Root architecture,early development and basal sweep in containerized and bare-rooted Douglas fir (Pseudotsuga menziesii)

Seedlings grown in containers often have deformed, spiralling, kinking root systems (reported especially in pine growing in colder climates like Fenno-Scandinavia). The current study examines the effect of containers on the root systems of Douglas fir planted in Ireland. A sample of sixteen 10-year-old Douglas fir trees, planted as either bare-rooted transplants (2/1) or containerized seedlings (Paperpot 610 (2/0)) on an acid brown earth site in Ireland, were excavated for root achitectural studies. In addition to thorough above-ground measurements, an assessment of basal sweep was also carried out. Root systems were systematically described and horizontal angles, cross-sectional areas (CSA), and maximum depths of all roots>5 mm in diameter were recorded. Various biomass ratios and estimates for dominant roots were also calculated. Symmetry of the root systems, max. and min. numbers, and CSA of roots for sectors of various sizes were compared for the two plant types. The initially (when planted) bigger bare-rooted transplants were still larger than the container-planted trees after ten years. Of the total above-ground fresh weight, the container stock had allocated more to the crown and less to the stem compared to bare-roots. The difference in root weights between stock types was small. Basal sweep occurred on average in 50% of the bare-roots and 35% of the container trees. The direction of the basal sweep leaning was concentrated to the NE, which coincided with the direction of the slope and the prevailing wind direction. No effect of planting position in relation to the direction of site preparation was found for basal sweep. The size of the root system, fresh weight and total cross-sectional area was on average for all trees correlated to both DBH and shoot fresh weights. For containers separately, however, only root area was correlated to DBH and stem fresh weight. In spite of the difference in the above-ground size, there were no significant differences in root numbers and root area (CSA) between the two plant types. No difference in rooting depth between plant types was found. When splitting the root system into 120° horizontal sectors (1/3 of the root system) the highest numbers of roots were concentrated in the NW direction. The highest amount of root area tended to be concentrated along a NW-SE diagonal, with a dominance for the latter (SE). Sectors without dominant roots (expected to be the future main structural, stabilizing roots), varied in size (94–178°) but were on average wider in bare-roots and on average concentrated in the NE direction and the downhill side of the slope. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of Restricted Root Growth on Carbohydrate Metabolism and Whole Plant Growth of Cucumis sativus L

The effects of varied rooting volumes on root growth and source leaf carbohydrate metabolism were studied in greenhouse-grown cucumber (Cucumis sativus L cv Calypso) plants. Plants were grown for 7 weeks in container volumes that ranged from 0.4 to 5.9 liters. Plants grown in the smaller containers exhibited less leaf expansion, lower root and shoot weight, and fewer lateral stems than plants grown in the 5.9 liter containers. Shoot/root ratio was not altered by the container volume, suggesting coordination of root and shoot growth due to rooting volume. Source leaf carbon exchange rates, assimilate export rates, and starch accumulation rates for plants grown in 0.4 liter containers were approximately one-half or less in comparison to those for plants grown in 5.9 liter containers. Starch concentrations per unit leaf area were maintained at high levels in source leaves of plants grown in 0.4 liter containers over the entire day/night cycle. Lower extractable galactinol synthase activities and higher galactinol concentrations occurred in leaves of plants grown in 0.4 liter container volumes. The reduced sink demand, induced by restricted root growth, may have led to increased starch concentrations and to a reduction in stachyose biosynthesis in cucumber source leaves.     

Understanding the impact of root morphology on overturning mechanisms: a modelling approach

BACKGROUND AND AIMS: The Finite Element Method (FEM) has been used in recent years to simulate overturning processes in trees. This study aimed at using FEM to determine the role of individual roots in tree anchorage with regard to different rooting patterns, and to estimate stress distribution in the soil and roots during overturning. METHODS: The FEM was used to carry out 2-D simulations of tree uprooting in saturated soft clay and loamy sand-like soil. The anchorage model consisted of a root system embedded in a soil block. Two root patterns were used and individual roots removed to determine their contribution to anchorage. KEY RESULTS: In clay-like soil the size of the root-soil plate formed during overturning was defined by the longest roots. Consequently, all other roots localized within this plate had no influence on anchorage strength. In sand-like soil, removing individual root elements altered anchorage resistance. This result was due to a modification of the shape and size of the root-soil plate, as well as the location of the rotation axis. The tap root and deeper roots had more influence on overturning resistance in sand-like soil compared with clay-like soil. Mechanical stresses were higher in the most superficial roots and also in leeward roots in sand-like soil. The relative difference in stresses between the upper and lower sides of lateral roots was sensitive to root insertion angle. Assuming that root eccentricity is a response to mechanical stresses, these results explain why eccentricity differs depending on root architecture. CONCLUSIONS: A simple 2-D Finite Element model was developed to better understand the mechanisms involved during tree overturning. It has been shown how root system morphology and soil mechanical properties can modify the shape of the root plate slip surface as well as the position of the rotation axis, which are major components of tree anchorage.     

Total soil water content accounts for augmented ABA leaf concentration and stomatal regulation of split-rooted apple trees during heterogeneous soil drying

A split-rooted containerized system was developed by approach grafting two, 1-year-old apple (Malus×domestica Borkh. cv 'Gala') trees to investigate the effect of soil moisture heterogeneity and total soil moisture content (θ(v)) on tree water relations, gas exchange, and leaf abscisic acid (ABA) concentration [ABA(leaf)]. Four irrigation treatments comprising a 2×2 factorial experiment of irrigation volume and placement were imposed over a 30-day period: control (C) [>100% of crop evapotranspiration (ET(c))] applied to both containers; PRD100 (>100% ET(c)) applied to one container only; and two treatments receiving 50% ET(c) applied to either one (PRD50) or both containers (DI50). Irrigation between PRD (partial rootzone drying) root compartments was alternated when θ(v) reached ~35% of field capacity. Maximum daily sap flow of the irrigated roots of PRD100 exceeded that of C roots throughout the experimental period. Pre-dawn water potential (Ψ(pd)) was similar between C and PRD100; however, daily water use and mid-day gas exchange of PRD100 was 30% lower. Slightly higher [ABA(leaf)] was observed in PRD100, but the effect was not significant and could not explain the observed reductions in leaf gas exchange. Both 50% ET(c) treatments had similar, but lower θ(v), Ψ(pd), and gas exchange, and higher [ABA(leaf)] than C and PRD100. Regardless of treatment, the container having the lower θ(v) of a split-rooted system correlated poorly with [ABA(leaf)], but when θ(v) of both containers or θ(v) of the container possessing the higher soil moisture was used, the relationship markedly improved. These results imply that apple canopy gas exchange and [ABA(leaf)] are responsive to the total soil water environment.     

The effect of mechanical stimulation on root and shoot development of young containerised Quercus robur and Robinia pseudoacacia trees

Thigmomorphogenesis is a well-studied process in agricultural crops and coniferous trees. Nevertheless, the effects on both shoot and root characteristics for deciduous woody species received little attention so far. In this study, the objective was to understand the effect of aboveground flexing treatments on the development of structural, mechanical and physiological root and shoot characteristics for two deciduous tree species, Black locust (Robinia pseudoacacia L.) and English oak (Quercus robur L.). Flexing treatments were performed using an electromechanical device with a rotating arm touching and bending the plants at regular intervals. A wide range of stem, shoot as well as root system characteristics was measured. The different flexing treatments altered above- and belowground plant development for both species, with strongest effects on Quercus and most significant differences between the control and the unidirectional flexing treatment. Some responses are in accordance with previous findings, such as stem eccentricity and reduced shoot elongation under unidirectional flexing, but others are renewing, such as the lower stomatal density and larger epidermal cell surface for the Quercus plants under variable flexing direction. Despite some common responses, both species frequently differed in the way they were affected. Belowground, Quercus plants under unidirectional flexing invested relatively more in their first order root and deeper second order roots, whereas Robinia plants allocated relatively more to fine root biomass and horizontal shallow roots. Both strategies potentially increased pull-out as well as overturning resistance in their own way. The presented findings are valid for young trees grown in small containers. Based on practical know-how and shortcomings experienced in the course of this experiment, methodological recommendations are formulated. We finally stress the complex variability in growth responses, especially for root systems, observed in different studies and related to dissimilarity in species, soil conditions, plant history or type of mechanical perturbation.     

Soil Temperature Regulates Fruit Color Change in ‘Algerie’ Loquat: Nutritional and Hormonal Control

In Rosaceae fruit tree species, fruit and roots grow opposite because of carbohydrate competition, and root activity is thus reduced by fruit growth. In agreement with this, for some of these species soil temperature has been suggested as a factor regulating fruit ripening, but the mechanism with which it works remains unknown. In this study, we reduced loquat root activity by lowering soil temperature, expecting faster fruit growth and advanced fruit ripening. Eight 4-year-old ‘Algerie’ loquat trees, budded onto seedling rootstock, and grown outdoors in 39-l plastic containers filled with sandy-loamy soil were used. The roots of four trees were cooled by placing the containers in a cooling compartment (9.5 °C), whereas those of the other four trees were maintained at air temperature (16.5 °C). We measured lateral root primordia emergence, fruit diameter and fruit color development, carbohydrates and nitrogen partitioning, as well as GA, CK, IAA, ABA, and JA content. Lowering soil temperature increased carbohydrate translocation to the fruit and reduced root N uptake and translocation to both the canopy and the fruit. Changes in plant hormones were also caused by reduced soil temperature, and fruit color advanced. Loquat fruit ripened 8–10 days earlier when soil temperature was reduced to 9.5 °C.     

Effect of root volume and nitrate solution concentration on growth,fruit yield,and temporal N and water uptake rates by apple trees

Meager information is available on the specific effects of root volume (V) and N concentration in the water (C_N) on uptake rates of water and N by apple trees, as related to fruit yield and tree growth. To investigate this relationship, Golden Delicious/Hashabi trees were grown for 5 years in containers of 200, 50 and 101. Trees in the 200–1 containers were irrigated with a nutrient solution containing 10.7±1.3, 7.1±1.5 or 2.5±1.0 mM NO₃. Trees in the remaining two container-volume treatments were uniformly supplied with a solution of 7.1±1.5 mM NO₃. Elevated C_N had no effect on the rate of water uptake, but increased the rate of N absorption by the trees from 2.4 to 4.8 g N tree⁻¹ day⁻¹ during July. The stimulated N uptake rate stemmed from enhanced fluxes of N uptake by the roots. C_N had a negligible effect on root weight and root permeability to NO₃ and water. The elevated N uptake rate did not result in greater fruit yield and growth, or greater N content in tree organs, indicating considerable release of N from living and decaying roots to the growth medium. Reducing the container volume decreased yield, total dry matter production and N and water uptake rates, but increased root permeability to NO₃ and water, and total soluble solids in fruits. The all-season average C_N in the irrigation solution above which N concentration in the transpiration stream was lower than the inflowing C_N was 4.2 mM NO₃.     

The effect of root architecture and root loss through trenching on the anchorage of tropical urban trees (Eugenia grandis Wight)

Eugenia grandis (Wight) is grown in urban environments throughout Malaysia and root systems are often damaged through trenching for the laying down of roads and utilities. We investigated the effect of root cutting through trenching on the biomechanics of mature E. grandis. The force necessary to winch trees 0.2 m from the vertical was measured. Trenches were then dug at different distances (1.5, 1.0 and 0.5 m) from the trunk on the tension side of groups of trees. Each tree was winched sideways again and the uprooting force recorded. No trenches were made in a control group of trees which were winched until failure occurred. Critical turning moment (TM_crit) and tree anchorage rotational stiffness (TARS) before and after trenching were calculated. Root systems were extracted for architectural analysis and relationships between architectural parameters and TM_crit and TARS were investigated. No differences were found between TM_crit and trenching distance. However, in control trees and trees with roots cut at 1.5 m, significant relationships did exist between both TM_crit and TARS with stem dimensions, rooting depth and root plate size. TARS was significantly decreased when roots were cut at 0.5 m only. Surprisingly, no relationships existed between TM_crit and TARS with any root system parameter when trenching was carried out at 0.5 or 1.0 m. Our study showed that in terms of TARS and TM_crit, mechanical stability was not greatly affected by trenching, probably because rooting depth close to the trunk was a major component of anchorage.     

A generic 3D finite element model of tree anchorage integrating soil mechanics and real root system architecture

Understanding the mechanism of tree anchorage in a forest is a priority because of the increase in wind storms in recent years and their projected recurrence as a consequence of global warming. To characterize anchorage mechanisms during tree uprooting, we developed a generic finite element model where real three-dimensional (3D) root system architectures were represented in a 3D soil. The model was used to simulate tree overturning during wind loading, and results compared with real data from two poplar species (Populus trichocarpa and P. deltoides). These trees were winched sideways until failure, and uprooting force and root architecture measured. The uprooting force was higher for P. deltoides than P. trichocarpa, probably due to its higher root volume and thicker lateral roots. Results from the model showed that soil type influences failure modes. In frictional soils, e.g., sandy soils, plastic failure of the soil occurred mainly on the windward side of the tree. In cohesive soils, e.g., clay soils, a more symmetrical slip surface was formed. Root systems were more resistant to uprooting in cohesive soil than in frictional soil. Applications of this generic model include virtual uprooting experiments, where each component of anchorage can be tested individually.     

Water uptake regulation in peach trees with split-root systems

The water uptake of 3- to 4-year-old peach trees ‘May-crest/Prunus Damas’ grown in an aerated nutrient solution was studied using a split-root system. Each container and the whole tree were weighed independently to measure water absorption by both parts of the root system and tree transpiration. Water potential of leaves was measured with a pressure chamber. Water potential of roots was estimated using root suckers sealed in plastic bags before the measurement. The nutrient solution was removed from one container so that half the root system was left in humid air for 48 h. Water potential of roots left in solution decreased, which (partly) maintained water absorption and thus transpiration. No modification of root hydraulic resistance was required to simulate the experimental results. Nevertheless, enhancement of absorption by the roots supplied with solution cannot compensate for the water loss by transpiration. Depletion of water from the plant essentially came from the non-absorbing roots. This was demonstrated by substituting vegetable oil for nutrient solution around one half of the split-root system, and by following the changes in root volume on the basis of Archimedes principle. Conflicting results in the literature about apparent changes in hydraulic resistance are discussed.     

Seed germination,seedling inoculation and establishment ofAlnus spp. in containers in greenhouse trials

Methods for production of containerized seedlings ofAlnus species were developed which permit nitrogen-fixing nodules to form on the root systems prior to outplanting, in order to provide an early nitrogen input during seedling establishment. The methods are based on procedures for inoculating root systems with suspensions ofFrankia (Actinomycetales), applied either directly in the container cell as a soil drench at the time of seeding, or as a root dip for seedlings transplanted into the containers. Germination of dried, stored seed was enhanced by light and by presoaking for 16 h in water. Pretreatments to overcome seed dormancy or to eliminate fungal pathogens did not further enhance germination. Some loss of seedlings was recorded in the early stages of growth shortly after germination, which is a factor in calculating projected seedling yield. Nodulation and seedling growth were evaluated in terms of growth media characteristics. Seedlings performed well in peat-vermiculite, at soil pH between 5.5 and 8.0.     

长白山阔叶红松林凋落物组成及其季节动态

为了解群落尺度上凋落物组成及其时空变化,对长白山阔叶红松林25 hm² 样地内2008年度收集的凋落物进行统计分析.结果表明: 一年间,150个收集器内收集的凋落叶分属35种树木,占样地内胸径≥1 cm树种数(52种)的67.3%;凋落物总量为29.39 kg,折合3918.4 kg·hm^-2,其中,阔叶、杂物、针叶和枝条凋落量分别占凋落物总量的61.7%、18.0%、11.7%和 8.6%;紫椴、水曲柳、蒙古栎、色木槭和春榆5个树种的叶凋落量占阔叶总凋落量的83.8%;不同树种的凋落量季节差异很大,61.9%的凋落物产生于9月13日至10月10日.其中,红松和紫椴叶凋落高峰出现在9月13-26日,蒙古栎、春榆和色木槭叶凋落高峰出现在9月27日-10月10日.收集器间凋落物量差异较大,其中68个收集器的年凋落量在150～200 g,1个收集器大于500 g;单个收集器全年最多可收集到18个树种的凋落叶,凋落叶种数为12种的收集器最多(32个).叶凋落量与样地内该树种的胸高断面积总和成正比.样地内凋落叶的分布存在明显的空间异质性,且收集器内凋落物的收集量与其所处的位置有关.     

Strain distribution during anchorage failure of Pinus pinaster Ait. at different ages and tree growth response to wind-induced root movement

Winching tests were carried out on 5- 13- and 17-year-old tap rooted Maritime pine (Pinus pinaster Ait.) in order to determine how the mode of anchorage failure changes throughout the life of a tree. As trees were pulled sideways, strain along the lateral roots was recorded using strain gauges attached to a strain indicator. Measurements of strain in the root system, taken during winching, provide information about root movement when loaded by wind. The mode of mechanical failure appeared to depend on tree age. The youngest trees bent over completely during winching, but did not break due to the plasticity of their trunks. The 13-year-old trees either broke at the base of the tree (due to the presence of grafting scar tissue) or at the base of the tap-root. The oldest trees broke at the base of the tap-root and sounds of roots breaking were also heard. Strain was twice as great in the trunk compared to the roots in the 5- and 13-year-old trees and was three times greater in the compression roots of 17-year–old trees compared to that in the trunk. In one 17-year-old tree, strain was found to increase at a distance of 35 cm in tension roots before decreasing again. Although the mode of failure changed with tree size, anchorage strength increased proportionally with the third power of trunk diameter, therefore another reason why failure differs with tree age must exist. In order to determine if different types of wood were being laid down in the lateral roots in response to wind loading, maturation strains, indicating the existence of mechanical stress in developing wood cells, were measured at different points along the roots. A high correlation was found between maturation strain and strain measured during winching, in roots that lay in the wind direction only. Therefore, trees appear to be able to respond to external loading stress, even at a local level within a root. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of root feeding by Diaprepes abbreviatus (Coleoptera: Curculionidae) larvae on leaf gas exchange and growth of three ornamental tree species

Diaprepes abbreviatus L. (Coleoptera: Curculionidae), feeds on a variety of ornamental plants grown in southern Florida. Studies were conducted to evaluate the effects of root feeding by D. abbreviatus larvae on leaf gas exchange and growth of three ornamental tree species commonly grown in southern Florida that are known hosts of this weevil: green buttonwood, Conocarpus erectus L.; live oak, Quercus virginiana Mill.; and pygmy date palm, Phoenix roebelenii O'Brien. These hosts were grown in containers and infested with weevil larvae. Net CO2 assimilation, transpiration, and stomatal conductance of CO, were measured monthly. Leaf, stem, and root fresh and dry weights of each species also were determined. In one of two tests, larval root feeding significantly reduced net CO2 assimilation, transpiration, and stomatal conductance of CO2 of infested green buttonwood trees. Leaf gas exchange of live oak was not affected by larval infestation. In addition to testing cumulative effects of multiple infestations of larvae, the effects of incremental infestations on leaf gas exchange and fresh and dry weights also were tested for each plant species. Net CO2 assimilation, transpiration, stomatal conductance of CO2, and dry weights of green buttonwood were reduced as a result of larval root feeding, whereas there was no effect of incremental larval infestations on leaf gas exchange of live oak or pygmy date palm within the experimental time frame. There was no effect of incremental larval infestations on dry weights of live oak, but leaf, stem, and dry root weight of pygmy date palm were lower for infested plants than for noninfested plants. Overall, green buttonwood was more susceptible to larval root feeding damage than either live oak or pygmy date palm.     

Not a load of rubbish: simulated field trials in large‐scale containers

Assessment of yield performance under fluctuating environmental conditions is a major aim of crop breeders. Unfortunately, results from controlled‐environment evaluations of complex agronomic traits rarely translate to field performance. A major cause is that crops grown over their complete lifecycle in a greenhouse or growth chamber are generally constricted in their root growth, which influences their response to important abiotic constraints like water or nutrient availability. To overcome this poor transferability, we established a plant growth system comprising large refuse containers (120 L ‘wheelie bins’) that allow detailed phenotyping of small field‐crop populations under semi‐controlled growth conditions. Diverse winter oilseed rape cultivars were grown at field densities throughout the crop lifecycle, in different experiments over 2 years, to compare seed yields from individual containers to plot yields from multi‐environment field trials. We found that we were able to predict yields in the field with high accuracy from container‐grown plants. The container system proved suitable for detailed studies of stress response physiology and performance in pre‐breeding populations. Investment in automated large‐container systems may help breeders improve field transferability of greenhouse experiments, enabling screening of pre‐breeding materials for abiotic stress response traits with a positive influence on yield.     

Effects of root architecture, physical tree characteristics, and soil shear strength on maximum resistive bending moment for overturning Salix babylonica and Juglans ailanthifolia

Effects of root architecture, physical tree characteristics, and soil shear strength on overturning moment due to flooding were investigated using Salix babylonica and Juglans ailanthifolia, exotic and invasive plants in Japanese rivers. Tree-pulling experiments that simulated flood action were conducted, and the resulting damage was examined to assess the effects of physical tree characteristics and root architecture on the maximum resistive bending moment (M _max) for overturning. In situ soil shear strength tests were conducted to measure soil strength parameters. The effects of species differences on the M _max were examined by analyzing root architecture. S. babylonica has a heart-root system that produces a greater overturning moment due to the strong root anchorage and the large amount of substrate that must be mobilized during overturning. J. ailanthifolia has a plate-root system that produces a smaller overturning moment. However, trees with the plate-root system may withstand overturning better due to an increased root:shoot ratio. The results of the study show that the M _max of a tree for overturning had significant (P < 0.05) correlations with a tree’s physical characteristics, including height (H), trunk diameter at breast height (D _bh), D _bh², height multiplied by the second power of D _bh (trunk volume index H × D _bh²), and root–soil plate depth (R _d), and root–soil plate radius (R _r). Considering the strategy of J. ailanthifolia to increase the root:shoot ratio for anchoring in the substrate, the trunk volume index (H × D _bh²) is a better parameter than D _bh² because it indirectly involves the difference in below-ground volume and surface area. Different soil cohesion values were found at different experimental sites, and the average M _max for overturning each species decreased linearly with increasing soil cohesion.     

Root–shoot allometry of tropical forest trees determined in a large-scale aeroponic system

Background and Aims

This study is a first step in a multi-stage project aimed at determining allometric relationships among the tropical tree organs, and carbon fluxes between the various tree parts and their environment. Information on canopy–root interrelationships is needed to improve understanding of above- and below-ground processes and for modelling of the regional and global carbon cycle. Allometric relationships between the sizes of different plant parts will be determined.

Methods

Two tropical forest species were used in this study: Ceiba pentandra (kapok), a fast-growing tree native to South and Central America and to Western Africa, and Khaya anthotheca (African mahogany), a slower-growing tree native to Central and Eastern Africa. Growth and allometric parameters of 12-month-old saplings grown in a large-scale aeroponic system and in 50-L soil containers were compared. The main advantage of growing plants in aeroponics is that their root systems are fully accessible throughout the plant life, and can be fully recovered for harvesting.

Key Results

The expected differences in shoot and root size between the fast-growing C. pentandra and the slower-growing K. anthotheca were evident in both growth systems. Roots were recovered from the aeroponically grown saplings only, and their distribution among various diameter classes followed the patterns expected from the literature. Stem, branch and leaf allometric parameters were similar for saplings of each species grown in the two systems.

Conclusions

The aeroponic tree growth system can be utilized for determining the basic allometric relationships between root and shoot components of these trees, and hence can be used to study carbon allocation and fluxes of whole above- and below-ground tree parts.     

Root anchorage of inner and edge trees in stands of Maritime pine (<Emphasis Type="Italic">Pinus pinaster</Emphasis> Ait.) growing in different podzolic soil conditions

Static winching tests were carried out in order to determine the mechanical resistance of Maritime pine to overturning. The tested stands were selected according to podzolic soil conditions: wet Lande, characterised by a shallow ground water table and a hard pan horizon, and dry Lande, with a deeper ground water table and a hard pan absent or broken up. As this soil horizon limits the vertical growth of tree roots, anchorage resistance was investigated with regards to the presence or absence of a hard pan underneath each tree. To determine if mechanical behaviour differed within a stand, trees from inside the stand and edge trees at the border exposed to prevailing winds were also tested. The critical turning moment (TM_crit,total) at the base of the stem was positively related to the variable (H × DBH²) (H, total tree height; DBH, tree diameter). Linear regression analyses between TM_crit,total and (H × DBH²) showed that the presence of a hard pan had no significant effect on anchorage resistance in uprooted trees. Stem failure occurred for 82% of trees on dry Lande when (H × DBH²) < 1 m³. Moreover, stem failure type on dry Lande indicated that trees were better anchored. On soil with a hard pan, edge trees were found to be 20% more resistant to overturning than inner trees. Edge trees differed from inner trees in that the soil-root plate was two times larger and also possessed a larger surface area on the windward side.     

培养容器容积对AM真菌生长发育的影响

研究宿主植物栽培容器对丛枝菌根(Arbuscularmycorrhizae,AM)真菌Glomusmosseae生长发育的影响。结果表明:小容积容器的根系密度相对较大,在菌根共生体建立初期,菌根真菌繁殖体与根接触的机会增大,对于菌根真菌的迅速侵染及共生体的迅速建立非常有利,同时还增大了根外菌丝二次侵染的机会,从而使菌根真菌生长发育形成了一个良性循环,最终有利于根外孢子的形成。容器对共生体的影响决不是简单的盆的体积问题,而与其面积和体积之比有关,也和种植密度有密切关系。     

Spacing patterns of an Acacia tree in the Kalahari over a 61-year period: How clumped becomes regular and vice versa

Nearest tree neighbour distances and the tree spatial formation on a large scale over time and space replicates were examined. The study was conducted in a natural savanna ecosystem in the Southern Kalahari, South Africa. Nearest tree neighbour and point pattern analysis methods were used to investigate changes in the spatial pattern of trees in two plots. Trees larger than 2 m canopy diameter were mapped. We used aerial photographs of the study area from 1940, 1964, 1984, 1993, and a satellite image from 2001 to follow two plots over time. Field work was carried out too for classification accuracy. We were able to identify and individually follow over 2400 individual trees from 1940 until 2001. Nearest neighbour analysis results indicate that dead trees were on average closer to their nearest neighbouring trees than living trees were to their neighbours. Most dead trees were on average 6 m from their nearest neighbours, while most living trees were about 20 m apart. Point pattern analysis results show a cyclical transition from clumped to random and sequentially to regular tree spacing. These transitions were not correlated across two plots. Generally, decreases in small-scale clumping coincided with periods of high mortality. Our findings show that regular, clumped, and random tree pattern can occur, pending on time, location, and scale within the location.