A Comparative Study of the Anchorage Systems of Himalayan Balsam Impatiens glandulifera and Mature Sunflower Helianthus annuus

The anchorage systems of Himalayan balsam Impatiens glanduliferaand mature sunflowers Helianthus annuus were investigated bycombining morphological and anatomical study of the root systemswith mechanical tests on roots and with studies in which matureplants were pulled over. The root system of balsam is dominated by large numbers of fleshytapering adventitious roots which point downwards from theirorigin at the wide stem base. Sunflowers, in contrast, havea tapering tap-root from which 20–30 well-branched lateralsemerge, pointing radially outwards and downwards. Roots of eachspecies have contrasting anatomy: those of balsam resemble stems,having a central watery pith and being strengthened peripherallyby lignification of vascular tissue; roots of sunflowers arestrengthened by a solid woody stele. Roots of both species arerigid in tension and, towards the base, in bending. Both species exhibited similar behaviour to that known for treessuch as Sitka spruce; when pulled over they rotated about ahinge leeward of the stem base and a root-soil ball was pulledout of the surrounding soil. Anchorage was resolved into threecomponents which, in order of decreasing magnitude, were (i)the resistance to pulling of the roots on the windward sideof the plant (and, for sunflower, the tap-root); (ii) the resistanceof roots and soil at the leeward hinge to rotation; and (iii)the weight of the root-soil ball. Sunflower had stronger anchoragebut achieved it at a greater cost in terms of the dry mass ofits root system. In each species, the morphology, anatomy and mechanical propertiesof the root system can be related to those of the stem. Thewide stem base of balsam allows large numbers of mechanicallyefficient fleshy roots to be attached whereas in sunflowersa woody tap-root system is necessary to anchor the much narrowerstem. Key words: Impatiens, Helianthus, roots, anchorage     

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     

Anchorage Mechanics of the Tap Root System of Winter-sown Oilseed Rape (Brassica napus L.)

The anchorage mechanics of mature winter-sown oilseed rape (‘Envol’)were investigated by combining a morphological and mechanicalstudy of the root system with anchorage tests on real and modelplants. Oilseed rape plants were anchored by a rigid tap root;the few laterals all emerged below the centre of rotation ofthe root system (approx. 30 mm below the soil surface). Whenplants were pulled over, the tap root bent and the top 30 mmmoved in the soil towards the direction of pull, creating acrevice on the opposite side. The maximum anchorage moment was2.9 ± 0.36 N m. Two main components of anchorage wereidentified: the bending resistance of the tap root and the resistanceof the soil on the near side to compression. The relative importanceof these components was determined by measuring both the bendingresistance of the tap root, and the resistance of metal tubesof varying diameter, inserted to various depths in the soil,to being pulled over. These tests showed that the tap root bendingmoment at failure could account for around 40% of anchoragemoment, while soil resistance could account for around 60%.The model tests on the tubes also help to shed light on theway in which the dimensions of tap roots will influence theiranchorage capability. Copyright 2001 Annals of Botany Company Anchorage, lodging, root bending resistance, mechanical properties, oilseed rape, Brassica napus L     

The anchorage mechanics of deep rooted larch, Larix europea L. japonica

The anchorage of deep rooted 16-year-old larch trees, Larixeuropea japonica, has been studied by combining winching testswith analyses of strain around the base of the trunk and rootsystem and mechanical tests on individual roots. These showedthat anchorage is provided by the laterals which emerge fromaround the stem base, sinker roots which emerge along theirlength, and tap roots positioned directly underneath the bole.During anchorage failure the leeward laterals are bent and eventuallybreak close to their base, whilst the windward laterals arepulled out of the ground, with their sinker roots intact. Afterinitially being confined by the soil and bending, the tap rootrotates in the soil. Anchorage failure is similar when the soilis dry as when it is wet, but failure occurs closer to the trunk.Strain measurements along the lateral roots revealed that thestresses were highest close to the trunk and that these regionsof the roots contribute most to tree stability. The two major components of anchorage were found to be the resistanceof leeward laterals to bending and the resistance of tap rootsand windward sinkers to uprooting. Bending tests on leewardlaterals revealed that they provide around 25% of tree anchorage.Almost 75% of the anchorage strength must, therefore, be providedby the windward sinkers and tap roots. Anchorage strength ofroots was positively correlated to their cross-sectional area.The vertical orientation of the sinkers makes the anchoragesystem of larch more efficient than the plate system formedby Sitka spruce on waterlogged soils and means that no root-soilplate is formed. Key words: Anchorage, root architecture, sinker roots, root bending strength, windthrow     

Responses of the Root Systems of Sunflower and Maize to Unidirectional Stem Flexure

Plants of two contrasting species of herbaceous annuals, thedicot sunflower (Helianthus annuusL.) and the monocot maize(Zea maysL.), grown in the glasshouse were subjected to regularunidirectional stem flexure. Differences in morphology and mechanicalproperties of roots and shoots were then investigated. Rootsystems were divided into quadrants around the axis of stimulationand differences in root morphology and mechanics between thezones were investigated. There were considerable differencesbetween roots in the leeward and windward zones compared withroots perpendicular to the axis of stimulation. First-orderlateral roots in both species were thicker, more rigid and morenumerous. These results suggest that plant roots respond locallyto mechanical stimulation. There were, however, also differencesin the responses of the two species. In sunflower, the tap rootand stem base became elliptical in cross section with the majoraxis lying in the plane of stimulation. The lateral roots offlexed sunflowers in both the leeward and windward zones showedsimilar growth responses: roots were thicker, more numerousand weighed more than those in the perpendicular zones. However,only leeward roots showed significant differences in their mechanicalproperties; roots were more rigid, stronger and stiffer. Incontrast, the leeward roots of maize were thicker and more numerous,with a greater biomass than the windward roots. However, onlyroots in the windward zone were stiffer than those in the perpendicularzone. These differences between sunflower and maize are relatedto their contrasting anchorage mechanics.Copyright 1998 Annalsof Botany Company Anchorage, biomechanics, adaptive growth, roots, thigmomorphogenesis,Helianthus annuusL.,Zea maysL.     

The Mechanics of Anchorage in Wheat Triticum aestivum L.: II. ANCHORAGE OF MATURE WHEAT AGAINST LODGING

The root system of mature wheat Triticum aestivum Marts Doveis dominated by the 7 to 15 adventitious roots which emergefrom the perimeter of the stem base, pointing radially outwardsand downwards. The basal, coronal region of these roots is thickand unbranched, attached to a rhizosheath of earth by a densecovering of root hairs and stiffened in bending by lignificationof outer layers of the cortex. Root lodging of plants involves bending of the coronal rootsat their base and axial movement of leeward and windward rootsthrough the soil; their resistance to these motions providemoments resisting lodging. A model of anchorage was producedby summing the resistance of each root to both forms of motionto give two anchorage components. The model was tested in aseries of mechanical experiments in which simulated lodgingwas followed by loading of individual roots; results supportedthe anchorage model and suggested that in the experimental conditionsthe two components of anchorage were approximately equal inmagnitude. The stem was about 30% stronger than the anchoragesystem. The coronal anchorage roots made up 4.4% of total dry mass;it is suggested that anchorage could be improved either by increasinginvestment in this region or by altering root orientation. Sequentialdevelopment of seminal and adventitious root systems is relatedto the changes in anchorage requirement with age.     

Root Growth and Water Uptake by Maize Plants in Drying Soil

Sharp, R. E and Da vies, W. J. 1985. Root growth and water uptakeby maize plants in drying soil.— J. exp. Bot. 36: 1441–1456. The influence of soil drying on maize (Zea mays L.) root distributionand use of soil water was examined using plants growing in thegreenhouse in soil columns. The roots of plants which were wateredwell throughout the 18 d experimental period penetrated thesoil profile to a depth of 60 cm while the greatest percentageof total root length was between 20–40 cm. High soil waterdepletion rates corresponded with these high root densities.Withholding water greatly restricted root proliferation in theupper part of the profile, but resulted in deeper penetrationand higher soil water depletion rates at depth, compared withthe well watered columns. The deep roots of the unwatered plantsexhibited very high soil water depletion rates per unit rootlength. Key words: Maize, roots, water deficit, soil water depletion     

The Responses of Field-grown Sunflower and Maize to Mechanical Support

The effects of mechanical support on two contrasting speciesof herbaceous annual, the dicot sunflower (Helianthus annuusL.) and the monocot maize (Zea mays L.), were investigated bycomparing the growth and mechanical properties of supportedplants and those which were left to sway freely in the wind. Providing support had its greatest effect on the more highly-stressedbasal areas of the plants, such as the lower stem and the baseof the lateral roots. The diameter of the stem bases of bothspecies was approx. 10% lower in supported plants, but therewas no difference between treatments in the diameter of thestem above 50 cm. Roots of both species also showed a reductionin rigidity and bending strength of 40–50% in the supportedplants compared with freely swaying plants. There was a significantreduction in the partitioning of biomass to the root systemsof supported plants of both species. There were differences in the way in which sunflower and maizeresponded to the provision of support; in sunflower, the reductionin lateral diameter was about twice that in maize, whereas inmaize the decrease in the number of first-order laterals wastwice that of sunflower. This study suggests that thigmomorphogenesismay be a localized response, but that different species canrespond in different ways to mechanical stimulation. Wind; support; anchorage; thigmomorphogenesis; Helianthus annuus L.; sunflower; Zea mays L.; maize     

The Effects of Soil Bulk Density on the Morphology and Anchorage Mechanics of the Root Systems of Sunflower and Maize

The effects of soil bulk density and hence strength on two contrastingspecies of herbaceous annuals, the dicot sunflower (HelianthusannuusL.) and the monocot maize (Zea maysL.), were investigatedby comparing the morphology and mechanics of field-grown plantsin soil with a low and high bulk density. Soil with a low bulkdensity had a significantly lower penetration resistance (118±4.4kPa) than the high bulk density soil (325±12.2 kPa;P<0.0001).Soil strength affected shoot and root systems of both speciesbut had no significant effect on shoot height. In both speciesroots were thicker closer to the stem base in strong soil comparedto those in weaker soil. Sunflower tap-roots growing in strongsoil tapered more rapidly than those in weak soil. Only in maize,however, were roots growing in weak soil stiffer than thosein strong soil. Despite only small absolute differences in thepenetration resistance of the soil both species growing in strongsoil had greater anchorage strength than those in weak soil.As a consequence more plants in weak soil lodged compared withthose growing in strong soil. This study shows that plants can,to a small extent, respond to changes in soil strength, butthat changes do not appear to compensate fully for alterationsin soil conditions. Furthermore it may be possible, by manipulatingsoil strength, to control lodging.Copyright 1999 Annals of BotanyCompany Roots, compaction, soil strength, anchorage mechanics, bulk density, thigmomorphogenesis, lodging,Helianthus annuusL.,Zea maysL.     

Effect of Root and Shoot Meristem Temperature on Shoot to Root Dry Matter Partitioning and the Internal Concentrations of Nitrogen and Carbohydrates in Maize and Wheat

Maize (Zea mays L.) and spring wheat (Triticum aestivum L.)were grown in nutrient solution at uniformly high air temperature(20 °C), but different root zone temperatures (RZT 20, 16,12 °C). To manipulate the ratio of shoot activity to rootactivity, the plants were grown with their shoot base includingthe apical meristem either above (i.e. at 20 °C) or withinthe nutrient solution (i.e. at 20, 16 or 12 °C). In wheat, the ratio of shoot:root dry matter partitioning decreasedat low RZT, whereas the opposite was true for maize. In bothspecies, dry matter partitioning to the shoot was one-sidedlyincreased when the shoot base temperature, and thus shoot activity,were increased at low RZT. The concentrations of non-structuralcarbohydrates (NSC) in the shoots and roots were higher at lowin comparison to high RZT in both species, irrespective of theshoot base temperature. The concentrations of nitrogen (N) inthe shoot and root fresh matter also increased at low RZT withthe exception of maize grown at 12 °C RZT and 20 °Cshoot base temperature. The ratio of NSC:N was increased inboth species at low RZT. However this ratio was negatively correlatedwith the ratio of shoot:root dry matter partitioning in wheat,but positively correlated in maize. It is suggested that dry matter partitioning between shoot androots at low RZT is not causally related to the internal nitrogenor carbohydrate status of the plants. Furthermore, balancedactivity between shoot and roots is maintained by adaptationsin specific shoot and root activity, rather than by an alteredratio of biomass allocation between shoot and roots.Copyright1994, 1999 Academic Press Wheat, Triticum aestivum, maize, Zea mays, root temperature, shoot meristem temperature, biomass allocation, shoot:root ratio, carbohydrate status, nitrogen status, functional equilibrium     

Gravitropism of Primary Roots of Zea mays L. at Different Displacement Angles

Primary roots of Zea mays were oriented at various angles fromthe vertical ranging from 99° to 1° and their subsequentbending analysed from filmed records. The maximum rate of bendingand the time before bending commenced both varied two-fold,but showed no correlation with the initial angle of tip displacement.Roots orientated to small initial angles (< 40°) oftenovershot the vertical and proceeded to oscillate around thisorientation, whereas roots oriented to large initial angles(> 60°) often failed to achieve the vertical. Roots inthis latter group resumed bending after an indeterminate time,or did so immediately after a second displacement of their tip,showing that they were not intrinsically unable to bend. Theapparently spontaneous resumption of bending after a temporaryplagiogravitropic phase is suggested as being due to noise inthe graviperception system in the root cap. The tips of rootsgrowing vertically downwards showed oscillatory bending movementsup to 10° either side of vertical. This angle correspondsto the minimum angle of displacement which induces gravitropicbending. Only when roots were oriented 10-20° from verticaldid they begin unequivocally to show a gravitropism since atsuch angles the deflection of their tips exceeded that due totheir natural oscillation.Copyright 1993, 1999 Academic Press Gravitropism, roots, Zea mays     

The Mechanics of Anchorage in Wheat Triticum aestivum L.: I. THE ANCHORAGE OF WHEAT SEEDLINGS

Model of the mechanics of uprooting lead to the identificationof ‘optimal’ anchorage systems which can withstanda given upward force at a minimum construction cost. Such systemshave many downward-pointing fibrous roots which are strengthenedprogressively towards the base. A study of the anchorage systemof 7- and 21-d-old wheat (Triticum aestivum L.) plants showedthat the plants possessed five seminal roots, of which onlythree pointed vertically. Each root was well suited for anchorage,being convered in root hairs and strengthened progressivelytowards the base by lignification of the stele. Strength andstiffiness of roots but not their mass per unit length increasedwith age. There was little interaction between roots when plantswere uprooted; the three vertical roots broke while the twohorizontal ones pulled out, as occurred when roots were pulledout singly, Uprooting forces increased with age and the rootsystem could withstand uprooting forces greater than those requiredto pull out upper leaves, so reducing the chances of the plantbeing uprooted by a herbivore, By 3 weeks a stiff adventitiousroot system, which would later help prevent the wheat lodging,was developing.     

Root to Shoot Communication in Maize Plants of the Effects of Soil Drying

Seedlings of Zea mays L. (John Innes hybrid) were grown withroots divided between two containers such that part of the rootsystem could reduce the water potential of the soil in its immediatevicinity while the rest of the root system was well suppliedwith water. When compared to plants rooted in two pots of moistsoil, drying of part of the root system resulted in partialclosure of stomata, even though leaf water potential, turgorand abscisic acid (ABA) content remained unaffected. When leafpieces were removed from the two groups of plants and incubatedunder conditions favourable for stomatal opening, stomata ofthe ‘half-watered’ plants still showed restrictedapertures. Incubation in kinetin (10 mmol m^–3) or zeatin(100 mmol m^–3) reversed the closure of stomata stimulatedby soil drying. These results suggest that a continuous supplyof cytokinin from roots may be necessary to sustain maximalstomatal opening and an interruption of this supply due to soildrying may act as an indicator of inhibited root activity, resultingin restricted stomatal opening and thereby restricted wateruse. Key words: Zea mays L., Soil drying, Stomata, Roots     

Acid phosphatase role in chickpea/maize intercropping

• Background and aims Organic P comprises 30–80 %of the total P in most agricultural soils. It has been proventhat chickpea facilitates P uptake from an organic P sourceby intercropped wheat. In this study, acid phosphatase excretedfrom chickpea roots is quantified and the contribution of acidphosphatase to the facilitation of P uptake by intercroppedmaize receiving phytate is examined. • Methods For the first experiment using hydroponics, maize(Zea mays ‘Zhongdan No. 2’) and chickpea (Cicerarietinum ‘Sona’) were grown in either the sameor separate containers, and P was supplied as phytate, KH₂PO₄at 0·25 mmol P L^–1, or not at all. The second experimentinvolved soil culture with three types of root separation betweenthe two species: (1) plastic sheet, (2) nylon mesh, and (3)no barrier. Maize plants were grown in one compartment and chickpeain the other. Phosphorus was supplied as phytate, Ca(H₂PO₄)₂at 50 mg P kg^–1, or no P added. • Key results In the hydroponics study, the total P uptakeby intercropped maize supplied with phytate was 2·1-foldgreater than when it was grown as a monoculture. In the soilexperiment, when supplied with phytate, total P uptake by maizewith mesh barrier and without root barrier was 2·2 and1·5 times, respectively, as much as that with solid barrier.In both experiments, roots of both maize and chickpea suppliedwith phytate and no P secreted more acid phosphatase than thosewith KH₂PO₄ or Ca(H₂PO₄)₂. However, average acid phosphataseactivity of chickpea roots supplied with phytate was 2–3-foldas much as maize. Soil acid phosphatase activity in the rhizosphereof chickpea was also significantly higher than maize regardlessof P sources. • Conclusions Chickpea can mobilize organic P in both hydroponicand soil cultures, leading to an interspecific facilitationin utilization of organic P in maize/chickpea intercropping.     

Leaf Extension in Zea mays: I. LEAF EXTENSION AND WATER POTENTIAL IN RELATION TO ROOT-ZONE AND AIR TEMPERATURES

The temperature of the roots and shoots of Zea mays plants werevaried independently of each other and the rates of leaf extensionand leaf water potentials were measured. Restrictions of leafextension occurred when root temperatures were lowered from35 to 0 °C, but leaf water potentials were lowered onlyat root temperatures below 5 °C. Similar changes in ratesof leaf extension were measured at air temperatures from 30to 5 °. Between 30 and 35 °C air temperature, in anunsaturated atmosphere, restrictions of leaf extension wereassociated with low leaf water potentials. It was concluded that, at root temperatures 5 to 35 °C,and shoot temperatures 5 to 30 °C, water stress was notthe main factor restricting the extension of Zea mays leaves.     

A comparative study of the response of the roots and shoots of sunflower and maize to mechanical stimulation

Despite numerous studies of the effects of mechanical stimulationon plant shoots, the response of roots to mechanical stimulationhas largely been neglected. In this study the effects of shootflexure on the morphology and mechanics of two contrasting speciesof herbaceous angiosperm, growing in a glasshouse were compared:maize (Zea mays), a monocot; and sunflower (Helianthus annuusL.) a dicot. Mechanical stimulation affected the root more than the shootcomponents. Root systems of mechanicallystressed sunflowershad a greater angle of spread and increased root number. Aswell as large morphological and weight effects, with increasesover the control of 33% in the length of rigid root and 38%in the dry weight of lateral roots, in sunflowers, there werealso mechanical effects. In both species roots of flexed plantswere more rigid, stronger and composed of stiffer material andtheir root systems also provided greater anchorage strength.In contrast, there was only a small reduction in shoot weightand shoot height in flexed plants and no effects on mechanicalproperties. There were differences in behaviour between species; maize rootmorphology responded less than that of sunflowers to mechanicalstimulation. The basal diameter of roots increased by only 8%compared with 16% in sunflowers, though the roots of both speciesshowed similar increases in material stiffness. This differenceis related to the lack of secondary thickening in the monocotscompared with the dicot sunflowers. Key words: Thigmomorphogenesis, Helianthus annuus L., Zea mays, anchorage, lodging     

Modelling of the Hydraulic Architecture of Root Systems: An Integrated Approach to Water Absorption--Distribution of Axial and Radial Conductances in Maize

The ‘Hydraulic Tree Model’ of the root system simulateswater uptake through root systems by coupling a root architecturemodel with laws for water flow into and along roots (Doussan,Pagès and Vercambre,Annals of Botany81: 213–223,1998). A detailed picture of water absorption in all roots comprisingthe root system is thus provided. Moreover, the influence ofdifferent distributions of radial and axial hydraulic conductancesin the root system on the patterns of water uptake can be analysed.Use of the model with Varney and Canny's data (1993) for flowalong maize roots demonstrated that a constant conductance inthe root system cannot reproduce the observed water flux profiles.Taking into account the existing data on hydraulic conductancesin maize roots, we fitted the distribution of conductances inthe root system to the observed flux data. The result is that,during root tissue maturation, the radial conductivity decreasesby one order of magnitude while the axial conductance increasesby about three orders of magnitude. Both types of conductanceexhibit abrupt changes in their evolution. Due to the conductancedistribution in the root system, appreciable water potentialgradients may develop in the roots, in both the branch rootsand main axes. An important point is that the conductance distributionin the branch roots described by the model should be relatedto the age of the tissue (and not the distance from the branchroot tip) and is therefore closely related to the developmentprocess. Thus for branch roots, which represent about 90% ofthe calculated total water uptake in 43-d-old maize, water absorptionwill depend on the opening of the metaxylem in the axes, andon the time dependent variation of the conductances in the branchroots.Copyright 1998 Annals of Botany Company Water; absorption; root system; architecture; model; hydraulic conductance;Zea maysL.     

Development of Golgi Apparatus in the Root Cap Cells of Maize (Zea mays L.) as Affected by Compacted Soil

Effects of soil mechanical impedance on the development of Golgiapparatus in the root cap cells of maize were studied undercontrolled soil-water conditions Heavily compacted soil (bulkdensity = 1.50 g cm^–2) had 3.3 to 3.4 times greater mechanicalimpedance than control soil (bulk density = 1.33 g cm^–3),but their oxygen diffusion rates were not significantly differentThe number of dictyosomes and the number and area of secretoryvesicles per unit area of tangentially sub-peripheral root capcells in the heavily compacted soil increased compared to thosein the control These results suggest that secretory activityof the root cap cells is promoted by soil mechanical impedance Dictyosome, Golgi apparatus, maize, mucilage, root cap, secretory activity, secretory vesicles, soil mechanical impedance, Zea mays L     

An Experimental Investigation of the Resistance of Model Root Systems to Uprooting

The architecture of a tree root system may influence its abilityto withstand uprooting by wind loading. To determine how theroot branching pattern may alter the anchorage efficiency ofa tree, artificial model root systems with different topologiesand branching angles were built. The root systems were embeddedat various depths in wet sand and the pull-out resistance measured.A model to predict the uprooting resistance from the data collectedwas designed, allowing predictions of anchorage strength withregards to architecture. The dominant factors influencing pull-outresistance were the depth and length of roots in the soil. Themost efficient type of branching pattern predicted by the programwas one with an increased number of roots deep in the soil.The optimum branching angle most likely to resist pull-out isa vertical angle of 90° between a lateral and the main axis.The predicted mechanically optimal radial angle between a lateralbranch and its daughter is between 0 and 20°. Values ofbranching angle are compared with those measured in real woodyroot systems of European larch and Sitka spruce. Root architecture; root anchorage; pull-out resistance; windthrow; Picea sitchensis ; Larix decidua