Multiple Nutrient Limitation Research Articles

Multiple nutrient limitation of the soil micro-food web in a tropical grassland revealed by nutrient-omission fertilization

Although involved in key functions of the terrestrial ecosystems, the activity and the diversity of soil microorganisms can be severely limited by energy and nutrients in weathered tropical soils. To optimize nutrient cycling for crop nutrition, assessing which nutrients limit the activity of the microbial food web is thus essential. This was our aim in this study carried out on a tropical ferrallitic soil from a natural grassland in Madagascar. For this purpose, we employed an innovative nutrient-omission approach in microcosms to test the distinct effects of omitting C, six nutrients (N, P, K, S, Ca, Mg) and a cocktail of micronutrients (B, Mn, Cu, Na and Mo) on the composition, biomass and activities of the microbial community and on the abundance and biomass of their nematode grazers. C and P were identified as primary limitations, but other nutrients (N, Mg and S) played significant roles as co-limiting factors. Some bacterial and fungal taxa were significantly associated to specific nutrient deficiencies and can act as biological indicators. Additionally, the abundance and biomass of microbial-feeding nematodes provided valuable insights into the responses of the soil microbial community to nutrient deficiencies. These findings contribute to our understanding of nutrient dynamics and microbial community growth in tropical grassland ecosystems and have implications for sustainable crop fertility management and ecosystem ecology in similar environments.

Co-limitation of N and P is more prevalent in the Qinghai-Tibetan Plateau grasslands.

Over the past three decades, the view of nutrient limitation has transferred from single-nutrient limitation to multiple-nutrient limitation. On the Qinghai-Tibetan Plateau (QTP), many nitrogen (N) and phosphorus (P) addition experiments have revealed different N- or P-limited patterns at many alpine grassland sites, whereas it is not clear what the general patterns of N and P limitation across the QTP grasslands. We performed a meta-analysis, containing 107 publications, to assess how N and P constrained plant biomass and diversity in alpine grasslands across the QTP. We also tested how mean annual precipitation (MAP) and mean annual temperature (MAT) influence N and P limitations. The findings show that plant biomass in QTP grasslands is co-limited by N and P. Single N limitation is stronger than single P limitation, and the combined positive effect of N and P addition is stronger than that of single nutrient additions. The response of biomass to N fertilization rate shows an increase firstly and then declines, and peaks at approximately 25g N·m-2·year-1. MAP promotes the effect of N limitation on plant aboveground biomass and diminishes the effect of N limitation on belowground biomass. Meanwhile, N and P addition generally decline plant diversity. Moreover, the negative response of plant diversity to N and P co-addition is strongest than that of single nutrient additions. Our results highlight that N and P co-limitation is more prevalent than N- or P-limitation alone in alpine grasslands on the QTP. Our findings provide a better understanding of nutrient limitation and management for alpine grasslands on the QTP.

Forest soil acidification consistently reduces litter decomposition irrespective of nutrient availability and litter type

Abstract Nitrogen (N), phosphorus (P) and acid deposition are co‐occurring in many ecosystems, likely with complex interactive effects on litter decomposition. Few studies have been conducted to distinguish the interactive effects of these three factors on forest litter decomposition. Thus, we performed a 5‐year litter decomposition experiment with N, P, acid addition in a temperate forest of Changbai Mountain in China, including four litter types from Pinus koraiensis, Quercus mongolica, Tilia amurensis and their mixtures. Our results showed that acid addition consistently reduced litter decomposition rate, irrespective of nutrient addition or litter types. In contrast, N and P addition had less impact on litter decomposition. Litter decomposition rate linearly reduced with decreasing soil pH, but positively increased with soil N availability. No relationship was found between soil P availability and litter decomposition. Soil enzyme activity played a key role in regulating litter decomposition response, such as acid phosphatase, xylosidase, N‐cacetyl‐b‐D‐glucosaminidase and α‐1,4 glucosidase. Besides, low‐quality litter (i.e. high C concentration, C:N and C:P ratio) amplified the negative effect of soil acidification on litter decomposition. This study suggests that soil acidification consistently decelerates litter decomposition in temperate forests, which is independent of soil nutrient availability and litter types. The intensifying soil acidification with continuous N deposition in the future will greatly reduce litter nutrient return to soil, increasing the risk of multiple soil nutrient limitation. A free Plain Language Summary can be found within the Supporting Information of this article.

Multiple-nutrient limitation of upland rainfed rice in ferralsols: a greenhouse nutrient-omission trial

To optimize the nutrient management of upland rice production on tropical ferralsols, a greenhouse experiment was established using the multi-nutrient omission approach. A reciprocal soil origin-rice cultivar transplant experiment was also conducted to better understand the relative contributions of the soil origin and the rice cultivar in rice nutrient limitation. We tested the deficiency of seven major and secondary nutrients [nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), and silicon (Si)] and a solution of six micronutrients (B, Mn, Cu, Co, Na, Mo) likely to limit the growth of two upland rice cultivars, Chhomrong Dan and Nerica 4, on two Ferralsols from the highlands of Madagascar. We found severe multiple nutrient deficiencies. For both cultivars, P, Ca, N, Mg omission significantly depressed the shoot and root dry biomass and their amounts in plant tissues. However, the main limiting nutrients were not the same in both soils. We conclude that the multinutrient deficiencies observed for rice growth in the Ferralsols are site-specific, even though P limitation appears to be in common, and requires a holistic consideration of the mineral fertility, including micronutrients.

A nutrient limitation mosaic in the eastern tropical Indian Ocean

The Indian Ocean accounts for about one fifth of global ocean net primary production but remains undersampled relative to other major ocean basins. The eastern tropical Indian Ocean is characterized by extremely low concentrations of both macronutrients and the micronutrient iron. We measured concentrations of dissolved and particulate trace metals (Fe, Mn, Zn, Pb) in the upper ocean along the GO-SHIP IO9N transect (28˚S to 17˚N, mostly along the 95˚E meridian) during a cruise in April 2016. Cellular quotas (metal/C) of Fe, Mn, Co, Ni, Cu, and Zn were measured in small eukaryotic flagellates (2–7 μm). Deckboard bottle incubation experiments were conducted at one station in each of three putative biogeochemical regions: southern Indian Ocean gyre (SIO, 28-10˚S); equatorial Indian Ocean (EqIO, 10˚S - 5˚N); Bay of Bengal (BoB, 5-17˚N). Nitrate and phosphate were below detection limits in surface waters across the transect. Dissolved and particulate Fe were <0.2 nM south of 10˚N and lowest in the EqIO. Cellular Fe/C quotas were approximately 6 μmoL/mol and did not vary along the transect, nor did cellular Mn/C or Co/C quotas. Cellular Ni/C and Zn/C quotas were significantly higher at the southern terminus. Nutrient addition experiments indicated that N was the primary limiting nutrient for autotrophs using chlorophyll a as a proxy, but biomass measurements of specific phytoplankton groups pointed to a more complex nutrient limitation mosaic. Prochlorococcus was limited by N in the EqIO but by multiple nutrients (N, P, and/or Fe) in the BoB. Synechococcus was limited by N in the EqIO and BoB, while small (<20 μm) eukaryotic phytoplankton were limited by N in the EqIO and by multiple nutrients in the BoB. Stoichiometric comparisons of cells and underlying source waters indicate a gradient of N and Fe stress along the transect. These data demonstrate that autotroph communities are poised near multiple nutrient limitation horizons in extremely oligotrophic waters far from micronutrient sources.

Multiple nutrients control threatened grassland vegetation in eastern South Africa

Grassland types associated with highly weathered upland soils derived from igneous dolerite and sedimentary sandstone in eastern South Africa are rich in restricted range plant species, and have been extensively destroyed for agriculture and other land uses. Anthropogenic increases in nutrient supply, including atmospheric N deposition, and changes in herbivore abundance may alter vegetation and threaten species in remaining fragments. We investigated the influence of multiple nutrient limitation and herbivory on the productivity, diversity, and composition of these distinctive grasslands, as part of the world-wide Nutrient Network. We examined nutrient limitation using three years of factorial additions of N, P+Ca, and K+micronutrients at two sites, one dolerite-derived and one sandstone-derived. Adding N and P+Ca increased aboveground productivity at both sites by 33–55%, indicating that these nutrients co-limited productivity. Adding N reduced species richness (by 11%) and effective species richness (by 24%) at the sandstone site; all nutrient additions also tended to reduce diversity at the dolerite site. At both sites, adding N increased the abundance of grasses at the expense of (N-fixing) legumes, which declined in relative abundance by 44–60%, whereas adding P+Ca tended to increase the abundance of legumes. At the dolerite site, a factorial fencing and nutrient addition experiment showed that large herbivores did not significantly influence vegetation during three years. Widely increasing atmospheric N deposition, and perhaps warming-induced increases in N mineralization at high elevation, will likely increase productivity, reduce diversity, and reduce legume abundance in these dolerite and sandstone grasslands, posing an additional challenge to conserving them.

Addition of multiple limiting resources reduces grassland diversity.

Niche dimensionality provides a general theoretical explanation for biodiversity-more niches, defined by more limiting factors, allow for more ways that species can coexist. Because plant species compete for the same set of limiting resources, theory predicts that addition of a limiting resource eliminates potential trade-offs, reducing the number of species that can coexist. Multiple nutrient limitation of plant production is common and therefore fertilization may reduce diversity by reducing the number or dimensionality of belowground limiting factors. At the same time, nutrient addition, by increasing biomass, should ultimately shift competition from belowground nutrients towards a one-dimensional competitive trade-off for light. Here we show that plant species diversity decreased when a greater number of limiting nutrients were added across 45 grassland sites from a multi-continent experimental network. The number of added nutrients predicted diversity loss, even after controlling for effects of plant biomass, and even where biomass production was not nutrient-limited. We found that elevated resource supply reduced niche dimensionality and diversity and increased both productivity and compositional turnover. Our results point to the importance of understanding dimensionality in ecological systems that are undergoing diversity loss in response to multiple global change factors.

Fine-root responses to fertilization reveal multiple nutrient limitation in a lowland tropical forest.

Questions remain as to which soil nutrients limit primary production in tropical forests. Phosphorus (P) has long been considered the primary limiting element in lowland forests, but recent evidence demonstrates substantial heterogeneity in response to nutrient addition, highlighting a need to understand and diagnose nutrient limitation across diverse forests. Fine-root characteristics including their abundance, functional traits, and mycorrhizal symbionts can be highly responsive to changes in soil nutrients and may help to diagnose nutrient limitation. Here, we document the response of fine roots to long-term nitrogen (N), P, and potassium (K) fertilization in a lowland forest in Panama. Because this experiment has demonstrated that N and K together limit tree growth and P limits fine litter production, we hypothesized that fine roots would also respond to nutrient addition. Specifically we hypothesized that N, P, and K addition would reduce the biomass, diameter, tissue density, and mycorrhizal colonization of fine roots, and increase nutrient concentration in root tissue. Most morphological root traits responded to the single addition of K and the paired addition of N and P, with the greatest response to all three nutrients combined. The addition of N, P, and K together reduced fine-root biomass, length, and tissue density, and increased specific root length, whereas root diameter remained unchanged. Nitrogen addition did not alter root N concentration, but P and K addition increased root P and K concentration, respectively. Mycorrhizal colonization of fine roots declined with N, increased with P, and was unresponsive to K addition. Although plant species composition remains unchanged after 14 years of fertilization, fine-root characteristics responded to N, P, and K addition, providing some of the strongest stand-level responses in this experiment. Multiple soil nutrients regulate fine-root abundance, morphological and chemical traits, and their association with mycorrhizal fungi in a species-rich lowland tropical forest.

Phytoplankton–bacterial interactions mediate micronutrient colimitation at the coastal Antarctic sea ice edge

Southern Ocean primary productivity plays a key role in global ocean biogeochemistry and climate. At the Southern Ocean sea ice edge in coastal McMurdo Sound, we observed simultaneous cobalamin and iron limitation of surface water phytoplankton communities in late Austral summer. Cobalamin is produced only by bacteria and archaea, suggesting phytoplankton-bacterial interactions must play a role in this limitation. To characterize these interactions and investigate the molecular basis of multiple nutrient limitation, we examined transitions in global gene expression over short time scales, induced by shifts in micronutrient availability. Diatoms, the dominant primary producers, exhibited transcriptional patterns indicative of co-occurring iron and cobalamin deprivation. The major contributor to cobalamin biosynthesis gene expression was a gammaproteobacterial population, Oceanospirillaceae ASP10-02a. This group also contributed significantly to metagenomic cobalamin biosynthesis gene abundance throughout Southern Ocean surface waters. Oceanospirillaceae ASP10-02a displayed elevated expression of organic matter acquisition and cell surface attachment-related genes, consistent with a mutualistic relationship in which they are dependent on phytoplankton growth to fuel cobalamin production. Separate bacterial groups, including Methylophaga, appeared to rely on phytoplankton for carbon and energy sources, but displayed gene expression patterns consistent with iron and cobalamin deprivation. This suggests they also compete with phytoplankton and are important cobalamin consumers. Expression patterns of siderophore- related genes offer evidence for bacterial influences on iron availability as well. The nature and degree of this episodic colimitation appear to be mediated by a series of phytoplankton-bacterial interactions in both positive and negative feedback loops.

Oligotrophication of a large, deep lake alters food quantity and quality constraints at the primary producer–consumer interface

To assess nutritional consequences associated with lake oligotrophication for aquatic consumers, we analyzed the elemental and biochemical composition of natural seston and concomitantly conducted laboratory growth experiments in which the freshwater key herbivore Daphnia was raised on natural seston of the nowadays (2008) oligotrophic Lake Constance throughout an annual cycle. Food quality mediated constraints on Daphnia performance were assessed by comparing somatic growth rates with seston characteristics (multiple regression analysis) and by manipulating the elemental and biochemical composition of natural seston experimentally (nutrient supplementation). Results were compared to similar experiments carried out previously (1997) during a mesotrophic phase of the lake. In the oligotrophic phase, particulate carbon and phosphorus concentrations were lower, fatty acid concentrations were higher, and the taxonomic composition of phytoplankton was less diverse, with a more diatom‐ and cryptophytes‐dominated community, compared to the previous mesotrophic phase. Multiple regression analysis indicated a shift from a simultaneous limitation by food quantity (in terms of carbon) and quality (i.e. α‐linolenic acid) during the mesotrophic phase to a complex multiple nutrient limitation mediated by food quantity, phosphorus, and omega‐3 fatty acids in the following oligotrophic phase. The concomitant supplementation experiments also revealed seasonal changes in multiple resource limitations, i.e. the prevalent limitation by food quantity was accompanied by a simultaneous limitation by either phosphorus or omega‐3 fatty acids, and thus confirmed and complemented the multiple regression approach. Our results indicate that seasonal and annual changes in nutrient availabilities can create complex co‐limitation scenarios consumers have to cope with, which consequently may also affect the efficiency of energy transfer in food webs.

Multiple resource limitation theory applied to herbivorous consumers: Liebig’s minimum rule vs. interactive co‐limitation

There is growing consensus that the growth of herbivorous consumers is frequently limited by more than one nutrient simultaneously. This understanding, however, is based primarily on theoretical considerations and the applicability of existing concepts of co-limitation has rarely been tested experimentally. Here, we assessed the suitability of two contrasting concepts of resource limitation, i.e. Liebig's minimum rule and the multiple limitation hypothesis, to describe nutrient-dependent growth responses of a freshwater herbivore (Daphnia magna) in a system with two potentially limiting nutrients (cholesterol and eicosapentaenoic acid). The results indicated that these essential nutrients interact, and do not strictly follow Liebig's minimum rule, which consistently overestimates growth at co-limiting conditions and thus is not applicable to describe multiple nutrient limitation of herbivorous consumers. We infer that the outcome of resource-based modelling approaches assessing herbivore population dynamics strongly depends on the applied concept of co-limitation.

Dynamics of nutrient uptake strategies: lessons from the tortoise and the hare.

Many autotrophs vary their allocation to nutrient uptake in response to environmental cues, yet the dynamics of this plasticity are largely unknown. Plasticity dynamics affect the extent of single versus multiple nutrient limitation and thus have implications for plant ecology and biogeochemical cycling. Here we use a model of two essential nutrients cycling through autotrophs and the environment to determine conditions under which different plastic or fixed nutrient uptake strategies are adaptive. Our model includes environment-independent costs of being plastic, environment-dependent costs proportional to the rate of plastic change, and costs of being mismatched to the environment, the last of which is experienced by both fixed and plastic types. In equilibrium environments, environment-independent costs of being plastic select for tortoise strategies—fixed or less plastic types—provided that they are sufficiently close to co-limitation. At intermediate levels of environmental fluctuation forced by periodic nutrient inputs, more hare-like plastic strategies prevail because they remain near co-limitation. However, the fastest is not necessarily the best. The most adaptive strategy is an intermediate level of plasticity that keeps pace with environmental fluctuations, but is not faster. At high levels of environmental fluctuation, the environment-dependent cost of changing rapidly to keep pace with the environment becomes prohibitive and tortoise strategies again dominate. The existence and location of these thresholds depend on plasticity costs and rate, which are largely unknown empirically. These results suggest that the expectations for single nutrient limitation versus co-limitation and therefore biogeochemical cycling and autotroph community dynamics depend on environmental heterogeneity and plasticity costs. Electronic supplementary material The online version of this article (doi:10.1007/s12080-010-0110-0) contains supplementary material, which is available to authorized users.

Towards a more biologically realistic use of Droop's equations to model growth under multiple nutrient limitation

Droop's model was originally designed to describe the growth of unicellular phytoplankton species in chemostats but it is now commonly used for a variety of organisms in models of trophic interacti ...

Optimality-based modeling of nitrogen allocation and photoacclimation in photosynthesis

Abstract The ability to predict phytoplankton growth rates under light and nutrient limitation is fundamental to modeling the ocean carbon cycle. Equally fundamental is the ability to predict chlorophyll:carbon ratios, since satellite-based chlorophyll estimates are one of the few data sets to which model output can be compared globally. Because the Geider et al. [Geider, R.J., MacIntyre, H.L., Kana, T.M., 1998. A dynamic regulatory model of phytoplanktonic acclimation to light, nutrients, and temperature. Limnology and Oceanography 43, 679–694] model addresses both desiderata, it has become the model of choice for representing photosynthesis in a wide range of ecosystem models. The Geider et al. [Geider, R.J., MacIntyre, H.L., Kana, T.M., 1998. A dynamic regulatory model of phytoplanktonic acclimation to light, nutrients, and temperature. Limnology and Oceanography 43, 679–694] model follows previous models in positing that maximum photosynthetic rate can be reached only when nitrogen cell quota (nitrogen:carbon ratio) reaches a fixed maximum value q N , max C . Empirically, this assumption is contradicted by the extremely thorough data set of Laws and Bannister [Laws, E.A., Bannister, T.T., 1980. Nutrient- and light-limited growth of Thalassiosira fluviatilis in continuous culture, with implications for phytoplankton growth in the ocean. Limnology and Oceanography 25, 457–473] and by other studies: maximum growth rate does not seem to require maximum nitrogen cell quota. To the extent that existing models do not reflect this key characteristic, they may fail to yield reliable predictions of chlorophyll:carbon ratios as functions of nitrogen:carbon ratios. They also may fail to reflect differences in growth rates of competing phytoplankton species, an essential feature of state-of-the-art ecosystem models used in biogeochemistry simulations. In the present paper I replace the nitrogen limitation function of previous models by one that does not require maximum nitrogen cell quota to produce maximum photosynthetic rate. This new nitrogen-limitation function permits derivation of a steady-state optimality-based relationship between chlorophyll:carbon ratios and nitrogen:carbon ratios; the predictions of this new model are shown to be at least as good as predictions based on the “chlorophyll a synthesis regulation term” of Geider et al. [Geider, R.J., MacIntyre, H.L., Kana, T.M., 1996. A dynamic model of photoadaptation in phytoplankton. Limnology and Oceanography 41, 1–15; Geider, R.J., MacIntyre, H.L., Kana, T.M., 1998. A dynamic regulatory model of phytoplanktonic acclimation to light, nutrients, and temperature. Limnology and Oceanography 43, 679–694]. The Laws and Bannister [Laws, E.A., Bannister, T.T., 1980. Nutrient- and light-limited growth of T. fluviatilis in continuous culture, with implications for phytoplankton growth in the ocean. Limnology and Oceanography 25, 457–473] data suggest that the relationship between chlorophyll:carbon ratio and nitrogen cell quota is independent of nitrogen source (nitrate vs. ammonium) for nitrogen-limited cells. Finally, a full set of parameters for the Laws and Bannister [Laws, E.A., Bannister, T.T., 1980. Nutrient- and light-limited growth of T. fluviatilis in continuous culture, with implications for phytoplankton growth in the ocean. Limnology and Oceanography 25, 457–473] data set is estimated and used to predict chlorophyll:carbon and nitrogen:carbon ratios as functions of growth rate. This improved conceptualization of nitrogen:carbon and chlorophyll:carbon relationships in photosynthesis should provide a robust theoretical underpinning for a new generation of models of multiple-nutrient limitation.

Phytoplankton growth and stoichiometry under multiple nutrient limitation

Phytoplankton growth and stoichiometry depend on the availability of multiple nutrients. We use a mathematical model of phytoplankton with flexible stoichiometry to explain patterns of phytoplankton composition in chemostat experiments and nutrient drawdown dynamics that are found in the field. Exponential growth and equilibrium represent two distinct phases, each amenable to mathematical analysis. In a chemostat at a fixed dilution (growth) rate, phytoplankton stoichiometry matches the nutrient supply stoichiometry over a wide range at low growth rates and over a narrow range at high growth rates. In a chemostat with a fixed nutrient supply stoichiometry, phytoplankton stoichiometry varies with dilution rate nonlinearly, between the supply stoichiometry at low dilution rates and a species‐specific optimal ratio at high dilution rates. The flexible‐stoichiometry model we study predicts low equilibrium concentrations of two nutrients over a wide range of supply ratios, contrary to the predictions of a traditional fixed‐stoichiometry model. The model is in quantitative agreement with experimental data, except at extreme nutrient supply ratios, which require a negative feedback from quota to uptake to fit the data. Our analysis points to the importance of better understanding the regulation of uptake rates in determining phytoplankton stoichiometry and incorporating this knowledge into phytoplankton models.

Root allocation and multiple nutrient limitation in the New Jersey Pinelands

Abstract Current understanding of the effects of resource stress on plant communities emphasizes the adaptive integration of multiple limiting factors, but it has been difficult to directly demonstrate the fundamental assumption of the adaptive control of limitation. One model predicts a positive correlation between optimal allocation to the uptake of each resource and growth response to enrichment of that resource. Here we report a test of this prediction by a fertilization experiment in the New Jersey Pinelands Biosphere Reserve where limitation was measured by growth response to nutrient enrichments, and allocation was measured by root proliferation in microsites enriched by those same nutrients. Results suggest that a stand of regenerating Pinus echinata Mill. (shortleaf pine) was jointly limited by nitrogen and potassium, with a possible small effect of phosphorus. Root allocation was proportional to growth response, which supports the assumption of adaptive control of limitation.

Effects of mineral nutrients on the growth of bacterioߚ and phytoplankton in two southern reservoirs

Nutrient limitation of bacterioߚ and phytoplankton was studied simultaneously in two warmߚwater lakes in the southern United StatesߞJoe Pool Lake (JPL) and Eagle Mountain Lake (EML). Lakes were sampled approximately biweekly between March 1998 and December 1999 from a single station. Nutrient limitation was assessed through dilution bioassays in which nitrogen (N, 50 µM above ambient), phosphorus (P, 10 µM above ambient), carbon (C, bacterioplankton only, 83 µM above ambient), and trace nutrients (Tm, phytoplankton only) were supplied. In both lakes, growth of bacterioߚ and phytoplankton was stimulated by nutrient additions. Multiple nutrient limitation was common. P alone and in combination with N and C or Tm most frequently limited growth of both bacterio and phytoplankton in JPL. N alone and in combination with P and C or Tm most frequently limited growth of both bacterioߚ and phytoplankton in EML. Comparison of in situ growth rates to growth rates under potentially nutrient saturating conditions revealed that both bacterioߚ and phytoplankton in both lakes were growing well below maximum potential during warm months but near maximum potential during cooler months. This result was due to a combined effect of low temperature in winter and restricted nutrient availability in summer. Phytoplankton was generally more strongly limited by nutrient availability than was bacterioplankton, but there were occasions when the intensity of limitation shifted between communities.

Characterization of the starvation-survival response of Staphylococcus aureus.

The starvation-survival response of Staphylococcus aureus as a result of glucose, amino acid, phosphate, or multiple-nutrient limitation was investigated. Glucose and multiple-nutrient limitation resulted in the loss of viability of about 99 to 99.9% of the population within 2 days. The remaining surviving cells developed increased survival potential, remaining viable for months. Amino acid or phosphate limitation did not lead to the development of a stable starvation-survival state, and cells became nonculturable within 7 days. For multiple-nutrient limitation, the development of the starvation-survival state was cell density dependent. Starvation survival was associated with a decrease in cell size and increase in resistance to acid shock and oxidative stress. There was no evidence for the formation of a viable but nonculturable state during starvation as demonstrated by flow cytometry. Long-term survival of cells was dependent on cell wall and protein biosynthesis. Analysis of [35S]methionine incorporation and labelled proteins demonstrated that differential protein synthesis occurred deep into starvation.

Multiple nutrient limitation in unicellulars: reconstructing Liebig's law.

Liebig's law of the Minimum is reformulated in terms of biomass composition dynamics. The doctrine of the single limiting nutrient is shown to be invalid generally. The nutritional status of a unicellular organism is expressed in terms of state variables; one which represents the subsistence composition and a number of reserve surplus type variables. It is proposed that the property of being limiting should be defined in terms of the reserve surplus variables. On the basis of this definition, it can be decided whether a nutrient, or combination of nutrients, is limiting, both in transient and steady states. The concept of multiple limitation is shown to have two distinct meanings on these definitions. A non-interactive minimum model, based on a 'hard' minimum operator, is introduced. Smooth interactive models may be formulated which have this minimum model as a limiting case. One such model is described. Numerical simulations show how the behaviour of this smooth model can approximate that of the minimum model: apparently hard non-linearities can arise in the smooth model, through time-scale separation.

Seasonal and spatial patterns in macro- and micronutrient limitation in Joe Pool Lake, Texas

The roles of nitrogen, phosphorus, silicon, and trace nutrients in limiting algal growth were studied over a 1-yr period in three sites of a recently impounded, warm monomictic reservoir in north-central Texas using factorial dilution assay experiments. When lake temperature was >15°C, nutrients limited realized growth rates to half or less of potential growth. Nutrient limitation was obliterated in the fall by floods. Density stratification was not a prerequisite to nutrient limitation in spring. Both macro- and micronutrients were important in terms of frequency of experiments showing limitation and in terms of quantitative degree of limitation. Horizontal variability in the degree of limitation was absent; however, shallower sites showed more incidence of multiple nutrient limitation compared to a deep, near-dam site.