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Phosphorus Nutrition: Plant Growth in Response to Deficiency and Excess

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Abstract

Phosphorus (P) is an essential element determining plants’ growth and productivity. Due to soil fixation of P, its availability in soil is rarely sufficient for optimum growth and development of plants. The uptake of P from soil followed by its long-distance transport and compartmentation in plants is outlined in this chapter. In addition, we briefly discuss the importance of P as a structural component of nucleic acids, sugars and lipids. Furthermore, the role of P in plant’s developmental processes at both cellular and whole plant level, viz. seed germination, seedling establishment, root, shoot, flower and seed development, photosynthesis, respiration and nitrogen fixation, has been discussed. Under P-deficient condition, plants undergo various morphological, physiological and biochemical adaptations, while P toxicity is rarely reported. We also summarize the antagonistic and synergistic interaction of P with other macro- and micronutrients.
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M. Hasanuzzaman et al. (eds.), Plant Nutrients and Abiotic Stress Tolerance,
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Chapter 7
Phosphorus Nutrition: Plant Growth
inResponse toDeciency andExcess
HinaMalhotra, Vandana, SandeepSharma, andRenuPandey
Abstract Phosphorus (P) is an essential element determining plants’ growth and
productivity. Due to soil xation of P, its availability in soil is rarely sufcient for
optimum growth and development of plants. The uptake of P from soil followed by
its long-distance transport and compartmentation in plants is outlined in this chap-
ter. In addition, we briey discuss the importance of P as a structural component of
nucleic acids, sugars and lipids. Furthermore, the role of P in plant’s developmental
processes at both cellular and whole plant level, viz. seed germination, seedling
establishment, root, shoot, ower and seed development, photosynthesis, respira-
tion and nitrogen xation, has been discussed. Under P-decient condition, plants
undergo various morphological, physiological and biochemical adaptations, while P
toxicity is rarely reported. We also summarize the antagonistic and synergistic inter-
action of P with other macro- and micronutrients.
Keywords Abiotic stress · Macronutrients · Nutrient deciencies · Plant metabo-
lism · Soil fertility
7.1 Introduction
Next to nitrogen (N), phosphorus (P) is a vital nutrient for plant growth and produc-
tivity. Its concentration in plants ranges from 0.05% to 0.5% of total plant dry
weight. Though concentration of P in soil is 2000-fold higher than the plant, its xa-
tion in the form of aluminium/iron or calcium/magnesium phosphates renders it
unavailable for uptake by plants. Hence, plants often face the problem of P de-
ciency in agricultural elds. Diagnosing its deciency is a tedious task, since crops
generally display no visual symptoms at an early stage. Its deciency is often con-
fused with N since the veins of young leaves appear red under both deciencies.
However, no general chlorosis is seen in P-decient plants. P deciency reduces
H. Malhotra · Vandana · S. Sharma · R. Pandey (*)
Mineral Nutrition Laboratory, Division of Plant Physiology, ICAR- Indian Agricultural
Research Institute, New Delhi, India
172
plant growth which is attributed to either decrease in photosynthesis or increase in
energy investment. Its limitation negatively impacts crop yield and quality. It has
been estimated that P deciency reduces the crop yields on 30–40% of the world’s
aerable land. This necessitates the use of a large amount of phosphatic fertilizers to
correct its deciency. The phosphorus use efciency (PUE) is 15–20% in agricul-
tural elds indicating that most of the soil-applied P remains unavailable to plant
and leaches into ground and surface water leading to eutrophication (Correll 1998;
Smith 2003).
Phosphorus plays an important role in an array of cellular processes, including
maintenance of membrane structures, synthesis of biomolecules and formation of
high-energy molecules. It also helps in cell division, enzyme activation/inactivation
and carbohydrate metabolism (Razaq etal. 2017). At whole plant level, it stimulates
seed germination; development of roots, stalk and stem strength; ower and seed
formation; crop yield; and quality. In addition, availability of P increases the
N-xing capacity of leguminous plants. Hence, P is essential at all developmental
stages, right from germination till maturity.
Phosphorus is an important constituent of energy-rich compounds, including
adenosine triphosphate (ATP), cytidine triphosphate (CTP), guanosine triphosphate
(GTP), uridine triphosphate (UTP), phosphoenol pyruvate and other phosphory-
lated intermediate compounds. Hence, it supplies energy to drive various cellular
endergonic processes. Being a constituent of nucleic acids (DNA, RNA), it is essen-
tial for reproduction and protein synthesis. In order to maintain its role under inor-
ganic phosphate (Pi-deprived conditions), plants undergo various morphological,
physiological and biochemical adaptations. These include alterations in root archi-
tecture, formation of cluster roots, shoot development, organic acid exudation and
alternative glycolytic and respiratory pathways (Vance etal. 2003). In this chapter,
we present an overview of the uptake, translocation and the role played by P in vari-
ous processes both at cellular and whole plant level.
7.2 Uptake, Long-Distance Transport
andCompartmentation ofPhosphorus
Uptake is the rst step of the pathway involved in the movement of any element
from soil to roots and other plant parts. The availability of P in soil solution is
largely decided by soil components, including soil pH, texture, concentration of P,
metals and anions (Sanyal and De Datta 1991; Hinsinger 2001). The strong interac-
tion of P with soil components favours the ow of P from soil to roots via diffusion,
rather than by mass ow. Two pools of P occur in soil, organic (Porg ) and inorganic
(Pi). About 20–80% of the soil P exists in organic form, of which inositol hexaphos-
phate (phytic acid) is a major component. Rest of the P is present in inorganic form.
The activity of soil microbes releases the immobile forms of P to soil solution which
is then made available to the plants. Uptake of P is largely favoured between pH 5.0
H. Malhotra et al.
173
and 6.0 where it predominates in the monovalent form (H2PO4) (Furihata etal.
1992). Various inorganic forms of P, viz. H2PO4, HPO42 and H3PO4, occur in soil
solution at a concentration of 0.1–10μM, which is far lower than in plant tissue
(5–20 mM) (Hinsinger 2001; Shen etal. 2011). Due to concentration difference
between soil and plant, P is actively taken up by transporters present in root plasma
membrane against the concentration gradient. Moreover, to increase P uptake, plant
roots and microbes excrete various organic acids and extracellular phosphatases,
thereby acidifying the rhizosphere and causing easy movement of P inside the root
system (Comerford 1998; Hinsinger 2001). After entering the root surface, P fol-
lows a symplastic route to reach xylem and then from xylem to aerial parts of the
plant. The inter- and intracellular transport of P from xylem to the cytoplasm and
further to vacuole is an energy-dependent process (Ullrich and Novacky 1990).
Phosphorus uptake and transport is mediated by the presence of high- and low-
afnity transport systems that vary in their Michaelis-Menten constant (Km) values
and operate at low and high P concentrations, respectively (Furihata etal. 1992;
Smith etal. 2000; Guo etal. 2002). To prevent membrane hyperpolarization, the
transport of P is accompanied by one or two protons or singly (Na+) or doubly
charged cation (Reid etal. 2000; Sakano 1990; Schachtman et al. 1998). Many P
transporters have been identied in Arabidopsis (PHT1–4), barley (Hordeum vul-
gare PHT1), rice (Oryza sativa PHT1) and wheat (Triticum aestivum PHT1 and 2)
which are involved in the uptake of P from soil and translocation from root to xylem,
phloem, leaf, seed, chloroplast, mitochondria and Golgi body (Rausch and Bucher
2002; Miao etal. 2009; Huang etal. 2011; Liu et al. 2013). These are primarily
expressed in root and shoot vascular system (Hasan et al. 2016). Many genes,
including transcription factors and miRNA, are induced by phosphate starvation
(IPS) and aid in the regulation of P homeostasis. These include phosphate respon-
sive (PHO), an E3 ligase (SIZ1), phosphate starvation response (PHR), phosphate
transporter trafc facilitator (PHF), WRKY, ZAT6 and miR399 (Miura etal. 2005;
Devaiah etal. 2007; Liu etal. 2010a; Bayle etal. 2011; Lin etal. 2014; Wang etal.
2014; Su etal. 2015). However, the transporters involved in recycling of P from
older to young leaves are not fully understood. Also, the genetic regulation, tempo-
ral dynamics and contribution of these transporters to crop tolerance are poorly
known under low P conditions. Hence, further studies are needed to attain the com-
plete understanding of the mechanism underlying P uptake, utilization and transport
under P-decient conditions.
Pi is important in many enzyme-catalysed reactions inside the cell cytoplasm.
Hence, maintenance of its concentration in stable form is extremely essential. It
constitutes 0.05–0.5% of the plant dry weight, which is far lower than that of N and
K (Vance etal. 2003). The Pi pool is determined by various factors, such as pH of
cellular compartment and chemical form and functional behaviour of P.For exam-
ple, in slightly basic cytoplasm, Pi is equally partitioned between H2PO4 and
HPO42, while more acidic vacuole and apoplast contain H2PO4 as the dominant
form. The chemical form of P, as P-esters or P-lipids, changes with tissue type, age
and P availability. The existence of P species also varies with the functional prop-
7 Phosphorus Nutrition: Plant Growth inResponse toDeciency andExcess
174
erty, viz. metabolic, storage or cycling form. The cellular compartmentation of P
has been studied with various radioactive and NMR spectroscopy techniques
(Bieleski 1973; Ratcliffe 1994). These studies have conrmed the presence of 1–5%
of the total Pi in cytoplasm while vacuole being the major storage site of P.
7.3 Phosphorus Deciency andExcess
Eroded, weathered and calcium carbonate-rich soils are the common sites of P de-
ciency. About 80–90% of the soil P is unavailable to the plant due to its xation as
insoluble Ca-P, and hence plant P deciency is a common problem. Young plants
have a higher demand of P in comparison to mature plants which is why the de-
ciency symptoms are more prominent in the former. Under low P conditions, the
plant appears stunted with dark green foliage and reduced leaf surface area.
Decreased leaf expansion and hence smaller leaves occur as a result of the reduced
cell division and enlargement. The older leaves acquire purplish pigmentation due
to more anthocyanins synthesis under limited P conditions. Other symptoms include
upward tilting and curling of leaves and brown internal specks in tubers. Plant matu-
rity is also delayed under P limitation; however, these changes vary with the crop
species involved (Peaslee 1977). The reduction in shoot growth is comparatively
higher than the root growth, hence resulting in a lower shoot-to-root ratio.
Plants respond to P limitation by undergoing various physiological, biochemical
and metabolic changes. P-decient leaves allocate more carbon (C) from shoots to
roots, thereby enhancing the overall root growth. Being the primary source of nutri-
ents for plant growth and development, roots respond largely to P availability. To
cope up with P limitation, roots induce various chemical and biological changes,
which intensify the availability of soil P (Hinsinger 2001). The major ones include
alterations in root length, biomass, formation of cluster roots and release of organic
substances for more P availability.
Higher concentration of P is often found in the topsoil and it decreases with soil
depth. Many studies depicted changes in the root architecture, including morphol-
ogy, topology and distribution patterns, which helps to facilitate the uptake of P
from topsoil (Charlton 1996; Ge etal. 2000; Liao etal. 2001; Lynch and Brown
2001; Williamson etal. 2001). These changes include reduction of primary root
length while enhancement of lateral root density, root biomass, root hair density and
length, formation of cluster roots, along with greater root penetration capacity
(Jungk 2001; Williamson etal. 2001; Péret etal. 2011). These changes are induced
by alteration in carbohydrate distribution between roots and shoots as well as by
signalling of hormones, sugars and nitric oxide (Nacry et al. 2005; Vance 2010;
Wang et al. 2010). In addition to alterations in root architecture, other changes
include acidication of rhizosphere, exudation of low molecular weight organic
acids, secretion of acid phosphatases and photosynthesis-related enzymes and sym-
biotic and free-living associations with mycorrhizal fungi and plant growth-promot-
ing bacteria (Neumann and Römheld 2002; Singh and Pandey 2003; Chen etal.
H. Malhotra et al.
175
2006; Smith and Read 2008; Zhang et al. 2010; Vengavasi and Pandey 2016b).
Exudation of carboxylates (citrate and malate) enhances the mobility of sparingly
soluble P by chelation and ligand exchange (Vance et al. 2003; Hinsinger et al.
2005; Wang etal. 2007). The C required for increased organic acid synthesis is
provided by both photosynthetic CO2 xation as well as by CO2 xation in root.
Enhanced activities of phosphoenolpyruvate carboxylase (PEPC), malate dehydro-
genase (MDH) and citrate synthase (CS) and reduced activities of aconitase (AC)
have been reported in various crops (Neumann etal. 1999; Uhde-Stone etal. 2003;
Vengavasi etal. 2016). As a result of increased organic acids secretion under P de-
ciency, root acidication might occur by the release of protons that decreases the
rhizospheric pH by 2–3 units (Marschner 1995; Yan et al. 2002; Vengavasi and
Pandey 2016a). This increases the availability of sparingly soluble soil P.However,
the release of exudates might reduce the efciency of P mobilization (Shen etal.
2005) which stresses on the need to reconsider such assumptions to systematically
understand the interaction of soil P-rhizosphere-carboxylates.
Secretion of phosphatases under P deciency catalyses the hydrolysis of organic
P to increase its mobilization. This is accompanied by an enhanced catalytic activity
of plasma membrane H+ATPase (Yan et al. 2002). Also, their activity is greatly
determined by the pH, microorganisms and substrate availability in soil (George
etal. 2005). Soil P is successfully mobilized in the presence of phosphate-solubiliz-
ing bacteria and fungi which do so by any of the above-mentioned chemical changes
(acidication, release of exudates and enzymes) (Jones and Oburger 2011).
Along with increased P mobilization and uptake, plants adapt to P deciency by
conserving internal Pi pools and adopting alternative glycolytic pathways to bypass
the requirement of adenylate and Pi-dependent steps. The plant metabolism under P
deciency is switched from primary to secondary. This involves the enhanced syn-
thesis of various secondary metabolites including, avonoids, indole alkaloids,
polyamines, anthocyanins and phenolics. The enzymes, 3-deoxy-D-arabino-heptu-
losonate-7-phosphate synthase (DAHP), phenylalanine ammonia-lyase, chalcone
synthase, chalcone isomerase, 4-coumarate-CoA, cinnamoyl-CoA and cinnamyl
alcohol dehydrogenase, are shown to be upregulated under P-decient conditions.
Rather than consuming Pi, secondary metabolism functions in recycling large
amounts of Pi from phosphate esters and producing excess of reducing equivalents.
Thus, under P deciency, the acidication of cytosol activates the alternative oxi-
dase (AOX) and secondary metabolite pathway, which together causes the accumu-
lation of reducing equivalents.
To prevent the inhibition of photosynthesis under P deciency, plants undergo
alterations in their thylakoid membrane composition. This reduces the need for
membrane-bound Pi, thus making it available for photosynthesis. The phospholip-
ids in the membrane are replaced by sulpholipids by upregulation of sulpholipid-
synthesizing enzymes, SQD1 and SQD2 (Nakamura etal. 2009; Nakamura 2013;
Lal 2015). This helps to conserve P along with maintaining the membrane
integrity.
Phosphorus limitation induces the synthesis of acid phosphatase enzymes
(APases) in plants (Duff etal. 1994; Baldwin etal. 2001). Root-exuded APases are
7 Phosphorus Nutrition: Plant Growth inResponse toDeciency andExcess
176
implicated in the acquisition of P from soil organic P-esters. In addition to root-
exuded APases, intracellular APases function in the remobilization of P from senes-
cent tissue. This is an efcient mechanism to provide additional P for plant growth
under low P stress. Root-exuded or extracellular APases appear to be much more
stable than intracellular forms (Goldstein etal. 1988; Duff etal. 1989, 1991; Miller
etal. 2001). With increased root uptake and translocation of P to shoot, excess P
tends to accumulate in the older leaves, thereby causing Pi toxicity (Dong etal.
1998; Aung etal. 2006). Increased concentration of P inside older leaves also leads
to more uptake of N which delays the formation of reproductive organs.
7.4 Structural Role ofPhosphorus
In the plant tissues, P exists in either of the two forms: free inorganic orthophos-
phate form (Pi) or as organic phosphate esters. P is compartmentalized within the
plant cells depending on its total concentration. The metabolically active Pi form is
located in the cytoplasm, while excess of P is stored in the vacuole from where it is
supplied to cytoplasm on cellular demand. Hence, the vacuole has a buffering func-
tion and fulls the P demand of the cytoplasm under P deprivation. The esteried P
exists in various forms, nucleic acids, phospholipids, phosphorylated metabolites
and proteins. For most of the crops, the optimum P concentration is <4 mg g1
DW.Of all the pools of P, RNA forms the largest, followed by lipids, esters, DNA
and metabolically active Pi.
7.4.1 Nucleic Acids: Genetic Transfer
Phosphorus is a vital component of nucleic acids (DNA and RNA) that carry the
genetic information from one generation to the next. They form the largest pool of
total organic P in a plant and ranges from 0.3 to 2.0mg P g1 DW in various crops. Of
the nucleic acid pool, 85% is contributed by RNA (majorly rRNA) and the rest by
DNA.There are evidences of increased RNA concentration and hence protein synthe-
sis with the increased supply of P to the plant (Elser etal. 2010; Suzuki etal. 2010).
7.4.2 Sugar Phosphates
Sugar phosphates are the Pi esters formed by the phosphorylation of monosaccha-
ride sugars after their reaction with ATP.These phosphorylated compounds are the
prime intermediates of photosynthesis and in the synthesis and breakdown of starch.
These compounds include phytic acid, glucose-6-phosphate and dihydroxyacetone
phosphate. In addition, they are important constituents of glycolysis and respiratory
reactions.
H. Malhotra et al.
177
7.4.3 Phospholipids: Membrane Component
Phospholipids are an essential component of cell membranes. These consist of lipo-
philic and hydrophilic regions. The electric charge of the hydrophilic region helps
to make interactions between membrane and the charged ions. In P-decient cells,
phospholipids are often replaced by sulpholipids and/or galactolipids (Gaude etal.
2008; Byrne etal. 2011). This replacement has no major effect on proton permeabil-
ity but might increase the leakage of electrolytes responsible for chilling tolerance.
7.5 Growth andDevelopmental Role ofPhosphorus
7.5.1 Seed Germination
Seed P content is an important factor for seed germination and improved seedling
vigour. Seed P is the only P available to plants at the time of germination and helps
in supporting the early seedling growth. Although this P pool is of minor impor-
tance for mature plant, it has a prime role for the nutrition and faster establishment
of young seedlings. After seed germination, plant requirement of P is met from
growing media through roots. Zhu and Smith (2001) found increased soil P uptake
by high P wheat seeds as compared to low P seeds. This was mainly due to the better
development of root system in seeds of high P reserves (Zhu and Smith 2001).
During early days of seedling development, seed phytate P is hydrolysed, and non-
phytate P is then remobilized to support the growth of maize seedling (Nadeem
etal. 2011, 2012). However, in some reports, lower seed P concentration showed no
variation in seedling vigour, plant biomass and yield when compared to high seed P
plants, though some genotypes were found to be sensitive (Rose et al. 2012;
Pariasca-Tanaka etal. 2015). This implies that an optimum seed P concentration is
sufcient for seed germination, and hence, higher P concentration in seeds might be
of no use.
7.5.2 Increasing Root andShoot Strength
Phosphorus is an important element affecting the growth of plants right from the
cellular to whole plant level. These growth parameters include plant height, leaf
area, leaf number and shoot dry biomass. It plays an important role in cell division
and cell enlargement (Assuero etal. 2004). For timely appearance and development
of tillers in crop plants, P is essential (Rodriguez etal. 1998). The P-deprived leaf
cells are found to be smaller than P-sufced cells. Limited cell divisions and
enlargement results in overall reduction in the shoot biomass. However, the reduc-
tion in leaf expansion is not accompanied by a reduction in leaf dry weight. The leaf
7 Phosphorus Nutrition: Plant Growth inResponse toDeciency andExcess
178
dry weight is found to be higher due to the increased starch or celluloses and hemi-
celluloses. In general, the plant growth parameters are found to be more sensitive to
P availability than the photosynthesis (Halsted and Lynch 1996). This is due to the
reduced demand of assimilates by sink. The transport of assimilates from leaves to
roots and stems increases, while their utilization is decreased. This shows that C
utilization rather than C availability is the prime reason of reduced photosynthesis.
Also, no correlation has been reported between leaf photosynthetic rate and growth
response under Pi-limiting conditions. Increase in root biomass is considered as an
important adaptive strategy by plants under P-decient conditions with an aim to
explore for more P.But it is evident only at the beginning of P-limited environment.
Under long-term Pi-decient conditions, the relative growth rate decreases as a
result of reduced ATP concentration in roots (Gniazdowska etal. 1998). However,
genotypes with greater PUE tend to have higher root biomass and lower rates of
respiration than genotypes with lower PUE under P deprivation. This is suggested
as a way to maintain greater root biomass without any increase in overall root C
costs.
7.5.3 Flower andSeed Formation
Phosphorus plays an essential role in improving the reproductive growth of plants,
including ower and seed formation. P contributes to the production of anthocya-
nins in ower stalks, which was found to decrease under P-decient conditions.
This was attributed to decreased activities of phenylalanine ammonia-lyase (PAL)
and chalcone isomerase (CHI) (Chen etal. 2013). Large quantities of P are found in
seeds and fruit where it is believed to be essential for seed formation and develop-
ment. In cereal crops such as rice and wheat, majority of P taken up by plants is
stored in seeds. Thus, an inadequate supply of P can reduce seed size, seed number
and viability. Optimum P concentration in soil increases the seed number, seed dry
matter, seed yield and harvest index. Coating of seeds with 7g per kg of monoso-
dium phosphate enhanced the growth and yield of soybean plants (Soares etal.
2016). Also, Ma etal. (2002) compared the response of white lupin (Lupinus albus)
to various P concentrations in soil. They found that low soil P (5, 10 or 15mg per
kg) had a negative impact on owering time and ower number but no differences
were recorded with P supply higher than 20 mg per kg. Higher P concentration
(25–40mg kg1) succeeded in increasing the number of pods and hence yield in
soybean (Ma etal. 2002). P is a component of phytin, a major storage form of P in
seeds. Various crops differ in their concentration of phytate in seed. About 75% of
the total P in rice, wheat and maize is stored as phytin or closely related compounds,
while inorganic phosphate and cellular-P range from 4–9% to 15–25%, respectively
(White and Veneklaas 2012).
H. Malhotra et al.
179
7.6 Energy Transfer Reactions by Phosphorus
7.6.1 Energy-Rich Phosphates
Phosphorus is a vital component of high-energy bonds, including phosphoanhy-
dride, acyl phosphate and enol phosphate and plays an important role in cellular
metabolism. These high-energy phosphate-containing compounds transfer the
energy to acceptor molecules, thereby serving as sources of crucial cellular pro-
cesses. It plays an important role in photosynthesis right from the seedling growth
till grain formation and maturity.
Phosphoanhydride bond is the bond between two phosphoric acid molecules.
ATP, energy currency of cell, contains three phosphoryl groups (PO32) which are
linked by two high-energy phosphoanhydride bonds and one phosphoester bond
(Fig.7.1). The hydrolysis of ATP releases a large amount of free energy which is
utilized in various cellular processes of the organisms. The hydrolysis of γ, β and
α-phosphate releases an energy of 34.0, 27.2 and 13.8kJmol1, respectively. ATP is
utilized in many cellular processes, including synthesis of macromolecules, mem-
brane phospholipids and nutrient transport against a concentration gradient. Other
similar phosphoanhydride bonds are present in di- and triphosphate-containing
molecules in guanine, cytosine, uracil and thymine nucleosides. GTP and UTP are
important electron donors in gluconeogenesis and saccharide metabolism,
respectively.
The bond formed between phosphate and hydroxyl group attached to double-
bonded C is the enol phosphate bond. During glycolysis, phosphoenol phosphate
is formed from 2-phosphoglycerate. It is the highest energy liberating bond,
releasing energy equivalent to 61kJ mol1. The reaction of phosphate with car-
boxylic acid forms the acyl phosphate bond, liberating an energy of 49kJ mol1
on hydrolysis. A glycolysis intermediate, 1,3-bisphosphoglycerate, is an example
of acyl phosphate bond which transfers its phosphate group to ADP to form ATP
and 3-phosphoglycerate.
34.0 kJ mol
-1
HIGH ENERGY BOND
13.8
kJ mol
-1
27.2
kJ mol
-1
α
β γ
phosphatephosphate phosphate
ADENINE
RIBOSE
P P P
Fig. 7.1 Structure of adenosine triphosphate
7 Phosphorus Nutrition: Plant Growth inResponse toDeciency andExcess
180
7.6.2 Nutrient Transport
Nutrient transport through membranes of root, leaf and other plant organs is an
energy-dependent process which is carried out by adenosine triphosphate (ATP) or
other high-energy phosphorylated compounds. This is due to the impermeable
nature of the plasma membrane acting as a protective layer for cells. Hence, the
transport of nutrients acts against a concentration gradient through specic transport
proteins spanning the plasma membrane. Once inside the cell, nutrient easily moves
to another cell via symplastic or apoplastic pathway. Symplastic to apoplastic move-
ment for long-distance transport of nutrients occurs through epidermal and endoder-
mal cells, respectively. H+-ATPase is a major plasma membrane-bound proton pump
in plants that imports nutrient into the cell along with the export of H+ by utilizing a
three-phosphate-containing molecule, ATP (Sondergaard etal. 2004).
The rst transport barrier for any nutrient is the root. Plant roots contain special-
ized thin protrusions, called root hairs, which increase surface area for the uptake of
nutrients. After entering into the root symplast, nutrients are then transported to
xylem and phloem to ultimately reach leaves, fruits and seeds. High amounts of
plasma membrane H+-ATPase are detected in the epidermal and endodermal root
cells, xylem and phloem cells to facilitate the transport of nutrients by utilizing ATP
and exporting H+ (Parets-Soler etal. 1990; Jahn etal. 1998; Zhang etal. 2004).
7.7 Physiological Role ofPhosphorus
7.7.1 Photosynthesis andCarbon Utilization
The photosynthetic process relies highly on the availability of P.The primary sub-
strates for photosynthesis include Pi, CO2 and H2O that utilizes light energy in the
presence of chlorophyll forming sugars and ATP.This ATP serves as a driving force
to carry out various metabolic reactions within the plant and sugars help in the gen-
eration of other structural and storage components.
During photosynthesis, the initial step is photophosphorylation through which Pi
combines with ADP forming ATP, along with the discharge of a proton gradient
through an ATPase into the chloroplast stroma. The atmospheric CO2 is xed in the
chloroplast via photosynthetic carbon reduction (PCR) cycle, consuming ATP.For
every three molecules of CO2, nine Pi are consumed forming three molecules of O2.
Out of these nine Pi, eight are released into the chloroplast via PCR cycle, while one
is exported from chloroplast to the cytosol in the form of triose phosphate (triose-P)
where it is converted into sucrose, releasing and recycling Pi. This P is now available
to move back into the chloroplast to further form triose-P in chloroplast.
In chloroplast, the inner envelope is impermeable to hydrophilic solutes includ-
ing Pi and other phosphorylated compounds. Hence, the counter-exchange of vari-
ous metabolites such as triose-P, 3-phosphoglyceric acid (3-PGA) and Pi across the
H. Malhotra et al.
181
envelope is carried out via Pi translocators (Heber and Heldt 1981; Flugge and
Heldt 1984). Through these Pi translocators, the photosynthetically xed C is trans-
ported from chloroplast to cytosol in the form of triose-P and in exchange of Pi. Pi
released in the cytosol during sucrose synthesis is shuttled back into the chloroplast
via Pi translocator for the synthesis of ATP.External P levels regulate photosynthe-
sis by altering the function of the Pi translocator. Low P levels in cytosol reduce the
ow of triose-P into the chloroplast, thereby decreasing the Pi release from sucrose
synthesis in chloroplast and reducing ATP production required for PCR cycle. Also,
Pi translocator participates in the transport of ATP and NADPH produced during
photosynthesis to the extra-chloroplastic compartments.
Changes in Pi availability in cytoplasm alters the activation of enzyme (RuBisCO,
sedoheptulose-1,7-bisphosphatase and fructose-1,6-bisphosphatase) and amounts
of intermediates of the PCR cycle. The concentration of phosphorylated metabo-
lites, including RuBP, PGA, triose-P, FBP, F6P, G6P, adenylates, nicotinamide,
nucleotides and Pi, is reduced under P deciency. This happens due to the decreased
C supply as most of the C is diverted for starch production. However, the cytosolic
concentration of P remains stable due to the availability of P in vacuole, and hence
the vacuolar pool is found to lower under P-decient conditions. The requirement of
Pi for activation of RuBisCO has been shown by many authors (Heldt etal. 1978;
Bhagwat 1981). Sufcient concentrations of Pi in chloroplast inhibit the activities
of enzymes fructose-1,6-bisphophatase, sedoheptulose-1,7-bisphosphatase and
ribulose-5-phosphate kinase. Under low cytoplasmic P concentration, photosynthe-
sis is inhibited due to end product inhibition. The total organic and inorganic Pi
concentration remains constant inside the chloroplast. Hence, low Pi concentration
corresponds to high triose-P that limits photosynthesis. These together inactivate
RuBisCO due to the build-up of various metabolites such as ribulose-5-P and
PGA.Also, low Pi concentration limits photosynthesis by decreasing the ATP/ADP
ratio by reducing photophosphorylation that further limits the rate of C xation in
PCR cycle. It has been observed that Pi deciency leads to a decrease in Pi concen-
tration in stroma which limits photophosphorylation, thereby inhibiting the photo-
synthesis (Robinson and Giersch 1987).
Phosphorus is essential in maintaining the photosynthetic machinery that
includes PSI, PSII, LHCP, cyt-f, cyt-b and antenna mobility (Rychter and Rao
2005). As mentioned above, P is an important constituent of the thylakoid mem-
brane. Phosphorylation of apoproteins of antenna in thylakoid membrane is an
important step in photosynthesis. Under P deciency, the antenna becomes dephos-
phorylated due to activation of a phosphatase and a large proton gradient, thereby
reducing the mobility of antenna (Horton 1989). The long-term deciency of P
causes the photoinhibition of PSII.The rate of electron transport increases across
PSII under P-decient conditions, and the unused electrons are diverted to photores-
piration, thereby reducing CO2 xation. The increase in photorespiration plays an
important role in increasing the availability of Pi for photosynthesis.
Pi plays an important role in starch biosynthesis inside the chloroplasts. The
level of Pi controls the distribution of newly xed C between starch synthesis in
chloroplasts and sucrose synthesis in cytoplasm. Limited Pi supply in chloroplasts
7 Phosphorus Nutrition: Plant Growth inResponse toDeciency andExcess
182
shifts the ow of C towards starch. This is achieved through the stimulation of key
enzyme in starch biosynthesis, ADP-glucose pyrophosphorylase under low Pi and
high triose-P levels (Nielsen etal. 1998). Likewise, increased Pi concentration in
stroma induces the breakdown of starch. Starch degrades to form glucose-1-phos-
phate which is further converted to triose-P or PGA through oxidative pentose phos-
phate pathway or phosphofructokinase, respectively. This has been conrmed by
various kinetic studies (Pettersson and Ryde-Pettersson 1989; Preiss 1994).
The biosynthesis of sucrose is a Pi-regenerating step, which occurs in cytoplasm
from triose-P that is exported from the chloroplast. The cytosolic triose-P is rst
converted to hexose-P and then to sucrose. FBPase, sucrose-phosphate synthase
(SPS) and UDP-glucose pyrophosphorylase are the key enzymes regulating sucrose
biosynthesis in cytoplasm (Huber and Huber 1992, 1996; Stitt etal. 1983). Pi is a
negative regulator of these enzymes but a positive regulator of fructose-6-phos-
phate-2-kinase. Four molecules of triose-P are needed to form one molecule of
sucrose, and four Pi are liberated in this process. The release of Pi in this process
maintains the import of triose-P in cytoplasm through Pi translocator via the counter
exchange of Pi. Under conditions of low sucrose synthesis, triose-P remains in the
chloroplast to support starch synthesis. Low sink strength lowers sucrose synthesis
and hence increases the accumulation of triose-P in chloroplast to synthesize starch,
thereby restricting photosynthesis. For each molecule of sucrose formed, four Pi
molecules move into the chloroplast. Defective sucrose synthesizing machinery will
lead to decreased formation and hence transport of triose-P from chloroplast. The
accumulated photosynthates in chloroplast induce the conversion of fructose-6-P
(in PCR cycle) to starch. Hence, Pi levels regulate the distribution of C between
starch and sucrose synthesis. Also, it regulates the partitioning of photosynthates
between various plant tissues. Under P deciency, the low sink demand limits the
photosynthesis. Pi is released from sucrose synthesis with the help of phosphatase
that makes Pi available for entry into the chloroplast to form triose-P, and little or
none will be available for storage as starch. During low sink demand, excess triose-
P is stored as starch, thus reducing the rate of photosynthesis.
Phosphorus plays a vital role in the respiratory processes of the plant. Under
P-decient conditions, roots tend to respire via an alternative non-phosphorylating
pathway. This cyanide-resistant respiratory pathway results in reduced production
of ATP and ADP which affects the energy-dependent processes of the plant (Rychter
and Mikulska 1990; Rychter et al. 1992). This is achieved by skipping ATP-
dependent steps in glycolysis and activating PPi-dependent phosphofructokinase,
non-phosphorylating NADP-dependent glyceraldehyde-3-P dehydrogenase, PEPC,
NAD malic enzyme and MDH. This successfully bypasses the requirement of
enzymes, viz. ATP-dependent phosphofructokinase (PFK), Pi-dependent NAD-
dependent glyceraldehyde-3-P dehydrogenase, phosphoglycerate kinase and pyru-
vate kinase, to conserve ATP pools. The resulting increase in ATP/ADP ratio limits
mitochondrial respiration under P limitation. Owing to this, alternative non-phos-
phorylative respiratory pathways become active that includes rotenone-insensitive
H. Malhotra et al.
183
NADH dehydrogenase and cyanide-resistant alternative oxidase (AOX). This leads
to an increase in the ratio of NADH/NAD.The levels of respiratory intermediates,
viz. hexose phosphates and 3-phosphoglyceric acid (PGA), reduce during P de-
ciency. The activities of several glycolytic enzymes PFK, NAD-G3P-DH, 3-PGA
kinase and PK depend on the concentration of adenylate and Pi. The activities of
PFP and non-phosphorylating NAD-G3P-DH, PEP carboxylase and PEP phospha-
tase have been found to increase under P-deprived conditions.
7.7.2 Nitrogen Fixation
Legumes are a vital source of protein in human diet. They also play an essential role
in maintaining soil fertility. The fundamental phenomenon which makes legumes
important is their ability to carry out “atmospheric nitrogen xation”. The conver-
sion of non-useable form of nitrogen (N2) to useable form (NH3) is done by
Rhizobium bacteria, which resides in the root nodules of leguminous plants. These
bacteria need energy to grow and perform their basic functions. The energy is sup-
plied in the form of P rich molecule, ATP.This energy-rich molecule gets converted
into ADP with simultaneous release of inorganic phosphate providing the energy. At
least 16 molecules of ATP are hydrolysed for each molecule of N2 reduced.
NeHATP HO NH HADP Pi
2232
88 16 16
21
6++ ++↔+
++
−+
In addition to acting as a source of energy, P helps in increasing the density of
rhizobial bacteria in soil. For root nodule formation, root hairs must get infected by
these bacteria. The site where these bacteria infect root hair becomes the site of
nitrogen xation. As discussed above, P is one of the essential nutrients for root
growth promotion. P deciency not only affects plant growth but also highly impacts
the rate of nitrogen xation by causing a reduction of root nodules (Bonetti etal.
1984). In pea plants, it has been observed that an increase in P supply increases the
biomass of root nodules (Jakobsen 1985).
7.8 Crosstalk ofPhosphorus withOther Nutrients
The presence of P affects the availability of one or more of other nutrients in soil.
Interaction of P with both macro- and micronutrients is well studied, and it can be
either synergistic or antagonistic. Soil analysis before sowing helps in the detection
of limiting factors in soil, and giving optimum P levels in early stage can help in
enhanced availability of other nutrients, thereby increasing crop yield.
7 Phosphorus Nutrition: Plant Growth inResponse toDeciency andExcess
184
7.8.1 Macronutrients
Nitrogen (N) plays a vital role in plant metabolism and growth. The interaction
between P and N has been found to be synergistic. The ammonical-N fertilizer
increases the P availability to plant. P is one of the essential nutrients that help in
nitrogen xation, along with efcient use of N by plants. The combined application
of N and P increased the sorghum yield to 93bu/ac, while N alone resulted in a yield
of 71bu/ac (71 bushel/acre = 71×67.25=4774.75Kg/ha) (Schlegel and Bond 2017).
Phosphorus and K are required for proper growth of plant under control and
stressed conditions. For better corn yield, presence of both P and K is found to be
must. They together enhanced the grain yield by 64bu/ac as compared to 38–41bu/
ac when each was applied alone (Usherwood and Segars 2001). Proper ratio of both
P and K is essential for obtaining high yield in corn.
An antagonistic interaction exits between sulphur (S) and P in moong seeds. It
has been shown that combined application of S and P decreased the grain yield and
quality. In a greenhouse experiment, application of 40ppm S depressed the P con-
tent of vegetative portion by 18% and grains of moong by 12% (Aulakh and Pasricha
1977). Magnesium (Mg) helps in root formation, chlorophyll and photosynthesis.
One of the most important functions regulated by Mg is activation of kinase enzyme
and transfer of phosphate group.
7.8.2 Micronutrients
The interaction of P with micronutrients has been reported in a wide variety of
crops. Due to better understanding of functions of micronutrients in crop plants,
signicance of micronutrients in crop production has increased. One of the main
reasons for this is the availability of better analytical techniques. Micronutrients
play an important role in uptake and utilization of essential plant nutrients.
The interaction between P and boron (B) has been found to be synergistic in
maize grown in rened sand (Chatterjee etal. 1990). In lettuce plants, increase in
1000 seed weight (from 2.06 to 3.01g) was observed due to interaction between B
and P (Chowdhury etal. 2015). On the other hand, when different levels of copper
(Cu) were sprayed on leaves, a positive interaction was found between P and Cu in
lettuce (De Iorio etal. 1996). Iron (Fe) is found in abundance in the earth’s crust, but
still it is often a limiting resource for growth. This is mainly due to its low avail-
ability. Fe deciency can be diagnosed as interveinal chlorotic symptoms in young
leaves. Fe and P show antagonistic interaction in plant nutrition. It has been noticed
that P also affects the genes responsible for iron regulation (Zheng etal. 2009).
Optimal levels of molybdenum (Mo) improve utilization as well as increase P
uptake. In Brassica napus positive interaction between Mo and P has been detected.
It has been found that both Mo and P promote plant growth when applied together.
This is because Mo and P have benecial effects on each other’s’ absorption and
H. Malhotra et al.
185
translocation (Liu etal. 2010b). P and zinc (Zn) show antagonistic interactions in
soil or inside the plant. In corn seedlings grown in sandy soil, absence of a signi-
cant Zn-P interaction has been seen, but high P supply reduces Zn shoot content
(Drissi etal. 2015). At gene level, high levels of P downregulates high-afnity Zn
transporter, thus adversely affecting Zn mobilization within the oat seedlings
(Huang etal. 2000).
7.9 Conclusions
Yield losses due to global climatic change and mineral nutrient deciency are the
major concerns for researchers worldwide. The role of P in essential metabolic pro-
cesses including growth, photosynthesis, respiration and nitrogen xation has been
well documented in various studies. Limited availability of P in soil reduces the
uptake by plant and causes plant P deciency, thus affecting its overall growth and
development. To tackle P deciency, plants have developed numerous morphologi-
cal, anatomical, physiological and metabolic processes. However, to develop plants
with better adaptability to P stress and enhanced P use efciency, collaborations
between physiologists, geneticists and breeders are urgently required. Future
research trials should focus on improving the understanding of P uptake, utilization
and transport mechanisms under low P environment. Further, extensive research is
required in eld of root biology, along with identifying and enhancing gene expres-
sion for improved P acquisition and use efciencies.
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... Moreover, it also plays a role on the modulation of the photosynthetic response, and the stomatal conductance as well as P concentrations inside the stroma interact with the activity of enzymes like RuBisCO and fructose-1,6-bisphosphatase and Calvin's cycle efficiency (Kour et al., 2021). As an example, lower internal concentrations of P, lead to the decline of ribulose 1,5-bisphosphate (RuBP), glyceraldehyde 3-phosphate (triose-P), 3phosphoglyceric acid (PGA), glucose-6-phosphate (G6P), and nucleotides which in turn can lead to a decrease in the carbon dioxide uptake and later to a reduction in stomatal conductance (Malhotra et al., 2018). With such polyvalent implications to the working systems of several forms of life, P also has an important role in seed formation, root elongation, and resistance to biotic and abiotic stresses (Kour et al., 2021) and thus, plant deficiencies in such element may result in substantial crops' productivity loss. ...
... With such polyvalent implications to the working systems of several forms of life, P also has an important role in seed formation, root elongation, and resistance to biotic and abiotic stresses (Kour et al., 2021) and thus, plant deficiencies in such element may result in substantial crops' productivity loss. For instance, Malhotra et al. (2018) has shown that P-supplemented plants presented a higher degree of development of younger leaves as well as a greater root development in opposition to Pstarved plants, which showed a limited number of cell divisions and in a reduction of the shoot biomass at the end of the experiment. Nonetheless, under P starvation, plants may activate a secondary metabolism that itself involves the increment in root biomass. ...
... This strategy is considered effective to explore for more P in P-deficient conditions, however, it is a short-term compensatory behavior displayed as an emergency. On the long-term, due to the continuous consumption of ATP and its consequential decrease, the growth rate of roots starts to be reduced (Malhotra et al., 2018). This element is so fundamental, that toxicity to plants associated to P is rarely reported (Malhotra et al., 2018). ...
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... Phosphorus is crucial in various plant metabolic processes including energy generation and transformation during developmental processes such as germination, flowering, root expansion, photosynthetic activities, nitrogen fixation, carbohydrate metabolism, enzymatic activities etc. In addition, it is integral part of various structural and functional macromolecules such as adenosine triphosphate, proteins, nucleic acids, lipoproteins etc. [8]. In soil, phosphorous is present in two basic chemical forms i.e., organic (P o ) and inorganic forms (Pi). ...
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... Fosfor dibutuhkan tanaman dalam jumlah banyak setelah N dan merupakan unsur hara makro primer. Fosfat merupakan bahan penyusun dari adenosin ditriphosphate (ADP dan ATP) sebagai proses pertumbuhan dan perkembangan tanaman (Malhotra et al., 2018). Pemenuhan hara P berperan dalam pembentukan organ vegetatif dan reproduktif tanaman. ...
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... Application of phosphorus aids in seed germination, root development, flower initiation, fruit and seed development. To this end, phosphorus is needed at all developmental stages, from germination till maturity (Malhotra et al. 2018). However, today there is a scanty information available pertaining to optimum dose of nitrogen and phosphorus fertilizers. ...
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... Tese nutrients are key factors to overcome obstacles and promote the plant growth and yield [55,56]. Furthermore, P fertilization helped pineapples grow well and improve their height and fruit diameter ( Table 5) because P supports root development, fowering, and maturity of fruit [48,57]. ...
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... This practically-significant enrichment of major elements by HF showcases that plants accessed and transported significant amounts of the applied fertilizer to the needles. These results confirm the validity of fertilization treatment and can explain the enhanced growth and productivity by these macronutrients that drive plant growth and development (Guo et al. 2015(Guo et al. , 2016Malhotra et al. 2018;Hauer-Jákli and Tränkner 2019;Johnson et al. 2022). ...
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... The present results are in concurrence with the findings that soil available phosphorus (AP), N, and sulphur (S), have vital roles in several developmental and growth processes, viz. seed germination, seedling establishment, formation of chlorophyll and protein contents, grain yield, and whole plant development of winter barley and wheat cereals (Malhotra et al. 2018;Hlisnikovský et al. 2019). ...
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Understanding the changes of soil physicochemical and enzymatic parameters at different days after sowing (DAS) of crops is essential to maintain the soil nutrient availability and quality. This study was conducted at ICAR-NBPGR, Bhowali, Nainital, India, aimed to understand the changes in soil physicochemical and enzymatic parameters at different days after sowing (DAS) of wheat and barley crops. Soil samples were collected from the experimental plots (5 m × 5 m) of barley and wheat at different DAS and depths. The soil physicochemical and enzymatic parameters were determined at different DAS of barley and wheat. The results clearly indicated that the physicochemical attributes such as soil moisture content (SMC), acidity and basicity of soil (pH), electrical conductivity (EC), available phosphorus (AP), sulphur content (S), carbon to nitrogen ratio (C/N ratio), ammonium (NH4+-N) and nitrate (NO3−-N) were significantly different (p < 0.05) at 60 and 120 DAS while extractable sodium (Na), extractable potassium (K), and available phosphorus (AP) at 170 DAS for both the crops. Also, among the enzymatic attributes aryl sulphatase (AS), dehydrogenase (DHA), β-glucosidase (BGlu) and acid phosphatase (APase), urease (URE) were significantly different at 60, 120 and 170 DAS for both the crops. The PCA results showed that the DAS have a close relationship with AP, S, NH4+-N, NO3−-N, and soil enzyme URE. These findings will further help to strategize soil management practices involved in its sustainability without compromising soil health and food production.
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Phosphorus (P) induced zinc (Zn) deficiency has emerged as an important nutritional constraint for field crop production, and thus, it is essential to optimize P and Zn levels for balanced fertilizer applications. To study the effects of soil applied P and Zn fertilizers on Zn–P interactions and productivity of wheat crop, the experiment was conducted at Punjab Agricultural University, Ludhiana, India, during 2017–2018 and 2018–2019. The experiment, comprised two types of soils viz., low and high in P content, with four Zn levels (0, 2.5, 5, and 10 mg kg⁻¹) and five P levels (0, 5, 10, 20, and 30 mg kg⁻¹), conducted in complete randomized design with three replications. The results indicated that under low P soil, wheat yield, Zn and P uptake increased with Zn addition up to 5 mg kg⁻¹ and P addition up to 10 mg kg⁻¹. However, in high P soil, wheat yield, Zn and P uptake increased with Zn addition of 10 mg kg⁻¹ and with no P addition. Among different treatments, P10Zn5 gave the highest wheat yield, content, and uptake of Zn and P in low P soil. Similarly, in high P soil, treatment P0Zn10 reported the highest wheat yield, Zn and P uptake by wheat. The levels of Zn and P viz., P10Zn5 and P0Zn10 showed synergistic effects in terms of wheat yield, content, and uptake of Zn and P, respectively. Thus, the study is beneficial to optimize levels of P and Zn fertilization under low and high P soils.
Chapter
Adequate nutrition for plants involves 14 mineral elements. The elements that are required in larger amounts i.e., macronutrients include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S). In addition to these plants require some trace elements that are required in smaller amounts. These micronutrients include iron (Fe), Zinc (Zn), Boron (B), Copper (Cu), Molybdenum (Mo), Manganese (Mn), Nickel (Ni), Chlorine (Cl). Both macro and micronutrients play vital roles in plant growth, development and food grain production. These also play vital roles in enhancing tolerance abiotic/biotic stress. When present in adequate levels these mineral nutrients promote healthy growth in plants while their scarcity promotes abnormal growth in plants. In addition to this when present in excess concentrations these can prove toxic to the plant health. Plant nutrients are essential for providing healthy food to the ever-increasing population. Declining soil fertility poses a threat to crop yield especially in the developing nations. Plant nutrition is critical for commercial crop production. Nutritional programs frequently employ commercially produced inorganic or organic fertilizers delivered to the soil by broadcast, irrigation, or foliar sprays. The soil nutrient and plant nourishment program's purpose is to address the factors influencing crop nutrient utilization sustainably in order to improve plant performance. As a consequence, the goal is to have most of each important nutrient accessible in plant tissue to support the metabolic functions of the plant.
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Accurate assessments of soil properties are required to improve fertilizer management practices for crop production. Conventional chemical analysis in the laboratory is costly and time-consuming. Soil color is related to different soil compositions, while soil magnetic susceptibility (MS) has been found to reflect the abundance of magnetic minerals relevant to soil properties. Improving proximal sensing techniques for the analysis of soil color and MS provides opportunities for affordable and rapid assessments of soil properties. The aim of this study was to evaluate the potential use of soil color parameters and MS values to predict soil properties using stepwise multiple linear regression (SMLR), random forest (RF), and nonlinear regression approaches in lowland and upland fields in the central highlands of Madagascar. The target properties included the contents of soil organic carbon (SOC), total nitrogen (TN), oxalate-extractable phosphorus and iron (Feox), and the soil texture. The model prediction accuracy was assessed using the coefficient of determination (R²), root-mean-square error (RMSE), and the ratio of performance to interquartile distance (RPIQ). The use of soil color parameters yielded an acceptable prediction accuracy of the Feox content (loge Feox) for all rice fields (R² = 0.54, RMSE = 0.55, RPIQ = 1.70) using the RF algorithm, while the SMLR approach gave the most accurate prediction for upland fields with acceptable reliabilities for SOC, Feox, and clay and sand content prediction, with R² ranging from 0.43 to 0.67 and RPIQ from 1.63 to 1.77. In lowland fields, TN content was predicted with acceptable accuracy (R² = 0.34, RMSE = 0.49, RPIQ = 1.71) using SMLR with the color parameter. The combination of the soil color parameters with the MS value as predictor variables increased SOC prediction for lowland fields using the RF approach (R² = 0.57, RMSE = 6.37, RPIQ = 1.96). Use of the soil color and MS parameters was revealed to be a promising way to simplify the assessment of soil properties in upland and lowland ecosystems by using RF and SMLR approaches. A combined use of the soil color and MS parameters improved the prediction accuracy for the SOC content.
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Nitrogen and phosphorous are critical determinants of plant growth and productivity, and both plant growth and root morphology are important parameters for evaluating the effects of supplied nutrients. Previous work has shown that the growth of Acer mono seedlings is retarded under nursery conditions; we applied different levels of N (0, 5, 10, and 15 g plant⁻¹) and P (0, 4, 6 and 8 g plant⁻¹) fertilizer to investigate the effects of fertilization on the growth and root morphology of four-year-old seedlings in the field. Our results indicated that both N and P application significantly affected plant height, root collar diameter, chlorophyll content, and root morphology. Among the nutrient levels, 10 g N and 8 g P were found to yield maximum growth, and the maximum values of plant height, root collar diameter, chlorophyll content, and root morphology were obtained when 10 g N and 8 g P were used together. Therefore, the present study demonstrates that optimum levels of N and P can be used to improve seedling health and growth during the nursery period.
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High-molecular-weight secretory proteins and low-molecular-weight exudates (carboxylates, phenols, free amino acids and sugars) released from roots of soybean (Glycine max(L.) Merr.) differentially influence genotypic phosphorus (P) acquisition efficiency (PAE). We hypothesised that genotypes with higher root exudation potential would exhibit enhanced P acquisition, and screened 116 diverse soybean genotypes by labelling shoots with 14CO2 . A root 5 exudation index (REI) derived from total 14C in the root exudate at sufficient (250mM) and low (4mM) P levels was used to classify genotypes for PAE. Genotypes with REI>2.25 exhibited significantly higher exudation at low than at sufficient P, which in turn increased PAE. Under low P availability, efficient genotypes exude a greater quantity of organic compounds into the rhizosphere. This increases P availability to meet the crop requirement, enabling the crop to produce consistent biomass and seed yield with reduced fertiliser addition. Such maintenance of growth and yield potential by mining the 10 inherent soil P is a favourable trait in genotypes, reducing dependence on P fertilisers. Measuring REI at seedling stage to select P-efficient plants accelerates the screening process by accommodating large numbers of genotypes.
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Carboxylate efflux in response to low-phosphorus (P) is one of the plant’s adaptive strategies. Genotypic variation between the type and amount of root-exuded carboxylates determines the differential P acquisition efficiency (PAE) in soybean (Glycine max (L.) Merrill.). We compared direct (using HPLC) and indirect methods (total carbon exudation, and use of bromocresol purple dye) for quantifying root acidification. Total carbon exudation did not correlate to carboxylate efflux, whereas a significant linear relationship between exudate pH and carboxylate concentration suggested that measure of root acidification might predict the genotypic potential for low-P induced carboxylate efflux.
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Phosphorus is one of the most important nutrients for soybeans, but it presents a complex dynamic in the soil and can become unavailable. The split and localized application of this nutrient can be an effective approach to increase its availability. The aim of this study was to evaluate the effect of a split phosphorus dose applied to the soil and the seed coating with monobasic sodium phosphate on nodulation, growth and yield components of soybean cultivar BRS Valiosa RR. The experiment was conducted in a greenhouse in a completely randomized design in a 2×5×3 factorial arrangement, i.e., coating or not the seeds; five doses of phosphorus applied to the soil; and three times of splitting phosphate fertilizer. Phosphorus content in the index leaf (IL), dry matter of shoots, roots and nodules, yield components, and plant height were evaluated. There was an increase in nodulation and growth of plants with increased levels of phosphorus applied to the soil. In smaller doses, the seed coating and the splitting of phosphorus fertilizer increased nodulation, growth and yield components of plants. Thus, the splitting of the phosphorus dose, combined with seed coating, is indicated for increasing the yield components of soybean plants. © 2016, Associacao Brasileira de Tecnologia de Sementes. All rights reserved.
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The roots of most plants are colonized by symbiotic fungi to form mycorrhiza, which play a critical role in the capture of nutrients from the soil and therefore in plant nutrition. Mycorrhizal Symbiosis is recognized as the definitive work in this area. Since the last edition was published there have been major advances in the field, particularly in the area of molecular biology, and the new edition has been fully revised and updated to incorporate these exciting new developments. . Over 50% new material . Includes expanded color plate section . Covers all aspects of mycorrhiza . Presents new taxonomy . Discusses the impact of proteomics and genomics on research in this area.
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An understanding of the mineral nutrition of plants is of fundamental importance in both basic and applied plant sciences. The Second Edition of this book retains the aim of the first in presenting the principles of mineral nutrition in the light of current advances. This volume retains the structure of the first edition, being divided into two parts: Nutritional Physiology and Soil-Plant Relationships. In Part I, more emphasis has been placed on root-shoot interactions, stress physiology, water relations, and functions of micronutrients. In view of the worldwide increasing interest in plant-soil interactions, Part II has been considerably altered and extended, particularly on the effects of external and interal factors on root growth and chapter 15 on the root-soil interface. The second edition will be invaluable to both advanced students and researchers.
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Long-term research shows that phosphorus (P) and nitrogen (N) fertilizer must be applied to optimize production of irrigated grain sorghum in western Kansas. In 2015, N applied alone increased yields 66 bu/a, whereas N and P applied together increased yields up to 92 bu/a. Averaged across the past 10 years, N and P fertilization increased sorghum yields up to 76 bu/a. Application of 40 lb/a N (with P) was sufficient to produce 88% of maximum yield in 2015 which is slightly above the 10-year average. Application of potassium (K) has had no effect on sorghum yield throughout the study period. Average grain N content reached a maximum of ~0.7 lb/bu while grain P content reached a maximum of 0.15 lb/bu (0.34 lb P2O5/bu) and grain K content reached a maximum of 0.19 lb/bu (0.23 lb K2O/bu).