Ecology of endomycorrhizal association in black pepper (Piper nigrum L.), South India

de Azevedo M.M., de Oliveira J.S., Barata L.M., Monteiro G.G., Andrade E.E., Figueiredo P.L., Setzer W.N., da Silva J.K.

N S.T., Ray J.G.

Li S., Yang W., Hu J., Guo M., Li Y., Wang Y., Hu M., Zhang Y., Du D., Zhu X.

Arbuscular mycorrhizal fungi (AMF) play important roles in the dynamics of soil organic carbon (SOC), as they can promote its accumulation and the formation of soil aggregates, thereby increasing soil carbon storage. However, the impact of carbon input through AMF inoculation on SOC sequestration is still unclear. In this study, the effects of AMF on photosynthetic carbon transport and SOC accumulation in two types of black soils with either high or low SOC soils were analyzed by an outdoor pot experiment using isotope 13C labeling, thus, revealing the mechanism of action of AMF in stabilizing soil organic carbon fixation. The results showed that AMF symbiosis increased the allocation of photosynthetic carbon to the roots of the maize plant and soils. Inoculation with AMF also increased the proportions of soil macro-aggregates and the soil microbial biomass carbon content in low SOC soil, promoted the accumulation of soil aggregates, and enhanced the chemical composition of soil organic carbon. After returning the harvested labeled straw to the original pots the following year after planting, inoculation with AMF was found to increase the contents of hemicellulose and lignin at the time when maize kernels attained a plump appearance. AMF significantly increased glomalin-related soil protein in high SOC soil. In addition, AMF had a promoting effect on the decomposition of cellulose, hemicellulose, and lignin in the straw, which could subsequently increase the accumulation of carbon. We provide evidence for the promotion of soil aggregates, soil C accumulation, and SOC sequestration with AMF inoculation.

Li L., Shi Y., Xia W., Wang X., Xin Z., Liao Y., Sun X.

Soil amendments, including various types of fertilizers, are often used to control the uptake of heavy metals such as cadmium in cropping fields. The influence of these amendments on other members of the agroecosystem, such as arbuscular mycorrhizal fungi (AMF), remains less well investigated. Here, we established an experiment with the application of woody peat organic fertilizer and phosphate rock powder to examine its effects on AMF communities in two cadmium-contaminated vegetable crop fields (cucumber and pepper). We found that the application of phosphate rock powder enhanced soil phosphorus content, while the application of woody peat organic fertilizer enhanced soil nitrogen content, but neither influenced AMF abundance. We also found little influence of either amendment on measures of AMF diversity, except in one case where the Shannon index of diversity was lower in pepper fields amended with phosphate rock powder. We did, however, find significant shifts in the community composition and relative abundances of AMF taxa in the two vegetable fields, primarily as a result of shifts in the soil pH and nitrogen content.

Djotan A.K., Matsushita N., Fukuda K.

AbstractArbuscular mycorrhizal fungi (AMF) live in a community in the roots of host plants. Still, the patterns and factors that drive their spatiality and cohabitation remain uncovered, particularly that of trees in planted forests, which we aimed to clarify in Cryptomeria japonica, a major plantation tree in Japan. We analyzed 65 paired root and soil samples of Cryptomeria japonica trees collected from 11 microsite (MS) plots at two environmentally different forest sites in central Japan and measured soil pH, total phosphorus (TP), C, N, and the carbon-to-nitrogen ratio. Root AMF communities were recovered using Illumina’s next-generation amplicon sequencing targeting the small subunit of ribosomal DNA. We detected more than 500 AMF OTUs at each site but only three belonging to Dominikia, Rhizophagus, and Sclerocystis were dominant in the roots of C. japonica, detected each at an average relative abundance higher than 20%. Two showed negatively correlated spatial distributions and different associations with soil pH. Similarly, the physicochemical properties at MSs significantly determined the AMF assemblages in the roots of C. japonica. Dominikia, Rhizophagus, and Sclerocystis coexist in the roots of C. japonica where soil physicochemical properties, particularly pH, determine their spatial dynamic, turnovers, and cohabitation patterns. These findings highlight the importance of simultaneous colonization of plants by multiple AMF.

John S.A., Ray J.G.

Abstract Aims This study examined the diversity of arbuscular mycorrhizal fungi (AMF), mean spore density (MSD), and root colonization in relation to factors such as agroclimatic zones, rice varieties and soil types in paddy fields of South India. The aim was to understand how these factors influence AMF association in rice, facilitating their effective use as a biological tool in paddy cultivation. Methods and results AMF were identified through light microscopy of spores, while MSD and percentage-root-length colonization (PRLC) were measured using standard methods. Correlation and principal component analyses were performed to explore the interrelationships between AMF characteristics and various environmental, soil, and plant variables. Sixteen AMF species were identified across 29 rice varieties from three agroclimatic zones, 6 soil orders, and 18 soil series over 2 seasons. Notably, 70% of chemicalized rice fields lacked AMF spores, and only 50% exhibited root colonization. This study offers new insights into the role of AMF in rice cultivation. Conclusion The AMF diversity and root colonization in relation to environmental variables underscore their significant impact on AMF in particular crop fields.

Chien C., Tien S., Yang S., Lee C.

Abstract Background The symbiosis among plants, rhizobia, and arbuscular mycorrhizal fungi (AMF) is one of the most well-known symbiotic relationships in nature. However, it is still unclear how bilateral/tripartite symbiosis works under resource-limited conditions and the diverse genetic backgrounds of the host. Results Using a full factorial design, we manipulated mungbean accessions/subspecies, rhizobia, and AMF to test their effects on each other. Rhizobia functions as a typical facilitator by increasing plant nitrogen content, plant weight, chlorophyll content, and AMF colonization. In contrast, AMF resulted in a tradeoff in plants (reducing biomass for phosphorus acquisition) and behaved as a competitor in reducing rhizobia fitness (nodule weight). Plant genotype did not have a significant effect on AMF fitness, but different mungbean accessions had distinct rhizobia affinities. In contrast to previous studies, the positive relationship between plant and rhizobia fitness was attenuated in the presence of AMF, with wild mungbean being more responsive to the beneficial effect of rhizobia and attenuation by AMF. Conclusions We showed that this complex tripartite relationship does not unconditionally benefit all parties. Moreover, rhizobia species and host genetic background affect the symbiotic relationship significantly. This study provides a new opportunity to re-evaluate the relationships between legume plants and their symbiotic partners.

Varghese R., Ray J.G.

India, the center of origin and the country with the largest area of black pepper cultivation in the world has a low crop productivity in general. Furthermore, Kerala, the traditional black pepper region of India with the broadest crop area, is also one of the low crop productivity zones in the country. Therefore, a critical analysis of the cause of low black pepper productivity in Kerala was hypothesized to be crucial in analyzing the problems of pepper productivity globally. Accordingly, a random survey of the current diversity of the crop and the crop cultivated soil types of two different black pepper cultivation zones in the state was carried out. A critical analysis of the physicochemical soil parameters concerning natural variabilities such as agroclimatic zones, black pepper varieties, soil types, mode of cultivation, and black pepper-cultivated fields in two seasons was the crucial part of the study. The physicochemical soil parameters measured were field water content (FWC), soil pH, total organic carbon (TOC), soil available nitrogen (SAN), soil available phosphorous (SAP), and soil available potassium (SAK). The random survey revealed that 29 black pepper varieties are most intensively cultivated in the region over two main soil orders, Ultisols and Inceptisols, which included 13 soil series. The black pepper varieties commonly cultivated in the region are Karimunda (traditional cultivar) and Panniyur 1 (improved variety). The latter, the most widely cultivated variety in the region, showed the broadest amplitude to soil parameters such as FWC, TOC, SAN, SAP, and SAK. In general, most of the black pepper-growing fields of the region showed an acidic pH, high TOC, low SAN, high SAP, and moderate SAK with significant seasonal fluctuations. As a model study, it enabled us to trace the reasons for the low productivity of black pepper in Kerala. Overall, the study was fruitful in generating significant soil-related and other data concerning black pepper production, which will be beneficial to black pepper farming worldwide.

Lambais É.O., de Souza T.A., Késsia P., Nascimento G.D., Macedo R., de Bakker A.P., Lambais G.R., Dias B.O., da Silva Fraga V.

ABSTRACTThis study analyzed arbuscular mycorrhizal fungi (AMF) activity and soil chemical properties in Aspidosperma pyrifolium, Bauhinia ungulata, Caesalpinia pyramidalis, and Caesalpinia ferrea. AMF spores, root colonization, total glomalin‐related soil protein (T‐GRSP), easily extracted GRSP (EE‐GRSP), and soil chemical properties were measured four times (July 2019, 2020 and December 2019, 2020). Significant differences were observed in AMF spores, root colonization, T‐GRSP, and EE‐GRSP among the plant species and across seasons. For soil chemical properties, we observed differences among plant species. During the dry season, B. ungulata and C. pyramidalis had the highest AMF spores and root colonization (57.3 ± 0.27 spores 50 g soil−1 and 48.8 ± 1.05, respectively), whereas during the rainy season, C. pyramidalis and C. ferrea showed the highest AMF spores and root colonization (36.6 ± 0.13 spores 50 g soil−1 and 62.2 ± 1.17, respectively). A. pyrifolium showed the highest T‐GRSP in both seasons. On the basis of the soil chemical properties, we found that (i) A. pyrifolium, B. ungulata, and C. ferrea showed the highest soil organic carbon (1.32 ± 0.03 g kg−1), phosphorus (7.01 ± 0.26 mg kg−1), and soil pH (5.85 ± 0.23) and (ii) C. pyramidalis showed the highest Ca2+, Mg2+, Na+, H+ + Al3+, K+, and soil total nitrogen (1.36 ± 0.04, 0.73 ± 0.01, 3.72 ± 0.85, 4.56 ± 0.12 cmolc kg−1, 15.43 ± 1.53 mg kg−1, and 0.16 ± 0.01 g kg−1, respectively). Our results highlight the advantage of AMF spores as perennating structures over other AM fungal propagules in seasonal vegetation like Caatinga.

Albornoz F.E., Prober S.M., Bissett A., Tibbett M., Standish R.J.

Abstract Arbuscular mycorrhizal fungi (AMF) facilitate ecosystem functioning through provision of plant hosts with phosphorus (P), especially where soil P is limiting. Changes in soil nutrient regimes are expected to impact AMF, but the direction of the impact may depend on context. We predicted that nitrogen (N)‐only enrichment promotes plant invasions and exacerbates their P limitation, increasing the utility of AMF and promoting AMF diversity. We expected that enrichment with N, P and other nutrients similarly promotes plant invasions, but decreases the benefit and diversity of AMF because P is readily available for both native and exotic plants. We tested these hypotheses in eucalypt woodlands of south‐western Australia, that occur on soils naturally low in P. We evaluated AMF communities within three modified ground‐layer states representing different types of nutrient enrichment and associated plant invasions. We compared these modified states to near‐natural reference woodlands. AMF richness varied across ground‐layer states. The moderately invaded/N‐enriched state showed the highest AMF richness, while the highly invaded/NP‐enriched state showed the lowest AMF richness. The reference state and the weakly invaded/enriched state were intermediate. AMF richness and colonisation were higher in roots of exotic than native plant species. AMF community composition differed among ground‐layer states, with the highly invaded/NP‐enriched state being most distinct. Distinctions among states were often driven by family‐level patterns. Reference and moderately invaded/N‐enriched states each supported distinct groups of zero‐radius operational taxonomic units (zOTUs) in Acaulosporaceae, Gigasporaceae and Glomeraceae, whereas Gigasporaceae and Glomeraceae were nearly absent from the highly invaded/NP‐enriched state. Further, Diversisporaceae and Glomeraceae were most diverse in the moderately invaded/N‐enriched state. Synthesis. Both the nature of soil nutrient enrichment and plant provenance matter for AMF. N‐only enrichment of low‐P soils increased AMF richness, likely due to the introduction of AMF‐dependent exotic plant species and exacerbation of their P limitation. In contrast, multi‐nutrient enrichment, decreased AMF richness potentially due to a decrease in host dependence on AMF, regardless of host provenance. The changes in AMF community composition with nutrient enrichment and plant invasion warrant further research into predicting the functional implications of these changes.

Jafarian N., Mirzaei J., Omidipour R., Kooch Y.

Arbuscular mycorrhizal fungi (AMF) play a vital role in plant productivity and ecosystem functions. However, their responses to abiotic factors (i.e., climate, physiography, and soil properties) are unknown, especially across climatic gradients and slope aspects in arid and semi-arid ecosystems. In this study, using 60 composite soil samples, direct and indirect effects of climate factors and slope aspects on AMF diversity, composition and spore density were studied. The findings indicate that climate has a more direct influence on soil properties (P < 0.001) in comparison to slope aspect (P = 0.449). In contrast, climate significantly affected AMF diversity and composition, with the highest diversity in dryer areas. Soil pH had the highest correlation with different facets of AMF diversity. Structural equation modeling (SEM) indicated that only a small part of the variation in AMF diversity and spore density could be explained by climate characteristics, slope aspect and soil properties. Based on SEM results, climate was the most important determinant of AMF diversity and spore density; slope aspect had a less critical role. The outputs suggest that variations in AMF diversity are derived by the direct effects of climate and the indirect effect of soil chemical properties. In addition, with increasing dryness, sporulation and AMF diversity increased.

Ding Y., Gao X., Shu D., Siddique K.H., Song X., Wu P., Li C., Zhao X.

The synergy between bacteria and fungi is a key determinant of soil health and have a positive effect on plant development under drought conditions, with the potentially enhancing the sustainability of amending soil with natural materials. However, identifying how soil amendments influence plant growth is often difficult due to the complexity of microorganisms and their links with different soil amendment types and environmental factors. To address this, we conducted a field experiment to examine the impact of soil amendments (biochar, Bacillus mucilaginosus, Bacillus subtilis and super absorbent polymer) on plant growth. We also assessed variations in microbial community, links between fungi and bacteria, and soil available nutrients, while exploring how the synergistic effects between fungus and bacteria influenced the response of soil amendments to plant growth. This study revealed that soil amendments reduced soil bacterial diversity but increased the proportion of the family Enterobacteriaceae, Nitrosomonadaceae, and also increased soil fungal diversity and the proportion of the sum of the family Lasiosphaeriaceae, Chaetomiaceae, Pleosporaceae. Changes in soil microbial communities lead to increase the complexity of microbial co-occurrence networks. Furthermore, this heightened network complexity enhanced the synergy of soil bacteria and fungi, supporting bacterial functions related to soil nutrient cycling, such as metabolic functions and genetic, environmental, and cellular processes. Hence, the BC and BS had 3.0-fold and 0.5-fold greater root length densities than CK and apple tree shoot growth were increased by 62.14 %,50.53 % relative to CK, respectively. In sum, our results suggest that the synergistic effect of bacteria and fungi impacted apple tree growth indirectly by modulating soil nutrient cycling. These findings offer a new strategy for enhancing the quality of arable land in arid and semi-arid regions.

Shrestha S., Gautam T.P., Mandal T.N., Raut J.K., Goto B.T., Chaudhary S.

Arbuscular mycorrhizal fungi (AMF) are important ecosystem engineers that improve nutrient uptake and help plants adapt to a variety of abiotic stresses. Few studies have examined the relationship between AMF and a specific host tree along an elevation gradient. Shorea robusta is the dominant tree species in Nepal's tropical forests, with very high timber value. The goal of this study was to ascertain how edaphic factors and elevation gradient influence AMF colonization and spore density within the rhizosphere of Shorea robusta. The present study was conducted in four S. robusta dominated forests ranging from 82 m to 950 m asl. Among the four forests, Tarai Sal forest (TSF); Bhabar Sal forest (BSF) belonged to lower elevation Sal forest and Plateau Sal forest (PSF); Hill Sal forest (HSF) belonged to high elevation Sal forest. The percentage of AMF colonization and soil spore density were assessed by magnified intersect method and wet sieving and decanting method respectively. The edaphic factors viz. organic matter, nitrogen, phosphorous, potassium, pH, soil temperature, bulk density, moisture content, and water holding capacity of soil were determined by standard methods. Total AMF colonization ranged from 33% to 57%. Spore density, on the other hand, ranged from 25 to 366 per 100 g of soil. The maximum AMF root colonization and spore density for lower elevation Sal forest was 52% and 39/100 g of soil respectively while that for higher elevation Sal forest was 57% and 366/100 g of soil respectively. Pearson's correlation test revealed that total AMF colonization as well as spore density in the rhizosphere of S. robusta were affected by phosphorus content, pH, moisture content, water-holding capacity, soil temperature, and elevation. Moreover, the spore density was also affected by nitrogen content. Total AMF colonization and spore density were found to be highly correlated. Overall, the intensity of AMF colonization and spore density were higher in higher elevation Sal forest compared to the lower elevation Sal forest. This study can be used to gain insights into the active involvement of AMF in the sustainable management of the forest ecosystem.

Pang F., Li Q., Solanki M.K., Wang Z., Xing Y., Dong D.

Phosphorus (P) is an important nutrient for plants, and a lack of available P greatly limits plant growth and development. Phosphate-solubilizing microorganisms (PSMs) significantly enhance the ability of plants to absorb and utilize P, which is important for improving plant nutrient turnover and yield. This article summarizes and analyzes how PSMs promote the absorption and utilization of P nutrients by plants from four perspectives: the types and functions of PSMs, phosphate-solubilizing mechanisms, main functional genes, and the impact of complex inoculation of PSMs on plant P acquisition. This article reviews the physiological and molecular mechanisms of phosphorus solubilization and growth promotion by PSMs, with a focus on analyzing the impact of PSMs on soil microbial communities and its interaction with root exudates. In order to better understand the ability of PSMs and their role in soil P transformation and to provide prospects for research on PSMs promoting plant P absorption. PSMs mainly activate insoluble P through the secretion of organic acids, phosphatase production, and mycorrhizal symbiosis, mycorrhizal symbiosis indirectly activates P via carbon exchange. PSMs can secrete organic acids and produce phosphatase, which plays a crucial role in soil P cycling, and related genes are involved in regulating the P-solubilization ability. This article reviews the mechanisms by which microorganisms promote plant uptake of soil P, which is of great significance for a deeper understanding of PSM-mediated soil P cycling, plant P uptake and utilization, and for improving the efficiency of P utilization in agriculture.

Burak K., Yanardağ İ.H., Gómez-López M.D., Faz Á., Yalçin H., Sakin E., Ramazanoğlu E., Orak A.B., Yanardağ A.

Due to soils from arid regions with high lime and low organic matter content, farmers receive low yields along with high costs of agricultural inputs, which causes them to look for a solution. In this context, Arbuscular mycorrhizal fungi (AMF) have great potential to reduce fertilizer use by mediating soil nutrient cycles. However, little is known about studies of AMF inoculum on microbial biomass carbon (C), nitrogen (N), and phosphorus (P) cycling during vetch plant vegetation in calcareous areas. In this study, changes in soil biogeochemical properties related to soil C, N, and P cycling were investigated with five different AMF inoculations under vetch (common Vetch (CV; Vicia sativa L.) and Narbonne Vetch (NV; Vicia narbonensis L.) growing conditions. For the field study, a total of five different mycorrhizae were used in the experiment with the random plots design. AMF inoculation decreased the lime content of the soil, and the highest decrease was observed in NV with Glomus (G.) intraradices + G. constrictum + G. microcarpum inoculation (24.41 %). The highest MBC content was recorded in CV vetch G. intraradices (1176.3 mg C kg−1) and the highest MBN content in NV vetch G. intraradices + G. constrictum + G. microcarpum (1356.9 mg C kg−1). CAT activity of soils was highest in CV vetch G. intraradices (31.43 %) and lowest in NV vetch G. intraradices + G. constrictum + G. microcarpum (72.88 %), urease enzyme activity decreased in all treatments except G. constrictum + Gigaspora sp. and G. mosseae inoculations in CV. The highest DHG activity was detected in GF (15.72 %) AMFs in CV and GI (21.99 %) in NV. APA activity was highest in Glomus constrictum + Gigaspora sp. (23.33 %) in CV and Glomus fasciculatum (10.08 %) in NV. In CV plots, G. intraradices + G. constrictum + G. microcarpum (91.67 %) isolates had the highest and G. intraradices community had the lowest RC% (97.33 %) in mixed mycorrhiza species, while in NV plots G. fasciculatum inoculum had the highest and G. intraradices community had the lowest RC%. This study has important implications for the application of AMF for sustainable agriculture. When the results of the study were evaluated, the most effective AMF isolates in terms of C, N, and P cycles were G. constrictum + G. fasciculatum + Gigaspora sp. in Common vetch variety, and G. intraradices in Narbonne vetch variety.