International Journal of Farming and Allied Sciences Available online at www.ijfas.com © IJFAS Journal- - - / - / January, ISSN - © IJFAS Arbuscular Mycorrhizal fungi community, nutrient availability and glomalin in organic farming

Jasem aminifar * and Alireza sirousmehr

- PhD student of agronomy faculty of agronomy and plant breeding, University of Zabol, Iran

- Assistant professor, faculty of agronomy and plant breeding, University of Zabol, Iran

Corresponding author: Jasem aminifar

ABSTRACT: Organic agriculture promotes the use of agronomic practices and alternative technologies in accordance with the socioeconomic and ecological conditions, which is usually carried out by applying organic materials. Soil microbial communities have been considered a vital factor for the functioning of agroecosystems and success in organic farming. Among the soil microbial communities, Arbuscular mycorrhizal fungi (AMF) is key component of the soil microbiota, fundamental for soil fertility, plant nutrition and functioning of agroecosystems. Have been mentioned that, organic farmers manage for high (SOM). Furthermore, use of chemical materials, which can negatively impact soil biota, is also prohibited. As a consequence, soil microbial communities such as AMF are often higher in organic farming systems than conventional ones. Increasing in soil content of Arbuscular mycorrhizal fungi will be improve the efficiency of nutrient uptake, such as immobile phosphate ions. Which it seems that this improvement in nutrient availability could be important, especially in low nutrient status . Whereas glomalin is produced by Arbuscular mycorrhizal fungi, so it seems that with Increasing in Arbuscular mycorrhizal fungi content and activity, the concnetraion of glomalin in soil increace as well. As a consequence, high levels of glomalin result in better soil aggregate formation, which is important for and stability. In general, it seems that agricultural practices (organic farming in comparison with conventional farming) significantly can affect the Arbuscular mycorrhizal fungi communities and follow that the other agents which are in associated with AMF is affected as well.

Keywords: Arbuscular Mycorrhizal, glomalin, nutrient availability, organic farming

INTRODUCTION

Organic agriculture promotes the use of agronomic practices and alternative technologies in accordance with the socioeconomic and ecological conditions of the zone where the productive system is located, in particular as it refers to fertilization, which is usually carried out by applying organic materials such as manure, plant residues, or compost, much of which are produced inside the same farm (Shannon et al., ). Organic farming systems (OFSs) in comparison with conventional farming systems (CFSs), OFSs promote soil structure formation (Wright et al., ), enhance soil biodiversity (Mäder et al., ), and alleviate environmental stress (Altieri, ), because organic farming avoids synthetic chemical amendments and supplies organic fertilizer. Ecological processes provide key services for agriculture. Organically managed agroecosystems offer a unique context in which to study the ecological relationships between and biogeochemistry (Cavagnaro et al., ). Soil microbial communities are considered a vital factor for the functioning of agroecosystems and success in organic farming (Gosling et al., ). Arbuscular (AM) is the mutualistic symbiosis that exists between plant and fungi belonging to phylum Glomeromycota (Schuessler et al., ). AM fungi (AMF) are obligate symbionts, which form a symbiotic association with over of the terrestrial plants (Lee and Eom, ). AMF Intl J Farm & Alli Sci. Vol., ( ): - ,

are important for plant physiology, plant health, nutrient cycling, and soil aggregation, particularly for low input, sustainable agriculture systems (Bethlenfalvay and Barea, ). The role of AM fungi in plant growth and nutrition, and as potential drivers of biodiversity and regulatory processes in soil is not well understood. Direct and indirect effects on the soil biota may include altered plant exudation (Dixon et al., ), provisioning of high quality resources (hyphae and/or lipid rich spores) for soil grazers (Bakhtiar et al., ; Gange, ), localized changes in pH (Villegas and Fortin, ), and competition with other soil biota for soil resources (e.g., nutrients, water and space) (Tibbett, ). In addition, AMF provides enhanced drought resistance (Auge et al., ), improved resistance to foliar-feeding insects (Gange and West, ), increased tolerance to heavy metals and soil salts (Feng et al., ; Khan et al., ), and improved protection from soil pathogens (Smith and Read, ). Such effects may help explain reported effects of AM fungi on rhizosphere bacterial community composition (Marschner et al., ), and the wider soil community (Bakhtiar et al., ; Gange, ). AMF are strongly affected by anthropogenic activities (Giovannetti and Gianinazzi-Pearson, ), and intensive agricultural practices, such as crop rotation fertilization pest control and tillage impact AMF, reducing population biodiversity (Daniell et al., ). Organic agriculture has been shown to increase AMF colonization and propagule numbers (Galvez et al., ; Oehl et al., ), although low input practices used in such management system do not always allow the level of biodiversity to increase, even after a long time (Franke-Snyder et al., ). Hence, understanding the structure and the dynamics of AMF populations as affected by diverse agricultural practices represents an important prerequisite for the success of organic farming.

Arbuscular Mycorrhizal fungi communities Modern agricultural practices such as fertilization, biocide application, and monoculture affect the community composition and diversity of AM fungi (Oehl et al., ). In general, these agricultural practices have negative impacts on AM association. Soils in the conventional agricultural system are AM fungi-impoverished, particularly with regards to numbers of species (Eom et al., ). Management practices typical of conventional high input systems, particularly P fertilizer application and the use of biocides, are known to be deleterious to AM fungal symbiosis (Miller and Jackson, ; Thingstrup et al., ). Low-input organic farming systems have increasingly garnered interest due to their focus on natural resource conservation and reduction of environmental degradation. The general principals of organic farming include: ( ) exclusion of synthetic biocides; ( ) addition of organic fertilizers to the soil, including farmyard manure, compost and crop residue, and slow release mineral fertilizers such as rock phosphate; and ( ) use of crop rotation (IFOAM, ). Organic fertilizers do not appear to suppress AM fungi and may even stimulate them (Joner, ; Miller and Jackson, ). Additionally, although the effect of biocides on AM symbiosis is complex and not easily predictable, overuse of most biocides reduces AM fungi colonization rates and spore production (Schreiner and Bethlenfalvay, ). Organic farming relies heavily on active soil microbial communities and AM fungi play an important role in agroecosystem function. It has been reported that compared to conventional systems organic farming increases AM colonization, propagule numbers, and species diversity (Oehl et al., ; Ryan et al., ); however, the actual importance of AM symbiosis to particular crop species in organic farming remains to be determined. It is also well-known that different species of AM fungi have varying effects on plant growth, and high input conventional farming may select particular AM fungal species (Van der Heijden et al., ). In order to study different agricultural management practices such as conventional (CON), no-chemical (NOC), and organic farming systems (ORG) on arbuscular mycorrhizal (AM) symbiosis an experiment have been conducted on red pepper. The results have showed that the ORG inoculum significantly increased plant growth compared to inoculum from CON and NOC. A community analysis of AM fungi (AMF) using morphological features of spores revealed that AMF spore abundance and species diversity were significantly higher in ORG than in CON. Additionally, a community analysis of AMF colonizing roots using a molecular technique revealed higher AMF diversity in ORG than in CON. These results suggested that agricultural practices significantly influence AM fungal community structure and mycorrhizal inoculum potential (Lee et al., ). Have been reported that there was only slight differences in AM fungal populations between conventional and organic farming systems a few year after conversion ( years) (Bedini et al., ). while other authors have found an increase of AM fungal inoculum in organic farmed soils (Bending et al., ). It seems that for significant differences in content of AMF between conventional and organic farming systems more time is needed.

Nutrient availability Microbial processes are crucial for nutrient availability because only organic sources of nutrients can be used (USDA National Organic Program Standards). Organic farmers manage for high soil organic matter (SOM) and net N mineralization rates. Furthermore, use of synthetic pesticides, which can negatively impact soil biota (Miller and

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Jackson, ; Sukarno et al., ), is also prohibited (USDA National Organic Program Standards). As a consequence, microbial activity is often higher in organic than conventionally-managed soils (Carpenter-Boggs et al., ; Lundquist et al., ), community composition can be more complex (Mader et al., ), and in some instances, invertebrate density and biodiversity increases (Hole et al., ). Abundance of arbuscular mycorrhizal (AM) fungi may also increase under organic management (Mader et al., ). The fungal hyphae spread into the soil from host plant roots and improve the efficiency of nutrient uptake, such as immobile phosphate ions, as the fungal extra radical mycelium develop over the phosphate depletion zone that rapidly grows around the root of the plant (Smith and Read, ). AM fungi effectively increase the absorptive surface of the plant root system thereby providing access to soil-derived nutrients from sources not necessarily otherwise accessible to roots (Smith and Read, ). Although usually considered important primarily for P uptake, AM fungi can also increase both NH + and NO - uptake (Frey and Schüepp, ), and that of other nutrients including Zn, Cu, and K (Marschner and Dell, ). Such improvements in plant nutrition are of particular significance in soils of low nutrient status (Hetrick, ; Menge, ) and heterogeneous nutrient distribution (Cavagnaro et al., ; Tibbett, ), but may also be important for soils receiving frequent organic matter inputs as the primary source of nutrients, and those for which a complex soil food web regulates nutrient availability (de Deyn et al., ), such as organic farming systems.

Glomalin in soil AMF hyphae abundantly produce glomalin (Rillig, ), which is a brown to reddish-brown glycoprotein (Rilling et al., ). Glomalin is a major component of organic matter in soil and contributes to better soil aggregate formation, which is important for soil structure and stability against erosion (Wright et al., ; Wright and Upadhyaya, ). Glomalin, due to its recalcitrance, hydrophobicity, and adhesiveness play an important role as cementing material of the soil particles, at the same time acting as a highly stable form of organic C storage that could represent an important fraction of the total organic matter of the soil (Morales et al., ; Rillig and Mummey, ; Cornejo et al., a). As the hyphae senesce, glomalin is deposited within the soil, where it accumulates until it represents as much as of soil C (Rillig et al., , ) and N (Lovelock et al., ). Even though this compound could constitute an important global reservoir of C and N, environmental controls on glomalin are not well understood. In addition, the ecophysiological function of glomalin if any remains unknown, although (Gadkar and Rillig , ) have found evidence that glomalin may be related somewhat to a heat shock protein. Standing stocks of glomalin in soil are determined by its production and decomposition, and environmental conditions could affect the two fluxes independently (Rillig, ). Namely, glomalin production should be controlled directly by the abundance and community composition of AM fungi. In addition, standing root length, host plant availability, and plant nutrient balance might indirectly affect glomalin production by altering the allocation of photosynthesis to AM fungi. These plant characteristics are, in turn, partially influenced by the availability of + − − inorganic resources such as CO , NH , NO , PO , and water. Glomalin decomposition, on the other hand, might be altered by soil characteristics such as nutrient availability (which could influence microbial activity) and clay content (which could provide physical protection) (Nichols and Wright, ). Since AM fungi produce glomalin, soil stocks of glomalin may be indirectly influenced by actors that control AM growth. Globally, AM fungi are most abundant where standing lengths of fine roots and host plant availability are greatest (Treseder and Cross, ). This pattern is consistent with the notion that photosynthetic rates should determine absolute amounts of C available for AM fungi (Johnson et al., ). Plants often allocate more C to their AM symbionts when plant growth is limited by soil nutrients (Treseder, ). For example, N and P fertilization often reduces AM growth (Treseder, ) because nutrient limitation is alleviated. Land use change is one of the fastest and most widespread components of global change, and it can influence the prevalence of AM fungi. Tillage physically disrupts hyphal networks, so that conversion from conventional tillage to no-till practices often elicits an increase in standing crops of AM fungi (Kabir et al., ; Mader et al., ; McGonigle et al., ). Have been reported that globally, glomalin stocks were positively correlated with net primary productivity (NPP) but not with AM abundance. Rates of NPP may impose an upper bound for C available to AM fungi for glomalin construction (Treseder and Turner, ). The increase of glomalin levels is usually related to greater AMF activity in systems with organic substances (Oehl et al., ), or adding organic nutrient sources, such as cattle manure, compost, and crop stubble, which significantly stimulate mycorrhizal development (Douds et al., ; Joner, ). Results of Valarini et al ( ) have also showed that, in general, compost application increased soil pH, mycorrizal roots, mycelium length, glomalin levels, and water stable aggregates. (Lee and Yun , ) have also reported that the average concentrations of glomalin in the organic farming system was significantly higher than that in the conventional farming system.( Lee and Eom , ) in order to study effect of organic farming on spore diversity of Arbuscular

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Mycorrhizal fungi and glomalin in soil, eight soil samples have collected from organic and conventional farms in a central area of South Korea. They have reported that glomalin content was greater in organic farming soils than in conventional farming soils. These results suggest that agricultural practices significantly influence AM fungal community structure and glomalin contents, and that organic farming increases AMF species diversity. The use of environmentally friendly agricultural practices has been recognized as an important method of sustainable agriculture. Therefore, studies on AMF and agricultural practices are critical.

CONCLUSION

Interest in environmental conservation and food safety has recently increased and environmentally friendly agricultural practices have been recognized as an important farming system that could possibly solve the problem of environmental conservation and food safety by reducing the use of synthetic biocides and mineral fertilizers. The number of environmentally friendly agricultural products has increased rapidly. Losses in the diversity of organisms have been reported globally, including microorganisms in agroecosystems. Because of low diversity might relate to the loss of a functional role in the ecosystem and low ability to adapt to environmental changes, so agricultural practices should be maintained at minimum levels (Lee et al., ). The results clearly indicate that agricultural practices severely affect AMF abundance and community structure. Remarkably, the AMF communities differed not only in diversity but also in functional aspects (concentrations of glomalin) (Lee and Eom, ). The use of environmentally friendly agricultural practices has been recognized as an important method of sustainable agriculture. Therefore, studies on AMF and agricultural practices are critical (Lee and Eom, ). Also, have been reported that AMF played an important role in plant nutrition at organic farm, so that there were large positive effects of colonization of roots by AM fungi on plant nutrient contents (Cavagnaro et al., ). These findings suggest that agricultural practices should be converted from high-input agricultural systems into more sustainable organic agricultural systems (Lee and Eom, ).

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