Physiological energetics of the zebra musselDreissena polymorpha in lakes I. Growth and reproductive effort

Shell growth of tagged zebra mussels (Dreissena polymorpha) was monitored in lakes at 3 sites over 1 1/2 years. It varied greatly with the season and was almost absent during winter months. Shell growth was significantly correlated with seston concentration, but not with water temperature. The theoretical maximum size (L∞) of the v. Bertalanffy growth equation did not vary seasonally. Tissue weight underwent a pronounced seasonal cycle. In animals of 20 mm shell length, minimum weights recorded in September only corresponded to one quarter to one third of the maxima in late spring. Tissue weight of animals from the 3 sites was distinctly different. Carbohydrate content of the tissue stayed below 10 per cent and tended to be highest in spring. Spring maxima of lipids were very pronounced. These lipids were primarily located in the digestive gland. These data were combined with data of gonad size by Borcherding (1991). Results imply that production of reproductive tissue even continues at a retarded rate during winter months, if food conditions were favourable. With poor food conditions, no production of reproductive tissue was estimated during winter; this, however, was followed by an elevated rate of reproductive tissue production in spring. Weight specific production decreased with a weight exponent of −0.24. Shell and byssus production contributed only in the range of 10 per cent to total production. Reproductive effort showed maxima of 30 to 45%. It increased with shell length at 2 sites and decreased at the other site with the largest animals.     

Laboratory culture of the larvae of Conus textile Linné (Gastropoda: Toxoglossa)

The larvae of the Indo-Pacific gastropod Conns textile Linné were reared in the laboratory from hatching through metamorphosis. Larvae fed a mixed phytoplankton culture of Isochrysis galbana and Phaeodactylum tricornutum grew at a rate of 0.06 mm/day and began metamorphosing 16 days after hatching. Unfed control cultures yielded no metamorphically competent larvae. Laboratory-reared larvae metamorphosed spontaneously on the walls of the fïberglass rearing tanks when their average shell length was 1.5 mm. Measurements made on field-collected Conns textile juveniles indicate that the larvae metamorphose at the same size in the laboratory as they do in nature.Rates of larval shell length increase and dry weight increase paralleled each other until metamorphosis. At this point, shell growth slowed while dry weight increased suddenly. It is suggested that this weight increase reflects calcification and strengthening of the fragile larval shell upon entering the benthic environment.     

Studies on the prolonged storage of Metarhizium anisopliae conidia: effect of temperature and relative humidity on conidial viability and virulence against mosquitoes

The shell lengths, dried shell weights, soft tissue wet weights, and soft tissue dry weights were ascertained for noninfected Ilyanassa obsoleta and for the same snail species naturally infected with the following digeneans: Himasthla quissetensis, Zoogonus lasius, Cercaria dipterocerca, Lepocreadium setiferoides, Microphalloides nassicola, Stephanostomum tenue, and Microbilharzia variglandis. Analyses of the data obtained indicate that infection with all of the trematodes listed above causes neither enhanced growth of soft tissues nor accelerated lengthening of the shell. However, snails infected with sporocysts of Z. lasius have significantly heavier shells than do noninfected snails. These data suggest that infection with Z. lasius may have caused enhanced growth in the form of increased calcium deposition in the shell of I. obsoleta, possibly as a result of parasitic castration. In addition, the mean dry weight of the soft tissues of snails infected with M. variglandis, when normalized for shell length, is significantly lower than that of noninfected snails, possibly as a result of parasite-induced pathology. Finally, comparisons among infected snails indicate a trend toward increased soft tissue dry weight in snails infected with L. setiferoides, although the mean dry weight of these snails does not differ significantly from the mean dry weight of noninfected snails.     

Bathymetric adaptations of reef-building corals at davies reef,great barrier reef,Australia. I. Long-term growth responses of Acropora formosa (Dana 1846)

In situ rates of linear growth (branch extension) were measured for Acropora formosa (Dana) at depths of 5, 10, and 15 m. Estimates of radial branch growth and internal accretion were made at the shallowest and deepest sites. In addition, reciprocal transplant experiments between these two sites were conducted using branches of different lengths. The in situ results showed that individual branches at the deep site extended twice as fast, and deposited more calcium carbonate than branches at the shallow site. Branch initiation, however, was more rapid at the shallow site. Thus, if the extension of new lateral branches were included to obtain a measure of overall growth, rates were highest at the shallow site. The initial length of the transplanted branches significantly affected growth rates. Longer branches showed greater overall growth within all treatments. Branch extension rates, however, increased with initial branch length at the deep site, while tending to remain constant at the shallow site. This result is interpreted as evidence that the extension of each branch tip at the deep site was supported by translocated metabolites derived from a greater volume of zooxanthellae-bearing tissue than at the shallow site. A. formosa exhibits different growth patterns at different depths. At the deep site, extension is favoured over branch initiation. Consequently, translocation from a greater volume of tissue is presumably available to sustain the higher extension rate at each tip. At the shallow site, where extension is less rapid but branch initiation is more rapid, each tip probably receives translocate from a smaller volume of tissue. These mechanisms result in different growth forms at the two sites and are apparently adaptations to different environmental conditions. Light or water motion, or a combination of the two are proposed as probable controlling factors.     

A multivariate study of geographic variation in the whelk Dicathais

An analysis has been made of the variation in shell shape and shell characteristics of 889 Australian and New Zealand specimens of the genus Dicathais, using multivariate techniques. Shell measurements taken were: the overall length, length of spire, length of aperture, and width of aperture. Weight of the shell plus the preserved animal was also recorded. The sculpture of the shell, thickness of the lip, and the presence or absence of a reddish or purplish colouration or banding on the inside of the lip, were assessed qualitatively.Principal component analyses of the size measurements for each site showed that the first principal component, which accounted for greater than 95% of the variation at each site, was associated with variation in the ‘size’ of the animal. Canonical analysis of the size measurements showed a cline in shell shape from the animals on the western side of Australia to those on the eastern side of Australia and New Zealand. The resulting canonical variates were associated with variation in the ‘shape’ of the shell. Principal component analyses of the between-group matrix and of the within-group matrix of the size measurements showed that the site means exhibited a similar pattern of dispersion to that of the animals within each site.Canonical analysis of the shell characteristics showed that variation along the first canonical axis was largely produced by shell sculpture, while variation along the second resulted from differences in colouration/banding.The generalized variances of the correlation matrices for the size measurements showed that groups with similar shell shape were associated with the presence of granite substrata and/or mussel beds or, alternatively, with limestone substrata, but canonical correlation analysis of the relationship between the size measurements and shell characteristics showed that no consistent trend was evident over all sites.A subjective examination of the structure of the radula of 84 animals showed that two distinct morphological forms were present, but that they were not correlated either with sex or any of the named shell forms or site groupings.An analysis of the growth curves of 27 animals of the two forms from the eastern and western coasts of Australia, held in the laboratory, was carried out. The eastern coast form showed a loss of sculpturing and a change in shell shape when kept under west coast conditions and on a mussel diet.Water temperature, diet, substratum, and degree of exposure to wave action were all found to show associations with variations in either shell shape or shell characteristics. It is suggested that the selective force of the habitat which produces changes in shell shape and shell characteristics of the animals at any site is a complex of factors, many of which are interrelated. The genetic basis for the development of shell shape and production of the shell characteristics in Dicathais may be similar to that found in Nucella lapillus (L.) in the Northern Hemisphere.These data suggest that the Dicathais found at the sites studied in this investigation are all part of the same ‘population’, the shell shape and shell characteristics of the adult populations being determined both by selection and phenotypic expressions caused by the selective force of the habitat at each site. It is concluded that the genus consists of a single highly variable species.The value of the application of multivariate analyses to this type of study is shown to lie in the way in which the techniques provide an overall picture of the variation within sites and of the variation between sites.     

Relative abundance and growth of mussels (Mollusca: Eulamellibranchia) in pools 8,9 and 10 of the Mississippi River

SUMMARY. Twenty-three species of unionid mussels were sampled during the summer of 1975 from a 76-mile reach of the Upper Mississippi River; this represented eight species fewer than were recorded in a 1930–31 survey for the same section of the river. Of the 244 sites sampled in 1975, mussels were found at 116 sites and the ten most productive sites accounted for 40.8% of the 1205 mussels collected. There were as many as thirteen different mussel species taken from one sampling site. The two most abundant species ( Amblema peruviana and Megalonaias gigantea ) constituted 54.5% of the mussels sampled in 1975; these two species made up only 8.3% of the 1930–31 survey. Individuals of the twelve most abundant mussel species were aged, and shell-length growth equations were determined. In addition, shell-free dry weight growth rate and shell weight growth rate was determined for Amblema peruviana . The calculated annual production for A. peruviana (assuming a mean density of 1 per m²) was 482 mg/m² shell-free dry weight, and 14.471 g/m² shell weight.     

Biometric studies on the bivalvesAstarte elliptica,A. borealis andA. montagui in Kiel Bay (Western Baltic Sea)

The threeAstarte species were studied in June 1983 at two sites in Kiel Bay, Süderfahrt and Schleimünde, at 20 m depth. Shell length to live wet weight correlations are given for all three species; forA. elliptica also shell-free dry weight, shell dry weight, ash-free dry weight of the soft body and ash-free dry weight of the shell are recorded as functions of the shell length. In the logarithmic length/weight regression analysis the coefficients of slope forA. elliptica andA. borealis are 3. ForA. montagui, that coefficient is significantly greater than 3. Weight conversion factors, calculated forA. elliptica, revealed a mean weight composition of 31.5 % water in the mantle cavity and tissue water, 64.5 % shell ash, 2.1 % organic content of shell, 1.7 % organic content of the soft body and 0.4 % ash of the soft body. An isometric growth of shell length and shell breadth is confirmed forA. borealis, whileA. montagui exhibits positive allometric shell growth and changes its shape during life.     

An intertidal limpet species as a bioindicator: Pollution effects reflected by shell characteristics

Mollusc shells have been widely used for monitoring the bioavailability of contaminants in the aquatic environment. The present work examined malformations among the shells of the limpet Siphonaria lessoni from heavily polluted, light polluted and unpolluted sites in Argentina. Data on shell shape, thickness, dry weight, microstructure and semi-quantitative elemental composition was evaluated as well as soft tissue dry weight. Shells from the heavily polluted site were significantly (p < 0.001) thicker than those from other areas. SEM (scanning electron microscopy) analysis of thickened shells revealed the presence of globular malformations on inner shell surfaces. On heavily polluted shells, elemental composition analysis by EDS (electron dispersive spectroscopy) of such malformations indicated concentrations three times higher of carbon and four times lower of calcium and oxygen than the control. Light polluted shells presented concentrations two times lower of calcium. In addition, soft tissues were lighter at the heavily polluted site (p < 0.001). These data demonstrate the sensitivity of this abundant and widely distributed intertidal limpet to aquatic pollutants, and support the use of this limpet as a potential biomarker.     

The effects of sediment type on growth rate and shell allometry in the soft shelled clam Mya arenaria L

Hatchery-reared juvenile Mya arenaria L. were grown for 11 wk in replicated gravel, sand, mud, and pearl net treatments under flow-through sea-water conditions in Maine. Analyses of variance showed significant differences between sediment treatments for final shell length, dry meat weight, chondrophore growth increment, and percent shell weight. Growth of juvenile M. arenaria was more rapid in fine sediments than in coarse sediments or nets.Regression slopes of shell length-shell height and shell length-shell depth varied significantly between sediment treatments. Slower-growing clams from nets and gravel were more globose than clams from sand or mud treatments. Clams grown in sand were longer and narrower than those from mud. Differences in growth rates and shell form were attributed primarily to the physical properties of the substrata, and their effects on the scope for growth of M. arenaria.     

Plastic and Heritable Variation in Shell Thickness of the Intertidal Gastropod Nucella lapillus Associated with Risks of Crab Predation and Wave Action,and Sexual Maturation

The intertidal snail Nucella lapillus generally has thicker shells at sites sheltered from wave action, where crabs are abundant and pose a high risk of predation, than at exposed sites where crabs are rare. We studied two populations showing the opposite trend. We reciprocally transplanted snails between field sites and measured shell length, width and lip thickness of those recaptured 12 months later. Snails transplanted to the sheltered site grew larger than sheltered-site residents, which in turn grew larger than transplants to the exposed site. Relative shell-lip thickness was greater in residents at the exposed site than at the sheltered site. Transplants from shelter to exposure developed relatively thicker shells than their controls and relatively thinner shells from exposure to shelter. Progeny of the two populations were reared for 12 months in a common garden experiment presenting effluent from crabs feeding on broken conspecifics as the treatment and fresh sea-water as the control. The crab-effluent treatment decreased foraging activity, concomitantly reducing cumulative somatic growth and reproductive output. Juveniles receiving crab-effluent grew slower in shell length while developing relatively thicker shell lips than controls, the level of response being similar between lineages. F₂ progeny of the exposed-site lineage showed similar trends to the F₁s; sheltered-site F₂s were too few for statistical analysis. At sexual maturity, shell-lip thickness was greater in snails receiving crab-effluent than in controls, indicating plasticity, but was also greater in the exposed-site than in the sheltered-site lineage, indicating heritable variation, probably in degree of sexual thickening of the shell lip. Results corroborate hypotheses that ‘defensive’ shell thickening is a passive consequence of starvation and that heritable and plastic control of defensive shell morphology act synergistically. Shell thickening of juveniles was similar between lineages, contrary to hypotheses predicting differential strengths of plasticity in populations from low- or high-risk habitats.     

Shoot preformation in clones of Fraxinus pennsylvanica in relation to site and year of bud formation

Summary Shoot preformation was investigated in buds of four clones of Fraxinus pennsylvanica var. subintegerrima (Vahl) Fern. at two sites in Manitoba in the second (1988) and third (1989) growing seasons after grafting. More preformed primordia were produced in terminal buds in 1989 compared to 1988 at each site. Both terminal and lateral buds at Morden contained significantly more primordia than those at Winnipeg. The numbers of preformed primordia were significantly different among clones. Clone 3 produced the most and clone 1 the fewest primordia in terminal buds. Despite quantitative variation, the pattern was similar among clones for terminal buds at each site and in each year. A similar pattern was evident for lateral buds at the Winnipeg site in 1989 but at Morden, clones 4 and 1 had the largest number of preformed primordia. Data from 1989 revealed that numbers of primordia were correlated with bud dimensions, parent shoot length, diameter and number of leaves, and location of the bud on the parent. Shoot dry weight was also related to these variables and revealed a non-linear increase in dry weight with shoot length. Multiple regression, with parent shoot length and location of buds along the parent axis as independent variables provided a reliable indicator of preformation in the crown. Although there is a genotypic component to preformation, variation between sites, years and crown locations suggests plasticity in bud development.     

Physiological energetics of the zebra musselDreissena polymorpha in lakes III. Metabolism and net growth efficiency

Oxygen consumption and ammonia excretion of the zebra musselDreissena polymorpha from 3 sites in lakes were estimated regularly over the course of 1 1/2 years at ambient temperature. They showed a pronounced annual cycle, when expressed in absolute terms (at standard shell length) and in weight specific terms (at standard tissue weight). The atomic ratio of oxygen consumed to ammonia-N released (O/N ratio) was lowest in late summer at all sites (10 to 20) and highest during winter and spring (50 to > 100). The mean body weight exponent pooled from these sites was 0.78 (95% confidence interval±0.07) for the oxygen consumption rate and 0.80 (confidence interval±0.10) for the ammonia excretion rate. Both oxygen consumption and ammonia excretion were significantly correlated with the water temperature at the 2 shallow water sites, where temperature variation was most pronounced. Correlation with seston content or gonad volume were insignificant at these sites. The quotient of filtration capacity to oxygen consumption rate was about 3 times higher at the site with the poorest food conditions compared to the other sites. Net growth efficiency was highly variable; its annual average was 35 to 40 per cent and independent of locality and animal size.     

Experiments on orientation of the intertidal barnacle Tesseropora rosea (Krauss)

The intertidal barnacle Tesseropora rosea (Krauss) exhibits very marked directionality of orientation on sloping and vertical surfaces. The barnacles are orientated so that their cirral fans face the water current; this pattern was found within 1 wk after settlement. Adults also showed similar orientation to the water current at each site.Three manipulative experiments were done in the field to determine the consequences of incorrect orientation by the barnacles. Correct orientation was necessary for T. rosea to maintain its tissue weight, but experimental rotation of barnacles through 90° or 180° made no difference to rates of shell growth, mortality or weight of egg masses. Furthermore, this species was unable to re-orientate once it had metamorphosed, and orientation of newly-settled barnacles was not influenced by that of adults.     

Relative growth and reproductive cycle of the date mussel Lithophaga lithophaga (Linnaeus, 1758) sampled from the Bizerte Bay (Northern Tunisia)

Relative growth and the reproductive cycle of the date mussel Lithophaga lithophaga were studied from September 2002 to October 2003 in the Bizerte Bay (Northern Tunisia). Relationships between shell length and shell width, shell height as well as volume-related variables (shell dry weight, soft tissues dry weight and total wet weight) showed negative allometries in both sexes except for shell width in males (isometry) and shell height in both sexes (positive allometry). The sex ratio was unbalanced, within the length range of 6–48 mm, 49.43 % of the animals were males, 24.39 % females and 26.17 % sexually undifferentiated; within the length range of 49–92 mm, the respective values were 41.19, 52.7 and 6.1 %. Histological investigations as well as analyses of the condition index and the gonadosomatic index (CI and GSI) revealed the presence of a single reproductive cycle per year. Spawning occurred at the end of August and early September and was associated with a decrease in seawater temperature and salinity. A resting phase occurred in winter, coinciding with the lowest water temperatures. Histological examinations of the gonads of a total of 130 specimens revealed only two cases of hermaphroditism. The present study constitutes a useful baseline for a sustainable management of local wild stocks of L. lithophaga.     

Adaptation of five columnar cactus species to various conditions in the negev desert of Israel

Five species of columnar cacti were examined with the aim of introducing new orchard crops to the Negev desert of Israel. The species comprisedStenocereus gummosus, S. griseus, S. thurberi andPachycereus pringlei, all found in semi-arid regions of Mexico, andCereus peruvianus, which is grown in sub-tropical regions. Young seedlings were planted at four sites in the Negev. The sites differ in climatic conditions and water quality. Growth data, expressed as total stem length and stem biomass, was obtained after five to six years in the orchards. They showed thatC. peruvianus grew best in the site with moderate temperatures and good-quality water, whereas the other species also did well under more extreme conditions of high temperatures and brackish water. Growth of all species was significantly retarded at the site having water with the highest NaCl content. In the sixth year a severe drop in temperature at one of the sites caused extensive injury toC. peruvianus andS. griseus plants, raising doubts as to the suitability of that site for their cultivation. At this stageC. peruvianus is the most promising candidate for domestication. Its growth rate was much higher than that of the other species, yield was precocious and fruit of good quality. Stem tissue ion concentrations (dry weight basis) showed that accumulation of K⁺was similar at all four sites and that Na⁺and Ct were significantly higher (probably in toxic concentrations) at the site with the highest concentrations ofNa⁺and Cl~ ions in the water. At all sites Cl~ concentration inC. peruvianus was much lower than that in the other species indicating that the exclusion of Cl^- from the stems was not correlated to salt tolerance.     

Growth and tissue mass cycles in the infaunal bivalve Yoldia eightsi at Signy Island, Antarctica

Shell growth in Yoldia eightsi was measured over an austral summer and winter in 1992. In specimens < 12 mm length, growth was not significantly different between summer and winter periods, and the fastest recorded rate, 6.3 μm day⁻¹ was for 5-mm individuals during the winter. In summer, specimens of all lengths grew significantly, but in winter bivalves > 27 mm length did not increase in length. Tissue dry and ash-free dry mass (AFDM) cycles were assessed at monthly intervals between December 1988 and January 1991. ANCOVA indicated significant interannual and seasonal effects on this cycle. Tissue mass increased in the summer, coinciding with the phytoplankton bloom and the period of maximum sedimentation of organic material from the water column. A standard 20-mm-length animal reached a maximum AFDM of 114 mg in February 1990. The minimum value (68 mg AFDM) throughout the 2 years of measurements was in early December 1988, at the end of the austral winter. Periods of tissue mass increase were, therefore, decoupled from shell growth, at least in juveniles. Tissue mass was significantly higher in 1990 than 1989, which was mainly due to high organic contents in the summer (January to May). This was not consistent with the pattern of organic content in the sediments at the study site, but was in phase with the cycle in sediment chlorophyll a content. Tissue mass increase depended on major resource input during the summer, but Y. eightsi was capable of maintaining winter condition from stocks of benthic microalgae in years of poor ice cover. Tissue mass declined between April and July each year. This was accompanied by large falls in tissue ash content, and coincided with the spawning period in early June. These are the first monthly tissue mass data collected over a 2-year period for an Antarctic mollusc. They are the first such data indicating seasonal variation in tissue mass and showing a decoupling of shell and tissue growth in a polar bivalve. The P/B ratio calculated from these data was 0.106, which is slightly lower than previous values found for this species, but is in line with general values for Antarctic marine benthos. Accepted: 6 December 1999     

Seasonal variation in standing crop,density and leaf growth rate of the seagrass, Heterozostera tasmanica, in western Port and Port Phillip Bay,Victoria, Australia

Standing crop, density and leaf growth rate of Heterozostera tasmanica (Martens ex Aschers.) den Hartog along with light, temperature, nutrient and sediment characteristics were determined monthly for fifteen months at three study sites in Western Port and one site in Port Phillip Bay, Victoria, Australia. Erect vegetative stems of H. tasmanica were frequently branched, were present throughout the year and accounted for 25–60% of the above-sediment biomass, with the stem proportion higher during winter than summer. At three of the four sites there was a unimodal seasonal pattern in which minimum leaf standing crop (27–61 g dry wt. m^?2), density (600–2000 leaf cluster m^?2) and leaf productivity (0.34–0.77 g dry wt. m^?2 day^?1) generally occurred during winter (June–August) and maximum leaf standing crop (105–173 g dry wt. m^?2), density (2700–5000 leaf cluster m^?2) and leaf productivity (2.6–4.2 g dry wt. m^?2 day^?1) occurred during summer (December–February). A bimodal seasonal pattern with minimum standing crop and density during midsummer occurred at one site. This anomalous seasonal pattern may be due to exposure and desiccation stress during spring low tides. At the site receiving the lowest irradiance, standing crop, density and annual leaf production also were lowest, but length and width of leaves, shoot height and leaf growth rate per leaf cluster were the highest of the four study sites. On average, each leaf cluster at any one of the study sites produced 30–31 leaves per year with mean leaf turnover rates of 1.3–1.7% day^?1. Annual leaf production of H. tasmanica ranged from 410 to 640 g dry wt.m^?2 at the four sites.     

Effects of shoot position on shoot and leaf morphology of Avicennia marina in the hyperarid Red Sea coastal region of Egypt

We examined the effects of shoot position on shoot growth and morphology of Avicennia marina (Forssk.) Vierh. in the Red Sea coastal region of Egypt. To determine differences in morphological characteristics, we collected shoots from the upper and lower canopies of A. marina individuals in the wild and compared the morphological characteristics of these shoots. The study plot was established in an A. marina mangrove forest. Heights and diameters of individual trunks (n = 14) in the plot were measured at ground level. Then, five shoots with young but fully expanded leaves were collected from the upper and lower canopies of the individuals. We measured shoot length, and dry weight and also area, dry weight, thickness, and Soil Plant Analysis Development (SPAD) value of collected leaves. Our measurements showed that leaf area, dry weight, specific leaf area, and SPAD value of leaves from the upper canopy were smaller than those of lower-canopy leaves in most individuals. From the differences in traits between upper and lower leaves, we concluded that leaves in the upper canopy are typically adapted to high light levels, whereas leaves in the lower canopy exhibit adaptations to low light conditions. In addition, soil-water salinity at the study site was far higher than the optimum salinity for A. marina. Hence, it is also suggested the salinity level at this site may have influenced the reduced leaf size in the upper canopy.     

Biomass Accumulation and Main Stem Elongation of Durum Wheat Grown under Mediterranean Conditions

Detecting and exploiting genetic variation in biomass accumulationis of great importance for increasing wheat yield when the harvestindex is close to its upper limit. This study was undertakento analyse the pattern of biomass accumulation and main stemelongation in 25 durum wheat (Triticum turgidum L. ‘Durum’)genotypes. Field experiments were conducted over 2 years intwo environments contrasting in the amount of available water,in northeastern Spain. Plants were sampled at the main stagesof Zadoks' scale, and dry weight per plant, crop dry weight(CDW) and main stem length were measured at each stage. Measurementsfor growth traits and thermal time from sowing fitted betterto an asymmetric logistic peak curve than to the Richards logisticmodel. Four biological variables were computed from the curve.Differences among curves describing changes in biomass werefound to be greater between irrigated and rainfed sites thanbetween years. Drought stress had less effect on main stem elongationthan on biomass accumulation. Average dry weight per plant andCDW were reduced by drought by 42 and 38%, respectively, duemainly to similar reductions in the mean rate of growth of thetwo variables. In contrast, cycle length from sowing to themaximum values of dry weight per plant and CDW was only slightlymodified by drought. Copyright 2001 Annals of Botany Company Triticum turgidum L. ‘Durum’, durum wheat, biomass, crop dry weight, stem length, rate of growth, modelling, growth analysis, logistic peak curve     

Genotypic variation in wood properties and growth traits of triploid hybrid clones of Populus tomentosa at three clonal trials

To better understand the genetic control of growth traits (tree height, dbh, and stem volume) and wood properties (basic wood density and fiber length) in triploid hybrid clones of Populus tomentosa, genetic relationships among selected wood properties with growth traits were examined in 5-year-old clonal field trials located in Yanzhou, Gaotang, and Xiangfen, northern China. In total, 180 trees from 10 clones were sampled from the three sites. The site had a moderate effect on basic wood density (BWD), stem wood dry weight (DWT), and tree growth and had a highly significant effect on fiber length (FL) (P?<?0.001). Clonal effects were also significant (P?<?0.05) for all studied traits (except for diameter at breast height (DBH) and stem volume (SV)). Clone × site interaction was significant for all the studied traits except for FL. The estimated repeatability of clonal means for FL (0.91) was higher than for BWD (0.71), DWT (0.62), tree height (0.62), DBH (0.61), and SV (0.55). Intersite genetic correlation estimates indicated that wood properties were more stable than growth traits. Phenotypic correlation estimates between SV and BWD ranged from ?0.29 to ?0.10.