Ideal nutrient productivities and nutrient proportions in plant growth

Abstract I propose that one single formulation can be applied to relate growth and content of several nutrients, including the most important macronutrients, of most plant species. The plant growth rate is proportional to the nutrient content minus a given minimal concentration of the nutrient in minimum. The proportionality factor, the nutrient productivity, and the minimum concentration are species specific properties. The nutrient productivity formulation is shown to apply for very different plant species and for different nutrients.     

PAS kinase: integrating nutrient sensing with nutrient partitioning

Recent data suggests that PAS kinase acts as a signal integrator to adjust metabolic behavior in response to nutrient conditions. Specifically, PAS kinase controls the partitioning of nutrient resources between the myriad of possible fates. In this capacity, PAS kinase elicits a pro-growth program, which includes both signaling and metabolic control, both in yeast and in mammals. We propose that, like other kinases possessing these properties-AMPK and TOR, PAS kinase might be target for therapy of diabetes, obesity and cancer.     

Balancing nutrient supply and nutrient requirements in grazing sheep

Attempting to achieve a balance between the supply of and requirements for the major nutrients implies that demands for major nutrients can be adequately quantified, that the nutritive value of the consumed diet can be described in similar terms and that the diet actually consumed by the grazing sheep can be estimated, or at least predicted, from pasture and animal conditions. Several systems exist for defining the nutrient requirements of sheep and, whilst there are real differences between them, all are sufficiently accurate to allow their use in ration formulation and in grazing animal management. Similarly, nutritive value of feed components can be defined accurately. In grazing sheep, the major difficulty in balancing the supply of consumed nutrients against nutrient requirements is the estimation of diet composition and intake. Computer-based decision support tools are a useful aid to overcoming this problem. It is suggested that since profit derives from animal production per hectare and not per animal, the balancing of nutrient supply and requirements should not be attempted on an individual-animal basis.     

Effects of forest harvesting nutrient removals on soil nutrient reserves

Summary Intensive harvesting of native eucalypt forests is carried out in the Eden area in the south east coastal region of New South Wales, Australia. Soil nutrient capital and nutrient removals in forest harvesting were estimated together with potential impacts of these removals on the nutrient capital balance. Soils were anlysed from eighty sites for phosphorus fractions, including organic phosphorus fractions, and total and exchangeable cations. Based on typical forest harvesting systems, it was found that 3–4 kg phosphorus would be removed per hectare. Due to equilibrium between the various soil phosphorus components, depletion would not be solely from the more available pools. It is expected that at least four forest rotations (320 years) would be required before any detectable change would occur, within forest communities. A similar depletion estimate was calculated for the potentially most vulnerable cation, calcium. The other nutrient cations, magnesium and potassium had considerably greater reserves.     

Stoichiometry of consumer-driven nutrient recycling across nutrient regimes in streams

Stoichiometric constraints within ecological interactions and their ecosystem consequences may depend on characteristics of the abiotic environment such as background nutrient levels. We assessed whether consumer identity, via differing body stoichiometry, could regulate periphyton stoichiometry across nutrient regimes in open systems. In 60 flow-through artificial streams, we factorially crossed dissolved inorganic nitrogen levels (elevated = 294  μ g L⁻¹, ambient = 26  μ g L⁻¹) with dissolved inorganic phosphorus levels (DIP: elevated = 15  μ g L⁻¹, ambient = 3  μ g L⁻¹) and consumer type [crayfish (body N : P = 18), snails (body N : P = 28) or a control]. At ambient DIP, periphyton in the crayfish treatment had a lower %P and a lower C : P than periphyton in the snail treatment suggesting that consumer identity, probably mediated by differing P-excretion, regulated periphyton P content. At high DIP, consumer identity no longer affected periphyton elemental composition. Therefore, the stoichiometry of consumer-driven nutrient recycling and consumer identity may be less important to ecosystem functioning in environments with elevated nutrient levels.     

Constructing nutrient budgets

We present a formalised, yet flexible, scheme for classifying and symbolising the components of nutrient budgets. The scheme distinguishes hierarchically both among components of the ingesta and among the various sinks to which they are allocated. The primary terms in the budget are distinguished according to either methodological criteria (whether in a given time period they are retained by the animal or dissociated from the body) or functional criteria (whether they contribute to fitness). In both methodological and functional classifications, the primary terms of the budget may be progressively expanded to represent with increasing resolution nutrient allocation. The interplay between the various components of the ingesta and their subsequent allocation may be considered simultaneously using a two-dimensional nutritional matrix.     

Foliar nutrient dynamics and nutrient use efficiency in Cornus florida

Summary Growth rates and seasonal changes in foliar nitrogen, phosphorus, and calcium of Cornus florida L. (flowering dogwood) individuals were determined in three forest stands which differed in soil moisture and soil nutrient availability. Nutrient use efficiency of individual trees was measured by amount of leaf dry mass produced per unit nutrient invested, rates of nutrient resorption prior to litterfall, wood and leaf mass produced per unit nutrient turnover (=growth efficiency), projected uptake needs, and losses of nutrients to simulated throughfall leaching. Relative growth rates during this drought year, as determined by dimension analysis, were highest in the site with highest soil moisture, while 5-year average relative growth rates were highest in the most fertile site. Differences in nitrogen use efficiency were generally small, with the highest efficiencies in trees on the moistest site; in contrast, phosphorus use efficiency was consistently highest on the least fertile site. Foliar calcium levels increased throughout the year and calcium use efficiency was generally highest on the least fertile site. These data suggest that growth and nitrogen use efficiency were more strongly affected by differences in soil moisture than were phosphorus or calcium use, at least during this very dry year.     

Patterns of nutrient release from nutrient diffusing substrates in flowing water

As nutrient diffusing substrates age, the availability of nutrients to periphyton may decline with time either because of diffusion or dilution of nutrients into the water column or because of the effects of grazing by herbivores. Typically, large amounts of nutrients are added to nutrient diffusing substrates (NDS) to insure continuous enrichment throughout experimental periods of 2 to 8 weeks. This study examined the release of phosphates and nitrates from NDS exposed to three different current velocities (0.07 m s^–1, 0.11 m s^–1, 0.20 m s^–1) in recirculating laboratory flumes. Replicated agar samples from four treatments (control, nitrate (N), phosphate (P), and N+P) were sampled throughout 32 days (day 1, 2, 3, 6, 12, 18, 24, 32). Increasing concentrations of agar were required to solidify the P and N+P treatments.Nutrient release rates from NDS were independent of agar concentrations (with the exception of [PO₄] in the medium velocity flume). Nutrient concentrations in the agar of spiked samples declined substantially within a week when exposed to flowing water. Nitrates were retained in agar to a greater extent than phosphates particularly when NDS were exposed to low or medium flows. Although floods physically remove or abrade periphyton in natural streams, findings from this laboratory study suggest that ambient flows deplete the availability of nutrient concentrations to potential periphyton colonizers within the first week of incubation. Because of the rapid decline of nutrients from NDS, short incubation periods in natural running waters seem warranted.     

Microbial enzyme activity,nutrient uptake and nutrient limitation in forested streams

1. We measured NH₄⁺ and PO₄^?3 uptake length (S_w), uptake velocity (V_f), uptake rate (U), biofilm respiration and enzyme activity and channel geomorphology in streams draining forested catchments in the northwestern (Northern California Coast Range and Cascade Mountains) and southeastern (Appalachian and Ouachita mountains) regions of the United States. Our goal was to use measures of biofilm enzyme activity and nutrient uptake to assess nutrient limitation in forested streams across broad regional scales. 2. Geomorphological attributes, biofilm enzyme activity and NH₄⁺ uptake were significantly different among streams in the four study units. There was no study unit effect on PO₄^?3 uptake. The proportion of the stream channel in pools, % woody debris, % canopy closure, median substrate size (d₅₀), stream width (w), stream velocity (v), discharge (Q), dispersion coefficient (D) and transient storage (A_s/A) were correlated with biofilm enzyme activity and nutrient uptake in some study units. 3. Canonical correlation analyses across study units revealed significant correlations of NH₄‐V_f and PO₄‐V_f with geomorphological attributes (w, d₅₀, D, % woody debris, channel slope and % pools) and biofilm phosphatase activity. 4. The results did not support our expectation that carbon processing rates by biofilm microbial assemblages would be governed by stream nutrient availability or that resulting biofilm enzyme activity would be an indicator of nutrient uptake. However, the relative abundances of peptidases, phosphatase and glycosidases did yield insight into potential N‐, P‐ and C‐limitation of stream biofilm assemblages, and our use of biofilm enzyme activity represents a novel application for understanding nutrient limitations in forested streams. 5. Regressions of V_f and U against ambient NH₄⁺ and PO₄^?3 indicated that none of our study streams was either NH₄⁺ or PO₄^?3 saturated. The Appalachian, Ouachita and Coastal streams showed evidence of NH₄⁺ limitation; the Ouachita and Coastal streams were PO₄^?3 limited. As a correlate of nutrient limitation and saturation in streams, ratios of total aminopeptidase and phosphatase activities and the ratio of NH₄‐U to PO₄‐U indicate these forested streams are predominantly N‐limited, with only the streams draining Ouachita and Coastal catchments demonstrating appreciable levels of P‐limitation. 6. Our results comparing the stoichiometry of microbial enzyme activity with nutrient uptake ratios and with the molar ratios N and P in stream waters suggest that biological limitations are not strictly the result of stream chemistry and that the assessments of nutrient limitations in stream ecosystems should not be based on chemistry alone. 7. Our present study, along with previous work in streams, rivers and wetlands, suggests that microbial enzyme activities, especially the ratios of total peptidases to phosphatase, are useful indicators of nutrient limitations in aquatic ecosystems.     

Bryophytes and nutrient cycling

Direct information on nutrient cycling through bryophytes is limited and often incomplete. Evidence bearing on the sources and pathways by which nutrient elements are acquired (e.g. aerial deposition, throughfall and substratum) and lost (e.g. leaching and decomposition) is critically discussed. The need to distinguish between the extracellular and intracellular location of elements is emphasized. The involvement of microorganisms and the problems of accurately measuring decomposition are considered. A summary is given of recent laboratory work on the internal redistribution of elements in Rhytidiadelphus squarrosus and of field experiments involving fertilizer addition to Pseudoscleropodium purum; their significance is assessed.     

Predators buffer the effects of variation in prey nutrient content for nutrient deposition

Predator feeding behavior and digestion regulate the flow of nutrients through ecosystems by determining the fate of prey nutrients. Most predators feed on a diversity of prey items, which differ widely in traits including their nutrient content. Yet, relatively little is known of the mechanisms through which variation in prey nutrient content affects the form by which nutrients are deposited into the environment. The overall goal of this study was to test how variation in the nutrient content of prey affected the fate of nutrients following predation by an arthropod carnivore, the Carolina wolf spider Hogna carolinensis. We manipulated the macronutrient content of prey by varying the diet on which crickets were fed to produce prey treatments that differed in lipid and protein content. Nutrients were measured as both macronutrients and elements in prey and elements in excreta. We found that there was no effect of diet treatment on the amounts of elements or macronutrients in prey carcasses and excreta despite significant variation in the nutrient content of those prey. This is in contrast to studies of some aquatic systems where mass balance by consumers results in variation in excreta content depending on the nutrient content of food. Wolf spiders assimilated the majority of prey nutrients and deposited relatively small and similar amounts of nutrients following feeding. Hence, while prey can vary widely in nutrient content, our findings suggest that this variation has little effect on the amounts of nutrients deposited by predators.     

Variation in nutrient limitation and seagrass nutrient content in Bahamian tidal creek ecosystems

The traditional model of nutrient availability in coastal estuarine ecosystems is based on predictable inputs of nitrogen (N) and phosphorus (P) via riverine and oceanic sources, respectively. But coastlines with low nutrient input from these sources may not fit into this simple framework. Here we use observational (seagrass nutrient content) and experimental (nutrient enrichment assays) data for assessing nutrient availability and limitation for primary producers along a spatial transect extending from the mouth (nearest to the ocean) to the terminal portion (boundary with the terrestrial ecosystem) of three coastal mangrove-lined tidal creeks in The Bahamas. Compiling seagrass nutrient content from all sites showed a negative relationship between seagrass nutrient limitation (either N or P) and distance from mouth, but this pattern differed across sites with respect to which nutrient was more limiting. Our experimental results demonstrated patterns of decreased response by microalgae to dual nutrient enrichment in one site with distance from the creek mouth, and increased response to single nutrient enrichment in another, with the third showing no trend along this gradient. Our findings show that Bahamian mangrove wetlands are extremely nutrient-limited ecosystems, and that the most limiting nutrient varied among sites. In general, these ecosystems deviate from the typical paradigm of spatial nutrient limitation patterns in estuaries. We suggest that various site-specific biological and physical factors may be more important than large-scale hydrologic factors in driving trends of nutrient availability in coastal ecosystems under strong nutrient constraints, such as in The Bahamas. Our findings suggest that even minor changes in nutrient loading rates can have significant implications for primary production in subtropical oligotrophic systems.     

Improving nutrient efficiency as a strategy to reduce nutrient surpluses on dairy farms

Dutch nutrient policy aims at reducing leaching of agricultural nutrients by internalizing the negative externalities associated with inefficient nutrient use. This is done by taxation of nitrogen and phosphate surpluses that exceed a hectare-based threshold of maximum-allowed surpluses. One management strategy farmers may use to reduce the nutrient surpluses on their farms is to improve the nutrient efficiency of the agricultural production process. This study employs Data Envelopment Analysis (DEA) to calculate nitrogen and phosphate efficiencies and an overall nutrient efficiency measure for a 3-year panel of 114 Dutch dairy farms. Subsequent analyses show the impact of both farm intensity and nutrient efficiency on the nitrogen and phosphate surpluses. It appears that farm intensity has a positive effect on efficiency, but efficiency and intensity exert opposite influences on nutrient surpluses. This is especially the case for nitrogen. The magnitude of a possible reduction of nitrogen surpluses through a strategy of efficiency improvement is therefore limited by the intensity of the farming system, unless the technology with which nutrients are used by the farming system can be further improved or input/output ratios will be altered.     

Obesity by choice: the powerful influence of nutrient availability on nutrient intake

The consumption of nutrients by rodents is markedly influenced by the number of containers of each nutrient provided. Most rats given a choice from separate sources of protein, carbohydrate, and fat thrived if given one cup of each but half failed to thrive if given one cup of each and three extra cups of carbohydrate or fat. Rats given five bottles of sucrose solution and one bottle of water became fatter than rats given five bottles of water and one of sucrose. These studies in rats may point to a model for human obesity, in which the availability of food can override physiological controls of ingestion.     

Growth and nutrient uptake by soybean plants in nutrient solutions of graded concentrations

Soybean plants (Glycine max L. Merr. var. Hawkeye), grown in nutrient solutions maintained at graded concentrations showed a large response in both shoot dry weight and total ion uptake. Growth rate was dependent upon nutrient concentration, even when quantity of nutrient was not limiting. Peak periods for absorption of specific ions at certain growth stages were not exhibited. Rates of ion uptake by soybeans were generally proportional to the growth rate during the period of major growth. It is suggested that a dilute nutrient solution could provide sufficient nutrients for adequate root growth prior to major shoot growth, at which time a more concentrated nutrient solution is needed.