Autotoxicity of the soil of consecutively cultured tea plantations on tea (<Emphasis Type="Italic">Camellia sinensis</Emphasis>) seedlings

The production and quality of Tie-Guan-Yin tea (Camellia sinensis) decrease with time after continuous picking over multiple years. However, it is unclear how the soils of consecutively cultured tea plantations affect the growth of tree seedlings. In this study, soil samples were collected from 4-, 9-, and 30-age Tie-Guan-Yin plantations within the original production area, Longjuan town, Anxi County, China. The toxicity of soil samples were tested by laboratory bioassay. Then, new tea seedlings were transplanted in situ into the land of three age tea plantations. One year after transplantation, the growth indexes, physiological parameters (protective enzymes and primary metabolites), photosynthesis parameters, and main tea quality indicators were measured. The results showed that the 4-, 9-, and 30-age soils inhibited lettuce root growth by 10.32, 24.19, and 48.04 %, respectively. The consecutively cultured soil negatively impacted on the growth, physiology, photosynthesis, and overall quality of transplanted tea seedlings. For example, seedlings grown in the 30-age soil had 20 % lower growth rates, 17 % less soluble sugar, 28 % less soluble protein, 37 % less polyphenol, 34 % less theanine, 25 % less amino acid, 37 % less caffeine, and 40 % less of eight catechols than tea seedlings grown in new soil with no history of tea production. These results indicated that the soils of consecutively cultured tea plantations resulted in significant autotoxicity which negatively affected tea seedling growth, metabolism, tea yield, and tea quality. Greater understanding of the causes and mechanisms of autotoxicity is critical to the reclamation of longstanding tea plantation and improvement of the yield and quality of the tea they produce.     

Soil inoculation of lodgepole pine seedlings alters root-associated fungal communities but does not improve seedling performance in beetle-killed pine stands

Extensive tree mortality in forests can change the community composition of soil fungi altering seedling establishment, a process critical to forest restoration. Disturbances that result in the loss of ectomycorrhizal fungi, in particular, may impede the establishment of tree species reliant on these symbionts for their survival. Inoculation of seedlings with soil from intact forests may improve the establishment of seedlings in such disturbances but the method has rarely been tested in the field. Here, we assess whether soil inoculation improves lodgepole pine (Pinus contorta var. latifolia) seedling performance in conspecific stands with high levels of tree mortality caused by a mountain pine beetle (Dendroctonus ponderosae) outbreak and whether underlying soil type modifies inoculation effects. We first inoculated seedlings in a growth chamber with small amounts of soils (5% volume) originating from either intact (<10%) or “beetle-killed” (>70% pine basal area killed) conspecific stands or added no soil inoculum and, after 4 months, transplanted them into 15 beetle-killed stands. After two growing seasons, root-associated fungal communities of seedlings receiving inoculum from intact stands differed in composition from those receiving inoculum from beetle-killed stands or no inoculum. However, inoculation had no effect on seedling survival, height, or biomass. Site properties, including soil texture and the resident fungal community composition, overwhelmed the effect of soil inoculation on seedling performance. Seedling survival and shoot mass was higher in sandy than loamy soils. Restoration to improve seedling performance in beetle-killed stands should consider stand-level treatments as soil inoculation at the level evaluated was ineffective.     

Consequences of inoculation with native arbuscular mycorrhizal fungi for root colonization and survival of <Emphasis Type="Italic">Artemisia tridentata</Emphasis> ssp. <Emphasis Type="Italic">wyomingensis</Emphasis> seedlings after transplanting

In arid environments, the propagule density of arbuscular mycorrhizal fungi (AMF) may limit the extent of the plant–AMF symbiosis. Inoculation of seedlings with AMF could alleviate this problem, but the success of this practice largely depends on the ability of the inoculum to multiply and colonize the growing root system after transplanting. These phenomena were investigated in Artemisia tridentata ssp. wyomingensis (Wyoming big sagebrush) seedlings inoculated with native AMF. Seedlings were first grown in a greenhouse in soil without AMF (non-inoculated seedlings) or with AMF (inoculated seedlings). In spring and fall, 3-month-old seedlings were transplanted outdoors to 24-L pots containing soil from a sagebrush habitat (spring and fall mesocosm experiments) or to a recently burned sagebrush habitat (spring and fall field experiments). Five or 8 months after transplanting, colonization was about twofold higher in inoculated than non-inoculated seedlings, except for the spring field experiment. In the mesocosm experiments, inoculation increased survival during the summer by 24 % (p?=?0.011). In the field experiments, increased AMF colonization was associated with increases in survival during cold and dry periods; 1 year after transplanting, survival of inoculated seedlings was 27 % higher than that of non-inoculated ones (p?<?0.001). To investigate possible mechanisms by which AMF increased survival, we analyzed water use efficiency (WUE) based on foliar ¹³C/¹²C isotope ratios (δ ¹³C). A positive correlation between AMF colonization and δ ¹³C values was observed in the spring mesocosm experiment. In contrast, inoculation did not affect the δ ¹³C values of fall transplanted seedlings that were collected the subsequent spring. The effectiveness of AMF inoculation on enhancing colonization and reducing seedling mortality varied among the different experiments, but average effects were estimated by meta-analyses. Several months after transplanting, average AMF colonization was in proportion 84 % higher in inoculated than non-inoculated seedlings (p?=?0.0042), while the average risk of seedling mortality was 42 % lower in inoculated than non-inoculated seedlings (p?=?0.047). These results indicate that inoculation can increase AMF colonization over the background levels occurring in the soil, leading to higher rates of survival.     

Soil fumigation and phosphorus supply affect the formation of Pisolithus-Eucalyptus urophylla ectomycorrhizas in two acid Philippine soils

To examine the effects of microbial populations and external phosphorus supply of two Philippine soils on mycorrhizal formation, Eucalyptus urophylla seedlings were inoculated with two Pisolithus isolates and grown in fumigated, reinfested and unfumigated soil fertilized with four rates of phosphorus. The Pisolithus isolates used were collected from under eucalypts in Australia and in the Philippines. Soils were infertile acid silty loams collected from field sites in Pangasinan, Luzon and Surigao, Mindanao.Significant interaction was observed between inoculation, soil fumigation and phosphorus supply on mycorrhizal formation by the Australian isolate in Surigao soil but not in Pangasinan soil. Soil fumigation enhanced mycorrhizal formation by the Australian isolate but did not affect root colonization by the Philippine isolate. Root colonization by the Australian isolate was highest in the reinfested soil while for the Philippine isolate it was highest in the unfumigated soil. The Australian isolate was more effective than the Philippine isolate in promoting growth and P uptake of E. urophylla seedlings in both soils. Total dry weight and P uptake of E. urophylla seedlings inoculated with the Australian isolate were maximum in fumigated and in the reinfested Pangasinan and Surigao soils supplied with 8 mg P kg^-1 soil. In the unfumigated soil, growth of seedlings inoculated with the Australian isolate was significantly reduced. Seedlings inoculated with the Philippine isolate had the largest dry weights and P contents in unfumigated Pangasinan and Surigao soils supplied with 8 mg P kg^-1 soil.These results indicate that the performance of the Australian Pisolithus isolate was markedly affected by biological factors in unfumigated soil. Thus, its potential use in the Philippines needs to be thoroughly tested in a variety of unfumigated soils before its widespread use in any inoculation programme.     

Efficiency of different application methods of biocontrol agents and biocides in control of Fusarium root rot on some citrus rootstocks

Abstract

The efficiency of two biocontrol agents (Trichoderma harzianum NB and Bacillus subtilis NB) and two commercial biocides (Plant Guard and Rhizo-N) in controlling Fusarium root rot disease on some citrus rootstocks was evaluated under artificially infested soil in green house.

Fusrium root rot on citrus rootstocks seedlings i.e. sour orange (SO), volkamer lime (VL), rangpur lime (RP) and cleopatra mandarin (CL) was successfully controlled by dipping the root system of such seedlings in water suspensions of each biological treatment i.e. Trichoderma harzianum (spore suspension 5×10⁶ spore/ml), Bacillus subtilis (cell suspension 8×10⁷ cell/ml), Plant Guard (3 g/l) and Rhizo-N (4 g/l), then transplanted into artificially infested soil with Fusarium solani and drenched with enough water suspension of such biological treatments. Plant Guard (3 g/l) and Rhizo-N (4 g/l) were highly effective treatments in decreasing infection and severity of the disease, Fusarium density in rhizosphere soil and colonization of Fusarium solani in the roots of all tested seedlings.

Meanwhile, root dipping or soil drenching with the same treatments individually gave the least effect in reducing root rot incidenceon all tested rootstocks compared with application of the two methods together.

It should be noted that using biocontrol agents and commercial biocides could be successfully used in controlling root rot pathogens on citrus in commercial greenhouses or under field conditions before transplanting in new reclaimed lands in the desert.     

Mechanism of application nursery cultivation arbuscular mycorrhizal seedling in watermelon in the field

Arbuscular mycorrhizal fungi (AMF) colonisation of plant root facilitates the absorption of nutrients such as phosphorus (P) and enhances plant biotic and abiotic resistance generally. However, arbuscular mycorrhiza (AM) colonisation decreases with application of chemical fertiliser. Here, we investigated whether AMF inoculation in nurseries would facilitate AM colonisation and take physiological and ecological functions in watermelon (Citrullus lanatus) in the field. Pot experiments were carried out to study the change of AMF colonised seedling on physiology and gene expression in nursery site. Field experiments were performed to investigate the effect of nursery AMF inoculation on yield, quality and disease resistance of watermelon in the field. The results showed that nursery‐inoculated seedlings produced more dry matter and root surface area than non‐inoculated seedlings. Expression of the secretory purple acid phosphatase (PAP) genes ClaPAP10 and ClaPAP26 was up‐regulated following AMF colonisation. Accordingly, acid phosphatase activities at the root surface and P concentrations in seedling were enhanced. After transplantation to the field, the shoot dry matter and P concentration in old stem were higher in the nursery AMF inoculated seedlings than that in non‐AMF inoculated seedling. AMF inoculation also induced increase of yields and decrease of wilt disease indexes and soluble sugar content. In addition, acid phosphatase activities and AMF spore densities were increased by nursery‐inoculation in watermelon rhizosphere soil in the field. In conclusion, nursery colonisation AMF seedling enhanced watermelon growth and yield by improving the root growth and P acquisition in nursery cultivating stage, as well as optimised soil properties in the field. Nursery cultivation of watermelon seedling with AMF was an effective technique to reduce wilt disease in continuous cropped management in watermelon.     

Interactions Between Rhizoctonia Root Rot and the Foliar Common Bean Diseases Anthracnose and Rust

The effects of co‐inoculation of Rhizoctonia solani and Colletotrichum lindemuthianum or Uromyces appendiculatus at different inoculum levels were studied on the disease dynamics and on the growth of bean plants under greenhouse conditions. Bean seeds were sown in R. solani‐infested soil. Additional experiments in which seedlings were transplanted to infested soil were also carried out. Conidial suspensions of C. lindemuthianum or uredospores of U. appendiculatus were inoculated onto leaves at plant developmental stages V2 and V3, respectively. Interactions between root rot and the aerial diseases were observed depending on the inoculum levels and on the timing of R. solani inoculation. Anthracnose severity tended to be higher on R. solani‐infected plants. Conversely, R. solani infection significantly reduced diameter of pustules and rust severity. When seedlings were transplanted to soil infested with low levels of R. solani, root rot severity and density of R. solani in the soil were magnified at high levels of C. lindemuthianum or U. appendiculatus. In these experiments, a synergistic interaction between root rot and anthracnose was observed to affect the plant dry weight. Antagonistic effects on the plant dry weight were found for the combination root rot/rust only when seeds were sown in infested soil.     

The inhibition of seedling growth by crop residues in soil inoculated withPenicillium urticae Bainer

Summary Laboratory experiments were conducted to determine the effects of crop residues, without and withPenicillium urticae Bainer inoculation, on growth of wheat seedlings in soil. Fifty grams of Sharpsburg silty clay loam soil, containing 1% by weight of incorporated alfalfa, sorghum and corn stover residue, were placed in petri dishes, autoclaved, wetted to 40% moisture, and incubated at 24°C. for periods of 2, 3, and 4 weeks. One-half of the petri dishes were inoculated withP. urticae. Germination and seedling-shoot measurements were taken after 7 days of growth.The results of this study showed that (1) inoculation of soil generally reduced seedling height regardless of the residue treatment; (2) inoculation of soil containing corn and sorghum residues resulted in greater tissue production but reduced height of seedlings as compared to non-inoculated soils; and (3) in the absence of residues, the inoculated control soils were a better growth medium for wheat seedlings than were the non-inoculated control soils. In addition, alfalfa residues, especially in the presence ofP. urticae, were strongly inhibitory to the wheat seedlings, causing curling and reduced wheat-seedling root growth.Joint contribution from University of Nebraska and Soil and Water Conservation Research Division, Agricultural Research Service, U.S. Department of Agriculture, and Nebraska Agricultural Experiment Station, Lincoln, Nebraska, cooperating. Published with the approval of the Director as Paper No. 1242, Journal Series, Nebraska Agricultural Experiment Station.     

Contrasting response of seedlings of two tropical species Clusia minor and Clusia multiflora to mycorrhizal inoculation in two soils with different pH

Differences in mycotrophic growth and response to phosphorus (P) fertilization were studied in seedlings of two woody native species: Clusia minor L. and Clusia multiflora H.B.K. from a cloud montane forest of tropical America. Greenhouse investigation was undertaken to determine the relationships between mycorrhizal dependency of host species associated with P utilization and growth in two different soils contrasting in pH (acidic and neutral) and nutrient content. Four treatments were performed: sterilized soil; sterilized soil plus 375 mg/kg of triple superphosphate (TSP); sterilized soil inoculated with Scutellospora fulgida (20 g/pot); and sterilized soil plus S. fulgida and TSP, with 10 replications per treatment for the two species. Results showed that both Clusia species presented high growth response to increasing P availability, which indicates that the root morphology (magnolioid roots) of these species is not a limiting factor for the incorporation of P from soils. Plants inoculated with arbuscular mycorrhizal fungi (AMF) in acidic soil had significantly increased shoot and root biomass, leaf area and height, in comparison to the biomass of P-fertilized plants and nonmycorrhizal plants. In neutral soil, seedlings of C. minor and C. multiflora were negatively affected by inoculation with AMF. In contrast, a significant decrease in growth was observed when inoculated plants were compared with noninoculated plants on neutral soil. Results indicate that an increase in the availability of a limiting nutrient (P) can turn a balanced mutualistic relationship into a less balanced nonmutualistic one.     

Mycorrhiza formation and growth of Eucalyptus globulus seedlings inoculated with spores of various ectomycorrhizal fungi

 As many eucalypts in commercial plantations are poorly ectomycorrhizal there is a need to develop inoculation programs for forest nurseries. The use of fungal spores as inoculum is a viable proposition for low technology nurseries currently producing eucalypts for outplanting in developing countries. Forty-three collections of ectomycorrhizal fungi from southwestern Australia and two from China, representing 18 genera, were tested for their effectiveness as spore inoculum on Eucalyptus globulus Labill. seedlings. Seven-day-old seedlings were inoculated with 25 mg air-dry spores in a water suspension. Ectomycorrhizal development was assessed in soil cores 65 and 110 days after inoculation. By day 65, about 50% of the treatments had formed ectomycorrhizas. By day 110, inoculated seedlings were generally ectomycorrhizal, but in many cases the percentage of roots colonized was low (<10%). Species of Laccaria, Hydnangium, Descolea, Descomyces, Scleroderma and Pisolithus formed more ectomycorrhizas than the other fungi. Species of Russula, Boletus, Lactarius and Hysterangium did not form ectomycorrhizas. The dry weights of inoculated seedlings ranged from 90% to 225% of the uninoculated seedlings by day 110. Although plants with extensively colonized roots generally had increased seedling growth, the overall mycorrhizal colonization levels were poorly correlated to seedling growth. Species of Laccaria, Descolea, Scleroderma and Pisolithus are proposed as potential candidate fungi for nursery inoculation programs for eucalypts. Accepted: 7 May 1998     

Plant growth-promoting rhizobacteria affect the growth and nutrient uptake of Fraxinus americana container seedlings

Plant growth-promoting rhizobacteria (PGPR) are important catalysts that regulate the functional properties of agricultural systems. However, there is little information on the effect of PGPR inoculation on the growth and nutrient accumulation of forest container seedlings. This study determined the effects of a growth medium inoculated with PGPR on the nutrient uptake, nutrient accumulation, and growth of Fraxinus americana container seedlings. PGPR inoculation with fertilizer increased the dry matter accumulation of the F. americana aerial parts with delayed seedling emergence time. Under fertilized conditions, the accumulation time of phosphorous (P) and potassium (K) in the F. americana aerial parts was 13 days longer due to PGPR inoculation. PGPR increased the maximum daily P and K accumulations in fertilized seedlings by 9.31 and 10.44 %, respectively, but had little impact on unfertilized ones. Regardless of fertilizer application, the root exudates, namely sugars, amino acids, and organic acids significantly increased because of PGPR inoculation. PGPR inoculation with fertilizer increased the root, shoot, and leaf yields by 19.65, 22.94, and 19.44 %, respectively, as well as the P and K contents by 8.33 and 10.60 %, respectively. Consequently, the N, P, and K uptakes increased by 19.85, 31.97, and 33.95 %, respectively. Hence, PGPR inoculation with fertilizer can be used as a bioenhancer for plant growth and nutrient uptake in forest container seedling nurseries.     

Experimentation on Degradation of Petroleum in Contaminated Soils in the Root Zone of Maize (Zea Mays L.) Inoculated with Piriformospora Indica

Plant-based methods such as rhizodegradation are very promising for the remediation of petroleum-contaminated soils. Associations of plants with endophytes can further enhance their phytoremediation potential. In this study, a rhizobox experiment was conducted to investigate whether inoculation with the root-colonizing fungus Piriformospora indica could further enhance the degradation of petroleum hydrocarbons in the root zone of maize (Zea mays L.). The rhizoboxes were subdivided into compartments in accordance with distance from the plants. After filling the boxes with soil from a petroleum-contaminated site, seedlings that had either been inoculated with P. indica or not were grown in the middle compartments of the rhizoboxes and grown for 64 days. A plant-free treatment was included for control. The presence of roots strongly increased the counts of total and petroleum-degrading soil bacteria, respiration, dehydrogenase activity, water-soluble phenols and petroleum degradation. All these effects were also found in the soil adjacent to the middle compartments of the rhizoboxes, but strongly decreased further away from it. Inoculation with P. indica further enhanced all the recorded parameters without changing the spatial pattern of the effects. Inoculated plants also produced around 40% more root and shoot biomass than noninoculated plants and had greener leaves. Together, the results indicate that the treatment effects on the recorded soil microbial and biochemical parameters including petroleum hydrocarbon degradation were primarily due to increased root exudation. Irrespectively of this, they show that maize can be used to accelerate the rhizodegradation of petroleum hydrocarbons in soil and that inoculation with P. indica can substantially enhance the phytoremediation performance of maize.     

Frankia inoculation,soil biota,and host tissue amendment influence Casuarina nodulation capacity of a tropical soil

The effects of soil biota, Frankia inoculation and tissue amendment on nodulation capacity of a soil was investigated in a factorial study using bulked soil from beneath a Casuarina cunninghamiana tree and bioassays with C. cunninghamiana seedlings as capture plants. Nodulation capacities were determined from soils incubated in sterile jars at 21 °C for 1, 7, and 28 days, after receiving all combinations of the following treatments: ± steam pasteurization, ± inoculation with Frankia isolate CjI82001, and ± amendment with different concentrations of Casuarina cladode extracts. Soil respiration within sealed containers was determined periodically during the incubation period as a measure of overall microbial activity. Soil respiration, and thus overall microbial activity, was positively correlated with increasing concentrations of Casuarina cladode extracts. The nodulation capacity of soils inoculated with Frankia strain Cj82001 decreased over time, while those of unpasteurized soils without inoculation either increased or remained unaffected. The mean nodulation capacity of unpasteurized soil inoculated with Frankia CjI82001 was two to three times greater than the sum of values for unpasteurized and inoculated pasteurized soils. Our results suggest a positive synergism between soil biota as a whole and Frankia inoculum with respect to host infection.     

The effects of inoculum density and physical factors on the assessment of disease caused by Sclerotium rolfsii

Greenhouse and laboratory experiments were conducted to determine the effects of various physical factors on the assessment of disease caused by Sclerotium rolfsii using field and artificially infested soils. Lentil(Lens esculenta Moench) seedlings growing in trays or pots with sand were inoculated by surrounding them with a layer of soil infested with the pathogen. The number of dead plants was maximal within a 10-day period following inoculation. Seedling mortality increased with the number of sclerotia in the soil to a maximum that depended on seedling spacing, depth of the soil layer, and soil type.     

Restoration of high altitude forests in an area affected by a wildfire: Polylepis australis Bitt. seedlings performance after soil inoculation

Key message

Outplanted Polylepis australis seedling growth, survival and mycorrhizal response were not influenced by inoculation with soil from different vegetation types. Seedling inoculation would not be essential for reforestation practices.

Abstract

Polylepis forests are one of the most endangered high mountain ecosystems of South America and reforestation with native Polylepis species has been recommended. To determine whether native soil inoculation could help in reforestation success, a field trial was set up to evaluate the response of outplanted P. australis seedlings to the inoculation with soils from three vegetation types (a grassland, a mature forest and a degraded forest) and a sterile soil, used as control. We evaluated seedlings performance: growth and survival for 18 months, root/shoot ratio, phosphorous content and arbuscular mycorrhizal fungal (AMF) colonization. To interpret performance patterns we evaluated the colonization potential of the three inoculum soils and the changes of the AMF community composition of the seedlings rhizosphere in relation to inoculation treatment and season. Our main results showed no significant differences in seedlings survival and growth between treatments. The colonization potential of grassland and degraded forest soils was ~25 times greater than mature forest soil and specific spore density of some morphospecies varied with season. However, AMF spore community of seedlings rhizosphere became homogenized after outplanting and was similar between treatments after 12 months. Therefore, we conclude that soil inoculation is not essential for outplanted P. australis survival and increase in height, and thus all the tested soils could be used as inocula, including grassland soils which in practice are the easiest to collect.     

Ectomycorrhizal fungi promote growth of <Emphasis Type="Italic">Shorea balangeran</Emphasis> in degraded peat swamp forests

Shorea balangeran is an important component of peat swamp forests in Southeast Asia and is an important source of timber. However, S. balangeran has been decreasing in number due to overexploitation. The objective of this study was to investigate the effect of inoculation of native ectomycorrhizal (ECM) fungi on growth of S. balangeran in degraded peat swamp forest. Spores of Boletus sp., Scleroderma sp., and Strobilomyces sp. were collected from natural peat swamp forest in Indonesia. Seedlings of S. balangeran were inoculated with or without (control) spores and grown in sterilized peat soil under nursery conditions for 6 months. Then, the seedlings were transplanted into a degraded peat swamp forest and grown for 40 months. ECM colonization was 59–67% under nursery conditions and increased shoot height and weight. Shoot height, stem diameter, and survival rates were higher in inoculated seedlings than in control 40 months after transplantation. The results suggest that inoculation of native ECM fungi onto native tree species is useful for reforestation of degraded peat swamp forests.     

Hebeloma crustuliniforme modifies root hydraulic responses of trembling aspen (Populus tremuloides) seedlings to changes in external pH

The main objective of the study was to compare the effects of short-duration pH treatments on root hydraulic properties in trembling aspen (Populus tremuloides) seedlings that were either inoculated with the ectomycorrhizal fungus Hebeloma crustuliniforme or remained non-inoculated (control). Inoculated and non-inoculated plants were exposed in solution culture to the root zone pH ranging from 4 to 9 and their root hydraulic conductivity was examined using the hydrostatic method and after subjecting the plants to treatments with 100 ??M HgCl₂ (aquaporin blocker) and 0.02% trisodium 3-hydroxy-5,8,10-pyrenetrisulfonic acid (apoplastic transport tracer). In a separate experiment, pure cultures of H. crustuliniforme were also grown on a slid medium with the pH ranging from 4 to 9 to determine their pH growth optimum and changes in medium pH over time in the presence and absence of 8 mM NH₄NO₃. When grown in pure culture, H. crustuliniforme demonstrated maximum growth at pH 7?C8 and was capable of modifying the pH of its growth media, especially in the presence of NH₄NO₃. The plants that were inoculated with H. crustuliniforme had a maximum root hydraulic conductivity at pH 7. At this pH, root hydraulic conductivity was significantly higher compared with non-inoculated plants and showed greater sensitivity of root water transport to pH changes relative to non-inoculated seedlings. Relative apoplastic flux was largely unaffected by pH in inoculated seedlings. Fungal inoculation modified the response of root hydraulic conductivity to pH. The increased root hydraulic conductivity in inoculated seedlings was likely due to an increase in aquaporin-mediated cell-to-cell water transport, particularly at the higher pH. A possible role of fungal aquaporins in the root hydraulic conductivity responses of mycorrhizzal plants should be examined.     

The phytoprotective effects of arbuscular mycorrhizal fungi on Enterolobium contorstisiliquum (Vell.) Morong in soil containing coal-mine tailings

The purpose of this study was to evaluate the effects of arbuscular mycorrhizal fungi (AMF) on pacara earpod tree (Enterolobium contorstisiliquum) growth and phytoprotection in soil containing coal-mining waste. A greenhouse experiment was carried out with three inoculation treatment groups (non-inoculated, inoculated with Rhizophagus clarus, and inoculated with Acaulospora colombiana) in two substrates (0 or 30% tailings). After 90 days the seedlings were collected to quantify growth parameters, quality, mycorrhizal root colonization rate, and leaf content of chlorophylls and carotenoids. Macronutrients were quantified in the shoots; Cu, Zn, and Mn levels were measured in the shoots and roots; and glomalin content was measured in the rhizosphere. Colonization by A. colombiana (40%) promoted phytoprotection and better growth in seedlings planted in partial tailing substrate, due to the lower Cu (1.04 mg kg^?1) and Zn (13.4 mg kg^?1) levels in shoot dry mass and reduced translocation of these elements to the shoots. A. colombiana increased soil glomalin concentrations (2.98 mg kg^?1) and the accumulation of nutrients necessary for synthesizing chlorophylls and carotenoids in the leaves. Colonization by R. clarus (81%) produced no phytoprotective effects.     

氮沉降及菌根真菌对长白落叶松苗木根系构型及根际酶活性的影响

为探究氮沉降和接种菌根真菌对长白落叶松苗木根系构型和根际土壤酶活性的影响,以1年生长白落叶松(Larix olgensis)的盆栽菌根苗(简称+M,混合接种8种外生菌根真菌)和非菌根苗(简称-M,未接种处理)为研究对象,设置4个氮沉降处理(不施氮(0N,0 kg·N·hm^-1·yr^-1)、低氮(LN,15 kg·N·hm^-1·yr^-1)、中氮(MN,30 kg·N·hm^-1·a^-1)和高氮(HN,60 kg·N·hm^-1·a^-1)),测定直径0~0.5 mm根系的总根长、总表面积、总体积和根尖数等根系形态指标,对比分析氮沉降和接种菌根真菌处理对苗木根际土壤酶(β-1,4葡萄糖苷酶(BG)、亮氨酸氨基肽酶(LAP)、β-1,4-N-乙酰-氨基葡糖氨糖苷酶(NAG)、酸性磷酸酶(ACP)和碱性磷酸酶(ALP))活性的影响。结果表明:①长白落叶松苗木直径0~0.5 mm根系的总根长、总表面积、总体积和根尖数均随氮浓度的递增呈下降的趋势;在0N、LN和MN处理下,-M处理的根系形态指标均高于+M处理。②随氮浓度增加,+M和-M处理苗木根际土壤中BG、LAP、ACP和ALP活性均呈先增加后下降的趋势,而NAG活性呈下降的趋势。③+M和-M处理下,长白落叶松直径0~0.5 mm根系的形态指标与根际土壤BG活性均呈显著负相关关系(P<0.05);除根尖数外,其它根系形态指标与NAG活性相关性均为正相关(P<0.05)。综上所述,苗木菌根化处理削弱了氮沉降对落叶松苗木根系构型的影响;而低氮处理下,+M处理对苗木根际土壤酶的活化程度高于-M处理。     

Recovery of Soil Ammonia Oxidation After Long-Term Zinc Exposure Is Not Related to the Richness of the Bacterial Nitrifying Community

A soil sterilization–reinoculation approach was used to manipulate soil microbial diversity and to assess the effect of the diversity of the ammonia-oxidizing bacteria (AOB) on the recovery of the nitrifying community to metal stress (zinc). Gamma-irradiated soil was inoculated with 13 different combinations of up to 22 different soils collected worldwide to create varying degrees of AOB diversity. Two months after inoculation, AOB amoA DGGE based diversity (weighted richness) varied more than 10-fold among the 13 treatments, the largest value observed where the number of inocula had been largest. Subsequently, the 13 treatments were either or not amended with ZnCl₂. Initially, Zn amendment completely inhibited nitrification. After 6 months of Zn exposure, recovery of the potential nitrification activity in the Zn amended soils ranged from <10 % to >100 % of the potential nitrification activity in the corresponding non-amended soils. This recovery was neither related to DGGE-based indices of AOB diversity nor to the AOB abundance assessed 2 months after inoculation (p?>?0.05). However, recovery was significantly related (r?=?0.75) to the potential nitrification rate before Zn amendment and only weakly to the number of soil inocula used in the treatments (r?=?0.46). The lack of clear effects of AOB diversity on recovery may be related to an inherently sufficient diversity and functional redundancy of AOB communities in soil. Our data indicate that potential microbial activity can be a significant factor in recovery.