Maximum Potential Growth Rate Research Articles

Ecological relevance of flagellar motility in soil bacterial communities.

Flagellar motility is a key bacterial trait as it allows bacteria to navigate their immediate surroundings. Not all bacteria are capable of flagellar motility, and the distribution of this trait, its ecological associations, and the life history strategies of flagellated taxa remain poorly characterized. We developed and validated a genome-based approach to infer the potential for flagellar motility across 12 bacterial phyla (26 192 unique genomes). The capacity for flagellar motility was associated with a higher prevalence of genes for carbohydrate metabolism and higher maximum potential growth rates, suggesting that flagellar motility is more prevalent in environments with higher carbon availability. To test this hypothesis, we applied a method to infer the prevalence of flagellar motility in whole bacterial communities from metagenomic data and quantified the prevalence of flagellar motility across four independent field studies that each captured putative gradients in soil carbon availability (148 metagenomes). We observed a positive relationship between the prevalence of bacterial flagellar motility and soil carbon availability in all datasets. Since soil carbon availability is often correlated with other factors that could influence the prevalence of flagellar motility, we validated these observations using metagenomic data from a soil incubation experiment where carbon availability was directly manipulated with glucose amendments. This confirmed that the prevalence of bacterial flagellar motility is consistently associated with soil carbon availability over other potential confounding factors. This work highlights the value of combining predictive genomic and metagenomic approaches to expand our understanding of microbial phenotypic traits and reveal their general environmental associations.

Taxonomic and genomic attributes of oligotrophic soil bacteria.

Not all bacteria are fast growers. In soil as in other environments, bacteria exist along a continuum-from copiotrophs that can grow rapidly under resource-rich conditions to oligotrophs that are adapted to life in the "slow lane." However, the field of microbiology is built almost exclusively on the study of copiotrophs due, in part, to the ease of studying them in vitro. To begin understanding the attributes of soil oligotrophs, we analyzed three independent datasets that represent contrasts in organic carbon availability. These datasets included 185 samples collected from soil profiles across the USA, 950 paired bulk soil and rhizosphere samples collected across Europe, and soils from a microcosm experiment where carbon availability was manipulated directly. Using a combination of marker gene sequencing and targeted genomic analyses, we identified specific oligotrophic taxa that were consistently more abundant in carbon-limited environments (subsurface, bulk, unamended soils) compared to the corresponding carbon-rich environment (surface, rhizosphere, glucose-amended soils), including members of the Dormibacterota and Chloroflexi phyla. In general, putative soil oligotrophs had smaller genomes, slower maximum potential growth rates, and were under-represented in culture collections. The genomes of oligotrophs were more likely to be enriched in pathways that allow oligotrophs to metabolize a range of energy sources and store carbon, while genes associated with energy-intensive functions like chemotaxis and motility were under-represented. However, few genomic attributes were shared, highlighting that oligotrophs likely use a range of different metabolic strategies and regulatory pathways to thrive in resource-limited soils.

Seed biopriming using saline soil rhizobacteria from the coast of Kolaka Regency for enhancing seed viability and vigor of tomato (Lycopersicum esculentum L.)

The research was conducted to identify indigenous rhizobacteria that can be useful as growth promoters and adapted to saline soils. The isolate was isolated from saline soil rhizosphere on the coast in Kolaka district. The research was conducted in the Lab of Agronomy, on Agricultural Faculty in Halu Oleo University. The research carry out from April to September 2022. The study arranged in a completely randomized design (CRD) using of 15 test isolates. The test was carried out using a seed biopriming technique, then the seeds were germinated using a standard germination procedure. The results showed that all tested rhizobacterial isolates increase the viability and vigor of tomato seeds. There was an increase in maximum growth potential, seed germination, vigor index, and relative growth rate of seeds in the range of 85% to 89% when compared to control. There were 3 isolates of rhizobacteria which were more capable of reducing T50 and increasing seed germination of tomato seeds, namely KL6, KL10 and KL14 isolates. Further research is still needed to test the effectiveness of this isolate to increase tomato growth and yield under conditions of salinity stress in the field.

Psychrophilic properties of sulfate‐reducing bacteria in Arctic marine sediments

AbstractMicroorganisms in the seabed of most of the global oceans live at temperatures close to zero degrees, and in the polar regions even below. Respiration rates of endogenous sulfate‐reducing microorganisms in the polar seabed, however, are highest in the range of 18–30°C and much reduced at colder temperature. In the past, this was seen as indicative of poor adaptation to their cold habitat. We challenge this interpretation, and tested which temperature range allowed sulfate reducers to grow, by adding moderate amounts of volatile fatty acids to high‐arctic sediment. Initially, sulfate reduction was highest at 27°C in both Svalbard and NE Greenland. But sulfate reduction was not sustainable at this temperature and decreased rapidly over time. Below 26°C, however, sulfate reduction rates increased exponentially over time, indicating growth of sulfate‐reducing microorganisms. We used the increase in the sulfate reduction rates over 4 d to calculate potential growth rates of the endogenous sulfate reducers as function of temperature. From growth rates and respiration rates, we could further calculate the growth yield, also as function of temperature. Highest growth rates were observed at 18°C and growth yields peaked at even lower temperatures between 0°C and 10°C. The maximum growth yield at low temperature revealed a strong psychrophilic adaptation of the sulfate reducers in these Arctic sediments. The fact that growth yield was maximized at in situ temperature but maximum potential growth rate was not, is an indication that yield is the more important parameter for microbial competition in marine sediments.

Seasonal growth dynamics and maximum potential growth rates of Australasian snapper (Chrysophrys auratus) and yellow-eyed mullet (Aldrichetta forsteri)

Seasonality can have a major influence on growth dynamics of temperate teleosts that alternates between sustaining the maximum growth performance and confining it to its minimum. Yet the effects may not always be easily discernible, and species use different strategies to deal with annual oscillation in environmental variables. In this comparative study carried out in New Zealand snapper (Chrysophrys auratus) and yellow-eyed mullet (Aldrichetta forsteri) were exposed to seasonal conditions for 12 months under an ad libitum feeding regime to investigate whether an unrestricted diet can produce a clear seasonal response in their growth profile and, assuming that food is limiting in the wild, what would be their maximum potential growth rates. Data showed a strong seasonal effect on growth parameters and energy partitioning in snapper, whereas there were no seasonal dependent responses in mullet. Snapper showed exponential growth during the warm period and the opposite was evident in winter when growth ceased and become even negative. Mullet grew steadily all year around with only a slight deflection from the linear growth trajectory in winter. Snapper’s maximum growth rates corresponded with the highest ambient temperature in the peak of summer. Therefore, this study was not able to determine the maximum potential growth rates for snapper as it would possibly increase with further temperature rise. In contrast, mullet appeared to grow fastest at ∼17/18 °C. In terms of fish condition – snapper partitioned resources to maximise winter survival by switching from investment into growth to energy stores on transition between autumn and winter, whereas yellow-eyed mullet focused on maximising accumulation of visceral fat to reach optimal levels of ∼15 % body mass, which was independent of environmental temperature. Results from this study suggest that wild length-based growth rates in mullet may indeed be feed limited, whereas this cannot be suggested for wild snapper.

Maximum Growth Potential and Periods of Resource Limitation in Apple Tree.

Knowledge of seasonal maximum potential growth rates are important for assessing periods of resource limitations in fruit tree species. In this study we assessed the periods of resource limitation for vegetative (current year stems, and woody biomass) and reproductive (fruit) organs of a major agricultural crop: the apple tree. This was done by comparing relative growth rates (RGRs) of individual organs in trees with reduced competition for resources to trees grown under standard field conditions. Special attention was dedicated to disentangling patterns and values of maximum potential growth for each organ type. The period of resource limitation for vegetative growth was much longer than in another fruit tree species (peach): from late May until harvest. Two periods of resource limitation were highlighted for fruit: from the beginning of the season until mid-June, and about 1 month prior to harvest. By investigating the variability in individual organs growth we identified substantial differences in RGRs among different shoot categories (proleptic and epicormic) and within each group of monitored organs. Qualitatively different and more accurate values of growth rates for vegetative organs, compared to the use of the simple compartmental means, were estimated. Detailed, source-sink based tree growth models, commonly in need of fine parameter tuning, are expected to benefit from the results produced by these analyses.

Application of the DYRESM–CAEDYM model to the Sau Reservoir situated in Catalonia, Spain

AbstractThe aim of this work was to apply to the Sau Reservoir a one-dimensional hydrodynamic DYRESM model linked to the water quality CAEDYM model. And how hydrodynamic affects water quality in reservoirs, especially when have been used for water supply purposes. Thus, simulations were undertaken for 2 years between 2000 and 2001 with the aim of predicting thermal structure and water quality variables such as dissolved oxygen, dissolved inorganic phosphorus and chlorophyll in the reservoir. Inputs were meteorological data, river inflow and outflow data, morphometry parameters, an initial profile and file configuration data. The CAEDYM model also requires a configuration file and initial profiles for all the water quality data, as well as the calibration of different parameters such as sediment-dissolved oxygen, the sediment flux release rate of phosphorus and the maximum potential growth rate of phytoplankton. Temperatures simulation shows clearly a good agreement with the observed one during the stratif...

Predation pressure by avian predators suggests summer limitation of small‐mammal populations in the Canadian Arctic

Predation has been suggested to be especially important in simple food webs and less productive ecosystems such as the arctic tundra, but very few data are available to evaluate this hypothesis. We examined the hypothesis that avian predators could drive the population dynamics of two cyclic lemming species in the Canadian Arctic. A dense and diverse suite of predatory birds, including the Snowy Owl (Bubo scandiacus), the Rough-legged Hawk (Buteo lagopus), and the Long-tailed Jaeger (Stercorarius longicaudus), inhabits the arctic tundra and prey on collared (Dicrostonyx groenlandicus) and brown (Lemmus trimucronatus) lemmings during the snow-free period. We evaluated the predation pressure exerted by these predators by combining their numerical (variation in breeding and fledgling numbers) and functional (variation in diet and daily consumption rates) responses to variations in lemming densities over the 2004-2010 period. Breeding density and number of fledglings produced by the three main avian predators increased sharply without delay in response to increasing lemming densities. The proportion of collared lemmings in the diet of those predators was high at low lemming density (both species) but decreased as lemming density increased. However, we found little evidence that their daily consumption rates vary in relation to changes in lemming density. Total consumption rate by avian predators initially increased more rapidly for collared lemming but eventually leveled off at a much higher value for brown lemmings, the most abundant species at our site. The combined daily predation rate of avian predators exceeded the maximum daily potential growth rates of both lemming species except at the highest recorded densities for brown lemmings. We thus show, for the first time, that predation pressure exerted without delay by avian predators can limit populations of coexisting lemming species during the snow-free period, and thus, that predation could play a role in the cyclic dynamic of these species in the tundra.

The sensitivity of wood production to seasonal and interannual variations in climate in a lowland Amazonian rainforest

Understanding climatic controls on tropical forest productivity is key to developing more reliable models for predicting how tropical biomes may respond to climate change. Currently there is no consensus on which factors control seasonal changes in tropical forest tree growth. This study reports the first comprehensive plot-level description of the seasonality of growth in a Peruvian tropical forest. We test whether seasonal and interannual variations in climate are correlated with changes in biomass increment, and whether such relationships differ among trees with different functional traits. We found that biomass increments, measured every 3 months on the two plots, were reduced by between 40 and 55% in the peak dry season (July-September) relative to peak wet season (January-March). The seasonal patterns of biomass accumulation are significantly (p < 0.01) associated with seasonal patterns of rainfall and soil water content; however, this may reflect a synchrony of seasonal cycles rather than direct physiological controls on tree growth rates. The strength of the growth seasonality response among trees is significantly correlated to functional traits: consistent with a hypothesised trade-off between maximum potential growth rate and hydraulic safety, tall and fast-growing trees with broad stems had the most strongly seasonal biomass accumulation, suggesting that they are more productive in the wet season, but more vulnerable to water limitation in the dry season.

On the roles of cell size and trophic strategy in North Atlantic diatom and dinoflagellate communities

We have examined the inter‐ and intra‐group seasonal succession of 113 diatom and dinoflagellate taxa, as surveyed by the Continuous Plankton Recorder (CPR) in the North Atlantic, by grouping taxa according to two key functional traits: cell size (µg C cell−1) and trophic strategy (photoautotrophy, mixotrophy, or heterotrophy). Mixotrophic dinoflagellates follow photoautotrophic diatoms but precede their obligate heterotrophic counterparts in the succession because of the relative advantages afforded by photosynthesizing when light and nutrients are available in spring. The mean cell size of the sampled diatoms is smallest in the summer, likely because of the higher specific nutrient affinity of smaller relative to larger cells. Contrastingly, we hypothesize that mixotrophy diminishes the size selection based on nutrient limitation and accounts for the lack of a seasonal size shift among surveyed dinoflagellates. Relatively small, heterotrophic dinoflagellates (µg C cell−1 &lt; 10−3) peak after other, larger dinoflagellates, in part because of the increased abundance of their small prey during nutrient‐deplete summer months. The largest surveyed diatoms (µg C cell−1 &gt; 10−2) bloom later than others, and we hypothesize that this may be because of their relatively slow maximum potential growth rates and high internal nutrient storage, as well as to the slower predation of these larger cells. The new trait database and analysis presented here helps translate the taxonomic information of the CPR survey into metrics that can be directly compared with trait‐based models.

Microzooplankton dominate carbon flow and nutrient cycling in a warm subtropical freshwater lake

In a series of grazer‐gradient and dilution microcosm experiments, we compared grazing and nutrient mineralization by naturally co‐existing crustacean and microzooplankton assemblages from mesoeutrophic Lake Kinneret. Across two distinct seasonal plankton assemblages, microzooplankton dominated both phytoplankton and bacteria grazing and nitrogen (N) and phosphorus (P) mineralization. Mass‐specific ingestion rates by microzooplankton were ~20 times higher than ingestion rates of crustaceans. Although most carbon ingested by microzooplankton was in the form of bacteria, microzooplankton inflicted substantially higher mortalities (both in absolute terms and relative to maximum potential growth rates) on both phytoplankton and bacteria compared with crustaceans. Mass‐specific P and N excretion rates were also higher (by 70 and 50 times, respectively) than crustacean excretion rates. These results suggest that microzooplankton grazing and nutrient mineralization are driving forces affecting bacteria and phytoplankton dynamics, playing important roles in carbon and nutrient transfer to upper trophic levels even in pelagic freshwater systems containing abundant crustaceans.

Spring temperatures have a major effect on early stages of peach fruit growth

SummaryPrevious research has shown that Spring temperatures within 30 d after bloom (expressed as accumulated growing degree hours, GDH) are useful for predicting the harvest date of specific peach cultivars. The goal of the present research was to explore the relationship between GDH and additional environmental parameters on peach fruit development and growth during the period from the full bloom date (FBD) to the reference date (RD). Since heat accumulation during the first 30 d after bloom is a primary driver of fruit phenology, we hypothesised that years with high early Spring temperatures would result in smaller RD fruit size (RDFS) because trees cannot supply resources rapidly enough to support the potential growth associated with high rates of phenological development. Data on FBD, RD, and RDFS were collected at different locations in California between 1988 – 2004 and were analysed in conjunction with seasonal environmental data including accumulated GDH, rainfall, soil temperature, and solar radiation, from FBD to RD. Early Spring air temperatures appeared to be a primary environmental factor influencing RDFS. GDH accumulation during the first 30 d after bloom (GDH30) caused a decrease in the number of days between FBD and RD. RDFS increased with increases in the number of days between FBD and RD, and was negatively affected during years with high Spring temperatures. High GDH30 accumulations increased the rates of fruit growth d–1 but not enough to compensate for the shorter growth period from FBD to RD that occurred when GDH30 accumulation was high. The data supported the hypothesis that, with excessively high Spring temperatures, trees could not supply resources rapidly enough to support their maximum potential fruit growth rates.

Intra-canopy variability of fruit growth rate in peach trees grafted on rootstocks with different vigour-control capacity

SummaryThe aim of the present research was to study intra-canopy variability in fruit growth under conditions of low fruit-to-fruit competition in peach trees grafted on rootstocks with differing size-controlling capacity. The experiment was conducted on adult peach trees of two cultivars, each grafted on five rootstocks. Tree canopies were divided vertically into five layers. The diameter of 12 fruit per canopy layer was measured early in the growing season and at harvest. At harvest, the fresh weight of each selected fruit was also determined. After harvest, thirty shoots per tree bearing the selected fruit were harvested, and several parameters related to local carbon source availability, competition between vegetative and reproductive organs, vigour of the fruiting shoot, and position of the fruit on the fruiting shoot were measured. The results demonstrated that fruit variability within peach trees is very large, even when fruit-to-fruit competition is low. Fruit size at harvest decreased significantly and progressively from the top layers to the bottom layers of the canopy. Fruit growth was positively correlated with specific leaf weight, leaf area, and vigour of the fruiting shoot, and was negatively correlated with the vigour of current-season shoot growth on the fruiting shoot. However, the relative importance of each parameter depended on the cultivar. Rootstock affected the relationship between fruit growth and the measured parameters, and some rootstocks appeared to limit the maximum potential fruit growth rate. The measured parameters did not explain all the intra-canopy variability in fruit growth, suggesting that other factors also played a role. Interestingly, fruit size within 1 month of full bloom increased progressively from the top to the bottom of the canopy.

Light and growth rate effects on crop and weed responses to nitrogen

The nitrogen (N) response of competing plants may be affected by photosynthetically active radiation (PAR) availability and maximum potential growth rate, which determine N requirements. The responses of two crop (corn and soybean) and six weed species (common lambsquarters, common waterhemp, giant foxtail, velvetleaf, wild mustard, and woolly cupgrass) in low and high (150 and 450 μmol m−2s−1) PAR levels to daily fertilization with either low or high (0.2 or 7.5 mM) NH4NO3levels were studied. Leaf area of all species responded positively to N by 8 d after emergence (DAE) when grown in high PAR; in low PAR, most species did not respond until 11 DAE. Dry weight and leaf area of all species at 18 DAE were greater with high than with low N. These responses to high N were also greater in high than in low PAR for all species. Dry weights with high N were up to 100% greater in low PAR and up to 700% greater in high PAR than dry weights with low N. These responses suggest that low PAR reduced the benefit of N to the plants. The regression of relative growth rate (RGR) with high N to RGR with low N had a slope that was less than unity (β = 0.79), indicating that species with a higher RGR with high N experienced greater decreases in RGR with low N. Similarly, the sensitivity (change in RGR) of plants grown with high and low N was positively related to RGR with high N. RGR differences among crop and weed species may be related to differences in N requirement that could be exploited for weed management. RGR and seed size were negatively correlated, which may explain previous observations that small-seeded weeds were more sensitive to environmental stress.

Linking fine root traits to maximum potential growth rate among 11 mature temperate tree species

Summary There is limited understanding of patterns of variation that exist among root traits of different species, especially under field conditions. We contrasted 11 fast‐ and slow‐growing species paired within five evolutionary lineages to investigate whether root traits associated with soil resource acquisition were related to species’ potential growth rate. Measurements of root morphology, architecture, nitrogen and phenolic concentration, respiration and phosphorus uptake were taken on fine, non‐woody roots sampled from forest stands in central Pennsylvania, USA. Across all five contrasts, roots of fast‐growing species generally had higher specific root length, smaller diameters, greater degree of branching, and lower phenolic concentrations than those of slow‐growing species. This suggests differences in potential soil exploration and root defences among species differing in potential growth rate. There were no significant differences between fast‐ and slow‐growing species in root tissue density, respiration or P uptake. Lack of root physiological differences between species differing in growth rate contrasted with previous research on chamber‐grown seedlings. These results imply that, while roots of fast‐growing species may be constructed for more rapid soil exploration and shorter life span than those of slow‐growing species, root physiology is either more closely tied to overall plant physiology, which is more similar among mature trees, or masked by variation in soil microsites, root age or interactions with mycorrhizal fungi.

Can filter‐feeding fishes improve water quality in lakes?

1. In this paper we examine the potential of a cichlid fish species (Sarotherodon galilaeus) to both maintain positive growth rates through filter‐feeding on phytoplankton and improve water quality in Lake Kinneret through suppression of dinoflagellate (Peridinium gatunense) blooms.2. Seasonal plankton consumption by S. galilaeus from Lake Kinneret was examined experimentally by monitoring changes in plankton assemblages during 24 h in 5‐m3 mesocosms containing varying densities of fish. Taxon‐specific grazing rates ranged from 0 to 17 mg gfish day–1, with mean total consumption of 1.6% fish body weight per day. During the spring bloom of P. gatunense, S. galilaeus consumed mostly (94%) netphytoplankton (≥20 μm). The remaining 6% consisted mostly of nanophytoplankton (&lt;20 μm). During the summer and fall, net‐ and nanophytoplankton accounted for 54 and 42%, respectively, of the diet of S. galilaeus. Zooplankton and flagellated and ciliated protozoans made up the remaining 4%.3. Simulations using a fish bioenergetics model indicated that consumption rates (C) were near maximum in spring (90%Cmax), while consumption was reduced in summer‐fall (59%Cmax). Sarotherodon galilaeus obtains sufficient energy through filter‐feeding year‐round, although most growth (≥60%) occurs during the spring P. gatunense bloom.4. Despite efficient feeding on P. gatunense and nanophytoplankton by S. galilaeus, estimates of instantaneous plankton mortality caused by ingestion were two orders of magnitude lower than maximum potential plankton growth rates. Thus the potential for the S. galilaeus population in Lake Kinneret to positively affect water quality through algal suppression is low.

Specific growth rates of protozooplankton in the marginal ice zone of the central Barents Sea during spring

Protozooplankton growth was measured by incubation in a walk-in cooling room at 5°C of filtered seawater from six stations on a south–north transect from open water through drift ice and into fast ice in the central Barents Sea (72°30′N–76°32′N). Eight species of naked ciliates, two species of tintinnids, seven species of athecate dinoflagellates and nine species of thecate dinoflagellates grew in the 24 and 48 h bottle incubations. Maximum potential mean specific growth rates of 0.84, 0.59, 0.39 and 0.39 d−1, respectively, indicated a hierarchy in growth rates determined by taxonomic differences where growth of naked ciliates &gt; tintinnids &gt; athecate dinoflagellates &gt; thecate dinoflagellates. The mean±SD in situ temperature (4 to −1.8°C) corrected growth rates (Q10=2.8) for the six stations (0.74±0.31, 0.74±0.16, 0.25±0.16, 0.23±0.27 d−1) also suggested a higher growth for ciliates in comparison to dinoflagellates. Additionally, it revealed that the naked ciliates responded to the increased food availability, whereas this was not the case for all other groups of protozooplankton.

A Model of the Dynamics of Cowbirds and Their Host Communities

Few studies have examined the potential consequences of cowbird (Molothrus spp.) parasitism on entire avian communities. Because cowbirds are host generalists, an obvious opportunity exists for such community-level effects. We developed a model to predict how cowbird abundance affects and is affected by the relative abundances of different types of host species. Toward this end, we divided the passerine hosts of cowbirds into three categories, each having different population dynamic properties: (1) ejectors of cowbird eggs; (2) extinction-prone acceptors of cowbird eggs (species that decline in abundance in response to high levels of cowbird parasitism); and (3) insensitive acceptors of cowbird eggs (species that maintain their abundance even at high levels of cowbird parasitism). Ejectors are sinks for cowbird eggs and thus indirectly benefit extinction-prone hosts. Conversely, insensitive acceptors can raise cowbird young without a concomitant decrease in their own abundance; as such, they indirectly harm extinction-prone species. Although cowbird abundance is determined by the abundance of both ejectors and insensitive acceptors, the reverse is generally not true (i.e. their abundance is independent of cowbird abundance). The mathematical model of cowbird/host community dynamics we present consists of two ordinary differential equations that incorporate the above assumptions about the different classes of hosts and the manner in which they interact with cowbirds. The model predicts that extinction-prone species will have a higher potential to persist when one or more of the following exist: (1) ejectors are relatively more abundant than insensitive acceptors; (2) ejectors are abundant relative to extinction-prone carrying capacity; (3) maximum potential cowbird per-capita population growth rate is small; and (4) the potential effect of cowbirds on extinction-prone population growth rate is small. Extinction-prone species will decline or go extinct in reverse situations.

Picophytoplankton dynamics in the equatorial Pacific: diel cycling from flow-cytometer observations

The French JGOFS cruise FLUPAC was conducted in October–November 1994 in the western and central equatorial Pacific Ocean. During a 7-day time series at 150 °W, in addition to conventional sampling (four times per day from discrete depths between 0 and 150 m), a high frequency (hourly) experiment was performed by continuously pumping water at 5 m below the surface over 24 h. Flow cytometric measurements allowed us to recognise and to follow separately the two major components of equatorial picophytoplankton, the Prochlorococcus and the picoeukaryotes. The hourly surface experiment confirmed the synchrony of Prochlorococcus cell division and showed that picoeukaryotes exhibited a similar behaviour. The main consequence is that the maximum potential growth rate of picophytoplankton is one doubling per day for both cell groups. The vertical profiles indicated that the diel cycling extends throughout the surface layer for both algal groups. The cells were observed to divide daily from late afternoon to the middle of the night, and then to disappear, probably as a result of grazing. In the surface layer, variations of abundance allowed us to estimate a growth rate of about 0.6 day 1. Mean cell light scattering parFS as measured by the cytometer indicated a decrease in cell size concurrent with cell division and an increase during the photosynthetic growth phase.

A comparative study of leaf nutrient concentrations in a regional herbaceous flora.

Mineral nutrient concentrations were determined in leaves of 83 mostly herbaceous species collected from central England. Most samples were analysed for N, P, K, Ca, Mg, Na, Fe, Al, Mn, Cu and Zn. Concentrations of K, N and P showed similar levels of interspecific variability, with the highest concentrations being 6-9 times the lowest. Mg and (especially) Ca were much more variable, with the highest concentrations being 24 and 49 times the lowest respectively. Only in the case of P concentration was the majority of the variance in the data found at or below the species level. Most of the variance in Ca and Mg concentrations was between monocots and dicots. Concentrations of N and P were strongly positively correlated with each other. Only Ca and Mn were consistently associated with soil pH, positively and negatively respectively. Dicots tended to accumulate more Ca and Mn from high soil concentrations than did monocots. Concentration of P was significantly positively correlated with maximum potential relative growth rate. Plants of woodland and arable habitats contained high concentrations of P, and those of pasture and skeletal habitats contained low concentrations of P. The P: N ratio was higher in plants of arable habitats. Species with P-rich leaves tended to be currently increasing in abundance. The results suggest that plants with nutrient-rich foliage grow quickly, dominate nutrient-rich ecosystems and are generally increasing as a result of the eutrophication and disturbance arising from human exploitation.