Topic
Limiting factor
About: Limiting factor is a research topic. Over the lifetime, 197 publications have been published within this topic receiving 7784 citations.
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Papers
TL;DR: Genotypic variation in the temperature optimum for resource-saturated growth of microalgae has been used to provide envelopes of μm (maximum specific growth rate) as a function of temperature to suggest that, at their temperature optima, the cells are close to their maximum potential growth rate, based on the known kinetic properties of their catalysts.
Abstract: summary
Genotypic variation in the temperature optimum for resource-saturated growth of microalgae has been used to provide envelopes of μm (maximum specific growth rate) as a function of temperature. The Q10 value for μm for batch-cultured algae with optimal growth temperatures in the range 5–40°C is 1.88; rather higher values (Q10= 2.08–2.19) are found, albeit with lower μ values at a given temperature, for continuous cultures. The envelope approach selects μ values for the smallest cells from the taxa (members of the Chlorophyta and Bacillariophyta) with the highest μ values at a given temperature. Larger cell size, or membership of the Dinophyta, gives a decreased μ at a given temperature. Phenotypic change in μ, within a given genotype grown at sub-optimal temperatures, has a Q10 in excess of 1.88. Analysis of constraints on the resource-saturated value of μ in the fastest-growing micro-algae suggest that, at their temperature optima, the cells are close (within a factor of 2) to their maximum potential growth rate, based on the known kinetic properties of their catalysts, the need for kinetic heterogenity in catalyses in metabolic pathways, and the need to allocate some cell resources to structural and storage components. Phenotypic and genotypic responses to lower temperatures for growth, in terms of reallocation of resources to increase the quantity per unit biomass of catalyst? as a means of offsetting lower catalytic capacity at lower temperatures, are limited. An exception is the light-harvesting and reaction centre apparatus which catalyses the temperature-insensitive processes of light absorption, excitation energy transfer and primary photochemistry, and which is present (as assayed by photosynthetic pigment per unit biomass) in smaller relative amounts during resource-saturated growth at lower temperatures. The involvement of other low-temperature ‘adaptations’ (e.g. homeoviscous behaviour of thylakoid membranes) in offsetting low temperature effects on catalytic rates is not clear. The scope for increasing the quantity of temperature-sensitive catalysts in the biomass as a means of offsetting the effects of low temperature on resource-saturated μ is potentially higher in the Dinophyta with their relatively low μ at their temperature optimum; however, this option does not appear to be taken up by the Dinophyta which have unexceptional Q10 values for μ.
For resource-limited growth, the phenotypic effect of suboptimal temperatures on growth, when light is the limiting resource, is often less marked than when growth is light saturated. When a chemical nutrient is limiting, the temperature effect on growth of a given genotype is often, but not invariably, decreased. Cases in which the effect of temperature on growth rate is decreased under light-limiting conditions can be interpreted in terms of the intrinsically low Q10 of growth when temperature-insensitive reactions (light absorption, excitation energy transfer, primary photochemistry) are limiting and the acclimatory effects of changed temperature and light regimes for growth on resource allocation between pigment-protein complexes and downstream catalysts of temperature-sensitive reactions. Cases in which light-limited growth rate is quite temperature sensitive may be accounted for by a decrease in absorptance as a result of a lower pigment content per cell at low growth temperatures. For growth limited by chemical nutrients, the variable responses make analysis difficult. It is tempting to assign a low Q10 for μ under these conditions to a limitation by some transport process (diffusion through unstirred layers, or, less plausibly, the cell membrane) with a low Q10, although the evidence favouring this interpretation is not abundant.
764 citations
TL;DR: It is concluded, not that interval modulation rather than binary modulation “ought” to be the mode of action of the central nervous system, but that the contrary assumption is unsupported by considerations of efficiency.
376 citations
TL;DR: In this paper, a literature review summarizes the limiting factors for seagrass occurrence, and the effect positive feedbacks in SEAGrass systems have on these threshold levels.
Abstract: This literature review summarizes the limiting factors for seagrass occurrence, and the effect positive feedbacks in seagrass systems have on these threshold levels. Minimum water depth is mainly determined by wave orbital velocity, tide and wave energy; and maximum depth by light availability. Besides these, other limiting factors occur, such as an upper current velocity threshold, above which seagrasses are eroded, or a lower water current velocity threshold below which carbon exchange is limiting. In some locations organic matter content, sulphide concentration or nutrient availability are limiting. N-limitation is mainly reported from temperate terrigenous sediments, and P-limitation from tropical carbonate sediments. However, limiting factors sometimes change over the year, switching from light limiting to N- or P-limiting, and show at times regional variation. The effect seagrasses have on current reduction, trapping sediment and decreasing resuspension can lead to several changes in both the sediment and the water column. In the sediment, an increase in nutrient availability has been reported, and increases in organic matter, sediment height increases, and burial of the seagrasses. In the water column the effect is a reduction of the turbidity through a decrease of the sediment load, decreasing the attenuation coefficient, thereby increasing light availability. Due to the large effect light availability has on seagrass occurrence, the effect of an improvement of the light conditions by a reduction of the turbidity by seagrasses is probably the most important positive feedback in seagrass systems. The latter effect should therefore be incorporated in models that try to understand or predict seagrass changes. Generalization are difficult due a lack of studies that try to find relationships between seagrass architecture and sediment trapping (studying both turbidity reduction and nutrient increase) on a global level under a variety of different conditions. Areas for research priorities are identified.
335 citations
TL;DR: Grazing optimization is most likely to occur in systems with large losses of the limiting nutrient during recycling of plant detritus, or where herbivores bring nutrient from outside the ecosystem considered (which acts to reduce, or even make negative, the fraction of nutrient lost along the herbivoredetritus pathway).
Abstract: In a general theoretical ecosystem model, we investigate the conditions under which herbivores increase primary production and lead to grazing optimization through recycling of a limiting nutrient.
Analytical and simulation studies of the model lead to several general results. Grazing optimization requires that (1) the proportion of nutrient lost along the herbivore pathway be sufficiently smaller than the proportion of nutrient lost throughout the rest of the ecosystem; and that (2) inputs of nutrient into the system be greater than a threshold value, which depends on the sensitivity of plant uptake rate to an increase in soil mineral nutrient.
An increase in nutrient turnover rate is not sufficient to explain grazing optimization in the long term. When a nutrient is the single limiting factor, plant biomass and productivity at equilibrium are determined only by the balance of ecosystem inputs and outputs of nutrient. Processes that do not have an impact on these inputs or outputs have no effect on primary producers.
On the other hand, turnover rates are important for the transient dynamics of the system, and the equilibrium analysis is relevant only if it can be reached in a reasonable time scale. The equilibrium is not reached by a compartment with a very slow turnover rate, such as the resistant soil organic matter, before several centuries. On a small time scale, such a compartment can be considered constant, and the trend of the system is predicted with a simplified system.
The results at equilibrium are insensitive to the functional form used to describe herbivore consumption: the results obtained for simple, linear, donor-controlled herbivory also apply to most forms of more realistic, recipient-controlled herbivory.
We conclude that grazing optimization is most likely to occur in systems with large losses of the limiting nutrient during recycling of plant detritus, or where herbivores bring nutrient from outside the ecosystem considered (which acts to reduce, or even make negative, the fraction of nutrient lost along the herbivore detritus pathway).
305 citations
TL;DR: The results generally suggest that, even in dynamic environments, where equilibrium conditions are rare, resource competition among phytoplankton is a mechanism by which communities are continually structured.
Abstract: Species diversity is a key concept in ecology, yet the mechanisms regulating diversity in most systems are not completely understood. To address this issue, we analyzed the relationship between phytoplankton diversity and limiting resources (N, P, Si, and light) over two summers in three lakes in the Yellowstone (Wyoming, USA) region. Diversity was highly variable along temporal and spatial axes within lakes. We discovered a strong positive correlation between diversity and the number of resources at physiologically limiting levels. Consistent with resource-competition theory, we found the highest diversity to occur when many resources were limiting. Conversely, the lowest diversity occurred when few resources were measured at limiting levels. Sensitivity analyses demonstrated that threshold levels of resources (below which growth is limited and above which there is saturation for the resource) appear to exist in the natural environment, and that diversity is regulated in part by absolute levels of resources available to phytoplankton in aquatic systems. Threshold levels are generally in agreement with those determined to be limiting in prior physiological experiments. Consistent with previous observations, among-lake comparisons yielded a significant negative relationship between species diversity and system productivity. This result tentatively supports the hypothesis that the proximity of individual phytoplankton plays a role in the strength of competitive interactions. Our results generally suggest that, even in dynamic environments, where equilibrium conditions are rare, resource competition among phytoplankton is a mechanism by which communities are continually structured.
211 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 4 |
| 2020 | 3 |
| 2019 | 3 |
| 2018 | 1 |
| 2017 | 6 |
| 2016 | 4 |