Observations on the production and dispersal of spores, and infection by Rhynchosporium secalis

The numbers of spores of Rhynchosporium secalis washed from samples of barley plants taken weekly, varied markedly. No consistent association with amount of previous rainfall or length of the preceding dry period was detected. On potted seedlings exposed within a crop most infection occurred during long rain periods or when rain fell late in the evening; fewest lesions usually developed on seedlings prevented from touching adjacent plants. Rotorod traps fitted with a 13 mm diameter disc at the apex of each arm were operated under 24 cm diameter covers. Spores were collected on circular cover slips fixed to each disc with glycerine jelly. At all stages of crop growth more spores were trapped at ground level than at other heights tested up to 1 m. The number of spores trapped was not related to the quantity of or duration of rainfall but was related to the mean rate of fall during brief showers only. Efficiency of droplet retention was assessed in a wind tunnel. It declined rapidly when more than c. 5 pl was presented to the disc surface and was less at a wind speed of 1.0 than 0.5 m s-^l. Spore distribution on discs indicated that spores were washed from the surface during long rain periods.     

Ficus seed shadows in a Bornean rain forest

Due to their copious seed production and numerous dispersers, rain forest fig trees have been assumed to produce extensive and dense seed shadows. To test this idea, patterns of seed dispersal of two species of large hemiepiphytic fig tree were measured in a Bornean rain forest. The sample included four Ficus stupenda and three F. subtecta trees with crop sizes ranging from 2,000 to 40,000 figs (400,000 to 13,000,000 seeds). Seed rain out to a distance of 60 m from each study tree was quantified using arrays of seed traps deployed in the understory. These trees showed a strongly leptokurtic pattern of dispersal, as expected, but all individuals had measurable seed rain at 60 m, ranging from 0.2 to 5.0 seeds/m². A regression of In-transformed seed rain density against distance gave a significant fit to all seven trees' dispersal patterns, indicating that the data could be fitted to the negative exponential distribution most commonly fitted to seed shadows. However, for six of seven trees, an improved fit was obtained for regressions in which distance was also In-transformed. This transformation corresponds to an inverse power distribution, indicating that for vertebrate-dispersed Ficus seeds, the tail of the seed rain distribution does not drop off as rapidly as in the exponential distribution typically associated with wind dispersed seed shadows. Over 50% of the seed crop was estimated to fall below each fig tree's crown. Up to 22% of the seed crop was dispersed beyond the crown edge, but within 60 m of the tree. Estimates of the maximum numbers of seeds which could have been transported beyond 60 m were 45% for the two largest crops of figs, but were under 24% for the trees with smaller crops. Seed traps positioned where they had an upper canopy layer above them were associated with higher probabilities of being hit by seeds, suggesting that vertebrate dispersal agents are likely to perch or travel through forest layers at the same level as the fig crown and could concentrate seeds in such areas to some degree. The probability of a safe site at 60 m from the fig tree being hit by seeds is calculated to be on the order of 0.01 per fruiting episode. Fig trees do not appear to saturate safe sites with seeds despite their large seed crops. If we in addition consider the rarity of quality establishment sites and post-dispersal factors reducing successful seedling establishment, hemiepiphytic fig trees appear to face severe obstacles to seedling recruitment.     

Departure of migrating European robins, Erithacus rubecula, from a stopover site in relation to wind and rain

Migratory birds replenishing their fuel stores have to decide when to leave their stopover site for the next flight bout. We studied whether the decision to leave a stopover site depends on wind and rain conditions. From capture-recapture data of 1153 European robins collected during three autumns at a stopover site in Switzerland, we estimated the daily emigration probability with a newly developed multistate capture-recapture model that accounts for the occurrence of transients. We tested whether the variation in the daily emigration probabilities can be explained by wind speed, wind direction (both on the ground and 300 m above ground) or rain. Variation in emigration probability was largely explained by variation in wind at 300 m and rain. The emigration probability was highest (0.5) during nights with no or weak (<1.5 m/s) winds at 300 m and no rain, intermediate (0.15-0.2) on nights without rain and with medium wind (>1.5 m/s), and on nights with weak winds (<1.5 m/s) and rain; and almost zero during nights with rain and strong winds at 300 m. Wind direction at 300 m and wind conditions (speed and direction) on the ground had no influence on departure decision. We suggest that birds may consider cues other than wind speed at ground level to predict wind speed at higher altitudes, and that they consider wind direction only when aloft by selecting an optimal flight altitude. Wind speed aloft and rain appeared to be significant factors that synchronize bird migration spatially and temporally.     

Interannual and seasonal variations of energy and water vapor fluxes above a tropical seasonal rain forest in Xishuangbanna, SW China

The values and variation characteristics of energy components, their relationship with net radiation and the characteristics of water balance in the forest were analyzed, based on the observation data of energy fluxes, meteorological parameters and biomass in a tropical seasonal rain forest in Xishuangbanna from January 2003 to December 2004. The results show that annual net radiation was 3516.4 MJ/(m² · a) and 3516.6 MJ/(m² · a) in 2003 and 2004, respectively, of which 46% and 44% were used in latent heat flux, and 12% and 11% were lost as sensible heat flux. Annual mean canopy surface conductance was 10.3 mm/s and 10.0 mm/s in 2003 and 2004, respectively. Moreover, canopy surface conductance was lower in dry-hot seasons than in fog-cool and rainy seasons. Canopy surface conductance correlated significantly and positively with leaf area index, but negatively with water vapor pressure deficit. In general, canopy surface conductance was not affected directly by soil water content, but highly depended on soil moisture status when soil water content was below 0.15 m³/m³. Annual total evapotranspiration of this forest ecosystem in dry seasons was lower than that in rainy seasons, which was considered as one of the most important reasons that tropical seasonal rain forest could survive and flourish in Xishuangbanna at limit of water and heat.     

Seed rain and its relationship with above-ground vegetation of degraded Kobresia meadows

Seed rain is a crucial element in vegetation regeneration, but has been rarely studied in high altitude regions, particularly degraded Kobresia meadow. Weed infestation is a distinctive feature of pasture degradation in Kobresia meadows on the Tibetan plateau, the ecological mechanism of which is closely related with vegetation’s seed rain. In this paper we assess the effect of vegetation degradation on seed rain and consider its implication for restoration of degraded Kobresia meadows in the headwater area of Yellow river, through analysis of seed species composition, number of seeds landing per m² of soil surface, and their relationship with above ground vegetation. Vegetation degradation had an impact on the species composition and numbers of seeds in seed rain and their relationship with above-ground vegetation. Within the un-degraded meadow, which provided a closed vegetation cover, 35 % of the seed rain was of sedge and gramineae species. However, within the degraded meadows, as the extent of degradation increased, so the total number of seeds m^?2 increased, with those derived from sedge and gramineae species forming a declining proportion of the total. Degradation of Kobresia meadow on the Tibetan plateau is exacerbated by the seed input of weed species (such as Oxytropis ochrocephala, Carum carvi, Aconitum pendulum, Pedicularis kansuensis in this study). Therefore, a major priority for the restoration of such degraded meadows should be the elimination of these weeds from the above ground vegetation by human intervention.     

Interannual and seasonal variations of energy and water vapor fluxes above a tropical seasonal rain forest in Xishuangbanna, SW China

The values and variation characteristics of energy components, their relationship with net radiation and the characteristics of water balance in the forest were analyzed, based on the observation data of energy fluxes, meteorological parameters and biomass in a tropical seasonal rain forest in Xishuangbanna from January 2003 to December 2004. The results show that annual net radiation was 3516.4 MJ/(m² · a) and 3516.6 MJ/(m² · a) in 2003 and 2004, respectively, of which 46% and 44% were used in latent heat flux, and 12% and 11% were lost as sensible heat flux. Annual mean canopy surface conductance was 10.3 mm/s and 10.0 mm/s in 2003 and 2004, respectively. Moreover, canopy surface conductance was lower in dry-hot seasons than in fog-cool and rainy seasons. Canopy surface conductance correlated significantly and positively with leaf area index, but negatively with water vapor pressure deficit. In general, canopy surface conductance was not affected directly by soil water content, but highly depended on soil moisture status when soil water content was below 0.15 m³/m³. Annual total evapotranspiration of this forest ecosystem in dry seasons was lower than that in rainy seasons, which was considered as one of the most important reasons that tropical seasonal rain forest could survive and flourish in Xishuangbanna at limit of water and heat.     

Dispersal of Rhynchosporium secalis conidia from infected barley leaves or straw by simulated rain

Simulated rain (mean drop diameter c. 1 or 3 mm) was allowed to fall for 10 – 15 min on to barley leaves or straw infected by Rhynchosporium secalis (leaf blotch). The leaves were supported on a mesh through which run-off water drained and the straw was supported on a rigid surface on which run-off water collected. The numbers of R. secalis conidia and spore-carrying splash droplets collected by horizontal samplers (microscope slides and pieces of photographic film) decreased rapidly with increasing distance from and increasing height above the sources, with half-distances of 2 – 10 cm. Less than 10% of the spores or droplets reached heights of more than 30 cm. Incident drops 3 mm in diameter produced more spore-carrying droplets and dispersed more conidia than did 1 mm drops. The size category of splash droplets with the greatest proportion of the spore-carrying droplets dispersed by 3 mm drops was 200 – 400 μm, whether the source was infected barley leaves or barley straw. For leaves or straw the greatest proportions of spores were carried in droplets > 1000 μm in diameter. The mean diameter of spore-carrying droplets (478 μm) dispersed from free-draining leaves was less than that of droplets from straw plus run-off water (563 μm). However, the leaf source had more spores cm^-2 and the mean number of spores per droplet was greater (113 as opposed to 6·8) than for the straw source.     

Visual detection of wind-drift by high-flying insects at night: a laboratory study

Summary Locusta migratoria were tethered on a yaw-torque balance and flown in a wind tunnel of diamond-shaped cross-section. Slowly moving stripes of very low luminance were projected onto the two lower faces of the tunnel and a turning stimulus was generated by reversing the direction of stripe movement on one face relative to the other. It was found that the lower the pattern speed, the higher the luminance required to maintain a torque response. When our results were plotted together with optomotor thresholds taken or inferred from the data of other workers, a threshold curve extending over a luminance range from 10^–8 to 1 Lamberts (1 Lambert (L) = 3183 cd/m²), and a pattern speed range from 10^–2 to 1 °/s² °/s could be constructed. An implication of this threshold curve is thatLocusta flying in bright moonlight and as high as 2000 m could, in principle, detect the drift induced by a cross-wind of only 2.5 m/s. However, in the absence of the moon, this sensitivity to drift would be much reduced and it seems to be inadequate to explain some cases of down-wind orientation that have been observed by radar on moonless nights.     

海岸抗风植物黑松对净风和风沙流的生理响应

利用野外便携式风洞仪对盆栽黑松（Pinus thunbergii Parl）幼株在不同风速（6、9、12、15、18 m/s）、不同风沙流强度（0、1.00、28.30、63.28、111.82、172.93 g cm^-1 min^-1）、不同时间（10、20、30、40、50 min）进行了净风和风沙流吹袭,通过测定其叶片相对含水量（Relative water content,RWC）、丙二醛（Malondialdehyde,MDA）、可溶性糖、脯氨酸含量,及超氧化物歧化酶（superoxide dismutase,SOD）、过氧化氢酶（Catalase,CAT）、过氧化物酶（Peroxidase,POD）活力等变化规律以揭示黑松抗风沙流生长的生理适应机制。结果表明,在净风吹袭下,随着风速提高至15 m/s,黑松叶片RWC相对稳定,MDA含量和细胞膜透性小幅增加且较低,而脯氨酸含量下降17.5%。同时叶片SOD、CAT、POD活力也小幅增加。在风沙流吹袭下,随着风沙流风速提高至15 m/s,黑松在短时低风速吹袭时叶片RWC就开始下降（4.4%）,叶片平均MDA含量、细胞膜透性分别较对照增加61.3%、25.6%,脯氨酸含量增加8.9%,叶片SOD、CAT、POD活力分别较对照增加21.5%、30.4%、13.9%。同风速吹袭下,风沙流处理组叶片抗逆生理指标均高于净风处理。如15 m/s风速下,风沙流处理组叶片平均MDA、脯氨酸、可溶性糖含量分别较净风处理组高4.7%、36.6%、22.1%,SOD和CAT活力较净风处理组高21.5%、36.5%。在高风速（18 m/s）净风和风沙流吹袭中,随着风吹时间延长（50 min）,叶片MDA、脯氨酸、可溶性糖含量和SOD、CAT、POD活力均下降。研究表明,风吹袭中黑松叶片较高抗脱水力与其抗风性相关。风沙流引发的叶片失水可能是黑松抗逆生理变化的诱因。风吹袭下叶片失水能快速促使脯氨酸的积累和维持可溶性糖含量,以维护细胞中水分平衡。同时,叶片失水又快速激活抗氧化保护酶系统来防御和清除氧自由基、抑制膜脂过氧化维护细胞膜的完整性使黑松在风沙流吹袭中生存。黑松较强的渗透调节能力和抗氧化防御系统在其适应风沙流吹袭中起重要的生理调控作用。     

Lactose-H(OH) transport system of Escherichia coli Multistate gated pore model based on half-sites stoichiometry for high-affinity substrate binding in a symmetrical dimer

A model is proposed for the d-galactoside-H⁺(⁻OH) transporter of Escherichia coli that accounts for essentially all the experimental observations established for this system to date. In this model, the functional unit is postulated to be a dimer (consisting of two copies of lacY-specified polypeptide) which spans the membrane with a 2-fold symmetry axis in the membrane plane (Lancaster, J.R. (1978) J. Theor. Biol. 75, 35–50). The functional dimer is assumed to possess a single pore flanked by an inner gate (g_i) and an outer gate (g_o) and encompassing two oppositely oriented galactoside binding sites, designated m and μ. When g_o is open and g_i is closed under non-energized conditions, binding site m adopts a configuration defined as State A (i.e., m_o^A) exhibiting high affinity toward Class G^a galactosides (thiodigalactoside, melibiose, α-p-nitrophenylgalactoside) but low affinity for Class G^b galactosides (lactose, β-o-nitrophenylgalactoside, β-isopropylthiogalactoside), whereas binding site μ adopts State B (i.e., μ_o^B) displaying relatively high affinity toward Class G^b galactosides but comparatively low affinity for Class G^a galactosides; further, each m_o^A : μ_o^B dimer contains one thiol group whose reaction with N-ethylmaleimide inactivates the transporter unless blocked by galactoside binding at site m_o^A, while the second homologous thiol of the dimer is unreactive toward thiol reagents. Translocation of the m_o^A : μ_o^B dimer involves closing of g_o followed by opening of g_i, and causes the two thiols (as well as sites m and μ) to interchange roles in a symmetrical fashion: m_o^A : μ_o^B ↔ m_i^B : μ_i^A. In the presence of a substantial (negative) transmembrane Δμ~_H⁺, the m : μ dimer is postulated to undergo an electrogenic protein conformational change to a second form, ^*(m : μ), in which both sites m and μ possess low affinity toward internal Class G^b substrates; galactoside transport in both m : μ and ^*(m : μ) is assumed to be coupled to H⁺-symport (⁻OH-antiport) with a stoichiometry of approximately 1 : 1. Finally, five characteristic predictions of the half-sites model are outlined for further tests of its validity.     

Dispersal of Septoria nodorum Pycnidiospores by Simulated Rain and Wind

The influence of wind on the splash dispersal of Septoria nodorum pycnidiospores was studied in a raintower/wind tunnel complex with single drops or simulated rain falling on spore suspensions or infected stubble with windspeeds of 1.5 to 4 m/sec. When single drops fell on spore suspensions (depth 0.5 mm, concentration 7.8 × 10⁵ spores/ml) most of the spore-carrying droplets collected on fixed photographic film between 0–4 m downwind (windspeed 3 m/sec) were >200 μm in diameter. However, most spores were carried in droplets with diameter > 1000 μm, 70 % of which carried more than 100 spores. When simulated rain fell on infected stubble most of the spore-carrying droplets collected beyond 1 m downwind (windspeeds 1.4 and 4 m/sec) were <200 μm in diameter and none were >600 μm; most of these droplets carried only one spore. The distribution of splash droplets (with diameter >100 μm) deposited on chromatography paper showed a maximum at 40–50 cm upwind of the target but many more droplets were deposited 20–30 cm downwind, when single drops fell on a spore suspension (concentration 1.2 × 10⁵ spores/ ml) containing fluorescein dye with a windspeed of 2 m/sec; droplets were collected up to 3 m downwind but not more than 70 cm upwind. With a windspeed of 3 m/sec, numbers of sporecarrying droplets and spores collected on film decreased with increasing distance downwind; most were collected within 2 m of the target but some were found up to 4 m. When simulated rain fell on infected stubble, increasing the windspeed from 1.5 to 4 m/sec greatly increased the number of spores deposited more than 1 m downwind. At 1.5 m/sec none were collected beyond 2 m downwind, whereas at 4 m/sec some were collected at 4 m. A few air-borne S. nodorum spores were collected by suction samplers at a height of 40 cm at distances up to 10 m downwind of a target spore suspension on which simulated rain fell.     

Spore rain in relation to regional sources and beyond

While patterns of spore dispersal from single sources at short distances are fairly well known, information about ‘spore rain’ from numerous sources and at larger spatial scales is generally lacking. In this study, I sampled spore rain using a novel method consisting of 0.25–0.5 m² cotton cloth traps at nine sites in the boreo‐nemoral vegetation zone in eastern Sweden during two seasons, using Sphagnum spores as a model. Traps were located in various landscapes (mainland, islands). Additional trapping was done in an arctic area (Svalbard) without spore production. Spore densities were tested against distance from the nearest source and area of sources (open peatlands) within different radii around each site (5, 10, 20, 50, 100, 200, 300, 400 km). The cloth method appeared reliable when accounting for precipitation losses, retaining approximately 20–60% of the spores under the recorded amounts of precipitation. Estimated spore densities ranged from 6 million m^?2 and season within a large area source, via regional deposition of 50 000–240 000 spores m^?2, down to 1000 m^?2 at Svalbard. Spore rain for all sites was strongly related to distance from the nearest source, but when excluding samples taken within a source peatland, the amount of sources within 200 km was most important. Spores were larger at isolated island sites, indicating that a higher proportion originated from distant, humid areas. Immense amounts of Sphagnum spores are dispersed across regional distances annually in boreal areas, explaining the success of the genus to colonise nutrient poor wetlands. The detectable deposition at Svalbard indicates that about 1% of the regional spore rain has a trans‐ or intercontinental origin. The regional spore rain, originating from numerous sources in the landscape, is probably valid for most organisms with small diaspores and provides a useful insight in ecology, habitat restoration and conservation planning.     

Dispersal of large branchiopod cysts: potential movement by wind from potholes on the Colorado Plateau

Wind is suspected to be a primary dispersal mechanism for large branchiopod cysts on the Colorado Plateau. We used a wind tunnel to investigate wind velocities capable of moving pothole sediment and cysts from intact and disturbed surfaces. Material moved in the wind tunnel was trapped in filters; cysts were separated from sediment and counted. Undisturbed sediment moved at velocities as low as 5.9 m s^?1 (12.3 miles h^?1). A single all-terrain vehicle (ATV) track increased the sediment mass collected 10-fold, with particles moving at a wind velocity of only 4.2 m s^?1 (8.7 miles h^?1). Cysts were recovered from every wind tunnel trial. Measured wind velocities are representative of low-wind speeds measured near Moab, Utah. Wind can move large numbers of cysts to and from potholes on the Colorado Plateau. Our results indicate that large branchiopod cysts move across pothole basins at low-wind speeds; additional work is needed to establish velocities at which cysts move between potholes.     

Low airborne tenacity and spread of ESBL-/AmpC-producing Escherichia coli from fertilized soil by wind erosion

ESBL-/AmpC-producing Escherichia coli from organic fertilizers were previously detected on soil surfaces of arable land and might be emitted by wind erosion. To investigate this potential environmental transmission path, we exposed ESBL-/AmpC-positive chicken litter, incorporated in agricultural soils, to different wind velocities in a wind tunnel and took air samples for microbiological analysis. No data exist concerning the airborne tenacity of ESBL-/AmpC-producing E. coli. Therefore, we explored the tenacity of two ESBL/AmpC E. coli strains and E. coli K12 in aerosol chamber experiments at different environmental conditions. In the wind tunnel, ESBL/AmpC-producing E. coli were detected in none of the air samples (n = 66). Non-resistant E. coli were qualitatively detected in 40.7% of air samples taken at wind velocities exceeding 7.3 m s⁻¹. Significantly increased emission of total viable bacteria with increasing wind velocity was observed. In the aerosol chamber trials, recovery rates of airborne E. coli ranged from 0.003% to 2.8%, indicating a low airborne tenacity. Concluding, an emission of ESBL/AmpC E. coli by wind erosion in relevant concentrations appears unlikely because of the low concentration in chicken litter compared with non-resistant E. coli and their low airborne tenacity, proven in the aerosol chamber trials.     

Carbon dioxide exchange of a Russian boreal forest after disturbance by wind throw

The exchange of carbon dioxide (CO₂) between the atmosphere and a forest after disturbance by wind throw in the western Russian taiga was investigated between July and October 1998 using the eddy covariance technique. The research area was a regenerating forest (400 m × 1000 m), in which all trees of the preceding generation were uplifted during a storm in 1996. All deadwood had remained on site after the storm and had not been extracted for commercial purposes. Because of the heterogeneity of the terrain, several micrometeorological quality tests were applied. In addition to the eddy covariance measurements, carbon pools of decaying wood in a chronosequence of three different wind throw areas were analysed and the decay rate of coarse woody debris was derived. During daytime, the average CO₂ uptake flux was ?3 µmol m^?2s^?1, whereas during night‐time characterised by a well‐mixed atmosphere the rates of release were typically about 6 µmol m^?2s^?1. Suppression of turbulent fluxes was only observed under conditions with very low friction velocity (u* ≤ 0.08 ms^?1). On average, 164 mmol CO₂ m^?2d^?1 was released from the wind throw to the atmosphere, giving a total of 14.9 mol CO₂ m^?2 (180 g CO₂ m^?2) released during the 3‐month study period. The chronosequence of dead woody debris on three different wind throw areas suggested exponential decay with a decay coefficient of ?0.04 yr^?1. From the magnitude of the carbon pools and the decay rate, it is estimated that the decomposition of coarse woody debris accounted for about a third of the total ecosystem respiration at the measurement site. Hence, coarse woody debris had a long‐term influence on the net ecosystem exchange of this wind throw area. From the analysis performed in this work, a conclusion is drawn that it is necessary to include into flux networks the ecosystems that are subject to natural disturbances and that have been widely omitted into considerations of the global carbon budget. The half‐life time of about 17 years for deadwood in the wind throw suggests a fairly long storage of carbon in the ecosystem, and indicates a very different long‐term carbon budget for naturally disturbed vs. commercially managed forests.     

Structure and floristic composition of the lowland rain forest of Los Tuxtlas,Mexico

Physiognomy, structure and floristic composition of one hectare of lowland tropical rain forest was studied in detail at Los Tuxtlas, Mexico. Physiognomically, the Los Tuxtlas forest should be classified as lowland tropical high evergreen rain forest. The forest showed a closed canopy at 30–35 m. Of all woody, non-climbing species with a DBH1.0 cm 89.4% (94.5% of all individuals) were evergreen, 25.4% (59.5% of the individuals) had compound leaves, and over 80% of species (and individuals) had leaves in the notophyll and mesophyll size classes. The forest structure was characterized by a low density (2976 individuals with a DBH1.0 cm, 346 individuals with a DBH10.0 cm, per ha, excluding vines) with an average basal area (38.1 m², DBH1.0 cm, 34.9 m², DBH10.0 cm, per ha, excluding vines). This was attributed to the relative maturity of the forest on the study plot. The study plot contained 234 species (11 208 individuals with a height 0.5 m), of which 55.1% (34.8% of individuals) were trees, 9.4% (6.8%) shrubs, 3.4% (44.3%) palms, 20.1% (5.2%) vines, 6.8% (8.7%) herbs and 5.1% (0.3%) of unknown lifeform. Furthermore, 58 species of epiphytes and hemi-epiphytes were found. Diversity of trees, shrubs and palms with a DBH1.0 cm was calculated as Shannon-Wiener index (4.65), Equitability index (0.65), and Simpson index (0.10). The dominance-diversity curve showed a lognormal form, characteristic for tropical rain forest. The community structure was characterized by a relative dominance of Astrocaryum mexicanum in the understorey, Pseudolmedia oxyphyllaria in the middle storeys, and Nectandra ambigens in the canopy. Species population structures of 31 species showed three characteristic patterns, differentiated by recruitment: continuously high, discontinuously high, and continuously low recruitment. Height/diameter and crown cover/diameter diagrams suggested a very gradual shift from height growth to crown growth during tree development. Forest turnover was calculated as 138 years. Compared to other tropical rain forests the Los Tuxtlas forest had 1. similar leaf physiognomical characteristics, 2. a lower diversity, 3. a lower density, 4. an average basal area, and 5. a slow canopy turnover.     

Movement of apterous Sitobion avenae (Homoptera: Aphididae) in response to leaf disturbances caused by wind and rain

The effect of wind and rain on initiation of dispersal and subsequent distances moved by apterous Sitobion avenae was quantified in five laboratory experiments. Wind duration and type (steady and gusting), rain duration and intensity, and a combination of wind and rain were investigated. With increased duration of wind there was an increase in the average distance aphids moved. There was less movement when aphids were exposed to gentle gusting, than to steady wind or strong gusting. With increased duration of rain there was an increase in the proportion of aphids lost from plants. Under heavy rain, the proportion of aphids off the release plant, the distance moved by them and the proportion of aphids lost, was greater than for drizzle or light rain. When wind and rain were compared, rain had the greater impact on aphid dispersal. It was concluded that leaf disturbances caused by strong gusts of wind or large rain droplets are of considerable importance in the initiation of aphid dispersal, but that wetness alone is not.     

Solar heat gain in a desert rodent: unexpected increases with wind speed and implications for estimating the heat balance of free-living animals

We quantified metabolic power consumption as a function of wind speed in the presence and absence of simulated solar radiation in rock squirrels, Spermophilus variegatus, a diurnal rodent inhabiting arid regions of Mexico and the western United States. In the absence of solar radiation, metabolic rate increased 2.2-fold as wind speed increased from 0.25 to 4.0 m·s^-1. Whole-body thermal resistance declined 56% as wind speed increased over this range, indicating that body insulation in this species is much more sensitive to wind disruption than in other mammals. In the presence of 950 W·m^-2 simulated solar radiation, metabolic rate increased 2.3-fold as wind speed was elevated from 0.25 to 4.0 m·s^-1. Solar heat gain, calculated as the reduction in metabolic heat production associated with the addition of solar radiation, increased with wind speed from 1.26 mW·g^-1 at 0.25 m·s^-1 to 2.92 mW·g^-1 at 4.0 m·s^-1. This increase is opposite to theoretical expectations. Both the unexpected increase in solar heat gain at elevated wind speeds and the large-scale reduction of coat insulation suggests that assumptions often used in heat-transfer analyses of animals can produce important errors.Abbreviations absorptivity of coat to solar radiation - kinematic viscosity of air (mm²·s^-1) - reflectivity of coat to solar radiation - a r _B expected at zero wind speed (s·m^-1) - A _P projected surface area of animal on plane perpendicular to solar beam (cm²) - A _SKIN skin surface area (cm²) - b Coefficient describing change in r _B with change in square-root of wind speed (s^1.5·m^1.5) - d hair diameter (m) - d characteristic dimension of animal (m) - D _H thermal diffusivity of air (m²·s^-1) - E evaporative heat loss (W·m^-2) - I probability per unit coat depth that photon will strike hair - k constant equalling 1200 J·m^-3·°C^-1 - l _C coat depth m) - l _H hair length (m) - M metabolic rate (W·m^-2) - n density of hairs of skin (m^-2) - Q _A solar heat gain to animal (W·m^-2) - Q _I solar irradiance intercepted by animal (W·m^-2) - RQ respiratory quotient - r _A thermal resistance of boundary layer (s·m^-1) - r _B whole-body thermal resistance (s·m^-1) - r _E thermal resistance between animal surface and environment s·m^-1) - r _R radiative resistance (s·m^-1) - r _S sum of r _B and r _E at 0.25 m·s^-1 (s·m^-1) - r _T tissue thermal resistance s·m^-1) - T _AIR air temperature (°C) - T _B body temperature (°C) - T _E operative temperature of environment (°C) - T _ES standard operative temperature of environment (°C) - u wind speed (m·s^-1)     

广西靖西西南桦天然林种子雨的时空动态

以一片西南桦(Betula alnoides)天然林和一个西南桦独立单株为研究对象, 通过收集散种期内与林分或母树不同距离的种子以及测定风速和风向, 研究了西南桦群落和个体水平上种子雨的时空动态及其与风速和风向的关系。结果表明: 群落水平上, 西南桦种子散布的初始期、高峰期、消退期分别历时11天、32天和40天, 而个体水平上则为9天、25天和26天。高峰期内群落和个体水平的散种量分别占其总量的83.1%和68.7%, 而且白天的种子雨密度高于夜间; 西南桦个体白天种子雨密度最大的时段为12:00-16:00, 与此时段内风速较高有关。在个体水平上, 距离母树0-30 m范围内散落的种子占总散种量的79.6%; 而在群落水平上, 距离林缘0-45 m范围内集中了总散种量的81.2%。西南桦种子散布具有方向性, 无论个体还是群落水平上不同方向间种子雨密度差异极显著(p < 0.01), 与散种期内的主要风向有关; 而且种子雨密度与风速亦呈极显著正相关关系。研究结果将有助于揭示西南桦天然更新动态和更新机制, 亦为开展西南桦人工促进天然更新提供理论依据。     

Productivity, CO2/O2 exchange and hydraulics in outdoor open high density microalgal (Chlorella sp.) photobioreactors operated in a Middle and Southern European climate

Two variants of open photobioreactors were operated at surface-to-volume ratios up to 170 m⁻¹. The mean values for July and September obtained for photobioreactor PB-1 of 224 m² culture area (length 28 m, inclination 1.7%, thickness of algal culture layer 6 mm), operated in Třeboň (49^∘N), Czech Republic, were: net areal productivity, P _net = 23.5 and 11.1 g dry weight (DW) m⁻² d⁻¹; net photosynthetic efficiency (based on PAR – Photosynthetic Active Radiation), η = 6.48 and 5.98%. For photobioreactor PB-2 of 100 m² culture area (length 100 m, inclination 1.6%, thickness of algal culture layer 8 mm) operated in Southern Greece (Kalamata, 37^∘N) the mean values for July and October were: P _net = 32.2 and 18.1 g DW m⁻² d⁻¹, η = 5.42 and 6.07%. The growth rate of the alga was practically linear during the fed-batch cultivation regime up to high biomass densities of about 40 g DW L⁻¹, corresponding to an areal density of 240 g DW m⁻² in PB-1 and 320 g DW m⁻² in PB-2. Night biomass loss (% of the daylight productivity, P _L) caused by respiration of algal cells were: 9–14% in PB-1; 6.6–10.8% in PB-2. About 70% of supplied CO₂ was utilized by the algae for photosynthesis. The concentration of dissolved oxygen (DO) increased from about 12 mg L⁻¹ at the beginning to about 35 mg L⁻¹ at the end of the 100 m long path of suspension flow in PB-2 at noon on clear summer days. Dissipation of hydraulic energy and some parameters of turbulence in algal suspension on culture area were estimated quantitatively.