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Fulvic Acid (FA) for Enhanced Nutrient Uptake and Growth: Insights from Biochemical and Genomic Studies

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Potassium (K), one of the essential elements required for plant growth and development, determines leaf quality in tobacco (Nicotiana tabacum L.). Potassium (K) levels are relatively high in black soils (vertisols), but K uptake is severely hindered by the presence of remarkably high levels of calcium and magnesium. Our major objective was to enhance potassium uptake in black soils, which cover the major tobacco growing regions of Andhra Pradesh, India. Among several agronomic inputs such as soil amendments, fertilizer application, and plant growth regulators, we found that foliar application of fulvic acid (FA), one of the most bioactive humate molecules, enhanced K levels in leaves. Using next-generation sequencing (NGS), we identified changes in expression levels of a number of genes related to metabolic pathways implicated in plant growth and nutrient uptake upon FA application. Interestingly, starch levels in leaves were reduced concomitant with an increase in K attributable to FA application. We attempt to provide plausible reasons for these observed FA-induced changes. Our results suggested that FA acts in a manner similar to the plant hormone auxin in tobacco, influencing expression of key genes encoding transporters and enzymes involved in K uptake and starch metabolism. While fulvic acid has beneficial effects on plant growth, its mechanism of action is still unclear.
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Fulvic Acid (FA) for Enhanced Nutrient
Uptake and Growth: Insights from
Biochemical and Genomic Studies
Priya B. N. V.a, Mahavishnan K.a, Gurumurthy D. S.a, Bindumadhava
H.a, Ambika P. Upadhyaya & Navin K. Sharmaa
a ITC – Life Sciences & Technology Centre, ITC Limited, Bangalore,
Published online: 15 Oct 2014.
To cite this article: Priya B. N. V., Mahavishnan K., Gurumurthy D. S., Bindumadhava H., Ambika
P. Upadhyay & Navin K. Sharma (2014) Fulvic Acid (FA) for Enhanced Nutrient Uptake and Growth:
Insights from Biochemical and Genomic Studies, Journal of Crop Improvement, 28:6, 740-757, DOI:
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Journal of Crop Improvement, 28:740–757, 2014
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-7528 print/1542-7536 online
DOI: 10.1080/15427528.2014.923084
Fulvic Acid (FA) for Enhanced Nutrient Uptake
and Growth: Insights from Biochemical and
Genomic Studies
ITC – Life Sciences & Technology Centre, ITC Limited, Bangalore, India
Potassium (K), one of the essential elements required for plant
growth and development, determines leaf quality in tobacco
(Nicotiana tabacum L.). Potassium (K) levels are relatively high in
black soils (vertisols), but K uptake is severely hindered by the pres-
ence of remarkably high levels of calcium and magnesium. Our
major objective was to enhance potassium uptake in black soils,
which cover the major tobacco growing regions of Andhra Pradesh,
India. Among several agronomic inputs such as soil amendments,
fertilizer application, and plant growth regulators, we found that
foliar application of fulvic acid (FA), one of the most bioactive
humate molecules, enhanced K levels in leaves. Using next-gen-
eration sequencing (NGS), we identified changes in expression
levels of a number of genes related to metabolic pathways impli-
cated in plant growth and nutrient uptake upon FA application.
Interestingly, starch levels in leaves were reduced concomitant with
an increase in K attributable to FA application. We attempt to
provide plausible reasons for these observed FA-induced changes.
Our results suggested that FA acts in a manner similar to the
plant hormone auxin in tobacco, influencing expression of key
genes encoding transporters and enzymes involved in K uptake and
Received 26 February 2014; accepted 7 May 2014.
Current affiliation for Navin K. Sharma: The World Agroforestry Centre, NASC complex,
PUSA, New Delhi, India.
Address correspondence to Bindumadhava H., AVRDC – The World Vegetable Center,
South Asia Regional Office, ICRISAT campus, Patancheru 502 324, Hyderabad, Andhra
Pradesh, India. E-mail:
Color versions of one or more of the figures in the article can be found online at www.
Downloaded by [Bindumadhava H] at 19:49 20 October 2014
Fulvic Acid and Nutrient Uptake 741
starch metabolism. While fulvic acid has beneficial effects on plant
growth, its mechanism of action is still unclear.
KEYWORDS FCV tobacco, humus, NGS, potassium, starch
ABBREVIATIONS. (C and N) carbon and nitrogen; (FCV) flue-cured Virginia;
(FA) fulvic acid; (HA) humic acid; (NAA) naphthylacetic acid; (NGS) next-
generation sequencing; (PCR) polymerase chain reaction; (K) potassium;
(QC) quality control; (SBCS) southern black cotton soil.
Potassium is the lone essential plant nutrient that is not a constituent of
any plant part (Marschner 1995; Cakmak 2005). Potassium acts as a cat-
alyst for many of the necessary enzymatic processes in the plant and is
also involved in osmoregulation, i.e., regulation of water transport in the
xylem and opening and closing of the stomata (Raschke 1975). Potassium
exists in several forms in the soil, including mineral K (90% to 98% of total),
non-exchangeable K, exchangeable K, and dissolved or solution K (K ions)
(Tisdale et al. 1985). Even though K is abundant in many soils, the bulk of
it is in the form unavailable to plants. Potassium uptake by plants is also
influenced by type of soil. Calcareous soils tend to have high concentra-
tions of calcium ions (Ca) that dominate clay surfaces and limit K sorption.
High concentrations of Ca and magnesium (Mg) tend to limit K uptake by
competing for binding sites on root surfaces (Havlinet al.1999). Enhancing
potassium content in plants is key to improving yield and quality in several
crops (Geraldson 1985; Kanai et al. 2007;Lesteretal.2010). Potassium fertil-
izers are either applied directly to the soil or in the form of foliar spray. Foliar
application has been consistently shown to improve fruit quality attributes
in cucumber, mango, and muskmelon; soil application had little or no effect
(Tisdale et al. 1985; Brady and Weil 1999). Potassium enhanced color and
glossiness of chili fruits (Prabhavathi et al. 2008). Earlier studies have shown
that foliar application of potassium fertilizers, humic acids, and their deriva-
tives had improved K uptake in several crops (Wuzhong 2002; Demiral and
Koseoglu 2005;Lesteretal.2005,2006; Jifon and Lester 2009).
Many beneficial effects are attributed to foliar application of fulvic acid
(FA), including stimulation of plant metabolism, increased enzyme activity
(transaminase, invertase), increased bioavailability and uptake of nutrients
(Pascual et al. 1999), and increased crop growth and yield (Mylonas and Mc
Cants 1980; Xudan 1986). Fulvic acid has maximum influence on chemical
reactions because of the presence of more electronegative oxygen atoms
than any other humate molecules, which enhances membrane permeability
(Pascual et al. 1999).
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742 P. B. N. V . et al .
Potassium is considered one among organic and inorganic compounds
that influence the quality of tobacco; potassium is considered the element
of quality (Srinivas and Seshaiah 1993). Cured leaf color, grade, body, tex-
ture, fire-holding capacity, and aroma are significantly influenced by K
concentration (Krishnamurthy and Ramakrishnayya 1997;Juanetal.2005;
Mahavishnan, Priya, and Upadhyay, personal communication, July 2011).
In India, flue-cured Virginia (FCV) tobacco is grown mainly in the states of
Andhra Pradesh (southern black cotton soils [SBCS]) of Prakasam district)
and Karnataka.
In a previous study, we established positive effect of FA on carbon
translocation (Priya et al. 2011). In the same study, we also noted an increase
in K content of leaves. K-deficient plants had several-fold increase in sucrose
concentration and marked reduction in root growth compared with control
plants (Cakmak et al. 1994; Huber 1984; Marschner et al. 1996). The accu-
mulation of sugars and apparent increase in partitioning of fixed carbon
into starch was associated with declined sucrose phosphate synthase activ-
ity attributable to nutrient deficiency (Rufty and Huber 1983). Hence, along
with K uptake, we determined the starch content in leaf and explained
its association with leaf K. In the present study, we explore FA-associated
physiological, biochemical, and molecular changes that possibly enhance
K uptake and decrease starch content in FCV tobacco grown in the SBCS
Experimental Design
The SBCS soils are clay-to-clay loams throughout the profile, slightly alkaline
in reaction (pH 7.5 to 8.8). The experiments were laid out in a random-
ized complete-block design (RCBD) for first growing season (2007–2008).
However growing seasons of 2008–09 and 2009–10 were on-farm large-scale
trials. Sixty-day-old seedlings of variety CY 135 were planted during winter
(Oct–Nov) with a standard spacing of 65 cm x 65 cm. Recommended fertiliz-
ers dose of 50:50:50 (N:P2O5:K2O) were applied 20 days before transplanting.
Need-based prophylactic measures were taken to control pest and diseases.
Commercial grade FA (81% pure: MW-308.24) was obtained from East Coast
Seaweed Inc., India, and a concentration of 2mM was applied twice, i.e.,
45 and 60 days after planting (DAP). The first priming was done at 60 DAP
and subsequent primings were carried out at 7- to 10-day intervals. Leaves
from each harvest were cured, stripped, conditioned, and graded separately.
Analysis of variance (ANOVA) of phenotypic data was carried out using the
general linear model (GLM) of SAS software (version 9.3, 2011) (http://www.
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Fulvic Acid and Nutrient Uptake 743
Cured leaf samples were drawn based on plant positions from the bottom
of the plant (P, X, L, and T; see Figure S-1) as per the recommendation of
Central Tobacco Research Institute, India (CTRI). Priming (P) contains leaves
1–3 from the lower-most position, cutter (X) has leaves 4–9, leaf (L) position
has leaves from 10-15, and final top (T) position consists of leaves from
16–21 (Figure S-1). Laminas of the cured leaves were separated and ground
to a fine powder. Leaves from all the positions were analyzed for K and
starch content. Green leaf samples from only the “X” position were collected
7 days after first foliar application, snap-frozen in liquid nitrogen and used
for RNA extraction.
Potassium and Starch Analysis
K content of the leaf samples was analyzed using Atomic Absorption
Spectrophotometer (AAS) (Shimadzu, AA6300) in a measured quantity
(100mg) of sample wet-digested with Di-acid mix (nitric acid: perchloric acid,
9:4 ratio) (Jackson 1967). Estimation of starch was done as per McCready
et al. (1950) with slight modifications. Leaf tissue (200mg) was extracted
thrice with 10ml of sodium chloride-saturated methanol, followed by diges-
tion with 5ml of 6M perchloric acid for 10 min. Contents were filtered
(through Whatman filter paper grade 1) and filtrate was made up to 100ml
with distilled water. Ten ml of sample was mixed with 2.5ml iodine reagent
and final volume made up to 25ml with distilled water. Absorbance of sam-
ple was recorded at 600 nm using spectrophotometer (Agilent, 8453). Starch
estimation was done using a standard curve.
Potassium Uptake Assay
Two month-old tobacco seedlings were placed in Hoagland solution with
and without FA (2mM). Experiment consisted of 3 sets, i.e., absolute control
(100ml Hoagland solution), FA-Solution (0.0625g FA in 100ml of Hoagland
solution), and FA-Spray (100 ml Hoagland solution in a jar +foliar spray
of FA). Fulvic acid solution for foliar application was prepared by dissolv-
ing 0.0625g FA in 100ml water, and then 10ml of solution was sprayed on
each seedling. Samples (left over Hoagland solution) were taken at 72h and
analyzed for K using AAS (Shimadzu, AA6300).
Quantitative Real-Time PCR (qRT-PCR) Analysis
Tobacco plants grown in greenhouse were sprayed with FA (2mM) 45 days
after transplanting. Green leaf samples (X position) were collected after
6, 7, 8, 12, 18, and 24 h of foliar application of FA. Total RNA was
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744 P. B. N. V . et al .
isolated from tobacco leaf samples using RNA aqueous Kit (Ambion).
Synthesis of cDNA was carried out with an equal concentration of RNA for
each sample using high-capacity cDNA synthesis kit (Applied Biosystems)
after DNase treatment. Real-time PCR for AGPase small subunit (F-
AGGGCAGGGACGTA 3) was carried out using Power SYBR Green Master
Mix (Applied Biosystems). The PCR was carried out with 7500 RT PCR sys-
tem (Applied Biosystems) with following steps: initial denaturation at 94C
for 2 min, followed by 35 cycles of denaturation at 94C for 15 s, annealing
at 60C,andextensionat72
C for 15 s. The experiment was repeated at least
thrice, along with three independent biological replicates.
Next-Generation Sequencing (NGS) Analysis
The total RNA was extracted using TRIzol (Invitrogen) and the quality of RNA
checked by Bioanalyzer (Agilent 2100). Transcriptome libraries (single library
with average size of 250bp) for sequencing were constructed according to
the Illumina protocol outlined in “mRNA Sequencing Sample Preparation
Guide” (Cat #RS-931-1001, Rev. D). Next generation sequencing was carried
out at Genotypic Pvt Ltd, India, using Illumina Genome Analyzer IIx via syn-
thesis method with the read length of 72 bases single-end sequencing. Raw
reads were filtered using SeqQC_V2.1, a genotypic proprietary tool (http://, for quality control (Example
number of reads, bases, sequence length, nucleotide composition, and
adapter sequence search, etc.).
Transcriptome alignment was carried out using Bowtie V0.12.7, and
post-alignment was done by SAM 0.1.7. The aligned contigs were annotated
by homology sequence search with The Arabidopsis Information Resources
(TAIR) ( database. Expression value was calculated
using custom Perl code, based on which fold change was calculated by
comparing the FA-treated expression values with control values. Transcripts
with a fold change of <1 were regarded as down regulated, and the range
between 1to+1 as neutral and >+2 as up regulated. Pathways used to
illustrate changes in gene expression were obtained from KEGG Pathway
database (
Effect of FA Application on Leaf K and Starch Content
Foliar application of FA resulted in a significant increase in mean leaf K con-
tent and a reduction in the mean leaf starch content at all the leaf positions
of the plant (Table 1, Figure S-1). This result was consistent across the three
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Fulvic Acid and Nutrient Uptake 745
TABLE 1 Analysis of variance (ANOVA) using means across all leaf positions (P, X, L, and T)
for leaf K content (%) and starch content (%) following application of fulvic acid in flue-cured
Virginia tobacco for growing season 2007–08
Mean squares
Source of variation Df K content Starch content
Replications 2 0.01 0.05
Treatments 5 0.54∗∗ 10.27∗∗
Residual 12 0.01 0.84
CD (5%) 0.12 1.63
∗∗Denotes significance at the 1% probability level.
growing seasons (2007 to 2009), of which 2008 and 2009 were on-farm large-
scale trials. Potassium content in these samples ranged from 0.5% to 3.6%
across all three seasons with highest K content observed in P position leaf.
Average K content of all the leaf positions was clearly higher in FA-treated
samples than that in control leaves. The mean percent increase in K in FA-
treated samples was 33% over the control (Figure 1A). Leaf starch content
varied from 1.0% to 6.0% among FA-treated and control plants across all
three growing seasons, with lowest starch content in the P position leaf.
The mean percent decrease in leaf starch content was 22% over the con-
trol (Figure 1B). Among the other treatments explored in our earlier study
(Mahavishnan et al. 2011), application of naphthylacetic acid (NAA) led to an
increase in K content by 40% and a decrease in starch content by 30% com-
pared with the control. Though the humic substances (HS) have been shown
to contain auxin and an “auxin-like” activity, support for this hypothesis is
still fragmentary (Trevisan et al. 2010).
Numerous studies have shown that HS, not particularly FA, enhance
root, leaf, and shoot growth by stimulating water and nutrient uptake
(Piccolo et al. 1993; Trevisan et al. 2009, and references therein). These pos-
itive effects are explained as an interaction between HS and physiological
and metabolic processes (Nardi et al. 2002; Muscolo et al. 1999). The addi-
tion of HS stimulates nutrient uptake, cell permeability, and seems to regulate
mechanisms involved in plant growth stimulation (Canellas et al. 2008).
However, it is not easy to distinguish between the direct and indirect
effects of HS as some of the positive effects may be ascribed to a general
improvement of soil fertility, leading to a higher nutrient availability for plants
(Quaggiotti et al. 2004). While in other cases, HS seem to positively influence
metabolic and signaling pathways involved in the plant development by
acting directly on specific physiological targets (Trevisan et al. 2009;Figure
S-2). It is interesting to note that, in our experiments, only foliar spray of FA
but not soil application was found to be effective (Mahavishnan, Priya, and
Upadhyay, personal communication, July 2011).
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746 P. B. N. V . et al .
FIGURE 1 Effect of fulvic acid application on mean potassium (A) and starch (B) content
of flue-cured Virginia tobacco in different growing seasons (2007–2009). Error bars represent
standard deviation of the replicates (n =24). The alphabet represents the level of significance
(same alphabet indicates non-significance and different alphabet indicates significance of
treatment means for that particular growing season).
Relationship Between Leaf K And Starch Content
Foliar application of FA was found to enhance K and decrease starch con-
tent of the cured leaf at all leaf positions. We observed a strong inverse
relationship between K and starch in tobacco-cured leaf. Wherever K content
was higher than 2%, starch content was lower than 2% (r2=0.31, Figure 2).
Although the correlation coefficient was highly significant, it explained only
31% of the variation. This result was highly consistent across the three
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Fulvic Acid and Nutrient Uptake 747
FIGURE 2 Relationship between leaf potassium and starch content in flue-cured Virginia
tobacco (values represent the data obtained from control and fulvic acid treated samples of
three different growing seasons, 2007–2009). Values were significant at P =0.001 (∗∗∗).
seasons. Elevated starch content in tobacco has a negative effect on its
quality. Potassium is a highly mobile element that helps in maintaining
cell turgor (Krishnamurthy et al. 2001) and general plant growth (Taiz and
Zieger 2010). It is envisaged that potassium-induced cell expansion ener-
gizes normal metabolism mainly associated with carbon and nitrogen. This
activation leads to production of more carbohydrate (mainly sucrose) and
its translocation to growing parts, leaving behind less substrate for starch
synthesis in chloroplasts (Priya et al. 2011).
Similar results have been shown in cotton where low leaf K content was
associated with elevated leaf carbohydrate concentrations because of delay
in translocation (Pettigrew 1999) and high amounts of sugars under low K
condition in all parts of peanut (Mahaboob and Rao 1980). According to Rufty
and Huber (1983), limitation in translocation of sugars from source leaves
leads to enhanced partitioning of accumulated photosynthates into starch.
Decreased sink capacity has been shown to inhibit sugar transport, enhance
accumulation of sugars in leaves with concurrent increase in expression of
genes involved in carbohydrate storage, and suppress photosynthetic genes
and subsequent growth (Sheen 1990; Paul and Pellny 2003; Stitt et al. 2010).
Further, reportedly K plays a major role in the regulation of the carbohydrate
metabolism through control of starch-sugar balance and starch content is
higher under K starvation (White 1936).
Effect of FA Application on K Uptake
Hydroponic uptake assay revealed that the untreated control plants absorbed
around 0.5 mM of K only as against FA-treated plants (1 mM). Fulvic acid
applied either in solution or spray form increased the K uptake by 95% and
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748 P. B. N. V . et al .
FIGURE 3 Effect of fulvic acid on potassium uptake in seedlings. Data indicates that treated
plants absorbed more K (twofold) from nutrient medium than control plants. Values are
means with SD (minimum three replicates). The alphabet represents the level of significance
(same alphabet indicates non significance and different alphabet indicates the significance of
treatment means).
92% over untreated control (Figure 3). Fulvic acid application on tobacco
seedlings grown in a controlled environment caused in leaves about a 16%
increase in K content (Mylonas and McCants 1980). Rauthan and Schnitzer
(1981) reported that FA application led to a significant increase in K con-
centration in shoots of cucumber seedlings grown in hydroponics. Similar
HS-derived response of increased uptake of macro and micro-elements was
reported by several workers in other crop species (Chen and Aviad 1990;
Varanini and Pinton 1995; Nardi et al. 2002;Yaofu2005;Asiketal.2009).
Further, HS-stimulated uptake of nutrients and its involvement in regula-
tion of plant growth in maize was demonstrated (Canellas et al. 2008).
These studies suggested an increased ion influx was partially attributable
to transcriptional activation of major gene H+-ATPase, which possibly leads
to generation of favorable electrochemical gradient (Millerand Smith 1996).
Spraying humic acid has been shown to have a significant effect on physio-
logical traits, including nutrient uptake, improved plant growth, and yield of
eggplant (Ebrahim et al. 2012).
Quantitative Real-Time PCR (qRT-PCR) Analysis for Starch
Metabolism Gene
Expression of ADP-glucose pyrophosphorylase (AGPase) small subunit was
assayed by q-RT PCR in RNA isolated from the control and FA-treated tobacco
leaves collected at different time intervals post-FA application. The RNA from
leaves treated with NAA was used as a positive control in the experiment.
Application of FA and NAA resulted in threefold reduction in AGPase
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Fulvic Acid and Nutrient Uptake 749
FIGURE 4 Gene expression profile of ADP glucose pyrophosphorylase post fulvic acid and
naphthylacetic acid application (A), and time course of gene expression profile of ADP glu-
cose pyrophosphorylase (AGPase) in fulvic acid treated samples (B). Experiment was repeated
three times and similar pattern of down-regulation was observed.
transcript level (Figure 4A). A time course study found that the AGPase tran-
script levels were lowest at 12h post-application of FA (Figure 4B) and slowly
recovered by 48h. Down-regulation of AGPase, a rate-limiting enzyme in
starch biosynthesis (Taiz and Zieger 2010), reportedly reduces starch content
(Kwak et al. 2007; Sanjaya et al. 2011). Similar results were obtained by appli-
cation of NAA on small subunit of AGPase in tobacco cell lines (Miyazawa
et al. 1999). A decrease in AGPase transcript level was observed after 6h; a
maximum level was achieved at 12h and the level then slowly came down
to normal after 48h of application of 2, 4 dichlorophenoxyacetic acid, a
synthetic auxin (Miyazawa et al. 2002). The FA, which has an auxin-like
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750 P. B. N. V . et al .
activity, could have induced similar changes in AGPase gene expression and
starch levels.
Global Gene Expression Changes Upon FA Application with Specific
Emphasis on Potassium and Starch Metabolism
Transcriptome sequencing was carried out to elucidate the global gene
expression changes in FA- and NAA-treated leaf samples. High through-
put RNA sequencing with Illumina HiSeq2000 generated 20 and 40 million
single-end reads for the control and treated samples, respectively, with more
than 90% being high-quality reads. These reads were assembled and then
aligned against contigs assembled from tobacco transcriptome data (D. S.
Gurumurthy, personal comm. 2013) to obtain information on expression lev-
els for specific transcripts. Contigs that showed differential expressions were
annotated against TAIR database (
Transcriptome sequence of the treated plants revealed significant differ-
ences in gene expression pattern relative to the control. Gene expression
changes induced by FA application were similar to those induced by NAA,
but the fold-change was much higher with NAA treatment. A few genes
were down regulated 7-fold and many others were up regulated 12-fold
(Figure 5A and 5B). Expression of 5177 transcripts affected by foliar appli-
cation of FA was annotated and categorized based on their GO-ontology
function (Figure 6A-D). Many auxin-related pathways were up regulated,
including photosynthesis (Calvin cycle, light harvesting complexes), gly-
colysis (pyruvate kinase), cell division (cyclins, cyclin-dependent kinases,
mitogen-activated protein kinases [MAPK]), nitrogen fixation (nitrate trans-
porters, nitrate reductase), starch (amylases, water dikinase, glucosidases),
transcription factors, protein synthesis (translation initiation factors, ribo-
somes), and translocation of sugars (plastidic glucose translocator [PGLCT],
glucose phosphate translocator [GPT2]).
Annotated gene list was used to identify genes involved in K transport,
sugar, and starch metabolism to deduce the effect of FA on expression of
enzymes/proteins involved in their respective pathways. Many transporters
and channels involved in K uptake and mobilization were up regulated in FA-
and NAA-treated samples (Table 2). Ashley et al. (2006) and Philippar et al.
(1999) explained that auxin acted as a signal for low potassium and triggered
the plant to express high affinity transporters/channels for its uptake. One of
the reasons for enhanced K content in FA-treated leaves could be the auxin-
like effect of FA. Auxin-like effect of humic substances is not uncommon, as
reported by several workers (Nardi et al. 1994; Muscolo et al. 1998,1999)on
the basis of analytical and biochemical assays. Our NGS data indicate that
mode of action of FA in facilitating K absorption and transport may be similar
to that of auxin as it activates auxin-signaling pathway.
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Fulvic Acid and Nutrient Uptake 751
FIGURE 5 Gene expression pattern of whole genome as obtained by next generation
sequencing is expressed as Whisker plot for fulvic acid (A) and naphthylacetic acid (B) treated
leaves. The chart represents gene expression levels that have a range of 5to+15 fold (+2to
+15 fold: up regulated genes; 0.5 to +2 fold: neutral genes; 0.5 to 5 fold: down regulated
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752 P. B. N. V . et al .
FIGURE 6 Functional classification of transcripts (number indicated in parenthesis) of fulvic
acid (A and B) and naphthylacetic acid (C and D) treated leaves. Most of the up-regulated
genes are involved in photosynthesis and cell division followed by potassium transport and
starch degradation.
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Fulvic Acid and Nutrient Uptake 753
TABLE 2 List of transporters/channels that get over-expressed because of fulvic acid
application and their role in potassium mobilization (root to leaves)
S. No Transporters Function
1KUP/AKT1/PIP Transporters involved in K uptake from root
2 AKT 2 and 3 Phloem loading and transport of K to other parts
3 CNGC Transport of K to other parts
4KCO/KAT Transporter involved in mesophyll movement (in leaves) of K ion
Global gene expression profile indicates that various enzymes involved
in degradation of large molecules (starch) to simple sugars were up regulated
upon FA or NAA application (Figures S-3a & b). Enzymes such as amy-
lase, isoamylase, and glucan water dikinase, which catalyze initial reactions
of starch degradation (leads to glucans of different chain length), were
highly up regulated in FA-treated plants. The FA not only affects synthesis of
starch but also activates enzymes that degrade stored starch (Supplementary
Table 1). Sugar metabolism in wheat seedlings implicates involvement of FA
in up-regulation of starch-degrading enzymes (α-amylases) (Xu et al. 1998).
Our results are in agreement with a similar report on application of humic
acid in reducing starch synthesis in tobacco (Ye et al. 2009).
Thus, based on results obtained from biochemical and molecular stud-
ies, we can conclude that foliar application of FA enhances K uptake and
reduces starch in FCV tobacco of the SBCS region. Further, FA elicits almost
similar gene expression changes as those caused by auxin. These findings
also support the use of FA for crop species grown in soils where bioavail-
ability and accessibility of nutrients is a constraint in achieving higher yields.
Foliar application of FA has a significant beneficial influence on general qual-
ity of FCV tobacco of the SBCS region. Specifically, FA resulted in increased
leaf K and reduced starch contents. Molecular analysis revealed that FA
activated expression of high-affinity K transporters (enhanced K uptake),
degraded stored starch, and energized plant metabolism (efflux of trios-
PO4 for sucrose synthesis). We believe this is the first report on FCV tobacco
grown on black soils that provides encouraging and consistent results that
comprehensively highlight inclusive benefits of FA both from agronomic and
molecular dimensions.
We thank Dr. C.C. Lakshmanan, Head, ITC-LSTC, ITC Ltd., Bangalore, India,
for his continued support during the study. We appreciate Dr. M. Mani, Chief
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Scientist, Research division, research & technical staff of ILTD, Rajahmundry,
India, for supporting us to conduct field experiments and sample analysis.
We also thank Dr. PRS Reddy, CTRI, Rajahmundry, India, for his crucial input
for field experiment and Dr. Venkata Reddy (Agriscience) for useful sugges-
tions during the preparation of the manuscript. Ms. Priya personally thanks
Sravanthi and Pavani for their help during starch analysis. Editorial and use-
ful tips from the Corp R&D in-house manuscript committee are appreciated.
Overall support from team Agriscience, LSTC, is gratefully acknowledged.
Supplemental data for this article can be accessed on the publisher’s website.
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... A mixture of HA, FA, polysaccharides and carboxylic acids leads to decrease in apricot acidity (Drobek et al., 2019). Foliar application of FA enhances K levels in plants (Priya et al., 2014). ...
... In Ni-4 FA100 leads to significant increase of K content compared to Adest as well. This is supported in literature as well, as foliar application of FA was reported to enhance K levels in plants (Priya et al., 2014). In highest HM concentration Zn-2 and Ni-3, FA leads to significant decrease of K content. ...
The amount of heavy metals released into the environment increased tremendously in the last centuries, due to enhanced use in industry and daily life. Some heavy metals are important trace elements for plants, which therefore easily take them up and facilitate entry of these elements into the food chain. Heavy metals intake by humans mainly happens through consumption of plant- and animal-based food. They are non-degradable and therefore often accumulate in tissues, causing adverse effects to human health. While excess of heavy metals pose a great threat, not enough trace elements are problematic for plants, animals and humans as well. Zinc deficiency for example is the most common deficiency in soils for crop production and 33% of the world’s population suffers from the results of zinc deficiency as well. Previous studies suggest that biostimulants can be used to support plants in tolerance of high heavy metal concentrations or increase the content of important trace elements like zinc in crops, to battle deficiency in human nutrition, depending on the concentration and type of the biostimulant used. In this work the effect of foliar application of different concentrations of fulvic acid (FA) on Triticum aestivum, Amaranthus (A. cruentus and A. caudatus) and Thlaspi caerulescens, growing in in vitro cultures, hydroponics and soil, contaminated by different concentrations of zinc and nickel, was investigated. FA improved growth performance on several parameters (root hair length, root length, number of leaves, distance between root tip and first root hair) depending on the concentration of the FA applied, the concentration of the heavy metals and the plant species. Especially outstanding was the improvement of the mechanical properties of Amaranth and wheat in soil with increasing concentration of FA. Leaf surface and stem diameter in Amaranth increased visible with increasing FA oncentration, as well as the ability to recover faster and better after aphid invasion.
... The research shows that fulvic acid has a significant synergistic effect on chemical fertilizer, and can be used in agricultural production as soil conditioner or plant growth promoter (Linehan 1977;Yazdani et al. 2014). Fulvic acid has many advantages, including improving soil fertility, promoting nutrient absorption, and increasing crop yield (Pettit 2004;Verlinden et al. 2009;Priya et al. 2014). A large number of studies have shown that application of fulvic acid can increase chlorophyll content and enhance soil enzyme activity, thus increasing yield (Yang et al. 2017;Li et al. 2020a). ...
Full-text available
Fulvic acid fertilizer has great potential in increasing crop yield, improving soil fertility and maintaining agricultural sustainable development. However, there is insufficient research on garlic growth and soil nutrient with different types of fulvic acid fertilizer. This experiment was conducted to evaluate the effects of different fulvic acid fertilizers and dosages on garlic yield composition, quality, SPAD value in leaves, soil nutrient and enzyme activity in the garlic-cotton intercropping. A 2-yr field experiment was conducted using ‘Jinsuan-4’, and seven treatments were set: no fertilization (CK), conventional fertilization (CF), low-, medium- high amount of fulvic acid microbial agent (FA40, FA60, FA80), fulvic acid nutrient solution (L25), low amount of fulvic acid microbial agent with fulvic acid solution (FA40L25). In both years, FA40L25 had the highest garlic bolt yield, which increased by 1.57–40.58% compared with other fertilization treatments. The bulb yield of FA40L25 was significantly higher than that of conventional fertilization. In 2018, the content of allicin and soluble sugar increased by 9.23% and 11.22% compared with FA80, respectively. The available nutrients in soil at different growth stages were significantly increased in FA40L25 and FA80. Compared with FA40 and BFL25, the urease activity of soil treated with FA40L25 increased by 9.76% and 8.00%, respectively. FA40L25 can effectively improve garlic yield, soil available nutrients and enzyme activities, and contribute to the sustainable development of garlic agriculture in the future.
... Preliminary experiments have explored the effect of fulvic acid, seaweed extract, and molasses on water remediation, with these components originating from natural sources. Fulvic acid is a kind of humic acid with small molecular weight, high activity, and good water solubility, which is widely used in agriculture, medicine, and environment (Priya et al., 2014;Tian et al., 2018). Previous studies have found that fulvic acid can improve microbial activity, enhance metabolism, and promote growth mainly by stimulating the activities of a variety of enzymes (Li et al., 2016). ...
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Bioactivator is a kind of agent rich in nutrients and a variety of active substances, which is considered as one of the green methods to deal with the pollution of natural waters because of its high efficiency, low cost, environment-friendly, and causing no secondary pollution. In this study, a green bioactivator formulation composed of fulvic acid, seaweed extract, and molasses (fulvic acid 1.744 mg/L: seaweed extract 1.756 mg/L: molasses 0.5 mg/L) was obtained by mixture design experiments, which can improve the removal rates of COD and NH3-N by 15–25% and 7–15%, respectively, compared with untreated water. The effects of adding various carbon sources, trace elements, and growth factors on the basis of the developed formulation were explored to optimize the developed formulation and improve the effect of water remediation; the experiment results showed that sodium acetate and glucose as carbon sources were beneficial to the removal of NH3-N; Mn, Mo, and B as trace elements can further increase the COD removal rates by 5.0–8.2%; niacin and vitamin B12 (VB12) as growth factors can increase COD removal rate by 7.5% and 4.7%, respectively. This study provides a green biological activator with good application prospect, which can be applied to the remediation of polluted water.
... It minimizes the opening of stomata and the transpiration rate, thus minimizing the loss of water under well-watered and also drought conditions (Lu and Beamish 2001;Li et al. 2005;Anjum et al. 2011;Huang et al. 2020). Besides, the use of FA promotes the growth of roots (Canellas et al. 2002) thereby increasing the uptake of nutrients (Razavi and BahramParvar 2007;Yang et al. 2013;Priya et al. 2014;El-Helaly 2018;Justi et al. 2019;Wang et al. 2019). It was found by Zimmerli et al. (2008) that FA has the ability to remain in the soil under high salt concentration as well as a large range from pH. ...
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The present study was performed during two successive seasons 2019 and 2020 to investigate the effect of the soil application of fulvic acid (FA), seaweed extract (SE), and their different combinations on vegetative growth, yield, and fruit quality of six-years-old guava (Psidium guajava L.) cv. ‘Maamoura’. The trees were planted 4 × 4 m2 apart in clay soil under a flood irrigation system. They were treated three times starting from mid-March with one-month intervals with the following treatments: Control (water only), 3 and 4 g/L FA, 3 and 4 g/L SE, and their different combinations; 3 g/L FA + 3 g/L SE, 3 g/L FA + 4 g/L SE, 4 g/L FA + 3 g/L SE, and 4 g/L FA + 4 g/L SE. The results clearly showed that the application of FA or SE solely or in combinations increased shoot length and diameter, as well as leaf chlorophyll compared with the control. The treatments also increased fruit set percentage, fruit yield, and fruit physical and chemical characteristics such as fruit weight, size, TSS%, total reduced and non-reduced sugars, as well as leaf mineral content, while they decreased the fruit acidity compared with the control in the two seasons.
... Furthermore, FA have also been observed to promote transcriptional changes in the roots of Medicago sativa, up-regulating genes related to biological processes of N metabolism, nutrient transporters and hydrolases [63]. Other studies observed an increase in lipid content correlated with use of FA, as these substances seemingly up-regulated genes associated with lipid biosynthesis [64], as well as genes related to K transporters, starch degradation and plant metabolism [65]. As previously mentioned, abiotic stresses have a high impact on agricultural activity. ...
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As the world develops and population increases, so too does the demand for higher agricultural output with lower resources. Plant biostimulants appear to be one of the more prominent sustainable solutions, given their natural origin and their potential to substitute conventional methods in agriculture. Classified based on their source rather than constitution, biostimulants such as humic substances (HS), protein hydrolysates (PHs), seaweed extracts (SWE) and microorganisms have a proven potential in improving plant growth, increasing crop production and quality, as well as ameliorating stress effects. However, the multi-molecular nature and varying composition of commercially available biostimulants presents challenges when attempting to elucidate their underlying mechanisms. While most research has focused on the broad effects of biostimulants in crops, recent studies at the molecular level have started to unravel the pathways triggered by certain products at the cellular and gene level. Understanding the molecular influences involved could lead to further refinement of these treatments. This review comprises the most recent findings regarding the use of biostimulants in plants, with particular focus on reports of their molecular influence.
... As fulvic acid can enhance antioxidants, IAA, GA3 and Cytokines hormones and vitamins, it improves the vegetative growth in plants (Abd El-Hameed et al., 2014). Besides, Priya et al., (2014) reported that fulvic acid looks like the hormone of auxin in plant, which plays a good role in absorption of potassium and is responsible for the metabolism of starch. Fulvic acid can magnetize the molecules of water and facilitate the motion of nutrients like calcium, magnesium, iron, copper, and zinc to the roots of plants (Malan, 2015). ...
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This study was performed during 2019 and 2020 seasons on seven years old “Flame seedless” grape trees (Vitis vinefera L.). The trees were cultivated at 3 meters apart between rows and 2 meters between trees in the same row in a calcareous soil under drip irrigation system in a private orchard located at Nubaria, Beheira governorate, Egypt. The trees were sprayed three times, before flowering, during the full bloom and three weeks later with the following treatments: Control spray with water only, Fulvic acid at 1000, 1500 and 2000 ppm, Folic acid (vitamin B9) at 100, 150 and 200 ppm, Seaweed extract at 2000, 3000 and 4000 ppm. Besides, the combinations of 1000 ppm Fulvic acid +100 ppm Folic acid+ 2000 ppm Seaweed extract, 1500 ppm Fulvic acid + 150 ppm Folic acid + 3000 ppm Seaweed extract and 2000 ppm Fulvic acid + 200 ppm Folic acid + 4000 ppm Seaweed extract were also applied. The obtained results demonstrated that the foliar spray of Folic acid, Fulvic acid and Seaweed extract and their combinations improved weight, length, width, size and number of clusters. Furthermore, they also increased extremely weight of 100 berries and consequently the yield per vine in kg and the yield in ton per hectare, weight of juice, the percentages of total sugars, and total soluble solids as compared to control in the two seasons. The effect of Fulvic acid on the previous mentioned parameters was higher than the effect of Seaweed extractor Folic acid and its effect was better by the increasing the applied concentration where the best one was 2000 ppm, which gave the best results more than the other applied treatments in the two seasons. The best combination was Fulvic acid 2000 ppm + Folic acid at 200 ppm + Seaweed extract 4000 ppm.
Full-text available
Background and Objectives Fulvic acid has a relatively low molecular weight and contains a large number of oxygen and carbon-rich functional groups. Many of the beneficial effects of fulvic acid spray include stimulating plant metabolism, increasing the activity of transaminase and invertase enzymes, increasing bioavailability and nutrient uptake, as well as increasing crop growth and yield. Fulvic acid spraying solution helps to transfer minerals to metabolic sites within plant cells. Fulvic acid at certain stages of plant growth can be used as a major method to maximize plant production capacity. Due to the fact that calcium transfer is difficult, although the soil is rich in this element, so its foliar application is recommended. In addition, calcium deficiency leads to a decrease in root growth and leaf loss, but also leads to the production of poor quality fruits. Therefore, this study was carried out with the aim of investigating the use of fulvic acid and calcium as a spraying solution on growth and yield of Quince ‘Haj Agha Kishi’. Materials and Methods In order to investigate the effects of fulvic acid concentration and chelated calcium on quality and quantity of fruit indices of Quince ‘Haj Agha Kishi’ an experiment was conducted during 2017-2018 in kosar city, Ardabil province. The experiment was performed as a factorial in based on the randomized complete block design with four levels of fulvic acid application with concentrations of 0, 1, 2 and 3 per thousand and three levels of application of chelated calcium with concentrations of 0, 1.5 and 3 per thousand in three replications. The treatments were applied to six-year-old seedlings. The treatments were applied on the trees as a spray solution and applied three times: after fruit set, one and two months after fruit set. In this study, leaf chlorophyll content index was measured by Arnon method. The leaf area of the plant was measured with a level gauge, model AM300, In this study 10 leaves were randomly selected from each tree branch, the average leaf area was multiplied by the number of main and secondary branches, and the leaf area of each treatment was recorded as average. In order to determine the length, diameter and average weight of fruit, ten fruits were randomly harvested from treated trees, then the diameter and length of the fruits were measured with a caliper with an accuracy of 0.01 mm. Also, the weight of the fruits was determined with a scale of model GF800, made in Japan with an accuracy of 0.01 grams. Yield was calculated by measuring the total weight of the crop in each tree. Statistical analysis of data was performed using SAS 9.2 statistical software. Means were compared based on LSD lest at 1 or 5% and charts were drawn using EXCEL 2013 software. Results The results of data analysis of variance showed that the effects of chelated calcium and fulvic acid on leaf area, length, diameter, wet weight and fruit yield were significant (P<0.01). Based on the results, fulvic acid had a significant (P<0.05) effect on chlorophyll b and total chlorophyll content of leaf. The interaction of calcium ×fulvic acid treatments had a significant (P<0.01) effect on leaf area and fruit length. The highest total chlorophyll content of 1.20 mg.g-1 was obtained by using 3 per thousand concentration of fulvic acid and the lowest rate was 0.79 mg.g-1 in the control. The highest (5481.69 mm2) leaf area was obtained with the simultaneous use of 3 per thousand concentration of chelated calcium and 3 per thousand concentration of fulvic acid, which was significantly different from other levels. The lowest leaf area was also observed in control. Comparison of the means showed that the treatments of 3 per thousand concentration chelated calcium and 3 per thousand concentration of fulvic acid had the highest fruit yield with 167.63 and 135.30 kg, respectively. The lowest yield was recorded for control trees. Conclusion Increasing yield and quality is the most important goal in agricultural production. Due to the fact that biostimulants do not have adverse effects on soil and water. In order to maintain sustainable production should be used in the production program. Folic acid, as a biostimulant, improves plant metabolism and facilitates the absorption of elements. According to the findings of this study, application of fulvic acid and chelated calcium at 3 per thousand concentrations is recommended for Quince ‘Haj Agha Kishi’ to improve leaf efficiency and fruit yield.
Various oils, fats and emulsifiers in the composition of preparations for soil enrichment or plant protection can have a significant effect on the germination capacity and energy of sprouting of pea seeds. Fat of black soldier fly ( Hermetia illucens ) larvae can be used as a pesticide carrier as well as for increasing seed resistance to contamination with fungi and insects during storage and sprouting. Therefore, the aim of the study was to determine an effect of insect fat in a form of an emulsion on sprouting of pea seeds of the variety “Rodnik” depending on a type of an emulsifier or stabilizer. It was found that the use of 0.3 weight% of xanthan gum as a stabilizer for fat emulsion of black soldier fly ( Hermetia illucens ) larvae significantly increased the number of germinated seeds and the energy of seed sprouting. The use of 1–5 weight% of Tween 20 as an emulsifier for fat of black soldier fly ( Hermetia illucens ) larvae led to inhibition of seed growth. Lecithin, sodium caseinate and microcellulose with addition of fat of black soldier fly ( Hermetia illucens ) larvae also decreased the germination capacity and sprouting of pea seeds ( Pisum sativum L. ).
Potassium fulvic acid (BSFA) and potassium humate (KHM), as organic fertilizers, can improve soil structure, increase soil nutrient levels and prevent plant diseases. However, knowledge is limited regarding how BSFA and KHM influence soil microbial communities and the interrelationships between community members associated with Panax ginseng. Soil pH and nutrient content increased significantly as a result of the addition of BSFA and KHM. The pH, NH4⁺-N, NO3⁻-N, AP and AK increased by 1.72%-5.55%, 70.09%-108.39%, 35.38%-216.20%, 1.21%-14.19% and 3.40%-5.94%, respectively, in the BSFA and KHM treatments. The soil nutrient increase may be related to Micrococcaceae and arbuscular mycorrhizal fungi (AMF). The structure of the microbial community also changed radically from that of the control group, and Chloroflexi (2.69%-3.15%), Actinobacteria (4.33%-7.53%) and Acidobacteria (9.44%-11.62%) were the dominant microorganisms at the phylum level in bacteria. In contrast, the dominant fungi at the phylum level were Ascomycota (77.39%-78.08%), Glomeromycota (0.36%-2.68), Olpidiomycota (0.02%-3.78%) and Basidiomycota (0.80%-1.17%). Fusarium oxysporum and Ascomycota were biomarkers for BSFA and KHM, which may be related to pathogenic bacteria. Network analysis revealed that the association among members of the soil microbial community was more positive than negative following application of KHM, and more positive (62.5%) than negative (37.5%) correlations were observed between bacteria, whereas the fungal community exhibited more positive (97.3%) than negative (2.7%) correlations. PICRUST predicted the microbial function of adding KHM and BSFA to the soil, and these pathways mainly belong to the degradation and metabolism of organic matter, saprophytic organisms and plant pathogens. In summary, our study demonstrated that the addition of BSFA and KHM increased the nutrients in the ginseng soil and reshaped the microbial function in soils, providing a theoretical foundation for soil improvement and biological control of ginseng diseases. However, due to the limitations of greenhouse cultivation, additional long-term experiments on farmland with different climate changes are recommended.
Establishing better nitrogen (N) management strategies is of great significance for sustaining crop production and reducing environmental pollution. However, there is limited knowledge about N fertilizer management practices with soil nutrient supply, N leaching, crop productivity and nutrient use efficiency (NUE) reaching the desired level simultaneously. In this study, pot experiment was conducted to evaluate the effects of N fertilizer and in combination with fulvic acid (FA) on NUE and nutrient supply in a moderate-salinized soil (with total salt content 3.30 g kg⁻¹ and EC1:5 1.18 dS m⁻¹). Ten treatments were included: treatment without any addition (CK); 100%, 85% and 70% of the conventional inorganic N fertilizer addition rate (100% CF, 85% CF and 70% CF); 100% CF, 85% CF and 70% CF combined with 75 kg ha⁻¹ FA (100% CF + F1, 85% CF + F1, and 70% CF + F1), respectively; and 100% CF, 85% CF and 70% CF combined with 150 kg ha⁻¹ FA (100% CF + F2, 85% CF + F2, and 70% CF + F2), respectively. In order to further investigate the effects of combining N fertilizer and FA applications on soil N leaching losses, part of the fertilizer management practices were selected to conduct a soil leaching experiment. The results demonstrated that the Olsen-P for the upper 20 cm of soil was significantly affected by N fertilization (P ≤ 0.01). In the treatments with inorganic fertilization alone, the concentration of soil mineral N at 0–10 cm soil depth decreased with decreasing level of fertilizer N, while Olsen-P content and alkaline phosphatase activity decreased with increasing N fertilizer application rate. The application of FA significantly increased alkaline phosphatase activity. Overall, the total mineral N leaching losses increased exponentially with increasing annual fertilizer N application rates, while the addition of FA decreased the total mineral N leaching factor (TLFN). Furthermore, the results of multiple regression analysis revealed that wheat grain yield, plant P uptake, plant N uptake, harvest index of applied fertilizer N (HIN), partial factor productivity of applied fertilizer P (PFPP), recovery efficiency of P (REP) and recovery efficiency of N (REN) reached ≥85% of their maximum concurrently, when the application amounts of N fertilizer and FA varied from 300 to 370 kg ha⁻¹ and from 164 to 250 kg ha⁻¹, respectively. These results of this study provide a basis for appropriate nitrogen (N) management in salt-affected soils and for the improvement of the sustainability of agricultural development in China.
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Thoroughly updated and now in full color, the 15th edition of this market leading text brings the exciting field of soils to life. Explore this new edition to find: A comprehensive approach to soils with a focus on six major ecological roles of soil including growth of plants, climate change, recycling function, biodiversity, water, and soil properties and behavior. New full-color illustrations and the use of color throughout the text highlights the new and refined figures and illustrations to help make the study of soils more efficient, engaging, and relevant. Updated with the latest advances, concepts, and applications including hundreds of key references. New coverage of cutting edge soil science. Examples include coverage of the pedosphere concept, new insights into humus and soil carbon accumulation, subaqueous soils, soil effects on human health, principles and practice of organic farming, urban and human engineered soils, new understandings of the nitrogen cycle, water-saving irrigation techniques, hydraulic redistribution, soil food-web ecology, disease suppressive soils, soil microbial genomics, soil interactions with global climate change, digital soil maps, and many others Applications boxes and case study vignettes bring important soils topics to life. Examples include “Subaqueous Soils—Underwater Pedogenesis,” “Practical Applications of Unsaturated Water Flow in Contrasting Layers,” “Soil Microbiology in the Molecular Age,” and "Where have All the Humics Gone?” Calculations and practical numerical problems boxes help students explore and understand detailed calculations and practical numerical problems. Examples include “Calculating Lime Needs Based on pH Buffering,” “Leaching Requirement for Saline Soils,” "Toward a Global Soil Information System,” “Calculation of Nitrogen Mineralization,” and “Calculation of Percent Pore Space in Soils.”
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To study the effect of nitrogen fertilizer and foliar spraying of humic acid on yield and yield components of eggplant, an experiment was conducted in factorial format based on randomized complete block design with three replications in Astaneh Ashrafiyeh (north of Iran) during 2011 farming year. Factors of experiment consist of humic acid foliar spraying in three levels; H 1 : control (without humic acid spraying), H 2 : 25 mg/L and H 3 : 50 mg/L, and nitrogen fertilizer management with six levels; N 1 : control (no nitrogen and no nitroxin), N 2 : 40 kg/ha pure nitrogen, N 3 : 80 kg/ha pure nitrogen, N 4 : roots inoculation with nitroxin, N 5 : 20 kg/ha pure nitrogen +roots inoculation with nitroxin and N 6 : 40 kg/ha pure nitrogen + roots inoculation with nitroxin. At maturity, fruit yield, number of fruits per square meter, number of branches per plant, plant height, fruit length and fruit width were measured. Results showed that, the effect of foliar humic acid spraying on all measured traits had significant differences at 1% probability level. Also, effect of nitrogen fertilizer management on fruit yield, number of fruit per square meter, plant height, fruit length and fruit width at 1% and on number of branches per plant at 5% was significant. Interaction effect of foliar humic acid spraying and nitrogen fertilizer management on fruit yield at 1% and on number of fruit per square meter, plant height, fruit length and fruit width at 5% was significant and on number of branches per plant was non significant. The highest fruit yield was obtained from use of 50 mg/L humic acid spraying and also from 80 kg/ha nitrogen fertilizer.
Since the studies by Liebig (1856), it is well known that plants, as long as they are adequately supplied with light and mineral nutrients, can live in the absence of the organic and inorganic structural components of the soil. Nowadays the use of hydroponics is popular not only among plant physiologists but also in certain commercial activities.
In cultured Bright Yellow-2 (BY-2) tobacco (Nicotiana tabacum) cells, the depletion of auxin (2,4-dichlorophenoxyacetic acid) in the culture medium induces the accumulation of starch. This is accelerated by the addition of cytokinin (benzyladenine). Light and electron microscopic observations revealed that this amyloplast formation involves drastic changes in plastid morphology. The effects of auxin and cytokinin on amyloplast development were investigated by adding auxin or cytokinin to cells grown in a hormone-free culture. Auxin repressed amyloplast development, whereas cytokinin accelerated starch accumulation regardless of the timing of hormone addition. RNA gel-blot analysis revealed that the accumulation of the ADP-glucose pyrophosphorylase small subunit gene (AgpS), granule-bound starch synthase, and starch branching enzyme transcripts were also affected by hormonal conditions. High levels of AgpS, granule-bound starch synthase, and starch branching enzyme transcripts accumulated in amyloplast-developing cells grown in auxin-depleted conditions. Furthermore, the addition of auxin to the cells cultured in hormone-free medium reduced the level of AgpS transcripts, whereas the addition of cytokinin increased it, irrespective of the timing of hormone addition. These results suggest that auxin and cytokinin exert opposite effects on amyloplast development by regulating the expression of the genes required for starch biosynthesis.