Effects of substrate sterilization,fungicide treatment,and mycorrhization helper bacteria on ectomycorrhizal formation of pedunculate oak (Quercus robur) inoculated with Laccaria laccata in two peat bare-root nurseries

Summary Pedunculate oak seedlings (Quercus robur) inoculated with the ectomycorrhizal fungus Laccaria lacata were grown for 1 year on fertilized sphagnum peat in two nurseries. Three factors affecting microbial populations in the substrate were studied, fungicide treatment of the seeds, peat disinfection before sowing (methyl bromide or steam pasteurization), and inoculation with mycorrhization helper bacteria. Treatment of acorns with Iprodione had no depressive effect on mycorrhiza formation. Both disinfection techniques were equivalent, stimulating or depressing mycorrhiza formation depending on the initial microflora in the peat. The introduction of two previously selected mycorrhization helper bacteria (one Pseudomonas fluorescens and one unidentified fluorescent pseudomonad), isolated from L. laccata sporocarps associated with Douglas fir—L. laccata ectomycorrhizas in other nurseries, significantly increased the mycorrhizal rate from 30 to 53% of the short roots. The implications of these results for the controlled mycorrhization of planting stocks and the specificity of mycorrhization helper bacteria are discussed.     

Alder-poplar associations: Determination of plant nitrogen sources by isotope techniques

Summary Three¹⁵N isotopic dilution methods (¹⁵N natural abundance, labelled mineral fertilizer, and organic matter) were used to determine the proportion of N derived from different available sources in seedlines ofAlnus glutinosa andPopulus nigra planted together or in monoculture under natural climatic conditions. The proportion of N derived from N₂ fixation in associated alders was appreciably higher than that determined in monoculture. The reduction of soil N uptake by associated alders contributed to an increase in total plant N and biomass production in associated poplars. When slightly N-labelled organic matter (alder leaf litter) was incorporated into the soil, 10–15% of its initial N content was recovered in poplar tissues, showing that this N source makes an important contribution to the N yield of associated non-fixing plants. There were no significant differences between the results obtained by¹⁵N natural abundance and those obtained by labelled fertilizer methods, suggesting that the ¹⁵N method could be used to evaluate annual N budgets in natural ecosystems.     

Effect of cropping sequence,fertilizers and farmyard manure on vesicular-arbuscular mycorrhizal fungi in different crops over three consecutive seasons

Summary The influence of cropping sequence with and without fertilizer and farmyard manure application on vesicular-arbuscular mycorrhizae was studied over three consecutive seasons. In the first season maize was grown on all the plots. In the second season cowpea, groundnut and finger millet were raised on the same plots and in the third season, sunflower was grown on all the plots. The groundnut grown in the second season stimulated mycorrhizal root colonization, sporulation and infective propagules in the soil, and these effects were carried over to the next season. The plots cropped to finger millet in the second season had the lowest number of mycorrhizal spores. The application of farmyard manure stimulated vesicular-arbuscular mycorrhizae while fertilizers at the recommended level decreased the mycorrhizal propagules.     

Effect of mycorrhizal inoculation and soil restoration on the growth of Pinus halepensis seedlings in a semiarid soil

An experiment was carried out to evaluate the growth of mycorrhizal Pinus halepensis seedlings planted in a semiarid soil amended with urban refuse in southeast Spain. Three fungal species were used: Pisolithus tinctorius, Rhizopogon roseolus, and Suillus collinitus. After 8 months, inoculated seedlings grown under controlled conditions did not differ significantly from controls with regard to plant height and nutrient assimilation. Other features such as root development and stem dry weight showed that the plants grew better in the absence of mycorrhizal inoculation. The mycorrhizal seedlings and the controls were planted in three experimental plots treated with urban refuse (0, 6, and 12 Kg m^-2). After 1 year of growth under field conditions the results showed that the type of fungus inoculated significantly influenced P. halepensis development. This effect varied with the dose of urban refuse. Plant growth was encouraged by the application of refuse but only at the lowest dose. Under these conditions P. tinctorius was the most effective fungus and R. roseolus yielded poorer plant development. The highest application of urban refuse led to notably worse results and a significant decrease in seedling growth compared to controls. In the control plot (without refuse) S. collinitus was the most effective fungus in plant growth improvement. The smallest application of urban refuse had a positive effect on the assimilation of N, P, and K in seedlings inoculated with P. tinctorius and S. collinitus.     

Changes in soil organic matter and net nitrogen mineralization in heathland soils,after removal,addition or replacement of litter from Erica tetralix or Molinia caerulea

Summary The effects of different litter input rates and of different types of litter on soil organic matter accumulation and net N mineralization were investigated in plant communities dominated by Erica tetralix L. or Molinia caerulea (L.) Moench. Plots in which the litter on the soil had repeatedly been removed were compared with plots in the same plant community in which litter had been added to the soil. In another treatment, litter was removed and replaced by litter from the other plant community. Net N mineralization was measured in situ after 5 years. Less soil organic matter and soil N was found in plots in which litter had been removed, compared with control plots, or plots to which litter had been added, but these differences were significant for the Erica sp. soils only. Plots in which litter had been replaced and control plots did not differ significantly in the amount of soil organic matter. However, in both plant communities, the differences agreed with the faster decomposition rate of Molinia sp. litter compared with Erica sp. litter. The gravimetric soil moisture content was correlated positively with the amount of soil organic matter, both in the Erica sp. soils and the Molinia sp. soils. Net N mineralization rates (g N m^-2) differed significantly between treatments for Erica sp. soils but no for Molinia sp. soils. For Erica sp. soils, net N mineralization rates increased with increasing amounts of soil organic matter and soil N. Replacing the litter with Molinia sp. litter (which differs in chemical composition) had no clear additional effect on the net N mineralization rate.     

Effects of hexachlorocyclohexane on rhizosphere fungal propagules and root colonization by arbuscular mycorrhizal fungi in Plantago lanceolata

Lindane ( γ‐hexachlorocyclohexane or γ‐HCH) is an organochlorine insecticide previously used extensively for the control of agricultural pests. We studied the effects of soil HCH contamination on vegetation and its associated arbuscular mycorrhizas (AM). The polluted and unpolluted plots had similar plant cover, with the same species richness and abundance. Plantago lanceolata plants were selected for mycorrhizal analysis because of their presence in both plots and known mycotrophy. The presence of HCH appeared to have no significant effect on the extent of colonization of Plantago roots by AM, suggesting a similar functionality of the fungal symbionts. However, infective AM propagules, the density of AM spores and viable AM hyphae in the rhizosphere were much less in the HCH‐polluted soil than in the unpolluted plot. Pre‐inoculation of four plant species with an isolate of Glomus deserticola obtained from the HCH‐contaminated soil resulted in increased growth and fungal colonization of roots compared with plants pre‐inoculated with the introduced fungus G. macrocarpum or colonized by the consortium of indigenous AM fungal species, when those plants were transplanted to an HCH‐contaminated soil. This suggests that the fungus increases the tolerance of plants to the toxic soil environment. We conclude that herbaceous and woody plants can grow in soil with little P contaminated with <100 mg HCH kg^?1 with the help of tolerant AM, despite the detrimental effect of HCH on AM fungal propagules in soil. The effects of AM fungi on plant growth and soil microbial community structure in HCH‐polluted sites could be important for remediation of the pollutant through the microbial activity in the rhizosphere.     

Biological control of Rhizoctonia sp. root rot of Casuarina equisetifolia seedlings by Frankia spp. strains

Seventy Frankia spp. strains (nodulating N₂-fixing actinomycetes) were isolated from root nodules of Casuarina equisetifolia from different localities of Tamil Nadu state, India. From these, four strains (UMCe12, UMCe23, UMCe35, and UMce55) were selected. Their potential use as biological control agents for Rhizoctonia solani root rot disease of C. equisetifolia seedlings and their relative efficiency in nodule production were investigated. Between the two inoculum broadcast systems tested, seed-coating with Frankia spp. cell suspension was superior to the soil application of cells as sand-vermiculite-basal ammonium propionate inoculum. UMCe12 was the promising strain, offering the highest level of disease protection (81.1%) and nodule production (88.1%) in the R. solani-infested soil, followed by UMCe23 (60.3 and 65.5% of disease protection and nodule production, respectively), UMCe55 (53.5 and 58.2%), and UMCe35 (45.4 and 44.5%). Further, a significant positive correlation was observed between the dose of Frankia spp. and efficiency in both disease control and nodule production.     

Slash Pile Burning at a Norway Spruce Clear-cut in Southern Sweden

The effect of burning piles of slash on a Norway spruce clear-cut in southern Sweden was followed for 3 years. The vegetation cover, soil chemistry, soil water at a depth of 30–40 cm and runoff water were studied. The burnt plots were without vegetation for several months after burning, while the control plots were almost totally covered by Deschampsia flexuosa and Galium saxatile. The remaining mor horizon of the burnt plots had a pH of 6 compared with pH 4.4 in the control plots. This caused more intense nitrification of the burnt plots that, in turn, caused an acid push with high concentrations of hydrogen ions, nitrate and potassium in the soil water. After 1 year, a cover of D. flexuosa and G. saxatile had also developed on the burnt plots, and the soil water chemistry no longer indicated an elevated leakage of ions. Throughout the study period, no leaching effect was observed in the runoff water. This was explained by nutrient retention of a swamp forest with Betula pubescenson peat soil, surrounding the ditch collecting the runoff water. The increased risk of developing a nutrient imbalance in the next forest generation may strongly outweigh the short-term benefit of reduced competition between tree seedlings and forest floor vegetation, especially if the slash burning is not expected to be of any value for species conservation.     

Interactions of Glomus clarum with Acetobacter diazotrophicus in infection of sweet potato (Ipomoea batatas), sugarcane (Saccharum spp.), and sweet sorghum (Sorghum vulgare)

Summary Spores of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus clarum obtained from sweet potatoes grown in soil inoculated with this fungus and with an enrichment culture of Acetobacter diazotrophicus contained A. diazotrophicus and several other bacteria, including a diazotrophic Klebsiella sp. Inoculation of micropropagated sweet potatoes with G. clarum and A. diazotrophicus enhanced spore formation in soil compared to VAM inoculation alone. Plants inoculated with VAM spores containing the bacteria showed additional increases in the number of spores formed within roots. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM or when present within VAM spores. Micropropagated sugarcane seedlings inoculated with the same VAM spores containing the diazotrophs also contained much higher numbers of A. diazotrophicus in aerial parts than seedlings inoculated in vitro with the bacteria alone. When grown in non-sterile soil, the sugarcane seedlings again showed the greatest infection of aerial parts after inoculation with VAM spores containing the diazotrophs. This treatment also increased VAM colonization and the numbers of spores formed within roots. Similar effects were observed in sweet sorghum except that the aerial plant parts were not infected by A. diazotrophicus.     

Montezuma pine nutrient status as affected by alder densities nitrogen fertilization

Literature reports both positive and negative effects of N‐fixing alders on conifer growth in alder‐conifer stands. Such divergent effects probably result from poorly understood species interactions. The aim of this work was to examine how varying alder‐to‐pine ratios (APRs) and N fertilization affect pine nutrient status. A pseudo‐experiment was installed in each of two areas of regeneration (AR) with different amounts of radiation reaching alder. The experimental approach consisted of a series of pseudoreplicated plots with five APRs within each AR. Half of each plot received 200 kg N ha^–1. Data were interpreted by vector analysis. Alders in the AR 1987 induced needle‐biomass reductions, K deficiency, and P accumulation in pine needles. However, nutrient availability increased with the proportion of alders in the AR 1989, where alders received high sunlight due to a less dense pine stand. Nitrogen fertilization increased needle biomass and N in three out of five alder proportions where alders were sunlight‐limited. In the other stand, with the exception of the no‐alder and A4 plots, positive effects of N fertilization increased with decreasing alder density. We conclude that sunlight‐limited alders may not positively affect associated‐species growth even in N‐limited sites.     

胶质芽孢杆菌与苜蓿根瘤菌双接种对排土场紫花苜蓿生长和土壤性质的影响

为了明确胶质芽孢杆菌和苜蓿根瘤菌在矿区排土场复垦中的协同作用,以矿区排土场土壤作为基质进行盆栽试验,设置两菌单接种处理、双接种处理及对照,其中胶质芽孢杆菌和苜蓿根瘤菌用量分别为1.50%和0.25%,测定紫花苜蓿产量指标、叶片生理指标、土壤速效养分含量和土壤微生物指标。结果表明,接种胶质芽孢杆菌和苜蓿根瘤菌的各处理均能显著提高紫花苜蓿的产量指标,其中以双接种处理效果最优,将生物量和结瘤量分别比对照显著提高110.27%和124.32%;在生理指标方面,双接种处理效果低于单接种处理,未表现出协同作用;在土壤养分和微生物性质方面,单接种胶质芽孢杆菌仅显著提高土壤速效钾含量,单接种苜蓿根瘤菌对大部分指标均有显著效果,而双接种处理效果最佳,土壤碱解氮、速效钾含量比对照分别显著提高94.14%和84.55%,土壤微生物指标MBC含量、呼吸强度、蔗糖酶、脲酶、磷酸酶、过氧化氢酶活性比对照分别显著提高204.02%,65.86%,212.32%,91.87%,30.57%,51.87%。双接种处理对紫花苜蓿产量指标、养分和微生物指标表现出显著的协同作用。因此,1.50%用量胶质芽孢杆菌和0.25%用量苜蓿根瘤菌双接种能够有效提高排土场土壤的复垦效果,具有协同作用,可以作为矿区排土场复垦的高效方法。     

Variable effectivity of three vesicular-arbuscular mycorrhizal endophytes in Hedysarum coronarium and Medicago sativa

Summary Plants of Hedysarum coronarium L. and Medicago sativa L., inoculated with Glomus caledonium, were grown for 6 weeks in soils with increasing amounts of available phosphorus (P). H. coronarium showed no or very low levels of infection even at very low soil P content (4 ppm), while in M. sativa the highest soil P level (20 ppm) was associated with the lowest percentage of infection. Medicago sativa and H. coronarium grown for 16 weeks in a sandy soil showed clear effects of Glomus inoculation on shoot growth and P uptake. In M. sativa inoculation increased shoot growth and P uptake in all treatments considerably, while the P concentration in the shoot was depressed by G. caledonium. In H. coronarium inoculation with G. mosseae and G. occultum had only a modest impact on shoot growth; G. caledonium even depressed shoot growth significantly. Glomus inoculation had a positive impact on the P concentrations in the shoots of H. coronarium. The growth-depressing effect of G. caledonium on H. coronarium is discussed.     

Effects of mulch location on banana weevil,soil and plant nutrients,soil water and biomass in banana fields

Major constraints to banana (Musa spp., genome group AAA) production, a dietary staple for over 70 million people in sub-Saharan Africa, are pest infestations, poor nutrition and inadequate water. Although mulch can improve soil water and nutrient status, many farmers believe it also promotes the proliferation of banana weevil (Cosmopolites sordidus), one of the most serious banana pests. In this study, we evaluated the effects of mulch location (mulch to base of banana pseudostem; mulch recessed 1 m from the pseudostem) on banana weevil, soil and plant nutrient status, soil water, and banana growth and development. After 3 years, the fully mulched plots had significantly more soil Ca and Mg than plots that did not receive mulch. Banana foliar K concentration was significantly higher in both mulch treatments (full and recessed) than in the control (no mulch) plots. The mulched plots had greater recharge after rainfall events and higher soil water contents during dry periods due to increased infiltration in the mulched plots. However, the mulched plots also exhibited significantly higher banana weevil densities and greater plant damage than the control plots. There was no difference in weevil damage with mulch location, although weevil density was higher in the fully mulched plots throughout most of the trial. Despite greater weevil damage, the treatments that were mulched yielded significantly heavier bunches. Hence the effects of the mulch on soil water infiltration and banana foliar nutrient status outweighed the detrimental effects of banana weevil damage.     

Changes in biological activity of a degraded Mediterranean soil after using microbially-treated dry olive cake as a biosolid amendment and arbuscular mycorrhizal fungi

A field experiment was carried out to assess the effect of a combined treatment involving addition of Aspergillus niger-treated dry olive cake (DryOC) in the presence of rock phosphate, plus pre-transplant inoculation of seedlings with the arbuscular mycorrhizal (AM) fungi Glomus intraradices, Glomus deserticola or Glomus mosseae, on the establishment of Dorycnium pentaphyllum L., in a degraded semiarid Mediterranean area. Associated changes in soil labile C fractions, enzyme activities and aggregate stability were also observed. One year after planting, the combined treatment of fermented DryOC addition and inoculation with AM fungi, particularly with G. mosseae (on average 328% greater than control plants), had the strongest effect on the shoot biomass of D. pentaphyllum. Only the fermented DryOC addition increased assimilable P, total N and aggregate stability, the greatest increase being in the soil available P content (about four-fold higher than in the non-amended soil). Both the addition of fermented DryOC and the mycorrhizal inoculation treatments significantly increased enzyme activities of rhizosphere soil (dehydrogenase, protease-BAA, acid phosphatase and β-glucosidase). The microbially-treated DryOC proved to be an effective amendment for improving the soil quality which, in turn, enhanced the success of revegetation with mycorrhizal D. pentaphyllum seedlings.     

Tomato seedling development is improved by a substrate inoculated with a combination of rhizobacteria and fungi

Chile's seedling production industry has been growing for the last 10 years, and demand has actually reached 1250 million seedlings per year. This system has special relevance due to the high cost of seeds. In addition, there is an increasing demand for substituting synthetic agrochemicals. Therefore, the potential use of plant growth-promoting rhizobacteria (PGPR) in tomato production has been investigated. Before sowing, the micro-organisms provided by Biogram S.A. were inoculated into the substrate diluted in 250 mL/L unchlorinated water. The experiment was laid out in a ‘split-plot’ design with the two plant substrates as main plots and the inoculants as subplots, including six replicates per treatment. Tomato seedlings were grown using two different plant substrates: a mixture of 70% peat and 30% perlite by volume, and a substrate with 20% peat, 20% perlite and 60% compost by volume, both inoculated with Bacillus subtilis or Pseudomonas fluorescens or Bioroot®, which is a commercial product containing B. subtilis, P. fluorescens, Trichoderma harzianum, yeast, algae and Nocardia. For control, uninoculated tomato seedlings were grown on the respective plant substrates. Variance analysis did not identify significant interactions between substrate type (main plots) and inoculation treatment (subplots), P ≤ 0.05. There were significant differences between inoculants (P ≤ 0.05). Means were compared by using the Tukey's multiple range test. Tomato growth in terms of leaf area (cm²/plant) and shoot and root dry weight (g/10 plants) was improved for the seedlings grown on the substrate with 70% peat and 30% perlite, compared to the compost containing an alternative that is valid for both uninoculated perlite peat and all inoculated treatments where perlite peat was outstanding. Inoculation with Bioroot® improved the leaf area, shoot dry weight, root dry weight, radical contact area, volume of roots and root forks compared with the control without inoculation, when both plant substrates were analysed together. Thus, inoculation with Bioroot® can be recommended as an alternative to tomato seedling growers' dependence on synthetic agrochemicals.     

In situ net N transformations in pine,fir, and oak stands of different ages on acid sandy soil, 3 years after liming

Summary The effect of liming on in-situ N transformations was studied in two stands of different ages of each of Scots pine (Pinus sylvestris L.), Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], and common oak (Quercus robur L.). The stands were located on acid sandy soils in an area with high atmospheric N input. The organic matter of the upper 10-cm layer of the soil, including the forest floor, had a relatively high N content (C: N ratio <25) in all stands. Using a sequential core technique, N transformations were measured in both control plots and plots that had been limed 3 years previously with 3 t ha^-1 of dolomitic lime. Limed plots had a higher net NO _inf3 ^sup- production and a higher potential for NO _inf3 ^sup- leaching than the controls in all stands except that of the younger oak. Net N mineralization did not differ significantly between limed and control plots in oak stands and younger coniferous stands but was significantly lower in the limed plots of the older coniferous stands. It is concluded that long-term measurements of net N mineralization in limed forest soils are needed to evaluate the effect of liming with respect to the risk of groundwater pollution.     

Inoculation withGlomus mosseae improves N2 fixation by field-grown soybeans

Summary A field study carried out in a sandy, relatively acid Senegalese soil with a low soluble P content (7 ppm) and low vesicular-arbuscular mycorrhizal (VAM) populations showed that soybean responded toGlomus mosseae inoculation when the soluble P level in the soil had been raised by the addition of 22 kg P ha^–1. In P-fertilized plots, N₂ fixation of soybean, assessed by the A value method, was 109 kg N₂ fixed hat when plants were inoculated withRhizobium alone and it reached 139 kg N₂ fixed ha^–1 when plants were dually inoculated withRhizobium andGlomus mosseae using an alginate bead inoculum. In addition to this N₂ fixation increase (+28%),Glomus mosseae inoculation significantly improved grain yield (+13%) and total N content of grains (+16%). This success was attributed mainly to the low infection potential of the native VAM populations in the experimental site. In treatments without solubleP or with rock phosphate, no effect of VAM inoculation was observed.     

Relationship of root necrosis potential of soil to asparagus (Asparagus officinalis) decline in Switzerland

Summary The possible relationship between asparagus decline and the root necrosis potential (RNP) of soil was investigated for 11 asparagus and 4 nonasparagus soils. Asparagus seedlings were grown in each soil in climate chambers. A root necrosis index was used to determine RNP. RNP was correlated with the decline observed in the field for seven white asparagus crops, but not for three white and one green asparagus crops. Low RNP values were obtained from the soils not planted to asparagus.Fusarium oxysporum andF. oxysporum var. redolens accounted for 7070 of the fungi isolated from necrotic roots in RNP tests. BothFusarium were obtained from all soils. AllF. oxysporum andF. oxysporum var. redolens isolates tested were highly virulent on asparagus seedlings in inoculation experiments.F. solani, Penicillium verrucosum var.corymbiferum, andRhizoctonia violacea were isolated less frequently but were also highly virulent. It is concluded that soil RNP indicated a risk of decline caused by fusaria, but other soil factors were likely to be involved in the aetiology of decline. The study of these factors is necessary to develop a method for the prognosis of decline associated with fusaria.     

Selection of efficient vesicular-arbuscular mycorrhizal fungi for wetland rice (Oryza sativa L.)

Summary We tested the response of the wetland rice cultivar Prakash to inoculation with ten vescular-arbucular mycorrhizal (VAM) fungi (three selected from the first screening and seven isolated from local paddy fields) in a pot experiment under flooded conditions in order to select the most efficient mycorrhizal fungi to inoculate the rice nursery. A sandy clay loam soil was used as the substrate, fertilized with the recommended N and K levels (100 kg N ha^–1 as ammonium sulphate and 50 kg K ha^–1 as muriate of potash) and half the recommended level of P (25 kg ha^–1 as super phosphate). The inoculation was made into dry nursery beds and the beds were flooded when the seedlings were about 25 cm high, in 15 days. Twenty-eight-day old seedlings were transferred to pots filled with well puddled soil flooded with 5 cm of standing water. Based on the increase in grain yield and total biomass, Glomus intraradices and Acaulospora sp. were considered efficient and suitable for inoculation into rice nurseries.     

Population size and diversity of Frankia in soils of Ceanothus velutinus and Douglas-fir stands

The influence of host plants on Frankia populations was investigated using soils from Ceanothus velutinus (Dougl.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands. Population sizes of Ceanothus-infective Frankia in the soils were measured using plant bioassays with C. velutinus, C. sanguineus (Pursh), and C. integerrimus (H. & A.) as trap plants. The Frankia population in soil from the C. velutinus stand soil was about 10 times higher than that from the Douglas-fir stand. This result supports previous reports that, although the presence of host plants increases Frankia populations, Frankia persist without host plants. Nodulation capacities of the three trap plants were not significantly different. All nodules showed N₂ fixation activity using the acetylene reduction assay. The diversity of Frankia that nodulated trap plants was examined using repetitive intergenic DNA and the polymerase chain reaction (rep-PCR). A newly designed, direct repeat sequence and a BOX sequence were used as rep-PCR primers. The results showed that infective Frankia in the two soils contained a common group of Frankia as well as some Frankia strains unique to each soil. The level of host specificity of the infective Frankia was low; however, one group of Frankia nodulated only C. integerrimus seedlings. Taken together, the results suggest that the higher populations in the soil from the C. velutinus stand may be due to preferential increases in particular groups of Frankia.