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Phosphate Mobilisation by Soil Microorganisms
Abstract
Microorganisms are fundamental to the cycling of phosphorus (P) in soil-plant systems as they are involved in a range of processes that govern P transformations
and availability. Soil microorganisms in particular are able to release plant available P from otherwise sparingly available forms of soil P, through solubilisation and mineralisation reactions of inorganic and organic P, respectively. The potential of phosphate solubilising microorganisms (PSM)
to improve plant P nutrition is widely recognised, and the mechanisms involved are being investigated. The feasibility of developing efficient management systems based on PSM as biofertilisers is of current interest in rhizosphere biotechnology
. Mycorrhizosphere interactions involving PSM and their interaction with AM fungi is of further relevance for the acquisition, transport and supply of P to plant roots, and therefore to soil P cycling and plant P nutrition. Managing these interactions (mycorrhizosphere tailoring) provides an environmentally-acceptable agro-technological practice to improve agricultural sustainability.
... Phosphorus is a macro-element that is found in the cells of all living things. Prokaryotic and eukaryotic cells have developed mechanisms for the transport of inorganic phosphorus from the external environment to the cytoplasm, where it is used in the biosynthesis of phospholipids, sugar phosphates, nucleotides and other molecules (Barea and Richardson, 2015). Despite the fact that phosphorus is one of the most abundant molecules on the earth's surface, it is usually found in nonbioavailable forms, a fact that often leads to phosphorus being a nutrient that limits the growth of plants, bacteria and fungi (Sosa et al., 2019). ...
... Despite the fact that phosphorus is one of the most abundant molecules on the earth's surface, it is usually found in nonbioavailable forms, a fact that often leads to phosphorus being a nutrient that limits the growth of plants, bacteria and fungi (Sosa et al., 2019). In the soil, inorganic phosphorus is usually solubilized by plants and microorganisms (bacteria and fungi) through the production of a wide variety of weak acids such as citric, lactic, malic, ketoglutaric acid and others (Barea and Richardson, 2015). However, the organophosphorus species in soil and seeds often need to be hydrolysed by phosphatases in order to release inorganic phosphorus. ...
The use of extremophile enzymes for industrial purposes has become very significant since the beginning of this century and it is envisaged an ample use of enzymes for environmental applications (fertilisers, food and feed additives, biodegradation, pharma) as well as in the biosynthesis of compounds through design of novel biosynthetic pathways.
... promote growth by increasing the bioavailability of minerals viz., phosphorus and zinc, fixing atmospheric nitrogen, sequestration of iron through siderophores, and also by the production of phytohormones. In addition, biosynthesis of ethylene catabolism related 1-aminocyclopropane-1-carboxylate (ACC) deaminase, antibiosis, lytic enzyme production, detoxification and degradation of pathogens' virulence factors (Ahmad et al., 2008;Barea and Richardson, 2015) also contribute to the plant beneficial effects of Bacilli. Seed bacterization was often employed to study the effect of Bacilli or their formulations on plant growth (Kishore et al., 2005;Das et al., 2010). ...
... Phosphate solubilization by rhizobacteria promotes plant growth and yields (Lyngwi et al., 2016). Some species of bacteria, including Bacillus spp., possess the ability to mineralize and solubilize organic and inorganic phosphorus in the soil for quick access to the plant (Barea and Richardson, 2015). Microbial phytases, specially produced by Bacillus spp., were studied due to their PGP effects and diverse agrobiotechnological applications Sanguin et al., 2016). ...
The rhizosphere offers a quintessential habitat for the microbial communities and facilitates a variety of plant-microbe interactions. Members of the genus Bacillus constitute an important group of plant growth promoting rhizobacteria (PGPR), which improve growth and yield of crops. In a total of 60 bacterial isolates from the tomato rhizosphere, 7 isolates were selected based on distinct morphological characteristics and designated as tomato rhizosphere (TRS) isolates with a number suffixed viz., TRS-1, 2, 3, 4, 5, 7, and TRS-8. All the seven isolates were Gram positive, with in vitro plant growth promoting (PGP) traits like phosphate and zinc solubilization, and also produced indoleacetic acid (IAA), phytase, siderophore, hydrogen cyanide (HCN), and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, besides being antagonistic to other microbes and formed biofilm. The seven isolates belonged to the genus Bacillus as per the 16S rDNA sequence analysis. Phylogenetic tree grouped the isolates into four groups, while BOX-PCR fingerprinting allowed further differentiation of the seven isolates. The PGP activity of the isolates was measured on tomato seedlings in plant tissue culture and greenhouse assays. A significant increase in root colonization was observed over 15 days with all the isolates. Greenhouse experiments with these isolates indicated an overall increase in the growth of tomato plants, over 60 days. Isolates TRS-7 and TRS-8 were best plant growth promoters among the seven isolates, with a potential as inoculants to increase tomato productivity.
... The microorganisms involved in solubilizing minerals and organic phosphates are rife in soil (Barea & Richardson 2015). In nutrient deficient soils, these microorganisms utilize the energy derived from the breakdown of fresh carbon compounds to release Pi from organic sources (Arcand & Schneider 2006). ...
... There was a sequential increase in the shoot N, P and K concentrations in AM and non-AM maize shoots with increasing concentration of RP application. This is in accordance with studies where RP application has been shown to improve the concentration of P and other nutrients in plant tissues (Barea & Richardson 2015). The increased nutrient content of AM plants as observed in the present and other studies may be due to the extra radical hyphal contribution and probably also from the increased supply of nutrients at the root surface and mass flow resulting in an increased nutrient acquisition by roots (Frey & Schüepp 1993). ...
We evaluated the influence of arbuscular mycorrhizal (AM) fungus Scutellospora calospora on root architecture, growth, nutrient uptake, root phosphatase activity and mycorrhizal dependency of maize in 0-5% rock phosphate (RP) amended phosphorus (P) deficient soil. RP amendment significantly increased total root
length, number of roots in different orders, and root hair diameter of AM plants. The AM fungus positively influenced maize growth and nutrient uptake. Acid and alkaline phosphatase activities were higher for AM plants in RP amended soils. In contrast, increasing concentrations of RP reduced the percentage of AM fungus
colonization non-linearly. Thus, AM fungus inoculation along with RP amendment could substitute chemical fertilizers and make available the P in RP to the plants.
... In this context, there is ongoing research aimed at investigating an extensive variety of rhizobacteria possessing novel beneficial qualities like heavy metal detoxification (Barea and others 2013a), pesticide degradation/tolerance (Carvalhais and others 2013), salinity tolerance (Bashan and others 2014), biocontrol of phytopathogens and insects (Pii and others 2015) together with plant growth-promoting traits for instance, phytohormone (Barea and others 2013b;Lugtenberg 2015;others 2013, 2015), siderophore (Bakker and others 2013), 1-aminocyclopropane-1carboxylate, hydrogen cyanate (HCN), and ammonia production, and nitrogenase activity (Olivares and others 2013; Barea and Richardson 2015), and phosphate solubilization (Browne and others 2013;Barea and others 2013a). This review focuses on rhizospheric microbes that are advantageous for the plant. ...
... PGPRs have been recorded to solubilize precipitated phosphates to plants, representing a possible mechanism of plant growth promotion under field conditions (Verma and others 2001;Guo and others 2015). Synthesis of organic acids by rhizosphere microorganisms could be the possible reason for solubilization of inorganic P sources (Barea and Richardson 2015). Unfortunately, because of variable results, the commercial application of phosphate-solubilizing PGPB has been quite limited. ...
The rhizosphere of plant species is an inimitable ecosystem that harbors an extensive range of microbes. Research in the wide areas of rhizosphere biotechnology highlighting new bioinoculants has received ample attention during recent past, and suitable expertises have been developed. However, the global recognition of such technologies by farmers is still overwhelmed with doubts owing to limited shelf-life and efficiency of the products which demonstrate discrepancies. This review illustrates plant growth-promoting rhizobacteria with detailed emphasis on nutrient acquisition and potential roles in conferring tolerance against abiotic stresses. The review demonstrates the recent research in the field of genomic and proteomic analysis, where systematic characterization of potentially effective rhizobacteria is being carried out by screening the extensive bacterial gene pool based on modern molecular tools. The review concludes by emphasizing the efforts made in the proteomics field which could compensate for understanding of prompt evolution in microbe-derived and plant-derived protein and metabolite substitute that activates vulnerability or resistance.
... Phosphate-solubilizing microbes (bacteria, fungi, actinomycetes and cyanobacteria) are being explored as a means to solubilize phosphate for plant nutrition and such strains can constitute as much as 50% of the total soil bacteria population (Johnson and Loeppert, 2006;Sharma et al., 2013). Production of organic acids and chelation of mineral ions by these compounds, rather than acidification, appears to be a more effective mechanism for phosphate solubilization from iron or aluminum minerals (Barea and Richardson, 2015). However, most research to date has primarily focused on microbial production of organic acids such as gluconate, citrate, succinate and oxalate (Whitelaw et al., 1999;Illmer et al., 2003;Rashid et al., 2004;Barea and Richardson, 2015), rather than on other potential phosphate-solubilizing small molecules. ...
... Production of organic acids and chelation of mineral ions by these compounds, rather than acidification, appears to be a more effective mechanism for phosphate solubilization from iron or aluminum minerals (Barea and Richardson, 2015). However, most research to date has primarily focused on microbial production of organic acids such as gluconate, citrate, succinate and oxalate (Whitelaw et al., 1999;Illmer et al., 2003;Rashid et al., 2004;Barea and Richardson, 2015), rather than on other potential phosphate-solubilizing small molecules. ...
A large fraction of soil organic matter (SOM) is composed of small molecules of microbial origin. However, the biotic and abiotic cycling of these nutrients is poorly understood and is a critical component of the global carbon cycle. Although there are many factors controlling the accessibility of SOM to microbes, sorption to mineral surfaces is among the most significant. Here, we investigated the competitive sorption of a complex pool of microbial metabolites on ferrihydrite, an iron oxide mineral, using a lysate prepared from a soil bacterium, Pseudomonas stutzeri RCH2. After a 24-h incubation with a range of mineral concentrations, more than half of the metabolites showed significant decreases in solution concentration. Phosphate-containing metabolites showed the greatest degree of sorption followed by dicarboxylates and metabolites containing both nitrogen and an aromatic moiety. Similar trends were observed when comparing sorption of metabolites with an equimolar metabolite mixture rather than a bacterial lysate. Interestingly, ectoine, lysine, two disaccharides and uracil were found not to sorb and may be more bioavailable in iron oxide-rich soils. Additionally, the highest-sorbing metabolites were examined for their ability to mobilize mineral-sorbed phosphate. All phosphate-containing metabolites tested and glutathione released phosphate from the mineral surface within 30 min of metabolite addition. These findings of preferential sorption behavior within a complex pool of microbial metabolites may provide insight into the cycling of SOM and specific nutrient availability. Finally, the release of highly-sorptive metabolites may be an underexplored mechanism utilized by microbial communities to gain access to limited environmental nutrients.
... P availability is the most limiting factor for crop yield in many arable soils all over the world. Therefore, the capacity of some microorganisms to mobilize P from poorly available sources of this nutrient can help plant P nutrition (Barea and Richardson, 2015). In this section we focus on mechanisms whereby microbial activities result in an increased release of available P from sparingly available soil P forms, either inorganic (solubilisation) or organic (mineralisation). ...
... However, there is no clear evidence that this fungalmediated activity has any agronomic influence (Barea and Richardson, 2015). ...
Optimizing the turnover and recycling of nutrients, a fundamental issue for the sustainability and productivity of agro-ecosystems is depending on the functionality of a framework of plant-soil interactions where microbial populations are involved. Both mutualistic symbionts and saprophytic microorganisms living at the root-soil interfaces, the rhizosphere, or in the plant-associated soil, are recognized as essential drivers of nutrient cycling, availability and capture. Among the mutualistic symbionts, arbuscular mycorrhizal (AM) fungi are one of the most influential groups of soil biota because after establishing the AM symbiosis with most plant species they enhance plant nutrient uptake properties. Saprophytic microorganisms are recognized for their abilities to propel nitrogen (N) fixation and/or phosphorus (P) mobilization, two fundamental processes for sustain plant productivity. Mycorrhiza establishment changes the biological and physical-chemical properties of the rhizosphere, developing the socalled mycorrhizosphere. Particularly relevant is the mycorrhizosphere of legume plants since it also involves the symbiosis with N2 -fixing nodulating rhizobial bacteria. In this overview of mycorrhizosphere interactions related to nutrient cycling, after describing the protagonist microorganisms, the mechanisms responsible for nutrient acquisition by AM-plants are first analyzed. Then, the processes involved in mycorrhizosphere establishment and functions are described. Finally, the achievements derived from managing selected AM fungi and beneficial bacteria interactions (mycorrhizosphere tailoring) are discussed. The use of15N and32P to elucidate the contribution of the mycorrhizosphere components to plant nutrient acquisition is detailed. © 2015, Sociedad Chilena de la Ciencia del Suelo. All rights reserved.
... G. pyriformis establishes an endosymbiotic relationship with the cyanobacterium Nostoc punctiforme, where the cyanobacterium supplies organic compounds to the host fungus, which in turn provides minerals and water [17,18]. Interactions between phosphate-solubilizing bacteria and AMF are important for plant phosphorus (P) acquisition, enabling efficient mobilization and transport to plant roots [19][20][21][22]. Bacterial isolates from the mycorrhizosphere and hyphosphere of AMF, including Asia lannaensis, Rahnella sp., Pantoea sp., Pseudomonas sp., and Burkhoderia sp., displayed phosphate rock solubilization ability [23,24]. ...
Background
In addition to their role as endosymbionts for plant roots, arbuscular mycorrhizal fungi (AMF) engage in complex interactions with various soil microorganisms, the rhizosphere, and the root endosphere of host plants. They also host diverse prokaryotic groups within their mycelia, contributing to what is termed multipartite symbiosis. In this study, we examined the impact of three AMF species— Rhizophagus irregularis , R. clarus , and R. cerebriforme —combined with microbial bioaugmentation on the diversity and composition of bacterial communities in the mycelia and hyphosphere. Using a microcosm design to separate the influence of host plant roots from AMF mycelia and Illumina MiSeq amplicon sequencing to analyze the bacterial communities.
Results
Our results revealed that, while AMF identity and microbial bioaugmentation did not affect the structure of bacterial communities in the hyphosphere soil, they significantly altered the communities associated with their mycelia. Although all three AMF species belong to the same genus, with R. irregularis and R. clarus being closely related compared to R. cerebriforme , we observed variations in the bacterial communities associated with their mycelia. Interestingly, the mycelial bacterial community of R. cerebriforme contained 60 bacteriome core taxa exclusive to it, while R. clarus and R. irregularis had 25 and 9 exclusive taxa, respectively.
Conclusion
This study suggests that organismal phylogeny influences the bacterial communities associated with AMF mycelia. These findings provide new insights into AMF and bacterial interactions, which are crucial for the successful deployment of AMF inoculants. The taxonomic diversity of AMF inoculants is important for engineering the plant microbiome and enhancing ecosystem services.
... Dentre as rizobactérias promotores de crescimento vegetal (RPCV) a espécies Bacillus subtilis é conhecida como RPCP, sendo uma bactéria que ocorre e coloniza a rizosfera naturalmente e que promove o crescimento de plantas de forma direta ou indireta, conseguindo comportar-se sob múltiplos aspectos nas culturas nas quais se relacionam (CHAGAS JUNIOR et al., 2021a), podendo aumentar a disponibilidade de minerais, como fósforo, zinco, nitrogênio, além da capacidade de produção de fitormônios e sequestro de ferro pelos siderofóros (BAREA & RICHARDSON, 2015). Também, foi relatado por Camilo e Pietro-Souza (2023) que B. subtilis pode gerar algumas enzimas de bioproteção e produzir ácido indolacético (AIA) e solubilização de fosfato, que contribuem positivamente para o crescimento de plantas. ...
Rizobácterias do gênero Bacillus que são encontrados na rizosfera vivem em colônias, promovem o crescimento vegetal e apresentam potencial para o controle de fitopatógenos através da liberação de compostos voláteis. Diante disso o objetivo do estudo foi avaliar a eficiência do Bacillus subtilis Bs10 na promoção de crescimento de plantas de tomate e alface. O experimento foi realizado em bandejas com 25 plantas por tratamento. A inoculação de B. subtilis foi realizada no momento do plantio utilizando 1 mL de suspensão em cada célula. Foi utilizado o delineamento inteiramente casualizado com dois tratamentos, com e sem a inoculação de Bacillus. As avaliações para ambas as culturas foram realizadas aos 28 dias após a germinação onde foram determinadas a altura de plantas, massa seca da parte aérea (MSPA) e massa seca da raiz (MSR). A hipótese de igualdade entre as médias dos dois tratamentos avaliados foi feita pelo teste F da análise de variância para p = 0,05, utilizando o programa estatístico SISVAR. Durante as avaliações o tratamento com B. subtilis obteve os melhores resultados em todos os quesitos apresentando diferenças significativas com relação a testemunha. O tratamento com a inoculação de B. subtilis Bs10 apresentou maior MSPA nas mudas de alface e tomate, obtendo diferença significativa com relação a testemunha sem inoculação, sendo uma diferença superior, na alface com 21,67% a mais de MSPA comparando com a testemunha, e no tomate com 18,61%. Por tanto, de acordo com os resultados obtidos, o B. subtilis Bs10 é eficiente na promoção de crescimento de plantas de tomate e alface.
... Natural disturbances, climate change, and human activities often lead to changes or modifications in soil enzymatic activities (Gianfreda & Rao, 2008;Zhu et al., 2010) (Fig. 1). Additionally, soil microorganisms play a critical role in carbon (Cenkseven et al., 2017), nitrogen (Aka & Darici, 2005), and phosphorus (Barea & Richardson, 2015) cycling, as well as the mineralization of organic residues (Kocak & Darici, 2016). It is evident that microorganisms residing in the soil ecosystem are highly susceptible to changes in the soil environment and are regarded as early warning indicators for monitoring soil health (Kocak & Cenkseven, 2021;Kocak & Darici, 2022;Nielsen et al., 2002). ...
Soil enzymes have been recognized as crucial components of ecosystems since their initial report over a century ago. While enzymes in soil systems were initially used as descriptive parameters, they are now appreciated for their various properties in soil processes, microbial activities, and ecosystem responses to changes in management and climate. Invertase, an enzyme that plays a key role in the hydrolysis of sucrose into glucose and fructose, is present in microorganisms, plants, and animals. Biochar, a carbon-rich organic material obtained by , potentially leading to more sustainable plant production and reduced greenhouse gas emissions such as CO2 or CH4. Biochar can benefit soil microorganisms in numerous ways, including nutrient provision and protection from predators by adsorption in soil surfaces and pores. While the agricultural, economic, and practical applications of biochar have been extensively discussed in published books and book chapters, little information is available regarding the effects of biochar addition on soil invertase activity. The aim of this study was to investigate the impact of different biochar derived from various materials on invertase activity in soil based on the existing literature.
... 4,7,8,15 This process could possibly be favored by the accumulation of intracellular free Fe as a consequence of its competition with Al. 4,8 In acidic soils, naturally occurring toxic levels of Al usually coincide with scarce bioavailability of phosphorus (P) as a result of orthophosphate anions (Pi), the labile form of P assimilable by plants, forming inorganic complexes with Al and Fe oxides. 16,17 In addition, 30-60% of total soil P is integrated into complex organic molecules (soil organic P; Po), 18 which are not immediately bioavailable to plants. As a primary constituent of vital biomolecules and a key constituent of cellular processes, P is an indispensable macronutrient for all levels of life. ...
Aluminum (Al)-tolerant phosphobacteria enhance plant growth in acidic soils by improving Al complexing and phosphorus (P) availability. However, the impact of Al stress and P deficiency on bacterial biochemistry and physiology remains unclear. We investigated the single and mutual effects of Al stress (10 mM) and P deficiency (0.05 mM) on the proteome of three aluminum-tolerant phosphobacteria: Enterobacter sp. 198, Enterobacter sp. RJAL6, and Klebsiella sp. RCJ4. Cultivated under varying conditions, P deficiency upregulated P metabolism proteins while Al exposure downregulated iron-sulfur and heme-containing proteins and upregulated iron acquisition proteins. This demonstrated that Al influence on iron homeostasis and bacterial central metabolism. This study offers crucial insights into bacterial behavior in acidic soils, benefiting the development of bioinoculants for crops facing Al toxicity and P deficiency. This investigation marks the first proteomic study on the interaction between high Al and P deficiency in acid soils-adapted bacteria.
... Phosphorus (P) is the key limitation nutrient for tree growth in subtropical forests [1]. Although total soil P content may be sufficient [2], only small quantities of inorganic P-namely orthophosphate (H 2 PO 4 − and HPO 4 2− ) ions-can be directly absorbed by plant roots [3]. The dominant soil P pools, including low-solubility inorganic and highly complex organic P forms, can be transformed into orthophosphates by physical chemical reactions (i.e., dissolution and desorption) and biological activities (i.e., mineralization). ...
Although many studies have focused on the roles of soil microbes in phosphorus (P) cycling, little is known about the distribution of microbial P cycling genes across soil depths. In this study, metagenomic sequencing was adopted to examine the differences in the abundance of genes and microbial taxa associated with soil P cycling between organic and mineral soil in subtropical forests. The total relative abundance of inorganic P solubilizing genes was the highest, that of P starvation response regulating genes was second, and organic P mineralizing genes was the lowest. The soil organic carbon concentration, N:P ratio, and available P concentration were higher in the organic soil than the mineral soil, resulting in abundances of organic P mineralizing genes (appA and 3-phytase), and inorganic P cycling genes (ppa), whereas those of the inorganic P cycling genes (gcd and pqqC) and the P starvation response regulating gene (phoR) were higher in mineral soil. The four bacteria phyla that related to P cycling, Proteobacteria, Actinobacteria, Bacteroidetes, and Candidatus_Eremiobacteraeota were higher in organic soil; conversely, the three bacteria phyla (Acidobacteria, Verrucomicrobia, and Chloroflexi) and archaea taxa were more abundant in mineral soil. Therefore, we concluded that the distribution of genes and microbial taxa involved in soil P cycling differed among soil depths, providing a depth-resolved scale insight into the underlying mechanisms of P cycling by soil microorganisms in subtropical forests.
... Plant residues as poorly available Po can also be considerable P sources in agricultural ecosystems (Emsley and Hall, 1976). The immobilized P within the living soil microbial biomass (MBP) is also an important Po form in soils, typically representing about 5% of total P ( Barea and Richardson, 2015;White and Hammond, 2008). Similar to Pi, Po can also be bound to soil organic matter (SOM) or to metal ions (Matsushima et al., 2021). ...
Phosphorus (P) is a major limiting nutrient for plant growth implying an often-intensive competition between microorganisms and plants in the rhizosphere. Increasing the P availability in subsoils may help to mitigate potential future P fertilizer shortages and to overcome P limitations due to droughts, which mainly affect topsoils. Root exudates provide easily available carbon and energy sources for microorganisms to mobilize soil nutrients. Nonetheless, details regarding the distinct processes underlying P mobilization from various P sources (free vs. sorbed PO43−; low molecular vs. complex organic P, e.g. ATP vs. plant litter P) as affected by root exudates are poorly understood, especially in subsoils. This study aimed to identify the controlling factors and microbial processes regulating the availability of organic and inorganic P in top- and subsoils by 33P isotopic labeling. The focus was on the potential key role of root exudates in P mobilization. We found that microbial communities in top- and subsoils used high- and low-available mineral P to a similar extent, but that the subsoil communities were much more efficient in mobilizing and incorporating complex litter-derived organic P. This capability of subsoil communities was even enhanced when root exudates were present. Microbial activity and nutrient-mobilizing mechanisms (e.g., P-related enzymes) clearly increased by root exudate addition, an effect that was generally higher in sub-than in topsoils. We conclude that subsoil communities are well capable of mobilizing and using complex organic P sources, especially if root exudates accelerate overall activity and P cycling. Thus, high root exudation is highly relevant for crops, which depend on subsoil nutrients and litter-derived P. Accordingly, detritusphere P, e.g. in subsoil root channels, is likely to be plant-available because of exudate-induced microbial P (re-)cycling processes.
... PSMs are typically regarded as eco-friendly P fertilisers for raising agricultural output since they may mediate the basic soil P forms and orthophosphate levels. Soil microorganisms in particular have the capacity to liberate plant-accessible P from scarcely present forms of soil P through the solubilization and mineralization of inorganic and organic P, respectively (Barea and Richardson 2015;Whitelaw et al., 1999). Microorganisms significantly increase nutrient uptake and crop sustainability (Hassan and Nawchoo 2022). ...
Four effective phosphatase and phytase-producing fungi, Aspergillus candidus, Aspergillus ustus, Curvularia lunata, and Phoma species, were selected for their native P mobilisation under field conditions, using clusterbean and pearl millet as test crops. The main aim was to increase agro ecosystem productivity and get rid of the negative effects of chemical fertilisers. The inoculation of selected fungi resulted in a significant enhancement in the grain yield (16-28%), plant biomass (10-57%), straw yield (19-38%), and plant P absorption (2-10%) in clusterbean. There was between 6 and 61 % more in acid phosphatase activity, between 9 and 66 % higher in alkaline phosphatase activity and between 13 and 50 % additional phytase activity under inoculated plots of clusterbean as compared to the uninoculated (control) plots. Due to increased phosphatase and phytase enzyme activity of inoculated fungi, pearl millet saw improvements in grain yield, plant biomass, straw yield, and plant P uptake of 12-24%, 2-54%, 18-40%, and 3-12%, respectively. In pearl millet, 10-48%, 10-49%, and 6-47% improvement in acid phosphatase, alkaline phosphatase and phytase were recorded, respectively, at different growth periods compared to control. Among the four fungus examined, Phoma species was found to be the best P mobilizers, both under pearl millet and clusterbean. Irrespective of fungi and crops, P mobilisation from mineral sources was often higher than that from organic and phytin sources. Overall 40 to 85% more microbial than plant involvement was seen in the mobilisation of various P components. In general, 10.6-21.3% more mineral P and 11.5-19.2% more phytin P was hydrolyzed in clusterbean compared to pearl millet. Selected fungi are especially important for crop sustainability because they are effective under low phosphorus availability and when nutrients are bonded to organic matter and soil particles.
... microorganisms (Tian et al., 2021) because they take parts a key role in a number of processes that control P availability and transformations. Soil microorganisms have the potential to liberate plant-accessible P by the way of solubilization and mineralization of inorganic and organic P, respectively, from the sparsely available forms of soil P ( Barea and Richardson 2015;Whitelaw et al., 1999). The uptake of nutrients and crop sustainability are greatly improved by microorganisms (Hassan and Nawchoo 2022). ...
Four phosphate solubilizing/mobilizing fungi (Aspergillus candidus, Aspergillus ustus, Curvularia lunata and Phoma species) were isolated and tested for their population growth and efficiency towards phosphorus solubilization and mobilization from the native soil under both sterilised and non-sterile soil conditions after taking wheat as a test crop. The study is absolutely necessary in the present situation to know the exact contribution of plants and inoculated microorganisms for the mobilization of P from the native sources. The plant available phosphorus (P) in the experimental soil was less than 1% and among the 29% of organic phosphorus (Po), 70% was present as phytin form in the soil. The fungal population increased with time and a maximum of 15 to 16 times (under sterilized condition) and 12 to 13 times (under non-sterilized soil) was observed within four-week period. In sterilised soil, mobilization of plant unavailable P was higher, primarily because of an increase in the population of inoculated fungi. A positive influence on acid phosphatase and phytase activity was observed under wheat after inoculation, while alkaline phosphatase activity was not significantly affected in the test plants. In general, one third of the total plant-unavailable P was hydrolyzed by plants, whereas the contribution of inoculated fungi was observed at two-thirds. Plant contribution gradually increased with the plant growth period; maximum mineral and organic P hydrolysis generate by the plant sources was seen between 7 and 21 days. In general, more phytin P was hydrolyzed after 28 days of plant growth. The organic P was exhausted more than mineral P as well as contribution from microbial sources for mobilization of different P fractions was much more (52 to 87% of min-P, 53 to 87% of org-P and 50 to 80% phytin-P) than plant contribution (13 to 48%, 13 to 43% and 20 to 50% for min-P, org-P and phytin-P, respectively). The inoculation effect was more in an increase in plant biomass, root length, and plant P concentration. Among the four tested fungi, Phoma species was more efficient in disintegrate org-P as phytin, while Aspergillus ustus was establish to be the most efficient in min-P hydrolysis and enhance P nutrition for wheat plant. Our result clearly demonstrated the exact contribution from the efficient microorganisms for P mobilization from the different native P sources.
... PSB can produce or release either acidic or alkaline phosphatases to convert organic P (P o ) into the soluble inorganic form (P i ) to immobilize Pb and/or augment plant growth ( [219]; recently reviewed by [9,18,25]): ...
The increasing environmental and human health concerns about lead in the environment have stimulated scientists to search for microbial processes as innovative bioremediation strategies for a suite of different contaminated media. In this paper, we provide a compressive synthesis of existing research on microbial mediated biogeochemical processes that transform lead into recalcitrant precipitates of phosphate, sulfide, and carbonate, in a genetic, metabolic, and systematics context as they relate to application in both laboratory and field immobilization of environmental lead. Specifically, we focus on microbial functionalities of phosphate solubilization, sulfate reduction, and carbonate synthesis related to their respective mechanisms that immobilize lead through biomineralization and biosorption. The contributions of specific microbes, both single isolates or consortia, to actual or potential applications in environmental remediation are discussed. While many of the approaches are successful under carefully controlled laboratory conditions, field application requires optimization for a host of variables, including microbial competitiveness, soil physical and chemical parameters, metal concentrations, and co-contaminants. This review challenges the reader to consider bioremediation approaches that maximize microbial competitiveness, metabolism, and the associated molecular mechanisms for future engineering applications. Ultimately, we outline important research directions to bridge future scientific research activities with practical applications for bioremediation of lead and other toxic metals in environmental systems.
... It mainly includes two parts, one is that a set of organic acids (e.g. gluconic acid, citric acid and formic acid) are released by soil microorganisms to solubilize inorganic P forms (Yao et al., 2018), and the other is that a series of microbe-derived enzymes (e.g., phosphatase, phytase and carbon-phosphorus lyase) could mineralize organically fixed P (Barea and Richardson, 2015). Moreover, microorganisms harbor efficient P uptake and transport systems, assimilating inorganic P not only under the P-low but also P-rich environments (Hsieh and Wanner, 2010). ...
Microorganisms play essential roles in soil phosphorus (P) cycling and the regulation of P bioavailability, however, genetic information on microbial P cycling in response to nutrient inputs is largely unclear. Here, metagenomic sequencing and genome binning were used to investigate microbial functional traits under chemical and organic fertilization in three long-term field experiments across black soil region of Northeast China. The results revealed that manure amendments strongly affected microbial P cycle-related functional gene patterns, which were significantly and positively correlated with the contents of soil total P (TP) and available P (AP). Manure addition directly increased soil AP concentrations, and indirectly acted through the alterations of microbial functional genes involved in soil P cycling. Specifically, manure amendments consistently decreased abundances of phnC gene and increased gene abundances of phnP, opd, and phoN across three locations, suggesting the potentially inhibition of soil microbial P-uptake and transport and the promotion of soil microbial organic P-mineralization. Manure addition promoted microbial inorganic P-solubilization by enriching the ppa, gcd, and pqqC genes at two out of three locations, while chemical fertilizer (CF) addition slightly stimulated the functional gene abundances involved in microbial P-uptake and transport and P-starvation response regulation. In addition, soil AP content was negatively correlated with the phnC gene abundance but positively correlated with the gene abundances of opd and phoN. Moreover, 23 metagenome-assembled genomes (MAGs) were reconstructed covering all soil samples, all of which contained the phnC gene with the copy numbers varying from 1 to 19. Nevertheless, only bin44 had a negative correlation with soil AP (r = − 0.361, P = 0.030) and could be considered as a potential indicator regulating microbial P-uptake and transport. Taken together, manure inputs positively accelerated microbial P-transformations, which was beneficial for the establishment of efficient P management strategies in sustainable-intensive agriculture.
... The AMF symbiosis is based on the bidirectional exchange of nutrients . Basically, the fungus improves the host plant nutrition via an extensive mycelium network proliferating in the soil, while the plant provides the energy, from photosynthates to the fungus (Bago et al. 2002;Barea and Richardson 2015). In this context, several studies have also shown that AMF favor the adaptation of host plants exposed to abiotic stressors (Bissonnette et al. 2010;Janoušková and Pavlíková 2010), including phytotoxic Al 3+ , one of the main constraints for crop production in acidic Andisols as here targeted. ...
Soil is one of the main reservoirs of biodiversity on earth due to its physical, chemical, and microclimatic heterogeneity; in particular, it harbors a great diversity of microbial communities. Changes in land uses for crop production, mainly those that involve intense agricultural management, threaten soil diversity, compromising global ecosystem functioning and services. In this chapter, we give an up-to-date overview of the effect of two no-till agricultural practices (crop rotation (CR) versus soybean monocropping (MC)) on arbuscular mycorrhizal fungi (AMF) communities by gathering our data of five geographical locations of East-Central Argentina. The diversity was described considering AMF classification and functioning based on the morphological traits and ontogeny of spores. In addition, we analyzed our data considering three taxonomic categories: morphospecies, families, and orders. Fifty-nine AMF morphospecies were identified throughout the five geographical locations, and CR soils showed the highest AMF richness and spore density and the lowest evenness. Funneliformis mosseae and Glomus sp.4 morphospecies and Glomerales were significant indicators for CR. For MC, Acaulosporaceae and Diversisporales were significant indicators. Soil variables influenced the relative abundance of AMF depending on the family and order. Percentage of organic carbon and nitrogen was positively associated with CR and negatively with MC. Overall, no-till agricultural practices showed differences in their soil AMF communities and chemical properties, and management systems that include practices based on CR promote greater richness of AMF morphospecies.KeywordsGlomeromycotina Agroecosystems Taxonomic groups Morphospecies Land uses
... The AMF symbiosis is based on the bidirectional exchange of nutrients . Basically, the fungus improves the host plant nutrition via an extensive mycelium network proliferating in the soil, while the plant provides the energy, from photosynthates to the fungus (Bago et al. 2002;Barea and Richardson 2015). In this context, several studies have also shown that AMF favor the adaptation of host plants exposed to abiotic stressors (Bissonnette et al. 2010;Janoušková and Pavlíková 2010), including phytotoxic Al 3+ , one of the main constraints for crop production in acidic Andisols as here targeted. ...
Dipterocarpaceae is an important family of trees in Paleotropics that form ectomycorrhizal (EcM) symbiosis. In 1995, a Neotropical species, Pseudomonotes tropenbosii, was found in the Amazonian region in Colombia. Due to the EcM association of multiple species of dipterocarp trees in Asia and Africa, we hypothesized that P. tropenbosii might have EcM symbionts as well. In this study, 90 species of EcM fungi of P. tropenbosii were documented from aboveground/sporocarps (79 spp.) and belowground/root-tip samples (2 spp.). The EcM fungal community was dominated by the genera Clavulina (13 species), Russula (9 species), and Craterellus, Coltricia, and Cortinarius (6 species each). Differences in the diversity and richness of species across sites were found, independent of the abundance of P. tropenbosii and the proximity of the sites, suggesting that environmental differences among sites are important in structuring the EcM fungal communities. About half of the ECM fungal species of P. tropenbosii coexisted with species of Fabaceae and Pakaraimae dipterocarpacea (Cistaceae) occurring in geographically remote neotropical lowland rainforests. Noteworthy is the diversity of Clavulina found that is represented by 12 species of which 9 were described from Fabaceae-dominant forests in Guyana, unraveling a broad host diversity and widespread distribution of these EcM fungi. The EcM status of P. tropenbosii suggests that a Gondwana ancestor of the Dipterocarpaceae already presented the mutualistic relationship with EcM fungal taxa; however boreotropical migration or transatlantic dispersal has been also proposed, but this remains debated. More research is needed to fully understand the distribution patterns of EcM fungi in this tropical region and their role in nutrient cycling, including carbon sequestration, and its importance for plant distribution.
... Diverse bacterial strains such as Herbaspirillum, Azospirillum, Enterobacter, Azotobacter, Acetobacter and Pseudomonas increase the developmental reactions within the plant by either increasing the bioavailability of both micro and macro nutrients (e.g. iron, zinc and phosphorus), production of the phytohormones or by fixing atmospheric nitrogen (Ahmad et al., 2008;Barea and Richardson, 2015;Arya et al., 2020;Ummara et al., 2021;Nawaz et al., 2020). PGPR associated with cereals has received a greater interest in recent years and different studies noticeably established the positive and valuable effects of PGPR on overall growth and development of various plant species (Mehnaz et al., 2010;Zhang et al., 2012;Baliah et al., 2016;Teng et al., 2018;Chawngthu et al., 2020;Khanna et al., 2019a,b,c). ...
Two billion people worldwide take rice (Oryza sativa L.) as a staple food. Phosphorus (P) and Nitrogen (N) are the major requirements of rice; although these are available in limited concentrations within rice growing regions. Among different types of Plant growth-promoting rhizobacteria (PGPR), Phosphate solubilizing rhizobacteria (PSRB) constitute an important class. These are known for plant growth promotion by enhancing P and N uptake. PSRB are nowadays used as biofertilizers to restore the soil health. Under the present investigation identification, characterization and optimization of phosphate solubilizing activity of these microbes at different pH, temperature and salt concentrations was carried out. Thirty-seven isolates were recovered from different regions of rice rhizosphere on Pikovskaya (PVK) agar among which 15 isolates were recovered from R.S. Pura, 12 isolates from Bishnah and 10 isolates were recovered from Akhnoor sector of Jammu, India. A prominent halo zone of clearance was developed around the colonies of 12 different isolates, indicating phosphate solubilization activity. Four distinct isolates were amplified, cloned and sequenced for taxonomic identification using 16S primers. The results indicated that PS 1, PS 2, PS 3, PS 4 were related to Pseudomonas aeruginosa, Bacillus subtilis strain 1, B. subtilis strain 2, B. subtilis strain 3, respectively. These strains when grown at a wide range of ecological factors showed maximum growth at pH between 6.8-8.8, temperature between 28°C-37°C and salinity between 1% - 2%. Screening for phosphate solubilization activity revealed that the halo zone diameter formed by these isolates extended from 2.1 to 3.2 mm. The phosphate solubilizing efficiency (SE) ranged from 35.4 to 50.9 with highest value of 50.9 by PS4 and maximum P solubilization of 10.22µg/ml was recorded by PS4 at 7th day. Phosphate solubilization activity of these identified PSRB strains can be utilized and explored in the rice growing belts of Jammu region which are deficient in phosphorus. MIC value for zinc sulphate heptahydrate in 12 isolates varied from 1 mg/ml to 6 mg/ml. Phosphate solubilization activity and MIC of these identified PSRB strains can be utilized and explored in the rice growing belts of Jammu region which are deficient in phosphorus.
... PGPRs for the solubilization of precipitated plant phosphates were registered as a possible plant growth support mechanism in field conditions (Verma et al. 2001;Guo et al. 2015). The reason for the solubilization of inorganic phosphorus might be the organic acid synthesis by rhizospheric microbes (Barea and Richardson 2015). The commercial use of PGPB phosphate solubilization was unfortunately limited due to variable results (Ghosh et al. 2014). ...
Over the last century, the effective application of organic fertilizers, herbicides, and
pesticides should not be overlooked in an agricultural environment. They help plant
growth initially while having a long-term negative impact. This practice not only
affects the land and its inhabitants but also threatens people’s lives through the food
chain. The soil has become extremely infertile and unproductive due to the rise in
soil pollution, condition of climate, soil pathogens, and extensive land overuse.
Food insecurity and the increasing population are evident at the low agro-yield. To
achieve auto-suffciency, a wide understanding of the microbial interaction and its
mechanism of action must be made, particularly in the tropic world, to be essential
to scientifc knowledge.
... fixation of nitrogen, phosphate solubilization, phytate mineralization, potassium solubilization and micronutrients. They also inhibit harmful microbes and other insects via different strategies like production of antimicrobial compounds, through competition for nutrients, creating infection among harmful insect populations (Barea et al. 2013;Barea and Richardson 2015). The rhizospheric soil contains an array of microorganisms, which are categorized into beneficial and deleterious microorganisms based on their effect on soil quality, crop growth and ultimately productivity (Jat et al. 2015). ...
The soil is a living entity and its significance and functions are irrefutable. Organisms present in the soil play a major role in sustainable soil health management. Current agrochemical-based nutrient management strategies can fulfil the demand of food to feed 7.8 billion humans living on earth, however, potential uses of agriculturally important microbial bioresources have been ignored, which can lead to compromise towards soil health and agro ecosystem sustainability. Major soil functions like nutrient and organic matter recycling, fertility, soil reclamation and ultimately tiny soil creatures called microbes, which comprise major portion of soil biota, manage soil and ecosystem health management. ABMs (Agriculturally beneficial microbes) include bacteria, actinobacteria, fungi and others which live in a mutualistic relationship along with plants (symbiotic/associative/free living/ endophytic) and make the nutrients available, play a major role in organic matter decomposition, produce phyto-hormones, phytoremediation and act as biocontrol agents for plant pests and diseases. These ABMs are supposed to be present in the soil, but looking to the sustainability and soil health, to enhance nutrient use efficiency, it is desirable to elevate their strength through direct application or following different agronomic interventions that enhance their abundance and activity. This review details the role of rhizospheric microorganisms and soil organic matter in soil quality management.
... Phospho-biofertilizers mainly contain bacteria and fungi that make available insoluble phosphorus to plants (Zhang et al., 2017). Several soil bacteria and some fungal species are able to solubilization of insoluble phosphate in the soil by secreting organic acids (Barea and Richardson, 2015), (Dissanayaka et al., 2018). These acids reduce soil pH and dissolve insoluble phosphate forms (Intorne et al., 2009). ...
Soil management techniques today are based on the chemical fertilizers used, which poses a serious menace to the environment and humans, and finding alternatives to chemical fertilizers is increasingly being felt. An ideal alternative to chemical fertilizer is biofertilizers that are eco-friendly and do not pose any danger to humans or animals. Biofertilizers use beneficial microbes that have multiple
properties to improve plant growth and soil characteristics. Beneficial microbes in biofertilizers increase crop production, soil fertility, help the plant in abiotic and biotic stress. There are many reports that indicate the decrease in chemical fertilizer usage along with the biofertilizer application. Beneficial microbes in biofertilizers use mechanisms that increase root growth and development and increase crop production. Mechanisms such as atmospheric nitrogen fixation, phosphorus solubilization, potassium releasing, siderophore production to increase the bioavailability of microelements such as iron and zinc, production of various phytohormones, production of ACC deaminase enzyme, production of anti-pathogenic agents such as antibiotics, hydrogen chloride, and lytic enzymes. The preparation and production of biofertilizers require knowledge and experience, and the production process of these fertilizers is very sensitive. Recently, the variety of these fertilizers has increased and one of the important points for success in the production of these fertilizers is the selection of a powerful microbial strain as well as a suitable carrier for the transmission of this microbe and its establishment in the rhizosphere. To the development of the biofertilizer production, and commercialize them, at the first need more studies and research to identification and isolation the top strains of useful PGP rhizobacteria, and furthermore development of advanced production technologies as well as establish the quality control section in the biofertilizer production process. The production of biofertilizers with promoting plant growth characteristics is one of the important goals of sustainable agriculture.
... Meanwhile, using microorganisms capable of dissolving phosphate is one of the important strategies in sustainable agriculture (Shen et al., 2011). Screening and qualitative testing of the ability to dissolve phosphate in microorganisms are performed by screening in a plate medium (Barea & Richardson, 2015). ...
Nowadays the negative effects of chemical inputs used in agriculture are obvious to everyone. Improving the quality and quantity of crops without adverse effects is one of the major challenges for agricultural researchers. A confident alternative to chemical fertilizers is biofertilizers. Plant growth-promoting rhizobacteria (PGPR) prepped in the form of microbial inoculants and used in agriculture can stimulate plant growth through various mechanisms. The biofertilizers if properly prepared and used scientifically, can have many positive effects, including reducing the cost of agricultural production and increasingenvironmental and human health. To biological products, quality control is an essential process including various stages from production to consumption.
Quality control consists of operations that can be performed in the laboratory and the field. In the present study, we investigated the four biofertilizers belonging to two companies. Biofertilizers' quality control in this work included bacterial viable cell numbers, bacterial genus and strains, and some plant growth promoting abilities such as strains’ ability in solubilizing insoluble phosphate, auxin, and siderophore production and also potassium releasing ability. In this chapter, different aspects of biofertilizers and their assessment and quality control have been studied.
... The PGPR must have the capacity to survive and multiply in rhizosphere microhabitats in a very less time in comparison to the other native microbes and to express the beneficial promotional activities for plant growth (Martinez-Viveros et al., 2010). N 2 -fixation, phosphate mobilization, and the release of other nutrients to the soil are the basic processes involved in PGPR regulated nutrient cycles (Richardson et al., 2009;Barea and Richardson, 2015). The other major group of mutualistic microbial symbionts are the AM fungi that are known to establish mycorrhizal associations with the roots of most plant species (Smith and Read, 2008;Vander-Heijden et al., 2015). ...
Microbial biotechnology is well established branch of biotechnology and which include the application of microorganisms with emerging modern techniques of biotechnology for the development of sustainable agriculture. Microbial biotechnology deals with the manipulation through genetic engineering of living organisms or their components to produce valuable products for various applications. Classical agriculture farming equipment and practices are reaching their limits of effectiveness in increasing agricultural productivity. Chemical fertilizers, pesticides, herbicides and other inputs have increased agricultural production, but simultaneously cause adverse effects on soil productivity and environmental quality. The broad application of microbes in sustainable agriculture is due to the genetic dependency of plants on the beneficial functions provided by symbiotic cohabitants. Therefore, microbial biotechnology and its applications in development of sustainable agriculture and environmental health are attracting the attention of microbiologists and biotechnologists. India’s large population placing more pressure on natural resources like soil and water, and affecting our ability to produce sufficient food, feed and fibre. Recently developed biotechnologies can provide appropriate new tools to find out the solutions of different specific problems of sustainable agriculture. The aim of this study was to conclude the diversified useful applications of microbial biotechnology for the development of sustainable agriculture using the different tools and techniques such as biofertilizers, biopesticides and value additions in crops.
... Microbiota in soil systems as cyanobacteria, bacteria and fungi with other soil organisms help in efficient nutrient cycling of P through mineralization and P immobilization (Barea and Richardson 2015). P mobilization from organic and AU3 Fig. 1.1 Various mechanisms of P recovery from wastewater with emphasis on algal route 1 Phosphorus Capture, Immobilization and Channeling Through Algae… inorganic P pools are carried out through enzymatic mineralization and insoluble P solubilisation respectively through various mechanisms i.e. carboxylates, phosphatases; exuding protons to release inorganic labile phosphates (Sharma et al. 2013) as provided in Fig. 1.2. ...
Excessive use of phosphorus (P) based fertilizers for improved agricultural productivity has resulted in nutrient enrichment and consequent deterioration of surface and ground waters. Naturally, available soil microbes in an agricultural set-up are capable of mineralization of organic P and/or solubilisation of inorganic P thus making it bioavailable to the crop systems. As an alternative to conventional P based fertilizers, wastewater rich in nutrients can be cheap and economic P sources ensuring phosphorous recycle and reuse. However, the treatment of these waters to check pathogens, heavy metals and other toxicants; conveyance and storage are practical constraints that limits the usage of wastewaters directly to croplands. Wastewater grown algae as proficient biofertilizer can be potentially used to immobilize P and channelize P to croplands. Such algal biomass abundantly growing in natural waters as well as in treatment ponds can be rich sources of nutrients due to their higher P uptake abilities, growth rate and productivity. Although there are huge opportunities for using algae as a bio-filter to recover P from wastewater streams. However, their use for tapping valuable P with present day technologies are still evolving and are in infancy. Efforts on understanding the mechanism of P uptake, immobilization in algal cells and subsequent P transport to agricultural soil systems are important. This can provide global solutions in stocking wastewater P and its sustainable reuse as algal-based P rich biofertilizer.
... Root phenes that expand the volume of the rhizosphere, such as root hair formation, and that position roots in P-rich domains, are more appealing as selection criteria for root exudates than are the exudates themselves, by positioning exudates in the most productive soil domains (Lynch, 2011). Microorganisms capable of mobilizing P, especially through solubilization, are being used commercially as bioinoculants, with mixed and often limited success, which may again be due to the chemical and microbial complexity and diversity of agricultural soils (Barea & Richardson, 2015). ...
Nutrient‐efficient crops are a solution to the two grand challenges of modern agriculture: improving food security while reducing environmental impacts. The primary challenges are (1) nitrogen (N) and phosphorus (P) efficiency; (2) potassium (K), calcium (Ca), and magnesium (Mg) efficiency for acid soils; and (3) iron (Fe) and zinc (Zn) efficiency for alkaline soils. Root phenotypes are promising breeding targets for each of these. The Topsoil Foraging ideotype is beneficial for P capture and should also be useful for capture of K, Ca, and Mg in acid soils. The Steep, Cheap, and Deep ideotype for subsoil foraging is beneficial for N and water capture. Fe and Zn capture can be improved by targeting mechanisms of metal mobilization in the rhizosphere. Root hairs and phenes that reduce the metabolic cost of soil exploration should be prioritized in breeding programs. Nutrient‐efficient crops should provide benefits at all input levels. Although our current understanding is sufficient to deploy root phenotypes for improved nutrient capture in crop breeding, this complex topic does not receive the resources it merits in either applied or basic plant biology. Renewed emphasis on these topics is needed in order to develop the nutrient‐efficient crops urgently needed in global agriculture.
... In the rhizosphere and mycorhizosphere, microorganisms involved in N or P cycling are mainly centered on N2-fixers, P-mobilizers, and AM fungi. Barea and Richardson (2015) indicated that the capacity of some microorganisms to mobilize P from poorly available sources of this nutrient can help plant P nutrition. Barea (2015) indicated that bacteria belonging to diverse genera, collectively termed "rhizobia," can fix N 2 in mutualistic symbiosis with legume plants, while others (actinomycetes), belonging to the genus Frankia, form N 2 -fixing nodules on the root of the so-called "actinorrhizal" plant species. ...
... In the rhizosphere and mycorhizosphere, microorganisms involved in N or P cycling are mainly centered on N2-fixers, P-mobilizers, and AM fungi. Barea and Richardson (2015) indicated that the capacity of some microorganisms to mobilize P from poorly available sources of this nutrient can help plant P nutrition. Barea (2015) indicated that bacteria belonging to diverse genera, collectively termed "rhizobia," can fix N 2 in mutualistic symbiosis with legume plants, while others (actinomycetes), belonging to the genus Frankia, form N 2 -fixing nodules on the root of the so-called "actinorrhizal" plant species. ...
Organic Farming
Global Perspectives and Methods
2019, Pages 1-16
Chapter 1 - Contribution of Organic Farming Towards Global Food Security: An Overview
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Terence EpuleEpule
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https://doi.org/10.1016/B978-0-12-813272-2.00001-X
Abstract
This chapter verifies the contributions of organic and inorganic farming within the context of global food security. This chapter is based on data obtained from a synthesis of existing literature obtained through Google Scholar, the Scientific Citation Index (SCI) database, and ISI Science. The first part of this work explores the conceptual issues around organic and inorganic farming; this is followed by a synthesis of the potential effects of organic and inorganic farming on global food security and finally the effects of organic and inorganic farming on food security in Africa. The results from this synthesis show that organic farming can indeed reduce global food insecurity but there is a limitation to the extent to which this can be obtained as it has been observed that there is a threshold beyond which a combination of organic and inorganic farming options produce the best effects and organic farming alone cannot sustain production. A system dependent on organic farming is rather complex and may warrant that: the current scale of arable production be expanded while the farmers need to be trained on how to valorize the advantages of organic farming especially in Africa. Understanding how to make use of other components of agro-ecology is mandated. The weaknesses of conventional farming must be evaluated in detail by setting up pilot agro-ecology farms and comparing their yields with conventional farms around the world in general and in Africa in particular. Most of the studies consulted recommend either inorganic farming or a combination of inorganic and organic. Therefore, as a way forward, farmers must be given the opportunity to take decisions on which way to go and this should be based on the availability of sufficient information on the economic, social, and environmental sustainability implications of their actions. In addition, the markets for farm inputs should become more competitive and efficient, and this will trigger lower prices and better services to the farmers.
... In the soil, P is most often found in apatite, which is a group of phosphate minerals. Apatite wear causes the release of phosphate anions in low amounts (1% of total soil phosphorus) (Barea and Richardson, 2015). Phosphate anions participate in reactions that limit their availability to plants, forming compounds (e.g., several forms of tricalcium phosphate, iron phosphate or aluminum phosphate) in the form of salts in solution, crystalline salts or salts adsorbed by soil colloids. ...
... The high prices of nitrogen fertilizers and their low use efficiency in rice fields (Choudhury and Khanif, 2004) have encouraged agronomists and producers to evaluate the use of alternative nutrient sources that are both sustainable and environment-friendly. Plant growth-promoting rhizobacteria (PGPR) colonize the rhizosphere of monocots (Fibach-Paldi et al., 2012;Kazi et al., 2016) and dicots (Jalilian et al., 2012) and stimulate plant growth by means of nitrogen fixation (Olivares et al., 2013), production of phytohormones (Lugtenberg, 2015) and siderophores (Bakker et al., 2013), and phosphorous solubilization (Barea et al., 2015). Among PGPRs, Azospirillum species are aerobic heterotrophs bacteria that fix N non-symbiotically in the rhizosphere of plants from the Poaceae family such as rice (Fibach-Paldi et al., 2012) and wheat (Kazi et al., 2016). ...
Herbicides, as a major part of weed control strategy in paddy fields, have different impact on growth and activity of soil-beneficial bacteria such as Azospirillum species. A field experiment was conducted at Sefid Rood Livestock and Agricultural Company, northern Iran, to investigate the possibility of chemical weed control in paddy fields inoculated with Azospirillum lipoferum. The experiment was designed in a factorial arrangement based on a randomized complete block with three replicates. The factors were Azospirillum application (inoculation with or without Azospirillum lipoferum) and weed management regime (butachlor application with supplementary hand-weeding, bensulfuron methyl application with supplementary hand-weeding, combination of butachlor and bensulfuron methyl application with supplementary hand-weeding, hand-weeding at 15, 30, and 45 days after transplanting, and no weeding [not weeded during the rice-growing period). The results showed that plants inoculated with A. lipoferum produced 19% higher grain yield compared to plants that were not inoculated. The highest grain yields were recorded for plots treated with butachlor with supplementary hand-weeding (4,512 kg ha-1) and for those treated with a combination of butachlor and bensulfuron methyl with supplementary hand-weeding (4500.5 kg ha-1). The lowest yield (3494.3 kg ha-1) was recorded for weedy plots. No significant interaction was detected between A. lipoferum application and weed management regime for grain yield, indicating that the herbicides had no adverse effect on the efficiency of A. lipoferum in promoting growth and grain yield of rice. There was no significant difference in the dry weights of weed between inoculated and non-inoculated plots. The dry weights of weed in hand-weeded and herbicide-treated plots were significantly lower than that of the weedy plot. In conclusion, the result of this experiment confirms the possibility of chemical weed control in paddy fields inoculated with A. lipoferum.
... Soil microorganisms are key regulators in soil P mobilization and transformation because they can enhance soil P availability through inorganic P solubilization and organic P mineralization, which is controlled by the regulation of P-cycling genes and expression of phosphatases (Stout et al., 2014(Stout et al., , 2016. Bacteria and fungi isolated from plant rhizospheres have been shown to solubilize various inorganic P pools and hydrolyze organic P ( Barea and Richardson, 2015). Under Pdeficient conditions, microorganisms have been shown to activate (or deactivate) diverse P-cycling genes and express microbial phosphatase enzymes to induce mobilization of not readily available P pools (Richardson and Simpson, 2011). ...
Microorganisms mobilize phosphorus (P) from soil and make it available for plants. However, the role of microbial activity in soil P dynamics especially among different P pools is poorly understood largely due to methodological limitations. In this study, we analyzed the oxygen isotope ratios in phosphate (δ18OP) of sequentially extracted inorganic P (Pi) pools (H2O-Pi, NaHCO3-Pi, NaOH-Pi, and HCl-Pi) in a long-term agricultural research field in Henan, China with different fertilization histories and coupled with soil enzyme activity and P-cycling bacteria gene abundance studies. Results showed the dominant enzymes were alkaline phosphatase (APase) and phosphodiesterase (PDE), and the functional genes for P-cycling were bpp, cphy, phoX and pqqC. After long-term P fertilization, the δ18OP values of H2O-Pi, NaHCO3-Pi and NaOH-Pi pools approached to or achieved equilibrium, suggesting that the externally applied P was actively mobilized and cycled by soil microorganisms and speciated into different P pools. Based on the extent of isotope excursion among different Pi pools, the equilibrium fractionation oriented the source signature in the NaHCO3-Pi and NaOH-Pi pools, and HCl-Pi pool could be derived from P fertilizer but through multistep reactions, and mixed with the HCl-Pi from rock weathering product, which constituted HCl-Pi pool in the non-P treatments. Overall, the long-term P fertilization especially the balanced fertilization with nitrogen (N), P and potassium (K) was found to be beneficial for extensive utilization of soil P with abundant biological uptake and cell-internal Pi cycling. Variation partitioning analysis (VPA) indicated that the expression of functional genes may be stimulated to mobilize soil P under specific P pools distribution in this alkaline environment. Overall, our findings provide new insights to understand the roles of microbial activities in soil P biogeochemistry that are useful for agricultural P sustainability.
... Directly, rhizobial isolates synthesize many plant growth hormones e.g. auxins (Zahir et al., 2010), cytokinins (Senthilkumar et al., 2009), abscisic acid (Boiero et al., 2007) and gibberellins (Boiero et al., 2007) and secrete many other chemicals beneficial to plant growth such as siderophores (Huang and Erickson, 2007), exopolysaccharides Hussain et al., 2014a), ACC-deaminase (Duan et al., 2009), phosphatases (Afzal and Bano, 2008), phosphohydrolases (Gugi et al., 1991), phytase (Glick, 2012), etc. Rhizobia also enhance availability to the plant by mobilizing the nutrients in the soil and improving the soil structure (Barea and Richardson, 2015). Indirectly, rhizobia improve plant health by improving the self-defense of plant through induction of systemic resistant (Reddy, 2013) against harmful insects, pathogens, diseases and viruses (Huang and Erickson, 2007). ...
Salinity is one of the major factors which affect overall food production of the world, especially in arid and semi-arid regions. Present study was conducted to evaluate the effectiveness of four [two from chickpea (CRM-7 and CRM-9) and two from lentil (LMR-5 and LMR-10)] different strains of rhizobia individually as well as their consortium for reducing the effect of salinity on the growth and yield of maize in pot experiment under wire house conditions. Salinity stress negatively affected the growth, yield, quality parameters and chlorophyll contents of maize. However, rhizobial inoculation significantly reduced the adverse effects of salinity. Multi-strain rhizobial inoculation proved better approach than sole rhizobial inoculation. Improvement in plant height (34%), grain yield (49%), cob length (67%) and weight (25%), relative water content (57%), crude protein (34%), quality parameters N (34%), P (36%) and K (36%) in grains, and chlorophyll contents (37, 37 and 46% in chlorophyll a, b and carotenoids, respectively) was observed by consortial inoculation (LMR-5, LMR-10, CRM-7 and CRM-9) compared to unstressed un-inoculated control at 8 dS m⁻¹. Among separate inoculation, chickpea rhizobial isolates performed better than lentil rhizobial isolates in inducing salinity tolerance in maize. It can be suggested that rhizobium consortium has better potential to promote growth and yield of maize than separate use of these strains. However, site specific field evaluation is required to confirm capability of consortial inoculant to get maximum benefit in terms of better growth and yield.
... Organic phosphates are formed primarily by biological processes. They are contributed to sewage by body wastes and food residues, and also may be formed from orthophosphates in biological treatment processes or by receiving water biota (76,77).Phosphorus is essential to the growth of organisms and can be the nutrient that limits the primary productivity of a body of water. In instances where phosphate is a growth-limiting nutrient, the discharge of raw or treated wastewater, agricultural drainage, or certain industrial wastes to that water may stimulate the growth of photosynthetic aquatic micro-and microorganisms in nuisance quantities. ...
Science the ground water quality is important for drinking and other applications and given that this area has a dry climate and drinking water supply by transferring from other cities,due to far distance,is difficulties. Considering to underground water resources in this area will be reasonable and inevitable. In this study groundwater resources quality of Sistan and Baluchistan with determine and evaluation important chemical parameters of Sulfate,Phosphate,Calcium,Sodium,Magnesium,Potassium,Chloride ions and Nitrate ions was reviewed. For this 357 water samples at the 2015 collected from designated wells in the area and transported to laboratory according to standard methods and analyzed.The Result showed that maximum concentration of Calcium in Konarak with 136 mg/l,Potassium in Konarak with 8.38 mg/l,Potassium in Konarak with 8.38 mg/l,Sodium in Zahedan with 416 mg/l,Chloride in Zahedan with 410 mg/l,Nitrate & Nitrate in Iranshahr with 15 mg/l,Phosphorus in Zahedan with 0.012 mg/l,Sulfatein Zahedan with 509 mg/l and Magnesiumin Zahedan with 47 mg/l. most citiesparameters concentration to be within the standards/guidelines recommended by international organizations. Finally,result showed that Groundwater quality (Phosphorus,Magnesium,Nitrate & Nitrate,Calcium,Chloride) of Sistan Baluchistan is good for water suppling except sodium,Chloride and Sulfate parameter that need attention and treatment in some city such as Zahedan and Chabahar. © 2016,International Journal of Pharmacy and Technology. All rights reserved.
... Nevertheless, few studies have assessed the effects of either AMF or other plant growth-promoting microorganisms on plant metabolic pathways, and most that have been conducted under controlled greenhouse conditions in sterilized natural media as a control (Lekberg and Koide 2014; Glaeser and others 2015) have analyzed only target compounds (Walker and others 2011; Salvioli and others 2015). In this context, there is ongoing research aimed at investigating an extensive variety of rhizobacteria possessing novel beneficial qualities like heavy metal detoxification (Barea and others 2013a), pesticide degradation/tolerance (Carvalhais and others 2013), salinity tolerance (Bashan and others 2014), biocontrol of phytopathogens and insects (Pii and others 2015) together with plant growth-promoting traits for instance, phytohormone (Barea and others 2013b; Lugtenberg 2015; Parray and others 2013, 2015), siderophore (Bakker and others 2013), 1-aminocyclopropane-1- carboxylate, hydrogen cyanate (HCN), and ammonia production, and nitrogenase activity (Olivares and others 2013; Barea and Richardson 2015), and phosphate solubilization (Browne and others 2013; Barea and others 2013a). This review focuses on rhizospheric microbes that are advantageous for the plant. ...
... Beneficial saprophytic rhizosphere microbes improve The processes involved in nutrient cycling by PGPR include nitrogen fixation, phosphate mobilization and the release of other nutrients to soil solution (Richardson et al., 2009;Barea and Richardson, 2015). ...
An intensive agricultural production is necessary to satisfy food requirements for the growing world population. However, its realization is associated with the mass consumption of non-renewable natural resources and with the emission of greenhouse gases causing climate changes. The research challenge is to meet sustainable environmental and economical issues without compromising yields. In this context, exploiting the agroecosystem services of soil microbial communities appears as a promising effective approach. This chapter reviews the research efforts aimed at improving a sustainable and healthy agricultural production through the appropriate management of soil microorganisms. First, the plant-associated microbiome is briefly described. Then, the current research technologies for formulation and application of inocula based on specific beneficial plant-associated microbes are summarized. Finally, the perspectives and opportunities to manage naturally existing microbial populations, including those non-culturable, are analyzed. This analysis concerns: (i) a description of the already available, culture-independent, molecular techniques addressed at increasing our understanding of root-microbiome interactions; (ii) how to improve the ability of soil microbes for alleviating the negative impacts of stress factors on crop productivity; and (iii) whether plants can structure their rootassociated microbial communities and, leading on from this, whether the rhizosphere can be engineered (biased) to encourage beneficial organisms, while prevent presence of pathogens. © 2015, Sociedad Chilena de la Ciencia del Suelo. All rights reserved.
Soil microbial communities host a large number of microbial species that support important ecological functions such as biogeochemical cycling and plant nutrition. The extent and stability of these functions are affected by inter-species interactions among soil microorganisms, yet the different mechanisms underpinning microbial interactions in the soil are not fully understood. Here, we study the extent of nutrient-based interactions among two model, plant-supporting soil microorganisms, the fungi Serendipita indica, and the bacteria Bacillus subtilis. We found that S. indica is unable to grow with nitrate - a common nitrogen source in the soil - but this inability could be rescued, and growth restored in the presence of B. subtilis. We demonstrate that this effect is due to B. subtilis utilising nitrate and releasing ammonia, which can be used by S. indica. We refer to this type of mechanism as ammonia mediated nitrogen sharing (N-sharing). Using a mathematical model, we demonstrated that the pH dependent equilibrium between ammonia (NH3) and ammonium (NH+4) results in an inherent cellular leakiness, and that reduced amonnium uptake or assimilation rates could result in higher levels of leaked ammonia. In line with this model, a mutant B. subtilis – devoid of ammonia uptake - showed higher S. indica growth support in nitrate media. These findings highlight that ammonia based N-sharing can be a previously under-appreciated mechanism underpinning interaction among soil microorganisms and could be influenced by microbial or abiotic alteration of pH in microenvironments.
Egypt faces challenge in supplementing animal feed requirements which add huge pressure on the budget and foreign currency reserves annually leading to the importance of finding alternative solutions. The sprouted barley is considered one of these recent alternatives to animal feed which faces challenges in controlling the rate of seed germination due to the growth of fungi that consume the oxygen necessary for germination in addition to aflatoxins formation and its harmful effect on animal health. Biofertilizers plant growth promoting bacteria PGPB is considered a practice and safe solution. In this work, five tomato rhizobacterial strains were isolated and identified using 16S rRNA gene and were closely related to Bacillus amyloliquefaciens , Peribacillus frigoritolerans , Pseudomonas flourescens , Bacillus pumilus , and Paenibacillus uliginis , respectively. We reported here that most of these five isolates exhibited multiple PGP characteristics (PGPC), including the production of ACC deaminase, Indole-Acetic Acid (IAA), chelating siderophores and phosphate solubilization. Bacillus amyloliquefaciens BMG150 isolate exhibited the highest values for all the PGPC except siderophores production (1457 nmol, 37.4 µg/ ml, and 3.7 mg/ml, respectively). We also scanned the presence/ absence of the non-ribosomal peptide gene clusters in the five isolates as an important PGPC using bioinformatics tools and NRPs degenerate primers. All five isolates showed the presence of NRPs gene clusters with the superiority of NRPs number for the strain Bacillus amyloliquefaciens BMG150 (surfactin, fengycin or plipastatin, iturin and bacillibactin siderophore). According to these results, we used this latter strain, Pseudomonas flourescens PMG01 separately and a formula of the other three isolated strains as biofertilizers in sprouted barley cultivation which proved their efficiency in promoting their growth characteristics and reduced fungal growth which reflected on protein pattern.
Soil is a source of various forms of life on the earth and performs various services in the ecosystem. Nitrogen, phosphorus, potassium and sulphur are the major nutrients required by for the growth and development of plants. Microorganisms, present in large numbers in soil, help in the nutrient recycling by various processes including decomposition of organic matter and breakdown of the insoluble forms of nutrients to make them available to plants. Bacteria, fungi, actinomycetes, algae and archaea belonging to different genera help to facilitate recycling of nutrients. Additionally, the processes performed by microorganisms other than decomposition and breakdown also facilitate to provide other micronutrients to plants. Sustainable agriculture is one of the consequences along with other contributions by microorganisms towards healthy soil. This chapter focuses on the importance of microorganisms in the recycling of nutrients and improving the quality, structure and nutrient status of soil.
The cycling dynamics and supply–demand balance of nutrients can provide useful information for improving the management of tree plantations and maintaining their long-term productivity. Phosphorus (P) is an essential nutrient for plant growth; however, its cycling characteristics and availability in soils along different stand developmental stages remain unclear, especially in intensively managed plantations. In this study, we examined the stocks, distribution, flux, and supply–demand balance of P across a chronosequence of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.; Taxodiaceae) plantations aged 3, 8–11, 16, 21, 25, 29, and 32 years. <22.18% tree P stock allocated for stem across a chronosequence, suggesting that only stem harvest could return more than three-quarters of tree P stock to soil. The annual P resorption, P return, and P-use efficiency increased with stand age, indicating strong P recycling. Indicators of P acquisition and recycling strategies significantly increased with stand age and promoted P fluxes. The combination of acquisition and recycling strategies might favor the entrainment of P into the biological cycle. With the increase in stand age, the available soil P stocks initially decreased and then increased after 11 years, while the annual P uptake increased at first and then stabilized after 22 years. Based on the best fitted model, the lower soil P supply and higher tree P demand in 9- to 40-year-old plantations revealed that timely and appropriate fertilization could enhance soil P supply and improve stand productivity. This work provides crucial information about the time of fertilization and appropriate harvest methods for the sustainable management of forest P nutrition.
In soils, phosphorus (P) is present in relatively large amounts, but for plants and microorganisms, P remains complexed under unavailable forms. To access the unavailable forms of P, plants interact with soil microorganisms such as arbuscular mycorrhizal fungi (AMF) and phosphate degrading bacteria (PDB) that can act synergically to improve plant P nutrition. In practice, we aim to stimulate microorganism properties for phosphate degradation and transport to the plant in agricultural soils.
Firstly, 17 bacterial isolates were characterized for their ability to degrade insoluble P complexes and plant growth promoting rhizobacteria (PGPR) traits such as the production of auxins and the formation of biofilms via the production of was added extracellular polymeric substances. Secondly, two Bacillaceae isolates were selected regarding their compatibility in co-culture and ability to promote PGPR traits. In the greenhouse and in pots containing an agricultural soil, tubers of Solanum tuberosum cv. Jazzy were inoculated with each individual isolate, and both isolates. We showed that bacterial inoculation positively impacted plant P nutrition, growth, and yield as well as indigenous arbuscular mycorrhizal rate. Our results suggest that the bacterial consortium synergically interacts with indigenous AMF community to improve plant P nutrition and yield, without changing associated microbial communities.
Grapevines (Vitis vinifera L.) were one of the first fruit species to be domesticated and nowadays are the world’s most economically important fruit crop. Nowadays, at global level, viticulture is facing various challenges that need to be addressed, based on scientific support. On one hand, water scarcity in the frame of climate change scenarios is of major concern since climate models to 2050 predict that droughts would increase by the middle of the century accompanied by increases in temperature. Viticulture in Chile as a case study is very interesting due to the existence of different edaphoclimatic conditions in its nearly 4300 km from north to south, where prestigious world-class wine companies are found. Interestingly, the wine production areas have been moving fast toward the South, to areas with higher winter and spring precipitations but lower temperatures. Even though plantations have been slowly increasing in Southern Chile, viticulture is facing a new constraint such as the production on Andosols, very acidic, phosphorous (P) fixing, and prone to induced aluminum (Al) toxicity. In fact, there is a growing interest from wine producers, universities, research centers, and in general in the scientific community, in improving the understanding of the ecosystem services that could be granted by products based on microorganisms such as biostimulants that correspond to bioformulations with a scientific-technological base in which the base is made up of species of one or more microorganisms whose name in the research stage is inoculant, inoculum, or inocula. Special emphasis on high-tech agriculture has acquired arbuscular mycorrhizal fungi-based biostimulants.KeywordsInoculants
Vitis
AMF bioestimulantsGrapesSustainable viticulture
Direct plant growth promotion can be achieved by several mechanisms. Indirect plant growth promotion occurs by protection of the plant against pathogens, most often fungi but also bacteria and viruses. This chapter discusses the role of companies in the complicated, time‐consuming, and expensive process from harvesting seeds to food on the plate. Mycorrhizal fungi live in symbiosis with more than 80% of the land plants. Mycorrhizal fungi can be considered as an extension of the root system. A potentially valuable product is often patented to protect its application. Discoveries at universities are published, often in specialized journals. The authorization process of plant protection products consists of evaluation of dossiers of the active microorganism and of the formulated product. Many chemical firms have recognized the demand for biological products and have become active in the biological crop protection business.
Soil, as an important constituent, is not only useful for producing food but also for maintaining environmental sustainability. It contains microorganisms with useful traits, which are necessary for enhancement of agricultural productivity. Rhizosphere, one of the complex ecosystems on Earth, is a hot spot for these microorganisms, which are beneficial for plant growth and development. Rhizospheric microorganisms play an important role in improving efficient use of nutrients, such as nitrogen, and crop sustainability. In the functioning of rhizospheric microorganisms, plant genotype plays a crucial role. Current advances in the understanding of plant natural pathways have resulted in the discovery of many of the enzymes and corresponding genes. These genes are required for the biosynthesis and transport of a variety of rhizosphere signaling molecules, supporting metabolic engineering to control the rhizosphere. Moreover, genetic variations have been revealed in several crops such as cereals, particularly maize, wheat, and rice. The rhizosphere has been targeted for efficient use of nutrients, most notably, of nitrogen, phosphorus, and potassium. Although utmost progress is being made for potassium. Numerous studies reported that drought tolerance in wheat was improved by rhizospheric bacteria. Further, preparing isolates of rhizospheric bacteria from harsh environments is a promising as well as a novel way to improve plant water‐use efficiency. Important bacterial species like Rhizobium , Pseudomonas , Azospirillum , and Bacillus found to have positive impacts on crops by enhancing both above and belowground biomass and hence play positive roles in achieving sustainable agriculture. These new advancements importantly contribute toward solving food‐security issues under changing climatic conditions. Harnessing rhizosphere microbiomes for drought‐resilient crop production can improve plant growth, and they offer the potential to increase crop resilience to future drought. Therefore plant–microbe interactions are indispensable for combating food crisis, which is one of the greatest global challenge.
Soil is considered as a reservoir for microorganisms. A small fraction of soil consists millions of microbes, and microbial activity is referred as maximum near the root zone simply referred as rhizosphere zone. The rhizosphere is defined as the soil zone that exists near the plant roots. Due to plant roots and soil interaction, microbial activity is found maximum in the area. As they are referred as the most active, microbes play a defined role in soil and plant health. This chapter aimed to focus on microbial diversity in the rhizosphere zone and its significance to the crop and soil. A diverse population of microbes associated with different activities in the rhizosphere zone is discussed in detail in this chapter.
The use of chemical fertilizers to supply the elements needed by plants is the predominant way that the continuation of this approach can cause irreparable damage to the soil and the environment. Excessive use of chemical fertilizers will lead to the destruction of soil, and soil destruction will mean the destruction of plants and the lack of food for humans, so overcoming these problems is one of the concerns of agricultural scientists. The best option to reduce the damage of chemical fertilizers is to use the ability of soil microbes to increase plant growth and yield. There are many reports on the positive effects of these microbes in the soil and it has been shown that the use of beneficial soil microbes can promise agricultural production without harming the environment.
The present book is about using the potential of soil microbes to overcome the problems caused by the use of chemical fertilizers in the long run. This book discusses various beneficial soil microbes such as rhizospheric bacteria of different genera. The production of bio-fertilizers in order to take advantage of the abilities of these bacteria is also discussed in different chapters of this book. The formulation, production, preparation, and application of bio-fertilizers are also given in different chapters of this book. Finally, this book contains useful information for those interested in sustainable agriculture, bio-fertilizers and beneficial soil microbes that stimulate plant growth.
Phylogenetic analysis of more than 4000 annotated bacterial acid phosphatases was carried out. Our analysis enabled us to sort these enzymes into the following three types: 1) class B acid phosphatases, which were distantly related to the other types, 2) class C acid phosphatases, and 3) generic acid phosphatases (GAP). While class B phosphatases are found in a limited number of bacterial families, which include known pathogens, class C acid phosphatases and GAP proteins are found in a variety of microbes that inhabit soil, fresh water and marine environments. As part of our analysis we developed three profiles, named Pfr‐B‐Phos, Pfr‐C‐Phos and Pfr‐GAP, to describe the three groups of acid phosphatases. These sequence‐based profiles were then used to scan genomes and metagenomes to identify a large number of formerly unknown acid phosphatases. A number of proteins in databases annotated as hypothetical proteins were also identified by these profiles as putative acid phosphatases. To validate these in silico results, we cloned genes encoding candidate acid phosphatases from genomic DNA, or recovered from metagenomic libraries or genes synthesized in vitro based on protein sequences recovered from metagenomic data. Expression of a number of these genes, followed by enzymatic analysis of the proteins, further confirmed that sequence similarity searches using our profiles could successfully identify previously unknown acid phosphatases. This article is protected by copyright. All rights reserved.
The current novel method uses vesicular-arbuscular mycorrhiza (VAM) fungi as green technology for controlling global warming. This method relates the usual dual symbiosis in favor of extracting more biomass via putting back CO2 into its original form, i.e., fuel. A trait is provided where a fungus is applied to the soil of plants to activate the process of reduction reaction of CO2 into starch followed by biomass to biofuel. The trait is comprised of fungi Glomus fasciculatum and plant Conocarpus erectus L. under seasonal variation with excessive pressure of CO2. The process narrates the highest photosynthetic activity, consequently creating biomass, which is assimilated into the plant tissues through polymerization of glucose into starch and cellulose. The present investigation revealed that VAM symbiosis induced modification in plants’ structure which results in deep root growth, high stomatal conductance, and high nutrient uptake including P, rapid C, and N metabolism. It was suggested that these modifications in various environmental conditions provide help in plants’ survival, with efficient recycling of CO2 into biomass production.
Exploiting the agroecosystem services of soil microbes appears as a promising effective approach to alleviate the negative impacts on soil systems and crop production. Lack of soil organic matter (SOM) is a prevalent feature of degraded soils. Different biological soil amendments, such as organic manure, compost, vermicompost, indigenous microbes, and crop residues, are widely used in reclamation of degraded soils. The biological soil amendments also furnish a valuable source of fertilizer for growing rice and maize and also boost physicochemical and biological parameters of soil such as water holding capacity, moisture content, electrical conductivity, organic carbon content, and population of beneficial microbes which directly correlates to soil health and fertility. However, efficiency of amendments applied based on variety of factors including the composition and characteristics, soil microflora, and environmental conditions can accelerate initial reclamation and lead to self-sustaining primary productivity of crops. On the other hand, high cost of chemical fertilizers, pesticides, and other agricultural inputs and their harmful environmental legacy have encouraged researchers to explore the use of microbial-mediated amendments to play a central role in raising productivity and inhibition/suppression of pathogenic population below levels at which they cause economic and other effects to the crops as well as the environment. Biological control can be achieved through one or more mechanisms, viz., antibiosis, competition for nutrients and/space, induced resistance, plant growth promotion, and rhizosphere colonization ability. Potent biocontrol agents such as Bacillus sp., Pseudomonas sp., and Tricoderma sp. prove to be very promising in controlling soilborne diseases of rice and maize crops employing both antibiosis and induction of host resistance. Determination of the modes of action of biocontrol agents is obligatory to provide higher level of protection to crop under a particular environmental condition that exists in divergent agroecosystems. This chapter reviews an insight of mechanisms of biological soil amendments and biocontrol agents and their emphasis on soil amelioration with the goal of a sustainable agricultural system.
The interactive effect of phosphate-solubilizing bacteria and arbuscular mycorrhizal (AM) fungi on plant use of soil p sources of low bioavailability (endogenous or added as rock phosphate [RP] material) was evaluated by using soil microcosms which integrated 32P isotopic dilution techniques. The microbial inocula consisted of the AM fungus Glomus intraradices and two phosphate-solubilizing rhizobacterial isolates: Enterobacter sp. and Bacillus subtilis. These rhizobacteria behaved as 'mycorrhiza helper bacteria' promoting establishment of both the indigenous and the introduced AM endophytes despite a gradual decrease in bacterial population size, which dropped from 107 at planting to 103 CFU g-1 of dry rhizosphere soil at harvest. Dual inoculation with G. intraradices and B. subtilis significantly increased biomass and N and P accumulation in plant tissues. Regardless of the rhizobacterium strain and of the addition of RP, AM plants displayed lower specific activity (32P/31P) than their comparable controls, suggesting that the plants used P sources not available in their absence. The inoculated rhizobacteria may have released phosphate ions (31P), either from the added lip or from the less-available indigenous P sources, which were effectively taken up by the external AM mycelium. Soluble Ca deficiency in the test soil may have benefited P solubilization. At least 75% of the P in dually inoculated plants derived from the added RP. It appears that these mycorrhizosphere interactions between bacterial and fungal plant associates contributed to the biogeochemical P cycling, thus promoting a sustainable nutrient supply to plants.
The rhizosphere is a site of intense interactions between plant and microorganisms. Molecular signaling between partners underpins the development of both the beneficial and pathogenic interactions that occur between plants and bacteria in nature. Despite the general acceptance that plant root exudates can influence the behavior and structure of bacterial communities in the rhizosphere, very little is known about the molecular mechanisms involved in this phenomenon. Analysis of the rhizospheric communities incorporating both established techniques, and recently developed “omic technologies,” can now facilitate investigations into the molecular basis underpinning the establishment of plant–microbial interactomes in the rhizosphere. These different molecular-based strategies employed to elucidate the complex interactions that occur between plant and bacterial communities in the rhizosphere are summarized in this chapter.
Phosphorus (P) is vital for plant growth. However, most added soluble P forms insoluble phosphates. Therefore, inorganic P (Pi) accumulates in soils. Soil organic P (Po) is another important reserve (20 to 80% of total soil P). To be available for plant Po must first be mineralized by soil microorganisms. The variability of the results of inoculation trials with P solubilizing microorganisms (PSMs) clearly reflects the complexity of the interactions occurring in the soil-plant-microbes-fauna ecosystem. Important points overlooked in previous studies will be presented and perspectives of the use of PSMs to allow the plant to benefit from soil reserves in Pi and Po will be discussed.
Microbial communities inhabiting soil or rhizosphere play important roles in growth and development of plants. Of these, phosphate-solubilizing
bacteria (PSB) play fundamental roles in biogeochemical phosphorus cycling in agro-ecosystems. Phosphate-solubilizing microbes
transform the insoluble phosphorus to soluble forms by acidification, chelation, exchange reactions, and polymeric substances
formation. The use of phosphate-solubilizing microbes in agronomic practices helps not only to offset the high cost of phosphatic
fertilizers but also to mobilize insoluble phosphorus in the fertilizers and soils to which they are applied. And hence, application
of such naturally occurring organisms possessing multiple growth-promoting activities hold greater promise for increasing
the productivity of crops including legumes. Another agronomically promising organism is rhizobia which are known exclusively
for its ability to form symbiosis with legumes and enrich nitrogen pool of soil, can also facilitate plant growth by synthesizing
plant growth regulators and solubilizing insoluble phosphorus besides providing nitrogen to plants. In addition, under low
nitrogen fertilizer inputs, availability of phosphorus is a major factor restricting the rate of N2-fixation in legumes. The combined inoculation of N2-fixers, PSB, and mycorrhizal fungi could be more effective than single organism for providing a more balanced nutrition for
legume plants under conditions of reduced nutrient inputs. In this chapter, the strategic and applied research conducted so
far to understand as to how PSB along with other symbionts enhance nutrient availability to legumes and concomitantly improve
yield are reviewed and discussed. The application of synergically interacting yet phylogenetically diverse microbes is likely
to help sustaining the legume productivity in different agricultural production systems.
Phosphorus is an important plant nutrient which is in short supply in many agricultural soils. Because much of the soluble phosphate (P) applied to soils as fertilizer is “fixed” by the soil and rendered less available to plants, the long-term application of P fertilizers has resulted in an accumulation of total soil P, most of which is poorly soluble. Many soil fungi, predominantly of the genera Aspergillus and Penicillium, have been shown to possess the ability to solubilize sparingly soluble phosphates in vitro by secreting inorganic or organic acids. Growth promotion and increased uptake of P by plants inoculated with P-solubilizing fungi have also been reported by many investigators.
Recent research on arbuscular mycorrhizas has demonstrated that AM fungi play a significant role in plant phosphorus (P) uptake, regardless of whether the plant responds positively to colonization in terms of growth or P content. Here we focus particularly on implications of this finding for consideration of the balance between organic carbon (C) use by the fungi and P delivery (i.e. the C-P trade between the symbionts). Positive growth responses to arbuscular mycorrhizal (AM) colonization are attributed frequently to increased P uptake via the fungus, which results in relief of P deficiency and increased growth. Zero AM responses, compared with non-mycorrhizal (NM) plants, have conventionally been attributed to failure of the fungi to deliver P to the plants. Negative responses, combined with excessive C use, have been attributed to this failure. The fungi were viewed as parasites. Demonstration that the AM pathway of P uptake operates in such plants indicates that direct P uptake by the roots is reduced and that the fungi are not parasites but mutualists because they deliver P as well as using C. We suggest that poor plant growth is the result of P deficiency because AM fungi lower the amount of P taken up directly by roots but the AM uptake of P does compensate for the reduction. The implications of interplay between direct root uptake and AM fungal uptake of P also include increased tolerance of AM plants to toxins such as arsenate and increased success when competing with NM plants. Finally we discuss the new information on C-P trade in the context of control of the symbiosis by the fungus or the plant, including new information (from NM plants) on sugar transport and on the role of sucrose in the signaling network involved in responses of plants to P deprivation.
The rhizosphere is a complex environment where roots interact with physical, chemical and biological properties of soil. Structural and functional characteristics of roots contribute to rhizosphere processes and both have significant influence on the capacity of roots to acquire nutrients. Roots also interact extensively with soil microorganisms which further impact on plant nutrition either directly, by influencing nutrient availability and uptake, or indirectly through plant (root) growth promotion. In this paper, features of the rhizosphere that are important for nutrient acquisition from soil are reviewed, with specific emphasis on the characteristics of roots that influence the availability and uptake of phosphorus and nitrogen. The interaction of roots with soil microorganisms, in particular with mycorrhizal fungi and non-symbiotic plant growth promoting rhizobacteria, is also considered in relation to nutrient availability and through the mechanisms that are associated with plant growth promotion.
Summary 22
References 33
In natural conditions, mycorrhizal fungi are surrounded by complex microbial communities, which modulate the mycorrhizal symbiosis. Here, the focus is on the so-called ‘mycorrhiza helper bacteria’ (MHB). This concept is revisited, and the distinction is made between the helper bacteria, which assist mycorrhiza formation, and those that interact positively with the functioning of the symbiosis. After considering some examples of MHB from the literature, the ecological and evolutionary implications of the relationships of MHB with mycorrhizal fungi are discussed. The question of the specificity of the MHB effect is addressed, and an assessment is made of progress in understanding the mechanisms of the MHB effect, which has been made possible through the development of genomics. Finally, clear evidence is presented suggesting that some MHB promote the functioning of the mycorrhizal symbiosis. This is illustrated for three critical functions of practical significance: nutrient mobilization from soil minerals, fixation of atmospheric nitrogen, and protection of plants against root pathogens. The review concludes with discussion of future research priorities regarding the potentially very fruitful concept of MHB.
This chapter discusses the soil biogeochemical cycling of inorganic nutrients and metals. Soil microorganisms have a profound effect on the transformations involved in a large number of biogeochemical cycles other than carbon (C) and nitrogen (N), such as the macronutrients phosphorus (P) and sulfur (S), and various micronutrients and environmental pollutants. A conceptual model for the cycling of a generic nutrient or metal element illustrates the continuous flow of energy, water, nutrients, and other materials across the ecosystem's boundaries. Meteorologic transfers consist of windblown particulate matter, dissolved substances in precipitation, and gases. Geologic fluxes include soluble and particulate matter transported by surface and subsurface water flow and the mass movement of mineral materials during events such as erosion, landslides, or lava flows. This chapter focuses on phosphorus, sulfur, micronutrients and trace metals. Environmental significance of P, S, and metal biogeochemistry is described along with microorganisms as unifiers of elemental cycles in soil.
Microbial populations living at the root–soil interfaces, the rhizosphere, are immersed in a framework of interactions known to influence plant growth and health, and soil quality. In the past years, research has been focused on improving the understanding of the diversity, dynamics, and significance of rhizosphere microbial populations, and to gain more information on the molecular determinants of their cooperative interactions. Thus the aim of this chapter is to review current knowledge on microbial interactions that take place in the rhizosphere scenario, with emphasis on ecological and molecular issues. In particular, this article summarizes and discusses significant aspects of this topic including: (i) activities of the diverse trophic and functional groups of rhizosphere microorganisms and their interactions with the plant; (ii) analysis of the direct microbe–microbe interactions focused on those benefiting agroecosystem developments; (iii) analysis of beneficial microbial interactions involving arbuscular mycorrhiza, the omnipresent fungus–plant beneficial symbiosis, which occurs in the so-called mycorrhizosphere. The trends of this thematic area will be outlined to suggest what research is needed in the future.
Modern agriculture is heavily dependent on the application of chemical inputs, including fertilizers and pesticides. Because of concerns regarding economics, human health, and environmental protection, viable alternatives to these chemicals are being sought. The exploitation of specific rhizosphere microorganisms as biofertilizers and biopesticides has the potential to improve plant growth and/or to reduce the incidence of soilborne disease. Pseudomonas spp., in particular, are known to exhibit multiple plant-growth-promoting characteristics involved in biocontrol and biofertilization.Previous work based on both culture-dependent and culture-independent approaches showed that different agricultural practices can lead to changes in the composition of Pseudomonas population at both the phylogenetic and functional levels. These studies have suggested that there is potential for the manipulation of agricultural strategies such as crop rotation, crop type, and fertilizer input to develop favorable microbial communities, including Pseudomonas, at the phylogenetic and functional levels. In this chapter, current knowledge regarding the potential contribution of Pseudomonas spp. in soil phosphate cycling is summarized.
Interactions between vesicular-arbuscular (VA) mycorrhizal fungi and phosphate-solubilizing bacteria were studied in a low-phosphate alkaline soil amended with 0, 0.1% and 0.5% rock phosphate. Endogone (E3 and yellow vacuolate spore types) and two bacteria able to solubilize rock phosphate in vitro and produce plant growth regulating substances were used as inocula. Lavender (Lavandula spica var. vera L.) plants with mycorrhiza plus bacteria (either E3 plus bacteria or “yellow vacuolate” plus bacteria treatments) took up more total P than plants with either Endogone or bacteria separately at each concentration of rock phosphate. Plants not inoculated with bacteria or Endogone derived no benefit from the rock phosphate.
Microorganisms are involved in a range of processes that affect the transformation of soil phosphorus (P) and are thus an
important component of the soil P cycle. In particular, soil microorganisms are effective in releasing P from inorganic and
organic pools of total soil P through solubilization and mineralization. The microbial biomass in soil also contains a significant
quantity of immobilized P that is potentially available to plants. Microorganisms therefore are critical for the transfer
of P from poorly available soil pools to plant available forms and are important for maintaining P in readily available pools.
These processes are likely to be most significant in the rhizosphere of plants.
The rhizosphere is defined as the soil around the roots that is influenced by the root (Hiltner 1904). Due to the release of easily decomposable compounds by the roots (root exudates), the rhizosphere is characterized by high microbial density. Rhizosphere microorganisms strongly influence nutrient uptake by plants by either enhancing or decreasing nutrient availability.
Rhizosphere microbial communities are a subset of the soil microbial community, but are often quite distinct from those in the bulk soil (Foster 1986; Marilley and Aragno 1999; Gomes et al. 2001; Berg et al. 2002). Rhizosphere communities are influenced by soil and plant factors. Soils can have distinct microbial communities (Gelsomino et al. 1999; Carelli et al. 2000), as a result of the soil physical and chemical characteristics (e.g. soil texture, nutrient and organic matter content and pH) and environmental factors such as climate and vegetation. Plants contribute to these physical and chemical properties by depositing between 1% and 25% of their net photosynthetic production, which includes dead roots, sloughed-off cells and soluble compounds (Merbach et al. 1999). A large proportion of the root exudates such as sugars, organic acid anions or amino acids are easily degradable by microorganisms in the rhizosphere resulting in high microbial density and activity in the rhizosphere (Foster 1986; Kandeler et al. 2001).
Isotopic (32P) dilution approaches have been used to evaluate the extent at which inoculated phosphate-solubilizing bacteria (PSB) and
arbuscular mycorrhizal (AM) fungi improve plant use of soil P sources of low bioavailability, either endogenous or added as
rock phosphate (RP). This paper firstly examines the conceptual background, the main achievements and the state of the art
on the related topics. Then, a model own experiment is described and discussed to offer a comprehensive view on the effects
and mechanisms involved, and to propose the appropriate methodological approaches. Measurements of the specific activity (32P/31P) of P in plants grown in 32P-labelled soil, and the subsequent calculations of the amount of plant P derived from either the bio-available (isotopically
labelled) soil sources or from the added RP, allow to conclude that the dually (AM + PSB)-inoculated plants were able to use
otherwise unavailable P sources, resulting in an improvement of plant P acquisition. The proposed mechanism is that the inoculated
PSB actually release phosphate ions (31P) from sparingly soluble phosphates, ions which are taken up by the external AM mycelium to be transferred to the plant.
Phosphorus (P) is essential for plant growth and fecundity. It is an integral component of genetic, metabolic, structural and regulatory molecules, in many of which it cannot be substituted by any other elements. Tissue P concentrations in well fertilized plants approximate 0.4–1.5% of the dry matter (Broadley et al. 2004), most of which is present as nucleic acids and nucleotides, phosphorylated intermediates of energy metabolism, membrane phospholipids and, in some tissues (principally seeds), as inositol phosphates. Some P also occurs in phosphoproteins and as inorganic phosphate (Pi) and pyrophosphate (PPi). It has been estimated that small metabolites, nucleic acids and phospholipids
contribute approximately equally to leaf P content in P-replete plants (Figure 4.1; Marschner 1995; Dörmann and Benning 2002). Tissue P concentrations show no systematic differences between angiosperm species grown in P-replete conditions, but strong positive correlations occur between shoot P and shoot organic-N concentrations (Broadley et al. 2004). When plants are sampled from their natural environment, shoot N:P mass ratios vary between about 5:1 and 40:1 (e.g. Garten 1976; Thompson et al. 1997; Elser et al. 2000a; Tessier and Raynal 2003; Güsewell 2004; McGroddy et al. 2004; Güsewell et al. 2005; Han et al. 2005; Niklas et al. 2005; Wassen et al. 2005; Wright et al. 2005; Kerkhoff et al. 2006) and leaf N appears to scale as the 3/4 power of leaf P (Niklas et al. 2005; Niklas 2008). Ratios of 10:1 approximate the maximum critical organic-N:P ratios reported for a range of crop plants (Greenwood et al. 1980; Güsewell 2004). In general, leaf N:P ratios below 13.5 suggest N-limited plant growth, whilst leaf N:P ratios above 16 suggest P-limited plant growth (Aerts and Chapin 2000; Güsewell and Koerselman 2002; Tessier and Raynal 2003). Stoichiometric relationships between leaf N and leaf P appear to be a consequence of the requirements of N for proteins and of P for nucleic acids, membranes and metabolism (Elser et al. 2000b; Niklas 2008). Plant relative growth rate (RGR) is positively correlated with rRNA concentration and negatively correlated with protein concentration (Ågren 1988; Elser et al. 2000b; Niklas 2008).
Legumes, plant species of great agronomical and ecological interest, are known to establish beneficial symbiotic relationships
with two types of soil-borne microorganisms: N2-fixing bacteria and arbuscular mycorrhizal fungi. Additionally, the legume rhizosphere harbors other associative beneficial
microorganisms such as plant growth promoting rhizobacteria (PGPR). These microorganisms interact among themselves, and with
legume roots, to develop the multifunctional legume mycorrhizosphere, a scenario of diverse activities relevant for legume
productivity either in sustainable agriculture or in the maintenance of natural plant communities. This Chapter highlights
strategic and applied research conducted so far, which have allowed a comprehensive understanding of the formation and functioning
of the legume mycorrhizosphere. Manipulation of the microbial activities allows tailoring efficient mycorrhizosphere systems
for improving legume productivity. The technology for the production of efficient rhizobial, free-living PGPR, and AM-fungal
inoculants, nowadays commercially available, is likely to support sustainable and environmentally friendly low-input agrotechnological
practices. The possibilities to use these bioproducts to help a sustainable development of legumes in either agrosystems or
natural ecosystems are discussed.
Plant growth promotion by microbes Molecular microbial ecology of the rhizosphere
- Bjj Lugtenberg
- N Malfanova
- F Kamilova
Use of phosphate rocks for sustainable agriculture. Fertilizers and Plant Nutrition
- F Zapata
- R Roy
Making microorganisms mobilize soil phosphorus (eds) First international meeting on microbial phosphate solubilization. Developments in plant and soil sciences
- Ae Richardson
Acquisition of phosphorus and nitrogen in the rhizosphere and plant growth promotion by microorganisms
- A E Richardson
- J M Barea
- A M Mcneill
- AE Richardson
Phosphorus nutrition of terrestrial plants The ecophysiology of plant-phosphorus interactions
- Pj White
- Jp Hammond
Fresh perspectives on the roles of arbuscular mycorrhizal fungi in plant nutrition and growth
- S E Smith
- F A Smith
- SE Smith
Molecular-based strategies to exploit the inorganic phosphate-solubilization ability of
- P Browne
- M Barret
- Jp Morrissey
ed) Molecular microbial ecology of the rhizosphere
- J M Barea
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- R Azcón
- JM Barea