Consequences of floral visits by ants and invasive honeybees to the hummingbird‐pollinated,Caribbean cactus Melocactus intortus

The pink, tubular, nectariferous flowers of Melocactus intortus (Cactaceae) in Puerto Rico are visited by native hummingbirds (Anthracothorax dominicus), but also by invasive honeybees (Apis mellifera) and ants (Solenopsis sp.). We sought to determine if the bees and ants significantly alter the pollination of M. intortus by measuring pollinator effectiveness. Using traditional estimates of effectiveness (visitation rate and seed set), our results show that hummingbirds were the most effective pollinators as expected. Bees and ants were less effective, and their contributions were one‐fourth to one‐tenth of that observed for hummingbirds. We then modified this measure of effectiveness by adding two components, fitness of progeny and temporal availability of visitors, both of which refine estimates of flower visitor effectiveness. With these new estimations, we found that the effectiveness values of all three animal visitors decreased; however, the role of hummingbirds as the principal pollinator was maintained, whereas the effectiveness values of bees and ants approached zero. By these new measures of overall pollinator effectiveness, the invasive honeybees and ants have little effect on the reproductive success of M. intortus.     

Factors influencing seasonal and monthly changes in the group size of chital or axis deer in southern India

Chital or axis deer (Axis axis) form fluid groups that change in size temporally and in relation to habitat. Predictions of hypotheses relating animal density, rainfall, habitat structure, and breeding seasonality, to changes in chital group size were assessed simultaneously using multiple regression models of monthly data collected over a 2 yr period in Guindy National Park, in southern India. Over 2,700 detections of chital groups were made during four seasons in three habitats (forest, scrubland and grassland). In scrubland and grassland, chital group size was positively related to animal density, which increased with rainfall. This suggests that in these habitats, chital density increases in relation to food availability, and group sizes increase due to higher encounter rate and fusion of groups. The density of chital in forest was inversely related to rainfall, but positively to the number of fruiting tree species and availability of fallen litter, their forage in this habitat. There was little change in mean group size in the forest, although chital density more than doubled during the dry season and summer. Dispersion of food items or the closed nature of the forest may preclude formation of larger groups. At low densities, group sizes in all three habitats were similar. Group sizes increased with chital density in scrubland and grassland, but more rapidly in the latter—leading to a positive relationship between openness and mean group size at higher densities. It is not clear, however, that this relationship is solely because of the influence of habitat structure. The rutting index (monthly percentage of adult males in hard antler) was positively related to mean group size in forest and scrubland, probably reflecting the increase in group size due to solitary males joining with females during the rut. The fission-fusion system of group formation in chital is thus interactively influenced by several factors. Aspects that need further study, such as interannual variability, are highlighted.     

Rhizobium meliloti inoculation of alfalfa selected for tolerance to acid,aluminum-rich soils

Alfalfa (Medicago sativa L.) growth and nodulation in acid soil is reduced because the plant and its bacterial symbiontRhizobium meliloti cannot tolerate acid, aluminum-rich soil. A study was conducted to determine if a relatively acid-tolerant alfalfa germplasm combined with a relatively acid-tolerantR. meliloti strain could overcome these limitations. In a light room study, an acid-tolerant alfalfa germplasm inoculated with a more acid-tolerantR. meliloti strain produced greater top growth, nodule number and weight, and acetylene reduction values in an unlimed soil (pH 4.6) than the same germplasm inoculated with a relatively acid-sensitiveR. meliloti strain or an acid-sensitive germplasm inoculated with either a relatively acid-tolerant or acid-sensitiveR. meliloti strain.     

Production ofBeauveria bassiana [Deuteromycotina: Hyphomycetes] in different liquid media and subsequent conidiation of dry mycelium

Mycelium ofBeauveria bassiana can be grown in liquid culture, filtered, and the mycelium dried. After rehydration the mycelium sporulates. Two carbohydrate sources (sucrose and maltose), and one nitrogen/vitamin source (yeast extract) were tested for mycelium growth and subsequent conidial production. Maximum mycelium growth (12.31 mg/ml), in liquid culture, was in the sucrose (3.5%)/yeast extract (3.5%) medium, but mycelium from a maltose (2%)/yeast extract (0.75%) medium produced the maximum of 4.62×10⁶ conidia/mg dry mycelium after incubation in moist Petri dishes. Using the data on mycelium yield (in liquid culture) and conidial production (by dry mycelium) it is calculated that the sucrose (3.5%)/yeast extract (3.5%) and the maltose (2%)/yeast extract (0.75%) media produce most conidia per media volume (an equivalent of 3.52–3.72×10⁷ conidia/ml).      

Specific photoperiodic stimulation of dry matter production in a high-latitude cultivar of Poa pratensis

Vegetative plants of Poa pratensis L. cv. Holt (origin 69°N) raised in short days gave large and significant increases in plant dry weight, plant height and leaf area upon exposure to continuous light, compared with 8-h short days, at essentially identical daily inputs of radiant energy (8-h summer daylight ± low intensity extension). For example, by the fourth harvest (after 26, 34 and 46 days at 21, 15 and 9°C, respectively), the dry weights of plants in long days were 81, 163 and 195% greater than those of the corresponding short-day controls at the respective temperatures. Plant leaf areas in long days were between two and four times as large as control values by the end of the experiment. This was mainly due to increased leaf length caused by long-day stimulation of cell extension and division. However, the photoperiod did not affect the partitioning of assimilates amongst leaves, culms and stolons. Most of these effects could also be brought about by exogenous gibberellin application to plants in short days. However, in contrast to the effect of long days, gibberellin treatment also induced stem internode elongation even in these vegetative plants. Examination by standard growth analysis procedures revealed that the observed increases in relative growth rate were due primarily to increased net assimilation rate followed, several days later, by increases in leaf area ratio when newly-emerged leaves began to constitute a significant proportion of the leaf area. It is concluded that these reactions are of great adaptive significance for growth at the marginal temperatures prevailing at high latitudes.     

Three-year measurement of methane emission from an Indonesian paddy field

Yearly and seasonal (rainy and dry seasons) variations of CH₄ emission from a Sumatra paddy field were measured for 3 years. The mean CH₄ emission rates during the growth period were in the range of 16.0–26.1 mg CH₄ m^-2 h^-1 for the chemical fertilizer plots and 23.3–34.9 mg CH₄ m^-2 h^-1 for the plots with rice straw application, respectively. The increase in the amounts of CH₄ emission by rice straw application were from 1.3 to 1.6 times. There was no significant difference in the mean CH₄ emission rates between rainy and dry seasons.Total amounts of CH₄ emitted during the period of rice growth were in the ranges of 29.5–48.2 and 43.0–64.6 g CH₄ m^-2 for the plots applied with chemical fertilizer and those with rice straw application, respectively. Nearly the same amounts of CH₄ were emitted in the first and second half of the growth period, irrespective of rice straw application.     

Effect of bicarbonate and root zone temperature on uptake of Zn,Fe, Mn and Cu by different rice cultivars (Oryza sativa L.) grown in calcareous soil

Pot experiments were conducted with a calcareous soil (Inceptisol) to elucidate the effects of bicarbonate (0 and 20 mM) and root zone temperature (15° and 25°C) on the uptake of Zn, Fe, Mn and Cu by "Zn-efficient" and "Zn-inefficient" rice cultivars. Bicarbonate decreased concentrations and total uptake of Zn in shoots of "Zn-inefficient" cultivars, especially of IR 26 at 25°C, but not in Zn-efficient cultivars. Bicarbonate decreased concentrations and uptake of Fe in shoots of Zn inefficient cultivars, particularly in IR 26. Concentrations and total uptake of Mn were lower in bicarbonate treatment in the Zn-inefficient cultivars at 15°C, and in all cultivars at 25°C. However, concentration and uptake of Cu were not affected by bicarbonate in all cultivars. Compared to the 25°C root zone temperature, the concentrations and total uptake of both Zn and Cu in shoots at 15°C were lower in Zn-inefficient than in the Zn-efficient cultivars. The results indicate that Zn-efficiency in rice is causally related to high tolerance of plant to elavated bicarbonate concentrations in soil solution.