Beech Roots Research Articles

In situ ageing of fine beech roots ( Fagus sylvatica) assessed by transmission electron microscopy and electron energy loss spectroscopy: description of microsites and evolution of polyphenolic substances

Root biomass is quantitatively and qualitatively important in most ecosystems, but its contribution to the pool of organic matter in the soil is not clear. This work was designed to specify root ageing on an ultrastructural scale by transmission electron microscopy combined with microanalysis by electron energy loss spectroscopy. This approach is very suitable for studying the soil/plant interface, and for semi-quantitative analysis of the evolution of polyphenolic substances during root evolution. Three root segments were studied according to a gradient of root senescence: the apical and basal segments of the mycorrhiza and the mycorrhiza-carrier root. Each segment contained a certain proportion of senescent cells, some of which were of fungal origin, and this proportion increased as the root aged. In the three segments, the soil/plant interfaces were differentiated, and the micro-organisms observed in situ were described. Senescent root cells contained many polyphenolic substances and our results showed that these substances were, according to the root segment, differently associated with Ca, N and Si. When all these ultrastructural data are correlated with more global data, they can be usefully applied to root cell physiology, microbiology and pedology. This approach makes it possible to specify the evolution of organic matter in situ in soils whatever its origin.

Diurnal courses of ammonium net uptake by the roots of adult beech (Fagus sylvatica) and spruce (Picea abies) trees

Differences in ammonium net uptake by the roots of beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst) trees between day and night were examined during the growing seasons in 1995 and 1996 using the depletion technique. In addition, diurnal courses of ammonium net uptake of both species were analysed in five sets of uptake experiments in May and September 1997 and were related (1) to the content of carbohydrates, organic acids and total soluble non protein N (TSNN) in the fine roots, and (2) to xylem flow densities and soil temperature. During the growing seasons 1995 and 1996, ammonium net uptake of beech was significantly lower during the night than during the day at 5 of 8 dates of measurement. On average, uptake rates during the night amounted to 50% of the uptake rates during the day. In spruce, the mean values of ammonium net uptake rates determined were similar between day and night during both growing seasons. In beech, the assessment of diurnal courses showed highest ammonium uptake rates during noon and in the afternoon and minima at midnight. In May 1997, comparable, but less pronounced diurnal patterns of ammonium uptake were observed in spruce, whereas in September 1997, ammonium uptake by spruce was constant during the day. Since no distinct differences in carbohydrate and organic acid contents in fine roots were observed during the diurnal courses and since the addition of sucrose into the artificial soil solutions root tips were exposed to did not alter ammonium uptake, depression of uptake by C- and/or energy limitation during night could be excluded. The TSNN contents in the fine roots of beech (May and September 1997) and spruce (May 1997) showed a diurnal pattern inverse to ammonium uptake. It is concluded that the enrichment of TSNN compounds during night that is apparently caused by a reduction of xylem transport is responsible for the down-regulation of ammonium net-uptake.

Comparative studies on the fine root status of healthy and declining spruce and beech trees in the Bavarian Alps and occurrence of Phytophthora and Pythium species

Investigations on root and crown status of spruce and beech were carried out on selected trees in the ‘Werdenfelser Land’ area (Bavarian Alps, Southern Germany). In addition, the association of fine root pathogens of the genera Phytophthora and Pythium with the trees’ rhizosphere was studied. In a variety of stands representing various site conditions, soil and root samples were taken from 12 spruce (Picea abies) pairs and eight beech (Fagus sylvatica) pairs. Each pair consisted of a healthy and a declining tree as indicated by crown transparency. The root status was characterized using a set of parameters, and correlations between crown and fine root status were observed. In spruce, most parameters decreased significantly with increasing crown transparency, whereas in beech, correlations were less pronounced. The total number of lateral roots per cm small root (diameter 2–5 mm) was significantly lower in both species for declining trees compared to healthy trees. Pythium spp. were isolated from 15 of 24 soil samples taken from under spruce, and from eight of 16 samples from under beech. Phytophthora citricola was found in two beech stands only. Among the isolated species, Pythium anandrum, Pythium inflatum and Pythium acrogynum were identified according to morphological features. After polymerase chain reaction‐restriction fragment length polymorphism analysis, residual Pythium isolates were assigned to four different groups. No crown transparency‐dependent differences in isolation frequency were found. In soil infestation tests, all species tested caused root damage on both young spruce and beech plants, with P. citricola being the most aggressive pathogen. Additionally, Pythium‐infected beeches showed severe leaf chloroses and necroses. Due to their low isolation frequency, Phytophthora spp. are not considered to play a major role in the decline of spruce and beech in the investigated area. Pythium spp., however, were isolated frequently, showed pathogenicity towards the fine roots of spruce and beech, and are therefore considered to be at least contributing factors in the decline of Bavarian mountain forests.

Test speed and other factors affecting the measurements of tree root properties used in soil reinforcement models

Measured values of the mechanical properties of tree roots are found to be affected by a number of factors. Shear properties of tree roots are found to be partly influenced by size of the testing equipment, level of soil compaction, deformation of the root material and estimated width of the shear zone in the soil, etc. Among others, tensile root properties are found to be affected by factors such as season, age, root types or species, root preparation before experiment, clamping procedure of the root, and rate of elongation used. The aims of this paper were (1) finding an appropriate clamping procedure for root measurements; and (2) studying the effect of elongation rate on stress–strain relationships of beech ( Fagus sylvatica L.) roots. It was found that problems associated with root clamping (i.e., in root experiments) such as breakage of the root sample close to the jaws of the clamping devices and slippage may be eliminated by introducing wooden blocks of appropriate hardness within the jaws of the clamps and exerting a suitable clamping force, respectively. An appropriate wood hardness and suitable clamping force were found by conducting a number of initial trial experiments. Tensile experiments conducted with beech roots pairs showed that elongation rate does influence the stress–strain relationships of roots. In general, stress values of beech roots were found to increase between 8 and 20% for an increase in the rate of elongation from 10 to 400 mm/min. Similar findings have been reported in textile fibres.

Ultrastructural study of the biogeochemical cycle of silicon in the soil and litter of a temperate forest

SummaryThe biogeochemical cycle of silicon is closely linked to the plant cycle. We have studied the relations between silica and organic matter during humification in a temperate deciduous forest, an acid brown soil ecosystem, the characteristics of which suggest that plants play a major role in the recycling of soluble silica. Our ultrastructural approach consists in identifying the occurrence of biogenic silica in the beech roots, in young and old beech leaves in litter and in the underlying microaggregates of the topsoil. The microaggregates were either sampled directly in situ or isolated by size fractionation.Observations of ultrathin sections by transmission electron microscopy at a micrometric scale were combined with electron energy loss microanalysis, which enabled us to identify the silica phases and their associated mineral and organic environments. Some silica deposits were identified in the cell walls of both the beech roots and the beech leaves, whereas pure silica occurred in the root cortical cells as a layer which was closely associated with polyphenolic substances. The ultrastructural study of the microaggregates showed a close association between Si‐cell wall residues and Si‐polyphenolic residues. We also identified a specific bacterial activity that seemed to be related to the degradation of siliceous cell walls. The microquartz in the topsoil showed morphological and analytical transformations that might be considered as weathering. Both ultrastructural observations and the electron energy loss microanalysis showed the presence of biogenic silica and silica‐organic material in litter and soil, and these techniques should enable us to follow the biogeochemical cycle in ecosystems and the bioavailability of silicon.

Soil solution chemistry in the rhizosphere of beech (Fagus silvatica L.) roots as influenced by ammonium supply

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Vertical distribution and radial growth of coarse roots in pure and mixed stands of Fagus sylvatica and Picea abies

The vertical distribution of roots greater than 2 mm diameter was determined from digital images covering 116-m2 profile walls in soil pits in pure stands of European beech (Fagus sylvatica L.) and of Norway spruce (Picea abies (L.) Karst.) and in a mixed stand of both species. Radial root growth was assessed for roots greater than 5 mm diameter by growth ring analysis. Beech roots showed maximum density at the 10- to 20-cm depth, whereas the density of spruce roots decreased exponentially with increasing soil depth. Roots of both species reached the maximum excavation depth (1 m) in their monospecific stands. However, the root system of spruce was shallower in the mixture with beech, where large roots (diameter (d) >20 mm) were limited to the upper 10 cm. Beech roots reached the same rooting depth as in the pure stand but showed higher root densities in deeper soil layers. Neither root diameter nor root growth of any species was correlated with soil depth. Radial root growth of beech exceeded that of spruce significantly in both pure and mixed stands. Radial growth rate of beech roots further increased when mixed with spruce. The enhancement of beech root growth in the mixed stand suggests a higher belowground competitive ability of beech compared with spruce; as a result the spruce root system developed even shallower in the mixed versus in the pure stand.

Root competition between beech and oak: a hypothesis.

Little is known about below-ground competition between different tree species in mixed forests. We investigated the evidence for asymmetric competition between fine roots (<2mm) of adult European beech (Fagus sylvatica) and sessile oak (Quercus petraea) trees in a mixed temperate beech-oak forest by (1) conducting fine-root growth experiments in the field (root chamber technique), (2) comparing the fine-root mass of two-species and monospecific plots, and (3) analysing the density and overlap of beech and oak root systems in shared soil volumes. Field experiments with root chambers, which allow fine-root endings to grow under controlled conditions for several months, showed that beech grew more rapidly than oak roots when both species were grown together. In the mixed beech-oak wood, where stem densities and leaf areas of the two species were similar, beech outnumbered oak three- to five-fold in fine-root biomass, and root tip and ectomycorrhiza numbers, which led to a much greater root:shoot ratio (root area index:leaf area index, RAI:LAI) for beech (3.9) than oak (1.7). The remarkably small fine-root biomass of oak was attributed to competitive replacement by beech roots as indicated by comparison with monospecific oak wood. Although oak had much less fine-root mass than beech, oak outnumbered beech in the coarse root fraction (2<d<5mm) resulting in a greater fine root:coarse root ratio in beech than oak. The fine-root systems of the two species completely overlapped in the nitrogen-rich organic topsoil but differed with respect to their horizontal distribution patterns: beech root biomass increased with increasing distance from a beech stem whereas oak root mass was not dependent on stem distance. Beech (but not oak) root mass was correlated with the thickness of the organic topsoil horizons which, at average, were thicker at greater distances from beech stems. We conclude that beech fine roots colonise nitrogen-rich patches in the organic horizons of this forest more successfully than do oak roots. Our results (root chamber experiments, oak root abundance in mixed vs. monospecific wood, beech root dominance in the organic topsoil) suggest that asymmetric interspecific root competition in favour of beech exists in this stand.

Survival and Growth of Fagus sylvatica Seedlings Root-pruned Prior to Transplanting under Competitive Conditions

Bare-rooted seedlings are normally root-pruned prior to transplanting to facilitate the planting process. This study was designed to determine the effect of root-pruning on subsequent survival and growth of transplanted beech under competitive conditions. Two-year-old beech seedlings (Fagus sylvatica L.) were transplanted in a mixture of grasses with below-ground competition for water and nutrients and grown for 2 yrs with no irrigation or fertilization. Before transplanting, the root systems were pruned to 7, 13 and 19 cm; alternatively, coarse roots (>2 mm) or fine roots (<2 mm) were removed and unpruned plants were used as controls. Survival and growth were compared with seedlings grown under standard conditions. Mortality increased in correspondence with severity of pruning. Total plant dry weight (DW) was lower and root:shoot ratio higher in competitive compared with standard conditions. Removal of fine roots depressed plant DW under both standard and competitive conditions, whereas removal of coarse roots did so only under competitive conditions. The results indicate that roots of beech should not be pruned prior to transplanting, regardless of transplanting conditions, and that fine roots are necessary for regrowth in transplanted beech.

Measurement of stress–strain relationship of beech roots and calculation of the reinforcement effect of tree roots in soil–wheel systems

Evidence from forestry shows that part of the forest floor bearing capacity is delivered by tree roots. The beneficial effect varies and diminishes with increasing number of vehicle passes. PLAXIS is a commercially available finite element code that can calculate stresses, strains and failure states of soil mechanical problems. It can cope with unsaturated reinforced soil. Tree roots have a stiffness and a failure strength. They show elastic as well as plastic behaviour. They also show fatigue phenomena in repeated loading. Rooting intensity and root patterns of forest trees are complicated, but some information is available. This paper summarizes published data on mechanical properties of tree roots, and presents new measuring results of these properties. The paper further presents results of finite element calculations with PLAXIS for forest soil loaded by a tyre. This includes situations with and without reinforcement by tree roots. The reinforcement effects are, a.o., decrease of wheel rut depth and rolling resistance, decrease of damage to soil structure by the wheel load, and as a negative effect, damage to the tree root system. The magnitude of these effects depends on a number of parameters: stiffness and strength of the tree roots; soil mechanical properties like cohesion, angle of internal friction, compression index, preconsolidation stress; depth of a hard sublayer (if present); distance between vehicle and tree; rooting pattern; adhesive and frictional properties of the soil–root interface; tyre load and contact surface. The presented calculation results, which are based on realistic input data, show the sensitivity of the reinforcement effect to the listed variables.

Seasonal variations of symbiotic ultrastructure and relationships of two natural ectomycorrhizae of beech (Fagus sylvatica/Lactarius blennius var. viridis and Fagus sylvatica/Lactarius subdulcis)

This study concerned two perennial ectomycorrhizae of beech: Fagus sylvatica L./Lactarius blennius var. viridis and Fagus sylvatica L./Lactarius subdulcis, collected in a natural forest site. Nutritional exchanges existing between beech roots and fungi were evaluated over a seasonal cycle by studying the variations of ultrastructure, polyphosphate and nitrogenous granules and glycogen content (periodic acid thiocarbohydrazide silver test). The acid phosphatase activity, which is an indicator of the intensity of the physiological activity of symbiosis partners, was also revealed by transmission electron microscopy. The occurrence of the two ectomycorrhizae in the soil was not related to the climatic conditions. In winter, the number of polyphosphate and nitrogenous granules was high in the fungi, and glycogen was abundant in the cytoplasm of hyphae. In late winter, an intense acid phosphatase activity was revealed on plasmalemmas of live hyphae. It could indicate the beginning of fungal reserve mobilization, which progressively disappeared as spring progressed. In summer, glycogen was quasi non-existent and only few polyphosphate and nitrogenous granules were observed. At this period, the acid phosphatase activity was weak. Finally, in autumn and early winter, glycogen and granules were progressively restored in fungal structures. Relationships between changes of granules and glycogen content and the physiological states of each symbiont throughout the year are discussed.

The root systems of Fraxinus excelsior and Fagus sylvatica and their competitive relationships

Following reports from field foresters on so-called beech regeneration dieback, the root systems and competitive relationships of sapling-stage mixtures of beech ( Fagus sylvatica L.) and ash ( Fraxinus excelsior L.) were investigated in vivo and in vitro . Ash has a plate-root system from an early age, and beech a heart-root system. The distribution of ash roots is determined by competition for light under a closed overstorey of beech while the distribution of beech roots changes if there is competition with ash roots. In a replacement series experiment in a greenhouse, interspecific competition for water strongly reduced growth and survival of beech saplings. It is concluded that this competition for water could be the reason for beech regeneration dieback on sites where it occurs.

Nitrate transport processes in Fagus-Laccaria-Mycorrhizae

The contribution of influx and efflux of NO3 - on NO3 - net uptake has been studied in excised mycorrhizae of 18–20 week old beech (Fagus sylvatica L.) trees. Net uptake rates of NO3 - followed uniphasic Michaelis-Menten kinetics in the concentration range between 10 μM and 1.0 mM external NO3 -, with an apparent Km of 88±7 μM, and a Vmax of 110±7 nmol g-1 root f.wt. h-1. The relative xylem loading of N, i.e. the portion of NO3 - taken up that was loaded into the xylem vessels as NO3 - plus reduced N, was constant over the concentration range tested (4.6–7.7%). NO3 - influx proceeded linearly with increasing external NO3 - supply. When the assumed regulators of net NO3 - uptake, i.e. NH4 + or L-glutamate, were applied together with NO3 -, net uptake rates of NO3 - decreased. This inhibitory effect was caused by a reduction of NO3 - influx rather than an enhanced efflux. The comparison of the present data with a recent study with non-mycorrhizal beech roots (Kreuzwieser et al., 1997; J. Exp. Bot. 48, 1431–1438) revealed that mycorrhization leads to reduced rates of NO3 - net uptake. This effect is caused by reduced influx plus enhanced efflux of NO3 - as compared with non-mycorrhizal beech roots.

Real‐time Quantitative PCR: DNA Determination in Isolated Spores of the Mycorrhizal Fungus Glomus mosseae and Monitoring of Phytophthora infestans and Phytophthora citricola in their Respective Host Plants

AbstractSpecific primers and dual‐labelled fluorogenic probes were designed for polymerase chain reaction (PCR)‐based detection of both, mycorrhizal and pathogen DNA. Based on the on‐line connection with an automated ABI Prism 7700 sequence detector, amplicon quantification was directly performed during the PCR. The starting copy numbers of target sequences present in each reaction were calculated by comparing the Ct‐values of unknown samples to the Ct‐values of standards with known amounts of DNA. The Ct‐value depends on the input of starting copies and is defined as that cycle number at which a statistically significant increase in the reporter fluorescence can first be detected. DNA was extracted from 11 as well as 100 spores of the mycorrhizal fungus Glomus mosseae and quantified by using the fluorescent PCR technology. Furthermore, DNA of Phytophthora infestans, causal agent of late blight of potatoes, was quantified after extraction from artificially infected potato tubers and naturally infected field plants. Phytophthora citricola DNA, causing root‐rot diseases, was quantified after isolation from artificially inoculated seedling roots of beech and oak. The results demonstrate that novel real‐time PCR techniques are a powerful universal tool in modern phytopathological research.

Effect of vegetation on chemical composition of H horizons in incipient podzols as characterized by [formula omitted] NMR and pyrolysis-GC/MS

In a primary vegetation sequence on wind blown sands in the Netherlands, podzolization becomes evident under pine forest with various undergrowth and is more expressed under the subsequent beech forest. Recognizable podzol-B horizons appear together with H (humified O) horizons. In order to investigate whether the vegetation influences H horizon composition and the water-soluble fraction of this horizon, H horizons of three subsequent succession stages ( Pinus/Empetrum–Fagus/Vaccinium–Fagus without undergrowth) were sampled, fractionated, and analysed with 13 C CPMAS-NMR, pyrolysis-GC/MS, and by pollen analysis. Water soluble and NaOH soluble fractions of the three H horizons were very similar, suggesting that the humified material in the H horizon was formed exclusively from pine litter and that beech litter, yearly added to the soil surface in large amounts, did not influence the composition of the H horizon. The fact that the input of beech litter into the H horizon under beech was small was supported by very low amounts of Fagus pollen in all H layers. Humin fractions of the three H horizons were remarkably different, which was mainly due to varying amounts of beech root litter. The similarity of the water soluble organic matter fractions suggested that a direct relation between vegetation and organic matter mobilized by humification in the H horizon only exists under pine forest. Hence, increased podzolization under beech was probably not due to changing organic matter input, but to the factor time.

The significance of ectomycorrhizal fungi for sulfur nutrition of trees

Sulfur nutrition of plants is largely determined by sulfate uptake of the roots, the allocation of sulfate to the sites of sulfate reduction and assimilation, the reduction of sulfate to sulfide and its assimilation into reduced sulfur-containing amino acids and peptides, and the allocation of reduced sulfur to growing tissues that are unable to fulfill their own demand for reduced sulfur in growth and development. Association of the roots of pedunculate oak (Quercus robur L.) and beech (Fagus sylvatica L.) trees with ectomycorrhizal fungi seems to interact with these processes of sulfur nutrition in different ways, but the result of these interactions is dependent on both the plant and the fungal partners. Mycorrhizal colonisation of the roots can alter the response of sulfate uptake to sulfate availability in the soil and enhances xylem loading and, hence, xylem transport of sulfate to the leaves. As a consequence, sulfate reduction in the leaves may increase. Simultaneously, sulfate reduction in the roots seems to be stimulated by ectomycorrhizal association. Increased sulfate reduction in the leaves of mycorrhizal trees can result in enhanced phloem transport of reduced sulfur from the leaves to the roots. Different from herbaceous plants, enhanced phloem allocation of reduced sulfur does not negatively affect sulfate uptake by the roots of trees. These interactions between mycorrhizal association and the processes involved in sulfur nutrition are required to provide sufficient amounts of reduced sulfur for increased protein synthesis that is used for the enhanced growth of trees frequently observed in response to ectomycorrhizal association.

Sulphate uptake and xylem loading of mycorrhizal beech roots.

Beech nuts (Fagus sylvatica L.) were germinated and grown in soil inoculated with the ectomycorrhizal fungus Laccaria laccata or Paxillus involutus for 18-20 wk. The success of mycorrhizal infection was monitored by measuring the ergosterol contents of the mycorrhizas. Ergosterol levels ranged from 122±23 μg g-1 d. wt (Laccaria mycorrhizas) to 94±36 μg g-1 d. wt (Paxillus mycorrhizas), indicating that ectomycorrhizal symbiosis was established. In root incubation chambers, rates of sulphate uptake and the xylem loading of sulphate of excised mycorrhizas were investigated. Both types of mycorrhizas showed saturation kinetics in external sulphate concentrations from 2·5-1000 μmol l-1 . Linearization of these kinetics revealed two phases with low apparent Km (Laccaria mycorrhizas: 15±3 μmol l-1 ; Paxillus mycorrhizas: 13±3 μmol l-1 ) and Vmax (Laccaria mycorrhizas: 19±3 nmol h-1 g-1 f. wt; Paxillus mycorrhizas: 25±4 nmol h-1 g-1 f. wt) at low external sulphate concentrations and significantly higher kinetic constants at higher sulphate supplies. Relative xylem loading, i.e. the portion of sulphate loaded into the xylem that was taken up, remained constant over the entire concentration range investigated (c. 4-7% of the sulphate taken up). If trees were supplied for 72 h with different N and sulphur concentrations, both uptake of sulphate and relative xylem loading were unaffected by sulphur availability, but modulated by N supply. Nitrogen depletion diminished the rates of sulphate uptake in Laccaria and Paxillus mycorrhizas. In response to higher N availability combined with sulphur depletion, sulphate uptake of Laccaria mycorrhizas, but not of Paxillus mycorrhizas, increased. Organic compounds considered to be possible signals for the regulation of sulphate uptake were fed to excised mycorrhizas. l-Cysteine but not l-methionine and glutathione (γ-Glu-Cys-Gly) inhibited sulphate uptake of the two mycorrhizas and xylem loading of sulphate was stimulated rather than inhibited by l-Cys in both types. In Paxillus mycorrhizas glutathione had a similar effect. O-Acetyl-l-serine (OAS), a precursor of l-cysteine, stimulated sulphate uptake, but did not affect xylem loading. Apparently, OAS, generated in N metabolism, and l-cysteine, a product of assimilatory sulphate reduction, act as antagonists, together mediating regulation of sulphate uptake.

Interaction of phloem-translocated amino compounds with nitrate net uptake by the roots of beech (Fagus sylvatica) seedlings

Interaction of phloem-translocated amino compounds with nitrate net uptake by the roots of beech (Fagus sylvatica) seedlings

Interaction of phloem-translocated amino compounds with nitrate net uptake by the roots of beech (Fagus sylvatica) seedlings

From these results it is concluded that phloem transport of amino compounds, especially of Gln and Asp, In the present study two experimental approaches from the shoot to the roots mediates regulation of were used to investigate the influence of changes in nitrate net uptake by the roots of beech trees in order the allocation of amino compounds in the phloem of to adapt this process to the nitrogen demand of the beech (Fagus sylvatica L.) seedlings on nitrate net whole plant. uptake by the roots. In a first set of experiments Gln or Asp were directly fed into the phloem of the epicotyl Key words: Amino compounds, phloem transport, nitrate via bark flaps. These compounds were previously net uptake, NH 3 fumigation, regulation, Gln, Asp, Arg. found to be allocated in the phloem of adult beech trees and were shown to inhibit nitrate net uptake

Axial stress–strain relationships of fine roots of Beech and Larch in loading to failure and in cyclic loading

Vegetation roots contribute to the bearing capacity and stability of soils. In existing models of soil reinforcement by roots (land slide models), axial stress–strain relationships of roots play a central role. Such relationships were measured on fine roots of beech and larch. Results of loading to failure are presented by failure stress and failure strain. Results of cyclic loading are presented for each loading cycle by overall moduli of stiffness in loading and unloading, and elastic and plastic strain increments. The thinnest roots lost up to 60% of their water content during loading to failure, and showed failure strains up to 16%. The shape of the stress–strain curves was non-linear, but independent of diameter of tested roots. The modulus of stiffness was relatively low and incremental plastic strain was relatively high for the first loading cycle. The incremental plastic strains in cyclic loading tended to decrease with increasing root diameter.