Variation In Growth Response Research Articles

Evaluation of eight forest fertilizer response estimators by means of a simulation study

Eight estimators of total fertilizer response (simple difference, ratio, covariance, and regression estimators) commonly used to determine the results of fertilization experiments were evaluated using a simulation study. An individual tree model based on equations developed for Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) was used to project the growth of fertilized and unfertilized plots under several different experimental conditions. The effects of number of plots, plot size, initial plot variability, stand age at the time of fertilization, length of response period, and differing growth responses to fertilization on the relative performance of the estimators were evaluated. Covariance and regression estimators provided the best estimates as long as there was sufficient data to determine model parameters. In almost all cases measures of growth were preferable to measures of yield. For the simple difference and ratio estimators strong linear relationships were observed between bias and pre-treatment differences in yield or growth between fertilized and unfertilized experimental units. Variability in growth response to fertilization did not influence the relative performance of the estimators. The more critical factor was the variability in unfertilized growth as this is what must be predicted in order to estimate fertilizer response.

The Influence of Nitrogen Sources on Growth and Protein Metabolism of Nectria haematococca Berk. & Br.

Summary Isolate II (IMI No. 267377) of Nectria haematococca (Fusarium solani) was highly virulent for cvs. “Marglobe” and “Pusa Ruby” causing higher per cent of pre- and post-emergence killing of tomato seedlings. On the other hand isolate I (IMI No: 267376) had high virulence for cvs. “Punjab Chuhara”, “Best of All”, and “Early Dwarf”. In both isolates increase in mat accumulation was rapid and linear between 10–15 days of growth. Nitrogen source of the medium and age of the culture determined the variation in growth response, protein build up, protease activity and size and composition of amino acid pool. Protein accumulation, protease activity and amino acid composition which varied with age of culture could be indirect determinants of virulence of the isolates of N. haematococca . High protein content and high protease activity with profuse liberation of amino acids at an early growth stage enables the pathogen to cause pre-emergence death of tomato seedlings. Similarly, late stage accumulation of protein by the pathogen enhances virulence and results in prominent post-emergence damping off of the seedlings.

Effects of Flow Speed on Growth of Benthic Suspension Feeders.

In separate experiments in 1991 and 1992, the sensitivities of growth rates of six species of benthic suspension feeder to flow speed were tested in a series of turbulent pipe flows. Species examined were the cheilostome bryozoan Membranipora membranacea (1991); the serpulid polychaete Pseudochitinopoma occidentalis (1991); and the barnacles Balanus glandula (1991), B. crenatus (1992), Semibalanus cariosus (1992), and Pollicipes polymerus (1992). In both experiments, animals were exposed to one of five constant, narrow ranges of speed that varied from about 2-15 cm s-1. Growth rates of Membranipora and Pseudochitinopoma in 1991 declined significantly and monotonically with increasing flow speed, despite evidence that at faster flows there were greater concentrations of suspended food available and higher particulate fluxes. In contrast, there was no detectable relationship between speed and growth of B. glandula over the same range of flow speeds in 1991. Results of the 1992 experiment indicated variability in growth responses among three species of barnacle. Growth rates of S. cariosus and P. polymerus were insensitive to flow speed, whereas growth rates of B. crenatus increased from low speeds to a maximum at an intermediate speed of about 8 cm s-1, and then tended to decrease at higher speeds. Combined results of the two experiments indicate that the growth response of animals to flow was most obviously related to the relative flow energy of the animal's natural habitat. Growth rates of animals that typically experience relatively weak flows (P. occidentalis, M. membranacea, and B. crenatus) were affected significantly by flow speed, whereas growth rates of animals from comparatively high-energy environments (B. glandula, S. cariosus, and P. polymerus) were relatively insensitive to flow speed. In contrast, animal morphology and behavior were not obviously related to growth responses to flow. A key to understanding the impact of flow on a suspension-feeder's growth may be the animal's ability to handle and process particles that have impacted the feeding apparatus and to deliver them to the point of ingestion.

Genetic variation in competitive ability of some shade-tolerant and shade-intolerant Pacific Coast (USA) conifers

Abstract Variability in growth response to stocking density and neighbor composition was compared among half-sibling families of four tree species representing two pairs of shade-tolerant and shade-intolerant species, each pair from the same life zone. The hypothesis was that the wider regeneration niche of shade-tolerant species, which establish both in disturbed areas and within closed forests, would produce greater genetic variability among families than occurs in shade-intolerant species, which establish primarily in disturbed areas. Families of western hemlock (Tsuga heterophylla (Raf.) Sarg.), coast Douglas fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) and Pacific silver fir (Abies amabilis (Dougl.) Forbes) varied in their responses to stocking density, but those of noble fir (A. procera Rehd.) did not. As hypothesized, shade-tolerant species were significantly more variable than shade-intolerant ones, a result consistent with electrophoretic studies of shade-tolerant and -intolerant plants and supportive of the hypothesis that at least a portion of genetic variability contained within populations represents adaptation to variable environments.

Seasonal and year to year variation in performance of Gordonia acuminata seedlings in different light environments

The effects of light environment on temporal growth and allocation patterns in the subtropical Chinese evergreen tree Gordonia acuminata, a gap-dependent species, were studied during its first 2 years of growth. Seedlings were grown in full sun (S100), 55% of full sun (S5S), 33% of full sun (S33), and 18% of full sun (S18). During the 1st year, plant size and leaf dynamics were monitored nondestructively. The best growth was at S33. Growth rates fluctuated more from season to season in treatments of higher relative light exposure, largely owing to sun-imposed inhibition of growth in summer. Leaf size was to a large extent ontogenetically determined. Additionally, a size reduction with increasing light exposure was shown for individual leaves that had expanded during a given ontogenetic phase. In the 2nd year relative growth was best at S55 (first 6 months) and in full sun (second 6 months), successively, which resulted in S55 plants outgrowing the initially bigger S33 plants. Self-shading and smaller relative investment in leaf area were associated with a reduction of sun-imposed inhibition and thus with enhanced growth in sun in the 2nd year. The large seasonal and year to year variation in growth response to relative light exposure may have important consequences for the success of young Gordonia plants in gaps of different sizes or formed in different seasons. Key words: broad-leaved evergreen seedlings, gaps, growth, morphology, ontogeny, seasons, subtropical China.

An assessment of spruce growth response specificity after inoculation with coexistent rhizosphere bacteria

The influence of inoculation with rhizosphere bacteria on hybrid spruce (Picea glauca × engelmannii) seedling growth was investigated by isolating bacteria from the rhizosphere of naturally regenerating spruce seedlings collected from two ecologically distinct zones of British Columbia. Forty bacterial strains from spruce were screened in a seedling growth experiment, and several strains were shown to stimulate spruce seedling growth. The three most effective spruce growth promoting strains from each ecological zone were then tested in a seedling growth response specificity experiment in which seed, soil, and bacteria from both spruce ecosystems were examined in all possible treatment combinations, including pasteurized soil. Spruce seedling growth was primarily affected by seed and soil source (Salmon Arm > Mackenzie for both factors), and by soil pasteurization (pasteurized > unpasteurized). Significant growth effects due to bacterial treatment in the specificity experiment occurred only in pasteurized soil, but seedling biomass accumulation was stimulated by up to 59% in response to inoculation. There was no evidence of growth response specificity that was related to plant – bacteria adaptation within spruce ecotypes; two of the Mackenzie bacterial strains significantly inhibited growth of Mackenzie seedlings in Mackenzie soil, but two strains stimulated the growth of Salmon Arm seedlings, one in each soil type. Two Salmon Arm strains significantly stimulated growth of Mackenzie seedlings on Salmon Arm soil, and two strains stimulated the growth of Salmon Arm seedlings, one in each soil type. Seedling biomass was greater when treatments of spruce seed, soil, and rhizosphere bacteria that originated from the same geographic site were pooled and compared with treatments in which at least one factor originated from the other site. However, this effect was explained by the significant seed × soil interaction in the absence of bacteria; mean seedling biomass was greatest when spruce seed and soil treatments with the same geographic origin were pooled and compared with unrelated seed – soil combinations. Seedlings from pooled treatments were also significantly larger when bacteria and soil had a common geographic origin, but only when tested in pasteurized soil. Our results indicate that spruce growth promoting rhizosphere bacteria can be isolated from naturally regenerating spruce seedlings, but growth response variability was observed between trials. Seedling growth promotion by bacterial strains was not related to the use of spruce ecotypes, soil, and (or) rhizosphere bacteria with a common geographic origin. Key words: spruce seedlings, growth, inoculation, rhizosphere bacteria.

Calcium‐induced modification of aluminum toxicity in sorghum genotypes

Abstract Effects of calcium (1, 2 and 5 mM) and aluminum (0, 15 and 45 μM) on growth and internal nutrient concentrations were examined with 12 sorghum genotypes (Sorghum bicolor (L.) Moench) in a nutrient solution experiment with a factorial design. At 1 (or 2) mM Ca the severity of root damage induced by Al well reflected the genotypical variation in growth response to Al toxicity. Severity of Al‐induced root damage slightly decreased with increasing Ca level. Moreover, Ca at 5 mM amplified the Mg deficiency induced by Al, as seen from both heavier deficiency symptoms and lower internal Mg concentrations. Under conditions of Al stress at a high Ca supply, induced Mg deficiency apparently predominated the genotypical differentiation in growth response to Al toxicity. An antagonism between Al‐ and Ca ions for uptake was hardly found with the sorghum genotypes. However, the genotypes differed in Ca efficiency, a characteristic which may be relevant in assessing their sensitivity to Mg deficiency.

Species and clonal variation in growth responses to waterlogging and submersion in the genusSalix

SynopsisThe responses of clones of a range of willow species to waterlogging and total submersion were compared in glasshouse experiments using specially constructed perspex tanks. Up to 13 weeks of waterlogging had little effect on form and growth rates of above-ground parts of two clones ofSalix caprea L. and one clone ofS. cinerea L. A second clone ofS. cinerearesponded differently to the other three clones by significantly increasing its leaf area and stem dry weight, suggesting that it is likely to be more tolerant of waterlogging.Plant parts below the waterline in the waterlogging treatment responded very differently to the same parts on control plants. All waterlogged plants developed hypertrophied lenticels within four weeks, followed by significant increases in stem diameter. In each clone most of the pre-existing root system died by the end of the waterlogging treatment. All clones formed adventitious roots which varied considerably between the species and to a lesser extent between clones within each species. InS. cinereamany short, fine, much-branched roots grew vertically upwards until they reached the water surface. InS. cinereaclone 90 they originated from both the pre-existing woody roots and from the hypertrophied lenticels on the submerged portions of the stems. InS. cinereaclone 12 they developed only from the hypertrophied lenticels. New roots produced by waterloggedS. capreaclones were long, sparsely branched and floated on or near the surface of the water. As inS. cinereaclone 90 they originated from both the pre-existing woody roots and the submerged hypertrophied lenticels. Whereas roots of the control plants of all clones were mostly ectomycorrhizal, those of the waterlogged plants had no mycorrhizae. In a second waterlogging experimentS.×sericans, S. viminalisandS. fragilisproduced adventitious roots more like those ofS. capreathanS. cinerea. Plants of all clones removed from the waterlogging treatment after 16 days and kept with their soil at field capacity thereafter produced many new roots from their old root balls. After 32 days waterlogging no such recovery occurred.Total submersion caused much more severe damage to the aerial parts of all tested species than waterlogging. After eight days submersion the shoot tips ofS. fragiliswere beginning to rot and by day 25 those ofS.×sericansandS. viminaliswere rotting too. Subsequently shoots developed from axillary buds which remained unaffected by rot throughout the experiment. InS. cinereashoot growth ceased after eight days and terminal buds were formed which remained dormant but healthy throughout the experiment. Submersion caused progressive loss of pre-existing leaves in all species. Some newly formed leaves of each species developed epinastic deformities after > 16 days of submersion. All species exceptS. cinereashowed significant reductions in root dry weight after 32 days of submersion.In a second submersion experiment responses of three clones each ofS. purpureaandS. viminaliswere compared. Shoot growth was reduced significantly in four of the six clones after 14 days. No further reductions occurred in the next 14 days of submersion. Root dry weight also decreased, but it took 28 days of submersion to produce the greatest effect. The faster growing clones of each species were more adversely affected by submersion in terms of both reduced shoot growth and root growth than those which grew more slowly.Considerable intraspecific variability in responses to waterlogging and submersion have been shown in these experiments by clones not selected for their variation in flooding tolerance. This suggests that selection and breeding could lead to the development of flood-tolerant cultivars of species such asS. cinereaandS. capreawhich are not noted for their ability to withstand inundation.

Changes in mandibular length before, during, and after successful orthopedic correction of Class II malocclusions, using a functional appliance

Forty-seven girls were successfully treated with a functional appliance (FA). To be included in this study, the rate of increase in mandibular length during treatment had to be greater than twice the mean rate for a subgroup of 20 of these patients evaluated during a pre-FA observation period. The mean mandibular growth rate was 6 mm per year while the FA was activated. In the ensuing months, cephalograms were taken at intervals coinciding with five post-FA phases, including complete edgewise treatment and retention. During the post-FA phase of initial edgewise treatment, the mandibular growth rate was dramatically reduced when compared with 47 controls matched for age, sex, and initial SN:GoGn angle. Selected individual cases are presented to illustrate the great variability in growth responses that were obtained. This study found highly significant increases in mandibular length still present 2 years after treatment, diminished but still significant gains after 3 years, and no significant difference after 4 years.

Regional Variation in Growth Response of Coastal Douglas-Fir to Nitrogen Fertilizer in the Pacific Northwest

Abstract Hypothesis-testing for differences in growth responses among physiographic strata, thinning levels, and fertilizer dosage levels resulted in a set of empirical models for predicting volume increment response of even-aged coastal Douglas-fir to nitrogen fertilizer. Absolute and percent responses are estimated for stands both thinned and unthinned, as a function of dosage levels and physiographic provinces. Although not "highly" significant, the physiographic factor was retained in the models for purposes of refinement. For. Sci. 36(3):625-640.

Histologic analysis of costochondral and sternoclavicular grafts in the TMJ of the juvenile monkey.

Variability in growth response of the mandible after replacement of the mandibular condyle with the costochondral junction of a rib (CCJ) is common. Other donor graft sites that are more similar to the mandibular condyle might be more suitable for mandibular condylar replacement. Previous studies have shown the histomorphologic and developmental similarities between the sternoclavicular joint (SCJ) and temporomandibular joint (TMJ). The purpose of this study was to evaluate histologically short-term adaptations within the TMJ after replacement of the mandibular condyle with the autogenous sternal head of the clavicle, and to compare these adaptations with autogenous CCJ and mandibular condyle (surgical control) transplants. Bilateral vertical ramus osteotomies were performed in 12 juvenile Macaca mulatta with the left condyle being immediately replaced and the right condyle removed and replaced with either the sternal head of the clavicle or costochondral junction of a rib. All grafts were stabilized with maxillomandibular fixation for five weeks. Two animals in each group were killed at five, 11, and 17 weeks postsurgery and prepared for histologic analysis. The results indicate that: 1) incorporation of all grafts into the recipient site occurred and all animals had good mandibular function and occlusion throughout the follow-up period; 2) the clavicular and mandibular condylar grafts were incorporated sooner than the CCJ grafts; 3) clavicular graft changes resembled those of the condylar grafts histologically while the costal grafts remained inert and unchanged; and 4) a new condylar process with cartilage similar to that of a normal mandibular condyle regenerated in the costal graft animals from cells presumably contributed by the periosteum of the mandibular ramus and TMJ capsule.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison ofSpartina alterniflora loisel. Transplants from different locations in a man-initiated marsh in North Carolina

Short and tall height form transplants ofSpartina alterniflora from Beaufort were compared with intermediate height form plants from three other North Carolina locations (Oregon Inlet, Ocracoke Island, and Snow’s Cut) at a common site for five growing seasons to determine variation in growth response as related to marsh initiation. In September, 5 months after planting, there were significant differences in height, basal area, and aboveground dry weight among transplants from the five locations. By the end of the second growing season, 17 months after planting, Beaufort short plants were still significantly shorter than those from any other location except Oregon Inlet and Beaufort tall plants were still taller than Beaufort short or Oregon Inlet plants. For the first two growing seasons, flowering occurred sequentially from north to south based on the site of origin of the transplants. Of five measures of growth, only the number of flowering culms m−2 differed significantly by the end of the third growing season, 29 months after planting. Over the 5 years, Beaufort tall plants at higher elevation and exposed to shorter periods of inundation decreased in height while the height of Beaufort short plants remained essentially unchanged. The reverse was observed in the lower elevation zone, inundated longer, where Beaufort short plants increased in height and the height of Beaufort tall plants remained essentially unchanged. Results support the ecophene, rather than ecotype, status of short and tall height forms. Results further indicate that transplants from different locations, over a relatively narrow latitudinal range, can vary in several measures of growth response for several growing seasons and suggest that it would be best to use transplants from stands of intermediate height form from recently colonized sites for stabilization and initiation of marsh development projects.

Maintenance of genetic polymorphism under conditions of genotype-dependent growth and size-selective mortality

Associations between heterozygosity at one or more electrophoretically detected enzyme loci and growth rate have been reported for several species of plants and animals, including several commercially important species of finfish and shellfish. The general pattern is for heterozygotes to grow faster than homozygotes, although there is some variation in growth response even within a species. Regardless of the physiological or biochemical basis of genotype-dependent growth, polymorphism at a locus affecting growth rate in an overdominant manner may be lost if larger individuals have a greater mortality rate than smaller ones. In an exploited population, mortality of this sort is likely to result from size-selective fishing pressure. Using a continuous-time single-locus model of natural selection, we have related the maintenance of polymorphism at a locus to two measures of fishing effort: β, the legal minimum size below which there is no mortality, and f, an instantaneous mortality rate owing to fishing (above the legal minimum size). We considered two different models of fishing mortality. In model 1, fishing mortality above the legal minimum size is constant; in model 2, fishing mortality is a linear function of size (above β). Numerical analysis of model 1 indicates that maintenance of polymorphism requires either a low rate of fishing mortality or a value of β that is close to zero or close to the maximum attainable size. Analysis of model 2 gives similar results, suggesting that the conclusions are not dependent on the exact form of the mortality function.Key words: heterozygosity, growth, size, mortality.

Genetic Variability in Growth Response of Chicks to Cold Brooding Temperature

Genetic variability in adaptation to brooding at a reduced temperature was examined by comparing 1 to 14-day body weight gains of progeny from 28 sire families of the Athens-Canadian randombred population brooded at 32.2 C and at 26.7 C. The 1 to 7-day gain of the chicks brooded at 26.7 C was significantly depressed, but 7 to 14-day gain was not significantly depressed by brooding at the reduced temperature. Heritability estimates averaged over the two trials were .31, .23, and .35 for the 1 to 7-, 7 to 14-, and 1 to 14-day weight gains of groups brooded at 32.2 C and .55, .59, and .67 for the gain of groups brooded at 26.7 C. The heritability estimates for the difference in weight gain of families brooded at the two temperatures was .78.

Effects of some common pesticides on growth and metabolism of the unicellular algae Skeletonema costatum, Amphiprora paludosa, and Phaeodactylum tricornutum

Abstract The marine unicellular algae Skeletonema costatum, Amphiprora paludosa, and Phaeodactylum tricornutum were exposed to dimethoate and bayluscide in laboratory bioassays. There was variation in growth response of the species and metabolism of metabolic products. For S. costatum, the 96-h EC50 values of dimethoate were 9.5, 10.65, and 11.2 ppm for dry weight, protein content, and number of cells, respectively, while for carbohydrate and chlorophyll content it was 11 ppm. EC50 values of bayluscide were 81, 64, 71, 76, and 69 ppb for dry weight, protein content, cell count, carbohydrate content, and chlorophyll content, respectively. For Amphiprora paludosa, EC50 values of dimethoate were 12.5, 10, and 10.5 ppm for dry weight, cell count, and carbohydrate content, respectively, whereas for protein and chlorophyll content it was 10.8 ppm. The EC50 values of bayluscide were 1520, 1450, and 1300 ppb for dry weight, cell count, and carbohydrate content, respectively, while for protein and chlorophyll content it was 1700 ppb. For P. tricornutum, 96-h EC50 values of dimethoate were 6.85, 11.2, 9, 8.5, and 10.2 ppm for dry weight, protein content, cell count, carbohydrate, and chlorophyll content, respectively. For bayluscide they were 45.5, 34, and 41.5 ppb for dry weight, protein content, and cell count, respectively and 44 ppb for carbohydrate and chlorophyll content.

The role of food particle size in the growth of juvenile Atlantic salmon (Salmo salar L.)

The effect of particle size of a commercial pelleted feed on the growth of Atlantic salmon from first feeding alevins to first and second year smolts was investigated using 20‐day feeding experiments. Ten experiments were performed over a two year period, each comprising six groups of fish separately selected from stock populations. Each group was presented with one of six sizes of food particle ranging from larger than the respective mean mouth breadth (100% feed size), through 50%, 25%, 12·5%, 6·25% to 3·125%. Experiments were performed in six radial flow/circumferential drain tanks under ambient photoperiod and water temperature. Growth rate was found to be closely related to feed size. Maximum growth in each case was shown only on one size of particle; larger and smaller sizes resulted in reduced growth. The particle size for maximum growth increased in direct proportion to fish length. Fish from 4·2 to 20·3 cm in length showed maximum growth on particle diameters 0·022 to 0·026 × fish fork length (PFR). First feeding alevins were found to show comparable growth rate on particle diameters 0·0115 to 0·090 PFR. Some seasonal variation in growth response was indicated. The results are discussed in relation to developmental and seasonal effects. Possible factors affecting the energetics of prey size related differential growth are discussed.

Platelet factors and the human vascular wall: Variations in growth response between endothelial and medial smooth muscle cells

In the present investigations, the effects of platelet factors on DNA-synthesis by human arterial and venous smooth muscle and venous endothelial cells were compared. Also studied was the role of such factors in restimulating quiescent endothelial cultures and in endothelial reaction to injury. Aortic smooth muscle cells grown in medium containing 10% human serum prepared from plasma poor in platelets (PPPS) reached 9.7%+/-SE 0.65 labelling index when continuously exposed to [3H] thymidine (1 muCi/ml). When lysate from gel-filtered platelets was added, the index was 19.4% +/- SE 1.13 (P less than 0.01) and in the presence of serum derived from platelet rich plasma (PRPS) it reached 24.6% +/- SE 1.22 (P less than 0.01). Similar results were obtained with smooth muscle cells from umbilical veins. In constrast, platelet factors did not significantly affect DNA-synthesis in endothelial cultures. They reached 25.6% +/- SE 1.97 when grown in medium containing PPPS as compared to 21.9% +/- Se 2.53 (P greater than 0.05), when exposed to PRPS. The ability of sera to stimulate DNA-synthesis in endothelial cultures rendered quiescent by 24 h exposure to medium containing 1.4% serum albumin (labelling index 1.83% +/- SE 0.14) was not affected by platelet factors. Platelet lysates alone were not sufficient to restimulate the quiescent cells (labelling index 3.03% +/- SE 1.06) (P greater than 0.05). Platelet factors did not affect the proliferative response following experimental mechanical injury to endothelial monolayers in vitro. We conclude that while platelet factors are essential for human vascular smooth muscle cells to achieve optimal growth, they are not indispensable for endothelial cell proliferation. It is suggested that these cellular differences in growth requirements may play an important role in human atherogenesis.

Predicting nitrogen fertilizer response in unthinned stands of Douglas‐fir

Abstract The mineralization potential of forest soils is a useful tool in predicting nitrogen fertilizer response in unthinned stands of Douglas‐fir. As the mineralization potential of the soil increased, diameter growth for 200 lbs/A of added N decreased. Significant growth response could not be detected when mineralizable nitrogen level was above 46 ppm. Percent stocking is also an important variable in predicting diameter growth response in these stands. For a given nitrogen level, response decreased with increasing stocking. When stocking and mineralizable nitrogen are used together, they account for a significant portion (86%) of the variation in growth response.

Growth Responses of Coastal Halophytes to Inorganic Nitrogen

Intraand interspecific variation in growth responses to inorganic nitrogen (NH+ or NO-) has been studied in halophytic species grown in sand culture. Populations of Aster tripolium, Plantago maritima, Salicornia europaea agg. and Triglochin maritimna from the upper levels of a salt marsh at Stiffkey, Norfolk, have slower growth rates than corresponding populations from a low marsh at the same locality. Populations of Aster tripolium and Plantago maritima from the upper marsh away from drainage channels grow slower than populations close to channels. Species characteristic of the low marsh such as Halimione portulacoides, Aster tripolium and Suaeda maritima have fast growth rates compared with the rates of species abundant in the upper marsh such as Armeria maritima and Limonium vulgare. Although there is seasonal variation in the concentrations of soluble inorganic nitrogen in the sediments of the two marshes, the values obtained are similar for both marshes, but the upper marsh, unlike the lower marsh, becomes hypersaline in summer. It is suggested that the slower growth response to nitrogen of plants from the upper marsh away from drainage channels is the result of selection for plants with relatively low growth rates, which are able to survive the period of stress during the summer months when the soil is hypersaline.

Utilization of n-alkanes by Cladosporium resinae.

Four different isolates of Cladosporium resinae from Australian soils were tested for their ability to utilize liquid n-alkanes ranging from n-hexane to n-octadecane under standard conditions. The isolates were unable to make use of n-hexane, n-heptane, and n-octane for growth. In fact, these hydrocarbons, particularly n-hexane, exerted an inhibitory effect on spore germination and mycelial growth. All higher n-alkanes from n-nonane to n-octadecane were assimilated by the fungus, although only limited growth occurred on n-nonane and n-decane. The long chain n-alkanes (C(14) to C(18)) supported good growth of all isolates, but there was no obvious correlation between cell yields and chain lengths of these n-alkanes. Variation in growth responses to individual n-alkane among the different isolates was also observed. The cause of this variation is unknown.