Rhizomorph Behaviour in Armillaria mellea (Fr.) Quel.: With one Figure in the text: Saprophytic Colonization of Woody Substrates in Soil

Rhizomorphs put out by Armillaria mellea from small woody inoculain glass tubes of moist soil were tested for their ability tocolonize segments of willow shoots, previously killed by autoclavingand then buried for various periods in soil before inoculationwith A. mellea. The degree of saprophytic colonization of thesesubstrate segments by A. mellea was assessed by reburying themin fresh tubes of moist soil, and recording weekly growth incrementsof rhizomorphs put out from them over a period of 5 weeks. Aperiod of previous burial in soil up to 3 weeks was found notto diminish availability of the substrate segments to A. mellea,but with longer periods substrate value for A. mellea progressivelydeclined. Segments of living, green shoots of willow provideda consistently better substrate for A. mellea than did deadsegments, and these living segments maintained their substratevalue over periods (up to 7 weeks) of previous burial in soil.These results are interpreted in terms of competition betweenA. mellea and other soil fungi. In the infection of living tissues,A. mellea benefits from the exclusion of competitors by hostresistance. In the saprophytic colonization of dead tissues,A. mellea has the advantage of its capacity to decompose celluloseand lignin, which are substrates restricted to a minority ofsoil fungi.     

Infection Foci of Armillaria mellea in First-rotation Hardwoods

Infection foci of Armillaria mellea, often 10–20 m indiameter, were discovered in first-rotation plantings of oakand beech on former arable or heathland sites—they werecommonly associated with thinning stumps containing the fungus.Since the foci were scattered and contained different mycelialtypes of A. mellea it seemed probable that they had arisen asa result of stump infection by basidiospores. There was evidencethat many years had elapsed between stump infection and theproduction of rhizomorphs, and that subsequent growth of thesedepended upon the presence of suitable living roots. Largeroaks seemed little affected whereas many small and medium-sizedtrees had been killed. Armillaria mellea, infection foci in plantations, tree stumps, basidiospores     

Studies on the mechanisms of barley seed deterioration

The type of chemical treatment used to control regrowth from hardwood stumps affects their colonization by fungi. Since such stumps often act as sources of infection for Armillaria mellea this may have important consequences. Ammonium sulphamate generally favours growth of species causing rapid decay, some of which compete well with A. mellea, whereas 2,4,5-trichlorophenoxyacetic acid tends to promote growth of Chondro-stereum purpureum which is replaced by A. mellea. The former treatment is recommended for situations where serious damage from A. mellea seems likely to occur, because the best hope of control is to ensure rapid killing of stump roots. Prompt colonization of stumps was obtained by inoculating the cut surface with spores of a wood-rotting fungus and then treating it with 40% ammonium sulphamate. In birch stumps jointly inoculated with Coriolus versicolor and A. mellea the amount of wood occupied by the latter after 4 yr was greatly reduced by comparison with controls inoculated with A. mellea alone. Stump inoculation might be worth developing for use in valuable plantations and other intensively managed areas such as parks and gardens, especially where measures such as stump excavation are impracticable.     

Twist-to-bend ratios of woody structures

Flexural rigidity (El), or resistance to bending loads, andtorsional rigidity (GJ), or resistance to twisting loads, weremeasured on a variety of woody structures-bamboo culms, threekinds of hardwood trunks, two softwood trunks, two vines, andpine roots. The ratios of these rigidities, EI/GJ, was highestand relatively constant for bamboo and hardwoods, slightly lowerfor softwoods, and lower still for vines and roots. All valueswere substantially above those for circular cylinders of ordinaryisotropic materials; since all specimens were nearly circularin cross-section, the high values reflect the elastic moduliof wood rather than geometric factors. While all material showedsubstantial creep under torsional loading, only the vine, Wisteria,crept appreciably under flexural loading as well. Key words: Wood, trees, flexural rigidity, torsional rigidity, biomechanics     

Evaluation of the heat pulse velocity method for measuring sap flow in Pinus patula

Information on the water use of Pinus patula plantations isrequired to predict the impact of forest plantations on waterresources in South Africa. The heat pulse velocity (HPV) methodis a promising technique for measuring water use by trees, andhas been shown to measure sap flows accurately in a varietyof hardwood trees. This method has not been sufficiently verifiedfor pine trees where the presence of a strongly-defined ringstructure in the sapwood gives rise to a complex radial patternof sap flow. The purpose of this study was to compare wateruptake by cut trees to simultaneous HPV sap flow measurementsin the same tree. Fourteen trees were used for this comparison.Results showed that HPV sap flow estimates consistently overestimatedcut-tree uptake by an average of 49%. The bias is attributedto heat averaging across non-conducting latewood rings. Wateruptake was found to be highly correlated to the product of under-barkcross-sectional area and wound-corrected mean HPV, and it issuggested that this empirical relation provides a more appropriateway of estimating water use by this species. Key words: Heat pulse velocity, sap flow, Pinus patula, transpiration     

Rhizomorph Behaviour in Armillaria mellea (Vahl) Quel: II. Logistics of Infection

The growth of rhizomorphs of Armillaria mellea from small woodyinocula through tubes of soil was characterized by a progressivedecline in weekly growth increments. Initial growth rate wasrelated to the size of the inoculum food-base; the subsequentdecline is attributed partly to depletion of nutrient reservesin the inoculum through fungal respiration and growth, and partlyto competition for nutrients between the main growing apex ofthe rhizomorph and its subordinate branch apices. The vigourof infection of potato tubers by rhizomorphs from such smallwoody inocula increased with size of the inoculum, and decreasedwith increasing distance between inoculum and tuber. When inoculumpotential of A. mellea was low, the fungus was generally overtakenin the tuber tissues by soft-rotting bacteria, which preventedits further advance.     

The Increase in Anchorage with Tree Size of the Tropical Tap Rooted TreeMallotus wrayi, King (Euphorbiaceae)

The mechanical development of the anchorage system of the taprooted tropical speciesMallotus wrayiKing (Euphorbiaceae) wasinvestigated by pulling over and examining trees with a diameterat breast height (d_bh) of 4.2 cm to 14.3 cm. The mode of mechanicalfailure depended upon the size of the tree: thicker trees (d_bhapprox.9 cm) failed in the ground with their tap roots pushing intothe soil on the winchward side; in smaller trees (d_bhapprox.7 cm) the trunk snapped before anchorage failure; and in verysmall trees (of d_bh<6 cm) neither type of failure occurredand the trees returned to their original upright position undamagedafter the test. The anchorage strength of the trees was correlatedwith the second power of trunk diameter rather than with thethird power that theory suggests is optimal because tap rootsdid not show an isometric increase in length or diameter. Thereforeas trees grow larger the ‘factor of safety’ againstanchorage failure falls, making them prone to fail in theirroots. These results suggest that only relatively small treespecies can rely solely on the tap root to prevent uprooting.It may be for this reason that most larger trees develop thicklateral roots.Copyright 1998 Annals of Botany Company Anchorage, tap roots, scaling,Mallotus wrayi, isometric growth, functional development, windthrow, root systems.     

Above- and Below-ground Production of Young Scots Pine (Pinus sylvestris L.) Trees after Three Years of Growth in the Field under Elevated CO2

Scots pine (Pinus sylvestris L.) seedlings were grown for 3years in the ground in open top chambers and exposed to twoconcentrations of atmospheric CO₂(ambient or ambient + 400 µmol mol^-1) without addition of nutrients and water. Biomassproduction (above-ground and below-ground) and allocation, aswell as canopy structure and tissue nitrogen concentrationsand contents, were examined by destructive harvest after 3 years.Elevated CO₂increased total biomass production by 55%, reducedneedle area and needle mass as indicated, respectively, by lowerleaf area ratio and leaf mass ratio. A relatively smaller totalneedle area was produced in relation to fine roots under elevatedCO₂. The proportion of dry matter in roots was increased byelevated CO₂, as indicated by increased root-to-shoot ratioand root mass ratio. Within the root system, there was a significantshift in the allocation towards fine roots. Root litter constituteda much higher fraction of fine roots in trees grown in the elevatedCO₂than in those grown in ambient CO₂. Growth at elevated CO₂causeda significant decline in nitrogen concentration only in theneedles, while nitrogen content significantly increased in branchesand fine roots (with diameter less than 1 mm). There were nochanges in crown structure (branch number and needle area distribution).Based upon measurements of growth made throughout the 3 years,the greatest increase in biomass under elevated CO₂took placemainly at the beginning of the experiment, when trees grownin elevated CO₂had higher relative growth rates than those grownunder ambient CO₂; these differences disappeared with time.Symptoms of acclimation of trees to growth in the elevated CO₂treatmentwere observed and are discussed. Copyright 2000 Annals of BotanyCompany Elevated CO₂, Pinus sylvestris, biomass production, allocation, fine roots, root litter, crown structure, nitrogen, C/N ratio     

The function of buttress roots: a comparative study of the anchorage systems of buttressed (Aglaia and Nephelium ramboutan species) and non-buttressed (Mallotus wrayi) tropical trees

The anchorage mechanics of mature buttressed trees of Aglaiaand Nephelium, and of non-buttressed Mallotus wrayi have beeninvestigated by combining a study of the morphology of theirroot systems with a series of anchorage tests. Both types possessed tap roots, but only buttressed trees possessedsinker roots, which branched from the ends of the buttresses.The anchorage strength of the buttressed trees was almost double(10.6 kNm) that of the unbuttressed ones (4.9 kNm), and themaximum moment was generated at lower angles. In but tressedtrees, the leeward buttresses were pushed into the soil beforebending and eventually breaking towards their tip, whilst thewindward buttresses pulled out of the soil or delaminated ifthey possessed sinker roots. The tap root rotated in the soilto windward. In contrast, during failure of unbuttressed treesthe tap root both moved and bent towards the leeward, the windwardroots were pulled out of the soil, and the leeward lateralssimply buckled. Strains along but tresses were much higher thanalong the laterals of unbuttressed trees. These results suggest that buttresses act in both tension andcompression and make a much larger contribution to anchoragethan the thin laterals of non-buttressed trees. The relativecontribution of the but tresses was determined by carrying outa further series of anchorage tests in which both buttressedand unbuttressed trees were pulled over after all their lateralshad been cut away. These trees were therefore only anchoredby their taproot. Failure of both types was similar to intactunbuttressed trees, and they had similar anchorage strengthstoeach other, 4 kNm, around 80% of the value for intact non-buttressedtrees, but only 40% of the strength of intact buttressed trees.Buttresses therefore contribute around 60% of the anchorageof buttressed trees, producing around six times more anchoragethan the thin laterals of unbuttressed trees. Key words: Anchorage, root architecture, sinker roots, tap roots, root bending strength, buttresses     

The Role of Host Vigour in the Susceptibility of Pines to Fomes annosus

The resistance of suppressed pines to F. annosus and in particularthe role of such trees as infection foci in disease-free standsis a matter of potential significance for the spread of thepathogen. Mycelial inoculations showed that, in contrast todominant trees, the roots of very heavily suppressed trees possessno active resistance to the spread of the pathogen. However,at this extreme stage of suppression root-surface-fungi canalso invade the roots and to a considerable extent replace thepathogen. Spore inoculations of small root wounds gave similarresults except that the rate of infection was very much slower. Mycelial inoculations with F. annosus, Leptographium lundbergii,Peniophora gigantea, and Trichoderma viride were carried outin the trunks of pines suffering from different degrees of suppression.The fungi differed in their adaptation to the host, L. lundbergiibeing the most specialized to the biological, chemical, andphysical characteristics of pine wood and T. viride the least.This adaptation was shown to be inversely related to the competitivesaprophytic ability of each fungus, including the ability toproduce and tolerate antibiotics.     

Cluster Roots in Casuarinaceae: Role and Relationship to Soil Nutrient Factors

N₂-fixing actinorhizal trees in the family Casuarinaceae areeconomically of great interest in tropical and sub-tropicalzones because they are used for many purposes including protectionagainst wind, stabilization of sand dunes and the productionof firewood and charcoal. They are usually able to grow in sandysoils with low fertility by virtue of their ability to fix N₂.The objective of this review is to discuss briefly the roleof mycorrhizas and, more extensively, that of cluster (proteoid)roots, developed by a number of species of Casuarinaceae toimprove the absorption of nutrients other than N from soil,especially those needed for N₂fixation and growth. After evaluatingthe actual relationships between mycorrhizas and the Casuarinaceae,we highlight the possible role of cluster roots as an effectivealternative to mycorrhizas, and as a means of improvement ofgrowth of the trees in nutrient-deficient soils. This raisesthe question of what triggers the formation of cluster rootsin the Casuarinaceae. In addition to phosphorus deficiency,iron deficiency seems to be a major factor inducing the formationof cluster roots in Casuarina glauca and C. cunninghamiana.The number of cluster roots and the precocity of their formationare directly related to plant chlorosis due to Fe deficiency,as expressed by the critical concentration of chlorophyll inthe shoot (0.60 mg g ^{- 1}shoot f.wt). The effect of the nitrogensource on cluster root formation is discussed in relation topH values in the plant culture solution. The number of clusterroots formed in nitrate-fed plants increases with pH in therange of 5 to 9. Experiments carried out with alkaline and acidicsoils show that cluster roots are only produced when they areneeded to overcome soil nutrient deficiency due to the immobilizationof nutrient elements (P and Fe) by soil alkalinity. The possibleinvolvement of ethylene in the initiation and/or the morphogenesisof cluster roots is discussed. Copyright 2000 Annals of BotanyCompany Casuarinaceae, Casuarina cunninghamiana, Casuarina glauca, cluster roots, ethylene, iron deficiency, phosphorus deficiency, proteoid roots     

Rhizomorph Behaviour in Armillaria Mellea (Vahl) Qu?l: I. Factors controlling Rhizomorph Initiation by A. Mellea in Pure Culture

Experiments on rhizomorph initiation by Armillaria melleainagar plate culture are described, showing that production ofrhizomorph initials is controlled by a nutritional mechanism.     

Modelling the Seasonal Nitrogen Partitioning in Young Sycamore (Acer pseudoplatanus) Trees in Relation to Nitrogen Supply

A model of nitrogen partitioning during the seasonal growthof sycamore (Acer pseudoplatanus) seedlings was developed andtested against data from trees grown with two contrasting levelsof nitrogen supply. The model considered each tissue type (roots,trunk, stems and leaves) as sources and sinks for nitrogen andused flow equations to simulate the dynamics of nitrogen partitioningduring a growing season, with increases in tissue dry matteras driving force variables. Withdrawal of nitrogen from leavesduring senescence was allocated back to other tissues assuminga linear decrease in leaf mass. The model was fitted to data from trees grown in sand culturewith 6·0 molN m^-3 (high N) supplied with the irrigation.Model parameters thus determined were used to predict nitrogenpartitioning in trees grown with 1·0 molN m^-3 (low N)in the same year, and for trees from both treatments given eitherhigh or low N during a second year. The model accurately predictedthe nitrogen content of roots and leaves and gave small errorsin the amount of nitrogen partitioned to stems. In contrast,the nitrogen content of the trunks were over-estimated due toa failure to simulate the decreased in nitrogen content foundat the start of the growing season. The ability of the modelto simulate nitrogen partitioning by changes in tissue dry matterin trees of varying size and nitrogen status is discussed andpossible modifications to model partitioning of trunk nitrogenmore accurately suggested.Copyright 1993, 1999 Academic Press Modelling, nitrogen partitioning, ¹⁵N supply, Acer pseudoplatanus (sycamore), young seedlings     

Determination of Water, Solute and Turgor Potentials of Mycelium of Various Basidiomycete Fungi causing Wood Decay

Using thermocouple psychrometry, the water, solute and turgorpotentials of hyphae of Phallus impudicus and Serpula lacrimans,cords of P. impudicus, Phanerochaete velutina and S. lacrimansand rhizomorphs of Armillaria mellea were determined. A comparisonwas made between laboratory- and field-grown cords of P. impudicusand P. velutina. Comparison was made also between the waterrelations of the hyphae at the growing front, and hyphae ofthe more distal, basal regions. Similarly, the growing regionsof cords/rhizomorphs were compared with the older, non-extendingbasal regions of the same structures. In all cases gradientsof water and turgor potentials were found from basal, olderregions to younger, extending regions. These results are discussedin relation to the mechanism of translocation in fungi. Key words: Mycelium, Basidiomycotina, Turgor gradients, Translocation     

Complete Nucleotide Sequence of the Chloroplast Genome from the Tasmanian Blue Gum, Eucalyptus globulus (Myrtaceae)

The complete nucleotide sequence of the chloroplast genome ofthe hardwood species Eucalyptus globulus is presented and comparedwith chloroplast genomes of tree and non-tree angiosperms andtwo softwood tree species. The 160 286 bp genome is similarin gene order to that of Nicotiana, with an inverted repeat(IR) (26 393 bp) separated by a large single copy (LSC) regionof 89 012 bp and a small single copy region of 18 488 bp. Thereare 128 genes (112 individual gene species and 16 genes duplicatedin the inverted repeat) coding for 30 transfer RNAs, 4 ribosomalRNAs and 78 proteins. One pseudogene (-infA) and one pseudo-ycf(-ycf15) were identified. The chloroplast genome of E. globulusis essentially co-linear with that of another hardwood treespecies, Populus trichocarpa, except that the latter lacks rps16and rpl32, and the IR has expanded in Populus to include rps19(part of the LSC in E. globulus). Since the chloroplast genomeof E. globulus is not significantly different from other treeand non-tree angiosperm taxa, a comparison of hardwood and softwoodchloroplasts becomes, in essence, a comparison of angiospermand gymnosperm chloroplasts. When compared with E. globulus,Pinus chloroplasts have a very small IR, two extra tRNAs andfour additional photosynthetic genes, lack any functional ndhgenes and have a significantly different genome arrangement.There does not appear to be any correlation between plant habitand chloroplast genome composition and arrangement.     

Mobilizable carbon reserves in young peach trees as evidenced by trunk girdling experiments

The seasonal patterns in concentrations of both soluble (NSC-S)and insoluble (NSC-I) non-structural carbohydrates, in 3-year-oldpeach trees (Prunus persica L. Batsch) grown in sand cultureare described. The ability of trees to mobilize their carbohydratereserves in response to scion-trunk girdling, which preventsphotosynthate transport toward the roots, was tested at fourphenological stages. Girdling induces a NSC-I depletion in rootsand rootstock-trunk bark and a NSC-I accumulation in leavesand shoots. On the contrary, the NSC-S concentrations of theorgans located both above and below girdling were not significantlyaffected by the treatment. Consequently, when phloem transportbreaks down, trees, whatever their growing stage, mobilize carbohydratereserves below the girdle to maintain the soluble sugar contentsat the same level as in control trees. Key words: Girdling, non-structural carbohydrates, Prunus persica L., carbon reserves, seasonal patterns     

Observations on the Biology of Fomes annosus, with Particular Reference to East Anglian Pine Plantations: II. Spore Production, Stump Infection, and Saprophytic Activity in Stumps

F. annosus produces conidia abundantly in culture but rarelyunder natural conditions. Sporophorea are formed on stumps anddying trees throughout the year provided that the humidity issufficiently high. Spore discharge in the plantations may occurat any time of year, but slowa down or ceases during very dryweather. It takes place at low temperatures, ceasing only whensporophores freeze. In the laboratory, F. annosus basidiospores germinate in relativehumidity exceeding 92 per cent. on freshly cut, unsterilizedpine wood. Viability is lost rapidly in light at temperaturesabove 15°C. Under humid conditions F. annosus spores will infect freshlycut pine stumps. There is evidence that spores of F. annosus washed down intosoil remain viable for at least a short period and that stumpscovered with soil are infected from this source. F. annosusspores can infect stumps for only a few weeks after felling,colonization after a longer interval probably beingprevdntedby competing fungi. In stumps inoculated with a mixed suspensionof F. annosus and Peniophora gigantea spores, Fomes at firstcolonized the wood but was soon replaced by P. gigantea. Otheraspects of competition are discussed. The incidence of natural infection in stumps and the factorsaffecting it are discussed Growth rates of F. annosus on malt agar and in lengths of pineroot are given. The fungus grows in stump roots at about 1 m.per year, and so closely approaches adjacent trees within ayear of thinning the plantation: In large stumps, F. annosusmay survive 15 or even 30 years after felling. Data are givenwhich suggest that the infective capacity of stumps containingF. annosus is greater in alkaline than in acid mils, while replacementby other fungi is slower. Competition of F. annosus with other fungi during colonizationof stumps is discussed. The parasite can grow along roots alreadyoccupied by certain fungi but not along roots containing others.The probable course of succession in stumps rotted by F. annousis described.     

Dry-matter Production by Pinus sylvestris L.

This paper contains the data for the gross weight and relativeproportions of canopy, bole, and roots in a series of twelveeven-aged forest stands. From these it is possible to describe the growth curves of treesof Pinus sylvestris in Britain under the observed conditionsand the production of dry matter per unit area of such standsof trees. The following general results are given: regressionsrelating weight to bole, height, and diameter; the relativegrowth of leaves, roots, and bole; annual increments of drymatter; relative growth-rates per unit leaf area or per unitdry weight per annum. Some comparative data are given for Pinus nigra (one plantation)which is more productive than Pinus sylvestris.     

Responses of young trees to wind and shading: effects on root architecture

Two wind tunnels were designed to detect influences of windon the development of the root systems of young trees: Piceasitchensis and Larix decidua were grown in the first and L.decidua only in the second. In the second experiment, the taproot of each L. decidua seedling was removed in order to mimicthe formation of a shallow root-plate. Responses of shoot growthto wind stress were small, although uneven irradiance levelsresulted in asymmetric growth of both shoots and roots; thedistribution of root biomass around the tree was related spatiallyto that of shoot growth In both experiments there was an increase in the number of largewindward and leeward roots in both species. In the first experiment,the sum of the crosssectional area (