Mycorrhizas and C and N transformations in the rhizospheres of Pinus sylvestris,Picea abies and Betula pendula seedlings

Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) seedlings were grown in a greenhouse for four months in three different soils. The soils were from a field afforestation site on former agricultural land: soil from a pine site, soil from a spruce site and soil from a birch site. Pots without seedlings were included. The aim was to discover, independent of the effects of the different quality of aboveground litter and microclimate under the tree species, whether the roots change the microbial activities and chemical characteristics of the soil, whether the changes are dependent on the tree species, and whether the changes vary in different soils. Pine, spruce and birch had, on average, five, one and six meters of roots, respectively. Birch had by far the highest number of short root tips, on average 11 450 per seedling, compared to 1900 and 450 in pine and spruce seedlings, respectively. The majority of the short roots of pine and spruce were brown sheathed mycorrhizas, and those of birch were mycorrhizas in an early stage of development. The seedlings caused no major changes in either the soil pH or the concentrations of nutrients in the soils, but did affect the microbial characteristics of the soils. The effect of the tree species did not differ in different soils. Microbial biomass C and N, C mineralization rate and the concentration of ergosterol were all higher under birch and pine than under spruce and in plantless soils. Nitrate concentrations were lowest under pine and birch, but rates of net N mineralization, nitrification and denitrification did not differ under different seedlings. The stimulative effect of pine and especially birch on soil microbes was possibly due to them having more roots and releasing more root exudates to soil. There were, however, indications that not only the length/mass of roots determined the changes in microbial activities, but also differences in root activities per unit of root or in the quality of root exudates.     

6种外生菌根真菌对西南桦幼苗的接种效应

【背景】西南桦是兼具内生、外生菌根的典型菌根营养型树种,菌根化育苗是其壮苗培育的有效措施。【目的】揭示外生菌根真菌对西南桦无性系幼苗生长和养分含量的影响,为其菌根化育苗筛选优良外生菌根真菌提供科学依据。【方法】以BY1、FB4、FB4+和A5等4个西南桦优良无性系为研究对象,选用土生空团菌(Cenococcumgeophilum)、松乳菇(Lactariusdeliciosus)、黄硬皮马勃(Scleroderma flavidum)、多根硬皮马勃(S. polyrhizum)、褐环乳牛肝菌(Suillus luteus)和红绒盖牛肝菌(Xerocomuschrysenteron)6个外生菌根真菌进行盆栽接种试验,分析接种处理间及无性系间苗高、地径、生物量以及养分含量差异。【结果】6个菌种均能与西南桦无性系幼苗形成外生菌根共生体,接种多根硬皮马勃与黄硬皮马勃显著促进了幼苗生长和养分吸收(P0.05),说明其与幼苗的亲和力明显优于其它菌种。尽管菌根侵染率在4个无性系之间无显著差异(P≥0.05),但各菌种对FB4、BY1幼苗生长的促进作用显著强于其它2个无性系。【结论】多根硬皮马勃和黄硬皮马勃可作为西南桦菌根化育苗的优选菌种。     

Characterization of wall-bound invertase isoforms of Picea abies cells and regulation by ectomycorrhizal fungi

In culture, the ectomycorrhiza-forming fungi Amanita muscaria (Pers. ex Fries) Hock. and Hebeloma crustuliniforme (Bull. ex Fries) Quel. only grow on media with glucose or fructose but not with sucrose as sole carbohydrate source. This is due to their lack of wall-bound invertase activity. Therefore, utilization of sucrose by the fungi within a mycorrhizal association is believed to depend on the wall-bound invertase activity of the host. This enzyme activity was studied in the apoplast of suspension cultured cells of Picea abies (L.) Karst. An ionically and a tightly wall-bound isoform of acid invertase were found that function as β-d -fructofuranoside-fructohydrolases (EC 3.2.1.26). The ionically bound enzyme could be easily released from walls of intact cells with buffer of high ionic strength. In its native form, the ionically bound invertase isoform is a monomeric protein with a molecular mass of 61 kDa, as determined by gel filtration and SDS-PAGE. Glycoprotein nature of the enzyme was demonstrated with antibodies directed against the digoxigenin-labeled protein. The K_m values of both enzymes for sucrose, their natural substrate, are relatively high (ionically bound invertase K_m= 16 mM, tightly bound invertase K_m= 8.6 mM). Activity of both wall-bound invertase isoforms strongly depends on the apoplastic pH. They have a narrow pH-optimum and exhibit highest activity at pH 4.5. with elevated activity between pH 4.5 and 6.0. Furthermore, fructose acts as competitive inhibitor of both isoforms, whereas glucose is not inhibitory. Unloading of sucrose from host cells to the apoplastic interface of the Hartig net in ectomycorrhizae appears to depend on the rate of hydrolysis by the wall-bound invertase of the host. Since the activity of the plant invertase depends on the actual pH value and the fructose concentration in the mycorrhizal interface, we suggest that the fungus can actively influence the activity of the plant invertase by acidification of the cell wall and by fructose uptake. Thus, the fungus itself can regulate its own supply of glucose and fructose.     

Effects of aluminium on growth and nutrient uptake of Betula pendula seedlings

The response to aluminium concentrations was evaluated for birch seedlings ( Betula pendula Roth, formerly Betula verrucosa Ehrh.) by using a growth technique that provides stable internal concentrations of nutrients in plants. Aluminium was added as aluminium nitrate and aluminium chloride and pH was kept at 3.8±0.2 by adding HCl or NaOH. The seedlings were grown in two different series of nutrient treatments, either with near-optimum conditions (relative addition rate 25% day⁻¹) or with constant nutrient stress (relative addition rate 10% day⁻¹) before the aluminium addition. Growth reduction occurred at aluminium concentrations greater than 3 m M , and lethal effects at aluminium concentrations greater than 15 m M . In plants subjected to near-optimum conditions before aluminium addition, the internal nutrient concentrations decreased with increasing aluminium concentration for all macronutrients. The concentration of the macronutrients N, K and P decreased gradually with increasing aluminium concentration, while the concentration of Ca and Mg decreased fairly abruptly when aluminium concentrations exceeded 1 m M . The same tendency was observed in nutrient stressed birch seedlings, but the pattern was more scattered. Relative growth rate of the seedlings was not affected by a low Ca/Al ratio. In all treatments, the molar Ca/Al ratio in/on the roots was below 0.2 at the end of the experiments. As decrease in growth occurs only at high aluminium concentrations, there is no reason to suggest that aluminium in acid soils is growth limiting for natural birch stands.     

Ethylene effects on cambial activity and cell wall formation in hypocotyls of Picea abies seedlings

Ethylene regulation of cell division in the vascular cambium and cell wall formation was studied in hypocotyls of Norway spruce ( Picea abies [L.] Karst.) seedlings. Cuttings from 6-week-old seedlings were placed in water culture to which compounds affecting the synthesis and action of ethylene were added. After a 3-week treatment period, growth, ethylene production, morphology and cell wall composition of the hypocotyls were determined. Addition of high concentrations of the potent ethylene releasing agent 2-chloroethylphosphonic acid (ethrel), which increased ethylene emission by more than twice compared to control plants, inhibited the expansion of xylem cells while stimulating the incorporation of cell wall material, especially cellulose. Addition of small amounts of ethrel, which slightly stimulated ethylene emission, led to increases in the size of xylem cells, the amount of phloem tissue and the number of intercellular spaces in the cortex, and thus to increased hypocotyl diameter. However, no significant change in cell wall composition was detected. When ethylene production was decreased by adding Co²⁺ to the nutrient solution, differentiation of new xylem was disturbed, but the rate of cell division was not affected. Although the incorporation of cell wall material was inhibited, the proportions of lignin and cellulose in the wall appeared to remain unchanged. Silver ions stimulated the expansion of both xylem and cortex cells, but had no significant effect on cell wall formation. We conclude that ethylene has a role in regulating the incorporation of wall carbohydrates.     

秦岭辛家山林区云杉外生菌根真菌多样性

摘要:【目的】为了研究秦岭辛家山林区云杉外生菌根真菌多样性状况。【方法】通过野外调查结合形态学和分子生物学鉴定方法。【结果】与秦岭辛家山林区云杉共生的外生菌根真菌有37 种不同的类型,包括1种子囊菌、34种担子菌和2 种未知种,分属于10科14属,其中丝伞盖属(Inocybe sp.)是优势类群,厌味红菇(Russula nauseosa)是优势种,蜡伞属(Hygrophorus sp.)、丝伞盖属1 (Inocybe sp.1)、柔膜菌属(Helotiaceae sp.)、Tomentella coerulea、Lactarius deterrimus是常见种,其他31种是少见种。【结论】云杉外生菌根真菌群落优势种的数量较多,而种类相对却较少;少见种的数量较少,而种类相对却较多;对于西部生态系统极度退化干旱区,鉴定出一些少见种进一步的开发和利用具有非常重要的现实意义。     

Responses of ectomycorrhizal Populus tremuloides and Betula papyrifera seedlings to salinity

Roots of trembling aspen (Populus tremuloides Michx.) and paper birch (Betula papyrifera Marsh.) seedlings were inoculated with Hebeloma crustuliniforme or Laccaria bicolor and treated with 25 mM NaCl for 6 weeks. Both tree species appeared to be relatively tolerant of the applied NaCl treatment and did not develop visible leaf symptoms that are characteristic of salt injury. Salt treatment reduced total dry weights in aspen and birch, but did not significantly affect transpiration rates and root hydraulic conductance. Salt-treated ectomycorrhizal aspen maintained higher root hydraulic conductance compared with non-mycorrhizal plants. Na and Cl concentrations increased in shoots and roots of mycorrhizal and non-mycorrhizal aspen and birch in response to NaCl treatment. Roots of NaCl-treated aspen inoculated with H. crustuliniforme had over twofold higher concentrations of Na compared with non-mycorrhizal NaCl-treated plants. Similarly to aspen, Na and Cl concentrations increased in roots and shoots of NaCl-treated birch seedlings. However, in birch, there were no significant differences in Na and Cl concentrations between mycorrhizal and non-mycorrhizal plants. The results suggest that salt exclusion by the ectomycorrhizal associations is host-specific or/and that the processes leading to salt exclusion are activated in ectomycorrhizal plants by a threshold salt level which may vary between plant species.     

Effects of aluminium on growth and root reactions of phosphorus stressed Betula pendula seedlings

The impact of two constant non-toxic levels of Al stress (0.2 and 0.4 mM) on growth and ³²P uptake capacity on sub-optimal (P-limited) Betula pendula seedlings grown in sand culture was examined.Seedling growth was under optimum controlled conditions in a growth chamber where nutrient additions were made at a predetermined relative addition rate (R_A) of 10% day^-1. Three treatment groups of seedlings 0, 0.2 and 0.4 mM Al were harvested at 15, 29 and 42 days. The excised roots were exposed to a ³²P-labelled solution for 15 minutes to measure their capacity for P uptake. Growth was determined by weighing the roots, stems and leaves of the seedlings.Growth data showed that relative growth rate (R_G) should equal the R_A of P the most limiting nutrient, which was supplied at P/N 3% instead of an optimal 15%. Therefore, Ingestad's theory can also be used succesfully in sand culture and this may be particularly important for future studies of root and rhizosphere exudates. Low levels of Al (< 0.2 mM) in combination with low P supply significantly lowered the R_G of the birch seedlings by further reducing P supply. However, previous studies of birch seedling growth and nutrient uptake using Ingestad's solution culture technique with optimumal P supply did not show any effect of Al on growth untill the Al was in excess of 3 mM. Aluminium was not directly toxic to the plants and therefore roots could respond to the ³²P bioassay.     

Effects of aluminium on the growth and mineral composition of Betula pendula Roth

Aluminium (Al) is rhizotoxic and is often present in acidic soils at activities high enough to inhibit root elongation. The objectives of the present study were to assess the level of Al tolerance in different races of Betula pendula Roth (Silver Birch) and to investigate how growth and nutrient acquisition were affected by Al. A solution culture technique was employed which simulated natural soil solutions. Aluminium at low concentrations (2 and 5 mg l(-1)), enhanced the growth of two races of B. pendula originating from soils poor in Al (FM and KP). In contrast, Al, at all concentrations tested, inhibited growth in an Al-sensitive race (KR) whose provenance was a calcareous soil. At concentrations >/=10 mg l(-1), Al reduced growth in FM and KP races, while growth increased with increasing Al (up to 25 mg l(-1)) in the Al-tolerant, SMM, race. Aluminium altered both root and leaf architecture. Low Al concentrations (<5 mg l(-1)) significantly increased leaf expansion, and high concentrations (>25 mg l(-1)) reduced leaf expansion. In the Al-sensitive race, KR, there was a loss of apical dominance, and both lateral and primary roots were stunted and swollen, with increasing Al concentrations. These results demonstrated pronounced racial differences in tolerance to Al by B. pendula that could be predicted from the soil environment of each race.     

青蒿素对外生菌根真菌化感效应

青蒿素是治疗疟疾的首选药物,主要从黄花蒿(Artemisia annua L.)中提取,然而黄花蒿在生长过程中会向周围环境分泌青蒿素。为正确评估青蒿素对森林生态系统中的重要成分""外生菌根真菌的影响,试验以重庆地区有代表性的两株外生菌根真菌——褐环乳牛肝菌(Suillus luteus)Sl 8和松乳菇(Lactarius delicious)Ld 3为材料,研究了青蒿素对菌丝生长,H+和有机酸分泌,以及养分吸收的影响。结果表明,在液体培养基中加入青蒿素,外生菌根真菌的生长受到明显抑制,菌丝生物量降幅高达26.89%(Ld 3)和89.13%(Sl 8);Ld 3分泌H+和草酸的能力增强,而Sl 8分泌量下降。随着青蒿素浓度的增加,菌丝的N、P、K含量及吸收量显著减少。当培养基中青蒿素达到80 mg/L时,Ld 3的N、P、K吸收量比不加青蒿素的处理分别降低了50.55%、46.30%和42.28%;Sl 8几乎丧失对N、P、K的吸收能力。说明青蒿素不同程度地抑制了外生菌根真菌的生长和养分吸收,但对H+和草酸的分泌作用因菌株不同而异。     

Diversity and community composition of ectomycorrhizal fungi in a dry deciduous dipterocarp forest in Thailand

Large forest areas of South-East Asia, are dominated by the Dipterocarpaceae tree family, which contains many important timber species. Unlike many other tropical trees, Dipterocarpaceae rely on ectomycorrhizal (ECM) root symbiosis for their mineral nutrition. This study aims to document the richness and community composition of ECM fungi in a dry deciduous forest in Thailand. Combining morphological and molecular identification methods revealed 69 species of ECM fungi that belong to 17 phylogenetic lineages. The /russula-lactarius, /tomentella-thelephora, /sordariales, /sebacina and /cantharellus lineages were the most species-rich. The fungal richness is comparable to other tropical rain forest sites, but the phylogenetic community structure has elements of both tropical and temperate ecosystems. Unlike tropical rain forests, the Cenococcum geophilum complex was one of the most frequent fungal taxa that had a relatively high ITS genetic diversity over the small sampling area. This study provides the first snapshot insight into the fungal community of dry dipterocarp forests. However, it is necessary to broaden the spatial and temporal scales of sampling to improve our understanding of the below-ground relations of dry and humid tropical forests.     

红皮云杉外生菌根菌单接种及混合接种对苗木生长的影响

以提高外生菌根真菌对红皮云杉苗木促生长效果为目的,在前期研究的基础上,采用菌株配对培养的方法对获得的云杉外生菌根真菌进行混合接种菌株组合筛选;采用沟施菌剂方法,对3年生红皮云杉移床苗进行外生菌根菌菌株组合野外混合接种试验,同时以各菌株野外单接种作为对照,研究外生菌根真菌单接种及混合接种对红皮云杉苗木生长的影响。试验结果表明:供试菌株及菌株组合对红皮云杉苗木生长均有一定的促进作用。菌株L15促生长效果最佳,接种100d苗木高生长高于对照30.88%,地径高于对照15.29%。组合L15/025与L15/009促苗木生长效果低于单接种L15的效果,高于单接种009和025的效果。接种菌株010和组合L15/025的苗木与对照相比,叶绿素含量提高差异显著,叶绿素a水平分别高于对照59.15%、54.61%,叶绿素b水平分别高于对照76.34%和67.78%。除接种菌株010的苗木外,其他处理苗木其过氧化氢酶活性与对照相比均有所降低。所有处理苗木的根系活力均低于对照。综上,外生菌根菌高效菌株与一般菌株混合接种会弱化高效菌株自身接种效果;苗木过氧化氢酶活性、苗木根系活力与苗木的生物量间无相关性。     

The effect of elevated CO2 and temperature on the secondary chemistry of Betula pendula seedlings

The effect of elevated atmospheric CO₂ and temperature on resource allocation and secondary chemistry of white birch (Betula pendula Roth) under a non-limiting nutrient and water supply was investigated. Birch seedlings were grown in closed-top chambers exposed to ambient CO₂ and temperature, elevated atmospheric CO₂ (700 ppm), elevated temperature (2°C above ambient) and a combination of elevated CO₂ and temperature for one growing season. Elevated CO₂ significantly increased the total biomass of the seedlings. The combined effect of the elevated CO₂ and temperature treatments further increased the total biomass, but not significantly. The content of nitrogen and water decreased, while some secondary compounds (such as condensed tannins and flavonol glycosides) increased in leaves subjected to CO₂ enrichment. Elevated temperature increased the concentration of total flavone aglycones and decreased that of total HPLC-phenolics in the leaves, due to the decrease in individual flavonol glycosides, cinnamoylquinic acids and (+)-catechin. There were no significant interactive effects between CO₂ and temperature in the phenolic concentrations of the leaves and in the stems, while the number of resin droplets in the top part of the stems showed significant interaction. This clearly implies that carbon allocation into secondary metabolites in the leaves and stems differ under enhanced CO₂ and temperature, and the combined effect of CO₂ and temperature on the herbivore resistance of birches, is lower than that of CO₂ and temperature alone.