Nutrient utilisation,growth performance and blood metabolites in Murrah buffalo calves (Bubalus bubalis) divergently selected for residual feed intake

The aim of this study was to evaluate differences in efficiency of feed utilisation between buffalo calves with low and high residual feed intake (RFI) by comparing feed intake, nutrient digestibility, growth traits and blood metabolites. Eighteen male Murrah buffalo calves (aged 4–6 months; 70 ± 1.0 kg body weight) were fed ad libitum with a total mixed ration for 120 d. Based on linear regression models involving dry matter intake (DMI), average daily gain (ADG) and mid-test metabolic body size, calves were assigned into low and high RFI groups. The RFI varied from ?0.33 to +0.28 kg DM/d with an average RFI of ?0.14 and 0.14 kg DM/d in low and high RFI calves, respectively. Calves had a mean DMI of 1.9 and 2.4 kg/d and an ADG of 0.5 and 0.6 kg/d in low and high RFI groups, respectively. Low RFI calves ate 19.0% less DM each day and required significantly less metabolisable energy for maintenance compared with high RFI calves (12.5 vs. 16.7 MJ/d). Nutrient digestibility and nitrogen balance did not differ among low and high RFI calves. In more efficient animals (low RFI calves) higher (p < 0.05) plasma level of growth hormone, insulin-like growth factor-1 (IGF-1), triiodothyronine (T₃) and lower concentration of thyroxin hormone were detected. No significant differences in levels of insulin, hydroxyproline, plasma and urine creatinine, total protein and albumin between high and low RFI groups were found. Blood metabolites showed significant (p < 0.05) differences at initial and final stages of study in both groups. At final stage of study, RFI showed negative correlations with growth hormone, IGF-1, T₃, urine creatinine and albumin. Low RFI buffalo calves are more efficient in feed utilisation and the differences in blood metabolites are probably due to differences in feed intake and body metabolism.     

Concentration and transport of dissolved and suspended substances in the Orinoco River

The Orinoco River, which is hydrologically unregulated and has a minimally disturbed watershed, was sampled quantitatively over a four-year interval. In conjunction with the sampling, a method was developed for quantifying statistical uncertainty in the estimates of annual transport. The discharge-weighted mean concentration of total suspended solids in the Orinoco River is 80 mg/l, which corresponds to total annual transport of 90 × 10⁶ t/y, or, expressed per unit of watershed area, 960 kg/ha/y, of which 96% is inorganic. The mean for dissolved solids is 34 mg/l, of which 25 mg/l is inorganic. The total transport of inorganic material, with a small allowance for bedload, is 128 × 10⁶ t/y, which corresponds to an erosion rate of 4 cm/1000 y. Concentrations of dissolved and suspended constituents derived from rock weathering are very low because of dilution from high runoff (1190 mm/y), coverage of the southern part of the drainage by shield rock, and minimal watershed disturbance. Seasonal patterns in dissolved and suspended constituents are repeated with a high degree of consistency from one year to the next. For most variables, relationships between transport and discharge are described adequately by a power function. There are three categories of response to changing discharge: purging (exponent > 1: soluble organic fractions and all particulate fractions), dilution (exponent 0–1: major ionic solids and silicon), and conservation (exponent < 0: nitrate, interannual). Variability across seasons and across years is highest for the particulate constituents, but within this group variability is lower for the organic than for the inorganic components. Major ions that originate primarily from the atmosphere have a higher seasonal variability than major ions that originate primarily from weathering. Potassium and soluble silicon have the lowest variabilities. Variability is much lower across years than across seasons for most constituents. Because of high runoff per unit area, the Orinoco drainage has a high specific transport of organic carbon (72 kg/ha/y, 6.8 × 10⁶ t/y, 1.6% of global river transport), even though the concentrations of organic carbon in the river are not exceptionally high (mean, 4.4 mg/l dissolved, 1.4 mg/l particulate). Concentrations of ammonium (35 μg/l as N) and of nitrate (80 μg/l as N) are high given the undisturbed nature of the watershed and the high amount of runoff. The high transport rate for total nitrogen (5.7 kg/ha/y, 0.54 × 10⁶ t/y, l.5% of global river transport) can be sustained only by high rates of nitrogen fixation within the watershed. Concentrations of soluble phosphorus are within the range expected for undisturbed river systems (20 μg/l), but concentrations of particulate phosphorus are low because the amounts of particulate matter are small and the phosphorus per unit weight of suspended matter is low. Phosphorus transport (0.75 kg/ha/y) can be accounted for easily by weathering of the parent material, even within the Guayana Shield, where weathering rates are lowest. Biological modification of nutrient and carbon fractions during transit along the main stem are minimal.     

Sulfur cycling in a forested Sphagnum bog in northern Minnesota

The mass balance and internal cycle of sulfur within a small forested,Sphagnum bog in northern Minnesota are presented here based on a 4-year record of hydrologic inputs and outputs (precipitation, throughfall, streamflow, upland runoff) and a 3-year measurement of plant growth and sulfur uptake. Concentrations and accumulation rates of inorganic and organic sulfur species were measured in porewater. The bog is a large sink for sulfur, retaining 37% of the total sulfur input. Because of the relatively large export of organic S (21% of inputs), retention efficiency for total-S (organic S + SO ₄ ⁼ ; 37%) is less than that for SO ₄ ⁼ (58%). There is a dynamic cycle of oxidation and reduction within the bog. Annual oxidation and recycling of S is equal to total inputs in the center of the bog. Plants receive 47% of their uptake requirement from atmospheric deposition, 5% from retranslocation from foliage, and the remainder from sulfur remineralized from peat. Mineralization is most intense in the aerobic zone above the water table. Inorganic sulfur species comprise <5% of the total sulfur burden within the peat.     

A comparative study on nutrient cycling in wet heathland ecosystems

Summary The term relative nutrient requirement is introduced in order to measure and to compare the nutrient losses from different perennial plant populations and the amount of nutrient that they need to absorb to compensate these losses. The relative nutrient requirement (L) is defined as the amount of the growth-limiting nutrient that must be taken up to maintain or replace each unit of biomass during a given time interval (e.g., mgN g^-1 biomass year^-1). It is derived that in a plant community with two competing perennial plant populations, species¹ will become dominant if the relative competition coefficient k ₁₂ (sensu De Wit 1960) exceeds the ratio between the relative nutrient requirements of the two species (L ₁/L ₂), whereas species 2 will become dominant, if k ₁₂ is below this critical ratio. The above-ground litter production was measured inwet heathland communities dominated by Erica tetralix or by Molinia caeruleain order to estimate N and P losses from theaboveground biomass and to calculate the relative N and P requirements of these species. Molinia lost during one year 63% and 34%, respectively, of the amount of N and P present in the above-ground biomass at the end of the growing season. These losses were in Erica 27% and 31%, respectively. The relative N requirements of the two species show the same difference: 7.5 and 2.6 mg N g^-1 yr^-1, respectively, in Molinia and in Erica. Also the relative P requirement of Molinia is higher as well as that of Erica (0.18 versus 0.08 mg P g^-1 yr^-1). The relative competition coefficient of Molinia with respect to Erica (k _me ) is equal to unity under unfertilized conditions but increases with increasing nutrient supply. Under nutrient-poor conditions k _me is below the critical ratio of the relative nutrient requirements of the two species (L _m /L _e =2.9 or 2.3), so that Erica will be the dominant species. After an increase in nutrient availability k _me increases and exceeds this critical limit which results in Molinia replacing Erica. During the last 20 years this replacement of Erica-dominant communities by monocultures of Molinia has been observed in almost all wet heathlands in The Netherlands along with a strong increase in nitrogen availability.     

Ecological energetics of Central European grasshoppers (Orthoptera: Acrididae)

Summary Biomass and energy budgets and food utilization efficiencies of laboratory and wild populations of three Central European grasshopper species, Chorthippus parallelus (Zetterstedt), C. biguttulus (L.), and Gomphocerus rufus (L.), were studied between 1979 and 1984. Larval consumption is relatively low in C. biguttulus (C=4.3 kJ/ind.) compared with C. parallelus and G. rufus (4.9 kJ/ind.). In the adult phase (maturity) consumption rates of C. biguttulus and G. rufus (6.9 kJ/ind.) are similar, but higher in C. parallelus (7.3 kJ/ind.). The energy content decreases from the egg (23.2–24.3 J/mg dw) and body tissue (22.1–23.2 J/mg dw) to faeces (16.6–18.1 J/mg dw). The energy contents of faeces differ significantly between the species, indicating different rates of food conversion (on Dactylis glomerata). On average, the assimilation rates are about 30%, slightly lower in G. rufus. Approximate digestibility (A/C) ranges from 28.2 (G. rufus) to 35.7 (C. biguttulus) without great differences between larvae and adults. In contrast, the efficiency of conversion of ingested food (P/C) differs significantly between larval (10–11) and adult stages (3.4–3.6), and so to a much higher degree does the efficiency of conversion of digested food (P/A), from 30.3–33.5 in the larval to 9.5–14.9 in the adult period. Based on 5-year (C. parallelus) and 2-year studies (G. rufus) of the population dynamics and life tables, the energy budgets of wild populations were calculated and summarized into diagrams. Depending on the annually fluctuating densities, in both populations about 1%–2% of net primary production was consumed, and another 5%–9% was cut and dropped. The proportion of production of the grasshopper populations (body tissue) used for egg production differs in C. parallelus (28%) and G. rufus (44%). The energy cycling owing to energy storage in the living eggs amounts to 2%–3% of the total energy consumed by the population. The results are compared with the available data for grasshoppers in the literature.     

Photosynthesis and stomatal characteristics of Striga hermonthica in relation to its parasitic habit

Photosynthesis and stomatal characteristics of the angiosperm parasite Striga her-monthica (Del.) Benth. have been compared with those of Antirrhinum majus L. cv. Suttons Yellow Rust Resistant, a related, non-parasitic species. The concentration of photosynthetic pigments in S. hermonthica leaves was less than 40% of those of A. majus leaves. Light saturated CO₂ assimilation rate of S. hermonthica was less than 40% that of A. majus on a chlorophyll basis and under 20% than of A. majus on a leaf area basis.
Stomata of Striga showed only partial closure in darkness, remained open in water stressed leaves and showed little response to exogenously applied abscisic acid. Stomatal conductance and transpiration were considerably higher in Striga compared with Antirrhinum . The high transpiration and low photosynthetic rates of S. hermonthica resulted in a low water use efficiency. The water relations of Striga leaves, while seemingly inappropriate for growth in drought prone environments, do appear to maximise nutrient and water acquisition from the host and as such may be an adaptation to the parasitic habit.     

Water stress effects on leaf elongation,leaf water potential,transpiration, and nutrient uptake of rice,maize, and soybean

A pot experiment was conducted in the greenhouse to determine and compare the responses of rice (Oryza sativa L. var, IR 36), maize (Zea mays L. var. DMR-2), and soybean (Glycine max [L.] Merr. var. Clark 63) to soil water stress. Leaf elongation, dawn leaf water potential, transpiration rate, and nutrient uptake in stressed rice declined earlier than in maize and soybean. Maize and soybean, compared with rice, maintained high dawn leaf water potential for a longer period of water stress before leaf water potential. Nutrient uptake under water stress conditions was influenced more by the capacity of the roots to absorb nutrients than by transpiration. Transport of nutrients to the shoots may occur even at reduced transpiration rate It is concluded that the ability of maize and soybean to grow better than rice under water stress conditions may be due to their ability to maintain turgor as a result of the slow decline in leaf water potential brought about by low, transpiration rate and continued uptake of nutrient, especially K, which must have allowed osmotic adjustment to occur.     

Nutrient translocation from green algal symbionts to the freshwater sponge Ephydatia fluviatilis

The symbiosis between the freshwater sponge Ephydatia fluviatilis and a chlorella-like green alga is not obligate and only occurs when the sponge grows in the light. The algae accumulate intracellular pools of sucrose and glucose and translocate between 9 and 17% of the total photosynthate to the host. The principal product translocated is glucose which is fed directly into the sponge metabolic pool. White sponges transplanted back into the river in the shade grew logarithmically with a mean doubling time of 12 days. Sponges transplanted into illuminated habitats did not grow. It is unknown how the sponge acquires its algal symbiont.     

Prediction of phosphorus and nitrogen concentrations in lakes from both internal and external loading rates

A model predicting phosphorus and nitrogen concentrations from loading rates was tested using data collected from a shallow, nutrient-rich lake where both internal and external loading occurred. Predicted nutrient concentrations agreed closely with obaerved values and it is suggested that the model could be used to predict the reduction in loading rate required to effect lake restoration.     

Specifically UV-sensitive photoreactivable mutant of Salmonella abony

A new type of UV-sensitive mutant was isolated in Salmonella abony. The war 12 mutation causing UV sensitivity did not affect photoreactivability of UV damage or sensitivity to γ-rays, methyl methanesulfonate (MMS), mitomycin (MC) or 4-nitro-quinoline I-oxide (4NQO).Mutation uvr I2 appeared to be near the uvr B gene of Salmonella: the frequencies of contransduction of uvr B2 and uvr I2 mutations with gal were found to be 3% and 6% respectively.Close localization of the uvr I2 and uvr B2 mutations, the possibility of recombination between them and their phenotypic differences (both uvr B2 and uvr I2 mutants show quantitatively different Hcr phenotypes and different sensitivities to MC and 4NQO) suggest that the uvr B2 and uvr I2 mutations might be localized in different cistrons of an operon controlling the first step of excision repair.