The Effects of Irradiance on Uptake and Assimilation of Nitrate by Young Barley Seedlings

The nitrogen economy of barley plants growing in a range ofirradiances from full shade (less than 0·5 W m^–2)to 119 W ^m–2 has been examined by analysing levels oftotal, organic and nitrate nitrogen, and by determining nitratereductase activity in leaf extracts. It has been confirmed thatroot growth is reduced in low irradiances which are also associatedwith a lower level of total nitrogen in the plant, and hencewith a lower uptake of nitrate. In all parts of the plant thelevel of organic nitrogen is higher in high light intensitybut nitrate-nitrogen as a proportion of the total is greatestin low irradiances. In the first leaf accumulation of free nitrateis substantially greater in low irradiances. The data indicate a higher level of nitrate assimilation inhigh irradiances and nitrate reductase activity in leaf extractsis higher in such conditions. When the first leaf is shadednitrate reductase activity falls to undetectable levels afterabout 4 days, but in the case of the second leaf, where thisis shaded, some reductase activity is always found, althoughthis is substantially less than that in unshaded conditions. It is concluded that in vitro rates of nitrate reduction mayover-estimate nitrate assimilation determined as increase inorganic nitrogen.     

Bacterial Symbiote Activation of Insect Parthenogenese Reproduction

ORGANISMS existing in mutualistic interrelationships often show unusual chemical interdependencies; for example, the pupation of the beetle Xyleborus ferrugineus depends on a sterol source provided by its ectosymbiotic fungi^{1, 2}. We now report that bacterial endosymbiotes are transmitted transovarially in this beetle. We also present evidence that natural maturation of the oocytes and haploid parthenogenesis in this insect depend on its bacterial symbiotes.     

Peat carbon stocks in the southern Mackenzie River Basin: uncertainties revealed in a high-resolution case study

The organic carbon (C) stocks contained in peat were estimated for a wetland‐rich boreal region of the Mackenzie River Basin, Canada, using high‐resolution wetland map data, available peat C characteristic and peat depth datasets, and geostatistics. Peatlands cover 32% of the 25 119 km² study area, and consist mainly of surface‐ and/or groundwater‐fed treed peatlands. The thickness of peat deposits measured at 203 sites was 2.5 m on average but as deep as 6 m, and highly variable between sites. Peat depths showed little relationship with terrain data within 1 and 5 km, but were spatially autocorrelated, and were generalized using ordinary kriging. Polygon‐scale calculations and Monte Carlo simulations yielded a total peat C stock of 982–1025 × 10¹² g C that varied in C mass per unit area between 53 and 165 kg m^?2. This geostatistical approach showed as much as 10% more peat C than calculations using mean depths. We compared this estimate with an overlapping 7868 km² portion of an independent peat C stock estimate for western Canada, which revealed similar values for total peatland area, total C stock, and total peat C mass per unit area. However, agreement was poor within ～875 km² grids owing to inconsistencies in peatland cover and little relationship in peat depth between estimates. The greatest disagreement in mean peat C mass per unit area occurred in grids with the largest peatland cover, owing to the spatial coincidence of large cover and deep peat in our high‐resolution assessment. We conclude that total peat C stock estimates in the southern Mackenzie Basin and perhaps in boreal western Canada are likely of reasonable accuracy. However, owing to uncertainties particularly in peat depth, the quality of information regarding the location of these large stocks at scales as wide as several hundreds of square kilometers is presently much more limited.     

Factors Influencing Reporting and Harvest Probabilities in North American Geese

ABSTRACT We assessed variation in reporting probabilities of standard bands among species, populations, harvest locations, and size classes of North American geese to enable estimation of unbiased harvest probabilities. We included reward (US$10, $20, $30, $50, or $100) and control ($0) banded geese from 16 recognized goose populations of 4 species: Canada (Branta canadensis), cackling (B. hutchinsii), Ross's (Chen rossii), and snow geese (C. caerulescens). We incorporated spatially explicit direct recoveries and live recaptures into a multinomial model to estimate reporting, harvest, and band-retention probabilities. We compared various models for estimating harvest probabilities at country (United States vs. Canada), flyway (5 administrative regions), and harvest area (i.e., flyways divided into northern and southern sections) scales. Mean reporting probability of standard bands was 0.73 (95% CI = 0.69–0.77). Point estimates of reporting probabilities for goose populations or spatial units varied from 0.52 to 0.93, but confidence intervals for individual estimates overlapped and model selection indicated that models with species, population, or spatial effects were less parsimonious than those without these effects. Our estimates were similar to recently reported estimates for mallards (Anas platyrhynchos). We provide current harvest probability estimates for these populations using our direct measures of reporting probability, improving the accuracy of previous estimates obtained from recovery probabilities alone. Goose managers and researchers throughout North America can use our reporting probabilities to correct recovery probabilities estimated from standard banding operations for deriving spatially explicit harvest probabilities.     

Obligate costs of parental care to offspring: egg brooding-induced hypoxia creates smaller, slower and weaker python offspring

Python egg brooding typifies parental care because it consists of multiple behaviours that provide for multiple developmental needs. For example, tightly coiling around the eggs benefits embryonic water balance, but periodic female postural adjustments improve embryonic gas exchange. Regardless of these postural adjustments, egg brooding creates a hypoxic intra-clutch environment that constrains embryonic metabolism. We further examined this novel and useful parental care model to determine: (1) any fitness-related costs of egg brooding to offspring; (2) whether any long-term costs are alleviated by postural adjustments. We artificially incubated Children's python ( Antaresia childreni ) clutches and modulated oxygen partial pressure ( P O₂) to create three treatments: normoxic (NRM, 20.3 kPa O₂), brooding [BRD, P O₂ profile typical of clutch P O₂ ( P O_2clutch) in maternally brooded clutches, 15.8–19.3 kPa O₂] and low (LOW, predicted P O₂ profile of maternally brooded P O_2clutch if females did not make postural adjustments, 14.4–18.6 kPa O₂). Using various metrics from ∼12 days pre-hatching to 14 days post-hatching, we demonstrated that NRM offspring were larger, faster and stronger than BRD offspring. As only hatchling heart mass differed between BRD and LOW treatments (LOW > BRD), postural adjustments may not alleviate hypoxia-related costs to embryos. Our results demonstrate that parental care may represent a compromise between competing developmental needs and thus entails obligate costs to the offspring.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 414–421.     

Sexual dimorphism and interpopulation differences in lizard hind limb length: locomotor performance or chemical signalling?

Intraspecific variation in morphology has often been related to fitness differences through its effects on performance. In lizards, variation in hind limb length can be shaped by natural selection for increased locomotor performance, sexual selection on the number or size of femoral pores involved in chemical signalling, or both. Here, we analyse the selective forces involved in sexual dimorphism and differences in hind limb length between two populations of Psammodromus algirus living at different elevation. Males were more robust and had longer hind limbs and limb segments than females, and low‐elevation lizards had longer limbs than high‐elevation lizards. However, differences in locomotor performance were small and non‐significant, making natural selection for faster runs an unlikely explanation for the observed pattern. On the other hand, males had more femoral pores than females, and lizards had more pores at lower elevation, although the difference was significant only for males (which invest more in chemical signalling). In males, the number of pores, which remains constant along a lizard's life, was not correlated with hind limb length. However, femur length was positively correlated with mean pore size, allowing low‐elevation males to have larger than expected pores, which could increase the effectiveness with which they spread their signals in a dry and warm habitat where chemicals become volatile rapidly. Also, saturation of the sexual coloration of the head was higher for low‐elevation males, suggesting that sexual selection pressures may be more intense. Overall, our results indicate that sexual selection plays a significant role in shaping intraspecific variation in hind limb length. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 318–329.     

The Effects of Root Cooling and the Light--Dark Transition on Growth of Primary Leaves of Phaseolus vulgaris L.

Use of Rotary Variable Displacement Transducers attached togrowing primary leaves of Phaseolus vulgaris has shown thatwhen the root systems were rapidly cooled from 23°C to 10°Cleaf extension rate fell to very low values within a few minutes.When the root systems were returned to 23°C leaf extensionincreased almost immediately to overshoot the control rateswithin 5–10 min, before declining to control values overthe next 50–60 min. When lights went off at the end ofthe day cycle there was an immediate and very large increasein leaf extension rate in both root-cooled and control plants;the rate then slowly declined over the next 60 min. This effectwas seen when the photoperiod was artificially shortened orlengthened and was reduced in magnitude when the photoperiodwas ended gradually by dimming the lights. The effect was notattributable to effects on leaf temperature but appears to bethe result of an endogenous rhythm interacting with the endof the photoperiod. At the beginning of the photoperiod therewas a gradual reduction in leaf extension rate occurring over30–45 min. Key words: Phaseolus vulgaris, leaf growth, extension rate, root cooling, wall extensibility, turgor     

The effect of partially resistant potato clones and aldicarb on the multiplication of the potato cyst nematode Globodera pallida in field trials

Potato cultivars with different degrees of resistance to Globodera pallida (PCN) were trialled at three infested sites in 1983, 1984 and 1985. These trials were primarily intended to assess the effects of PCN damage on the yield of tubers and consequently the sites chosen had high initial population densities of G. pallida. The population density of G. pallida was determined from samples taken both pre-planting and post-harvest and results showed that there were significant differences between the clones in the nematode multiplication rates. Although actual rates of multiplication varied between sites the relative differences between clones were maintained across sites. Under the susceptible control cultivars the populations generally increased even in the presence of nematicide. The partially resistant clones gave best control, as measured by nematode multiplication, at the sites with the highest initial population densities but gave good control at all sites when treated with nematicide irrespective of initial population density. The role of partial resistance in integrated control systems and the effectiveness of nematicides against G. pallida is discussed.