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Plant Mineral Nutrition
Anthony J Miller,
John Innes Centre, Norwich, UK
Several inorganic minerals are essential for plant growth
and these are usually obtained by roots from the soil.
Availability of minerals in the soil is determined by the
physical and chemical characteristics of the soil. Plants
can directly influence nutrient availability around the
root surface; this zone is called the rhizosphere. Plants
adjust root architecture and exudation according to their
nutrient requirements and under deficiency these chan-
ges can be a marker for nutrient status. Nutrients are
taken up from the soil using plasma-membrane located
transporter proteins and excess is stored in the cell
vacuole or converted into polymerised storage forms. For
crops it is essential to match nutrient supply to demand
throughout the growth season to obtain the maximum
yield. These nutrient storage forms can be used as agri-
cultural indicators of crop nutrient status and the
potential for fertilizer leaching losses. Membrane trans-
porters provide a gateway for nutrient entry into plants,
but the selectivity of these filters can breakdown when
chemically similar minerals are present at very high con-
centrations. The minerals may not be essential for
growth, but they can enter plant cells and cause toxicity.
Introduction
Plants require some specific elements from the external
environment and these are usually obtained by roots from
the soil. Less typically nutrients can also be taken up across
the surface of leaves or in specialised structures in the few
types of plants that can catch and digest insects. The
quantities of each element required by plants can be used to
define them as being either macro- or micro-nutrients. A
complete list of the mineral nutrients found in plants is
shown in
Table 1
, and this type of information is obtained
by chemical analysis of the previously digested leaf or
whole plants. Specific parts of the plant, like seeds, accu-
mulate some microelements to much higher concentrations
– for example, the zinc or iron levels can be 10–20 times
higher than the values given in
Table 1
.See also:Plant
Macro- and Micronutrient Minerals
The elements that are essential for growth serve both
structural and biochemical roles in the plant and many
have multiple functions. It is difficult to specifically classify
the role of each nutrient, but they can be placed into general
types based on function (see
Table 1
). Type I nutrients are
bound into the structure of carbon compounds, such as
nucleic acids and proteins. Type II nutrients are required
for energy storage and transport. Type III nutrients are
linked with cell wall structure and Type IV are integral as
constituents of enzymes or other molecules required for
metabolism (e.g. chlorophyll and ferredoxin). Type V can
activate enzymes or control their activity and Type VI
nutrients serve as major cellular osmotica.
Nutrient Availability
The physical and chemical characteristics of the soil
determine the availability of nutrients to uptake by plant
roots. The nutrients dissolved in soil water are those that
are generally available for uptake and this is why most
plants can be successfully grown in hydroponics or water
culture. In soil the plant can directly influence nutrient
availability in the area around the root surface; this zone is
called the rhizosphere. Root-mediated localised changes in
pH and soil microbes can directly influence the water
solubility of many nutrients. For example, a more acidic
rhizosphere pH dissolves soil mineral phosphorus,
increasing solubility and making the nutrient available for
uptake by plant roots. A plant can adjust these root
properties according to their nutrient requirements and
under deficiency these changes can be a marker for nutrient
status. Many plants (e.g. oilseed rape – Brassica napus)
excrete organic acids under deficiency (e.g. phosphorus
and iron) to increase the soil availability of these nutrients.
Furthermore, some plant roots excrete specific enzymes
and chelating molecules to improve soil nutrient avail-
ability, for example, phosphatases for phosphate and
siderophores for iron. Roots can encourage the growth of
particular types of bacteria and fungi that can solubilise
Introductory article
Article Contents
.
Introduction
.
Root Uptake
.
Homoeostasis, Storage and Measuring Nutrient Status
.
Deficiency and Toxicity
.
Future Prospects for Crop Nutrition
.
Acknowledgements
Online posting date: 15
th
July 2014
eLS subject area: Plant Science
How to cite:
Miller, Anthony J (July 2014) Plant Mineral Nutrition. In: eLS.
John Wiley & Sons, Ltd: Chichester.
DOI: 10.1002/9780470015902.a0023717
eLS &2014, John Wiley & Sons, Ltd. www.els.net
1
minerals in the soil making the nutrients more available for
root uptake. These microbial populations receive carbon
from the root to encourage their growth in the rhizosphere.
There is good evidence that although the soil type is
important, each type and even cultivar of plant can
encourage a specific population of fungi and bacteria that
can be a characteristic ‘fingerprint’ for that rhizosphere
(Berg and Smalla, 2009). For example, alfalfa roots select
in their rhizosphere for phenotypes of Pseudomonas fluor-
escens with enhanced motility (Martı
´nez-Granero et al.,
2006), although these have greater efficacy in biocontrol of
fungal pathogens the bacteria release siderphores that bind
iron and may make it available to plants. Comparing rice
cultivars, some roots each showed characteristic rhizo-
sphere selection of bacteria populations (Hardoim et al.,
2011). Rhizosphere bacterial populations can convert
nutrients into different forms that are more accessible for
uptake by roots (e.g. fixing gaseous nitrogen or nitrifica-
tion, converting ammonium to nitrite and nitrate), but they
can also engineer the physical environment by generating
local air-filled spaces or pores in the soil for gas exchange.
In addition, the rhizosphere bacteria can provide bridges
that maintain contact between soil particles and the root to
ensure water and dissolved nutrient delivery to the plant in
drying soils. The cataloguing of soil and rhizosphere bac-
teria and fungi has been revolutionized by improvements in
ribonucleic acid (RNA) and deoxyribonucleic acid (DNA)
sequencing and these techniques are independent of the
ability to culture the microbes (Hirsch et al., 2010).
See also:Genomics and the Rhizosphere;Phosphorus
Availability in the Environment;Rhizosphere
Root Uptake
Root architecture and membrane transporters are the main
factors determining root acquisition of available nutrients.
Plants can adjust their branching pattern and root hair
development to exploit locally available patches of higher
nutrient concentrations (see
Figure 1
). Roots show a fora-
ging growth pattern and when they encounter a rich
nutrient pocket in the soil their architecture changes to
Table 1 Mineral concentrations of typical whole plants
Element
Chemical
symbol
Concentration in dry matter Function and main roles in plant (with group
classification)ppm or % mmol g
21
Macronutrients
Nitrogen N 1.5% 1000 Chlorophyll, nucleic acids and proteins (I, VI)
Potassium K 1% 250 Enzyme activator, osmotic balance (V, VI)
Phosphorus P 0.2% 60 Energy supply (e.g. ATP), nucleic acids (I, II)
Sulphur S 0.1% 30 Nucleic acids and proteins (I)
Calcium Ca 0.5% 125 Cell walls, enzyme activator, signalling (III,V)
Magnesium Mg 0.2% 80 Chlorophyll (IV,V)
Silicon Si 0.1% 30 Cell walls (III)0.5
Micronutrients
Nickel Ni 0.05 ppm 0.001 Enzyme component (e.g. urease) (IV)
Molybdenum Mo 0.1 ppm 0.001 Enzyme component (e.g. nitrogenise) (IV)
Cobalt Co 0.1 ppm 0.002 Nitrogen fixation in legumes (IV)
Copper Cu 6 ppm 0.1 Respiration & oxido-reduction (IV, V)
Zinc Zn 20 ppm 0.3 Enzyme activation (IV,V)
Sodium Na 10 ppm 0.4 C4 photosynthesis in some plants (IV)
Manganese Mn 50 ppm 1.0 Chlorophyll synthesis, energy transfer (IV, V)
Boron B 20 ppm 2.0 Cell wall stability (III)
Iron Fe 100 ppm 2.0 Chlorophylll synthesis, energy transfer (IV, V)
Chlorine Cl 100 ppm 3.0 Photosynthesis, osmotic balance (V, VI)
Source: Modified from Epstein and Bloom (2005).
0.01 mM
1 mM
0.01 mM 1 mM
1 mM
1 mM
Localised 1 mM KNO3Uniform 1 mM KNO3
Drew et al. (1973) J. Exp. Bot. 24, 1189−1202
Figure 1 The pattern of barley root development showing localised
increased growth where nitrate is available at higher concentrations. This
pattern of development depends on the type of nutrient, but this localised
proliferation can be observed by many different species in response to the
major nutrients. Reproduced from Drew et al. (1973) with permission of
Oxford University Press. &Oxford University Press.
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2
Plant Mineral Nutrition
branch locally increasing the area for uptake and short-
ening the distance for diffusion (Mommer et al., 2012). The
upper layers of soil usually contain the highest amounts of
nutrients and so the top soil is frequently densely covered
with roots. Phosphorus is an example of a nutrient that
occurs in the top soil and bean roots proliferate in this layer
to acquire this nutrient (Lynch and Brown, 2001). Primary
roots grow deeper through the profile to exploit the water
and nutrient (e.g. nitrate) supplies that are often located
much lower in the soil. See also:Roots and Root Systems
Plants have gene families of nutrient transporters that
each specialise in the uptake of soil available nutrients, for
example, ammonium and nitrate. There are key steps in the
uptake of nutrients, these are transport across the plasma
membrane from the soil into root cells, storage in the
vacuole and loading of the long distance transport systems
in plants (phloem and xylem), unloading into the growing
tissues such as leaves or seeds. Each of these transport steps
is mediated by specific transporter proteins and they are
potential regulatory steps in the pathway for nutrient entry
into the plant. This regulation can occur by changes in gene
expression or by post-translational regulation of the pro-
tein. Often mutations in the transporter results in plants
that demonstrate nutrient deficiency symptoms under
normal supply conditions that would be adequate for a
wild type plant. But sometimes the mutation is hidden
because another transport in the family can step up
expression to compensate for the missing function. Some of
the plasma membrane transporters are also involved in
sensing the external availability of nutrients and these have
been described as ‘transceptors’ (Gojon et al., 2011). For a
recent list of the plant nutrient transporter families check
the ARAMEMNON website http://aramemnon.botani-
k.uni-koeln.de/. Although the gene families of nutrient
transporters have selectivity for each type of nutrient this
specificity can break down when concentrations of other
ions become high enough (see Section ‘Deficiency and
Toxicity’ below). The selectivity and transport rate of a
plasma membrane nutrient transporter can also be
important for determining crop nutrient use efficiency.
Some nutrients are acquired by beneficial interactions or
symbioses with bacteria and/or fungi. In symbiosis with
fungi, the plant benefits from the increased surface area
provided for mining nutrients from the soil, this has
obvious advantages for the acquisition of soil immobile
minerals, like phosphorus, but also for water uptake.
Together with bacteria, legumes can form a nitrogen-fixing
nodule that supplies nitrogen to the plant taken from the
air. A range of these symbiotic associations occur and their
importance to each individual plant for nutrient acquisi-
tion depends on the local availability of nutrients. In some
nutrient-poor soils a symbiotic relationship may be essen-
tial for the plant to grow and reproduce. These relation-
ships can also be important for plants growing in toxic
environments, for example, there are some plants that
tolerate soils containing heavy metals by forming fungal
mycorrhizal associations. See also:Improving Nutrient
Use Efficiency in Crops;Plant Nitrogen Nutrition and
Transport;Plant–Fungal Interactions in Mycorrhizas;
Root Nodules (Legume–Rhizobium Symbiosis)
Homoeostasis, Storage and
Measuring Nutrient Status
The interplay between plasma membrane uptake and
nutrient storage forms is balanced to maintain cytoplasmic
concentrations that are optimised for plant growth (
Figure
2
). Nutrient homoeostasis is the regulation of supply to
maintain an optimum environment for cellular biochem-
ical reactions in the cytoplasm. The balance or homo-
eostasis is important for a plant, yet very little is known
about how this cellular equilibrium is sensed and regulated
within individual plant cells. It has been proposed that
changes in root cytoplasmic nutrient concentrations can
signal nutrient status (e.g. nitrate, Miller and Smith, 2008;
potassium, Walker et al., 1996).
Excess nutrients are usually stored in cell vacuoles and
elemental analysis of whole tissue can be used to measure
nutrient pools. For example, manganese (Mn) tissue
accumulations can vary between plant species growing on
the same soil. The general critical threshold concentration
for the onset of Mn deficiency in leaves is in the range of 10–
20 mg kg
21
and it can particularly be a problem for plants
to acquire the metal in alkaline soils (Marschner, 1995). At
the other extreme, some rare plants can hyper-accumulate
leaf manganese to 10 000 mg kg
21
, for example, Gossia
species (Fernando et al., 2009). Nutrients can sometimes be
stored after conversion into specific forms, and the
amounts of these storage forms can also be used as indi-
cators of a plant’s nutrient status. For example, phos-
phorus can be stored as phytate in seeds, but the nutrient
can be stored in all cells to a lesser extent as phosphate in
the vacuole. Iron storage has been linked to accumulation
of the protein ferritin, particularly in legume seeds like peas
and beans, but this may result from iron toxicity rather
than a direct role in storage of the metal (Briat et al., 2010).
Nutrient transporters at the vacuolar membrane mediate
the storage and remobilization of nutrients, and like at
the plasma membrane, there are specific families of pro-
teins mediating these steps (Martinoia et al., 2012). The
activity of these vacuolar transporters must be regulated in
concert with those at the plasma membrane to achieve
homoeostasis and optimal cytoplasmic concentrations of
nutrients for metabolism and growth. Very high con-
centrations of some nutrients can result in toxicity in plants
(see
Figure 2
) and this occurs when the storage capacity is
exceeded by the supply. See also:Heavy Metal Adaptation;
Iron in Plants
The nutrient status of plants can be identified by whole
tissue digests followed by elemental analysis. Young leaf
material is usually used for this analysis because this tissue
is a good indicator of the whole plant nutrient status. The
concentration in dry matter of a given nutrient can then be
compared with tabulated values of the optimal range for
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Plant Mineral Nutrition
each type of crop. As this laboratory analysis can be time-
consuming, simpler assays have been developed that can be
used by farmers in a field. Small deficiencies in nutrients
may not present obvious symptoms, but can result in a sub-
maximal crop yield for farmers. The general nutrient status
of a crop can be assessed by the ‘greenness’ or chlorophyll
content using hand-held or tractor mounted devices for
measuring this parameter. Nitrogen supply is well-known
to influence the greenness of a crop. Insufficient phos-
phorus supply can also influence on wheat leaf chlorophyll
content and grain yield (
Figure 3
, left). The down-side of this
chlorophyll assessment method is that other factors like
pathogens or insect attack can complicate the measure-
ment. Plant leaf or petiole sap analysis can be used as an
indicator of nutrient status and portable equipment to
measure nutrient concentrations in the field is available.
Like whole tissue digests, sap analysis results can be com-
pared with previously determined optimal nutrient con-
centrations to decide if the crop needs more fertilizer.
Deficiency and Toxicity
As nutrients concentrations are critical for the processes
involved in metabolism and growth, a limited supply of any
nutrient will result in suboptimal stature and yield.
Nutrient deficiencies result in stunted growth, but there are
often other visual symptoms. Deficiency symptoms com-
monly include chlorosis, a yellowing of the leaf and stem
tissues. The precise pattern of the chlorosis can indicate
more specifically which nutrient is missing. For example,
nitrogen deficiency results in a general chlorosis, but iron-
deficient plants showing yellowing in the leaf between
veins. When specific elements, like phosphorus, are defi-
cient plants will develop a purple colouration due to the
production of large amounts of anthocyanins (see
Figure 3
,
right). These chemicals are produced when plants are
stressed and they have a biochemically protective role in
the cell. Tissue death or necrosis follows chlorosis as defi-
ciencies become more acute. In potassium-deficient plants
necrosis occurs along leaf margins, but in manganese-
deficient plants necrosis occurs between veins. For some
nutrients such as iron, the deficiency symptoms show first
in a young leaf; this suggests that the element is not easily
translocated from old to young leaves. Nitrogen, potas-
sium and magnesium are easily loaded into the phloem and
xylem and translocated from old leaves to younger devel-
oping leaves. For these nutrients, the older leaves exhibit
the deficiency symptoms. See also:Anthocyanins;Plant
Macro- and Micronutrient Minerals
As described above, very high concentrations of some
nutrients can result in plant toxicity (see
Figure 2
) although
this rarely occurs in nature. The normal entry route for
nutrients can become a way for toxic elements to enter
plants. For example, transporters for the uptake of trace
element metals can become a pathway for the entry of other
toxic metals like cadmium and under saline conditions
sodium can enter through potassium transporters as the
external abundance of sodium compared to potassium is so
high. The accumulation of these toxic elements in plants
Nutrient tissue concentration
40
80
0
Growth as percentage of maximum
Toxic
(symptoms)
Adequate
(no symptoms)
Transition zone with
minor or no symptoms
Deficiency with
symptoms
10% Reduction in growth
at critical concentration
Insufficient
(symptoms)
Figure 2 Diagram representation showing the relationship between plant growth and tissue concentration. The blue graph line represents the relationship
between plant growth and the nutrient concentration in tissue. Redrawn from Epstein and Bloom (2005).
eLS &2014, John Wiley & Sons, Ltd. www.els.net
4
Plant Mineral Nutrition
can be ameliorated by increasing the supply of the nutrient
that usually enters the plant via this transporter system.
See also:Potassium in Plants
Future Prospects for Crop Nutrition
When a nutrient deficiency can be detected in a crop there is
already likely to be a yield penalty. In other words, nutrient
status detection in plants is too late; therefore, new meth-
ods for measuring and predicting soil nutrient availability
are important for the early diagnosis of impending nutrient
limitations. This approach can ensure that the soil avail-
able nutrients are maintained at optimal levels for the crop,
but not at levels that result in fertilizer leaching. The
nutrient status of soil is usually assessed by taking core
samples in the field, then measuring the extracted nutrients
in the laboratory. The accuracy of this method depends on
the type of extraction used, but often it overestimates the
amount of the nutrient that is actually available for uptake
by roots. New more accurate methods for measuring soil
nutrient availability are important for improving crop
nutrition.
Figure 4
shows some of the future possible strategies for
improving nutrient use by crop roots. For example, the
inoculation of soil with specific types of bacteria tailored
for each crop may be a way of enhancing the nutrient
availability. Choosing the appropriate type of bacteria can
encourage root growth and health, promoting nutrient
cycling in the rhizosphere. Soil and seed could be inocu-
lated using beneficial microbes, with the species mix tai-
lored for each type of crop. In addition, the ability of the
plant to host particular types of bacteria may be enhanced
by the root exudate composition. There is some evidence
that modern crop cultivars may have lost some of the
chemical exudates found in ancestral varieties that can
influence nutrient availability in the rhizosphere. For
example, root exudates can contain nitrification inhibitors
P nutrition affects wheat leaf chlorophyll
P nutrition affects wheat grain yield
Low P
Low P
Sufficient P
Sufficient P
Strawberry leaf
showin
g
P deficienc
y
Strawberry leaf
with sufficient P
5
4
3
2
1
0
010 20 30 40 50 60 70 80
Days after anthesis
Flag leaf chlorophyll
(mg g−1 fresh wt)
80
60
40
20
0
0 10 20 30 40 50 60 70 80
Days after anthesis
Central spikelet
grain dry weight (mg)
Figure 3 The influence of varying phosphorus supply on wheat leaves and yield (left) and visual leaf symptoms in strawberry (right). Wheat figure shows
the effects of phosphorus supply on chlorophyll (upper) and grain yield (lower). Reproduced with permission from Kochian L (2002) Molecular physiology
of mineral nutrient acquisition, transport, and utilization. In: Bob B, Wilhelm G and Russell J (eds.) Biochemistry & Molecular Biology of Plants. Oxford,
Oxfordshire: John Wiley & Sons. ISBN 978-0-943088-39-6. &John Wiley & Sons.
Root strategies for improving nutrient acquisition
• Rhizosphere - exudates,
acidification, enzymes and
specific types of microbes.
• Uptake - transporters and
regulation.
• Root architecture - root hairs,
laterals, surface, depth and
penetration.
• Symbioses - mycorrhization and
nodulation.
Figure 4 Some future strategies for improving crop nutrient acquisition.
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5
Plant Mineral Nutrition
blocking the conversion of ammonium into nitrate (Sub-
barao et al., 2009). The plasma membrane transporters
that mediate the uptake of nutrients by roots may also be
targets for improved acquisition of nutrients. This may be
achieved by increasing the affinity of the transporter for the
nutrient or by modifying the regulation of transporter
activity, for example, by phosphorylation state of the
protein. Root architecture is another potential target as
increasing root area provides a larger area for the nutrient
acquisition. Some nutrients are acquired by beneficial
symbioses with bacteria and fungi, these relationships are
especially important in nutrient poor environments. These
symbioses are important for water and nutrient acquisition
and there is a scope for encouraging their development
more in agricultural soils.
Acknowledgements
Anthony J Miller is supported by grant funding (BB/
JJ004553 and BB/JJ004561) from the BBSRC and the John
Innes Foundation.
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Further Reading
Kalra YP (1998) Handbook of Reference Methods for Plant Ana-
lysis. New York, NY: CRC Press, Taylor and Francis Group.
Maathuis FJM (2013) Plant mineral nutrients. Methods and Pro-
tocols. Methods in Molecular Biology 953. New York, NY:
Springer, Humana Press.
White PJ, George TS, Dupuy LX et al. (2013) Root traits for
infertile soils. Frontiers in Plant Science 4: 1–7 (article 193).
http://journal.frontiersin.org/Journal/10.3389/fpls.2013.
00193/abstract
Xu G, Fan X and Miller AJ (2012) Plant nitrogen assimilation and
use efficiency. Annual Review of Plant Biology 63: 153– 182.
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Plant Mineral Nutrition
