Arbuscular Mycorrhizal Root Research Articles

The Synergy of Arbuscular Mycorrhizal Fungi and Exogenous Abscisic Acid Benefits Robinia pseudoacacia L. Growth through Altering the Distribution of Zn and Endogenous Abscisic Acid

The simultaneous effects of arbuscular mycorrhizal (AM) fungi and abscisic acid (ABA) on the tolerance of plants to heavy metal (HM) remain unclear. A pot experiment was carried out to clarify the effects of simultaneous applications of AM fungi and ABA on plant growth, Zn accumulation, endogenous ABA contents, proline metabolism, and the oxidative injury of black locust (Robinia pseudoacacia L.) exposed to excess Zn stress. The results suggested that exogenously applied ABA positively enhanced AM colonization, and that the growth of plants only with AM fungi was improved by ABA application. Under Zn stress, AM inoculation and ABA application increased the ABA content in the root/leaf (increased by 48–172% and 92%, respectively) and Zn content in the root/shoot (increased by 63–152% and 61%, respectively) in AM plants, but no similar trends were observed in NM plants. Additionally, exogenous ABA addition increased the proline contents of NM roots concomitantly with the activities of the related synthases, whereas it reduced the proline contents and the activity of Δ1-pyrroline-5-carboxylate synthetase in AM roots. Under Zn stress, AM inoculation and ABA application decreased H2O2 contents and the production rate of O2, to varying degrees. Furthermore, in the roots exposed to Zn stress, AM inoculation augmented the activities of SOD, CAT, POD and APX, and exogenously applied ABA increased the activities of SOD and POD. Overall, AM inoculation combined with ABA application might be beneficial to the survival of black locust under Zn stress by improving AM symbiosis, inhibiting the transport of Zn from the roots to the shoots, increasing the distribution of ABA in roots, and stimulating antioxidant defense systems.

Strong host-specific selection and over-dominance characterize arbuscular mycorrhizal fungal root colonizers of coastal sand dune plants of the Mediterranean region.

Sand dunes of the Mediterranean region constitute drought-stressed, low-fertility ecosystems. Arbuscular mycorrhizal fungi (AMF) are regarded as key components of their biota, that contribute to plant host adaptation and fitness. However, AMF community assembly rules in the roots of the psammophilous plants of coastal sand dunes have not been investigated. We studied the root colonizing AMF communities of four characteristic native plants of eastern Mediterranean coastal foredunes, in nine locations in Greece. Host-specificity (plant identity) was the major driver of AMF community assembly in the plant roots, while geographical distance between locations was not related to differences in the AMF communities. Additionally, colonizer AMF communities were characterized by over-dominance of a single operational taxanomic unit (OTUs), which was remarkably host-specific among locations. Wider dissimilarity in AMF communities was observed in small and disturbed (SD) sites compared to large and undisturbed (LU) sites, a trait that may be attributed to relaxed environmental filtering and facilitated AMF dispersal/immigration in SD sites from surrounding habitats. Overall, our results indicate that the assembly of root-colonizing AMF communities in the eastern Mediterranean sand dunes is characterized by strong biotic filtering (host identity), suggesting that co-adaptation processes may be more pronounced than previously proposed, under extreme environmental conditions.

Spatial changes of arbuscular mycorrhizal fungi in peach and their correlation with soil properties.

Arbuscular mycorrhizal (AM) fungi have beneficial effects on host plants, but their growth is influenced by various factors. This study was carried out to analyze the variation of AM fungi in soils and roots of peach (Prunus persica L. var. Golden Honey 3, a yellow-flesh variety) trees in different soil layers (0–40 cm) and their correlation with soil properties. The peach tree could be colonized by indigenous AM fungi (2.2–8.7 spores/g soil and 1.63–3.57 cm hyphal length/g soil), achieving 79.50–93.55% of root AM fungal colonization degree. The mycorrhizal growth, root sugars, soil three glomalins, NH4+-N, NO3−-N, available P and K, and soil organic matter (SOM) had spatial heterogeneity. Soil spores, but not soil hyphae contributed to soil glomalin, and soil glomalin also contributed to SOM. There was a significant correlation of soil hyphae with spore density, soil NO3−-N, and SOM. Root mycorrhiza was positively correlated with spore density, NH4+-N, NO3−-N, and easily extractable glomalin-related soil protein. Notably, spore density positively correlated with NO3−-N, available K, SOM, and root fructose and glucose, while negatively correlated with available P and root sucrose. These findings concluded that mycorrhiza of peach showed spatial distribution, and soil properties mainly affected/altered based on the soil spore density.

Short-term microbial responses to soluble inorganic P input in a tropical lowland rain forest in Amazonia

In non-flooded lowland rain forests with low soil phosphorus (P) in parts of Amazonia, P cycling largely occurs via leaf litter recycling by arbuscular mycorrhizal (AM) fungal symbionts. Occasional high input of P into these ecosystems occurs during drought years with increased litterfall. As the length and frequency of drought events are projected to increase in the region, a single-dose nutrient addition experiment was carried out to test how this would impact P cycling. An application rate of 4 kg P ha–1 was used, which corresponds to twice the amount of litter-derived P in an average year. It was hypothesized that i) the added mineral P would be immobilized by soil microorganisms, leading to measurable increase in soil microbial biomass carbon (C) and P and ii) AM colonization rate would be reduced by the pulse in mineral P available for plant uptake. The results did not support either of our hypotheses. The addition of P did not have an effect on AM root colonization, nor was P immobilized by soil microbiota during the experimental period. The lack of a difference between the control and treatment at our study site could be attributed to the relatively low one-off dose of P applied that did not change either the colonization rate of roots by AM fungi or the amount of soil available labile P. To obtain a mechanistic understanding of the availability, capture, and use of P by plant-symbiont associations in tropical rain forest ecosystems, further integrated studies of the soil-plant system combining long-term nutrient manipulations, modeling, and experimental approaches are required.

The relative contribution of indigenous and introduced arbuscular mycorrhizal fungi and rhizobia to plant nutrient acquisition in soybean/maize intercropping in unsterilized soils

It has been demonstrated that intercropped crops may benefit from inoculation with rhizobia or arbuscular mycorrhizal (AM) fungi in soybean/maize intercropping systems under sterilized conditions. Little is known about the relative contribution of indigenous and introduced AM fungi and rhizobia to nutrient acquisition of intercropped soybean and maize in unsterilized soils. In this study, we evaluated the effectiveness of indigenous and introduced AM fungi and rhizobia in a soybean/maize intercropping system under unsterilized soil conditions. The results show that introduced rhizobial inoculation promoted soybean nodulation and growth. Single AM fungal inoculation promoted indigenous rhizobial nodulation and increased maize AM root colonization, but had little effect on maize growth. Co-inoculation strongly increased plant dry weight, and nitrogen (N) and phosphorus (P) content of the intercropped soybean compared to those with only indigenous rhizobial and AM fungal communities, but had no effect on those of maize in the same intercropped system. These results indicate that AM fungal inoculation promoted nodulation by indigenous rhizobia. Effective rhizobial inoculation combined with introduced AM fungi may not only promote symbiotic N2 fixation, but also enhance rhizosphere processes, which has the potential to improve nutrient acquisition in the field. Soybean is a weak competitor compared with maize in intercropping systems. Inoculation with introduced AM and rhizobia ameliorated the growth suppression of intercropped soybean, but inhibited growth of intercropped maize, indicating that inoculation of introduced AM fungi and/or rhizobia partly shifted the competitive advantage from maize to soybean. In conclusion, introduced AM fungi and rhizobia contributed more than indigenous populations to promoting growth and nutrient acquisition of the intercropped soybean in unsterilized soils.

Root Colonization and Spore Abundance of Arbuscular Mycorrhizal Fungi Along Altitudinal Gradients in Fragmented Church Natural Forest Remnants in Northern Ethiopia.

Arbuscular mycorrhizal fungi (AMF) spore density and root colonization are considered sensitive to host species and abiotic factors such as climate and soil. However, there is a knowledge gap about how fragmented native forest remnants might contribute to AMF conservation, what is the AMF spore density and root colonization, and to what extent climate change, particularly warming, might impact AMF. The aim of the study was to quantify the AMF spore density and root colonization along altitudinal gradients in three agro-ecological zones of nine church forests in northern Ethiopia. Data were collected from 45 plots. All the surveyed church forest species were colonized by AMF. However, we found a significant (p < 0.05) decrease in root colonization and AMF abundance in forests at high elevation. The topsoil had significantly (p < 0.05) higher root colonization and AMF abundance than subsurface soil. We found strong negative correlations between altitude and both spore density and root colonization and soil fertility. While we cannot separate whether spore density was temperature or soil limited, we can demonstrate the importance of conserving certain tree species, particularly Ficus species, which harbor high spore densities, in both lowland and midland church forests. In the highland, no Ficus species were found. However, Hagenia abyssinica, another Rosales, had the highest spore density in the highland ecoregion.

Influence of Land Use Intensity and Management on Arbuscular Mycorrhizal Fungi-Avocado Symbiosis

This study was done to assess the effect of soil disturbance on arbuscular mycorrhizal fungi spore abundance and root colonization in avocado (Persea americana Mill.). Rhizosphere soil and root samples of avocado were collected from different farms in south Florida and analyzed for degree of mycorrhizal colonization in roots, spore density and diversity in soil along with soil characteristics. There was significant difference in the soil characteristics among the different farms. Similarly, there was a significant difference in the degree of mycorrhizal colonization in the roots and the arbuscular mycorrhizal fungi spore morphotypes among different land use and management practices. However, there was no significant difference in the total number of arbuscular mycorrhizal fungi spores among these sites. There was no correlation between the number of arbuscular mycorrhizal fungi spores and soil characteristics. However, arbuscular mycorrhizal fungi colonization in roots were strongly influenced by soil characteristics such as soil moisture, carbon, nitrogen, and organic matter. Further research is necessary to identify these AMF species and determine the role of in avocado growth tolerance to anthropogenic disturbance in highly disturbed urban soils.

Divergent root P uptake strategies of three temperate grassland forage species

Temperate grasslands are affected by nutrient deficiency and this deficiency is one of the main limiting factors for forage production, such as the grasslands of the Salado River Basin (Argentina), which exhibit low-P availability for plant growth. Alternatives to increase forage production include the selection of plant species adapted to grow under P deficiency, P fertilization, and arbuscular mycorrhizal (AM) fungi. In a pot experiment, we investigated the effect of low and high-P doses and AM fungi on the development of three forage species. The interaction of P addition and AM fungi increased L. tenuis (legume) biomass production and improve P nutrition, even with high-P dose, because of its higher P requirement to grow and lower ability for P uptake than grasses. High-P increased the biomass of S. arundinaceus (C3 grass) and P. coloratum (C4 grass), and AM fungi did not directly impact on plant growth of grasses, but did impact on P nutrition at either level of P fertilization. The specific P uptake of non-fertilized L. tenuis plants increased 97% due to AM inoculation and was the highest value among the three non-fertilized species. Furthermore, the specific P uptake of non-fertilized grasses was similar, despite the C metabolic pathway and AM fungi, but the specific root length was 70.88% lower for P. coloratum than for S. arundinaceus. Thus, the main strategy of L. tenuis was AM association, whereas that of S. arundinaceus was the highest ability of the root system to explore the soil. In P. coloratum, the strategy could not be explained by changes in specific root length or AM association. Our results would be an advantageous first step to promote better management of forage land sustainably while increasing forage production and preserve the beneficial effects of native AM communities in the Salado River Basin.

Arbuscular mycorrhizal fungus–induced decrease in phosphorus loss due to leaching in red soils under simulated heavy rainfall

Phosphorus (P) loss from the soil due to leaching is affected by plant roots and arbuscular mycorrhizal fungi (AMF). This paper aimed to (i) analyze the effects of plant roots and AMF on P concentrations in interflow and P loss from the soil due to leaching and (ii) explain whether there were interaction effects between plant roots and AMF on the loss of P from soils due to leaching. In this study, samples of red soil were collected from wasteland, farmland, and slopeland on the Yunnan Plateau. As a host plant, maize was cultivated in a dual-compartment cultivation system. There were mycorrhizal and hyphal compartments for the arbuscular mycorrhizal fungal inoculation treatment and root and soil compartments for the non-inoculation treatment. The maize biomass and P uptake, P concentrations in interflow within two soil layers (0–20 and 20–40 cm), and P losses due to leaching under simulated heavy rainfall (40 and 80 mm/h) were analyzed. Arbuscular mycorrhizal fungal inoculation significantly enhanced the biomass and P uptake of maize, but had little effect on P concentration in the interflow under 40 mm/h rainfall. In addition, Arbuscular mycorrhizal fungal inoculation resulted in a decrease of 37–65% in P concentration in interflow under 80 mm/h rainfall, and a decrease of 21–39% in the P loss from soils due to leaching under heavy rainfall (40 and 80 mm/h). Moreover, significant or highly significant positive correlations were observed between P concentrations in the interflow and the loss of P due to leaching from the red soil. Two-way analysis of variance indicated that AMF significantly or highly significantly decreased P concentrations in the interflow and decreased P loss from red soils due to leaching, whereas the root effects were insignificant. In addition, there was no interaction between AMF and maize roots. Our study indicated that the arbuscular mycorrhizal fungus–induced decreases in the loss of P due to leaching from red soils were caused by decreased P concentrations in the interflow. The potential for AMF to reduce P leaching from soils is an important ecological function.

Improved salinity tolerance of Medicago sativa and soil enzyme activities by PGPR

Abstract Abiotic stresses such as salinity are common adverse conditions that significantly affect agricultural productivity worldwide. This study aimed to select halotolerant plant-growth-promoting rhizobacteria (PGPR) capable to promote plant growth and to improve soil functioning under salinity stress conditions. Thirty-two bacterial isolates were studied for their PGP traits and NaCl resistance. Four selected potential PGPR were identified by using 16S rDNA sequencing and tested for their PGP traits in the presence of 2–6% NaCl. Their effect on growth, chlorophyll content, oxidative stress and root arbuscular mycorrhizal (AM) colonization of Medicago sativa, was studied under salt stress in pots experiment. The bacteria were also tested for their effect on soil enzyme activities. Overall results showed that the isolates displayed various PGP properties and variable levels of NaCl resistance. The four selected potential PGPR strains were identified as Pseudomonas putida, Alcaligenes sp., Klebsiella sp., and Pseudomonas cedrina. The bacteria retained most of the PGP traits in the presence of the tested concentrations of NaCl. The inoculation of M. sativa plants by the four strains allowed overcoming the negative effects of stress due to NaCl and increased plant growth, roots AM colonization and the leaves chlorophyll content, compared to the non-inoculated control. It also lowered the levels of the indicators of oxidative damage, malondialdehyde, hydrogen peroxide, and proline. Besides, the strains had a positive effect on soil phosphatase, β-galactosidase, and arylamidase activities. This study showed that the selected isolates have an interesting potential to be used as bio-inoculants for plants growing under salt stress.

Strigolactone biosynthesis, transport and perception.

Strigolactones (SLs) are plant hormones that regulate diverse developmental processes and environmental responses. They are also known to be root-derived chemical signals that regulate symbiotic and parasitic interactions with arbuscular mycorrhizal fungi and root parasitic plants, respectively. Since the discovery of the hormonal function of SLs in 2008, there has been much progress in the SL research field. In particular, a number of breakthroughs have been achieved in our understanding of SL biosynthesis, transport and perception. The discovery of the hormonal function of SL was quite valuable not only as the identification of a new class of plant hormones, but also as the discovery of the long-sought-after SL biosynthetic and response mutants. These mutants in several plant species provided us the genetic resources to address fundamental questions regarding SL biosynthesis and perception. Such mutants were further characterized later, and biochemical analyses of these genetically identified factors have uncovered the outline of SL biosynthesis and perception so far. Moreover, new genes involved in SL transport have been discovered through reverse genetic analyses. In this review, we summarize recent advances in SL research with a focus on biosynthesis, transport and perception.

Influence of 9 years of permanent raised beds and contour furrowing on soil health in conservation agriculture based systems in Tigray region, Ethiopia

AbstractConservation agriculture (CA) systems represent a set of three soil management principles: minimarbance, permanent soil cover and crop rotations ‐ whereas the CA‐based systems in this study add the bed and furrow tillage techniques as integral elements of CA. Studies on the effects of long‐term CA‐based systems on soil health and crop productivity are rare globally, particularly in Ethiopia. This study aimed at investigating the long‐term (2005–2013) influence of CA‐based systems on soil health and crop productivity in northern Ethiopia. The treatments we used include two types of CA‐based systems (permanent raised bed PRB and contour furrowing CF) and conventional tillage (CT) arranged in a randomized complete block design. Soil samples were collected at 0–10 cm soil depth to assess soil health. Piecewise structural equation modeling (PSEM) was used to analyze linkages between management practices, soil health and crop productivity. Arbuscular mycorrhizal fungi spore abundance and root colonization was higher in PRB followed by CF compared to CT (p &lt; 0.05). Significantly different soil N of 1.4 and 0.9 g kg−1 and available P of 6.7 and 4.1 ppm were recorded for PRB and CT, respectively. Higher straw and grain yield of 12 and 4.3, 10 and 3.5, 8 and 2.8 t ha−1 were recorded for PRB, CF and CT, respectively. Outputs of the PSEM highlighted two pathways in which CA‐based systems contributed to improved productivity: (a) via higher density of bacteria and improved hydraulic conductivity, and (b) via higher density of fungi and increase soil organic carbon content in the topsoil. The study concludes that CA‐based systems have the potential to improve crop productivity through improved soil health.

Irrigation and fertilization effects on arbuscular mycorrhizal fungi depend on growing season in a dryland maize agroecosystem

Arbuscular mycorrhizal (AM) fungi form mutualistic associations with most terrestrial plants and can enhance crop water and nutrition acquisition. It is thus important to elucidate the interactive impacts of water and fertilizer management on AM fungi for sustainable agriculture. Our study investigated the effects of irrigation (well-watered vs. drought) and fertilization (nitrogen (N), phosphorus (P), and NP) on AM fungi in soil and roots of maize (Zea mays L.) across three consecutive growth phases (jointing, tasseling, and mature). Drought significantly decreased AM fungal extra-radical hyphal density and root colonization rate at the tasseling and mature phases, respectively. Nitrogen and NP fertilization exerted a negative effect on AM fungal spore density under drought at the mature phase. Drought decreased AM fungal richness in soil and roots at the jointing and mature phases, respectively. AM fungal community composition in soil and roots was significantly different between the jointing phase and the tasseling and mature phases. AM fungal community composition was influenced by fertilization at the tasseling phase in soil, but by irrigation at the jointing and tasseling phases in roots. Our findings highlight the differential response of AM fungi in soil and roots to drought and fertilization during the various phases of maize development in this dryland agroecosystem.

Long-term effects of mixed planting on arbuscular mycorrhizal fungal communities in the roots and soils of Juglans mandshurica plantations

BackgroundEstablishing mixed plantations is an effective way to improve soil fertility and increase forest productivity. Arbuscular mycorrhizal (AM) fungi are obligate symbiotic fungi that can promote mineral nutrient absorption and regulate intraspecific and interspecific competition in plants. However, the effects of mixed plantations on the community structure and abundance of AM fungi are still unclear. Illumina MiSeq sequencing was used to investigate the AM fungal community in the roots and soils of pure and mixed plantations (Juglans mandshurica × Larix gmelinii). The objective of this study is to compare the differential responses of the root and rhizosphere soil AM fungal communities of Juglans mandshurica to long-term mixed plantation management.ResultsGlomus and Paraglomus were the dominant genera in the root samples, accounting for more than 80% of the sequences. Compared with that in the pure plantation, the relative abundance of Glomus was higher in the mixed plantation. Glomus, Diversispora and Paraglomus accounted for more than 85% of the sequences in the soil samples. The relative abundances of Diversispora and an unidentified genus of Glomeromycetes were higher and lower in the pure plantation, respectively. The Root_P samples (the roots in the pure plantation) had the highest number of unique OTUs (operational taxonomic units), which belonged mainly to an unidentified genus of Glomeromycetes, Paraglomus, Glomus and Acaulospora. The number of unique OTUs detected in the soil was lower than that in the roots. In both the root and soil samples, the forest type did not have a significant effect on AM fungal diversity, but the Sobs value and the Shannon, Chao1 and Ace indices of AM fungi in the roots were significantly higher than those in the soil.ConclusionsMixed forest management had little effect on the AM fungal community of Juglans mandshurica roots and significantly changed the community composition of the soil AM fungi, but not the diversity.

Diversity of arbuscular mycorrhizal (AM) fungi in mangroves of Chorao Island, Goa, India

For a desirable understanding of diversity and species composition of arbuscular mycorrhizal (AM) fungi, in true and associate mangrove plants, 17 true mangrove and their associate species belonging to ten families were assessed from Chorao Island, Goa, India. Maximum AM root colonization was recorded in Thespesia populnea and minimum in Avicennia marina. Rhizosphere soils of Ceriops tagal showed highest and that of Acrostichum aureum showed the least spore density. The results showed that the associate mangrove species were highly mycorrhizal compared to true mangrove plants. Our study recorded greater diversity involving thirty-two AM fungal species belonging to nine genera viz., Acaulospora, Claroideoglomus, Entrophospora, Funneliformis, Gigaspora, Glomus, Rhizophagus, Sclerocystis, and Scutellospora. Acaulospora was the dominant genus and A. dilatata was the dominant AM fungal species. Acaulospora dilatata was the most common AM species in both true and associate mangrove plants, revealing its wider adaptability.

Arbuscular mycorrhizal colonization outcompetes root hairs in maize under low phosphorus availability.

An increase in root hair length and density and the development of arbuscular mycorrhiza symbiosis are two alternative strategies of most plants to increase the root-soil surface area under phosphorus (P) deficiency. Across many plant species, root hair length and mycorrhization density are inversely correlated. Root architecture, rooting density and physiology also differ between species. This study aims to understand the relationship among root hairs, arbuscular mycorrhizal fungi (AMF) colonization, plant growth, P acquisition and mycorrhizal-specific Pi transporter gene expression in maize. Using nearly isogenic maize lines, the B73 wild type and the rth3 root hairless mutant, we quantified the effect of root hairs and AMF infection in a calcareous soil under P deficiency through a combined analysis of morphological, physiological and molecular factors. Wild-type root hairs extended the rhizosphere for acid phosphatase activity by 0.5 mm compared with the rth3 hairless mutant, as measured by in situ zymography. Total root length of the wild type was longer than that of rth3 under P deficiency. Higher AMF colonization and mycorrhiza-induced phosphate transporter gene expression were identified in the mutant under P deficiency, but plant growth and P acquisition were similar between mutant and the wild type. The mycorrhizal dependency of maize was 33 % higher than the root hair dependency. The results identified larger mycorrhizal dependency than root hair dependency under P deficiency in maize. Root hairs and AMF inoculation are two alternative ways to increase Pi acquisition under P deficiency, but these two strategies compete with each other.

Resolving the mycorrhizal status of important northern hemisphere trees

Knowledge about mycorrhizal associations is important for understanding mineral nutrition, stress tolerance and regeneration dynamics of trees. Here we address the mycorrhizal status of 940 species of important trees growing in ecosystems or cultivated in temperate regions of the Northern Hemisphere by resolving conflicting mycorrhizal trait information. Using 3800 observations from the FungalRoot database, we show that mycorrhizal status is highly consistent within species, genera and most families. Most contradictory mycorrhizal designations result from putative diagnosis errors, such as reported ectomycorrhizas EcM) in otherwise arbuscular mycorrhizal (AM) trees (10% of records). Furthermore, the most commonly studied species are more likely to have incorrect designations in databases due to accumulation of errors. Here we provide a definitive mycorrhizal status based on careful evaluation of records, with additional support from detailed anatomical observations and physiological data. We also identify common causes for errors, such as complex root anatomy in the Cupressaceae and Rosaceae. We also present detailed microscopic images of root structural features in trees with EcM or AM associations. Most AM roots have a suberised exodermis, which forms a permeability barrier around plant-fungus interfaces in the cortex and also protects roots from unwanted fungi. EcM short roots also have highly specialised anatomical features. Tree root atatomical features demonstrate convergent evolution that is presumably linked to more efficient and specific mycorrhiza formation. We recommend that future metastudies use corrected databases and new errors be avoided by using appropriate methodology and consistent definitions of association types.

Biochars produced from coconut palm biomass residues can aid regenerative agriculture by improving soil properties and plant yield in humid tropics

Lignin-rich recalcitrant biomass residues of coconut palms viz. (i) mature coconut husk, (ii) tender (immature or green) coconut husk (iii) coconut leaf petiole and (iv) coir-pith were successfully pyrolysed using a simple charring kiln into carbon-rich, black, light weight and porous biochars. High alkalinity and good ash content made them fit for remediating acid soils. High potassium content in these biochars could help reduce the use of inorganic K. Thermogravimetric analysis showed the mass loss phases of husk and coconut leaf petiole biochars to be similar. However, all four biochars gave smooth curves indicating thermal stability of the product. Positive seed germination and earthworm avoidance tests proved their potential as soil amendment. Soil incubation studies with coconut biochars in graded doses, alone or in combination with coconut leaf vermicompost, increased the pH, organic carbon and potassium contents, and promoted plant-beneficial microbiota and enzyme activities. Pot studies with tender coconut husk biochar and coconut leaf vermicompost enhanced the dry weight of cowpea plants accompanied with increased arbuscular mycorrhizal sporulation and root colonization, and root nodule dry weight. A field trial resulted in higher chilli yields with tender coconut husk biochar + coconut leaf vermicompost addition. The results from our studies highlight the potential of pyrolysis as an innovative technology for quick recycling of highly recalcitrant coconut palm biomass residues to biochars as a local source of soil amendment to aid regenerative agriculture in humid tropics.

Effects of Forest Composition and Disturbance on Arbuscular Mycorrhizae Spore Density, Arbuscular Mycorrhizae Root Colonization and Soil Carbon Stocks in a Dry Afromontane Forest in Northern Ethiopia

We investigated arbuscular mycorrhizal fungi (AMF) spore density and root colonization in three distinct dry Afromontane forest plant communities, representing differing levels of disturbance and soil properties. Soil and root samples were collected from sixty-five 50 × 50-m plots from four plant communities. We collected data for AMF spore density, AMF root colonization and soil organic carbon stocks in 0–25 and 25–50 cm soil depth ranges. AMF spore density, and root colonization differed significantly among plant communities. The least disturbed Juniperus procera–Maytenus senegalensis (Jupr-Mase) plant community, which contained high tree and shrub density, had the highest AMF spore density, root colonization and soil carbon stocks. The most disturbed Cadia purpurea–Opuntia ficus-indica (Capu-Opfi) community which contained the lowest tree and shrub density supported the lowest AMF spore density, root colonization and soil carbon stocks. There was no significant difference in spore density between the two soil depths, but AMF root colonization was significantly higher in the upper soil than in the subsoil (p &lt; 0.001). The difference in soil properties was not uniform between plant communities. Conserving remnant dry Afromontane forests and restoring the degraded forests are critical to improve and maintain forest ecosystem functioning and sustain ecosystem services.

Chemical identification of 18-hydroxycarlactonoic acid as an LjMAX1 product and in planta conversion of its methyl ester to canonical and non-canonical strigolactones in Lotus japonicus

Strigolactones (SLs) are a group of plant apocarotenoids that act as rhizosphere signaling molecules for both arbuscular mycorrhizal fungi and root parasitic plants. They also regulate plant architecture as phytohormones. The model legume Lotus japonicus (synonym of Lotus corniculatus) produces canonical 5-deoxystrigol (5DS) and non-canonical lotuslactone (LL). The biosynthesis pathways of the two SLs remain elusive. In this study, we characterized the L. japonicus MAX1 homolog, LjMAX1, found in the Lotus japonicus genome assembly build 2.5. The L. japonicus max1 LORE1 insertion mutant was deficient in 5DS and LL production. A recombinant LjMAX1 protein expressed in yeast microsomes converted carlactone (CL) to 18-hydroxycarlactonoic acid (18-OH-CLA) via carlactonoic acid (CLA). Identity of 18-OH-CLA was confirmed by comparison of the methyl ester derivative of the MAX1 product with chemically synthesized methyl 18-hydroycarlactonoate (18-OH-MeCLA) using LC-MS/MS. (11R)-CL was detected as an endogenous compound in the root of L. japonicus.13C-labeled CL, CLA, and 18-OH-MeCLA were converted to [13C]-5DS and LL in plant feeding experiments using L. japonicus WT. These results showed that LjMAX1 is the crucial enzyme in the biosynthesis of Lotus SLs and that 18-hydroxylated carlactonoates are possible precursors for SL biosynthesis in L. japonicus.