丛枝菌根真菌提高盐胁迫植物抗氧化机制的研究进展

土地盐渍化是在自然环境和人为活动的双重作用下形成的全球性的重要生态问题,其会对植物造成渗透失衡、离子胁迫、氧化损伤等危害,导致植物生长缓慢、生物量减少甚至是绝产。丛枝菌根真菌(AMF)是一种普遍存在于土壤中的有益微生物,能够与大多数植物根系形成共生关系,其共生关系在多种逆境生态系统中均具有重要生态意义。AMF-植物共生体具有高效抗氧化系统,能够提高植物在盐胁迫下的抗氧化反应进而增强耐盐性。本文从氧化损伤、渗透调节、抗氧化机制和生物活性分子等角度,系统地阐述了丛枝菌根真菌提高植物抗氧化机制的研究进展,并提出了研究展望,以期为利用菌根生物技术提高植物耐盐性提供理论参考。     

Mycorrhiza‐mediated interference between cover crop and weed in organic winter cereal agroecosystems: The mycorrhizal colonization intensity indicator

The mycorrhizal fungi are symbiotic organisms able to provide many benefits to crop production by supplying a set of ecosystem functions. A recent ecological approach based on the ability of the fungi community to influence plant–plant interactions by extraradical mycelium development may be applied to diversified, herbaceous agroecosystems. Our hypothesis is that the introduction of a winter cereal cover crop (CC) as arbuscular mycorrhizal fungi (AMF)–host plant in an organic rotation can boosts the AMF colonization of the other plants, influencing crop–weed interference. In a 4‐years organic rotation, the effect of two winter cereal CC, rye and spelt, on weed density and AMF colonization was evaluated. The AMF extraradical mycelium on CC and weeds roots was observed by scanning electron microscopy analysis. By joining data of plant density and mycorrhization, we built the mycorrhizal colonization intensity of the Agroecosystem indicator (MA%). Both the CC were colonized by soil AMF, being the mycorrhizal colonization intensity (M%) affected by environmental conditions. Under CC, the weed density was reduced, due to the increase of the reciprocal competition in favor of CC, which benefited from mycorrhizal colonization and promoted the development of AMF extraradical mycelium. Even though non‐host plants, some weed species showed an increased mycorrhizal colonization in presence of CC respect to the control. Under intense rainfall, the MA% was less sensitive to the CC introduction. On the opposite, under highly competitive conditions, both the CC boosted significantly the mycorrhization of coexistent plants in the agroecosystem. The proposed indicator measured the agroecological service provided by the considered CCs in promoting or inhibiting the overall AMF colonization of the studied agroecosystems, as affected by weed selection and growth: It informs about agroecosystem resilience and may be profitably applied to indicate the extent of the linkage of specific crop traits to agroecosystem services, contributing to further develop the functional biodiversity theory.     

Diversity of arbuscular mycorrhizal fungi in Brazil's Caatinga and experimental agroecosystems

Cowpea (Vigna unguiculata) is a nutritious legume crop for both its grain and leaves and comprises an important component in both human and animal nutrition. In Brazil, the use of mulch, such as coconut fiber, and organic fertilizers to maximize cowpea production offers an alternative to conventional mineral fertilizer strategies. Farming practices affect the diversity and activity of soil microorganisms, including arbuscular mycorrhizal fungi (AMF), important plant growth promoters for legumes. Our objective was to determine the effect of mulching with coconut fiber and manure on AMF diversity in cowpea. Soil samples were collected from an Experimental Station in Petrolina, NE Brazil: one Caatinga (natural dry‐forest vegetation), one fallow, and one experimental site established in the fallow area and cultivated with cowpea receiving cattle manure and four doses (0, 12, 24, 48 t/ha) of coconut fiber. AMF species richness, abundance, and diversity were evaluated. Sixty‐four AMF species were recorded, with predominance of Glomeraceae and Acaulosporaceae. Highest species richness (47) was recovered from the Caatinga but AMF diversity was also high in the cultivated sites, demonstrating the importance of mycotrophic plants, such as cowpea, in crop production systems for the maintenance of AMF species richness. Although several species, such as Claroideoglomus etunicatum, Acaulospora scrobiculata, Glomus trufemii, and Paraglomus pernambucanum, revealed pronounced sporulation patterns, even high doses of coconut fiber did not affect AMF richness and diversity, compared to fallow. Consequently, cultivation of mycotrophic plants and use of organic manures are able to maintain high AMF species richness in tropical agroecosystems.     

Interrelated effects of mycorrhiza and free‐living nitrogen fixers cascade up to aboveground herbivores

Aboveground plant performance is strongly influenced by belowground microorganisms, some of which are pathogenic and have negative effects, while others, such as nitrogen‐fixing bacteria and arbuscular mycorrhizal fungi, usually have positive effects. Recent research revealed that belowground interactions between plants and functionally distinct groups of microorganisms cascade up to aboveground plant associates such as herbivores and their natural enemies. However, while functionally distinct belowground microorganisms commonly co‐occur in the rhizosphere, their combined effects, and relative contributions, respectively, on performance of aboveground plant‐associated organisms are virtually unexplored. Here, we scrutinized and disentangled the effects of free‐living nitrogen‐fixing (diazotrophic) bacteria Azotobacter chroococcum (DB) and arbuscular mycorrhizal fungi Glomus mosseae (AMF) on host plant choice and reproduction of the herbivorous two‐spotted spider mite Tetranychus urticae on common bean plants Phaseolus vulgaris. Additionally, we assessed plant growth, and AMF and DB occurrence and density as affected by each other. Both AMF alone and DB alone increased spider mite reproduction to similar levels, as compared to the control, and exerted additive effects under co‐occurrence. These effects were similarly apparent in host plant choice, that is, the mites preferred leaves from plants with both AMF and DB to plants with AMF or DB to plants grown without AMF and DB. DB, which also act as AMF helper bacteria, enhanced root colonization by AMF, whereas AMF did not affect DB abundance. AMF but not DB increased growth of reproductive plant tissue and seed production, respectively. Both AMF and DB increased the biomass of vegetative aboveground plant tissue. Our study breaks new ground in multitrophic belowground–aboveground research by providing first insights into the fitness implications of plant‐mediated interactions between interrelated belowground fungi–bacteria and aboveground herbivores.     

The role of community and population ecology in applying mycorrhizal fungi for improved food security

The global human population is expected to reach ∼9 billion by 2050. Feeding this many people represents a major challenge requiring global crop yield increases of up to 100%. Microbial symbionts of plants such as arbuscular mycorrhizal fungi (AMF) represent a huge, but unrealized resource for improving yields of globally important crops, especially in the tropics. We argue that the application of AMF in agriculture is too simplistic and ignores basic ecological principals. To achieve this challenge, a community and population ecology approach can contribute greatly. First, ecologists could significantly improve our understanding of the determinants of the survival of introduced AMF, the role of adaptability and intraspecific diversity of AMF and whether inoculation has a direct or indirect effect on plant production. Second, we call for extensive metagenomics as well as population genomics studies that are crucial to assess the environmental impact that introduction of non-local AMF may have on native AMF communities and populations. Finally, we plead for an ecologically sound use of AMF in efforts to increase food security at a global scale in a sustainable manner.     

Mycorrhiza and Phosphate Solubilizing Bacteria: Potential Bioagents for Sustainable Phosphorus Management in Agriculture

Phosphorus (P) is a critical nutrient that plays an essential role in improving soil fertility for optimum plant growth and productivity. It is one of the most deficient macro-nutrients in agricultural soils after nitrogen and is considered inadequate for plant growth and production. To P availability in soils, the farmers are applying huge amounts of synthetic P fertilizers that adversely affect the wider environment, groundwater, soil fertility and microbial population. Many beneficial microbes are known to release and supply soluble P for improving growth and yield of a variety of plants in a sustainable manner in P deficient soils. Thus, inoculation of these microbes, including arbuscular mycorrhizal fungi (AMF) and phosphate solubilizing bacteria (PSB) to soil to enhance crop production without harming the environment, is an alternative approach to chemical fertilizers. The combined role of AMF and PSB in P solubilization is not well understood and the application and mode of action of these microbial groups are often naive due to variation in the environment. Therefore, the current review article would develop a better understanding of the interactive role and mechanisms of AMF and PSB in improving P availability from both organic and inorganic sources in a sustainable crop production system. Finally, the current review would loop out further avenues for researchers interested to commercially produce effective AMF and PSB-based biofertilizers for sustainable management of phosphorus over a wide range of agricultural crops worldwide.     

Current developments in arbuscular mycorrhizal fungi research and its role in salinity stress alleviation: a biotechnological perspective

Arbuscular mycorrhizal fungi (AMF) form widespread symbiotic associations with 80% of known land plants. They play a major role in plant nutrition, growth, water absorption, nutrient cycling and protection from pathogens, and as a result, contribute to ecosystem processes. Salinity stress conditions undoubtedly limit plant productivity and, therefore, the role of AMF as a biological tool for improving plant salt stress tolerance, is gaining economic importance worldwide. However, this approach requires a better understanding of how plants and AMF intimately interact with each other in saline environments and how this interaction leads to physiological changes in plants. This knowledge is important to develop sustainable strategies for successful utilization of AMF to improve plant health under a variety of stress conditions. Recent advances in the field of molecular biology, “omics” technology and advanced microscopy can provide new insight about these mechanisms of interaction between AMF and plants, as well as other microbes. This review mainly discusses the effect of salinity on AMF and plants, and role of AMF in alleviation of salinity stress including insight on methods for AMF identification. The focus remains on latest advancements in mycorrhizal research that can potentially offer an integrative understanding of the role of AMF in salinity tolerance and sustainable crop production.     

Arbuscular mycorrhizal fungi reduce the construction of extrafloral nectaries in <Emphasis Type="Italic">Vicia faba</Emphasis>

Arbuscular mycorrhizal fungi (AMF) can alter the physiology and morphology of their host plant, and therefore may have indirect effects on insect herbivores and pollinators. We conducted this study to test the hypothesis that AMF can also affect insects involved in protection-for-food mutualisms. We examined the constitutive and inducible production of food rewards [extrafloral (EF) nectaries] in Vicia faba plants by manipulating the presence/absence of AMF and by simulating various levels of herbivory. Plants inoculated with AMF produced significantly fewer EF nectaries than uninoculated plants, even after accounting for differences in plant growth. In contrast to earlier studies, EF nectaries were not inducible: damaged plants produced significantly fewer EF nectaries than undamaged plants. Moreover, the effects of mycorrhizal and damage status on EF nectary production were additive. The reduction in EF nectaries in mycorrhizal plants potentially represents a mechanism for indirect effects of AMF on the protective insects that exploit EF nectaries as a food source (e.g., ants). Reduced reward size should result in reduced protection by ants, and could therefore be a previously unappreciated cost of the mycorrhizal symbiosis to host plants. However, the overall effect of AMF will depend upon the extent to which the reduction of EF nectaries affects the number and activity of ants and the extent to which AMF alter other aspects of host plant physiology. Our results emphasize the complexity of multitrophic interactions, particularly those that span belowground and aboveground ecology.     

陆地农业生态系统丛枝菌根真菌物种多样性研究进展

丛枝菌根真菌(AMF)是一种古老的、在自然界中普遍存在的土壤微生物,能与大部分陆生植物形成互惠互利的菌根共生体.在这种共生关系中,AMF从植物获取自身生长所需碳源的同时,帮助宿主吸收氮、磷等营养物质.AMF在农业生态系统中具有重要作用,能够促进植物生长、改善作物品质、提高植物抗逆性、稳定土壤结构、维护生态平衡和维持农业可持续发展.本文总结了近几年来陆地农业生态系统AMF的研究进展,着重从我国陆地农业生态系统AMF物种多样性、AMF生物多样性时空分布特征及影响AMF多样性的因素等几个方面,综述了陆地农业生态系统AMF的物种多样性,并对以后的研究进行了展望.     

Differential strategies of two species of arbuscular mycorrhizal fungi in the protection of maize plants grown in chromium-contaminated soils

Chromium (Cr) is a nonessential element for plants that is extremely toxic at high concentrations. Zea mays L. is a species of plant that has developed adaptive mechanisms to increase its tolerance and absorption capacity for this metal. One effective mechanism is to form associations with arbuscular mycorrhizal fungi (AMF), which help the plant cope with stress from heavy metals such as Cr. However, it is still not clear which species of AMF are more efficient as bioremediating agents for plants of agricultural importance. Here, we evaluated the effect of Gigaspora gigantea and Rhizophagus irregularis as protective agents of maize plants in soils contaminated with Cr at concentrations of 0, 48.5, 97 and 194 mg kg^?1 under greenhouse conditions. Maize tolerance to Cr was corroborated, as well as increased absorption of this element by plants associated with both species of AMF. G. gigantea caused an increase in nitrogen content and greater translocation of Cr to the aerial part of the plant; R. irregularis registered an increase in the formation of arbuscules and vesicles with increasing metal concentration and greater retention of Cr in the roots of the plants. Based on these results, we can conclude that the analyzed species of fungi use different strategies, with similar effectiveness, to enhance the absorption capacity of Cr by the plant and influence the differential deposition of this metal in various parts of the plant.

     

Bacillus amyloliquefaciens GA1 as a source of potent antibiotics and other secondary metabolites for biocontrol of plant pathogens

Background  

Phytopathogenic fungi affecting crop and post-harvested vegetables are a major threat to food production and food storage. To face these drawbacks, producers have become increasingly dependent on agrochemicals. However, intensive use of these compounds has led to the emergence of pathogen resistance and severe negative environmental impacts. There are also a number of plant diseases for which chemical solutions are ineffective or non-existent as well as an increasing demand by consumers for pesticide-free food. Thus, biological control through the use of natural antagonistic microorganisms has emerged as a promising alternative to chemical pesticides for more rational and safe crop management.     

The Effect of Stereochemistry on the Biological Activity of Natural Phytotoxins,Fungicides, Insecticides and Herbicides

Phytotoxins are secondary microbial metabolites that play an essential role in the development of disease symptoms induced by fungi on host plants. Although phytotoxins can cause extensive—and in some cases devastating—damage to agricultural crops, they can also represent an important tool to develop natural herbicides when produced by fungi and plants to inhibit the growth and spread of weeds. An alternative strategy to biologically control parasitic plants is based on the use of plant and fungal metabolites, which stimulate seed germination in the absence of the host plant. Nontoxigenic fungi also produce bioactive metabolites with potential fungicide and insecticide activity, and could be applied for crop protection. All these metabolites represent important tools to develop eco‐friendly pesticides. This review deals with the relationships between the biological activity of some phytotoxins, seed germination stimulants, fungicides and insecticides, and their stereochemistry. Chirality 25:59–78, 2013. © 2012 Wiley Periodicals, Inc.     

Arbuscular Mycorrhizal Fungi as Components of Sustainable Soil-Plant Systems

Abstract

Increased pressure for food production has, in recent years, led to the development of intensive agricultural systems that use significant quantities of inorganic fertilizers and pesticides. However, there is now substantial evidence for the environmental costs of this high-input strategy and this has led to demands for agricultural systems to be modified in order to make them more sustainable. Arbuscular mycorrhizal fungi (AMF) play a key role in natural and agricultural ecosystems through major functions in the enhancement of plant phosphorus and nitrogen nutrition, nutrient and soil conservation, and the biological control of plant pathogens. They are essential to the sustainability of systems and their importance in agricultural ecosystems is likely to increase as inputs are reduced and/or rationalized. In order to maximize their benefits it is essential to ensure that management practices include minimum tillage, reduced use of inappropriate fertilizer, appropriate crop rotations with minimal fallow, and rationalized pesticide use. Furthermore, crop breeders should take full account of the symbiosis in selection. Future research should be targeted to understanding the functional ecology of AMF in agroecosystems.     

微藻源生物刺激剂的制备及在设施农业中的应用

化肥和农药的过量使用导致的农业面源污染已经成为我国环境污染的重要组成部分,对农业绿色高效安全生产及设施农业带来了巨大挑战。寻找新型的传统化肥替代品、提高化肥使用效率及保护生态环境是亟待解决的重大问题。生物刺激剂是具有调控植物生长作用的成分和(或)微生物的统称,用于农业生产,可改善土壤理化性质与群落微生物,能促进作物的代谢与生长,增强对营养物质的吸收和利用,提升作物抗逆能力及提高作物产量与产品品质。微藻体内具有结构新颖、功能独特的天然活性物质,是制备新型生物刺激剂的理想来源。微藻用于环境治理的同时,可获得足量的微藻生物质来制备生物刺激剂,从而达到治理环境、降低成本及提质增效的目的。就微藻源生物刺激剂的定义及功能、微藻全细胞和天然活性物质生物刺激剂的制备、应用效果及对植物和土壤的作用原理进行综述,以期为微藻源强效生物刺激剂的规模化制备及农业生产应用奠定理论基础和提供生产实践指导。     

Mycorrhizal fungi as mediators of defence against insect pests in agricultural systems

• 1 Below‐ground organisms influence above‐ground interactions in both natural and agricultural ecosystems. Among the most important below‐ground organisms are mycorrhizal fungi, comprising ubiquitous and ancient plant mutualists that have significant effects on plant growth and fitness mediated by resource exchange with plants. In the present study, we focus on the effects of arbuscular mycorrhizal fungi (AMF) on crop defence against insect pests.
• 2 AMF alter the availability of resources used by crop plants to manufacture defences against pests and to compensate for pest damage. However, AMF also provide plants with nutrients that are known to increase insect performance. Through potentially opposing effects on plant nutritional quality and defence, mycorrhizal fungi can positively or negatively affect pest performance.
• 3 Additionally, AMF may directly affect gene expression and plant defence signalling pathways involved in the construction and induction of plant defences, and these effects are apparently independent of those caused by nutrient availability. In this way, AMF may still influence plant defences in the fertilized and highly managed systems typical of agribusiness.
• 4 Because AMF can affect plant tolerance to pest damage, they may have a significant impact on the shape of damage–yield relationships in crops. Potential mechanisms for this effect are suggested.
• 5 We highlight the need for continuing research on the effects of AMF identity and the abundance on crop defences and tolerance to pest attack. Much work is needed on the potential effects of mycorrhizal colonization on plant signalling and the induction of direct and indirect defences that may protect against pest damage.

     

Promiscuous arbuscular mycorrhizal symbiosis of yam (Dioscorea spp.), a key staple crop in West Africa

Yam (Dioscorea spp.) is a tuberous staple food crop of major importance in the sub-Saharan savannas of West Africa. Optimal yields commonly are obtained only in the first year following slash-and-burn in the shifting cultivation systems. It appears that the yield decline in subsequent years is not merely caused by soil nutrient depletion but might be due to a loss of the beneficial soil microflora, including arbuscular mycorrhizal fungi (AMF), associated with tropical “tree-aspect” savannas and dry forests that are the natural habitats of the wild relatives of yam. Our objective was to study the AMF communities of natural savannas and adjacent yam fields in the Southern Guinea savanna of Benin. AMF were identified by morphotyping spores in the soil from the field sites and in AMF trap cultures with Sorghum bicolor and yam (Dioscorea rotundata and Dioscorea cayenensis) as bait plants. AMF species richness was higher in the savanna than in the yam-field soils (18–25 vs. 11–16 spp.), but similar for both ecosystems (29–36 spp.) according to the observations in trap cultures. Inoculation of trap cultures with soil sampled during the dry season led to high AMF root colonization, spore production, and species richness (overall 45 spp.) whereas inoculation with wet-season soil was inefficient (two spp. only). The use of D. cayenensis and D. rotundata as baits yielded 28 and 29 AMF species, respectively, and S. bicolor 37 species. AMF root colonization, however, was higher in yam than in sorghum (70–95 vs. 11–20%). After 8 months of trap culturing, the mycorrhizal yam had a higher tuber biomass than the nonmycorrhizal controls. The AMF actually colonizing D. rotundata roots in the field were also studied using a novel field sampling procedure for molecular analyses. Multiple phylotaxa were detected that corresponded with the spore morphotypes observed. It is, therefore, likely that the legacy of indigenous AMF from the natural savanna plays a crucial role for yam productivity, particularly in the low-input traditional farming systems prevailing in West Africa.     

Arbuscular mycorrhiza influences carbon‐use efficiency and grain yield of wheat grown under pre‐ and post‐anthesis salinity stress

• Soil salinity severely affects and constrains crop production worldwide. Salinity causes osmotic and ionic stress, inhibiting gas exchange and photosynthesis, ultimately impairing plant growth and development. Arbuscular mycorrhiza (AM) have been shown to maintain light and carbon use efficiency under stress, possibly providing a tool to improve salinity tolerance of the host plants. Thus, it was hypothesized that AM will contribute to improved growth and yield under stress conditions.
• Wheat plants (Triticum aestivum L.) were grown with (AMF+) or without (AMF?) arbuscular mycorrhizal fungi (AMF) inoculation. Plants were subjected to salinity stress (200 mm NaCl) either at pre‐ or post‐anthesis or at both stages. Growth and yield components, leaf chlorophyll content as well as gas exchange parameters and AMF colonization were analysed.
• AM plants exhibited a higher rate of net photosynthesis and stomatal conductance and lower intrinsic water use efficiency. Furthermore, AM wheat plants subjected to salinity stress at both pre‐anthesis and post‐anthesis maintained higher grain yield than non‐AM salinity‐stressed plants.
• These results suggest that AMF inoculation mitigates the negative effects of salinity stress by influencing carbon use efficiency and maintaining higher grain yield under stress.

     

Mycorrhizal-induced growth depression in plants

As plant mutualists, one would not expect arbuscular mycorrhizal fungi (AMF) to cause growth depression of their host plants. The mechanism responsible for negative effects of AMF is still debated and so here we review the possible abiotic and biotic reasons for AMF-induced growth depression in plants: 1) The Phytocentric explanations, include: a) AMF and non-mycotrophic plants, b) different growth stages of plants. 2) The Mycocentric explanations, include: a) Low effective AMF species, b) The existence of vesicles, c) Genetic variability of AMF, and d) Geographic origin of AMF. 3) Unbalanced C-for-nutrient-trade, involving both partners and 4) Indirect effects of other organisms. We note deficiencies in previous studies and suggest improvements in experimental designs such as the use of realistic mixtures of AM fungal species, and growing plants in mixtures in field situations, rather than single pot studies, with and without fungi. Determining whether and how AM fungi cheat on their hosts will enable a better understanding of their roles in natural communities and their use as biofertilizers in agriculture.