind speeds. The surface feature responsible for the sea spike echo was visually identified as a short wave crest, occurring on the windward side of the paddle wave, driven to extreme steepness by the passage of the faster paddle wave crest. Long decorrelation times observed in the field are also seen in these studies, of the order of 500 ms for horizontal polarization and less than 5 ms for vertical. We suggest that rather than Bragg scatter, the occurrence of similar ubiquitous features on the ocean are responsible for horizontally polarized low grazing angle sea scatter at the X band for low to moderate winds, and perhaps at other frequencies as well.

Forage tree legumes. II. Investigation of nitrogen transfer to an associated grass using a split-root technique

In an earlier field experiment in this series, we found no significant transfer of N between Leucaena or Gliricidia and Panicum maximum. The glasshouse study reported here employed a split-root technique, whereby trees of leucaena and gliricidia were grown in boxes with 15N fed to one half of the root system and the transfer of N to the other half of the box was measured by sampling tree and planted grass. Detection of l5N in the grass tops and roots from the unlabelled half of the box was used to indicate N transfer from the tree roots to the grass. Transfer of labelled N to the grass amounted to 4.1% in the first 6 week period when 15N was being injected into the tree root zone. A harvest of the tree and grass was made at 6 weeks and both allowed to regrow for a further 6 weeks with no further addition of l5N. Over the entire 12 week experimental period 7.6% of the labelled N from the tree was transferred to the grass. The low proportion of N transferred from tree legume to the grass in this experiment, where herbage was cut and removed, is similar to the findings in the earlier field experiment and indicates that, in such a system, little direct beneficial effect of N fixation would be expected in an understorey grass or food crop.

The Impact of Contingent Reinforcement on Retail Salespersons' Performance Behaviors:

This study systematically replicates an earlier field experiment (Luthans, Paul & Baker, 1981) that found a contingent reinforcement intervention having a positive impact on functional and dysfunctional performance behaviors of salespersons in a large department store, but no reversal when there was a return to baseline conditions. By using tighter controls in the field setting, the present study found generally similar results during the intervention but, importantly, also found a reversal to occur during the post intervention phase. Implications the results have for behavioral management of salespersons' performance are discussed.

Physiological Correlates of Demographic Patterns in Three Sympatric Namib Desert Rodents

Water metabolism in three sympatric Namib Desert rodents (Gerbillurus paeba, Desmodillus auricularis, and Rhabdomys pumilio) was measured using a complete water-balance methodology, with the objective of relating physiological characteristics to population-level properties in these species. Desmodillus auricularis was found to be capable of maintaining water balance on a diet of considerably lower water content than that needed by the other two species. Physiological differences among these species are correlated with differences in (a) their reproductive response to the provision of drinking water in an earlier field experiment; (b) the seasonality of their demographic patterns; and (c) particular features of their life histories. An argument is presented that the water-conserving abilities of these species are intimately related to population processes: G. paeba and R. pumilio, with relatively high water needs, are restricted to breeding during brief periods of high water availability, and their lifehis...

Splash and discontinuous runoff as creators of fine sandy lag deposits with kalahari sands

Earlier field experiments have shown that the sandy dome-shaped hills south of Kinshasa are denuded by the combined action of splash and discontinous runoff. The sandy cover of a typical hill becomes progressively finer downhill where the slope is steeper. Laboratory experiments on similar sands demonstrate that splash has a preference for the coarse modal fraction. Simulated disturbed rough laminar runoff exports slightly coarser sands than does splash, even over gentle slopes where the regime is subcritical. But splash leaves the grains over 0.6 mm while discontinuous run-off selects even these for rapid transportation. Study of the transportation rates of both mechanisms conclusively demonstrates that splash creates a coarse lag on the summital sections of the Amba hill but that discontinuous runoff leaves a progressively finer residue, which is being transported, as the slope becomes steeper. Silt is also protected from erosion but it is not known to what extent the creation of a filtration pavement is responsible for this. The critical grain-size limit, below which the relative concentration increased, is 0.215 mm, both in the field and in the laboratory. This critical limit is some-what finer than the median grain-size of the Kalahari sands covering the hilltops and also of the fabricated bimodal sands.

Automobile-Speed Estimation Using Movie-film Simulation

A silent movie film made by shooting through the windscreen of a car driven at different constant speeds was shown in an auditorium, and subjects asked to estimate the speed of the car. Of the 70 subjects who participated, 35 sat at the front and the remainder at the back. The speed estimates of those seated at the back were, on average, some 11 per cent higher than those at the front. An explanation for this effect is given. It is shown that those at the correct perspective distance from the screen ( in the present case, those at the front) will receive an impression of speed which most closely resembles the actual speed of the car. The speed estimates from the front of the auditorium most closely resembled those observed in an earlier field experiment when the subjects' hearing was diminished. It is concluded that the movie technique provides a good simulation of the task in the field experiment if the following two qualifications are made. First, the movie must be viewed from close to the correct perspective distance. Second, a silent movie corresponds to the real situation in which the observer is prevented from hearing.