Differences In Relative Growth Rate Research Articles

Unraveling the forage productivity puzzle: Comparing fast and slow-growing grasses.

Functional traits are powerful tools for distinguishing between plants with different resource acquisition strategies. Fast-growing plants normally dominate resource-rich habitats and present trait values associated with high productivity, such as high specific leaf area (SLA), short leaf lifespan, and rapid leaf elongation rate (LER). In contrast, slow-growing species have a higher leaf weight ratio (LWR), leaf lifespan (LLS), and phyllochron, which are useful traits for survival in stressful and unfertile environments, but are normally thought to be incompatible with high productivity, even under fertile conditions. We tested the hypothesis that slow-growing forage grasses have demographic parameters (tiller population density and canopy density) that offset their slow individual traits, making them as productive as fast-growing species when grown in fertile soil. Species with contrasting growth strategies (Arrhenatherum elatius L. and Festuca arundinacea Schreb cv. Quantum II, fast and slow-growing species, respectively) were cultivated in 45 m2 field plots and subjected to the same cutting regime and nitrogen supply level. Functional traits and canopy attributes were continuously measured during 8 growing cycles after the establishment of the swards. A. elatius had higher SLA, LER, leaf senescence, and leaf appearance rates, whereas F. arundinacea had higher LLS and LWR values. Conversely, there were no differences in relative growth rate or forage accumulation. F. arundinacea was able to offset their plant functional traits, typically associated with slow-growing grasses, with some demographic parameter like higher tiller population density, allowing it to be as productive as the fast-growing A. elatius when both were grown in fertile soil. Therefore, we suggest cautionary use of traditional plant functional traits to explain and predict the annual productivity of slow-growing grasses.

Whole-plant and leaf determinants of growth rates in progenies of Genipa americana L. (Rubiaceae).

Genipa americana (Rubiaceae) is a fruit tree with broad phytogeographic domain and suitable for different silvicultural systems in the tropics. The knowledge associated with the relative growth rate of species such as G. americana, provides important guidelines for the effective establishment and survival of seedlings after planting in the field. In this study we investigated differences in growth, biomass allocation and photosynthesis of seedlings originating from different mother plants of G. americana in southern Bahia, Brazil. For this, we evaluated fifteen variables associated with carbon balance at the whole plant and leaf scales of twelve G. americana progenies. All seedlings grew over a period of 198 days under similar microclimatic conditions with approximately 65% full sun. Our results showed significant differences in the relative growth rates (RGR), with the highest and lowest mean values being 29.0 and 38.0 mg g-1 day-1, respectively. Differences in RGR between G. americana progenies were highly related to differences in biomass allocation at both whole plant and leaf scales. From a practical point of view, we demonstrate that the selection of mother plants to produce seedlings with higher growth rates, and consequently greater establishment capacity in field plantings, can be made from evaluations of growth and biomass allocation variables at the whole plant scale.

Effects of pH and salinity on survival, growth, and enzyme activities in juveniles of the sunray surf clam (Mactra chinensis Philippi)

The study investigated the impact of salinity and pH changes on the survival, growth, and antioxidant enzyme activity in Mactra chinensis Philippi (1.00 ± 0.10 cm shell length, 0.75 ± 0.04 cm shell height), a marine clam species. Juveniles were exposed to various pH levels (5.4 - 9.6) and salinities (5 - 35 psu) for up to 20 days at 19 ± 0.5 ˚C. The individual effect of salinity and pH on juveniles were evaluated under pH 8.0 and salinity 30 psu, respectively. The results indicated that the highest survival rates were observed at pH 8.0 (85%, salinity = 30 psu) and salinity 30 psu (95%, pH = 8.0). The survival rates were significantly reduced at extreme pH (≤ 7.2; ≥ 8.4) and salinities (≤ 15; 35 psu). Additionally, oxidative stress was observed in clams exposed to low pH and salinity as indicated by the decreased activities of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). Notably, no significant difference in relative growth rates was observed between salinity 25 and 30 psu, between pH 7.8/8.4 and pH 8.0. Our results provide information on potential impact of pH and salinity changes on economically important bivalve species and may be used to optimize pH and salinity in aquaculture.

Eco-physiological response mechanism of Tamarix chinensis to soil water changes in coastal wetlands of the Yellow River Delta

Elucidating the effect of soil moisture on the adaptation of dominant plants in coastal wetlands is important for predicting the evolution of vegetation in the region. In this paper, Tamarix chinensis, a dominant species in the Yellow River Delta, was used as the object to study the changes of its growth and physiological parameters with increasing soil salinity under different moisture conditions (normal watering, persistent drought and persistent waterlogging). Different salt stress (2‰, 5‰, 8‰, 12‰, 16‰, and 20‰) using pot experiments was also used to reveal the mechanism of soil moisture on its salt tolerance. The results showed that the relative growth rate between 5‰-8‰ soil salinity was the largest, and growth was significantly inhibited above 20‰. Among different moisture conditions, the difference in relative growth rate under normal watering and persistent drought were nonsignificant, while both were significantly lower than those under persistent waterlogging. With increasing soil salinity, relative water content and total chlorophyll content significantly decreased, and cell membrane permeability (malondialdehyde), sodium ion, osmoregulatory substances (proline, soluble protein), and protective enzyme activity (SOD) significantly increased, while changes in non-structural carbohydrates (NSC) were not significant. Compared with normal watering and persistent waterlogging, persistent drought had the lowest leaf relative water content, total chlorophyll content, and sodium ions, and the highest cell membrane permeability, osmoregulatory substances and protective enzyme activity. With increasing treatment time, the relative leaf water content and total chlorophyll content significantly decreased, and cell membrane permeability, osmoregulatory substances and protective enzyme activity increased more significantly than normal watering and persistent waterlogging. NSC increased under normal watering and persistent waterlogging, while significantly decreased under persistent drought. Correlation analysis showed that the relationships between sodium ions, total chlorophyll content and malondialdehyde were various under different moisture conditions. Under persistent drough, malondialdehyde was significantly positively correlated with relative conductivity, superoxide dismutase, proline, soluble protein and soluble sugar. Total chlorophyll content was the key indicator reflecting the salt and waterlogging tolerance of T. chinensis under normal watering and persistent waterlogging, while cell membrane damage was under persistent drought. In summary, T. chinensis has strong salt and waterlogging tolerance, but persistent drought with salt stress can have serious impacts on its growth and survival.

Supplementary Tables. Statistical analysis of the difference in relative growth rates between treatment groups in Growth and Differentiation Trials

Supplementary Tables. Statistical analysis of the difference in relative growth rates between treatment groups in Growth and Differentiation Trials

Effects of salinity and temperature on growth and survival of diploid and tetraploid larvae of the Pacific oyster, Crassostrea gigas

Tetraploid of Crassostrea gigas was first reported in the 1990s, but its biological characteristics are seldomly known. To understand the adaptation of tetraploid larvae to salinity and temperature, the effects of salinity treatments (10, 15, 20, 25 and 30 psu) and temperature treatments (18, 23 and 28 °C) on the growth and survival of tetraploid and diploid larvae were comparatively studied. In salinity treatments, the accumulative survival rate (ASR) and relative growth rate (RGR) of tetraploid larvae were generally lower than that of diploid larvae (P < 0.05). The maximum ASR and RGR of tetraploid larvae occurred at 30 psu, with the values of 41.09% and 152.91%, respectively. At day 16, the maximum difference in ASR between diploid and tetraploid larvae was 36.41% at 20 psu, and the maximum difference in RGR of diploid and tetraploid larvae was 62.36% at 10 psu. The ASR and RGR of tetraploid larvae were lower than that of diploid larvae under temperature treatments (P < 0.05). The maximum ASR and RGR of tetraploid larvae occurred at 28 °C, with the values of 19.67% and 235.40%, respectively. The ASR of both diploid and tetraploid larvae decreased sharply in the first four days. The RGR of larvae at 18 °C was much lower than that at 23 °C and 28 °C (P < 0.05). Hence, a salinity range of 25–30 psu and a temperature range of 23–28 °C are suitable culture conditions for tetraploid larvae. These results indicate that the natural environment conditions can meet the temperature and salinity requirements for the survival and growth of tetraploid larvae. However, tetraploid larvae are less adaptable to temperature and salinity than diploid larvae. The environmental adaptability of tetraploid needs further improvement.

Plant functional traits shape growth rate for xerophytic shrubs.

Trade-offs exist for xerophytic shrubs between functional traits, involving in water loss and assimilate accumulation, can contribute to its survival and growth rate regulation in arid environments. However, growth analysis based on plant functional traits has been focused on the study of herbs and woody species. It is still unclear how the functional traits of xerophytic shrubs regulate their growth rate. In this study, we selectedeight xerophytic shrubs as samples to analyze the regulation process of the functional traits of shrubs on growth rate. Plants were cultivated for three years, and three harvests (every one year) were carried out. Factors explaining between-species differences in relative growth rate (RGR) varied, depending on whether different ages were considered. The results showed that RGR was positively correlated with net assimilation rate, but there was a significant negative correlation with leaf area ration (LAR), specific leaf area (SLA), and leaf biomass ratio in the age 1. However, in the age 2, RGR showed a significant positive correlation with the morphological traits (i.e., leaf area ration and specific leaf area), but not with physiological traits (i.e., net assimilation rate) and leaf biomass allocation. Our results suggested that the fluctuation of environmental factors affects the regulation path of the plant functional traits on RGR of xerophytic shrubs. However, the analysis of causality model showed that no matter in which age, net assimilation rate and leaf area ration principally drive the variation in RGR among xerophytic shrubs.

Effects of light source and photoperiod on growth of duckweed Landoltia punctata and its water quality

This study investigated the effects of light source [LED white (LW), fluorescent white (T5) and LED blue (LB)] and photoperiod (12:12, 16:08, 24:00 light/dark) on growth of duckweed Landoltia punctata and the resulting effects on its water quality for 16 days. The average daily relative growth rate (RGR) reached about 0.519 g d−1. Both light source and photoperiod had no significant difference on the mean RGR; however, their interaction had significant effects on duckweed's growth (p ≤ 0.05). Moreover, except T5 (24:00) > [T5 (12:12) ≥ T5 (16:08) ≥ LB (24:00)], LW (12:12) > [T5 (16:08) ≥ LB (24:00)], and LB (12:12) > LB (24:00), there were no differences in RGR in all pair-comparisons of treatment (p ≤ 0.05). Nitrate (NO3−) mostly influenced weight increment (WI), 70%. For light source and photoperiod effects on water quality, no total ammonia nitrogen (TAN) was detected in all treatments after 16 days, while NO3− increased gradually. In addition, results show that most of the total nitrogen (TN) was contributed from NO3− (R2 = 0.9999). Overall, our findings could contribute on producing duckweed in a controlled and programmed condition for maximum production and quality. Constructed models and practical application contribute in predicting nutrients sensitivity and proven useful in water management or water quality assessments.

Exposure of earthworm (Eisenia fetida) to rice straw biochar: Ecotoxicity assessments for soil-amended programmes

Increasing attentions of agricultural straw-derived biochar on biological interactions in soil environment have been gained following the benefits obtained from its role of soil conditioner. However, scientific probing on its unintended effects on soil organisms remain largely understudied. In this study, an avoidance test and a 14-day of incubation experiment in earthworm Eisenia fetida were conducted in field soil amended with rice straw-derived biochar (RSB) to evaluate its eco-toxic effect. Results showed earthworms strongly avoided soil amended with RSB from 7.5% to 15% at statistically significant levels. Subsequent 14-day incubation experiment with RSB rates up to 5% without avoidance responses showed these doses did not cause statistically significant difference in relative growth rate and survival rate regardless of incubation time of 7 or 14 d. Data obtained from 5% RSB application not only led to decrease in activities of digestion-related enzymes including Na+-K+-ATPase and cellulose, but facilitated some abnormities of intestinal epithelial tissue. Meanwhile, skin structure deterioration mainly related to upper stratum corneum appeared both in 2.5% and 5% amendments application. Additionally, RSB usage rates up to 2.5% and 5% also led to significant decrease in ROS and MDA but accompanied with unaffected antioxidant enzymes of SOD and CAT. Even importantly, only 5% amendment induced coelomocyte DNA damage supported by increased values of tail DNA% and OTM. Our research identified statistical effect thresholds related to RSB application rates and suggests that lower amendment with RSB no more than 1% have no eco-toxic effect on earthworms Eisenia fetida, whereas some adverse impact mainly found in higher addition up to 5%, which provide safe supporting for usual loading of soil with lower rates of RSB as soil conditioner to soil organisms in practice production.

Comparative Evaluation on Combined Ecotoxic Effects of Nitrofurazone and NH4CI Using Two Ciliated Protists as Model Organisms: Population Dynamics and Growth Rates

Ecotoxic effects of antibiotics or ammonium have been confirmed independently in aquatic animals, but few studies have investigated their combined effects. In aquaculture ecosystems, these pollutants frequently coexist, and often in high concentrations. In this study, the combined effects of antibiotic nitrofurazone and NH4Cl on the population dynamics and growth rates of two species of ciliated protists, Euplotes vannus and Pseudokeronopsis rubra, were investigated. Profiles of the dose-responses were visualized, and interactions between the two pollutants were quantified by the response surface method (RSM). Results showed that 1) the dynamics of the population growth differed significantly between the testd ciliates and varied with the concentrations of the pollutants; 2) the relative growth rate (RGR) of both ciliates decreased significantly with increased pollutant concentrations, while the difference in RGR between the two ciliates was not significant; 3) RSM analysis demonstrated an additive effect of nitrofurazone and NH4Cl on the RGR in both ciliates. In brief, ecotoxic effects can be caused by nitrofurazone and ammonium independently on the two test ciliates, and such effects can be strengthened when they present at the same time. These findings offer a valuable reference for evaluating combined ecotoxic effects caused by multiple pollutants in aquaculture ecosystems.

The Effects of Temperature and Potassium Fertilizer on the Growth, Yield, and Biochemical Parameters of Ipomoea batatas var. Antin-1

The impact of temperature and potassium fertilizers on the growth, yield, and basic biochemical characteristics of sweet potato, &lt;em&gt;Ipomoea batatas &lt;/em&gt;var. Antin- 1, was investigated in lowland and highland terrains. In this study we aimed to determine the different traits of the sweet potato, based on its morphology, physiology, and biochemical composition, following treatments with a potassium fertilizer at different temperatures. The study was undertaken using a nested factorial design. The first factor was temperature at each of the two sites: T1 (lowland) and T2 (highland). The second factor was potassium fertilizer (K&lt;sub&gt;2&lt;/sub&gt;O) nested within the temperature factor and consisting of four levels of K: K0 (0 kg/ha), K1 (50 kg/ha), K2 (100 kg/ha), and K3 (150 kg/ha). Each potassium treatment was replicated three times at each location. Plant vegetative growth in the lowland region, with a daily average temperature of 26.8 °C, tended to be more bushy, with several different morphological properties: The main stem was longer (160.7 cm) and spreading, the stem diameter was greater, and the petioles were significantly longer in the lowland plants compared with the highland plants; however, no differences were observed in the leaf characteristics. The differential temperature (depending on altitude) resulted in significant differences in relative growth rates (RGR) and net assimilation rates (NAR); the values for RGR-1 and NAR-1 in the lowlands were higher than those in the highlands. The tuber weight, yield index, anthocyanin accumulation, and glucose content were significantly higher in the highland crops than in the lowland plants, which grew under relatively higher temperatures. Potassium applications caused significant differences in the anthocyanin content (mg/100 g fresh weight), anthocyanin production (kg/ha), and glucose production (kg/ha) at different locations.

Spatiotemporal Differences in the Regional Cortical Plate and Subplate Volume Growth during Fetal Development.

The regional specification of the cerebral cortex can be described by protomap and protocortex hypotheses. The protomap hypothesis suggests that the regional destiny of cortical neurons and the relative size of the cortical area are genetically determined early during embryonic development. The protocortex hypothesis suggests that the regional growth rate is predominantly shaped by external influences. In order to determine regional volumes of cortical compartments (cortical plate (CP) or subplate (SP)) and estimate their growth rates, we acquired T2-weighted in utero MRIs of 40 healthy fetuses and grouped them into early (<25.5 GW), mid- (25.5-31.6 GW), and late (>31.6 GW) prenatal periods. MRIs were segmented into CP and SP and further parcellated into 22 gyral regions. No significant difference was found between periods in regional volume fractions of the CP or SP. However, during the early and mid-prenatal periods, we found significant differences in relative growth rates (% increase per GW) between regions of cortical compartments. Thus, the relative size of these regions are most likely conserved and determined early during development whereas more subtle growth differences between regions are fine-tuned later, during periods of peak thalamocortical growth. This is in agreement with both the protomap and protocortex hypothesis.

Three-dimensional analysis of inter-and intraspecific variation in ontogenetic growth trajectories of planktonic foraminifera

Abstract Planktonic foraminifera grow by adding chambers onto their tests, modifying their surface area, volume, porosity, and ornamentation with each addition. This process results in a wide variety of adult morphologies and preserves a record of the early morphology. With high-resolution three-dimensional imaging techniques, precise measurements can be made on previously inaccessible parameters like surface area and volume of the test interior. Here, we used three-dimensional images (microCT scans) of extant planktonic foraminifera from plankton tows and sediment traps to measure and compare the variation in chamber and whole test volume within and between seven morphospecies. By incorporating data from Caromel et al., (2015), we were able to explore the extent of interspecific variation in growth (i.e., total volume) with each chamber addition from a total of 12 extant species. All species measured approximately adhered to log-linear growth trajectories through the majority of their ontogeny. Species exhibited characteristic deviations from the log-linear growth trajectory and were grouped into three categories on the basis thereon. The volume of the first chamber—the proloculus—varied by more than two orders of magnitude. However, subtle differences in relative growth rates could make up for the initial variation proloculus size, such that the correlation between proloculus size and biovolume decreased through ontogeny. Intraspecific variation in proloculus size, cavity volume at the final five chamber stages, and terminal calcite volume was pronounced in the seven morphospecies investigated and attributed environmental and ontogenetic differences among individuals. Finally, we generated linear models for estimating cell volume and calcium carbonate test volume from linear measurements (major and minor axis) that are more accurate than the spherical equivalents used previously.

Species-habitat association affects demographic variation across different life stages in an old-growth temperate forest

The sustainability of tree populations in old-growth temperate forests has motivated many ecologists to investigate the mechanisms by which species coexistence is maintained in a local-scale habitat. Species-habitat association could indicate assembly rules that support demographic processes in a particular habitat due to the effect of spatial distribution. In this study, we hypothesized that plant performance with a positive association is better than that for species with a negative association or with no association. We used demographic census data from 2010 and 2015 from the 9-ha Liangshui forest dynamic plot in northeastern China. A one-way ANOVA was used to examine the variation in the relative growth rate (RGR) and mortality rate (MR) in three life stages (saplings, juveniles, and adults) in different habitat types and to analyse the variations in the recruitment rate (RR) in different habitat types. The habitat types were determined by multivariate regression trees (MRT). The three habitat types are Hab I (very high soil organic carbon with a moderate slope), Hab II (low soil organic carbon with a gentle slope), and Hab III (low soil organic carbon with a strong slope). A t-test comparison was performed to compare the differences in RGR and MR between the positive associations group and the non-positive associations (negative and no association) group. The species habitat association statuses were determined by a torus translation test. We used a generalized linear mixed-effects model to analyse the effect of habitat types, diameter and habitat association status on the demographic rate in three different life stages. The RGR of the saplings was significantly higher than that of the juveniles and adults in the three habitat types (P < 0.001). The variation in the MR in the saplings and juveniles in habitats with high soil organic carbon was significantly higher than that in the adults (P < 0.001). However, the variation in the RR showed no significant difference among the three habitat types. The RGR in the saplings and juveniles with positive habitat associations was significantly lower than in those with negative and no habitat associations (P < 0.001). Moreover, the MR in the saplings with positive habitat associations was significantly higher than in those with negative and no habitat associations (P < 0.05). The species-habitat association status significantly affected tree survival, growth, and recruitment. These results demonstrate both positive and negative effects on forest dynamic processes across different life stages. Our study indicated that habitat association status has a significant influence on variation in demographic rates. We suggest that including different life stages in different habitat types is the key to obtaining ecological insight about forest dynamic processes, mechanisms of species coexistence, and maintenance of sustainable forest ecosystems.

EFFECT OF ADDED FAT SOURCES IN GROWING RATIONS IN SOME PRODUCTIVE TRIATS OF WHITE QUIAL

This experiment was conducted on 120 white quails during 4-6 weeks of age which were divided into 4 treatments with 3 replicates (10 birds in each replicate).The experimental treatments were T1 (control group) reared on standard ration without adding fat، while the treatments T2،T3 and T4 were feed the standard rations with adding 3% of vegetable oil، vegetable hydrolyzed fat and animal tallow respectively. Results showed that there was a significant increase (p≤0.05) in body weight، body gain in T4. While there were no significant differences in relative growth rate for all treatments except in fifth week، where the third treatment was better than second and fourth treatment but feed and protein consumption did not differ between all treatments. There were a significant improvement in feed conversion ratio and protein conversion ratio in T4 treatment comparing with other treatments. The third treatment had best economic efficiency while the fourth treatment had the best production index.

Gradual in vitro Evolution of Cefepime Resistance in an ST131 Escherichia coli Strain Expressing a Plasmid-Encoded CMY-2 β-Lactamase.

BackgroundIn a previous report, a clinical ST131 Escherichia coli isolate (Ec-1),producing a plasmid-encoded AmpC β-lactamase CMY-2, evolved in vivo under cefepime (FEP) treatment to the FEP-resistant Ec-2 strain expressing an extended-spectrum β-lactamase CMY-33. To compare factors responsible for in vitro and in vivo FEP resistance, we reproduced in vitro FEP resistance evolution in Ec-1.MethodsFEP-resistant mutants were generated by subjecting Ec-1 (FEP MIC = 0.125 mg/L) to sub-inhibitory concentrations of FEP. MICs were obtained by broth microdilution or Etest. Strains were sequenced on an Illumina HiSeq platform. Transcriptional levels and plasmid copy numbers were determined by real-time PCR. Outer membrane proteins (OMPs) were extracted and separated by SDS-PAGE. Growth kinetics was evaluated by measuring OD450.ResultsThe CMY-2 expressed by Ec-1 evolved to a CMY-69 (strain EC-4) by an Ala294Pro substitution after 24 passages. After 30 passages, the FEP MIC increased to 256 mg/L (strain EC-32). SDS PAGE did not reveal any lack of OMPs in the mutant strains. However, blaCMY transcription levels were up to 14-times higher than in Ec-1, which was partially explained by mutations in the upstream region of repA resulting in a higher copy number of the blaCMY-harboring IncI1 plasmid. All mutants showed a slight growth defect but no significant difference in relative growth rates compared to Ec-1.ConclusionIn vitro sub-inhibitory concentrations of FEP resulted in the selection of resistance mutations altering the H-10 helix of the CMY-2 and increasing the plasmid copy number. Appropriate dosing strategies may help preventing resistance evolution during treatments.

Fitness costs associated with multiple resistance to dicamba and atrazine in Chenopodium album.

Detrimental pleiotropic effects of resistance mutation(s) were observed for multiple-resistant phenotypes (resistant to both atrazine and dicamba). The multiple-resistant phenotypes had lower growth rates and less capacity for vegetative growth compared to the phenotypes only resistant to atrazine. The fitness costs that are conferred by herbicide resistance alleles can affect the rate of herbicide resistance evolution within populations. We evaluated the direct fitness costs involved with multiple resistance to dicamba and atrazine (R1 and R2) in Chenopodium album by comparing the performance of multiple-resistant phenotypes to those phenotypes that were only resistant to atrazine (S1 and S2). The R1 and R2 phenotypes were consistently shorter and produced less dry matter than the S1 and S2 phenotypes. The R1 and R2 phenotypes were shown to have lower relative growth rates (RGR) and net assimilation rates (NAR) than the S1 and S2 phenotypes at an early stage of growth. However, there was no significant difference in RGR between the R1 and R2 and, S1 and S2 phenotypes at a later stage of growth, though the R1 and R2 phenotypes still had a lower NAR at this later stage. Further investigations using a neighbouring crop competition approach showed that the R1 and R2 phenotypes were weaker competitors, and exhibited significantly less capacity for vegetative growth compared to the S1 and S2 phenotypes during competition. Overall, the results of this study revealed multiple- resistance to atrazine and dicamba endowed a significant fitness penalty to C. album, and it is possible that the frequency of multiple-resistant individuals would gradually decline once selection pressure from herbicides was discontinued.

The effects of temperature, salinity and irradiance upon the growth of Sargassum polycystum C. Agardh (Phaeophyceae)

Sargassum polycystum C. Agardh, a brown alga that is widely distributed in tropical areas, has significant economic value by virtue of its use as food, traditional medicine, animal fodder, and chemical products in Asian countries. In order to explore suitable conditions for the aquaculture of this alga, we used 9–10 cm long branches of S. polycystum to assess the effects of various environmental factors, including temperature, salinity, and irradiance upon the relative growth rate (RGR), photosynthetic pigment content, and chlorophyll fluorescence characteristics of this species. Data showed that S. polycystum exhibited a relatively broad tolerance to various environmental conditions, and grew well in different conditions of temperature, salinity, and irradiance, ranging from 15 to 25 °C, 20–40 PSU, and 10–80 μmol photons·m−2·s−1. The maximum RGR of S. polycystum occurred at 23 °C, 32 PSU, and 20–80 μmol photons·m−2·s−1 (P < 0.05). Temperature had a significant effect (P < 0.05) upon RGR and the chlorophyll fluorescence characteristics of S. polycystum, and lower temperature (10 °C) led to rapid reductions in the maximal photochemical quantum yield of photosystem II (F v/F m) and non-photochemical quenching (NPQ) values. Salinity exhibited a relatively weak effect upon the growth of S. polycystum, and the plant was able to survive at salinities from 16 to 40 PSU; during a two-week cultivation period, significant differences in RGR were not observed among different salinity conditions until 2 weeks of cultivation. Chlorophyll a and carotenoid content of S. polycystum decreased as irradiance increased (P 80 μmol photons·m−2·s−1). These physiological data provide valuable data related to the successful cultivation of S. polycystum under controlled conditions.

Long-term changes in stand growth dominance as related to resource acquisition and utilization in the boreal forest

Temporal changes in stand growth dominance, i.e. a measure of the relative contribution of different-sized trees to the total stand growth, may play a role in the commonly observed decline in forest productivity over time through a shift in resource acquisition and utilization between dominant and non-dominant trees. We hypothesized that the expected decreases in both growth dominance (GD) and relative growth rate (RGR) over time were related to decreases in leaf biomass of dominant trees or increases in allocation to leaf biomass of non-dominant trees. To better understand these potential relationships, we quantified stand growth dominance and some functional components (specific leaf area, leaf weight ratio, net assimilation rate, nitrogen per unit leaf area and nitrogen use efficiency) of the relative growth rate of dominant and non-dominant trees along forest development stages in the eastern Canadian boreal forest using a 1067-year-long post-fire chronosequence. As expected, stand growth dominance decreased with stand development, and was closely related to differences in RGR between dominant and non-dominant trees. Decline in both growth dominance and differences in RGR between 100 and 200years after fire was related to greater biomass partitioning to leaves in non-dominant trees, coupled to better light acquisition capacity of non-dominant trees, which appeared in stands that were >75-years-old. In old-growth stands, the growth advantage of non-dominant trees over dominant trees involved other mechanisms, such as higher photosynthetic rates and better resource use efficiency in the non-dominant trees. Overall, the observed decrease in stand growth dominance with increasing age was explained mainly by declining resource acquisition and utilization in dominant trees rather than through improved resource acquisition and utilization of non-dominant trees.

Physiological responses of a green algae (Ulva prolifera) exposed to simulated acid rain and decreased salinity

In order to evaluate the combined effects of simulated acid rain (SAR) and salinity on the physiological responses of macroalgae, Ulva prolifera was cultured under three salinity treatments (5, 10, 25 ‰) and at different pH, i.e., at pH 4.4 (C), pH 4.4(F), where the pH of the culture increased from 4.4 to approximately 7.8 during the cultivation period, or in absence of SAR at pH 8.2(C), at 100 μmol(photon) m–2 s–1 and 20°C. Compared to 25‰ salinity, Relative growth rate (RGR) of U. prolifera was enhanced by 10‰ salinity, but decreased by 5‰ salinity. No significant differences in RGR were observed between the pH 8.2(C) and pH 4.4(F) treatments, but the chlorophyll a content was reduced by SAR. Negative effects of SAR on the photosynthesis were observed, especially under low salinity treatments. Based on the results, we suggested that the U. prolifera showed a tolerance to a wide range of salinity in contrast to the low pH induced by acid rain.