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Root architectural traits of rooted cuttings of two fig cultivars: Treatments with arbuscular mycorrhizal fungi formulation
Abstract
Many fruit tree species develop symbioses relationships with mycorrhizal fungi by which they improve their efficiency in water and nutrient uptake and, in turn, increase their vegetative growth and productivity, particularly under stressful environments. These benefits origin from the effects that mycorrhizal determined on the root architecture, morphology and physiology. Usually, few attentions has been devoted to the tree root structure and function, especially, in fig plants during their growth phase in the nursery. Recently, several root traits or phenes have been reported as fundamental for the root functions such as the root length ratio (plant’s potential for the exploitation of soil resources); root mass ratio (allocation traits); the root fineness and tissue density (structural traits); the root very fine, fine and coarse (functional traits). Aim of the study was to test the effects of an arbuscular mycorrhizal fungi (AMF) on the root architecture traits of self-rooted cuttings of two fig (Ficus carica L.) cultivars: Dottato and Natalese. The root architecture traits were evaluated by image analysis system (WinRHIZO). Single root traits and rooting architecture models were statistically tested by univariate and multivariate analysis, respectively. This study confirmed that also the Ficus carica was positively responsiveness to the mycorrhizal inoculation but with cultivar-dependent patterns. Further, the fig with coarse root architecture is more responsive to the fungi inoculation and the AMF induced different root architecture models in Natalese and Dottato suggesting diverse root strategies for exploiting the soil resources.
... It emphasizes that assessment of the root structure architecture (RSA) is highly correlated with the establishment of plant-fungal symbiosis. The RSA permits a closer inspection of the impacts of AMF on the root morphology of a host plant by deliberating the trends of several root parameters along this symbiotic relationship (Caruso et al., 2021). ...
... Among the RSA parameters examined, the data gathered were significant (p<0.05) to confirm the responsiveness of the root diameter and surface area towards the inoculation of AMF. Accordingly, researchers of related studies have confirmed that increased morphological traits in inoculated eggplants allow these plants to develop coarse RSA compared to uninoculated plants (Caruso et al., 2021). Thus, increased diameter and surface area strongly account for the apparent relatively coarser and denser root system of the AMF + V group as can be observed in Figure 2. Improved RSA parameters have been studied to confer advantageous qualities on plants that would aid in performing various biological mechanisms that enable them to withstand destructive environmental conditions (Caruso et al., 2021). ...
... Accordingly, researchers of related studies have confirmed that increased morphological traits in inoculated eggplants allow these plants to develop coarse RSA compared to uninoculated plants (Caruso et al., 2021). Thus, increased diameter and surface area strongly account for the apparent relatively coarser and denser root system of the AMF + V group as can be observed in Figure 2. Improved RSA parameters have been studied to confer advantageous qualities on plants that would aid in performing various biological mechanisms that enable them to withstand destructive environmental conditions (Caruso et al., 2021). Furthermore, a study had shown that positive alterations induced by mycorrhizal treatment on root parameters like total diameter could be highly correlated with the modified nutritional status of plants (Yao et al., 2009) suggesting that scrutiny on this biological aspect could delineate the induced enhancements of AMF obtained in this study. ...
Solanum melongena L. is among the most economically valued horticultural crops globally. In the Philippines, the annual production of this staple crop increases continually. However, several biotic and abiotic factors deteriorate its overall growth and productivity. Recently, the use of sustainable biofertilizers such as arbuscular mycorrhizal fungi (AMF) is gaining interest because of their beneficial impacts on overall plant productivity. One way of examining plant productivity is through root structure architecture (RSA) assessment. Hence, this study aimed to investigate the effects of AMF on the RSA of eggplants to supplement valuable data on its beneficial effects as a biofertilizer. Seedlings were inoculated with four treatment conditions AMF + vermicompost (AMF + V), AMF alone (AMF), NPK fertilizer (NPK), and native soil (C) followed by RSA assessment Results showed that treatments AMF + V and AMF alone significantly promoted lateral root branching. Furthermore, the total diameter and surface area showed a significant increase under treatment AMF + V. Overall, the mycorrhizal-root association presented enhancement towards eggplant RSA which strongly establishes the efficacy of AMF as a promising solution in promoting sustainable agriculture.
... Meanwhile, optimal K nutrient management strategy for sustainable and environmentally protective crop production was using KIUE genotypes in combination with appropriate soil fertilization (Romheld and Kirkby, 2010). It is acknowledged that root architecture plays a fundamental role for water and nutrients uptake from soil and in turn, yield production (Alhadidi et al., 2021;Caruso et al., 2021). Optimizing root morphology of sweet potato are effective methods guaranteeing yield production of sweet potato. ...
... On the one hand, plant genotypes were considered in this study. Root morphological indexes (root DM, total root length, root surface area, root volume, root diameter, root branch number, and root tip number) should be analyzed when checking root growth state (Alhadidi et al., 2021;Caruso et al., 2021). As shown in the recent study, Glomus intraradices induced different root architecture models (length, surface area, average diameter, and biomass) in relation to the cultivars of Ficus carica, suggesting diverse root strategies for exploiting the soil resources (Caruso et al., 2021). ...
... Root morphological indexes (root DM, total root length, root surface area, root volume, root diameter, root branch number, and root tip number) should be analyzed when checking root growth state (Alhadidi et al., 2021;Caruso et al., 2021). As shown in the recent study, Glomus intraradices induced different root architecture models (length, surface area, average diameter, and biomass) in relation to the cultivars of Ficus carica, suggesting diverse root strategies for exploiting the soil resources (Caruso et al., 2021). In this study, FM and CE inoculation increased root tip number of "N1" in the swelling stage and optimized multiple indexes of root morphology of "Xu28" during the whole growth stage under the condition with K application (Figure 4), indicating that AMF differentially regulated root morphology of low-KIUE and high-KIUE sweet potato. ...
Sweet potato is a typical “potassium (K)-favoring” food crop and strongly dependent on arbuscular mycorrhizal fungi (AMF). Recent studies show the importance of K and AMF to morphology optimization and nutrient uptake regulation of sweet potato; meanwhile, the interaction exists between K and K use efficiency (KIUE) in sweet potato. To date, only a few studies have shown that AMF can improve plant K nutrition, and whether the benefits conferred by AMF on plant are related to K remains unclear. In this study, low-KIUE genotype “N1” and high-KIUE genotype “Xu28” were used as experimental sweet potato; Funneliformis mosseae (FM) and Claroideoglomus etunicatum (CE) were used as experimental AMF. In a pot experiment, plants “N1” and “Xu28” were inoculated with FM or CE, and applied with or without K fertilizer to uncover the effects of K application and AMF inoculation on the root morphology and nutrient absorption of sweet potato during their growing period. Results demonstrated that AMF inoculation-improved root morphology of sweet potato highly relied on K application. With K application, AMF inoculation significantly increased root tip number of “N1” in the swelling stage and optimized multiple root morphological indexes (total root length, root surface area, root volume, root diameter, root branch number, and root tip number) of “Xu28” and CE had the best optimization effect on the root morphology of “Xu28”. In addition, CE inoculation significantly promoted root dry matter accumulation of “Xu28” in the swelling and harvesting stages, coordinated aerial part and root growth of “Xu28”, reduced the dry matter to leaf and petiole, and was beneficial to dry matter allocation to the root under conditions of K supply. Another promising finding was that CE inoculation could limit K allocation to the aboveground and promote root K accumulation of “Xu28” under the condition with K application. The above results lead to the conclusion that K and CE displayed a synergistic effect on root development and K acquisition of high-KIUE “Xu28”. This study could provide a theoretical basis for more scientific application of AMF in sweet potato cultivation and will help further clarify the outcomes of plant-K–AMF interactions.
... Furthermore, Comlekcioglu et al. (2008) observed a positive effect on the root system growth of the fig cultivar Alkuden in response to different Glomus species. Additionally, Caruso et al. (2021) reported that Ficus carica was positively responsive to the mycorrhizal inoculation but with cultivar-dependent patterns. However, AMF studies of fegra fig have not been conducted. ...
... Comlekcioglu et al. (2008) reported that mycorrhizal inoculation increased the shoot, root dry weight, zinc, and phosphorus uptake of micropropagated plantlets of fig (Ficus carica). Caruso et al. (2021) confirmed that Ficus carica was positively responsive to the mycorrhizal inoculation but with cultivar-dependent patterns, and all root growth parameters of the cultivar Natalese treated with AMF were increased compared with those not treated with non-AMF. It has been previously reported that inoculation with G. margarita and G. albida significantly improved growth and root development of micropropagated fruit species such as blackberry (Rubus fruticosus 'P45') (Dewir et al. 2023a) and red dragon fruit (Hylocereus polyrhizus) (Dewir et al. 2023b). ...
... Furthermore, Comlekcioglu et al. (2008) observed a positive effect on the root system growth of the fig cultivar Alkuden in response to different Glomus species. Additionally, Caruso et al. (2021) reported that Ficus carica was positively responsive to the mycorrhizal inoculation but with cultivar-dependent patterns. However, AMF studies of fegra fig have not been conducted. ...
... Comlekcioglu et al. (2008) reported that mycorrhizal inoculation increased the shoot, root dry weight, zinc, and phosphorus uptake of micropropagated plantlets of fig (Ficus carica). Caruso et al. (2021) confirmed that Ficus carica was positively responsive to the mycorrhizal inoculation but with cultivar-dependent patterns, and all root growth parameters of the cultivar Natalese treated with AMF were increased compared with those not treated with non-AMF. It has been previously reported that inoculation with G. margarita and G. albida significantly improved growth and root development of micropropagated fruit species such as blackberry (Rubus fruticosus 'P45') (Dewir et al. 2023a) and red dragon fruit (Hylocereus polyrhizus) (Dewir et al. 2023b). ...
Fegra fig ( Ficus palmata ) is an important fruit-yielding crop and potential rootstock for grafting Ficus carica . The acclimatization phase is a pivotal step during the micropropagation of plants. During this study, the mycorrhization of micropropagated fegra fig plants with two arbuscular mycorrhizal fungi (AMF; Gigaspora margarita and Gigaspora albida ) to enhance their growth and survival during the acclimatization stage was investigated. The AMF were mixed in equal proportions and the acclimatizing fegra fig plantlets were treated for 8 weeks. The leaf pigments, i.e., chlorophyll a [2.56 mg·g ⁻¹ fresh weight (FW)], chlorophyll b (1.08 mg·g ⁻¹ FW), total chlorophyll (3.67 mg·g ⁻¹ FW), and carotenoid (1.34 mg·g ⁻¹ FW), of AMF-treated plants were higher than those of non-AMF plants. The number of stomata per unit was higher in the AMF-treated plants (16.00), the density of stomata per unit area (88.40 mm ² ) of AMF-treated plants was similar to that of non-AMF treated plants, and the number of epidermal cells (79.00) was higher in the AMF-treated plants. The AMF-treated plants were taller and had more leaves, a greater leaf area, and higher shoot FW and dry weight. The AMF-treated plants also had the greatest total root length values, greatest surface areas of roots, and greatest total root volume and diameter compared to those of non-AMF plants. Additionally, the AMF-treated plants had a 100% survival rate, whereas a survival rate of 95% was recorded for non-AMF plants. These findings emphasize the importance of biological acclimatization of micropropagated fegra fig plants with AMF.
... The root length, root volume, and number of root branches were all affected to varying degrees, and the root configuration of licorice under different AMF strains was also distinguishing. When plants were inoculated with AMF, the root morphology changed and the root tip necrosis rate was significantly reduced, thus promoting water absorption and root growth [26]. Under AMF treatment, the results of the growth change in Ammopiptanthus mongolicus seedlings were consistent in that the treatment promoted biomass accumulation and root growth [27]. ...
Several studies have been devoted to seeking some beneficial plant-related microorganisms for a long time, and on this basis, it has been found that arbuscular mycorrhizal fungi (AMF) have a considerable positive impact on plant health as a biological fungal agent. In this study, we focused on the effects of different AMF on the growth dynamics and root configuration of licorice under saline and alkali conditions. The metabolites of licorice under different AMF were assessed using liquid chromatography–tandem mass spectrometry (LC-MS/MS). Funneliformis mosseae (Fm) and Rhizophagus intraradices (Ri) were added as different AMF treatments, while the sterilized saline–alkali soil was treated as a control. Samples were taken in the R1 period (15 d after AMF treatment) and the R2 period (45 d after AMF treatment). The results showed that the application of AMF significantly increased the root growth of licorice and significantly increased the biomass of both shoot and root. A total of 978 metabolites were detected and divided into 12 groups including lipids, which accounted for 15.44%; organic acids and their derivatives, at 5.83%; benzene compounds and organic heterocyclic compounds, at 5.42%; organic oxides, at 3.78%; and ketones, accounting for 3.17%. Compared with the control, there were significant changes in the differential metabolites with treatment inoculated with AMF; the metabolic pathways and biosynthesis of secondary metabolites were the main differential metabolite enrichment pathways in the R1 period, and those in the R2 period were microbial metabolism in diverse environments and the degradation of aromatic compounds. In conclusion, the use of AMF as biofertilizer can effectively improve the growth of licorice, especially in terms of the root development and metabolites, in saline–alkali soil conditions.
... For 20 min at 90 • C, root was stained with a 0.05 %, trypan blue and dye. Roots that had been stained were left in lactoglycerol overnight to separate the colors (Caruso et al., 2021;Tajuddin and Salleh, 2022). The gridline intersects approach was used to examine and measure the AMF root colonization rate using optical microscope. ...
Drought is a potent abiotic stressor that arrests crop growth, significantly affecting crop health and yields. The arbuscular mycorrhizal fungi (AMF), and plant growth-promoting rhizobacteria (PGPR) can offer to protect plants from stressful environments through improving water, and nutrient use efficiency by strengthening plant root structure and harnessing favorable rhizosphere environments. When Acaulospora laevis (AMF) and Bacillus subtilus (PGPR) are introduced in combination, enhanced root growth and beneficial microbial colonization can mitigate drought stress. To assess this potential, a pot experiment was done with maize (Zea mays L.) to explore the effects of A. laevis and B. subtilus under different water levels (well-watered = 80 %; moderate water stress = 55 %; and severe water stress = 35 %) on maize yield, soil microbial activities, nutrients contents, root, and leaf functioning. Plants exposed to severe drought stress hampered their root and leaf functioning, and reduced grain yield compared with control plants. Combined use of AMF and PGPR increased root colonization (104.6 %– 113.2 %) and microbial biomass carbon (36.38 %–40.23 %) under moderate to severe drought conditions over control. Higher root colonization was strongly linked with elevated ACC (aminocyclopropane-1-carboxylic acid) production, subsequently enhancing water use efficiency (21.62 %–12.77 %), root hydraulic conductivity (1.9 %–1.4 %) and root nutrient uptake under moderate to severe drought conditions. Enhanced nutrient uptake further promoted leaf photosynthetic rate by 27.3 %–29.8 % under moderate and severe drought stress. Improving leaf and root physiological functioning enhanced maize grain yield under stressful environments. Furthermore, co-inoculation with AMF-PGPR reduced cellular damage by lowering oxidative enzyme levels and increasing antioxidative enzyme activities, improving plant performance and grain yield under stressful environments. Conclusively, the synergistic interaction of AMF with PGPR ensured plant stress tolerance by reducing cellular injury, facilitating root-leaf functioning, enhancing nutrient-water-use-efficiencies, and increasing yield under drought stress.
... Another study reported that inoculation of American ginseng (Panax quinquefolius L.) with arbuscular mycorrhizal fungi (AMF) resulted in enhanced nutrient uptake and modified the abundance and diversity of rhizosphere microorganisms [99]. Similarly, the mycorrhizal growth response (Glomus intraradices) on the root architecture traits of fig cultivars (Dottaeto and Natalese) has been observed in detail by Caruso et al. [100]. The study reported positive synergism between fungal inoculation and nutrient foraging by the host plant. ...
Over the past half century, limited use of synthetic fertilizers, pesticides, and conservation of the environment and natural resources have become the interdependent goals of sustainable agriculture. These practices support agriculture sustainability with less environmental and climatic impacts. Therefore, there is an upsurge in the need to introduce compatible booster methods for maximizing net production. The best straightforward strategy is to explore and utilize plant-associated beneficial microorganisms and their products. Bioinoculants are bioformulations consisting of selected microbial strains on a suitable carrier used in the enhancement of crop production. Fungal endophytes used as bioinoculants confer various benefits to the host, such as protection against pathogens by eliciting immune response, mineralization of essential nutrients, and promoting plant growth. Besides, they also produce various bioactive metabolites, phytohormones, and volatile organic compounds. To design various bioformulations, transdisciplinary approaches like genomics, transcriptomics, metabolomics, proteomics, and microbiome modulation strategies like gene editing and metabolic reconstruction have been explored. These studies will refine the existing knowledge on the diversity, phylogeny and beneficial traits of the microbes. This will also help in synthesizing microbial consortia by evaluating the role of structural and functional elements of communities in a controlled manner. The present review summarizes the beneficial aspects associated with fungal endophytes for capitalizing agricultural outputs, enlists various multi-omics techniques for understanding and modulating the mechanism involved in endophytism and the generation of new bioformulations for providing novel solutions for the enhancement of crop production.
... In return, mycorrhizal fungi can also obtain carbon sources from host plants for growth and reproduction (Smith and Read 2008). AM induced positive effects on plant root growth and nutrition, e.g., Caruso et al. (2021) found that AM fungi significantly increased dry weight, length, surface area, and average diameter in morphological traits. For karst plants, He and Zhong (2012) also illustrated that AM fungi significantly enhanced the root length, volume, surface area, and tips of Cinnamomum camphora seedlings and the acquisition of N and P for Broussonetia papyrifera roots (He 2019;He et al. 2007). ...
Arbuscular mycorrhizal (AM) fungi can affect plant growth by regulating competition. Nutrient-deficient karst habitats contain abundant plants that compete for nutrients through interspecific or intraspecific competition, involving the nutritional transformation of litter decomposition. However, how plant competition in the presence of AM fungi and litter affects root development and nutrition remains unclear. A potted experiment was conducted, including AM fungus treatment with or without Glomus etunicatum, the competition treatment concerning intraspecific or interspecific competition through planting Broussonetia papyrifera and Carpinus pubescens seedlings, and the litter treatment with or without the mixture of B. papyrifera and C. pubescens litter leaves. The root morphological traits were analyzed, and nitrogen (N), phosphorus (P), and potassium (K) were measured. The results showed that AM fungus differently affected the root morphological development and nutrition of both competitive plants, significantly promoting B. papyrifera roots in the increase of dry weight, length, volume, surface area, tips, and branches as well as N, P, and K acquisitions regardless of litter addition. However, there was no apparent influence for C. pubescens roots, except for the diameter in the interspecific competition with litter. The root dry weight, length, volume, surface area, and tips of B. papyrifera under two competitive styles were significantly greater than C. pubescens regulated by AM fungus, presenting significant species differences. The responses of the relative competition intensity (RCI) on root morphological and nutritional traits indicated that AM fungus and litter both asymmetrically alleviated more competitive pressure for B. papyrifera than C. pubescens, and the interspecific competition facilitated more root morphological development and nutrition utilization by endowing B. papyrifera root superiority relative to C. pubescens compared with the intraspecific competition. In conclusion, interspecific competition is more beneficial for plant root development and nutrition than intraspecific competition in the presence of AM fungus and litter via asymmetrically alleviating competitive pressure for different plants.
... The root growth parameters measured were as follows: total root length (cm), total root surface area (cm 2 ), average root diameter (cm), total root volume (cm 3 ), number of root tips, and number of root forks. Additionally, total root length was distributed into three root diameter classes, following the criteria applied by Caruso et al. [52]: very fine (≤0.5 mm), fine (>0.5-≤1.0 mm), and large (>1.0 mm). ...
The spatial arrangement and growth pattern of root systems, defined by the root system architecture (RSA), influences plant productivity and adaptation to soil environments, playing an important role in sustainable horticulture. Florida’s peach production area covers contrasting soil types, making it necessary to identify rootstocks that exhibit soil-type-specific advantageous root traits. In this sense, the wide genetic diversity of the Prunus genus allows the breeding of rootstock genotypes with contrasting root traits. The evaluation of root traits expressed in young seedlings and plantlets facilitates the early selection of desirable phenotypes in rootstock breeding. Plantlets from three peach × (peach × almond) backcross populations were vegetatively propagated and grown in rhizoboxes. These backcross populations were identified as BC1251, BC1256, and BC1260 and studied in a completely randomized design. Scanned images of the entire root systems of the plantlets were analyzed for total root length distribution by diameter classes, root dry weight by depth horizons, root morphological components, structural root parameters, and root spreading angles. The BC1260 progeny presented a shallower root system and lower root growth. Backcross BC1251 progeny exhibited a more vigorous and deeper root system at narrower root angles, potentially allowing it to explore and exploit water and nutrients in deep sandy entisols from the Florida central ridge.
... The R/S ratio of AM inoculated plants was remarkably higher than non-AM ones indicating their direct role in enriching the roots system and acting as an effective mode of stress resistance. Moreover, higher root growth indicates that pigeon pea plants might have invested more in root production for resource capture under mycorrhizal inoculations, as reported in wheat as well as faba bean (Qiao et al. 2015) and fig cultivars (Caruso et al. 2021). AM inoculations counteracted the negative effects of Cd on nodular efficacy in terms of increased NN and NDW which further correlated with higher N and P concentration in the plant tissues. ...
Cadmium pollution of soil restricts growth and yield of crop plants. Arbuscular mycorrhizae play significant roles in imparting tolerance to Cd toxicity by establishing symbiotic association with the host plants species. The present study therefore evaluated the effects of four arbuscular mycorrhizal fungal species (AMF), i.e. Claroideoglomus claroideum (AM1), Claroideoglomus etunicatum (AM2), Funneliformis mosseae (AM3) and Rhizoglomus intraradices (AM4), in modulating physiological and molecular attributes of Cd-stressed (Cd – 0, 50 mg/kg) Cajanus cajan (L.) Millsp. (pigeon pea) plants. Application of Cd reduced growth (more in roots than shoots), nitrogen fixing potential and yield. It also led to generation of reactive oxygen species as well as membrane leakiness. AMF supplementations improved growth, nutrient acquisition, rhizobial symbiosis, reduced oxidative burden and Cd uptake by enhancing the synthesis of thiols (cysteine, reduced and oxidized glutathione, phytochelatins, non-protein thiols). Activity of glutathione reductase increased significantly in AMF inoculated plants which imparted redox balance by improving GSH/GSSG ratio in roots and shoots. Quantitative RT-PCR analysis displayed abundance of transcripts encoding two metal chelator genes; metallothionein (CcMT1) and phytochelatin synthase1 (isoforms CcPCS1X1, CcPCS1X2 and CcPCS1X4) which expressed more in roots than leaves of Cd-stressed AMF plants. Moreover, expression level of CcMT1 was more intense than CcPCS1 indicating higher ability of MTs to combat Cd stress than PCS. R. intraradices was the most efficient in inducing the expression of metal responsive genes than other three species suggesting its promising role in the amelioration of Cd toxicity in pigeon pea.
... The measurements of the root-growth parameters were total root length (cm), total root-surface area (cm 2 ), average root diameter (mm), total root volume (cm 3 ), number of root tips, and number of root forks. Additionally, the root length was estimated for each root diameter class, following the criteria applied by Caruso et al. [54]: very fine (≤0.5 mm), fine (from >0.5 mm to <1.0 mm), and large (>1.0 mm). ...
Rootstocks are fundamental for peach production, and their architectural root traits determine their performance. Root-system architecture (RSA) analysis is one of the key factors involved in rootstock selection. However, there are few RSA studies on Prunus spp., mostly due to the tedious and time-consuming labor of measuring below-ground roots. A root-phenotyping experiment was developed to analyze the RSA of seedlings from ‘Okinawa’ and ‘Guardian’TM peach rootstocks. The seedlings were established in rhizoboxes and their root systems scanned and architecturally analyzed. The root-system depth:width ratio (D:W) throughout the experiment, as well as the root morphological parameters, the depth rooting parameters, and the root angular spread were estimated. The ‘Okinawa’ exhibited greater root morphological traits, as well as the other parameters, confirming the relevance of the spatial disposition and growth pattern of the root system.
... Roots were stained with 0.05% trypan blue and dye for 20 minutes at 90 °C. Stained roots were kept in lactoglycerol overnight for color separation (Caruso et al. 2021;Tajuddin and Salleh 2022). AMF root colonization rate was observed and recorded with an optical microscope (Zeiss Axio Lab.A1 having 10 Mp camera) using the gridline intersect method. ...
Purpose
In drought-prone soils, plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungus (AMF) might positively affect water uptake and crop yield via rhizosphere interactions.
Methods
Sole and combined additions of Bacillus amyloliquefaciens producing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and Rhizophagus irregularis into rhizospheric soils were performed under well-watered (WW; 80% field water capacity), moderate water stress (MWS; 50% FWC) and severe water stress (SWS; 35% FWC) in pot-cultured wheat (Triticum aestivum L.).
Results
In moderate and severe drought stress, water use efficiency (WUEB) was increased by 27.9–34.3% in PGPR and 20–22.1% in AMF treatments, respectively, and grain yield was improved by 20.03–30.77% in PGPR and 12.13–34.34% in AMF treatments, respectively, compared with control (CK). Importantly, the co-inoculation of AMF and PGPR significantly promoted WUEB by 11.12–27.77% and grain yield by 18.26–21.68% compared to the average value of two sole inoculations in MWS and SWS treatments, respectively. WUEY and biomass production followed a similar trend as WUEB and yield. Particularly, the above parameters were significantly enhanced with the prolonged developmental stages (p < 0.05). ACC deaminase significantly reduced ACC accumulation in MWS and SWS, enhanced AMF root colonization, and promoted rhizosphere microbial biomass carbon and nitrogen levels across all three developing stages. Furthermore, AMF-PGPR co-inoculation enhanced chlorophyll and carotenoid contents during anthesis while reducing them during pre-harvesting. Enhanced water uptake and root activities upsurged photosynthetic traits throughout the growing season.
Conclusion
AMF-PGPR co-inoculation acted as a promising solution to cope with the droughted environment via root activities for stronger water capture.
... Roots were stained with 0.05% trypan blue and dye for 20 minutes at 90 ℃. Stained roots were kept in lactoglycerol overnight for color separation (Caruso et al. 2021; Tajuddin and Salleh 2022). AMF root colonization rate was observed and recorded with an optical microscope (Zeiss Axio Lab.A1 having 10 Mp camera) using the gridline intersect method. ...
Purpose
In drought-prone soils, plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungus (AMF) might positively affect water uptake and crop yield via rhizosphere interactions.
Methods
Sole and combined additions of Bacillus amyloliquefaciens producing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and Rhizophagus irregularis into rhizospheric soils were performed under well-watered (WW; 80% field water capacity), moderate water stress (MWS; 50% FWC) and severe water stress (SWS; 35% FWC) in pot-cultured wheat (Triticum aestivum L.).
Results
In moderate and severe drought stress, water use efficiency (WUEB) was increased by 27.9–34.3% in PGPR and 20-22.1% in AMF treatments, respectively, and grain yield was improved by 20.03–30.77% in PGPR and 12.13–34.34% in AMF treatments, respectively, compared with CK. Importantly, the co-inoculation of AMF and PGPR significantly promoted WUEB by 57.46–98.49% and grain yield by 131.82–94.94% compared to the average value of two sole inoculations in MWS and SWS treatments, respectively. Biomass production followed a similar trend as yield. Particularly, the above parameters were significantly enhanced with the prolonged developmental stages (p < 0.05). ACC deaminase significantly reduced ACC accumulation in MWS and SWS, enhanced AMF root colonization, and promoted rhizosphere microbial biomass carbon and nitrogen levels across all three developing stages. Furthermore, AMF-PGPR co-inoculation enhanced chlorophyll and carotenoid contents during anthesis while reducing them during pre-harvesting. Enhanced water uptake and root activities upsurged photosynthetic attributes throughout the growing season.
Conclusion
AMF-PGPR co-inoculation acted as a promising solution to cope with the droughted environment via root activities for stronger water capture.
... Hence, our understanding of RSA is still inadequate, especially for woody plants, the main constituents of forested terrestrial ecosystems, whose large and multiple root systems are hidden deeper underground, which increases the difficulty of exploring their structure and function . Previous studies of RSA have mainly relied on root growth or related characteristics, such as root diameter, specific root length, specific root surface area, and fine root biomass (Dorairaj et al., 2020;Madsen et al., 2020;Caruso et al., 2021). Moreover, these parameters cannot intuitively describe the spatial phenotypes of the distribution, arrangement, and location of fine roots in the soil, the growth medium (Luo et al., 2020). ...
The root system architecture (RSA), being a key characteristic of the root economic spectrum, describes the spatial arrangement and positioning of roots that determines the plant's exploration of water and nutrients in the soil. Still, it remains poorly understood how the RSA of woody plants responds to the demand for water and nutrients in different soil environments and how the uptake of these resources is optimized. Here we selected single-species plantations of Cupressus funebris and determined their topological index (TI), revised topological index (qa and qb), root link length (RLL), root branching rate (Rb and Ri:Ri+1), and in situ soil physicochemical properties to assess which root foraging strategies adopt in different soil environments among Guang'an City (GA), Suining City (SN), Mianyang City (MY), and Deyang City (DY) in China. We also tested the potential effects of different nutrients upon RSA according to its plastic phenotype. Principal component analysis (PCA) showed that levels of soil nutrients were the highest at DY, followed by MY and SN, and lower at GA. A dichotomous branching pattern was observed for GA, SN, and MY, but a herringbone branching pattern for DY. The RLL was ranked as GA, > SN, > MY > DY. The Rb of GA, SN, and MY was significantly lower than that of DY (p < 0.05). Among the different city regions, values of R1/R2 were the largest in different regions and those of R4/R5 the smallest. The cross-sectional area of the root system did not differ between any two connected branch orders. The TI, qa, and RLL were significantly and negatively correlated with soil's water content, porosity, total nitrogen, total potassium, available nitrogen, and available phosphorus (p < 0.05), whereas they all had significant, positive relationships with soil temperature (p < 0.05). The Rb was significantly and positively correlated with total potassium in soil (p < 0.05). Redundancy analysis showed that total potassium was the main factor driving variation in RSA. Our results emphasize that the RSA is capable of corresponding plastic alterations by changing its number of internal or external links and the root link length of fine roots vis-à-vis a heterogeneous environment, thereby optimizing the rates of water capture and space utilization.
... Our results therefore confirm that sensitivity to IBA dosage varies among species and their cultivars. As argued by [52], the root fineness (Figure 3), recorded image analysis techniques, could be a very important trait for the water and nutrient uptake in woody cuttings. ...
Adventitious root (AR) formation is a key step in stem cutting propagation of economically important woody ornamentals. Inadequate environmental and hormonal conditions can lead to the production of an insufficient or modest number of ARs in stem cutting, with a consequent decrease in quality. The aim of this research was to optimize wild sage and glossy abelia autumn stem cutting propagation protocols, using image analysis to assess the effects of different IBA concentrations and cultivars on AR quality. For both taxa, the treatments were: four IBA concentrations: 0, 1250, 2500 and 5000 mg L−1 and two cultivars: ‘Little Lucky’ (cv1) and ‘Yellow’ (cv2) from Lantana, and ‘Canyon Creek’ (cv1) and ‘Eduard Goucher’ (cv2) from Abelia. Results show that IBA application is not needed to enhance rooting ability; however, IBA concentration is an important factor determining the best overall AR quality in both taxa. In wild sage applying 5000 mg L−1 IBA improved AR quality in ‘Little Lucky’, increasing the root number, total length, surface area and number of forks and crossings, but decreased quality in ‘Yellow’. In glossy abelia ‘Edouard Goucher’, 5000 mg L−1 IBA increased the root number, but 1250 mg L−1 IBA improved AR quality; ‘Canyon Creek’ did not perform as well as cv2 at these concentrations. This study confirms that sensitivity to IBA dosage varies among species and their cultivars. Findings may help the commercial nursery industry produce higher quality cuttings.
Arbuscular mycorrhizal fungi (AMF) are known to enhance plant growth via stimulation of root system development. However, the extent of their effects and underlying mechanisms across different citrus genotypes remain to be fully elucidated. This study investigates the impact of Funneliformis mosseae (F. mosseae) inoculation on plant growth performance, root morphology, phosphorus (P), and indole-3-acetic acid (IAA) concentrations, as well as the expression of related synthesis and transporter genes in three citrus genotypes: red tangerine (Citrus tangerine ex. Tanaka), kumquat (Fortunella margarita L. Swingle), and fragrant citrus (Citrus junos Sieb. ex. Tanaka). Following 12 weeks of inoculation, significant improvements were observed in plant height, shoot and root biomass, total root length, average root diameter, second-order lateral root development, root hair density, and root hair length across all genotypes. Additionally, F. mosseae inoculation significantly increased root P and IAA concentrations in the three citrus genotypes. Notably, phosphatase activity was enhanced in F. margarita but reduced in C. tangerine and C. junos following inoculation. Gene expression analysis revealed a universal upregulation of the P transporter gene PT5, whereas expressions of the auxin synthesis gene YUC2, transporter gene LAX2, and phosphatase gene PAP1 were commonly downregulated. Specific to genotypes, expressions of YUC5, LAX5, PIN2, PIN3, PIN6, and expansin genes EXPA2 and EXPA4 were significantly upregulated in C. tangerine but downregulated in F. margarita and C. junos. Principal component analysis and correlation assessments highlighted a strong positive association between P concentration, P and auxin synthesis, and transporter gene expressions with most root morphology traits, except for root average diameter. Conversely, IAA content and phosphatase activities were negatively correlated with these root traits. These findings suggest that F. mosseae colonization notably enhances plant growth and root system architecture in citrus genotypes via modifications in P transport and IAA accumulation, indicating a complex interplay between mycorrhizal symbiosis and host plant physiology.
Biostimulant application can be considered an effective, practical, and sustainable nutritional crop supplementation and may lessen the environmental problems related to excessive fertilization. Biostimulants provide beneficial properties to plants by increasing plant metabolism, which promotes crop yield and improves the quality of crops; protecting plants against environmental stresses such as water shortage, soil salinization, and exposure to sub-optimal growth temperatures; and promoting plant growth via higher nutrient uptake. Other important benefits include promoting soil enzymatic and microbial activities, changing the architecture of roots, increasing the solubility and mobility of micronutrients, and enhancing the fertility of the soil, predominantly by nurturing the development of complementary soil microbes. Biostimulants are classified as microbial, such as arbuscular mycorrhizae fungi (AMF), plant-growth-promoting rhizobacteria (PGPR), non-pathogenic fungi, protozoa, and nematodes, or non-microbial, such as seaweed extract, phosphite, humic acid, other inorganic salts, chitin and chitosan derivatives, protein hydrolysates and free amino acids, and complex organic materials. Arbuscular mycorrhizal fungi are among the most prominent microbial biostimulants and have an important role in cultivating better, healthier, and more functional foods in sustainable agriculture. AMF assist plant nutrient and water acquisition; enhance plant stress tolerance against salinity, drought, and heavy metals; and reduce soil erosion. AMF are proven to be a sustainable and environmentally friendly source of crop supplements. The current manuscript gives many examples of the potential of biostimulants for the production of different crops. However, further studies are needed to better understand the effectiveness of different biostimulants in sustainable agriculture. The review focuses on how AMF application can overcome nutrient limitations typical of organic systems by improving nutrient availability, uptake, and assimilation, consequently reducing the gap between organic and conventional yields. The aim of this literature review is to survey the impacts of AMF by presenting case studies and successful paradigms in different crops as well as introducing the main mechanisms of action of the different biostimulant products.
Sustainable farming of horticultural plants has been the focus of research during the last decade, paying significant attention to alarming weather extremities and climate change, as well as the pressure of biotic stressors on crops. Microbial biostimulants, including plant growth-promoting bacteria (PGPB) and arbuscular mycorrhizal fungi (AMF), have been proven to increase plant growth via both direct and indirect processes, as well as to increase the availability and uptake of nutrients, boosting soil quality, increasing plants' tolerance to abiotic stress and increasing the overall quality attributes of various horticultural crops (e.g., vegetables, fruit, herbs). The positive effects of microbial biostimulants have been confirmed so far, mostly through symbiotic interactions in the plant-soil-microbes ecosystem, which are considered a biological tool to increase quality parameters of various horticultural crops as well as to decrease soil degradation. However, more research is needed to address future challenges of crop production through revealing the mechanisms of action and identifying response patterns of crops to various microbial products. The present review aims to present the most up-to-date results regarding the practical applications of microbial biostimulants in horticultural species, including case studies of successful paradigms for the most important microbial genera of PGPB and AMF. Moreover, the mechanisms of the actions are briefly described while future remarks are also discussed, aiming to suggest further needs to be addressed for the successful establishment of microbial biostimulants in sustainable horticultural crop production.
Different compounds with bioactive constitutents can be applied as biostimulants to increase plant growth and development under both normal and stressful conditions. Biostimulants utilization can be considered as a sustainable and beneficial nutritional crop management, and may decrease the negative impacts associated with excessive chemical fertilization. Google scholar (scholar.google.com), Science Direct (sicencedirect.com), CAB Direct (cabdirect.org), Springer Link (springerlink.com), Scopus (scopus.com), Web of Science (web of knowledge.com), Taylor and Francis (tandfonline.com), and Wiley Online Library (onlinelibrary.wiley.com) have been checked. The search was done to all manuscript sections according to terms "Glomus intraradices", "Trichoderma atroviride", "Trichoderma reesei", "Heteroconium chaetospira", "Artherobacter spp.", "Acinetobacter spp.", "Enterobacer spp.", "Pseudomonas spp.", "Ochrobactrum spp.", "Bacilus spp.", "Rhodococcus spp.", "Biostimulants", and "Plant growth promotion". On the basis of initial check, Titles and Abstracts have been reviwed on the basis of online literature, and then articles were read carefully. Withinin the framework of sustainable crop management, this review article was aimed to provide an overview of the application of the most common fungi and bacteria as plant biostimulants on various crops.
Root system characteristics are of fundamental importance to soil improvement and underground resource acquisition in riparian buffer strips. Root architectural traits determine the in situ space‐filling properties of a root system. The aims of this study were to examine the grassland root morphological characteristics in the vegetation zone from the lower reaches of Yellow River. Five natural homogeneous grasslands including Imperata cylindrica, Phragmites australis, Cynodon dactylon, Artemisia argyi and Juncellus serotinus were selected. Seven root architecture parameters including fractal dimension, total root length, total root surface area, total root volume, average diameter, root crossing number and root tip number were analyzed, and comprehensive scores were evaluated using principal component analysis. The results showed that average root diameter of the five herbaceous plants was ranged from 0.42 to 0.78 mm. The total root length, total root surface area, total root volume, root crossing number and root tip number of I. cylindrica and P. australis were significantly higher than those of C. dactylon, A. argyi and J. serotinus. The main factors influencing root architecture were average diameter, total root surface area and total root volume through principal component analysis. I. cylindrica had the highest comprehensive score, followed by P. australis, A. argyi, C. dactylon and J. serotinus. I. cylindrica and P. australis would be good competitors for both soil resource acquisition and soil quality improvement due to their root traits. These results could provide a scientific basis for evaluating the ecological function of riparian vegetation.
The increasing popularity of avocado (Persea americana) fruit has led to a rise in environmental impacts of avocado production. There is an urgent need to adopt sustainable nutrient practices in avocado nurseries and orchards to reduce nitrogen (N) pollution without compromising productivity. However, there is little understanding of how avocado rootstocks respond to different N fertilisation strategies. We investigated the effects of a plant growth-promoting rhizobacterium (PGPR) from the genus Paraburkholderia on growth of Reed avocado seedlings fertilised with either inorganic N fertiliser (iN) or combined inorganic N with organic manure-based fertiliser (iNoN). We studied plant growth and N acquisition, mineral N (NH4⁺-N and NO3⁻-N) in leachate, potting-mix physicochemical properties, and rhizosphere microbial communities. PGPR increased N uptake efficiency (NUpE) in seedlings fertilised with iNoN by 23% compared with iNoN without PGPR, 120% compared with iN without PGPR, and 71% compared with iN with PGPR. No significant differences in growth or mineral N leaching were observed between the iNoN and iN treatments. However, both uninoculated and PGPR-inoculated plants with iNoN fertiliser had greater plant N uptake and rhizosphere microbial-biomass N than uninoculated plants with iN fertiliser. Potting medium with iNoN fertiliser had higher N retention than with iN fertiliser, regardless of PGPR inoculation. Our results provide evidence that PGPR effects on N uptake efficiency are regulated by N form and N availability. The beneficial effects of PGPR inoculation when co-applied with a combination of inorganic and organic N fertiliser indicate that PGPR-based technologies can improve nitrogen recovery in avocado nurseries.
Citrus, cherry, plum, peach, apple, pear, nectarine, apricot, grape, kiwifruit, pomegranate, fig, olive and pistachio along with several native fruits such as wild black cherry and pecan are important temperate horticultural fruit species which are of keen interest to farmers. The roots of these species are naturally inoculated with mycorrhizal fungi. As the harvest time of fruits under Mediterranean climatic conditions is earlier than in many other regions, consequently there is an economic advantage for horticultural producers. Many soils in the Mediterranean region are deficient in plant nutrients (such as N, P, Zn, Fe and Mn) due to high clay and lime contents, often coupled with alkaline pH and limited water resources. To achieve an optimum plant growth, and obtain good fruit yield, chemical fertilizers are used. However, the excess use of chemical fertilizers negatively affects viable soil microorganisms, especially mycorrhizal fungi. Recent trends for the protection of the environment and the demand for healthy and ecologically-produced food, suggest minimal or no use of chemicals in agricultural production. Mycorrhizal fungi can promote plant root growth in marginally poor soils and under environmental stress. Mycorrhizal inoculation can contribute to the production of high quality fruit trees with balanced mineral nutrient uptake. In this work, the effect of mycorrhizal fungi on growth and nutrient uptake of micro-propagated cherry, grapevine, fig and banana rootstocks were investigated during acclimation and plant establishment. Banana and fig plantlets were also produced through micro-propagation. Several types of mycorrhizal fungi were used. Mycorrhizal inoculated plants had high shoot and root dry weight, greater nutrient uptake than non-mycorrhizal plantlets. Under field conditions, the effect of several mycorrhizal species on orange, mandarin and lemon trees was successfully demonstrated. Mycorrhizal inoculation also significantly increased the P and Zn uptake. Different mycorrhizal fungi differentially affected nutrient uptake and this effect depended upon the species. Mycorrhizal dependency of a range of tree species was assessed. It has been found that many plants, including citrus, pistachio, cherry, banana and grapevine rootstocks are dependent on mycorrhizae for P nutrition. Overall, it is concluded that utilizing AM fungi can make a useful contribution to horticultural plant growth, nutrient uptake and also fruit quality. © 2018 International Society for Horticultural Science. All rights reserved.
An investigation has been made about the Arbuscular Mycorrhizal Fungi (AMF) spore population and root colonization in 20 medicinal plants selected and collected from district Charsadda at early winter and summer seasons during session 2014-2015. The spore density of AMF ranged from 80 spores per 100gm-1 , and root colonization from 20-80%. The lowest spore density was recorded in Cestrum nocturnum, Ficus carica, Aquilaria agallocha and the highest spore density was recorded in Sedum dendroideum, Cannabis sativa, Triticum aestivum, and Mentha longifolia, Withania somnifera while absent in Brassica campestris, Amaranthus viridis. The spore density of AMF and root colonization by these fungi varied from species to species, season to season, and also affected by host plant growth stages (vegetative-fruiting).AM fungi association was more observed at fruiting stage and low at vegetative and flowering phases of host. The most dominant species of AMF were Glomus followed by Sclerocystis and Acaulospora species.
To explore the relationships between morpho-physiological traits and drought tolerance, we evaluated here the response to water stress exhibited by a collection of peanut (Arachis hypogaea L.) landraces traditionally grown in different climatic regions of the Algerian Maghreb. Upon applying a multivariate statistical approach to the data obtained from water-stressed plants, two components were identified: 1) the 'root vigour', associated to a long root system, exhibiting both deep and laterally spreading rooting pattern, abundant N2-fixing nodules, and pronounced stem growth; 2) the 'above-ground physiological mechanisms', associated to the ability to maintain greener leaves and cooler canopy temperature, via permissive values of leaf water potential allowing a certain degree of stomatal perviousness, even under conditions of severe water stress. On such bases, it became possible to identify a subgroup of peanut landraces which could be considered as parental lines in breeding programs for those cultivation environments facing endemic water shortage.
Abiotic stresses (such as salinity, drought, cold, heat, mineral deficiency and metals/metalloids) have become major threats to the global agricultural production. These stresses in isolation and/or combination control plant growth, development and productivity by causing physiological disorders, ion toxicity, and hormonal and nutritional imbalances. Some soil microorganisms like arbuscular mycorhizal fungi (AMF) inhabit the rhizosphere and develop a symbiotic relationship with the roots of most plant species. AMF can significantly improve resistance of host plants to varied biotic and abiotic stresses. Taking into account recent literature, this paper: (a) overviews major abiotic stresses and introduces the arbuscular mycorrhizae symbiosis (b) appraises the role and underlying major mechanisms of AMF in plant tolerance to major abiotic stresses including salinity, drought, temperature regimes (cold and heat), nutrient-deficiency, and metal/metalloids; (c) discusses major molecular mechanisms potentially involved in AMF-mediated plant-abiotic stress tolerance; and finally (d) highlights major aspects for future work in the current direction.
Photosynthesis by leaves and acquisition of water and minerals by roots are required for plant growth, which is a key component of many ecosystem functions. Although the role of leaf functional traits in photosynthesis is generally well understood, the relationship of root functional traits to nutrient uptake is not. In particular, predictions of nutrient acquisition strategies from specific root traits are often vague. Roots of nearly all plants cooperate with mycorrhizal fungi in nutrient acquisition. Most tree species form symbioses with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. Nutrients are distributed heterogeneously in the soil, and nutrient-rich “hotspots” can be a key source for plants. Thus, predicting the foraging strategies that enable mycorrhizal root systems to exploit these hotspots can be critical to the understanding of plant nutrition and ecosystem carbon and nutrient cycling. Here, we show that in 13 sympatric temperate tree species, when nutrient availability is patchy, thinner root species alter their foraging to exploit patches, whereas thicker root species do not. Moreover, there appear to be two distinct pathways by which thinner root tree species enhance foraging in nutrient-rich patches: AM trees produce more roots, whereas EM trees produce more mycorrhizal fungal hyphae. Our results indicate that strategies of nutrient foraging are complementary among tree species with contrasting mycorrhiza types and root morphologies, and that predictable relationships between below-ground traits and nutrient acquisition emerge only when both roots and mycorrhizal fungi are
considered together.
Although fine roots are important components of the global carbon cycle, there is limited understanding of root structure–function relationships among species. We determined whether root respiration rate and decomposability, two key processes driving carbon cycling but always studied separately, varied with root morphological and chemical traits, in a coordinated way that would demonstrate the existence of a root economics spectrum ( RES ).
Twelve traits were measured on fine roots (diameter ≤ 2 mm) of 74 species (31 graminoids and 43 herbaceous and dwarf shrub eudicots) collected in three biomes.
The findings of this study support the existence of a RES representing an axis of trait variation in which root respiration was positively correlated to nitrogen concentration and specific root length and negatively correlated to the root dry matter content, lignin : nitrogen ratio and the remaining mass after decomposition. This pattern of traits was highly consistent within graminoids but less consistent within eudicots, as a result of an uncoupling between decomposability and morphology, and of heterogeneity of individual roots of eudicots within the fine‐root pool.
The positive relationship found between root respiration and decomposability is essential for a better understanding of vegetation–soil feedbacks and for improving terrestrial biosphere models predicting the consequences of plant community changes for carbon cycling.
To explore the relationships between morpho-physiological traits and drought tolerance, we evaluated here the response to water stress exhibited by a collection of peanut (Arachis hypogaea L.) landraces traditionally grown in different climatic regions of the Algerian Maghreb. Upon applying a multivariate statistical approach to the data obtained from water-stressed plants, two components were identified: 1) the 'root vigour', associated to a long root system, exhibiting both deep and laterally spreading rooting pattern, abundant N2-fixing nodules, and pronounced stem growth; 2) the 'above-ground physiological mechanisms', associated to the ability to maintain greener leaves and cooler canopy temperature, via permissive values of leaf water potential allowing a certain degree of stomatal perviousness, even under conditions of severe water stress. On such bases, it became possible to identify a subgroup of peanut landraces which could be considered as parental lines in breeding programs for those cultivation environments facing endemic water shortage.
In this review, effect of mycorrhizal inoculation on citrus growth, nutrient and water uptake, and mycorrhizal dependency was searched. Arbuscular mycorrhiza (AM) is symbiotic associations between 90% of higher plants and fungi. Since citrus plants have very few and short root hair, in order to get sufficient nutrient and water, they need mycorrhizal colonization. It has been shown that the host plant was a factor affecting the interaction between mycorrhizal fungi. It has been shown that greater fungal activities in AM hyphae have a significant effect on citrus growth and nutrient uptake.
In vitro propagated fig genotype 01-IN-06 plants (which were propagated and rooted in the MS free media) were used to screen the most suitable arbuscular mycorrhizae fungi for enhancing plant growth by improving nutrient uptake under glasshouse conditions. G. mossea, G. etunicatum, G. intraradices, G. macrocarpium, G. caledonium, G. margarita, G. clarium and their cocktail was used as inoculum. Experiment was designed with three replications having five plants in each treatment and also control plants which were not treated with mycorrhiza. Mycorrhizal inoculation increased fig plant shoot, root dry weight, zinc and phosphorus uptake. Also, AMF significantly increased root infection. G. caledonium and G. margarita gave a high response to the plant growth, nutrient uptake and root infection.
Viticulture is a major worldwide economic sector with a vine area of 7.52 million ha, wine production of 288 Mhl, and wine exports of 26 billion euros. Nevertheless, viticulture has to adapt to new challenges of pest management, such as pesticide reduction, and climate change, such as increasing droughts. Viticulture adaptation can benefit from arbuscular mycorrhiza, a plant–fungus symbiosis. Here, we review the ecosystemic services of arbuscular mycorrhiza for grapevine production. The major points are the following: (1) arbuscular mycorrhiza fungi increase grapevine growth and nutrition by a better access to soil nutrients and by activating the regulation of plant transport proteins for phosphorus (P), nitrogen (N), and other elements. (2) Arbuscular mycorrhiza fungi increase the tolerance to abiotic stresses such as water stress, soil salinity, iron chlorosis, and heavy metal toxicity. (3) Arbuscular mycorrhiza fungi protect against biotic stresses such as root diseases. (4) Arbuscular mycorrhiza fungi produce glycoproteins and a dense hyphal network that increases soil stability and save soil nutrients up to 14 % of the grape production income. (5) P fertilisation reduces mycorhization. (6) Using herbaceous plants as cover crops favors arbuscular mycorrhiza fungi.
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.
Grapevines form mutualistic symbioses with arbuscular mycorrhizal (AM) fungi that have been shown to enhance plant growth and nutrition. In the field, AM fungal populations may be low or nonexistent (in fumigated soils), suggesting the need for AM inoculation of grapevine plants at the nursery. Addition of AM fungal inoculum to rooting substrate could be an effective strategy for the nursery production of mycorrhizal plants. The effects of inoculation of three grapevine rootstocks on root morphology and growth were tested. Results indicated that inoculation with the AM fungus Glomus aggregatum in rooting beds of grapevine cuttings changed root morphology, increasing branching of first-order lateral roots. When rooted cuttings were transplanted to pots, with soil sufficient in P and including indigenous AM fungi, and grown for nine months, a significant growth enhancement was found in two of the inoculated rootstocks. Glomus aggregatum, alone or in synergy with the indigenous AM fungi, seemed to have a higher affinity for 161-49 Couderc, the roots of which were more extensively colonized and exhibited a greater positive growth response.
The effects of some selected arbuscular mycorrhizal (AM) fungi, Gigaspora margarita and Glomus mossae on the growth and the role of soluble amino acids of two contrasting cocoa cultivars (ICS84 tolerant and SNK10 sensitive) against black pod disease caused by Phytophthora megakarya were investigated. Root colonization by AM fungi is between 50 and 70% 18 weeks after planting. Tested AM fungi significantly increased all the plant growth parameters (height, number of leaves, shoot and root matter) and P uptake as compared to non‐inoculated plants in pot experiments. AM fungi inoculated cocoa reduced the disease severity. Compared to the control, the soluble amino acid levels increased with inoculation of the AM fungi strains in the necrotic stems of disease on inoculated cocoa plants. Significant relationships between amino acids and disease severity observed for two cocoa cultivars imply that the induction of specific amino acids synthesized by leaves, such as arginine, cysteine and glutamic acid, may represent potential candidate molecules for adaptation of such cultivars to P. megakarya disease. Inoculating seedlings with AMF in nurseries could enhance the development of cocoa plants protected against P. megakarya.
Suboptimal availability of water and nutrients is a primary limitation to plant growth in terrestrial ecosystems. The acquisition of soil resources by plant roots is therefore an important component of plant fitness and agricultural productivity. Plant root systems comprise a set of phenes, or traits, that interact. Phenes are the units of the plant phenotype, and phene states represent the variation in form and function a particular phene may take. Root phenes can be classified as affecting resource acquisition or utilization, influencing acquisition through exploration or exploitation, and in being metabolically influential or neutral. These classifications determine how one phene will interact with another phene, whether through foraging mechanisms or metabolic economics. Phenes that influence one another through foraging mechanisms are likely to operate within a phene module, a group of interacting phenes, that may be co-selected. Examples of root phene interactions discussed are: (1) root hair length × root hair density, (2) lateral branching × root cortical aerenchyma (RCA), (3) adventitious root number × adventitious root respiration and basal root growth angle (BRGA), (4) nodal root number × RCA, and (5) BRGA × root hair length and density. Progress in the study of phenes and phene interactions will be facilitated by employing simulation modeling and near-isophenic lines that allow the study of specific phenes and phene combinations within a common phenotypic background. Developing a robust understanding of the phenome at the organismal level will require new lines of inquiry into how phenotypic integration influences plant function in diverse environments. A better understanding of how root phenes interact to affect soil resource acquisition will be an important tool in the breeding of crops with superior stress tolerance and reduced dependence on intensive use of inputs.
Plant root systems have a key role in ecology and agronomy. In spite of fast increase in root studies, still there is no classification that allows distinguishing among distinctive characteristics within the diversity of rooting strategies. Our hypothesis is that a multivariate approach for “plant functional type” identification in ecology can be applied to the classification of root systems. The classification method presented is based on a data-defined statistical procedure without a priori decision on the classifiers. The study demonstrates that principal component based rooting types provide efficient and meaningful multi-trait classifiers. The classification method is exemplified with simulated root architectures and morphological field data. Simulated root architectures showed that morphological attributes with spatial distribution parameters capture most distinctive features within root system diversity. While developmental type (tap vs. shoot-borne systems) is a strong, but coarse classifier, topological traits provide the most detailed differentiation among distinctive groups. Adequacy of commonly available morphologic traits for classification is supported by field data. Rooting types emerging from measured data, mainly distinguished by diameter/weight and density dominated types. Similarity of root systems within distinctive groups was the joint result of phylogenetic relation and environmental as well as human selection pressure. We concluded that the data-define classification is appropriate for integration of knowledge obtained with different root measurement methods and at various scales. Currently root morphology is the most promising basis for classification due to widely used common measurement protocols. To capture details of root diversity efforts in architectural measurement techniques are essential.
Nutrient deficiency, especially zinc (Zn) and phosphorus (P), is a common nutritional problem for the production of some crops in Turkey. This problem results in the application of increasing amounts of several fertilizers. Mycorrhizal inoculation or the indigenous potential of mycorrhizae in the soil is a critical factor in crop production under low supply of Zn and P. The effects of selected mycorrhizal inoculation on growth and Zn and P uptake of maize and green pepper were investigated in Zn- and P-deficient calcareous soils from Central Anatolia. Soils were sterilized by autoclaving and plants were grown for 7 weeks in pots under greenhouse conditions with inoculation of two selected arbuscular mycorrhizal (AM) species (Glommus moseea and G. etunicatum) at three rates of P (0, 25, 125 mg P kg soil) and two rates of Zn (0 and 5 mg Zn kgsoil). Without mycorrhizal inoculation, shoot and root dry matter production were severely affected by P and Zn deficiencies, and supply of adequate amounts of P and Zn significantly enhanced plant growth. When the soil was inoculated with mycorrhizal inoculation, the increasing effects of P and Zn fertilization on plant growth remained less pronounced. In accordance with growth data, mycorrhizae inoculation enhanced P and Zn concentration of plants, especially under low supply of P and Zn. The results obtained indicate that maize and green pepper are highly mycorrizal–dependent (MD) plant species under both low P and Zn supply and mycorrhizae play an essential role in P and Zn nutrition of plants in P and Zn-deficient soils. Although addition of P and Zn increased plant growth and plants are mycorrhizal dependent on P and Zn nutrition however dependence is much more dependent on P nutrition.
Arbuscular mycorrhizal fungi (AMF) are important for plant growth since they increase mineral influx. However, symbiosis efficiency is affected by many environmental factors. This study evaluated the effects of different treatments (+/- phosphorus; +/- liming; +/- organic matter; field, sandy or clayey soil textures) on root colonization (RC) of peanuts, sorghum and maize. The combination of these resulted in seventy-two treatments. The 2×2×2×3×3 factorial experiment was laid out in a randomized design. All data were subjected to variance analysis and the means were compared (Tukey at P<0.05). Three months after seed germination, roots were collected to evaluate the percentage of RC. Results showed that soil texture and liming were the most important factors influencing colonization percentage in maize, sorghum and peanuts by AMF. Significant differences were also observed between the phytobionts. Organic matter (OM) had very little influence and phosphorus addition had no effect on RC.
Mycorrhizas are considered to be classic mutualisms. Here, we define mutualism as a reciprocal increase in fitness of the symbionts, and we review the evidence for mycorrhizal mutualism at the community, whole-plant, and cellular scales. It is difficult to use results of most mycorrhizal studies because (i) fungal contribution to nutrient uptake is not accurately estimated, (ii) increased growth is not necessarily correlated with increased plant fecundity or survival, especially in communities, and (iii) benefits that occur only at certain times of year, or under specific extreme conditions, may not be detected. To produce the nonmycorrhizal controls required to study mutualism in the field, soil microflora and fauna must be severely perturbed; therefore, it is virtually impossible to evaluate effects of mycorrhizas on plant fitness under realistic conditions. Using the evidence available, we conclude that mycorrhizas can occupy various positions along the continuum from parasitism to mutualism, depending on the specific plant and fungal genotypes and their abiotic and biotic environments. Although we discuss the possibility of defining mycorrhizas by some physiological characteristic, we conclude that mycorrhizas should be defined on a structural or developmental basis and that any requirement to demonstrate mutualism be eliminated.
In nature, the root systems of most plants develop intimate symbioses with glomeromycotan fungi that assist in the acquisition of mineral nutrients and water through uptake from the soil and direct delivery into the root cortex. Root systems are endowed with a strong, environment-responsive architectural plasticity that also manifests itself during the establishment of arbuscular mycorrhizal (AM) symbioses, predominantly in lateral root proliferation. In this review, we collect evidence for the idea that AM-induced root system remodeling is regulated at several levels: by AM fungal signaling molecules and by changes in plant nutrient status and distribution within the root system.
The identification of morpho-physiological traits related to drought tolerance and high yield potential is a challenge when selecting sugar beet genotypes with greater tolerance to water stress. In this paper, root morphological parameters, antioxidant systems, leaf relative water content (RWC) and H+-ATPase activity as key morpho-physiological traits involved in drought tolerance/susceptibility of sugar beet were studied. Genotypes showing a different drought tolerance index (DTI) but a similar yield potential, under moderate (−0.6 Mpa) and severe (−1.2 MPa) water stress, were selected and their morpho-physiological traits were investigated. The results showed a wide genetic variation in morpho-physiological parameters which demonstrated the different adaptive strategies under moderate and severe drought conditions in sugar beet. In particular, an efficient antioxidant system and redox signalling made some sugar beet genotypes more tolerant to drought stress. The alternative strategy of other genotypes was the reduction of root tissue density, which produced a less dense root system improving the axial hydraulic conductivity. These results could be considered as interesting challenge for a better understanding of the drought tolerance mechanisms in sugar beet.
Under nutrient heterogeneous soil conditions, the ability of plants to compete for resource acquisition was closely related to the plasticity of root architecture, intended as a change of topology and geometry. Root architecture variations in response to different nitrate supplies of co-generic citrus rootstocks, 'Rough Lemon' (Citrus jambhiri Lush), 'Sweet Orange' (Citrus sinensis (L) Osbeck), 'Cleopatra Mandarin' (Citrus reshni Hort ex Tan.), and 'Sour Orange' (Citrus aurantium L.) are reported here. Root architecture was gauged by an image-specific analysis system (WinRHIZO). Based on the topological index, root topology of citrus rootstocks varied in response to nitrate treatments. In terms of root geometry, external-external and, to a lesser degree, internal-internal links of all rootstocks changed in response to nitrate supply. Among the rootstocks, 'Cleopatra Mandarin', both in terms of root topology (high TI) and root geometry (high length of exterior and interior link), could be considered less competitive owing to resource acquisition compared to the other rootstocks.
Despite their difference in potential growth rate, the slow-growing Brachypodium pinnatum and the fast-growing Dactylis glomerata co-occur in many nutrient-poor calcareous grasslands. They are known to respond differently to increasing levels of N and P. An experiment was designed to measure which characteristics are affected by nutrient supply and contribute to the ecological performance of these species. Nutrient acquisition and root and shoot traits of these grasses were studied in a garden experiment with nine nutrient treatments in a factorial design of 3 N and 3 P levels each.
D. glomerata was superior to B. pinnatum in nutrient acquisition and growth in all treatments. B. pinnatum was especially poor in P acquisition. Both species responded to increasing N supply and to a lesser extent to increasing P supply by decreasing their root length and increasing their leaf area per total plant weight. D. glomerata showed a higher plasticity. In most treatments, the root length ratio (RLR) and the leaf area ratio (LAR) were higher for D. glomerata. A factorization of these parameters into components expressing biomass allocation, form (root fineness or leaf thickness) and density (dry matter content) shows that the low density of the biomass of D. glomerata was the main cause for the higher RLR and LAR. The biomass allocation to the roots showed a considerable plasticity but did not differ between the species. B. pinnatum had the highest leaf weight ratio. Root fineness was highly plastic in D. glomerata, the difference with B. pinnatum being mainly due to the thick roots of D. glomerata at high nutrient supply. The leaf area/leaf fresh weight ratio did not show any plasticity and was slightly higher for B. pinnatum.
It is concluded, that the low density of the biomass of D. glomerata is the pivotal trait responsible for its faster growth at all nutrient levels. It enables simultaneously a good nutrient acquisition capacity by the roots as well as a superior carbon acquisition by the leaves. The high biomass density of B. pinnatum will then result in a lower nutrient requirement due to a slower turnover, which in the long term is advantageous under nutrient-poor conditions.
Plants and their arbuscular mycorrhizal fungal symbionts interact in complex underground networks involving multiple partners.
This increases the potential for exploitation and defection by individuals, raising the question of how partners maintain
a fair, two-way transfer of resources. We manipulated cooperation in plants and fungal partners to show that plants can detect,
discriminate, and reward the best fungal partners with more carbohydrates. In turn, their fungal partners enforce cooperation
by increasing nutrient transfer only to those roots providing more carbohydrates. On the basis of these observations we conclude
that, unlike many other mutualisms, the symbiont cannot be “enslaved.” Rather, the mutualism is evolutionarily stable because
control is bidirectional, and partners offering the best rate of exchange are rewarded.
Ecology Letters (2010) 13: 394–407
Mycorrhizal fungi influence plant growth, local biodiversity and ecosystem function. Effects of the symbiosis on plants span the continuum from mutualism to parasitism. We sought to understand this variation in symbiotic function using meta-analysis with information theory-based model selection to assess the relative importance of factors in five categories: (1) identity of the host plant and its functional characteristics, (2) identity and type of mycorrhizal fungi (arbuscular mycorrhizal vs. ectomycorrhizal), (3) soil fertility, (4) biotic complexity of the soil and (5) experimental location (laboratory vs. field). Across most subsets of the data, host plant functional group and N-fertilization were surprisingly much more important in predicting plant responses to mycorrhizal inoculation (‘plant response’) than other factors. Non-N-fixing forbs and woody plants and C4 grasses responded more positively to mycorrhizal inoculation than plants with N-fixing bacterial symbionts and C3 grasses. In laboratory studies of the arbuscular mycorrhizal symbiosis, plant response was more positive when the soil community was more complex. Univariate analyses supported the hypothesis that plant response is most positive when plants are P-limited rather than N-limited. These results emphasize that mycorrhizal function depends on both abiotic and biotic context, and have implications for plant community theory and restoration ecology.
Root, stem and leaf traits are thought to be functionally coordinated to maximize the efficiency of acquiring and using limited resources. However, evidence is mixed for consistent whole‐plant trait coordination among woody plants, and we lack a clear understanding of the adaptive value of root traits along soil resource gradients. If fine roots are the below‐ground analogue to leaves, then low specific root length ( SRL ) and high tissue density should be common on infertile soil. Here, we test the prediction that root, stem and leaf traits and relative growth rate respond in unison with soil fertility gradients.
We measured fine root, stem and leaf traits and relative growth rate on individual seedlings of 66 tree species grown in controlled conditions. Our objectives were (i) to determine whether multiple root traits align with growth rate, leaf and stem traits and with each other and (ii) to quantify the relationships between community‐weighted mean root traits and two strong soil fertility gradients that differed in spatial extent and community composition.
At the species level, fast growth rates were associated with low root and stem tissue density and high specific leaf area. SRL and root diameter were not clearly related to growth rate and loaded on a separate principal component from the plant economic spectrum.
At the community level, growth rate was positively related to soil fertility, and root tissue density (RTD) and branching were negatively related to soil fertility. SRL was negatively related and root diameter was positively related to soil fertility on the large‐scale gradient that included ectomycorrhizal angiosperms.
Synthesis . Root, stem and leaf tissue traits of tree seedlings are coordinated and influence fitness along soil fertility gradients. RTD responds in unison with above‐ground traits to soil fertility gradients; however, root traits are multidimensional because SRL is orthogonal to the plant economic spectrum. In contrast to leaves, trees are not constrained in the way they construct fine roots: plants can construct high or low SRL roots of any tissue density. High RTD is the most consistent below‐ground trait that reflects adaptation to infertile soil.
Climate variables including temperature, atmosphere CO2, and precipitation are expected to change during this century. As consequence, in the short- and long-term, the increase of soil temperature, salinity, drought, and waterlogging stresses could be the more exceeding problems for agricultural productivity and the functioning of the natural ecosystems. Root system represents the first and more sensitive target of the climate change, being seriously damaged in its form and function, and consequently strongly contributes to limit plant growth, development and crop productivity. This review focuses on changes of root morphology, architecture, distribution and dynamics, and on essential root physiological processes, such as water and nutrient uptake in response to soil warming, salinity, drought, and waterlogging. The literature appear sometimes to be controversial due to the complexity of root system characterized by different root types, genetically, developmentally, and functionally distinct, and by diverse root morphological parameters such as total root length, biomass, specific root length (SRL), and tissue density and fineness differently involved on root stress responses. For example, the change on total root length and dry weight, the lateral root formation, the depth of rooting and the root dynamics represent the preferential strategy for plant species in water-limited environments. Whereas, the development of aerenchyma, tissue containing enlarged gas spaces with a low-resistance pathway to oxygen, often accompanied by the aerotropic and extensive lateral roots formation, the herringbone-type root architecture, the emergence of adventitious roots and the presence of anatomical barriers are expressed in flooded root. Salinity reduces plant growth and yield by two mechanisms, osmotic stress and ion cytotoxicity. It is difficult to separate the osmotic effect from specific ion effects that overlap during the development of salinity stress, thereby some uncertainty exists regarding the relative importance of both mechanisms. The responses of root cells are finalized to maintain their own correct functionality, despite the condition of elevated Na+ concentration. The genetic diversity of the root system in the plant response to climate change was also reported.
Behind the root “form” changes, many metabolic and physiological pathways are involved in the plant adaptation to climate change. The maintenance of lower respiration rate, carbohydrate metabolism and cell expansion and elongation, often mediated by hormones, are expressed in roots grown in dry soil. At molecular level, the deposition of proline, metabolite responsible of the total osmotic adjustments, the higher expansin and xyloglucan endotransglycolase/hydrolase (XTH) activities, enzymes of the cell wall extension, represent the physiological mechanisms implemented by plants for improving their drought tolerance. In waterlogging soils and also in presence of salinity, the adaptation of physiological mechanisms are addressed to improve the cellular energy status and reduce the accumulation of toxic end products that acidify the cytosol or damage membrane integrity. Remarks on proteomic and molecular aspects which represent a future approach to individuate the plant strategies for their adaptation to the climate change are also included.
• The identification of plant functional traits that can be linked to ecosystem processes is of wide interest, especially for predicting vegetational responses to climate change. Root diameter of the finest absorptive roots may be one plant trait that has wide significance. Do species with relatively thick absorptive roots forage in nutrient-rich patches differently from species with relatively fine absorptive roots?
• We measured traits related to nutrient foraging (root morphology and architecture, root proliferation and mycorrhizal colonization) across six coexisting arbuscular mycorrhizal (AM) temperate tree species with and without nutrient addition.
• Root traits such as root diameter and specific root length were highly correlated with root branching intensity, with thin-root species having higher branching intensity than thick-root species. In both fertilized and unfertilized soil, species with thin absorptive roots and high branching intensity showed much greater root length and mass proliferation but lower mycorrhizal colonization than species with thick absorptive roots. Across all species fertilization led to increased root proliferation and reduced mycorrhizal colonization.
• These results suggest that thin-root species forage more by root proliferation whereas thick-root species forage more by mycorrhizal fungi. In mineral nutrient-rich patches, AM trees seem to forage more by proliferating roots rather than mycorrhizal fungi.
Common bean (Phaseolus vulgaris) is cultivated throughout Latin America and Africa, and for the European community, in Italy and Spain, areas are mainly subjected to drought stress which is predict to worsen by regional climatic models. The aims of this work were to identify the drought-tolerant and drought-sensitive bean landraces using drought tolerance and phenotypic plasticity indexes and to dissect the root morphological and 2D-architecture traits related to drought tolerance. Thirty-one landraces from diverse gene pools and areas of the Calabria region (South Italy), with different habits and morphological traits, were screened for drought tolerance in a hydroponic system. Root phenotyping was conducted by image analysis. Drought tolerance screening identified two landraces as drought tolerant and sensitive, respectively. Under drought stress, the drought-tolerant landrace exhibited several interesting root traits such as a higher root length, surface area and, above all, the fineness of the whole root systems and, with emphasis, of the higher order roots. Drought stress induced plastic root responses in both bean landraces but with contrasting patterns. The drought-tolerant landrace exhibited a dimorphic-rooted strategy, which could be included in future utility for bean breeding programmes in drought-prone environments.
This study tests the hypothesis that plant species of low mycorrhizal dependency (MD) tend to limit vesicular-arbuscular mycorrhizal (VAM) colonization more than species of high MD. Mycorrhizal dependency (MD = VAM plant dry weight/non-mycorrhizal plant dry weight) was determined for six citrus rootstocks in three green-house trials in a sterilized, P-deficient soil. In order to isolate the process of VAM colonization from shoot growth responses, colonization of the rootstocks with the same scion was examined in high-P soil in a rootstock field trial. Colonization of roots of known age was evaluated in soil cores extracted from beneath the canopy of mature trees. Initially, the soil was replaced in the resultant holes after dry sieving to remove roots and mix VAM fungal propagules (disturbed soil). Extraradical (ER) colonization of young roots in disturbed soil increased rapidly up to 5 weeks and approached that of mixed-age roots in undisturbed soil by 19 weeks. Intraradical (IR) colonization of young roots increased up to 19 weeks and was less than that of mixed-age roots. Differences in IR colonization of rootstock species that developed with time were correlated with their ER colonization at 10 and 19 weeks. Variation among citrus rootstocks in colonization of new roots was not related to root diameter or root extension rate. Colonization of rootstocks at 19 weeks was positively correlated (r =0.88-0.99, P < 0.05) with rootstock MD in P-deficient soil. Therefore, our data support the hypothesis that species that have evolved root systems that are less dependent on mycorrhizas have also evolved presently unknown mechanisms to regulate mycorrhizal colonization and presumably, carbon expenditure on the fungus.
Aims Our aim was to explore the way that root system type affects mycorrhizal growth response of plants.
Methods An extensive meta-analysis with 943 peer-review publications was conducted to test the difference in mycorrhizal responses between taproot plants and plants with a fibrous root system.
Results We found that taproot plants showed greater growth response (biomass, P and N uptake) to colonization by arbuscular mycorrhizal fungi (AMF) than do plant species with fibrous root systems. This response pattern was dependent on stress types, AMF identity and species richness, and particularly the type of stress (abiotic vs. biotic). Taproot plants respond more to AMF than plants with a fibrous root system; but no difference was shown under biotic stress. The interaction effect seen for AMF and biotic stress was significantly higher for plants with fibrous root system, but was not significant between taproot plants and abiotic stress. Difference in biomass response was only found for Glomeraceae and Gigasporaceae between the two types of plants, while difference was found in P uptake response for Glomeraceae and Claroideoglomeraceae. However, plants with fibrous root system showed higher growth response than taproot plants under nematode stress.
Conclusions Taproot plants might be more dependent on mycorrhiza than plants with fibrous root system. This indicates that environmental conditions can modify the relative abundance of taproot plants and plants with fibrous root system through mycorrhizal functioning, which will regulate plant community dynamics and processes.
The aim of this work was to assess the effects of a combined inoculum of a rhizobacterium and an arbuscular mycorrhizal (AM) fungus on plant responses to phytoplasma infection, and on phytoplasma multiplication and viability in Chrysanthemum carinatum plants infected by chrysanthemum yellows phytoplasma (CY). Combined inoculation with Glomus mosseae BEG12 and Pseudomonas putida S1Pf1Rif resulted in some resistance to phytoplasma infection (about 30%), delayed symptom expression in nonresistant plants, improved growth of the aerial part of the infected plants (+68·1%), and altered root morphology (root tip number: +49·9%; branching degree: +82·8%). Combined inoculation with the two beneficial microorganisms did not alter CY multiplication and viability. In inoculated and infected plants, phytoplasma morphology was typical of senescent cells. A more active and efficient root system in double-inoculated plants probably mediated the effects of the two rhizospheric microorganisms in the infected plants. The practical application of rhizospheric microorganisms for mitigating phytoplasma damage, following evaluation under field conditions, represents an additional tool for the integrated management of phytoplasmosis.
The symbiosis between arbuscular mycorrhizal ( AM ) fungi and plants is evolutionarily widespread. The response of plant growth to inoculation by these fungi (mycorrhizal growth response; MGR ) is highly variable, ranging from positive to negative. Some of this variation is hypothesized to be associated with root structure and function. Specifically, species with a coarse root architecture, and thus a limited intrinsic capacity to absorb soil nutrients, are expected to derive the greatest growth benefit from inoculation with AM fungi.
To test this hypothesis, previously published literature and phylogenetic information were combined in a meta‐analysis to examine the magnitude and direction of relationships among several root architectural traits and MGR .
Published studies differed in the magnitude and direction of relationships between root architecture and MGR . However, when combined, the overall relationship between MGR and allocation to roots, root diameter, root hair length and root hair density did not differ significantly from zero.
These findings indicate that possessing coarse roots is not necessarily a predictor of plant growth response to AM fungal colonization. Root architecture is therefore unlikely to limit the evolution of variation in MGR .
Absorptive root traits show remarkable cross‐species variation, but major root trait dimensions across species have not been defined.
We sampled first‐order roots and measured 14 root traits for 96 angiosperm woody species from subtropical C hina, including root diameter, specific root length, stele diameter, cortex thickness, root vessel size and density, mycorrhizal colonization rate, root branching intensity, tissue density, and concentrations of carbon and nitrogen ([N]).
Root traits differed in the degree of variation and phylogenetic conservatism, but showed predictable patterns of cross‐trait coordination. Root diameter, cortex thickness and stele diameter displayed high variation across species (coefficient of variation ( CV ) = 0.51–0.69), whereas the stele:root diameter ratio and [N] showed low variation ( CV < 0.32). Root diameter, cortex thickness and stele diameter showed a strong phylogenetic signal across species, whereas root branching traits did not, and these two sets of traits were segregated onto two nearly orthogonal (independent) principal component analysis ( PCA ) axes.
Two major dimensions of root trait variation were found: a diameter‐related dimension potentially integrating root construction, maintenance, and persistence with mycorrhizal colonization, and a branching architecture dimension expressing root plastic responses to the environment. These two dimensions may offer a promising path for better understanding root trait economics and root ecological strategies world‐wide.
The effect of the mycorrhizal inoculation on survival rate, growth, nutrient uptake and root morphology during the acclimatization period and plant establishment of micropropagated juvenile or adult cherimoya plants (Annona cherimola Mill.) was determined. Although mycorrhizal colonization did not improve the survival rate of plants, which was already high in non-inoculated plants, it had a positive effect on plant development (shoot length, leaf number, leaf area and fresh and dry weights). Mycorrhizal juvenile plants tripled the macronutrients and increased by four the micronutrient uptake, and mycorrhizal adult plants increased by two phosphorus and all micronutrients, with copper uptake increased five times. Moreover, mycorrhizal colonization changed the root morphology of adult plants increasing three-fold the total number of roots, doubling the number of first-order laterals and increasing second-order laterals by four. Total root length was also increased three-fold, adventitious root length was almost doubled, first-order laterals tripled and second-order roots length increased four-fold. The effect of mycorrhizal colonization seems to be stronger or different in juvenile than in adult plants, suggesting that ontogenic stage is an important factor determining mycorrhizal effect and the plant performance during the acclimatization period.
S ummary
Seedlings of five citrus rootstocks were grown in a low phosphorus (P) sandy soil and were either (1) inoculated with Glomus intraradices Schenck & Smith, (2) non‐inoculated and fertilized with P, or (3) non‐inoculated without added P. The order of mycorrhizal dependency (MD) of the five rootstocks was sour orange = Cleopatra mandarin > Swingle citrumelo > Carrizo citrange > trifoliate orange. The less dependent rootstocks, trifoliate orange and its hybrid Carrizo citrange, had greater leaf P, finer roots (greater length per unit of dry root) and slower growth rates than sour orange and Cleopatra mandarin. Rootstocks with lower MD also generally had greater hydraulic conductivity of roots, and greater transpiration and CO 2 assimilation rates. Under well‐watered conditions, VAM plants of all five rootstocks did not differ in morphology, anatomy or physiology from non‐mycorrhizal plants fertilized with P of similar size, growth rate and P status.
S ummary
Assessment of infection is an essential part of many studies involving VA mycorrhiza. A summary is given of the range of techniques that have been used. We calculated the standard error of four methods of assessment based on observations of stained root samples either randomly arranged in a petri dish or mounted on microscope slides. The methods are based on presence or absence of infection at root/grid intersect points, on a visual estimate of percentage cortex occupied by fungus or on estimates of length, or presence or absence of infection in root pieces mounted on slides. The number of replicate observations required for a given standard error % infection can be read from the curves provided. The advantages of the different methods of assessment are discussed and reasons given why they all probably overestimate the true values.
The relationships between net nitrate uptake and root morphology and topology were investigated in wheat (Triticum durum Desf.) and citrus (Citrus volkameriana Ten. & Pasq.) seedlings in which root systems were modified by supplying different nutrient concentrations. Root morphological and topological changes were assessed by the number of root tips, the total root length, and the topological index. The net nitrate uptake process was evaluated during the induction and inhibition "feedback" regulation phases. In wheat seedlings, an increase in the external nitrate concentration, at either high or no phosphate, brought about an increase in number of root tips but did not affect total root length. A similar pattern was observed in citrus seedlings. Citrus seedlings also exhibited a shift in root branching pattern from herringbone to dichotomous with an increase in the external nitrate concentration. Conversely, wheat root topology was unaffected by nutrient treatments. A high level of nitrate supplied to wheat and citrus root systems reduced the full induction of the nitrate uptake rate and cumulative nitrate uptake but increased the half-time of reaching the full induction in net nitrate uptake (t1/2kind). Finally, a negative correlation between number of root tips and t1/2kind was found in both species, while only in citrus seedlings was a positive correlation between t1/2kind and the topological index observed. The data suggest that root morphology has a greater effect on nitrate uptake than root topology.Key words: root morphology, root topology, net nitrate uptake, Citrus volkameriana, Triticum durum.
The degree of plant growth change associated with arbuscular mycorrhizal (AM) colonization is expressed as mycorrhizal dependency (MD). In this review, previous reports on the differences in MD among plant species or cultivars were surveyed, and the factors affecting the differences are discussed. Mean values of MD were 44% for field crops (37 species), 56% for forage crops (46 species), 70% for wild grasses and forbs (140 species), 79% for trees (26 species), and 56% for all plants (250 species), indicating that the cultivated plant species showed a lower MD than the wild plant species. MD was negatively correlated with root morphological characteristics such as root length, root dry weight, root hair length, density of root hairs, the ability of roots to acquire phosphate from soil, and the phosphorus utilization efficiency of the host plant. Inoculation of arbuscular mycorrhizal fungi (AMF) for low input systems should be carried out in considering differences in MD.
The production of fine roots is one of the principal means by which carbon, fixed during photosynthesis, enters the soil, and quantifying the production for particular combinations of environmental and biotic factors is important for predicting the sequestration of carbon in the soils of grassland ecosystems. Arbuscular mycorrhizal fungi (AMF) can have a major effect on the production of roots, and we studied how colonization by AMF affects the lifespan of roots. Twenty per cent of control roots of Trifolium repens survived for longer than 42 days whereas 37% survived that long in AMF-colonized plants. The overall survival of the roots of Lolium perenne was less than in T. repens: around 10% of roots survived beyond 42 days and this was not affected by AMF colonization. Previous studies have shown that lifespans of roots can be affected by temperature. We tested the hypothesis that these observations are linked to a change in the morphology of the root system caused by temperature and also by AMF. We found that inoculation with AMF in a microcosm study using Plantago lanceolata grown at various temperatures, with and without AMF, showed no clear effect of AMF on branching patterns. Temperature had a significant effect on total lengths, numbers and branching rates of some higher orders of roots. Total lengths of both secondary and tertiary roots grown at 27°C were about double those of plants grown at 15°C. Colonization by AMF tended to reduce this effect. Evidently the effect of colonization by AMF on root lifespan depends on the species. Increased branching, and thus a greater proportion of ephemeral roots, was responsible for shortening the lives of the roots at increased temperature, which suggests a strong link between lifespan and morphology.
The relation between root age and root function is poorly understood, despite its importance to root longevity.
The effect of root age on respiration rates and ³² P‐uptake kinetics was determined for roots excavated from mature apple and citrus trees (median root life spans of 30 vs 300 d). To evaluate whether root longevity maximizes the efficiency of nutrient capture, daily and lifetime efficiencies were calculated by dividing simulated P‐uptake benefits (solute transport model) by age‐specific respiration costs.
We found that: respiration rates and P uptake capacity change with root age in a species‐specific way; and soil characteristics that determine the rate of nutrient depletion in the rhizosphere are as important as changes in root physiology in determining the age at which a root reaches its maximum efficiency.
Further testing of the efficiency of nutrient capture as a predictor of root life span requires measurement of both soil properties and age‐specific physiology of roots including their mycorrhizal fungi.
1. A major benefit of the mycorrhizal symbiosis is that it can protect plants from below-ground enemies, such as pathogens. Previous studies have indicated that plant identity (particularly plants that differ in root system architecture) or fungal identity (fungi from different families within the Glomeromycota) can determine the degree of protection from infection by pathogens. Here, we test the combined effects of plant and fungal identity to assess if there is a strong interaction between these two factors.
2. We paired one of two plants (Setaria glauca, a plant with a finely branched root system and Allium cepa, which has a simple root system) with one of six different fungal species from two families within the Glomeromycota. We assessed the degree to which plant identity, fungal identity and their interaction determined infection by Fusarium oxysporum, a common plant pathogen.
3. Our results show that the interaction between plant and fungal identity can be an important determinant of root infection by the pathogen. Infection by Fusarium was less severe in Allium (simple root system) or when Setaria (complex root system) was associated with a fungus from the family Glomeraceae. We also detected significant plant growth responses to the treatments; the fine-rooted Setaria benefited more from associating with a member of the family Glomeraceae, while Allium benefited more from associating with a member of the family Gigasporaceae.
4. Synthesis. This study supports previous claims that plants with complex root systems are more susceptible to infection by pathogens, and that the arbuscular mycorrhizal symbiosis can reduce infection in such plants – provided that the plant is colonized by a mycorrhizal fungus that can offer protection, such as the isolates of Glomus used here.
Root turnover is important to the global carbon budget as well as to nutrient cycling in ecosystems and to the success of individual plants. Our ability to predict the effects of environmental change on root turnover is limited by the difficulty of measuring root dynamics, but emerging evidence suggests that roots, like leaves, possess suites of interrelated traits that are linked to their life span. In graminoids, high tissue density has been linked to increased root longevity. Other studies have found root longevity to be positively correlated with mycorrhizal colonization and negatively correlated with nitrogen concentration, root maintenance respiration and specific root length. Among fruit trees, apple roots (which are of relatively small diameter, low tissue density and have little lignification of the exodermis) have much shorter life spans than the roots of citrus, which have opposite traits. Likewise, within the branched network of the fine root system, the finest roots with no daughter roots tend to have higher N concentrations, faster maintenance respiration, higher specific root length and shorter life spans than secondary and tertiary roots that bear daughter roots. Mycorrhizal colonization can enhance root longevity by diverse mechanisms, including enhanced tolerance of drying soil and enhanced defence against root pathogens. Many variables involved in building roots might affect root longevity, including root diameter, tissue density, N concentration, mycorrhizal fungal colonization and accumulation of secondary phenolic compounds. These root traits are highly plastic and are strongly affected by resource supply (CO2, N, P and water). Therefore the response of root longevity to altered resource availability associated with climate change can be estimated by considering how changes in resource availability affect root construction and physiology. A cost–benefit approach to predicting root longevity assumes that a plant maintains a root only until the efficiency of resource acquisition is maximized. Using an efficiency model, we show that reduced tissue Nconcentration and reduced root maintenance respiration, both of which are predicted to result from elevated CO2, should lead to slightly longer root life spans. Complex interactions with soil biota and shifts in plant defences against root herbivory and parasitism, which are not included in the present efficiency model, might alter the effects of future climate change on root longevity in unpredicted ways.
Root morpho-topology and net nitrate uptake of two citrus seedlings, Volkamer Lemon and Carrizo Citrange, grown at two nitrogen supplies (NO3-N 5 μM and 1000 μM, respectively) were studied. Root morphological and topological parameters were gauged by an image-specific analysis system (WinRHIZO). Net nitrate uptake was estimated using the nitrate depletion method. The main findings showed that Carrizo seedlings had a dichotomous branching root system characterized by high root tip numbers and long 2nd
order lateral roots. Conversely, Volkamer root systems had a herringbone structure with a long tap root and 1st
order lateral root. Nitrate treatment did not seem to affect the pattern of the two genotypes, except for the 2nd
order lateral roots (Carrizo more than Volkamer) and root/shoot ratio and root mass ratio (Volkamer more than Carrizo) that were significantly different at low nitrate supply. Nitrate treatments induced a diverse net nitrate uptake regulation between citrus rootstocks. Indeed, at low nitrate supply, Carrizo showed a more efficient nitrate acquisition process in terms of: 1) higher net nitrate uptake maximum of the inducible high affinity transport system or ‘full induction’ (A), (2) higher cumulative nitrate uptake (A
t
) and (3) lower t1 parameter defined as the half time of the net nitrate uptake rate of the inducible transport system during the induction phase, compared to Volkamer. Conversely, at the high nitrate level, only the genotypical difference of the t1 parameter was maintained. The results suggested that, at the low nitrate level, the morphological root traits such as higher 2nd
order lateral roots and greater root tip numbers of the Carrizo compared with Volkamer seedlings, enhance the capacity to absorb nitrate from nutrient solution.
The use of commercial inoculants containing non-resident arbuscular mycorrhizal fungi (AMF) is an emerging technology in field crop production in Canada. The objective of this study was to assess the impact of AMF inoculants containing either a single species (Glomus irregulare) or mixed species (G. irregulare, Glomus mosseae, and Glomus clarum) on AMF root colonization and consequent plant growth parameters of field pea grown using pot cultures. Field pea was grown in both sterilized and non-sterile (i.e., natural) field-collected soil containing resident AMF and received three inoculation treatments: uninoculated control, G. irregulare only, and a mixture of AMF species of G. irregulare, G. mosseae, and G. clarum. After 42 days, the AMF community assembled in field pea roots was assessed by cloning and sequencing analysis on the LSU-ITS-SSU rDNA gene, together with a microscopic assessment of colonization, biomass production, nutrient uptake, and N(2) fixation. The identity of AMF inoculants had a significant effect on field pea performance. The mixed species AMF inoculant performed better than the single species G. irregulare alone by promoting mycorrhizal colonization, field pea biomass, N and P uptake, and N(2) fixation and did not result in a significant compositional change of the AMF community that subsequently assembled in field pea roots. In contrast, the single species G. irregulare inoculant did not significantly enhance field pea biomass, N and P uptake, and N(2) fixation, although a significant compositional change of the subsequent AMF community was observed. No significant interactions affecting these measurements were detected between the resident AMF and the introduced AMF inoculants. The observation that the mixed species AMF inoculant promoted plant growth parameters without necessarily affecting the subsequent AMF community may have important implications regarding the use of non-resident AMF inoculants in agricultural production.
Roots function dually as a support system and as the nutrient uptake organ of plants. Root morphology changes in response to the soil environment to minimize the metabolic cost of maintaining the root system, while maximizing nutrient acquisition. In response to nutrient-limiting conditions, plants may increase root fineness or specific root length (root length per gram root weight), root/shoot ratio, or root hair length and number. Each of these adaptations involves a different metabolic cost to the plant, with root hair formation as the least costly change, buffering against more costly changes in root/shoot ratio. Mycorrhizal symbiosis is another alternative to such changes. Plants with high degrees of dependence on the symbiosis have coarser root systems, less plasticity in root/shoot ratio, and develop fewer root hairs in low-fertility soils. In nutrient-limited soils, plants highly dependent on mycorrhiza reduce metabolic cost by developing an even more coarse or magnolioid root system, which is less able to obtain nutrients and thus creates a greater dependence of the plant on the symbiosis. These subtle changes in root architecture may be induced by mycorrhizal fungi and can be quantified using topological analysis of rooting patterns. The ability of mycorrhizal fungi to elicit change in root architecture appears to be limited to plant species which are highly dependent upon mycorrhizal symbiosis.
Eighteen Prunus rootstock cultivars were inoculated with three arbuscular mycorrhizal fungi under greenhouse conditions in order to evaluate their affinity for mycorrhizal colonization. The rootstocks were peach–almond hybrids, peaches, plums and cherries of Spanish, French and Italian origin. Mycorrhizal colonization was low in plants inoculated with Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe, and Glomus etunicatum Becker and Gerdemann. In contrast, Glomus intraradices Schenck and Smith, proved to be the most infective endophyte, achieving the highest mycorrhizal colonization rate in most of the rootstocks evaluated. Species of Prunus insititia L. were the only botanical group to show a consistently high affinity for mycorrhizal colonization with G. intraradices.
Plant root system architecture is essential characteristics in relation to nutrient acquisition by root system from soil volume. Many environmental factors can affect the establishment of root system architecture, e.g. arbuscular mycorrhizal (AM) fungi. We inoculated the trifoliate orange (Poncirus trifoliata L. Raf.) seedlings with four AM fungal species in rhizoboxes, with non-inoculated seedlings as control. Using the WinRHIZO® image analysis system, the root system architecture of seedlings was characterized. Results indicated that AM colonization did not affect the tap root length, the average root diameter, the basal root growth angle in spite that four AM fungal species exerted differential influence on the plant growth. Contrastingly, AM colonization significantly reduced the total root length, the root volume, the root surface area, but promoted the formation of lateral roots of high order. In addition, AM colonization induced more fine roots and less coarse roots. To our knowledge, it is the first report on the influence of AM fungi on the distribution of root diameter size classes. The mechanisms and implication of AM fungi on root system architecture is discussed.
The study reports diversity of arbuscular mycorrhizal fungal (AMF) species in the rhizosphere of an endangered anticancerous herb - Curculigo orchioides Gaertn. in its natural habitat. A total of 18 species of AMF, belonging to three genera (Acaulospora, Glomus and Gigaspora) were recorded, with Glomus microcarpum being the most abundant species type. The AMF species composition across the study sites appeared to be influenced by soil pH rather than soil P and vegetation. Acaulospora laevis spores were restricted to sites where the soil pH was acidic. The effectiveness of these native AMF species on growth performance of C. orchioides plants was compared under experimental conditions. In general, the mycorrhizal plants were superior in most of the evaluated parameters, but the extent to which the growth of mycorrhizal plants was influenced varied with the inocula used. The plants inoculated with mixed consortia containing maximum AMF species richness exhibited improved growth in comparison to consortia containing lower AMF diversity and monospecies cultures. The variable plant responses observed with any two consortia having same species richness in the present study could be due to variable component AMF species and their relative abundance. These results emphasize the need to protect the below-ground diversity of AMF and recommend their usage for restoration practices.
Central to the mutualistic arbuscular mycorrhizal symbiosis is the arbuscule, the site where symbiotic phosphate is delivered. Initial investigations in legumes have led to the exciting observation that symbiotic phosphate uptake not only enhances plant growth but also regulates arbuscule dynamics and is, furthermore, required for maintenance of the symbiosis. This review evaluates the possible role of the phosphate ion, not only as a nutrient but also as a signal that is necessary for reprogramming the host cortex cell for symbiosis.