Mycorrhizal Colonization Rate Research Articles

Effects of organic contaminants on arbuscular mycorrhiza formation: A meta-analysis

Arbuscular mycorrhizal fungi (AMF) function mostly depends on their colonization to roots. However, it has not been systematically clear how arbuscular mycorrhiza (AM) formation is affected by organic contaminants. In this study, a meta-analysis was performed to estimate the effects of three groups of organic contaminants (polycyclic aromatic hydrocarbons (PAHs), crude oil, and pesticide) in soil on mycorrhizal colonization rates (MCRs) from various moderators, such as AMF (genus, species, and inoculation mode), contaminant (level, type, and source), and experimental conditions (plant type, duration, and soil sterilization). Our results showed that all MCRs (total, vesicular, arbuscular and hyphal) significantly decreased under the stresses of three contaminants. Generally, pesticide caused larger decrease in all MCRs than PAHs and crude soil except for vesicular MCRs. Mixed AMF showed larger decrease in the total and vesicular MCRs than single AM fungus, but contrary trends in the arbuscular and hyphal MCRs. Moreover, man-made contaminant seemed to produce larger negative effects on the total, vesicular, and arbuscular MCRs than industry contaminant. The inhibitive effects of three contaminants on the total and vesicular MCRs increased with increasing experimental duration, and were larger in the non-sterilized soil than in the sterilized soil. Hyphal and spore growth were also inhibited by three contaminants in most cases. Hyphal length and spore number of single AM fungus were lower than those of mixed AMF, and pesticide produced larger inhibition on the hyphal length and spore number than PAHs and crude oil. Similar trend was found in the non-sterilized soil relative to the sterilized soil. This study indicated that AM formation and AM structure were negatively affected by three organic contaminants, whereas the inhibitive degrees varied with AMF, organic contaminant and experimental conditions.

Enhanced rock weathering increased soil phosphorus availability and altered root phosphorus-acquisition strategies.

Enhanced rock weathering (ERW) has been proposed as a measure to enhance the carbon (C)-sequestration potential and fertility of soils. The effects of this practice on the soil phosphorus (P) pools and the general mechanisms affecting microbial P cycling, as well as plant P uptake are not well understood. Here, the impact of ERW on soil P availability and microbial P cycling functional groups and root P-acquisition traits were explored through a 2-year wollastonite field addition experiment in a tropical rubber plantation. The results show that ERW significantly increased soil microbial carbon-use efficiency and total P concentrations and indirectly increased soil P availability by enhancing organic P mobilization and mineralization of rhizosheath carboxylates and phosphatase, respectively. Also, ERW stimulated the activities of P-solubilizing (gcd, ppa and ppx) and mineralizing enzymes (phoADN and phnAPHLFXIM), thus contributing to the inorganic P solubilization and organic P mineralization. Accompanying the increase in soil P availability, the P-acquisition strategy of the rubber fine roots changed from do-it-yourself acquisition by roots to dependence on mycorrhizal collaboration and the release of root exudates. In addition, the direct effects of ERW on root P-acquisition traits (such as root diameter, specific root length, and mycorrhizal colonization rate) may also be related to changes in the pattern of belowground carbon investments in plants. Our study provides a new insight that ERW increases carbon-sequestration potential and P availability in tropical forests and profoundly affects belowground plant resource-use strategies.

Rapid positive response of young trees growth to warming reverses nitrogen loss from subtropical soil

Abstract Global warming is widely expected to alter nitrogen (N) cycling in terrestrial ecosystems by accelerating N transformations in soils. However, it is unclear how warming will affect plant–soil N cycling in subtropical ecosystems. Here, we measured the N transformations including net ammoniation, nitrification, nitrous oxide emissions and nitrate in soil solution throughout the plant–soil continuum with 2 years of experimental soil warming (+5°C) in a young subtropical Chinese fir mesocosm. Seasonal variations of soil and plant (foliage and root) N concentrations and isotopes (δ15N), foliar water use efficiency and arbuscular mycorrhizal colonization rate were measured. Soil warming significantly increased net ammonization and nitrification of the soil, together with the transient positive response observed in inorganic N of the soil. Warming increased nitrate N fluxes in soil solution and nitrous oxide emissions in the first year but not in the second year, suggesting N losses through leaching and gaseous in the initial period of warming. Warming primarily induced enrichment of 15N in foliage relative to the soil, which was attributed to the trade‐offs of persistent increases in plant N uptake caused by enhanced tree growth and a decrease in N losses with continuous warming. Furthermore, young trees' growth and N uptake capacity can rapidly acclimate to climate warming as a result of warming‐induced increases in arbuscular mycorrhizal colonization and foliar water use efficiency. Our findings highlight that warming accelerates the plant–soil N cycle and promotes young trees' growth and N uptake, which in turn reduces soil N lost from this subtropical ecosystem. Therefore, our study suggests that the competition for N between plants and microbes governs whether subtropical forests are opened or closed N cycle systems under climate warming. We predict that subtropical young forests can still maintain their high productivity because young trees can maintain their N uptake capacity and adequate soil N supply in facing future climate warming. Read the free Plain Language Summary for this article on the Journal blog.

Differences in Fine Root Foraging Traits of Two Dominant Tree Species (Cunninghamia lanceolata and Quercus acutissima) in Subtropical Forests

Root biomass and length growth, functional traits, and their responses to soil nutrient availability are crucial for resource acquisition under environmental change. Previous studies have focused on the response of root morphological, architectural, and chemical traits to fertilization, while less attention has been given to root biomass and length growth, as well as mycorrhizal symbiosis, impeding a full understanding of root resource acquisition strategies. Here, using a nutrient addition experiment (control, inorganic, and organic nutrients), we explored the responses of function-based root (absorptive fine roots [AFRs] versus transport fine roots [TFRs]) growth, functional traits (morphological, architectural, and chemical traits), and mycorrhizal colonization of C. lanceolat and Q. acutissim, which are the dominant tree species in subtropical China. The results showed that the fine root biomass and total root length of AFRs for both tree species basically decreased significantly after nutrient addition, but TFRs responded less sensitively than AFRs. Nutrient addition significantly increased the mycorrhizal colonization rate in C. lanceolata but decreased it in Q. acutissima. The diameter of AFRs for C. lanceolata increased significantly, while the branch ratio and branch intensity decreased significantly in both inorganic nutrients (NPK) and organic nutrients (F); however, the opposite response pattern occurred for Q. acutissima. Fine root biomass, total root length, and root nutrient concentration exhibited the most plastic responses to changes in nutrient availability. The magnitude of the plastic response of fine root traits was slightly higher in the NPK treatment than in the F treatment. Our findings suggest that the responses of fine root traits and mycorrhizal fungi to nutrient addition were species-specific: C. lanceolata depended on mycorrhizal fungi for resource acquisition, while Q. acutissima could acquire soil nutrient resources by increasing root branching. The contrasting nutrient acquisition strategies between tree species may facilitate plant species coexistence and distribution under soil nutrient change. Fine root biomass and total root length emerged as more pivotal indicators for nutrient acquisition strategies compared to morphological traits.

Defense responses and symbiotic functional initiation in trifoliate orange‒arbuscular mycorrhizal fungi interaction

Arbuscular mycorrhizal fungi (AMF) trigger beneficial effects on their hosts, but it is unknown how plants modulate their defense responses during root colonization of AMF and the symbiotic benefits are initiated. The purpose of this study was to analyze the root mycorrhizal colonization process of trifoliate orange and the responsive patterns of plant growth, root peroxide hydrogen (H2O2), antioxidant enzymes and their encoding gene expression, and sugar, lipid and phosphate transporter protein gene expression at 7‒56 days of inoculation (doi) with Funneliformis mosseae (Fm). Fm developed appressoriums on the root surface at 7 doi, followed by abundant arbuscules in root cortical cells at 28 doi, intracellular vesicles at 42 doi, and root mycorrhizal colonization rate of 41.54% at 56 doi. Plant growth improvement by Fm started at 28 doi. The immune defense response of roots was initiated at 7 doi, as evidenced by the increase of H2O2 levels and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity, as well as the up-regulation of PtMn-SOD, PtCu/Zn-SOD, PtPOD, and PtCAT expression, which lasted until 14 doi. Starting at 28 doi, a sugar transporter gene (PtSWEET), a lipid transporter gene (PtSTR), and a phosphate transporter gene (PtPT6) were initiated to be up-regulated, followed by the up-regulation of PtSTR2, PtPT3, and PtPT5 at 42 doi and PtFe-SOD at 56 doi. Arbuscule formation and plant growth improvement together at 28 doi suggested that arbuscules trigger improved growth responses of host plants. This study also reveals the initiation of host immune defense response and function in early root AMF colonization.Graphical

Arbuscular Mycorrhizal Fungi, Especially Rhizophagus intraradices as a Biostimulant, Improve Plant Growth and Root Columbin Levels in Tinospora sagittata

Tinospora sagittata is a columbin-rich medicinal plant, but its columbin levels are reduced under artificial cultivation conditions. The objective of this study was to analyze the effects of inoculations with Diversispora versiformis (Dv), Funneliformis mosseae (Fm), Rhizophagus intraradices (Ri), and mixed inoculation (Dv + Fm + Ri) (Mix) on growth performance, root morphology, leaf photosynthetic physiology, and root columbin levels in T. sagittata. These arbuscular mycorrhizal fungi (AMF) were able to colonize the roots, as evidenced by a root mycorrhizal colonization rate ranging from 17% to 48% and soil hyphal lengths ranging from 17.51 cm/g to 32.02 cm/g, with the Mix treatment being the greatest. AMF inoculations improved plant height (16–151%), leaf number (119–283%), shoot (37–211%), and root biomass (22–318%) to varying extents, with Ri and Mix treatments being the most prominent. AMF-treated plants presented relatively greater root total length, projected area, surface area, volume, and average diameter, especially those treated with Ri and Mix. AMF inoculations also significantly improved the leaf nitrogen balance index, transpiration rate, and stomatal conductance, while the photosynthesis rate and chlorophyll index varied by AMF species, along with a decrease in intercellular CO2 levels. Root columbin levels ranged from 0.524 mg/g to 5.389 mg/g, and AMF inoculation significantly increased root columbin levels by 228–928%, with Ri being the most significant. Root columbin levels were significantly positively correlated with soil hyphal length, root total length, root projected area, root surface area, root volume, and root average diameter, but not root AMF colonization rate. This study demonstrates for the first time that AMF, especially Ri, can be employed as a biostimulant to promote growth as well as root columbin levels in T. sagittata, where AMF-triggered improvement in root morphology is an important reason for promoting root columbin levels.

Positive Changes in Fruit Quality, Leaf Antioxidant Defense System, and Soil Fertility of Beni-Madonna Tangor Citrus (Citrus nanko × C. amakusa) after Field AMF Inoculation

Citrus plants rely heavily on arbuscular mycorrhizal fungi (AMF) due to their lack of root hairs. Most experiments have been conducted with AMF inoculation under potted conditions, while field inoculation of AMF on citrus, especially a high economic hybrid tangor variety Beni-Madonna (Citrus nanko × C. amakusa), has been rarely recorded. This study aimed to analyze the effects of two AMF inoculations (a single Funneliformis mosseae and a mixture of F. mosseae, Diversispora versiformis, and Rhizophagus intraradices) on the internal and external fruit quality, leaf antioxidant defense system, and soil fertility and structure of top-worked Beni-Madonna tangor citrus trees. Three and a half years after AMF inoculations, soil hyphal length and root mycorrhizal colonization rate increased by 61.2–101.8% and 15.85–29.6% in inoculated plants, respectively. Inoculated trees had higher external fruit coloration value, fruit horizontal diameter, and fruit weight, and lower fruit rigidity than uninoculated trees. AMF-inoculated trees had higher glucose levels of fruit peels, fructose and sucrose levels of fruit fleshes, and the ratio of fruit soluble solids/titratable acids, as well as lower titratable acids concentrations than non-AMF-inoculated trees. AMF inoculation significantly increased leaf nitrogen balance index, chlorophyll index, peroxidase, catalase, superoxide dismutase, and glutathione reductase activities, as well as reduced glutathione and oxidized glutathione concentrations, resulting in lower hydrogen peroxide and malondialdehyde levels when compared to the uninoculated treatment. In addition, inoculated trees presented higher soil nutrient levels, including organic carbon, available K, and Olsen-P as, well as soil aggregate stability (based on mean weight diameter) than uninoculated trees. This study concluded that field AMF inoculation improved fruit quality, enhanced leaf antioxidant defense system, and improved soil fertility of Beni-Madonna trees, with mixed AMF being prominent in improving fruit quality and F. mosseae being prominent in enhancing leaf antioxidant defense system and improving soil fertility.

Nutrient uptake strategy selection by first-order roots of Juglans mandshurica under shading and phosphorus limitation

We investigated root growth of 1-year-old Juglans mandshurica seedlings under different light environments and varying doses of phosphorus fertilizer, to understand the relationship between root resource acquisition strategies and the variations of light and phosphorus availability. There were four shading intensities (full light, 65% full light, 35% full light, and 20% full light) along with three doses of phosphate fertilizer (0 (CK), 200% soil background available phosphorus, and 500% soil background available phosphorus). We measured in root morphology characteristics, architectural characteristics, and mycorrhizal colonization rates of first-order roots. The results showed that average diameter, average root length, and mycorrhizal colonization rates of first-order roots gradually decreased, and the specific root length, specific surface area, branching ratio and branching intensity showed a trend of first increasing and then decreasing with the increases of shading degree. As the phosphorus content decreased, the first-order root diameter gradually became thinner, and the mycorrhizal infection rate gradually increased. Root morphology and architecture of J. mandshurica would undergo adaptive changes under shade, adapting to the shading environment by expanding specific root length, specific surface area, branching ratio and branching intensity. Under phosphorus limitation, root system of J. mandshurica would increase phosphorus absorption through symbiosis with mycorrhizal fungi. When J. mandshurica was artificially regenerate in forest land with a light transmittance of 35%, root morphology and architecture would adapt to the shading environment. The symbiosis between J. mandshurica and mycorrhizal fungi would be enhanced under phosphorus limitation, which could improve phosphorus absorption of roots.

Arbuscular Mycorrhizal Fungi Colonization of Jatropha curcas Roots and Its Impact on Growth and Survival under Greenhouse-Induced Hydric Stress

Arbuscular mycorrhizal fungi (AMF) provide benefits to host plants by enhancing nutrition and overall fitness. In this study, AMF species were isolated from the soil rhizosphere of Jatropha curcas and were identified and evaluated for their potential in fostering the development of Jatropha seedlings within a controlled greenhouse environment. The first experiment assessed the interplay between hydric stress and AMF inoculation on mycorrhizal colonization. The next experiment examined the impact of quercetin on mycorrhizal colonization. Out of 204 glomerospores corresponding to 28 species spanning 10 genera, Acaulospora (14) and Scutellospora (5) were the most abundant taxa. Six new records of AMF for Costa Rica are reported. Mycorrhizal colonization was observed in 43.2% of Jatropha plants (34.7% by AMF typical hyphae; arbuscules 8.9%; coils 5.6%; and vesicles 5.4%). Significant survival effects due to AMF inoculation under hydric stress were observed. On day 85, non-mycorrhizal plants subjected to hydric stress showed a mere 30% survival rate, whereas their mycorrhizal counterparts under hydric stress exhibited survival rates of 80% and 100% with and without irrigation, respectively. Furthermore, plants with irrigation and mycorrhizas showed greater hydric stress tolerance and superior growth. The inoculated plants, irrespective of irrigation, demonstrated mycorrhizal colonization rates of 63% and 72%, respectively. Quercetin did not affect Jatropha’s growth, but there were differences in AMF root colonization. In summary, these findings accentuate the viability of a native consortium in augmenting Jatropha survival, warranting consideration as a potent biofertilizer within greenhouse settings. The AMF described can be used for Jatropha propagation programs.

Arbuscular mycorrhizal symbiosis alleviates arsenic phytotoxicity in flooded Iris tectorum Maxim. dependent on arsenic exposure levels

Arsenic (As) pollution in wetlands has emerged as a serious global concern, posing potential threat to the growth of wetland plants. Arbuscular mycorrhizal fungi (AMF) can alleviate As phytotoxicity to host plants, but their ecological functions in wetland plants under flooding conditions remain largely unknown. Thus, a pot experiment was conducted using Rhizophagus irregularis and Iris tectorum Maxim. exposed to light (15 and 30 mg/kg As) and high (75 and 100 mg/kg As) levels of As, to investigate the intrinsic mechanisms underlying the effects of mycorrhizal inoculation on plant As tolerance under flooding conditions. The mycorrhizal colonization rates ranged from 31.47 ± 3.92 % to 60.69 ± 5.58 %, which were higher than the colonization rate (29.55 ± 13.60%) before flooding. AMF significantly increased biomass of I. tectorum under light As levels, together with increased phosphorus (P) and As uptake. Moreover, expression of arsenate reductase gene RiarsC and a trace of dimethylarsenic (1.87 mg/kg in shoots) were detected in mycorrhizal plants, suggesting As transformation and detoxification by AMF exposed to light levels of As. However, under high As levels, AMF inhibited As translocation from roots to shoots, and facilitated the formation of iron plaque. The immobilized As concentrations in iron plaque of mycorrhizal plants were respectively 1133.68 ± 179.17 mg/kg and 869.11 ± 248.90 mg/kg at 75 and 100 mg/kg As addition level, both significantly higher than that in non-inoculated plants. Irrespective of As exposure levels, mycorrhizal symbiosis decreased soil As bioavailability. Overall, the study provides insights into the alleviation of As phytotoxicity in natural wetland plants through mycorrhizal symbiosis, and potentially indicates function diversity of AMF under flooding conditions and As stress, supporting the subsequent phytoremediation and restoration of As-contaminated wetlands.

Soil patch heterogeneity improves plant productivity and nutrients regulated by arbuscular mycorrhizal fungi

AbstractThe interlacing and mosaic distribution of karst soil and rock result in the high spatial heterogeneity of the natural karst habitat. Karst plants are suffered from spatially heterogeneous microhabitats with different‐sized patches. Arbuscular mycorrhizal (AM) fungi are crucial in regulating plant productivity and nutrients in heterogeneous karst environments. However, how spatial patch heterogeneity influences plant productivity and nutrient utilization by AM fungi regulation in karst soil remains unclear. A simulated heterogeneity experiment regarding soil grid patches was conducted by planting Bidens pilosa into a microcosm of a square device. Experimental treatments included the mycorrhizal fungus treatments inoculation with (M+) or non‐inoculation with (M−) Glomus etunicatum fungus, and the spatial heterogeneity treatments involved homogeneous patches (HO), heterogeneity‐small patches (HS), and heterogeneity‐large patches (HL). The growth and nutritional traits of plants were analyzed. The results showed that AM fungus promoted the productivity and nutrient uptake of B. pilosa by substantial increases in biomass, nitrogen (N) accumulation, phosphorus (P) accumulation, and N/P ratio. The spatial heterogeneity promoted the biomass and N and P accumulations of B. pilosa when inoculating with AM fungus. The mycorrhizal colonization rate and hyphae length were greater in HS than in HO and HL under the M+ treatment, with a greater response ratio of biomass, N and P under HS conditions. These indicated that the heterogeneous small patches had a greater promotion of the biomass production and nutrients of B. pilosa with inoculation of AM fungus because extensive fungal hyphae can acquire soil resources in more distant patches outside the root zone with more economical metabolic costs compared to roots. We thus conclude that patch heterogeneity contributes to plant productivity and nutrient utilization regulated by AM fungi in karst soil, and the broader nutrient capture induced by extraradical hyphae of AM fungi may be an adaptive mechanism for karst plants to cope with heterogeneous environmental conditions.

Management of the mycorrhizal and rhizobial associations to mitigate the negative effects of Grevillea banksii on the development of Dalbergia trichocarpa an endemic tree species

This study aims to improve the development of Dalbergia trichocarpa, a Malagasy native tree species, on a soil invaded by Grevillea banksii, an invasive plant species in eastern part of Madagascar, by inoculating seedlings with mycorrhizal fungal, Rhizophagus irregularis and AMFn strains or rhizobial STM609 and Rn strains, or a mixed rhizobial-mycorrhizal strains. After five months of growth, the results showed that single or dual inoculation boosted significantly the development of D. trichocarpa, compared to control treatments and all parameters measured were markedly different between the time periods of plant invasions. Indeed, the dry mass of aerial biomass was significantly higher in inoculated seedlings than in control seedlings. It was also observed that the number of nodules and the arbuscular mycorrhizal colonization rates of D. trichocarpa increased significantly with inoculated plantlets. However, soil inoculated with the rhizobial strain STM609 alone showed a significantly high global soil microbial activity and the dual inoculation has promoted the soil acid phosphatase activity. These results suggest that dual inoculation with rhizobial and arbuscular mycorrhizal strains was significantly beneficial to the growth, nodulation and mycorrhizal colonization rates of D. trichocarpa in the soil overgrown by G. banksii, an invasive exotic plant species. Thus, this biotechnology can be used for restoration of degraded ecosystems in Madagascar with native tree species.

Evaluating the Dynamics of Mycorrhizal Populations and Wilt Severity in Chili Cultivation Regions

Chili peppers (Capsicum annuum L.) are a widely cultivated spice and vegetable globally, with their origins rooted in Mexico. The primary diseases impacting chili production encompass Anthracnose, Phytophthora, Leaf blight, Fusarium wilt, bacterial wilt, damping-off, and root rot, among others. In recent years, there has been a growing concern surrounding Fusarium wilt, caused by Fusarium oxysporum. This study aimed to investigate the fluctuations in mycorrhizal populations and the severity of wilt in chili farming regions within the state during the 2017-18 growing season. In each district, ten fields were examined, with two to three fields representing each village. The most substantial mycorrhizal colonization rate and the number of sporocarps in the soil were identified in Mahendragarh, with a mycorrhizal colonization rate of 17.3% and 260 sporocarps per 200 g of soil. Fatehabad district followed with a mycorrhizal colonization rate of 13.1% and 182 sporocarps per 200g of soil. The lowest values were recorded in Hisar district, with a mycorrhizal colonization rate of 11.5% and 138 sporocarps per 200g of soil. Wilt severity was most pronounced in Fatehabad district at 7.9%, followed by Mahendragarh at 7.3%, and was least severe in Hisar at 5.2%.

Effects of combinations of arbuscular mycorrhizal fungal species on tomato growth and Fusarium wilt control

In this study, we investigated the effects of combinations of arbuscular mycorrhizal (AM) fungal species on tomato seedling growth and Fusarium wilt control. The study was conducted in greenhouse pot experiments using the tomato (Solanum lycopersicum) variety Fusan 88 and the fungi Funneliformis mosseae, Diversispora versiformis, Claroideoglomus etunicatum, and Rhizophagus intraradices as inoculants. The results showed higher mycorrhizal root colonization rates in all inoculation mixtures than in single-inoculum treatments, while growth-promotion effects differed significantly among AM fungal species and their combinations. Except for inoculation with F. mosseae alone, other inoculation treatments significantly promoted the growth of tomato seedlings. Of all fungal species, R. intraradices had the most significant effect on promoting seedling growth, as observed in all inoculum combinations containing this species. The greatest effect on seedling growth was observed for combined inoculation with D. versiformis + R. intraradices, which led to increases in above- and belowground biomass of 67.74 % and 100 %, respectively, compared to the control (CK), followed by C. etunicatum + R. intraradices, which led to increases in above- and belowground biomass of 61.29 % and 100 % compared to CK. Redundancy analyses showed that compared to the other three species, R. intraradices had more significant effects on promoting plant nitrogen, phosphorus, and potassium uptake and increasing above- and belowground dry weight. Mycorrhizalized seedlings were more resistant to Fusarium wilt and had lower malondialdehyde content and higher catalase, superoxide dismutase, and polyphenol oxidase activity in tomato plants. The lowest Fusarium wilt disease index value was 39.96 %, for mixed inoculation with F. mosseae + D. versiformis + C. etunicatum; this was 34.28 % lower than that of CK, and the control effect was 34.27 %, followed by inoculation with C. etunicatum + R. intraradices, which had a disease index value of 41.48 %, 31.78 % lower than that of CK, with a control effect value of 31.76 %. Therefore, we transplanted tomato seedlings inoculated with C. etunicatum + R. intraradices, which had both good growth-promotion and disease-resistance effects, to a greenhouse for sand culture under conditions of high water and fertilization. The mycorrhizal relationships developed in these plants at the seedling stage remained stable throughout the tomato reproductive period. The mycorrhizal seedlings had a significantly lower incidence of Fusarium wilt and lower disease index values, indicating better disease control than observed in non-mycorrhizal seedlings. The mycorrhizal plants produced fruits with a significantly higher soluble-sugar content and sugar:acid ratio (30.8 % and 42.3 % higher, respectively, than CK) and a significantly lower organic acid content (11.5 % lower than CK). Thus, mycorrhization significantly improved tomato plants’ growth, disease resistance, and fruit quality. These findings lay a foundation for the application of mycorrhizal fungi in tomato agriculture.

Insight into regulation of adventitious root formation by arbuscular mycorrhizal fungus and exogenous auxin in tea plant (Camellia sinensis L.) cuttings.

Adventitious root (AR) development, affected by various biotic and abiotic factors, is the most important procedure in tea plant (Camellia sinensis L.) cutting propagation. Establishing symbiotic relationships with most terrestrial plants, AMF (Arbuscular mycorrhizal fungus) can mediate the AR formation of several herbaceous and woody plants in previous studies. In this paper, effects of combined application of AMF and exogenous auxin on AR formation of cuttings from different tea plant varieties ('Pingyangtezao', 'Longjing 43' and 'Longjingchangye') were studied. Then we also performed RNA-Seq analysis with 'Pingyangtezao' cuttings aiming to find the possible auxin-related pathway of AM fungal regulation on AR formation. To accurately uncover the regulatory mechanism of AMF on AR formation of tea cuttings, rooting process were separated into four stages (S0, non-rooting; S1, AR protrusion; S2, AR formation and S3, AR elongation) at the same sampling time. Results showed that IBA treatment increased the mycorrhizal colonization rate, especially in 'Pingyangtezao' variety (from 37.58% to 46.29%). Both inoculating AMF and addition of IBA promoted the AR formation, and rooting of different tea plant varieties showed different dependence on auxin. AMF could alleviate the effect of auxin-related inhibitors (2,3,5-triiodobenzoic acid, L-α-(Aminooxy)-β-phenylpropionic acid and α-(phenylethyl-2-oxo)-IAA) on rooting of tea cuttings, even though the colonization of AMF was hindered at various degrees. Transcriptomic analysis showed that different numbers of differentially expressed genes (DEGs) at various rooting stages of tea cuttings with the most at S2 stage (1360 DEGs), indicating the increasing regulation by AMF with the development of AR. Similar trend was found in auxin-related DEGs, and family genes of YUC, GH, PIN, LAX, SAUR, AUX, and ABP involved in the AM fungal regulation on AR formation of tea cuttings. Additionally, AMF strongly mediated auxin transport and signal transduction pathways in tea cuttings as showed by the results of correlation analysis. Overall, interaction of AMF and exogenous auxin in promoting rooting and the preliminary mechanism of AMF regulating AR formation of tea cuttings was deciphered in this paper, which may provide a basis for further deep mechanistic research and cutting propagation of tea production.

Responses of rhizosphere fungi to the root economics space in grassland monocultures of different age.

Recent studies on root traits have shown that there are two axes explaining trait variation belowground: the collaboration axis with mycorrhizal partners and the conservation ('fast - slow') axis. However, it is yet unknown whether these trait axes affect the assembly of soilborne fungi. We expect saprotrophic fungi to link to the conservation axis of root traits, whereas pathogenic and arbuscular mycorrhizal fungi link to the collaboration axis, but in opposite directions, as arbuscular mycorrhizal fungi might provide pathogen protection. To test these hypotheses, we sequenced rhizosphere fungal communities and measured root traits in monocultures of 25 grassland plant species, differing in age. Within the fungal guilds, we evaluated fungal species richness, relative abundance and community composition. Contrary to our hypotheses, fungal diversity and relative abundance were not strongly related to the root trait axes. However, saprotrophic fungal community composition was affected by the conservation gradient and pathogenic community composition by the collaboration gradient. The rhizosphere AMF community composition did not change along the collaboration gradient, even though the root trait axis was in line with the root mycorrhizal colonization rate. Overall, our results indicate that in the long term, the root trait axes are linked with fungal community composition.

Effects of arbuscular mycorrhizal fungi on zinc uptake, translocation and accumulation in winter wheat during whole plant growth stages

Although arbuscular mycorrhizal fungi (AMF) could play important roles in zinc (Zn) uptake in host plants, the effects of AMF on Zn uptake and transport in winter wheat during the whole growth stage remain unclear. A pot experiment was conducted to investigate the effects of Funneliformis mosseae (Fm) and Claroideoglomus etunicatum (Ce) on Zn absorption, transport, and accumulation in winter wheat under different Zn levels (0, 2.5, and 25 mg kg–1) in soils. This study showed that there was a significant correlation between mycorrhizal colonization rate and Zn absorption efficiency in winter wheat roots during the post-anthesis period, but there was no significant correlation during the pre-anthesis period. AMF significantly increased Zn concentrations (0.64–0.81 times) in wheat grains under 0 mg kg-1 Zn level, but decreased Zn concentrations in wheat grains under 25 mg kg-1 Zn level. Additionally, under 0 and 2.5 mg kg–1 Zn treatments, AMF increased Zn absorption rate (3.3–14, 0.21–1.02 times) in roots at filling and maturity stages and the contribution of root Zn uptake (0.36–0.64, 0.27–0.37 times) to grain Zn. However, AMF decreased root Zn absorption rate (0.32–0.61 times) and increased the contribution of Zn remobilization (1.69–2.01 times) in vegetative tissues to grain Zn under 25 mg kg–1 Zn treatment. The present results would complement the mechanisms and effects of AMF on Zn absorption and transport in winter wheat and provide a potential method for the application of AMF to wheat grain Zn enrichment.

Positive effects of biochar application and Rhizophagus irregularis inoculation on mycorrhizal colonization, rice seedlings and phosphorus cycling in paddy soils

Phosphorus (P) is an essential element for plant growth but is often limiting in ecosystems; therefore, improving the P fertilizer use efficiency is important. Biochar and arbuscular mycorrhizal fungi (AMF) may enhance P cycling in paddy soils that contain high total P but low available phosphorus (AP). In this study, the effects of biochar and Rhizophagus irregularis inoculation on the organic and inorganic P contents and phosphatase activity of paddy soil, rice seedling growth, and AMF colonization ability were investigated. Compared with the control, biochar enhanced the percentage spore germination at day 7, hyphal length, most probable number, and mycorrhizal colonization rate of R. irregularis by, on average, 32%, 662%, 70%, and 28%, respectively. Biochar and R. irregularis altered soil P cycling and transformed soil P availability. Biochar and R. irregularis, either individually or in combination, increased the soil AP content by 2%–48%. Rice seedlings treated with biochar and R. irregularis produced greater biomass, and showed improved root morphology and higher nutrient uptake compared with those of the control. The results suggest that combined application of biochar and R. irregularis is beneficial for rice cultivation in paddy soils with high total P but low AP content.

Shift of root nitrogen-acquisition strategy with tree age is mediated by root functional traits along the collaboration gradient of the root economics space.

Root nitrogen (N)-uptake rate and uptake preference, and their association with root morphological and chemical traits are important to characterize root N-acquisition strategies of trees. However, how the root N-acquisition strategy varies with tree age, especially for those species that coexist at a common site, remains unknown. In this study, a field isotopic hydroponic method was used to determine the uptake rate and contribution of NH4+, NO3- and glycine, for three coexisting ectomycorrhizal coniferous species [Pinus koraiensis (Korean pine), Picea koraiensis (Korean spruce) and Abies nephrolepis (smelly fir)] at three age classes (young, middle-aged and mature) in a temperate forest. Concurrently, root morphological and chemical traits, as well as mycorrhizal colonization rate were determined. Our results show that the root uptake rate of total N and NH4+ gradually decreased across all three species with increasing tree age. The three species at all age classes preferred NH4+, except for middle-aged Korean spruce and mature smelly fir, which preferred glycine. In contrast, all three species showed the lowest acquisition of NO3-. According to the conceptual framework of 'root economics space', only a 'collaboration' gradient (i.e. dimension of root diameter vs specific root length or area) was identified for each species, in which root N-uptake rate loaded heavily on the side of 'do-it-yourself' (i.e. foraging N more by roots). Young trees of all species tended to exhibit the 'do-it-yourself' strategy for N uptake, and mature trees had an 'outsourcing' strategy (i.e. foraging N by a mycorrhizal partner), whereas middle-aged trees showed a balanced strategy. These findings suggest that shifts of root N-acquisition strategy with tree age in these species are mainly mediated by root traits along the 'collaboration' gradient, which advances our understanding of belowground competition, species coexistence and N cycling in temperate forests.

Temperature drives the coordination between above‐ground nutrient conservation and below‐ground nutrient acquisition in alpine coniferous forests

Abstract Above‐ground nutrient conservation via resorption processes and below‐ground nutrient acquisition from soils are two important mechanisms for plants to maintain nutrition and ecosystem functions. However, the mechanism by which plants coordinate these two nutrient strategies, especially for ectomycorrhizal (ECM)‐dominated conifers in alpine forests, remains unclear. We investigated the relationships between above‐ground nutrient conservation and below‐ground nutrient acquisition and their environmental drivers by measuring leaf nutrient (i.e. nitrogen [N] and phosphorous [P]) resorption efficiency, resource foraging‐ and uptake‐related root morphological (root diameter [RD], specific root length [SRL]/area [SRA]) and physiological (root tissue density [RTD], root N and P concentration) traits, mycorrhizal colonization rate (MCR), rhizosphere effect on soil N and P cycling, and environmental factors of 40 ECM coniferous populations on the eastern Tibetan Plateau, China. Our results showed that with increasing leaf nutrient (N and P) resorption efficiency, conifers shifted from depending on the ‘outsourcing’ strategy by mycorrhizal fungi (high MCR) to relying on the ‘do‐it‐yourself’ strategy of root mining (high rhizosphere effect on N‐ and P‐mining‐related enzyme activities) rather than on root foraging (high SRL and SRA) and preferred more conservative roots (high RTD and low root N and P concentrations). Temperature was the main factor driving a negative relationship of ECM fungi foraging, root uptake and a positive relationship of root mining with leaf nutrient resorption, while precipitation resulted in a decoupled relationship between root foraging and leaf nutrient resorption. Our findings demonstrate temperature‐driven and diverse collaborations (e.g. trade‐off or synergy) between below‐ground nutrient acquisition and above‐ground nutrient conservation strategies in alpine ECM conifers and highlight that the preference for below‐ground nutrient acquisition strategies could influence the above‐ground nutrient utilization strategy. This is insightful for a holistic understanding of the adaptation and responses of alpine forests to climatic change. Read the free Plain Language Summary for this article on the Journal blog.