Progress since the first international symposium: ‘Genetic aspects of plant mineral nutrition’, Beograd, 1982, and perspectives of future research

Summary The paper discusses the problems of genetic aspects of plant mineral nutrition in the light of the results presented at the First and Second Symposia on ‘Genetic Aspects of Plant Mineral Nutrition’ organized in Beograd in 1982 and Madison in 1985, respectively. On the basis of the results, future directions of research are discussed. The papers deal with the concentration and content of mineral nutrients in different genotypes, physiological and biochemical aspects of the genetic specificity of plant mineral nutrition, relations between plant genotypes and nitrogen fixing micro-organism strains, as well as with some related problems which have been investigated to a lesser extent. Particular attention is paid to papers and problems referring to genetic and breeding research work linked with genetic aspects of plant mineral nutrition as well as the possibilities of developing new cultivars requiring certain soil and mineral nutrition conditions for their cultivation.     

Effects of wheat plant inoculation with cytokinin-producing microorganisms on plant growth at increasing level of mineral nutrition

Triticum durum Desf. plants were grown for 11 days in sand culture on nutrient solutions with optimum or lowered content of mineral nutrients. Thereafter, the level of mineral nutrition was increased in some portion of deficient plants. Two days before, plants were inoculated with cytokinin-producing microorganisms of the Bacillus genus. Nutrition deficiency resulted in a decrease in the rate of plant biomass accumulation, which was correlated with the level of active cytokinins in both roots and shoots. After improving the mineral nutrition of noninoculated plants, the rate of their biomass accumulation increased and, by the end of experiment, their shoot fresh weight was 1.5-fold higher than in deficient plants; however, it was still by 20% lower than in plants continuously growing at optimum mineral nutrition. Inoculation resulted in the considerable increase in the cytokinin content in shoots as compared with all other treatments. In this case, after the improvement of plant mineral nutrition, the rates of growth and relative biomass accumulation increased sharply; as a result, these plants had the highest dry and fresh weights. Thus, inoculation with cytokinin-producing bacteria was beneficial for plant growth after their transfer from deficient to sufficient mineral nutrition.     

Phosphorus–zinc interactions in cotton: consequences for biomass production and nutrient‐use efficiency in photosynthesis

The fragmentary information on phosphorus (P) × zinc (Zn) interactions in plants warrants further study, particularly in plants known for their high P and Zn requirements, such as cotton (Gossypium hirsutum L.). The objective of this study was to investigate the effect of P × Zn interactions in a modern cultivar of cotton grown hydroponically. Biomass, mineral nutrition and photosynthetic parameters were monitored in plants receiving contrasting combinations of P and Zn supply. Root biomass, length and surface area were similar in plants with low P and/or low Zn supply to those in plants grown with high P and high Zn supply, reflecting an increased root/shoot biomass quotient when plants lack sufficient P or Zn for growth. Increasing P supply and reducing Zn supply increased shoot P concentrations, whilst shoot Zn concentrations were influenced largely by Zn supply. A balanced P × Zn supply (4 mM P × 4 μM Zn) enabled greatest biomass accumulation, while an imbalanced supply of these nutrients led to Zn deficiency, P toxicity or Zn toxicity. Net photosynthetic rate, stomatal conductance, transpiration rate and instantaneous carboxylation efficiency increased as P or Zn supply increased. Although increasing P supply reduced the P‐use efficiency in photosynthesis (PUEP) and increasing Zn supply reduced the Zn‐use efficiency in photosynthesis (ZnUEP), increasing Zn supply at a given P supply increased PUEP and increasing P supply at a given Zn supply increased ZnUEP. These results suggest that agricultural management strategies should seek for balanced mineral nutrition to optimize yields and resource‐use efficiencies.     

Influence of Soil Moisture on Soil Solution Chemistry and Concentrations of Minerals in the Calcicoles Phleum phleoides and Veronica spicata Grown on a Limestone Soil

Veronica spicata and Phleum phleoides are calcicole plants,mainly occurring on neutral or alkaline soil. An experimentof 16 weeks duration was performed in a glasshouse with theobjective of elucidating the influence of soil moisture levelon soil solution chemistry, and biomass concentrations and uptakeof mineral nutrients by the plants. Seven levels of moisture,corresponding to 35–85% of the water holding capacity(WHC) of the soil, were tested. Soil solution HCO₃, P and Mnconcentrations, and pH, increased, whereas Ca, Mg and Zn concentrationsdecreased, with increasing soil moisture. Concentrations ofK were highest at 50–70% WHC. Concentrations and amountsof P, Zn and Mn in the two species were usually related to soilsolution concentrations; these are elements with low solubilityand availability in calcareous soils. Concentrations of nutrientsin biomass were more influenced by soil moisture in V. spicatathan inP. phleoides . This indicates that P. phleoides is morecapable of controlling its uptake of mineral nutrients, whereasV. spicata is sensitive to variations in soil moisture. It isconcluded that variation in soil moisture regime may greatlyinfluence concentrations of mineral nutrients in calcareoussoil solutions and their uptake by plants. Species able to utilizethese solubility fluctuations may have an advantage in competitionfor nutrients. Variation in soil moisture content might evenbe a prerequisite for adequate acquisition of mineral nutrientsand growth of plants on limestone soils, thereby influencingthe field distribution of native plants among habitats. Copyright1999 Annals of Botany Company Calcareous, calcicole, concentration, mineral, moisture, nutrient, Phleum phleoides, soil, soil solution, uptake, Veronica spicata, water.     

Effect of mineral nitrogen on nitrogen nutrition and biomass partitioning between the shoot and roots of pea (Pisum sativum L.).

The effect of mineral N availability on nitrogen nutrition and biomass partitioning between shoot and roots of pea (Pisum sativum L., cv Baccara) was investigated under adequately watered conditions in the field, using five levels of fertiliser N application at sowing (0, 50, 100, 200 and 400 kg N ha^–1). Although the presence of mineral N in the soil stimulated vegetative growth, resulting in a higher biomass accumulation in shoots in the fertilised treatments, neither seed yield nor seed nitrogen concentration was affected by soil mineral N availability. Symbiotic nitrogen fixation was inhibited by mineral N in the soil but it was replaced by root mineral N absorption, which resulted in optimum nitrogen nutrition for all treatments. However, the excessive nitrogen and biomass accumulation in the shoot of the 400 kg N ha^–1 treatment caused crop lodging and slightly depressed seed yield and seed nitrogen content. Thus, the presumed higher carbon costs of symbiotic nitrogen fixation, as compared to root mineral N absorption, affected neither seed yield nor the nitrogen nutrition level. However, biomass partitioning within the nodulated roots was changed. The more symbiotic nitrogen fixation was inhibited, the more root growth was enhanced. Root biomass was greater when soil mineral N availability was increased: root growth was greater and began earlier for plants that received mineral N at sowing. Rooting density was also promoted by increased mineral N availability, leading to more numerous but finer roots for the fertilised treatments. However, the maximum rooting depth and the distribution of roots with depth were unchanged. This suggested an additional direct promoting effect of mineral N on root proliferation.     

Effects of manipulation of plant carbon nutrient balance on tall goldenrod resistance to a gallmaking herbivore

Summary Ramets from six Solidago altissima clones of known resistance to the stem gallmaker Eurosta solidaginis were grown with and without supplemental nutrients. In a greenhouse experiment, mated female Eurosta were allowed to oviposit in ramets that were subsequently grown through flowering and then harvested to determine biomass allocation. Supplemental nutrients increased plant biomass but did not affect resistance to this gallmaking herbivore. This result does not conform to the plant carbon/nutrient balance hypothesis which predicts that enhanced mineral nutrition will indirectly cause a reduction in carbon-based defensive chemistry. Our results indicate a strong genetic basis to ball gallmaker resistance since modification of host phenotype did not influence susceptibility. We suggest that evaluating the degree of genotypic or environmental control of plant resistance will be especially helpful in clarifying the patterns of defensive chemical responses.     

Effect of soil salinity and soil water availability on growth and chemical composition ofSorghum halepense L.

Summary Effects of soil salinity and soil water regime on growth and chemical composition ofSorghum halepense L. was studied with a view to evaluating its potential as a forage crop in saline soils. The experiment was conducted under controlled conditions using pot-culture with three levels of soil salinity (EC_e 0.5, 5.0, 10.0 ds/m) and three soil water regimes (60%, 40% and 20% of water holding capacity of the soil). High soil salinity and low soil water combiningly had an adverse effect on plant growth but the biomass production was appreciably high (57 to 75% of control) even under high soil salinity (EC_e 10 ds/m) when sufficient water was available. Belowground plant parts were relatively more salt-tolerant than shoots. There occurred an increase in the concentration of certain nutrients (N, Ca, Mg, TNC) in the plants in response to salinity, which along with increased root: shoot ratios was inferred as an adaptive feature of the plant for persistence under saline conditions.     

Nutritional status,essential oil changes and water-use efficiency of rose geranium in response to arbuscular mycorrhizal fungi and water deficiency stress

Stress induced by water deficit is considered to be a global problem and one of the most important factors limiting crop production in arid and semi-arid regions of the world. Application of certain microorganisms, including arbuscular mycorrhizal fungi (AMF), is considered to be an effective and sustainable strategy to mitigate the problem. A pot experiment was conducted in the field (from Feb. to Sep. in 2013–2014 in Isfahan, Iran) to assess the effectiveness of AMF inoculation on changes in biomass, essential oils, nutrient uptake and water-use efficiency of rose geranium (Pelargonium graveolens L.) experiencing stress induced by a deficit of water. The experiment was planned as a factorial experiment, using a completely randomized design, with two factors, including four AMF inoculation (non-mycorrhizal, Rhizophagus intraradices and Funneliformis mosseae inoculated, and the combination of both species) and three irrigation levels including well-watered (WW), moderate water deficiency (MWD) and severe water deficiency (SWD). The results indicated the occurrence of an adverse effect of water deficit on plant total biomass; however, AMF inoculation positively increased plant biomass compared to the non-inoculated ones under three irrigation levels. MWD condition resulted in higher essential oil (EO) content (12.4 %), water-use efficiency (WUE) (29.5 %) and glomalin-related soil proteins (GRSP) (19.1 %) in the plants compared to WW condition. Furthermore, all AMF inoculation improved EO content by at least 12 k%. The results also showed that severe water deficiency adversely affected the uptake of most nutrients by plants especially in non-inoculated plants. The results also revealed that, although EO production was under the control of irrigation regime, nutrient uptake was critically dependent on an association with mycorrhizae. Notwithstanding the fact that rose geranium can tolerate moderate drought stress, the high responsiveness of rose geranium to AMF under water deficiency stress confirms the key role of AMF in facilitating the production of this valuable crop in harsh environments. Dual infection of rose geranium with two AMF species could also synergistically affect biomass, essential oil content and mineral elements absorption.     

What controls plant nutrient use in high elevation ecosystems?

The importance of rock-derived mineral nutrients (P, K, Mn, Mg, and Ca) in plant physiological function is well established. However, one important and relatively unexplored question is whether or not the same rules of plant nutrient use efficiency apply to these essential elements even if they are not limiting to primary production. We examined conifer growth and nutrient use dynamics across sites with contrasting geologies (sedimentary and volcanic) that vary in both rock-derived mineral nutrient and N availability. Differences in bedrock geochemistry generally corresponded to differences in available soil nutrients, such that the volcanic site tended to have greater available nutrients. Foliar nutrient concentrations reflected both differences in bedrock chemistry and indices of available soil nutrients for P, K, and Mn. Aboveground biomass production did not follow expected patterns and was greater for trees growing on low nutrient sites, but only with respect to the annual woody increment. Fine litter production did not differ between sites. Finally, we found evidence for trade-offs between two commonly examined components of nutrient use efficiency (NUE): nutrient productivity (A _n) and mean residence time of nutrients. However, we did not find evidence for higher plant NUE in soils with lower nutrient availability for N or rock-derived nutrients.     

Soil space and nutrients differentially promote the growth and competitive advantages of two invasive plants

Aims Invasive plants commonly occupy disturbed soils, thereby providing a stage for understanding the role of disturbance-enhanced resources in plant invasions. Here, we addressed how soil space and soil nutrients affect the growth and competitive effect of invasive plants and whether this effect varies with different invaders.Methods We conducted an experiment in which two invasive plants (Bromus tectorum and Centaurea maculosa) and one native species (Poa pratensis) were grown alone or together in four habitats consisting of two levels of soil space and nutrients. At the end of the experiment, we determined the total biomass, biomass allocation and relative interaction intensity of B. tectorum, C. maculosa and P. pratensis .Important findings Across two invaders, B. tectorum and C. maculosa, increased soil nutrients had greater positive effects on their growth than increased soil space, the effects of soil space on root weight ratio were greater than those of soil nutrients, and their competitive effect decreased with soil space but increased with soil nutrients. These findings suggest that changing soil space and nutrients differentially influence the growth and competitive advantages of two invaders. Bromus tectorum benefited more from increased soil resources than C. maculosa. Soil space and nutrients affected the biomass allocation of C. maculosa but not B. tectorum. The competitive effect of B. tectorum was unaffected by soil space and soil nutrients, but the opposite was the case for C. maculosa. Thus, the effects of soil space and nutrients on growth and competitive ability depend on invasive species identity.     

Plant sulfur nutrition: From Sachs to Big Data

Together with water and carbon dioxide plants require 14 essential mineral nutrients to finish their life cycle. The research in plant nutrition can be traced back to Julius Sachs, who was the first to experimentally prove the essentiality of mineral nutrients for plants. Among those elements Sachs showed to be essential is sulfur. Plant sulfur nutrition has been not as extensively studied as the nutrition of nitrogen and phosphate, probably because sulfur was not limiting for agriculture. However, with the reduction of atmospheric sulfur dioxide emissions sulfur deficiency has become common. The research in sulfur nutrition has changed over the years from using yeast and algae as experimental material to adopting Arabidopsis as the plant model as well as from simple biochemical measurements of individual parameters to system biology. Here the evolution of sulfur research from the times of Sachs to the current Big Data is outlined.     

Biomass and mineral element responses of a Serengeti short-grass species to nitrogen supply and defoliation: compensation requires a critical [N]

Large mammalian herbivores in grassland ecosystems influence plant growth dynamics in many ways, including the removal of plant biomass and the return of nutrients to the soil. A 10-week growth chamber experiment examined the responses of Sporobolus kentrophyllus from the heavily grazed short-grass plains of Serengeti National Park, Tanzania, to simulated grazing and varying nitrogen nutrition. Plants were subjected to two clipping treatments (clipped and unclipped) and five nitrogen levels (weekly applications at levels equivalent to 0, 1, 5, 10, and 40 g N m⁻²), the highest being equivalent to a urine hit. Tiller and stolon production were measured weekly. Total biomass at harvest was partitioned by plant organ and analyzed for nitrogen and mineral element composition. Tiller and stolon production reached a peak at 3–5 weeks in unclipped plants, then declined drastically, but tiller number increased continually in clipped plants; this differential effect was enhanced at higher N levels. Total plant production increased substantially with N supply, was dominated by aboveground production, and was similar in clipped and unclipped plants, except at high nitrogen levels where clipped plants produced more. Much of the standing biomass of unclipped plants was standing dead and stem; most of the standing biomass of clipped plants was live leaf with clipped plants having significantly more leaf than unclipped plants. However, leaf nitrogen was stimulated by clipping only in plants receiving levels of N application above 1 g N m⁻² which corresponded to a tissue concentration of 2.5% N. Leaf N concentration was lower in unclipped plants and increased with level of N. Aboveground N and mineral concentrations were consistently greater than belowground levels and while clipping commonly promoted aboveground concentrations, it generally diminished those belowground. In general, clipped plants exhibited increased leaf elemental concentrations of K, P, and Mg. Concentrations of B, Ca, K, Mg, and Zn increased with the level of N. No evidence was found that the much greater growth associated with higher N levels diminished the concentration of any other nutrient and that clipping coupled with N fertilization increased the total mineral content available in leaf tissue. The results suggest that plants can (1) compensate for leaf removal, but only when N is above a critical point (tissue [N] 2.8%) and (2) grazing coupled with N fertilization can increase the quality and quantity of tissue available for herbivore removal. Received: 25 August 1997 / Accepted: 14 April 1998     

Effects of Eu and Ca on yield and mineral nutrition of wheat (Triticum aestivum) seedlings

Although fertilisers enriched in rare earth elements (REE) are widely used in agricultural practice, little is known yet about behaviour of the REE in soil–plant system. Among REE, europium (Eu) may be of highest interest. Eu may serve as an indicator of biogeochemical processes due to a change of its valence state under different environmental conditions. Since chemical characteristics of Ca and REE are similar, Eu may compete with Ca for organic ligands. In the present work we studied the influence of Eu and Ca on the growth and mineral nutrition of wheat seedlings. An application of Eu favoured germination and root growth, whereas in combination with Ca it produced a more sustained leaf growth. Eu affected uptake and distribution of certain nutrients in different parts of a plant. The content of Eu in all parts of wheat seedlings at the end of germination significantly increased. Transfer of the seedlings germinated in the Eu-rich medium into soil resulted in the release of Eu from the plants. Nevertheless, 9 days after the sowing, Eu concentration in the seedlings was still much higher than in the control plants.     

Mineral nutrition of carnivorous plants: A review

Plant carnivory is one of many possible adaptation strategies to unfavorable conditions, mostly low nutrient availability in wet, acid soils. The following issues concerning the mineral nutrition of carnivorous plants are reviewed: the relative importance of carnivory and root nutrition for growth; which nutrients (elements) from prey are of principal importance for growth; the relationship between mineral and organic nutrition based on carnivory; the interactions between carnivory and root mineral nutrition; and the importance of carnivory under natural conditions. Special attention is paid to aquatic carnivorous plants. Studies on mineral nutrition carried out in laboratory and/or greenhouse conditions are discussed separately from those carried out in field conditions. The emphasis of this review is on recapitulation of original data and conclusions of results from a variety of studies that approach carnivorous plants from an ecophysiological point of view.     

秦岭南坡锐齿栎林的生态环境及其营养积累

秦岭锐齿栎林 (含 0～ 6 0cm土层 )营养元素总储量达 182 .6 4 5～ 394 .70 1t·hm-2 ,植被占 0 .5 9%～2 .13% ;林分生物量为 131.713～ 5 0 3.82 2t·hm-2 ,乔木层占 92 .1%～ 99.2 % ;凋落物层现存量和营养元素积累量分别为 2 .897～ 33.999t·hm-2 和 10 4 .339～ 1136 .5 36kg·hm-2 .在一定范围内 ,林分生物量和营养元素积累量随密度的增加而增大 ;立地、林分条件相似的林分 ,生物量和营养元素积累量与林龄呈正相关 .林分针叶树占的比例越大 ,营养元素积累量越小 ,而且对生物量的影响远小于对营养元素积累量的影响 .在同一地区 ,立地、林分状况相似 ,林型不同 ,生物量及营养元素积累量差别不大 ,树种组成和林型不同林分的生物量和营养元素积累量均不同 .不同地区 ,生态和林分条件相似的林分的生物量和营养元素积累量也有差异 ;林型、结构相似林分生物量和营养元素积累量南坡 >北坡 ,中段 东段≈西段 .林分对营养元素利用率与海拔呈负相关 ,且南坡 >北坡 ,中段 >东西段 ,中段 >西段 >东段 .     

New food sources of essential trace elements produced by biotechnology facilities

Population satiety with trace elements (TE) is a problem that is widely discussed in nutrition science. For optimal nutrition, the form of TE eaten in food is very important. Organic forms of TE in nutrition are appropriate as human metabolism has adapted to these kinds of nutrients during species evolution. This is now considered a reason for the beneficial use of biotechnologically produced TE sources in human food. Advanced matrixes for TE incorporation are unicellular organisms such as yeast, lactobacilli and Spirulina. Addition of inorganic salts at certain concentrations into cultivation media enables the mineral ions to incorporate into the microbial biomass. As a consequence, the biomass becomes enriched with organic forms of incorporated TE, which are presented by their complexes with amino acids, proteins and probably lipids and polysaccharides. In addition, a new direction of research has made good advances, in which technology has been developed for production of organic forms of TE through complex formation between transition metals (zinc, copper, manganese, chromium, iron) with amino acids and peptides formed during enzymatic hydrolysis of food protein. This brief review discusses the results demonstrating the advances in the biotechnological production of new TE sources, to obtain food components destined for wide prophylaxis of TE deficiency or for dietary treatment of the adverse consequences of these deficiencies.     

The rhizosphere and plant nutrition: a quantitative approach

The role of the rhizosphere in relation to mineral nutrition is discussed within a quantitative framework using the Barber-Cushman model as a starting point. The uptake or release of nutrients by roots growing in soil leads to concentration gradients forming in the soil: the zone so affected is termed the rhizosphere. The nature of these gradients depends on three factors: the rate of uptake/release; the mobility of the nutrient in soil; and the rate of conversion between available and unavailable forms. The interplay between these factors determines the amount of mineral nutrients acquired by the plant and it is the complexity of the interplay which demands the use of mathematical models in order to understand which factors most limit uptake. Despite extensive experimental evidence of root-mediated changes to the physical, chemical and biological status of rhizosphere soil, the quantitative significance of these changes for mineral nutrition has not been assessed. The problems of making this quantitative transition are reviewed.     

Improving crop mineral nutrition

Background

Crops require adequate nutrition for the production of food, fibre and fuel, but soil conditions often limit the ability of crops to acquire mineral nutrients. To address this, mineral nutrients can be applied as inorganic or organic fertilisers to the soil or as liquid fertilisers to foliage. However, production and use of fertilisers can have negative environmental impacts. The articles in this Special Issue illustrate a number of ways to improve nutrient acquisition from the soil and their delivery through foliar application.

Scope

Articles highlighted here include those that discuss ways by which to assess a crop’s requirement for additional mineral elements, ways by which minerals can be supplied more effectively to crops both through roots and shoots, and ways by which the crop itself can be enhanced to acquire more mineral elements.

Conclusions

It is apparent from the information contained in this Special Issue that to improve the ability of crops to acquire mineral elements, a number of strategies are available. However, the success of any one intervention is dependent on how these strategies interact with the environment in which they are deployed and the suitability of the management system for the specific intervention.     

Application of biosolids in mineral sands mine rehabilitation: use of stockpiled topsoil decreases trace element uptake by plants

Mineral sands mining involves stripping topsoil to access heavy-mineral bearing deposits, which are then rehabilitated to their original state, commonly pasture in south-west Western Australia. Organic amendments such as biosolids (digested sewage sludge) can contribute organic carbon to the rehabilitating system and improve soil chemical fertility and physical conditions. Use of biosolids also introduces the risk of contamination of the soil-plant system with heavy metals, but may be a useful source of trace elements to plants if the concentrations of these elements are low in unamended soil. We expected that biosolids amendment of areas mined for mineral sands would result in increased concentrations of metals in soils and plants, and that metal uptake would be decreased by adding stockpiled topsoil or by liming. A glasshouse experiment growing a mixed annual ryegrass (Lolium rigidum)-subterranean clover (Trifolium subterraneum) sward was conducted using two soil materials (residue sand/clay and conserved topsoil) from a mineral sands mine amended with different rates of biosolids (0, 10, 20, 50 dry t/ha), and including a liming treatment (2 t/ha). Total concentrations of metals (As, Cd, Co, Cr, Cu, Ni, Pb and Zn) in soil increased with increasing rate of biosolids application. Metal uptake was generally lower where topsoil was present and was decreased by liming. With increasing biosolids application, plant metal concentrations increased for Cd, Ni and Zn but decreased or were erratic for other elements. In clover, biosolids application removed the Zn deficiency observed where biosolids were not applied. Plant uptake of all elements increased with increasing biosolids application, suggesting dilution by increased plant biomass was responsible for erratic metal concentration results. Despite the observed increases in uptake of metals by plants, metal concentrations in both species were low and below food standard thresholds. It is unlikely that a single application of biosolids in this system posed a threat from heavy metal contamination of soils or plants, and was beneficial in terms of Zn nutrition of T. subterraneum.     

Sodium—A Functional Plant Nutrient

Plant scientists usually classify plant mineral nutrients based on the concept of “essentiality” defined by Arnon and Stout as those elements necessary to complete the life cycle of a plant. Certain other elements such as Na have a ubiquitous presence in soils and waters and are widely taken up and utilized by plants, but are not considered as plant nutrients because they do not meet the strict definition of “essentiality.” Sodium has a very specific function in the concentration of carbon dioxide in a limited number of C₄ plants and thus is essential to these plants, but this in itself is insufficient to generalize that Na is essential for higher plants. The unique set of roles that Na can play in plant metabolism suggests that the basic concept of what comprises a plant nutrient should be reexamined. We contend that the class of plant mineral nutrients should be comprised not only of those elements necessary for completing the life cycle, but also those elements which promote maximal biomass yield and/or which reduce the requirement (critical level) of an essential element. We suggest that nutrients functioning in this latter manner should be termed “functional nutrients.” Thus plant mineral nutrients would be comprised of two major groups, “essential nutrients” and “functional nutrients.” We present an array of evidence and arguments to support the classification of Na as a “functional nutrient,” including its requirement for maximal biomass growth for many plants and its demonstrated ability to replace K in a number of ways, such as being an osmoticium for cell enlargement and as an accompanying cation for long-distance transport. Although in this paper we have only attempted to make the case for Na being a “functional nutrient,” other elements such as Si and Se may also confirm to the proposed category of “functional nutrients.”