Variable P supply affects N metabolism in a legume tree, Virgilia divaricata, from nutrient-poor Mediterranean-type ecosystems

Virgilia divaricata Adamson is a forest margin legume that is known to invade the N- and P-poor soils of the mature fynbos, implying that it tolerates variable soil N and P levels. It is not known how the legume uses inorganic N from soil and atmospheric sources under variable P supply. Little is known about how P deficiency affects the root nodule metabolic functioning of V. divaricata and the associated energy costs of N assimilation. This study aimed to determine whether P deficiency affects the metabolic status of roots and nodules, and the impact on the routes of N assimilation in V. divaricata.V. divaricata had reduced biomass, plant P concentration and biological nitrogen fixation during P deficiency. Based on adenylate data, P-stressed nodules maintained their P status better than P-stressed roots. V. divaricata was able to alter C and N metabolism differently in roots and nodules under P stress. This was achieved via internal P cycling by possible replacement of membrane phospholipids with sulfolipids and galactolipids, and increased reliance on the pyrophosphate (PPi)-dependent metabolism of sucrose via UDP-glucose (UDPG) and to fructose-6-phosphate (Fru-6-P). P-stressed roots mostly exported ureides as organic N and recycled amino acids via deaminating glutamate dehydrogenase. In contrast, P-stressed nodules largely exported amino acids. Compared with roots, nodules showed more P conservation during low P supply. The roots and nodules of V. divaricata metabolised N differently during P stress, meaning that these organs may contribute differently to the success of this plant in soils from forest to fynbos.The DST/NRF-Center of Excellence for Tree Health Biotechnology, based at the University of Pretoria, South Africa.http://www.publish.csiro.au/fphb2017Microbiology and Plant Patholog

Variation in phosphorus supply alters nitrogen metabolism in the nodules and roots of Virgilia divaricata, a Cape fynbos indigenous legume from the Cape Floristic Region

Thesis (PhD)--Stellenbosch University, 2016.ENGLISH SUMMARY: This study determined how phosphorus (P) deficiency alters the nitrogen (N) metabolism in the root nodules of Virgilia divaricata (Adamson). The legume is indigenous to nutrient rich forest soils, but is also known to grow across a wide range habitats these including N and P poorer soils of the mature fynbos, a nutrient-poor ecosystem in the Cape Floristic Region of South Africa. Although this implies that the legume has a wide functional tolerance for variable soil N and P levels, it is not known how the plant utilizes inorganic N under variable P supply. This was evaluated in three separate experiments. The first experiment identified the bacterial species that nodulate V. divaricata and their biological N2 fixing (BNF) efficiency during P deficiency. In the experiment, we also integrated the plant C and N metabolism to the N product exported via xylem to the shoots for plant use. Plants were grown at sufficient and low P levels, with four concentrations of inorganic N supply (NH4NO3). At both levels of P, soil N supply reduced the reliance of legumes on BNF. Although the bacterial composition of nodules remained unchanged by P and N supply, the nodule function was greatly altered. In this regard, plants reliant on only N2 at both P levels had higher and more efficient BNF, which resulted in greater plant N. At high P, plants exported more amino acids relative to inorganic N and ureides in their xylem sap, whereas at low P the plants exported more ureides relative to amino acids and NH4. The bacterial tolerance for changes in P and N determined via nodule metabolites and xylem export might be a major factor that underpins the growth of V. divaricata under these variable soil conditions. The second experiment determined whether the P deficiency affects the metabolic status of roots and nodules, and the consequent impact on the routes of N assimilation. The findings show that V. divaricata had a reduced biomass, plant P concentration and BNF during P deficiency. P stressed nodules maintained their P status better than P stressed roots. Furthermore V. divaricata was able to alter C and N metabolism in different ways in roots and nodules, in response to P stress. For both roots and nodules, this was achieved via internal cycling of P, by possible replacement of membrane phospholipids with sulpholipids and galactolipids and increased reliance on the PPi-dependant metabolism of sucrose via UDPG and to Fru-6-P. P stressed roots exported mostly ureides as organic N and recycled amino acids via deamination glutamate dehydrogenase (GDH). In contrast, P stressed nodules largely exported amino acids. Compared to roots, the nodules showed a greater degree of P conservation during low P supply. The third experiment identified the Glutamate dehydrogenase (GDH) transcripts, their relative expressions and activity in P-stressed V. divaricata roots and nodules during N metabolism. GDH might contribute to the functional tolerance of V. divaricata to variable soil N and P levels in the mature fynbos by aminating N via aminating GDH and recycling amino acids via deaminating GDH. The analysis of the GDH cDNA sequences in V. divaricata revealed the presence of GHD 1 and GHD 2 subunits, these corresponding to the GDH1, GDH-B and GDH3 genes of legumes and non-legume plants. The relative expression of GDH1 and GDH2 genes was analysed in the roots and nodules, our results indicate that two subunits were differently regulated depending on the organ type and P supply. Although both transcripts appeared to be ubiquitously expressed in the roots and nodules, the GDH1 transcript evidently predominated over those of GDH2. Furthermore, the higher expression of both GDH transcripts in the nodules than roots in this study may play a role in the ability of nodules to regulate and conserve their internal P better than roots during P deficiency. With regards to GHD activity, both aminating and deaminating GDH activities were induced during P deficiency.AFRIKAANSE OPSOMMING: Hierdie studie bepaal hoe fosfor ( P) tekort die stikstof (N) metabolisme verander in die wortelknoppies van Virgilia divaricata . Die peulplant is inheems aan ryk bosbodems voedingstof, maar is ook bekend om die N en P armer gronde van die volwasse Fynbos, 'n voedingstof -arm ekosisteem in die Kaapse Floristiese Streek van Suid-Afrika binne te val . Hoewel dit impliseer dat die peulplant 'n wye funksionele verdraagsaamheid vir N en P vlakke het, is dit nie bekend hoe die plant anorganiese N onder wisselende P aanbod gebruik nie. Dit is geëvalueer in drie afsonderlike eksperimente. Die eerste eksperiment het die bakteriële spesies wat V. divaricata en hul biologiese N2 vaststelling (BNF) doeltreffendheid tydens P-tekort nodulate, geïdentifiseer. In die eksperiment, het ons ook die C en N metabolisme aan die N produk wat uitgevoer word via xileem na die lote, geintegreerd. Plante is gegroei op voldoende en lae P-vlakke, met vier konsentrasies van anorganiese N. Op beide vlakke van P, grond N toevoer verminder die afhanklikheid van peulplante op BNF. Hoewel die bakteriële samestelling van nodules onveranderd gebly deur P en N toevoer, was die nodule funksie grootliks verander. In hierdie verband, plante afhanklik net N2 by beide P vlakke het hoër en meer doeltreffende BNF, wat gelei het tot 'n groter aanleg N. Met hoë P, het plante meer aminosure relatief tot anorganiese N en ureides in hul xileemsap, terwyl by lae P voer die plante meer ureides relatief tot sure en NH4 amino. Die bakteriële verdraagsaamheid vir veranderinge in P en N via nodule metaboliete en xileem uitvoer kan 'n belangrike faktor onder hierdie veranderlike grondtoestande onderlê. Die tweede eksperiment het bepaal of P-tekort die metaboliese status van die wortels en wortelknoppies affektuur, en die impak op die roetes van N assimilasie. Tydens P- tekort, het V. divaricata plante 'n verminderde biomassa en P konsentrasie. P- tekort wortelknoppies handhaaf hul P status beter as P beklemtoon wortels. V. divaricata kan C en N metabolisme verander in verskillende maniere in reaksie op P stres. Vir beide wortels en wortelknoppies, bereik dit via interne meganisme van P, deur moontlike vervanging van membraanfosfolipiede met sulpholipids en galactolipids en verhoogde afhanklikheid van die PPI-afhanklike metabolisme van sukrose via UDPG en FRU-6-P. Die derde eksperiment het die GDH transkripsies, hul relatiewe uitdrukkings en aktiwiteit in P-beklemtoon wortels en wortelknoppies tydens N metabolisme geïdentifiseer. Glutamaat dehidrogenase (GDH, EG 1.4.2-4) kan bydra tot die funksionele toleransie van V. divaricata veranderlike grond N en P-vlakke in die volwasse fynbos. Die relatiewe uitdrukking van GDH1 en GDH2 gene is ontleed in die wortels en wortelknoppies, wys dat twee subeenhede gereguleer afhangende van die tipe orrel en P aanbod. Alhoewel beide transkripsies verskyn word, is die GDH1 transkipsie oorheers oor GDH2. Verder kan die uitdrukking van beide GDH transkripsies 'n rol speel in die vermoë van wortelknoppies interne P te reguleer. Met betrekking tot GHD aktiwiteit, is albei aminating en deaminating GDH aktiwiteite veroorsaak tydens P-tekort

The effects of phosphorus (P) deficiency on growth and nitrogen fixation of Virgilia trees from the Cape Floristic Region (CFR)

Thesis (MSc)--Stellenbosch University, 2013.ENGLISH ABSTRACT: The aim of this study was to determine how P nutrition affects biological nitrogen fixation (BNF) via effects on the N2-fixing bacteria in the nodules of Virgilia species native to the Cape Floristic Region (CFR), South Africa. This was evaluated in 3 separate studies: The first study aimed to determine how phosphorus deficiency affects N nutrition of two legume tree species from the Mediterranean Fynbos ecosystem. This study showed that during prolonged P deficiency, V. divaricata maintained a constant biomass, while V. oroboides showed a decreased biomass. V. oroboides showed a decrease in nutritional concentrations, which resulted in the decrease of symbiotic nitrogen fixation (SNF). Both plants utilized atmospheric N more efficiently per nodule under P deficiency. Maximum photosynthesis decreased in V. oroboides, while V. divaricata maintained its photosynthesis. Both species also had greater carbon construction costs during P deficiency. V. divaricata showed clear adaptive features during P-deficiency, as it maintained its growth respiration. The two legume species appear to have different adaptations to P deficiency, which may influence their performance and distribution in their naturally low P environment. The second study aimed to evaluate if soil environmental conditions and mineral nutrient concentration play a major role in microbial communities in plant rhizosphere and nodulation during N2 fixation in legumes. Therefore this study firstly aimed to determine the composition of the N2 fixing bacterial population in the rhizosphere and nodules of V. divaricata. Secondly, it aimed to determine the contribution of these bacteria to N2 fixation during conditions of P deficiency in the Fynbos environment. In the study, the effects of phosphate (P) nutrition on N2 fixing bacterial community structures in Virgilia divaricata rhizosphere and nodules were examined in a pot experiment. V. divaricata were germinated in Fynbos soil as natural inoculum, transferred to clean sand cultures and supplied with 500 μM P and 5 μM P. The N2 fixing bacterial communities in the rhizosphere and nodules were examined based on the PCR-DGGE banding patterns of 16S rDNA and sequencing methods. The GenBank blast results revealed that V divaricata was efficiently nodulated by a wide range of root-nodule bacterial strains, including Burkholderia phytofirmans, Burkholderia sp. and Bradyrhizobium sp. during low P supply. The 15N natural abundance data also confirmed that 40-50% of the N nutrition was acquired through symbiotic N2 fixation. This is not only evidence of nodulation, but also an indication of the adaptation of a range of N2 fixing bacterial strains / species to the nutrient poor, sandy, acidic soil of the Mediterranean-type ecosystems of the Fynbos. The third study examined the physiological effects, such as N2 fixation parameters, plant dependence on N2 fixation, N preference, legume plant growth, carbon costs and amino acid biosynthesis during P deficiency and mineral N supply as NH4NO3 in a slow-growing, Fynbos legume tree, Virgilia divaricata. Continued application of NH4NO3 to the legume plant showed a greater increase in plant dry matter compared to plants with two nitrogen sources (mineral N and atmospheric N2) or plants that relied on atmospheric N2 fixation. Carbon construction costs were more pronounced in plants supplied with two N sources and during P deficiency. Maximum photosynthetic rates per leaf area increased during prolonged P deficiency, irrespective of the N sources. Though plants nodulated, plant dependence on N2 fixation decreased with the addition of NH4NO3. Roots and nodules of the P deficient plants showed an increase in asparagine content, most strikingly so in plants treated with a single source of N. These studies reveal that different legume species of the same genus, may employ contrasting adaptations in order to maintain N nutrition under P deficiency.AFRIKAANSE OPSOMMING: Die doel van hierdie studie was die bepaling van die wyse waarop fosfaat (P) voeding die biologiese stikstof binding (BNF) deur middel van die effek op N2-bindingsbakterië in die wortelknoppies van Virgilia spesies wat inheems tot die Kaap floraryke area (CFR), Suid Afrika is, affekteer. Drie aparte eksperimente is uitgevoer om die doel te evalueer: Die eerste studie het gepoog om te bepaal hoe 'n fosfaat tekort N voeding van twee peulplant spesies van die Mediterreense Fynbos ekosisteem affekteer. Hierdie studie het getoon dat V. divaricata 'n konstante biomassa tydens verlengde P tekort behou, terwyl V. oroboides ‟n verlaagde biomassa getoon het. V. oroboides het 'n verlaging in voedingskonsentrasies getoon, wat tot 'n verlaging in simbiotiese stikstof binding (SNF) gelei het. Beide plante benut atmosferiese N meer doeltreffend per nodule tydens P tekort. Die maksimum fotosintese in V. oroboides het afgeneem, terwyl V. divaricata sy fotosintese gehandhaaf het. Beide spesies het ook 'n groter koolstof konstruksie koste tydens P tekort gehad. V. divaricata toon duidelike aanpassingsmeganismes tydens P-tekort, aangesien hierdie species sy groei respirasie konhandhaaf. Dit wil voorkom asof die twee peulplant spesies verskillend aangepas is vir P tekort, wat hulle producksie en verspreiding in hulle natuurlike lae P omgewing mag beïnvloed. Die doel van die tweede studie was om te bepaal of grond omgewingskondisies en minerale voedingskonsentrasie 'n belangrike rol speel in die mikrobiese gemeenskappe in die plant risofeer en wortelknoppie vorming tydens N2 binding in peulgewasse. Eerstens het die studie dus gepoog om die samestelling van die N2 bindende bakteriële populasie in die risosfeer en die wortelknoppies van V. divaricata te bepaal. Ten tweede, is die bydrae van die bakterië tot N2-binding tydens P tekort kondisies in die Fynbos omgewing bepaal. In die studie is die effek van fosfaat (P) voeding op die N2-bindende bakteriële gemeenskapstrukture in die Virgilia divaricata risofeer en wortelknoppies in 'n pot eksperiment ondersoek. V. divaricata sade is in fynbos grond as 'n natuurlike inokulum ontkiem, waarna dit na skoon sand kulture oorgedra is en van 500 μM P en 5 μM P voorsien is. Die N2-bindende bakteriële gemeenskappe in die risofeer en wortelknoppies is op grond van die PCR-DGGE band patrone van die 16S rDNA en volgorde bepalingsmetodes ondersoek. Die GenBank Blast resultate het getoon dat V. divaricata doeltreffend deur 'n wye reeks wortel-wortelknoppie bakteriële stamme genoduleer is, insluitende insluitende Burkholderia phytofirmans, Burkholderia sp. en Bradyrhizobium sp. tydens lae P toediening. Die natuurlike 15N voorkoms data het ook bevestig dat 40-50% van die N voeding deur simbiotiese N2 binding bekom is. Dit dien nie net as bewys vir wortelknoppie vorming nie, maar ook 'n aanduiding van die aanpassing van 'n reeks N2 bindende bakteriële stamme/ spesies tot die voedingsarme, sanderige, suur grond van die Mediterreanse ekosisteem van die Fynbos. Die derde studie het die fisiologiese effekte soos bv. N2 fikserings faktore, die afhanklikheid van plante op N2 fiksering, N voorkeur, peulgewas groei, koolstof kostes en aminosuur biosintese tydens P tekort en minerale N toediening soos NH4NO3 in 'n stadig-groeiende, Fynbos peulgewasboom, Virgilia divaricata ondersoek. Volgehoue toediening van NH4NO3 aan die peulplant toon 'n groter toename in plant droë weefsel. Tydens P tekort is die koolstof bou koste meer verhoog in plante wat met twee N bronne voorsien is. Tydens verlengde P tekort het die maksimum fotosintese tempo per blaaroppervlakte toegeneem, ongeag die N bron. Alhoewel die plante wortelknoppies gevorm het, het die plant se afhanklikheid van N2 binding tydens die toediening van NH4NO3 afgeneem. Wortels en wortelknoppies van die P tekort plante het 'n toename in asparagien inhoud getoon, veral in die plante wat met 'n enkele bron van N behandel is.The DST/NRF-Center of Excellence for Tree Health and Biotechnology, based at the University of Pretoria, for their financial suppor

Encephalartos villosus and Vigna unguiculata L. (Walp) shared symbionts contribute to V. unguiculata plant nutrition and growth in nutrient-deficient ecosystems

Abstract Cycads are ancient plants that establish symbiotic associations with plant growth-promoting (PGP) microbes. These ancient associations are rarely contrasted with more recent associations involving PGP microbes and legumes. This study investigated if V. unguiculata growing in Encephalartos villosus acidic, and nutrient-deficient rhizosphere and surrounding soils may share similar symbionts. In addition, the biomass accumulation and plant nutrition in V. unguiculata growing in these soils was investigated. Vigna unguiculata seeds were grown in E. villosus rhizosphere and surrounding soils for 45 days. Thereafter, growth characteristics and plant nutrition were calculated. Vigna unguiculata plants grown in E. villosus rhizosphere and surrounding soils were nodulated by Paenibacillus, Bacillus, Peribacillus, Brevibacillus, Alkalihalobacillus, and Lysinibacillus species that were also identified in E. villosus coralloid roots. There were no significant differences in the total plant biomass, however, V. unguiculata plants in rhizosphere and surrounding soils invested more resources in belowground biomass. The findings of this study show that V. unguiculata and E. villosus growing in similar soil conditions may share the same symbionts promoting plant nutrient assimilation and growth.</jats:p

Symbionts in <i>Mucuna pruriens</i> stimulate plant performance through nitrogen fixation and improved phosphorus acquisition

Abstract Aims South Africa is mainly dominated by savanna and grasslands ecosystems which have been previously reported to be acidic and nutrient deficient, specifically with regard to phosphorus (P) and nitrogen (N). Mucuna pruriens (L.) DC, commonly known as velvet bean, is an indigenous legume in most African countries and has been reported to withstand these adverse soil conditions. The legume is used in many countries of the world for their medicinal value as well as for soil fertilization purposes. Although there are reports on M. pruriens growth and establishment in nutrient stressed ecosystems, no investigation has been conducted on M. pruriens symbiotic interactions, N source preference and associated growth carbon costs when subjected to P deficiency. In this study, we determined the impact of microbial symbionts on N nutrition and growth carbon costs of M. pruriens under P deficiency. Methods Microbe inoculation soils were collected from four geographical distinct KwaZulu-Natal locations. Thereafter, seeds were germinated in these natural soils and in early stages of nodule development, then seedlings were transferred in sterile quartz sand and supplied with Long Ashton nutrient media with varying P concentrations. Important Findings The 16S RNA sequence results revealed that M. pruriens was nodulated by Burkholderia sp., Paenibacillus sp. and Bacillus irrespective of P concentrations. Even though P deficiency resulted in decreased overall biomass/growth, the root biomass, nodule number and carbon costs increased. In addition, low P supplied saplings showed the highest arbuscular mycorrhiza fungi percentage root colonization. In M. pruriens, nitrogen derived from atmosphere had a positive correlation with P level and the saplings had a dual reliance on atmospheric derived N and soil derived N with increased reliance on soil N in low P supplied plants. Therefore, M. pruriens exhibited different morphological and microbial symbiosis when subjected to P deficiency. </jats:sec

Soil nutrient concentrations influence micronutrient concentrations in Eragrostis curvula seeds.

Food insecurity often results in malnutrition, manifesting as micronutrient deficiencies that disproportionately affect children under five, impairing their cognitive and physical development. While staple crops supply necessary calories and basic nutrients required for life sustenance, they frequently lack essential micronutrients needed for overall health, necessitating alternative food sources to address food insecurity and malnutrition. This study investigated the potential of Eragrostis curvula seeds as a micronutrient-rich addition to existing food systems and used analyses of covariance to evaluate the influence of soil characteristics on seed nutrient concentrations between two grassland sites in South Africa's Gauteng province: Jameson Park and Kaydale. Populations of E. curvula were identified in Jameson Park and Kaydale, Heidelberg, where rhizosphere soils from selected plants and seeds were harvested for nutrient concentration and soil characteristics analysis. Eragrostis curvula seeds were rich in essential micronutrients, including phosphorus (5041.5-5921.7 mg/kg), iron (72.2-145.4 mg/kg), potassium (4490.5-5531.2 mg/kg), zinc (44.9-65.4 mg/kg), copper (8.6-10.2 mg/kg), calcium (2978.4-16339.1 mg/kg), magnesium (2265.7-2538.4 mg/kg), and manganese (130.2-141.8 mg/kg). Significant site-specific variations were observed: seeds from Jameson Park had higher potassium and calcium concentrations, while Kaydale seeds had higher zinc and iron concentrations. Soil analyses revealed no significant differences in phosphorus, nitrogen, zinc, copper, exchange acidity, or total cation concentrations between the sites. However, calcium levels were significantly higher in Jameson Park soils, while Kaydale soils showed higher potassium, magnesium, and manganese concentrations. Soil nutrient concentrations were found to have a significant influence on seed nutrients. These findings emphasise the potential of E. curvula seeds to improve food security and alleviate micronutrient deficiencies, particularly among vulnerable populations such as young children

Alien invasive <i>Leucaena leucocephala</i> successfully acquires nutrients by investing in below-ground biomass compared to native <i>Vachellia nilotica</i> in nutrient-amended soils in South Africa

Abstract Soils in grasslands and savannas of southern Africa are acidic and nutrient-poor. Legume plants, such as Vachellia nilotica and alien invasive Leucaena leucocephala, are a major component of the vegetation there. Vachellia nilotica can establish in drought-prone environments, and is invasive in high rainfall areas. Leucaena leucocephala is an emerging invasive in South Africa and is ranked among the world’s 100 most invasive alien species. Alien plants can invade native habitats through their adaptability to low-resource soils, and thus can out-compete and displace native vegetation. We investigated the effects of phosphorus (P) deficiency and soil acidity on legume–microbe symbiosis, nitrogen (N) nutrition and carbon (C) growth costs of these two legumes in grassland soils. We used as inoculum and growth substrate soils collected from a long-term (&amp;gt;65 years) nutrient and lime-addition trial, the Veld Fertilizer Trial (VFT), located at Ukulinga Research Farm near Pietermaritzburg in South Africa. We used soils from three VFT treatments: soils fertilized with superphosphate (336 kg ha−1) applied once per year (+P), soils fertilized with superphosphate (336 kg ha−1) applied once per year with dolomitic lime (2250 kg ha−1) applied once every 5 years (P+L) and soils with no superphosphate and no dolomitic lime applications (Control). Seeds of V. nilotica and L. leucocephala were germinated and grown independently in these soils in green house conditions and harvested after 125 days for measurement of growth, legume–microbe symbiosis, N nutrition and C growth costs. Results showed that the two legumes had different growth adaptations. Vachellia nilotica grown in control soils and +P soils nodulated with various Burkholderia spp., while L. leucocephala did not nodulate in all soil treatments. Both legumes utilized for growth both atmospheric- and soil-derived N across all treatments thereby decreasing C growth costs. Vachellia nilotica grown in +P soils accumulated the most biomass and N nutrition. Leucaena leucocephala maximized specific N assimilation rates by investing in below-ground biomass accumulation in control soils. This shows that L. leucocephala possesses traits that are successful in acquiring nutrients by investing in below-ground biomass and relying on utilization of N from both the soil and the atmosphere.</jats:p

Nitrogen Source Preference and Growth Carbon Costs of Leucaena leucocephala (Lam.) de Wit Saplings in South African Grassland Soils

Leucaena leucocephala (Fabaceae) is native to Central America and has invaded many climatic regions of the tropics. In South Africa, the species is categorized as an emerging or incipient weed used as fodder, timber, firewood and in erosion control on degraded habitats. The species is common along the eastern subtropical regions of KwaZulu-Natal (KZN) Province, where it invades grasslands, savannas and edges of forests. Soils of these ecosystems are characterized as nutrient deficient and acidic. Using a pot trial, we determined the effects of the nutrient addition treatments on microbial symbiosis, N nutrition and biomass accumulation of L. leucocephala under greenhouse conditions. After 180 days of growth, plants were harvested, and their utilization of N derived from the atmosphere and from the soil was quantified through determination of δ15N values. L. leucocephala maintained growth and N nutrition by relying on both atmospheric- and soil-derived N across all soil treatments. The NDFA was significantly higher in high P (N1 + P, N2 + P and N3 + P) soils. L. leucocephala was able to nodulate with intermediate and fast-growing strains from the Mesorhizobium and Rhizobium genus in N2 + P grown plants. This shows that L. leucocephala possesses traits that are successful in acquiring nutrients, especially in nutrient limited conditions, by establishing plant symbiosis with multiple bacteria and relying on extracting N from the soil and from the atmosphere through the symbiosis.</jats:p

Phenolic acids and antioxidant regulation in Vigna unguiculata L. (Walp) growing in acidic and nutrient deficient grassland and savanna soils

Abstract PurposeSoil acidity and nutrient stress in grassland and savanna ecosystems are the major abiotic factors affecting crop production thus contributing to food insecurity. Some plants including crop legumes may thrive in acidic and nutrient stressed soil environments by regulating their secondary metabolites. In this study, we investigated how four Vigna unguiculata varieties regulated their phenolic acid concentrations and antioxidant capacities to better adapt to acidic and nutrient deficient grassland and savanna ecosystems.MethodsFour V. unguiculata varieties (IT18, Batch white, Brown mix and Dr Saunders) were grown in soils collected from four geographically distinct areas (Bergville, Ashburton, Izingolweni, Hluhluwe) in KwaZulu-Natal covering grassland and savanna ecosystems. Plants were analyzed for nutrient composition, arbuscular mycorrhizal fungi colonization percentage, root nodulating bacteria. Identification and quantification of phenolic acids was also done on both above ground and below ground plant parts. Oxygen radical absorbance capacity of the different V. unguiculata varieties was also determined. ResultsThere were differences in plant biomass and nitrogen and phosphorus nutrition across the four V. unguiculata varieties, with high arbuscular mycorrhizal fungi colonization of greater than 58%. V. unguiculata was nodulated by several bacterial strains including Bacillus, Paenibacillus, Delftia, Rhizobium and Bradyrhizobium All four V. unguiculata varieties had variations of phenolic acids across all soil types with vanillic acid and protocatechuic acid being the most abundant and constituted 22.59% and 17.22%, respectively of the total quantified phenolic acids. Principal component analysis showed that the four V. unguiculata varieties responded differently to the different soil types with respect to phenolic acid production. There were variations in correlations between the phenolic acids and plant biomass, plant nutrition, soil nutrition and arbuscular mycorrhizal fungi infection. Varieties IT18 and Batch white had relatively higher oxygen radical absorbance capacity (ORAC) across the four soil types and comparably higher plant biomass relative to Brown mix and Dr Saunders.ConclusionOverall, the current findings demonstrated that V. unguiculata has the potential of adapting to acidic and nutrient stressed grassland and savanna conditions through production of phenolic acids and enhanced antioxidant capacity.</jats:p