Spatial and Temporal Variability in Dissolved Inorganic Nitrogen Fluxes at the Sediment–Water Interface in Lake Illawarra, Australia

In this study, benthic flux measurements of inorganic nitrogen (i.e., $ {\text{NH}}^{ + }_{4} $ , $ {\text{NO}}^{ - }_{2} $ ?+? $ {\text{NO}}^{ - }_{3} $ ) were made using a batch incubation system at different stations (i.e., shallow sandy macrophyte and unvegetated beds, and deep central mud) over four seasons in Lake Illawarra, NSW, Australia, to study the influence of different primary producers (i.e., seagrasses, microphytobenthos (MPB) and macroalgae) and/or different sediment types (i.e., sand or mud) on the benthic fluxes. In general, nutrient fluxes displayed typical diel variations, with lower flux out of sediments (release) or enhanced uptake by the sediment in the light, due to the photosynthetic activities of the plant-MPB-sediment community in Lake Illawarra during photosynthetic periods. A distinct seasonal pattern of inorganic-N fluxes was also observed (e.g., the marked difference between summers 2002 and 2003). This may be explained by the seasonal variations in the biomass and activity (growing or decay phases) of MPB, seagrass and macroalgae, which may influence their nutrient assimilation and alter the chemical conditions of surface sediments that influence the benthic geochemical processes and thus benthic nutrient fluxes. On an annual basis, unvegetated sediments displayed net DIN effluxes, while seagrass beds showed a net DIN uptake, and the highest DIN uptakes coincided with the largest standing crop of seagrass and/or macroalgae and the highest levels of benthic community production. This may be due to the enhanced denitrification and/or assimilation activity by rooted plants and macroalgae, and the effect is most efficient during periods of net growth (e.g., in Spring 2002).     

双乙酸钠在肉鸭日粮中的添饲效果试验

选用1日龄健康樱桃谷肉鸭600只,随机分为3组,每组设4个重复,每个重复50只肉鸭,试验采用单因素完全随机试验设计。A组饲喂基础日粮,B组、C组在基础日粮的基础上分别添加0.2%、0.4%的双乙酸钠。试验结果表明:日粮中添加双乙酸钠对肉鸭日增重、瘦肉率有显著影响(P<0.05);对肉鸭的饲料转化率有极显著影响(P<0.01);对肉鸭的成活率和屠宰率、皮脂率无显著影响(P>0.05)。B组日增重比A组提高了8.65%(P<0.05),比C组提高了5.45%(P>0.05);B组料肉比较A组降低了11.52%(P<0.01),较C组降低了3.29%(P<0.05);B组的成活率与A组、C组间差异不显著(P>0.05);B组每只肉鸭分别比A、C组多盈利1.04元、1.06元。     

A study of naturally occurring cases of ovine foot abscess in New Zealand

A study was made of various aspects of 53 naturally occurring cases of foot abscess in sheep in New Zealand. Radiographic techniques were used to follow the progress of the lesion and from this it was concluded that foot abscess could be defined as an infection of the distal interphalangeal joint. The term foot abscess was considered preferable to the term "infective bulbar necrosis". The attack rate of foot abscess was reported to be higher for rams than for ewes and the condition was less prevalent during summer. Once infection was established in the distal interphalangeal joint a relatively uniform and thus predictable series of events took place that inevitably resulted in some permanent damage and deformity to the digit. If rupture of the axial collateral ligaments occurred, the joint became unstable and the degree of permanent deformity was greater. Treatment with antibiotics did not appear to markedly affect the progress of the lesion or the outcome, once infection had become established in the joint. Although the prognosis for complete recovery was poor, in most cases the foot healed sufficiently after a period of about two months to allow the animal to walk normally.     

Long-term consequences of topsoil mining on select biological and physical characteristics of two New Zealand loessial soils under grazed pasture

Soil chemical, biochemical, biological and structural properties were measured in two New Zealand loessial soils that were topsoil-mined 10 and 25 years ago respectively. Measurements at the 10-year site were compared to some earlier measurements made at this site and the data combined in a chronological sequence for analysis. Topsoil mining had a large, detrimental impact on the soil microbial biomass, the earthworm populations, easily mineralizable N and soil enzyme activities. However, most of these properties substantially recovered, to 80-90 per cent of the levels in unmined soils, within 10-25 years of restoration under pasture. In contrast, while total soil C and N were less affected by topsoil mining, their recovery was much slower. Stabilities of macro-aggregates of soil had fully recovered within 10-25 years after topsoil mining. The apparent changes in all the measured properties between 10 and 25 years of restoration were small in comparison with changes between 0-10 years of restoration after topsoil mining. The total C content of both soils under pasture appeared unlikely to attain the levels present in unmined soils. In soils undergoing restoration, the ratio of microbial C/total soil C may be a useful index of soil ‘biological stability’. Sulphatase activity may reflect the recovery of pasture production.     

Molecular mimicry regulates ABA signaling by SnRK2 kinases and PP2C phosphatases

Abscisic acid (ABA) is an essential hormone for plants to survive environmental stresses. At the center of the ABA signaling network is a subfamily of type 2C protein phosphatases (PP2Cs), which form exclusive interactions with ABA receptors and subfamily 2 Snfl-related kinase (SnRK2s). Here, we report a SnRK2-PP2C complex structure, which reveals marked similarity in PP2C recognition by SnRK2 and ABA receptors. In the complex, the kinase activation loop docks into the active site of PP2C, while the conserved ABA-sensing tryptophan of PP2C inserts into the kinase catalytic cleft, thus mimicking receptor-PP2C interactions. These structural results provide a simple mechanism that directly couples ABA binding to SnRK2 kinase activation and highlight a new paradigm of kinase-phosphatase regulation through mutual packing of their catalytic sites.     

Effects of size and temperature on metabolic rate

We derive a general model, based on principles of biochemical kinetics and allometry, that characterizes the effects of temperature and body mass on metabolic rate. The model fits metabolic rates of microbes, ectotherms, endotherms (including those in hibernation), and plants in temperatures ranging from 0 degrees to 40 degrees C. Mass- and temperature-compensated resting metabolic rates of all organisms are similar: The lowest (for unicellular organisms and plants) is separated from the highest (for endothermic vertebrates) by a factor of about 20. Temperature and body size are primary determinants of biological time and ecological roles.     

Opto-electronic counters for postlarvae and juveniles of Machrobrachium rosenbergii (de Man); design and tests of Type A counter

Postlarvae or juveniles of Macrobrachium rosenbergii produced in Mauritius are sold at unit price to prawn farmers and are counted individually by hand. This process is time consuming, labour intensive, subject to error and may stress the juveniles; safe rapid electronic counting would be highly advantageous.The design of the hydraulic component of a successful counter prototype, Type A, is described. The counter has 10 parallel channels through which juveniles are carried in a water current. The detection of juveniles passing through these channels can be done photo-electrically. The counter accepts juveniles up to 15 mm in length (eye orbit to tip telson) and has the significant advantage that it can be constructed using only simple hand tools.Survival and growth rate tests, and microscopic examination for damage to appendages of juveniles were done on machine counted and hand counted juveniles. There was no reduction of growth or survival caused by passage through the counter by comparison with the hand counting method, and it is concluded that the counter is not detrimental to juvenile prawns.About 70% of all juveniles tested showed highly variable amounts of damage. The great majority of this damage appears to originate in the hatchery tanks, prior to the experimental treatments. Only in the case of antennules could the use of the counter be shown to increase damage significantly, i.e. from 25% to 38%, but this has no detectable effect on subsequent survival or growth.This appears to be the first counter made specifically for counting macroscopic crustacean juveniles, and via suitable scaling, adaptation to counting other species of crustaceans, fish larvae, etc., should be possible.