Improved Growth Efficiency Research Articles

Thinning and Nitrogen Fertilization in a Grand Fir Stand Infested with Western Spruce Budworm. Part IV: An Ecosystem Management Perspective

Abstract A stand of grand fir, Abies grandis (Dougl.) Lindl., was thinned and (or) fertilized with 350 kg/ha of nitrogen during an outbreak of the western spruce budworm, Choristoneura occidentalis Freeman. With thinning, the leaf area index was reduced by >30%. Tree growth efficiency, measured as wood production per unit of leaf area, increased by 60% within 2 years. Thinning combined with fertilization improved growth efficiency by 140%. Fertilization without thinning brought a much delayed response in growth, awaiting some beneficial effects of defoliation. Fertilization provided tree roots in the upper soil horizons access to nitrogen during the spring, increasing the concentration of nitrogen in emerging foliage from 1 to 1.5% of dry weight and free amino adds levels 4-fold. Foliage enriched in amino acids increased shoot growth 3-fold, more than compensating for any nutritional benefits to insect larvae. From an ecosystem perspective, managers should recognize that allowing pine forests to be replaced with fir through fire protection and selective logging has increased the nitrogen demand beyond that readily supplied in the ponderosa pine/true fir type. Fertilizing with one application of nitrogen at the time of an insect outbreak may reduce mortality and associated fire hazard through a period of up to 5 years. For. Sci. 38(2):275-286.

Triethylarsenic and arsine as co-reagents: The novel manipulation of in-situ GaAs OMCVD growth chemistry to improve growth efficiency and safety

A dramatic improvement in the purity of GaAs epilayers grown by organometallic chemical vapor deposition from triethylarsenic (Et3As) and trimethylgallium (Me3Ga) was found to occur upon the addition of arsine (AsH3) as a co-reagent. The arsine was added to the Et3As in a 1:1 molar ratio to alter the in-situ reaction chemistry of the growth by providing active hydride ligands to the growing epilayer surface. These hydrides were expected to promote the elimination of surface-bound alkyl groups which otherwise could serve as carbon contaminant precursors. Good quality, n-type GaAs films were grown from the Et3As/AsH3/Me3Ga co-reagent combination, with purities far superior to those of films grown from Et3As and Me3Ga, and at V/III ratios and growth temperatures that were lower than those required for the growth of good quality GaAs from AsH3 and Me3Ga. Epilayers with specular surfaces grown from the co-reagent mixture were found to be n-type at V/III ratios of 5–40, and had carrier concentrations as low as 6x1014cm−3 with 77K mobilities ranging from 34,000–54,000 cm2/V·s. Secondary mass spectroscopy and photoluminescence data confirmed the reduced carbon content in these films.

Effect of Dietary Fat Supplement on Lipid Metabolism of Holstein Heifers

Twenty Holstein heifers were fed four rations containing 0, 10, 20, and 30% whole sunflower seed as a source of dietary fat. All rations consisted of alfalfa hay, sunflower hulls, and grain mixtures and were isonitrogenous at 12% crude protein and isocaloric at 2.6 Meal metabolizable energy per kilogram dry matter. Average body weight gains were not different among treatment groups. Heifers fed sunflower seed (fat) diets consumed less total dry matter, significantly improving growth efficiency (gain/feed). Concentration of total lipid and urea nitrogen in blood serum were increased whereas glucose was depressed with higher amounts of dietary fat. High fat diets (20 and 30%) elevated total lipid, triglyceride, and nonesterified fatty acids in the blood. Total and free cholesterol in blood also were increased, but high density lipoprotein-cholesterol remained unchanged with increasing concentration of dietary fat. Dietary fat was correlated positively with lipid components of blood serum and negatively with glucose.

Energetics of Streptococcal Growth Inhibition by Hydrostatic Pressure

Growth of Streptococcus faecalis in complex media with various fuel sources appeared to be limited by the rate of supply of adenosine-5' -triphosphate (ATP) at 1 atm and also under 408 atm of hydrostatic pressure. Growth under pressure was energetically inefficient, as indicated by an average cell yield for exponentially growing cultures of only 10.7 g (dry weight) per mol of ATP produced compared with a 1-atm value of 15.6. Use of ATP for pressure-volume work or for turnover of protein, peptidoglycan, or stable ribonucleic acid (RNA) did not appear to be significant causes of growth inefficiency under pressure. In addition, there did not seem to be an increased ATP requirement for ion uptake because cells growing at 408 atm had significantly lower internal K(+) levels than did those growing at 1 atm. Pressure did stimulate the membrane adenosine triphosphatase (ATPase) or S. faecalis at ATP concentrations greater than 0.5 mM. Intracellular ATP levels were found to vary during the culture cycle from about 2.5 mumol/ml of cytoplasmic water for lag-phase or stationary-phase cells to maxima for exponentially growing cells of about 7.5 mumol/ml at 1 atm and 5.5 mumol/ml at 408 atm. N,N'-dicyclohexylcarbodiimide at a 10 muM concentration improved growth efficiency under pressure, as did Mg(2+) or Ca(2+) ions at 50 mM concentration. These agents also enhanced ATP pooling, and it seemed that at least part of the growth inefficiency under pressure was due to increased ATPase activity. In all, it appeared that S. faecalis growing under pressure has somewhat reduced ATP supply but significantly increased demand and that the inhibitory effects of pressure can be interpreted largely in terms of ATP supply and demand.