Effect of tillage and crop on arbuscular mycorrhiza colonization of winter wheat and triticale under Mediterranean conditions

Large‐scale inoculation with arbuscular mycorrhizal fungi (AMF) is generally impractical in most regions and we have little understanding of the factors that determine inoculation success. Nevertheless, the ability to take full advantage of indigenous AMF for sustainable production needs to be developed within cropping systems. We used part of a long‐term field experiment to understand the influence of tillage and the preceding crop on AMF colonization over the growing season. Arbuscular mycorrhiza colonization rate was more affected by treatment (tillage or the combination of crop and preceding crop) than by the total number of AMF spores in the soil. Conventional tillage (CT) had a statistically significant negative effect (P ≤ 0.05) on spore numbers isolated from the soil, but only in the first year of study. However, the AMF colonization rate was significantly reduced by CT, and the roots of wheat, Triticum aestivum, L, cv. Coa after sunflower, Helianthus annuus L., were less well colonized than were those of triticale, X Triticosecale Wittmack, cv. Alter after wheat, but the affect of tillage was more pronounced than was the effect of crop combination. Under no‐till there was a significant increase in AMF colonization rate throughout the sampling period in both wheat and triticale, indicating that the extraradical mycelium previously produced acted as a source of inoculum. In general, triticale showed greater AMF colonization than wheat, despite the preceding crop being less mycotrophic. Under these experimental conditions, typical of Mediterranean agricultural systems, AMF colonization responded more strongly to tillage practices than to the combination of crop and preceding crop.     

Summer survival of arbuscular mycorrhiza extraradical mycelium and the potential for its management through tillage options in Mediterranean cropping systems

The potential to manage arbuscular mycorrhizal colonization within Mediterranean agricultural systems depends on the summer survival of extraradical mycelium. To investigate this further a three‐stage experiment was undertaken. The first stage was the creation of two contrasting levels of extraradical mycelium development, achieved by two contrasting levels of soil disturbance (typifying full tillage and no‐till). In the second stage, this differential mycelial inoculum was subjected to Mediterranean summer temperature and soil water regimes representing the post‐harvest fallow. During the third stage, corresponding to the next growing season, survival was evaluated without further soil disturbance (typifying no‐till conditions) using wheat as host crop. The results clearly indicate that the extraradical mycelium survived the prevailing summer conditions. The knowledge that extraradical mycelium can survive the Mediterranean summer encourages the use of tillage systems that minimize mechanical disturbance of the soil, such as no‐till. The results from this study suggest that by making the appropriate choice of crops to establish a mycorrhizal‐supportive rotation there can be opportunities for agro‐ecosystem management to benefit from the symbiotic relationship.     

植物泡囊丛枝菌根及其应用展望

阐述了植物泡囊丛枝菌根(VA菌根)的形态特征、对植物的营养作用及其与根瘤菌等微生物的关系,分析了环境条件、栽培管理和耕作制度等对VA菌根的影响.提出应加强VA菌根的基础研究,试验接种外来菌源以及利用土壤的原有菌源,以充分利用VA菌根这一潜在的生物资源使农作物持续稳定增产.     

Soil tillage and herbicide applications in pea: arbuscular mycorrhizal fungi,plant growth and nutrient concentration respond differently

ABSTRACT

We conducted a field- and pot experiment with peas to investigate the impact of soil tillage and herbicide applications on arbuscular mycorrhizal fungi (AMF), plant growth, phosphorus concentrations, C:N ratio in plants and yield. The field study was carried out in a long-term soil tillage experiment where four tillage treatments have been compared. Field soil from the experimental plots were used for the pot experiment. AMF were not affected by herbicide (MCPB) application, neither in the field nor in the pot experiments. However, AMF root colonization was enhanced by reduced tillage, minimum tillage and no-tillage practices, compared to conventional tillage. In the pot experiment, plant growth and nodulation of pea roots was negatively affected by the high herbicide dosage. In the field experiment neither tillage nor herbicide treatment exert specific effects on root growth parameters, phosphorus concentrations, C:N ratio and plant dry matter. This work demonstrates that an appropriate herbicide usage coupled with conservation soil tillage techniques can favour AMF root colonization and benefit plant growth.

Abbreviations: AMF: arbuscular mycorrhizal fungi; CT: conventional tillage; RT: reduced tillage; MT: minimum tillage; NT: no tillage; P: Phosphorus; C:N ratio: carbon:nitrogen ratio     

Assessing the progress of colonization by arbuscular mycorrhiza of four plant species under different temperature regimes

To capitalize on the benefits offered by arbuscular mycorrhizal fungi (AMF) in agricultural systems, the effect of low soil temperature has to be taken into consideration over large areas of the planet. However, the effect of suboptimal root‐zone temperatures on AMF colonization is poorly understood. It has been suggested that it depends on the host plant species. We hypothesized that this interdependence is a function of the parameter used to assess the presence of AMF in the roots. In a pot experiment with non‐sterilized soil, we investigated the influence of three soil temperatures (10, 15, and 20°C) on the progress of root colonization of four host plant species (Ornithopus compressus, Lolium rigidum, Triticum aestivum, and Zea mays) by indigenous AMF. Plant root density, arbuscular colonization rate (AC) and colonized root density (CRD) were assessed 14, 28, and 42 d after sowing. Based on CRD, the effect of temperature on the progress of root colonization by AMF was independent of the host plant species. The apparent influence of the host plant species was only due to the species‐specific effect of soil temperature on root growth and therefore on AC. The host plant species only determined the minimum temperature for the AM colonization initiation, possibly due to species‐specific response of root growth and exudation to cool temperatures.     

Liquid organic fertilizer sprayed on shoots of Phaseolus vulgaris stimulates arbuscular mycorrhiza colonization and phosphate solubilizing microorganisms in soil

Processed organic agricultural byproducts such as liquid organic fertilizer (LOF) are promising alternatives that can improve crop productivity while reducing mineral fertilizer use and improving sustainability. The effects on beneficial soil organisms, such as arbuscular mycorrhizal (AM) fungi and phosphate solubilizing microorganisms (PSM), caused by LOF spraying on shoots is poorly understood. Therefore, we evaluated how AM colonization and soil PSM are affected by LOF spraying on common beans (Phaseolus vulgaris L.) grown in a greenhouse. The LOF was obtained by anaerobically fermenting a mixture of fresh water, cattle manure, bovine milk, sugarcane molasses and mineral salts. LOF was applied twice on the plant shoots. Fresh and dry mass of root and shoot, P content, P accumulation in the shoots and AMF spore counts in the soil were not LOF dose dependent. However, we found that a 5% LOF application stimulated AM colonization and led to dose-dependence for calcium and aluminium phosphate solubilizing bacteria and fungi. These results show that LOF sprayed on shoots causes responses on soil communities. We therefore endorse the use of LOF in low input agriculture.     

Effect of Azospirillum inoculants on arbuscular mycorrhiza establishment in wheat and maize plants

Plant growth-promoting rhizobacteria and arbuscular mycorrhizal (AM) fungi represent two main groups of beneficial microorganisms of the rhizosphere. The role of different strains of Azospirillum on AM fungi development was evaluated by measuring the percentage of AM colonisation of the root system in durum wheat and maize plants, grown under both greenhouse and field conditions. The effect of wild-type Azospirillum brasilense strain Sp245 and genetically modified (GM) derivatives overproducing indole-3-acetic acid was assessed at greenhouse level in (1) three different cultivars of durum wheat, in the presence of indigenous AM fungi and (2) maize plants artificially inoculated with Glomus mosseae and Glomus macrocarpum. In addition, the establishment of natural AM fungal symbiosis was evaluated using Azospirillum lipoferum CRT1 in maize plants at field level. Despite the stimulatory effect of the different Azospirillum inocula on root growth, no significant differences in AM colonisation were found, independently of the AM fungus involved, either in wheat or in maize plants. Similarly, GM A. brasilense, which strongly stimulates root development, did not affect AM formation. Although these results were obtained in conditions in which the mycorrhization rate was moderate (15–30%), overall considered they indicate that the use of wild-type or GM Azospirillum phytostimulators does not alter mycorrhization.     

丛枝菌根真菌对玉米生长生态效应的影响

1996～1998年试验研究了大田不施肥条件下3种泡囊丛枝菌根真菌Arbuscular mycorrhizal fungi (AMF),即 Glomus mosseae(G.m)、Glomus versifome(G.v)、Sclerocystis sinousa(S.s)对玉米生长的生态效应.结果表明,AMF处理的玉米根系活力为对照的2.32～3.05倍,玉米N素吸收比对照增加24.14%～56.65%,玉米P素吸收比对照增加41.14%～78.29%,促进玉米生长发育显著;在灭菌条件下G.m、G.v、S.s处理分别比对照增产17.63%、22.91%和10.80%;而不灭菌条件下3个处理分别比对照增产10.35%、20.56%和4.53%,同时显著提高玉米的水分供应状况.     

Root herbivory by Tipula paludosa larvae increases colonization of Agrostis capillaris by arbuscular mycorrhizal fungi

The objective of this study was to determine if root-feeding by insect larvae affects subsequent colonization of roots by arbuscular mycorrhizal fungi. We investigated grazing by larvae of Tipula paludosa on colonization of Agrostis capillaris by two species of fungi, Glomus mosseae and G. intraradices. Host plants were subjected to 7 days of grazing only, continuous grazing for 42 days, or no herbivory. Those plants with no herbivory had significantly lower levels of colonization by arbuscules and hyphae compared to plants which were grazed for 7 or 42 days. The effect only occurred in the upper parts of the root system, where larvae were active. We suggest that this effect was most likely mediated by a change in quantity and composition of root exudates.     

Plant growth-promoting rhizobacteria alter rooting patterns and arbuscular mycorrhizal fungi colonization of field-grown spring wheat

The impact of plant growth-promoting rhizobacteria (PGPR) inoculants on the growth, yield and interactions of spring wheat with arbuscular mycorrhizal fungi (AMF) was assessed in field studies. The pseudomonad inoculants P. cepacia R55, R85, P. aeruginosa R80, P. fluorescens R92 and P. putida R104, which enhance growth and yield of winter wheat, were applied at a rate of ca. 10⁷–10⁸ cfu seed^-1 and plots established on pea stubble or summer fallow at two different sites in Saskatchewan. Plant shoot and root biomass, yield and AMF colonization were determined at four intervals. Plant growth responses were variable and dependent on the inoculant strain, harvest date and growth parameter evaluated. Significant increases or decreases were measured at different intervals but these were usually transient and final seed yield was not significantly affected. Harvest index was consistently increased by all pseudomonad inoculants; responses to strain R55 and R104 were significant. Root biomass to 60 cm depth was not significantly affected by inoculants except strain R104, which significantly reduced root dry weight. However, root distribution, root length and AMF colonization of roots within the soil profile to 60 cm were significantly altered by inoculants. Most of these responses were reductions in the assessed parameter and occurred at depths below 15 cm; however, strains R85 and R92 significantly increased root dry weight in the 0- to 15-cm zone. These results indicate that some PGPR inoculants may adversely affect mutualistic associations between plants and indigenous soil microorganisms, and suggest a possible reason as to why spring wheat growth was not consistently enhanced by these pseudomonad PGPR.     

Using arbuscular mycorrhiza to alleviate the stress of soil compaction on wheat (Triticum aestivum L.) growth

Since large areas of agricultural fields in the world become compacted every year, much effort has been made to reduce the adverse effects of soil compaction on plant growth. Mechanical methods to control soil compaction may be laborious and expensive; however, biological methods such as using arbuscular mycorrhiza (AM) may be more useful, economically and environmentally. The objectives of this study were: (1) to evaluate the effects of soil compaction on wheat (Triticum aestivum L.) growth, and (2) to evaluate if using AM of different origin can reduce the stressful effects of soil compaction on wheat growth. Unsterilized and sterilized soils, different levels of compaction and three species of arbuscular mycorrhiza were applied in four replicates. The experiments were conducted in the Soil and Water Research Institute, Karaj, Iran. Soil physical and chemical properties were determined. The AM increased wheat growth in both soils at different levels of soil compaction in both experiments. For root, shoot (P=0.1) and grain (P=0.05) dry weights increases were significant. AM enhanced root growth more than shoot growth under compaction (AM resulted in significant increase in root/shoot ratios, P=0.1). Due to its unique characteristics, AM may reduce the stressful effects of soil compaction on wheat growth, though its effectiveness may decrease with increasing compaction.     

The role of the external mycelium in early colonization for three arbuscular mycorrhizal fungal species with different colonization strategies

Arbuscular mycorrhizal fungi (AMF) differ in their rate and extent of colonization of both plant roots and soil but the mechanism responsible for these differences is unclear. We compared the external mycelium of three AMF isolates (Glomus intraradices, Glomus etunicatum and Gigaspora gigantea) during early colonization of plant roots. We investigated whether an AMF with the most rapid colonization would have higher numbers of infective structures (i.e., infection hyphae and contact points), an AMF with extensive root colonization would have more infection units, and (3) AMF with extensive soil colonization would have large numbers of all external features (including absorptive hyphae, runner hyphae and hyphal bridges). Using specially designed soil and root observation chambers, we followed the development of the external mycelium for 7 weeks. We found that rapid colonization rate was due, in part, to the presence of more infective structures, in particular more infection hyphae and root contact points. Second, the extensive root colonizer had more, larger infection units. Third, data did not support the hypothesis that the extensive soil colonizer had more external structures. These results show that differences in the architecture of the external mycelium are responsible, in part, for variation in the colonization strategy of AMF.     

The role of arbuscular mycorrhiza in legume symbiotic performance

Legumes may respond to non-rhizobial inoculants such as arbuscular mycorrhizal (AM) fungi either through an effect on plant growth or, in addition, through an effect on the function of the legume-Rhizobium symbiosis. We have examined the literature where the application of ¹⁵N isotope dilution methodology permits the effect of indigenous AM and AM inoculants to be quantitatively separated into plant-growth-mediated and biological N₂ fixation (BNF)-mediated components. These studies clearly demonstrate the beneficial effects that both indigenous and inoculated AM have on legume growth, N uptake and the proportional dependence of the legume on atmospheric N₂. While the published data allow an assessment of various biological, edaphic and environmental factors that affect the response of various legumes to AM inoculation, they also highlight the paucity of quantitative field data and the lack of understanding of the interaction of legume genotype with AM species with respect to legume symbiotic performance.     

Reaction of Mycorrhizal and Nonmycorrhizal Leucaena leucocephala to Charcoal Amendment of Mansand and Soil

A series of experiments were conducted to evaluate the influence of charcoal on the development of arbuscular mycorrhiza (AM) on Leucaena leucocephala roots and the contribution of the symbiosis to the phosphorus (P) nutrition and growth of the legume. Arbuscular mycorrhizal fungal colonization of plants raised in Mansand (crushed basalt) in the first experiment was reduced if the medium was amended with fine charcoal and not with coarse charcoal. Charcoal amendment had no effect on AM fungal colonization, AM symbiotic effectiveness measured as pinnule (subleaflet) P content, or on growth of L. leucocephala in soil in the first experiment and in Mansand and in soil in subsequent experiments. However, AM fungal colonization of L. leucocephala roots, P content of pinnules, and growth of the legume were significantly enhanced (P < 0.05) by AM fungal inoculation in all experiments regardless of the growth medium used or charcoal amendment.     

丛枝菌根作用下土壤中多环芳烃的残留及形态研究

采用盆栽试验方法,以苊为多环芳烃(PAHs)代表物,研究了丛枝菌根(AM)作用下土壤中 PAHs 的残留及形态.供试污染土壤中苊的起始浓度为 35.0 mg/kg.结果表明,AM作用下土壤中苊总残留量明显降低;接种摩西球囊霉菌Glomus mosseae或幼套球囊霉菌Glomus etunicatum后,供试两个污染土样中苊总残留降解率达32.7%～45.2%,比未接种对照高 6.8%～9.8%.有机溶剂提取态是土壤中苊残留的主要部分,AM 作用促进了苊各形态之间的转化;接种AM后土壤 1、2 中苊可脱附态和有机溶剂提取态残留量分别比对照降低了17.0%～37.8% 和 5.4%～26.6%,而结合态残留量比对照增加了12.2%～89.5%.AM 作用能降低土壤中苊可提取态残留含量;但培养55 天后土壤中仍有 65.7%～81.7% 苊属于可提取态残留,对生物有毒害风险.     

Investigation of alternate herbicides for effective weed management in glyphosate-tolerant cotton

ABSTRACT

Glyphosate-resistant (GR) weeds are the biggest concern for all cotton stakeholders worldwide. Currently, 43 weeds species are resistant to glyphosate and the number is increasing at an alarming rate. Soil residual/pre-emergence (PRE) herbicides like Pendimethalin and S-metolachlor can be effectively used for the control of GR weeds; however, their use is very limited at farmer’s side due to the adoption of herbicide-tolerant technology with complete reliance on glyphosate. The present study was conducted to evaluate the performance of PRE and post-emergence (POST) herbicides in glyphosate-tolerant (GT) cotton. The herbicide treatments were pendimethalin and S-metolachlor as PRE-residual, and glyphosate was applied as POST at 20 days after sowing (DAS) either alone or in combination with other herbicides like S-metolachlor, pendimethalin, and haloxyfop. A second application of glyphosate was made at 35 DAS. Results revealed that pendimethalin and S-metolachlor treatments gave 100% suppression of all dominant weeds and increased lint yield by 310–350% as compared to weedy control. In contrast, glyphosate applied once and twice, gave weed biomass reduction of only 10–86%, and increased lint yield by 136–185% over weedy control. This research established that PRE application of pendimethalin and S-metolachlor can be included in the weed management program of GT cotton.     

High colonization by native arbuscular mycorrhizal fungi (AMF) of rubber trees in small-holder plantations on low fertility soils in North East Thailand

Rubber tree is a very important crop in Thailand, representing an essential source of income for farmers. In the past two decades, rubber tree plantations have been greatly expanding in unfavorable areas, where climate conditions are difficult and soil fertility is very poor. To optimize latex yields, mineral fertilizers have been widely used. A better understanding of the roles of the biological compartment in soil fertility is essential to determine alternative management practices to sustain soil fertility and optimize latex yields. Arbuscular mycorrhizal fungi (AMF) are widely recognized as beneficial for plants, mainly through their role in improving plant nutrient uptake. The objective of this study was to assess the AMF populations in rubber tree plantations and the impact of both soil characteristics and plantation age on these communities. Our results showed that all rubber trees were highly colonized, regardless of the soil structure and nutrient contents. AMF colonization was not affected by the age of the trees, suggesting that maintaining the symbiosis is likely to be beneficial at all stages. A better understanding and management of the microbial communities would contribute to maintaining or restoring soil fertility, leading to a better tree growth and optimized latex yield.     

VA菌根对冬小麦利用养分和水分的影响

本文采用土培试验研究了水分胁迫状况下接种VA菌根真菌对冬小麦生长发育、养分吸收和水分利用的影响 .试验结果表明 :水分胁迫严重地抑制了植株地上部及根系的生长 ,影响了植株对养分的吸收利用 ;接种VA菌根真菌的植株体内氮磷营养状况得到改善 ,减轻了水分胁迫对植株生长的抑制程度 ,提高了干物质的累积 .因此 ,接种VA菌根真菌提高了冬小麦的抗旱性、促进了植株生长 ,并增加了根 /冠比值 .试验结果还表明 ,接种VA菌根真菌可增加冬小麦对水分的有效利用 ,提高了水分利用效率     

Influence of arbuscular mycorrhiza and phosphate rock on uptake of major nutrients by Acacia mangium seedlings on degraded soil

To investigate the effects of arbuscular mycorrhiza (AM) and phosphorus (P) source on the uptake of major nutrients by Acacia mangium seedlings, three P sources were used: (1) Gafsa phosphate rock (GPR), (2) China phosphate rock (CPR), and (3) triple superphosphate (TSP). The plant samples were analyzed at 60, 75, 90, 105, 120, and 135 days after planting (DAP) for their N, P, K, Ca, and Mg contents. The uptake of these nutrients was significantly influenced by AM inoculation. Nutrient use efficiency in the AM-inoculated seedlings was also significantly higher than that in uninoculated seedlings. The effect of P sources on the uptake of these nutrients decreased in the order of TSP>GPR>CPR>control. There was a significant (P<0.05) interaction effect of AM and P source on P and K uptake by A. mangium. The uptake of P and K by mycorrhizal seedlings supplemented with TSP was significantly higher than that provided with other sources of P treatments. As a natural and cheaper P source, GPR might be used in combination with AM for growing A. mangium seedlings on degraded tin tailings.