The architecture of Picea sitchensis structural root systems on horizontal and sloping terrain

The coarse root systems of 24 Sitka spruce (Picea sitchensis (Bong.) Carr.) trees, from a 40-year-old plantation in west Scotland, were extracted, digitised in three dimensions, and root topology was recorded. Roots were from trees grown on a steep (ca. 30°) north-facing slope, and from an adjacent horizontal area with similar gleyed mineral soil. The prevailing wind was across-slope from the west. Analysis of below-ground parts of the trees in comparison with those above-ground revealed a positive linear relationship between coarse root volume and stem volume. Most non-directional characteristics of the root systems were similar between trees on the slope and on flat terrain. Allocation of root mass around trees was examined in relation to the slope and the prevailing wind direction. Trees on the horizontal area had more root mass in leeward sectors than other sectors, but trees on the slopes had more root mass in the windward sectors than other sectors. Centres of mass of the root systems from the horizontal part of the site were not significantly clustered in any direction, but root systems of trees on the slope had centres of mass significantly clustered across the slope in the windward direction. For trees on the slope, the mean direction of the largest sector without structural roots was 4° from north, i.e. downslope. The results are discussed in relation to soil characteristics and the biomechanical behaviour of trees on slopes.     

Root architecture: Influence of metameric organization and emission of lateral roots

Abstract

It has yet to be established whether or not root architecture results from a metameric organization similar to that recognizable in the stem. To address this question, we have reviewed the data on the major cytological, histological and anatomical events underlying root development and on the intrinsic factors controlling these events. The evidence emerging from this review indicates that root architecture has a metameric organization that can be ‘deranged’ when environmental factors interfere with the intrinsic factors rhythmically controlling lateral root development. Metameric patterning occurs in the primary body of a root, but not in the secondary body. This difference can be attributed to the fact that primary and secondary body roots arise from completely different tissues. The root system of a woody plant is very complex, and its architecture is largely governed by roots with a secondary body organization that lack metameric patterning. The architectural contribution of the portion of roots with a primary body organization, where metameric patterning could be present, is negligible. This explains why it is difficult to recognize metameric patterning in the root architecture of these plants.     

Modelling root structure and stability

Summary Seven fully excavated 16 year-old root systems of Sitka spruce were analysed. All roots in excess of 1 cm diameter at their origin on the stumps were analysed, data being collected until root diameter declined to less than 0.5 cm.Root morphology and distribution was identified as a balance between systematic biological mechanisms and their disruption by environmental factors, particularly changes of soil density and soil surface contours. The biological mechanisms have been modelled and the model is capable of simulating root systems in response to a few simple input variablese.g. the number of roots originating at stumps, stem ratius, total number of roots of all ordersetc.Additionally equations have been developed to estimate the distribution of root diameter, and root weight at all distances from tree stems and a similar equation permits the estimation of tree diameter at chosen heights. These latter estimates being utilized to calculate the turning moment of stems when blown by the wind.The influence of the wind on turning moment is explored for simulated root systems of differing strength and gross morphology.     

Drought‐related tree death of savanna eucalypts: Species susceptibility,soil conditions and root architecture

Questions: For eucalypt savanna in northeast Australia subject to multi‐year rainfall deficits this paper asks whether (1) dominant tree species (Ironbarks, Boxes) are more drought susceptible than the sub‐dominant Bloodwoods; (2) whether soil moisture is beyond wilting point in surface soil layers but available at depth; (3) soil conditions (moisture availability and texture) are related to tree death during drought; (4) the root systems of the Boxes and Ironbarks are shallower than the Bloodwoods; and the survivors of drought within species have deeper root systems than those that died. Location: Central Queensland, Australia. Methods: Patterns of tree death between eucalypt species were compared from field data collected after drought. Soil conditions during drought were described and compared with patterns of tree death for the Ironbark Eucalyptus melanophloia. The basal area and orientation of coarse roots were measured on upturned trees after broad‐scale tree clearing, and compared between species, and between live and dead trees with tree size as a covariate. Results: Drought‐induced tree death was higher for dominant Ironbark‐Box than for sub‐dominant Bloodwoods. During a moderate to severe drought in 2004, 41% of 100 cm deep subsoils had soil matric potential less than‐5600 kPa. The drought hardy Bloodwoods had a greater root basal area and particularly so for vertical roots compared to the drought sensitive Ironbark‐Box. Within species there was no significant difference in root basal area characteristics between trees that were recently killed by drought and those that remained relatively healthy. Surface soil moisture availability was lower where tree densities were high, and tree death increased as surface soil moisture became less available. Tree death was also greater as the clay content of sub‐soils increased. Discussion: The study suggests species with roots confined to upper soil layers will suffer severe water stress. The results strongly indicate that root architecture, and the way it facilitates water use during drought, is important for the relative dominance of the tree species. Patchiness in drought‐induced tree death seems to be at least partially a product of heterogeneity in sub‐soil conditions and competition for soil moisture.     

Root water uptake and profile soil water as affected by vertical root distribution

Water uptake by plant roots is a main process controlling water balance in field profiles and vital for agro-ecosystem management. Based on the sap flow measurements for maize plants (Zea mays L.) in a field under natural wet- and dry-soil conditions, we studied the effect of vertical root distribution on root water uptake and the resulted changes of profile soil water. The observations indicate that depth of the most densely rooted soil layer was more important than the maximum rooting depth for increasing the ability of plants to cope with the shortage of water. Occurrence of the most densely rooted layer at or below 30-cm soil depth was very conducive to maintaining plant water supply under the dry-soil conditions. In the soil layers colonized most densely by roots, daytime effective soil water saturation (S _e) always dropped dramatically due to the high-efficient local water depletion. Restriction of the rooting depth markedly increased the difference of S _e between the individual soil layers particularly under the dry-soil conditions due likely to the physical non-equilibrium of water flow between the layers. This study highlights the importance of root distribution and pattern in regulating soil water use and thereby improving endurance of plants to seasonal droughts for sustainable agricultural productivity.     

Root growth as influenced by aggregate size

Summary This study examined the effects of aggregate size on root impedance and developed an equation to describe the root pressure necessary to avoid deflection around an aggregate. This critical root pressure was predicted to increase with increasing aggregate size, decreasing root diameter, and decreasing deflection angle. In growth chamber experiments, maize (Zea mays L.) seedlings were grown in A horizon material of Groseclose silt loam (Clayey, mixed, mesic, Typic Hapludult). The soil had been moist sieved into different aggregate sizes (0–1, 1–2, 2–3, and 3–6 mm diameter). The larger aggregates did constitute a slight root impedance as roots were deflected around them. Diameters of roots grown in 3–6 mm aggregates increased significantly, whereas root lengths were not always signficantly decreased. The smaller aggregates did not impede root growth and were readily displaced by roots. Large aggregates were more of an impedance to lateral roots than to main axes.     

Root architecture and allocation patterns of eight native tropical species with different successional status used in open-grown mixed plantations in Panama

We investigated biomass allocation and root architecture of eight tropical species with different successional status, as classified from the literature, along a size gradient up to 5 m. We focused on belowground development, which has received less attention than aboveground traits. A discriminant analysis based upon a combination of allocational and architectural traits clearly distinguished functional types and classified species according to successional status at a 100% success rate. For a given plant diameter, the pioneer species presented similar root biomass compared to the non-pioneer ones but higher cumulative root length and a higher number of root apices. A detailed study on the root system of a sub-sample of three species showed that the most late-successional species (Tabebuia rosea) had longer root internodes and a higher proportion of root biomass allocated to the taproot compared to the other two species (Hura crepitans and Luehea seemannii). Most pioneer species showed a higher leaf area ratio due to a higher specific leaf area (SLA). We conclude that the functional differences between pioneer and non-pioneer tree species found in natural forests were maintained in open-grown plantation conditions.     

A density-based approach for the modelling of root architecture: application to Maritime pine (Pinus pinaster Ait.) root systems

Root morphology influences strongly plant/soil interactions. However, the complexity of root architecture is a major barrier when analysing many phenomena, e.g. anchorage, water or nutrient uptake. Therefore, we have developed a new approach for the representation and modelling of root architecture based on branching density. A general root branching density in a space of finite dimension was used and enabled us to consider various morphological properties. A root system model was then constructed which minimizes the difference between measured and simulated root systems, expressed with functions which map root density in the soil. The model was tested in 2D using data from Maritime pine Pinus pinaster Ait. structural roots as input. We showed that simulated and real root systems had similar root distributions in terms of radial distance, depth, branching angle and branching order. These results indicate that general density functions are not only a powerful basis for constructing models of architecture, but can also be used to represent such structures when considering root/soil interaction. These models are particularly useful in that they provide a local morphological characterization which is aggregated in a given unit of soil volume.     

Root growth of potato crops on a marine-clay soil

Summary In 1982 and 1983 root samples were taken by auger from potato crops grown on marine clay in the Flevo-Polder. The roots increased their penetration depth throughout the periods of measurement, and ultimately reached depths between 80 cm and 100 cm below the hills. Between 50 and 60 days after emergence, decay of roots commenced, starting in the upper horizons. In the hill mean root length densities varied between 1 and 2 cm cm⁻³. Below the hills root density rarely exceeded 1 cm cm⁻³. The random variation in root density was equivalent to a coefficient of variation of 50%. There were significant effects of the position of sampling (relative to the centre of the plant) on root density; densities were usually lowest beneath the furrow. Depending on season and sampling date, total root length varied between 3.4 and 7.1 km m⁻², and root dry mass varied between 33 and 77 g m⁻². Representative figures for specific root length were 100–120 m g⁻¹ dry weight. About 90% of the root diameters were smaller than 0.44 mm; the most frequent class (35%) were roots with diameters between 0.12 and 0.20 mm.     

Root production and turnover in an upland grassland subjected to artificial soil warming respond to radiation flux and nutrients, not temperature

Root demographic processes (birth and death) were measured using minirhizotrons in the soil warming experiments at the summit of Great Dun Fell, United Kingdom (845 m). The soil warming treatment raised soil temperature at 2 cm depth by nearly 3°C. The first experiment ran for 6 months (1994), the second for 18 (1995–1996). In both experiments, heating increased death rates for roots, but birth rates were not significantly increased in the first experiment. The lack of stimulation of death rate in 1996 is probably an artefact, caused by completion of measurements in late summer of 1996, before the seasonal demography was concluded: root death continued over the winter of 1995–1996. Measurements of instantaneous death rates confirmed this: they were accelerated by warming in the second experiment. In the one complete year (1995–1996) in which measurements were taken, net root numbers by the end of the year were not affected by soil warming. The best explanatory environmental variable for root birth rate in both experiments was photosynthetically active radiation (PAR) flux, averaged over the previous 5 (first experiment) or 10 days (second experiment). In the second experiment, the relationship between birth rate and PAR flux was steeper and stronger in heated than in unheated plots. Death rate was best explained by vegetation temperature. These results provide further evidence that root production acclimates to temperature and is driven by the availability of photosynthate. The stimulation of root growth due to soil warming was almost certainly the result of changes in nutrient availability following enhanced decomposition. Received: 4 May 1999 / Accepted: 18 May 1999     

Lettuce, a shallow-rooted crop, and Lactuca serriola, its wild progenitor, differ at QTL determining root architecture and deep soil water exploitation

Wild plant species are often adapted to more stressful environments than their cultivated relatives. Roots are critical in exploiting soil resources that enable plants to withstand environmental stresses, but they are difficult to study. Cultivated lettuce (Lactuca sativa L.) and wild L. serriola L. differ greatly in both shoot and root characteristics. Approximately 100 F_2:3 families derived from an interspecific cross were evaluated in greenhouse and field experiments. In the greenhouse, root traits (taproot length, number of laterals emerging from the taproot, and biomass) and shoot biomass were measured 4 weeks after planting. In the field, plants were grown for 9 weeks (close to harvest maturity of the cultivated parent); mild drought stress was induced by withholding water for 1 week, and gravimetric moisture of soil was then determined for five depth increments between 0–100 cm. The families were genotyped using codominantly scored AFLP markers distributed throughout the genome. Composite interval mapping was used to analyze marker-trait associations. Quantitative trait loci were identified for differences between wild and cultivated lettuce for root architectural traits and water acquisition. Thirteen QTL were detected that each accounted for 28–83% of the phenotypic variation. The loci for taproot length (i.e., cm taproot length g^–1 plant biomass) and the ability to extract water from deep in the soil profile co-localized in the genome. These coincident loci were identified in separate experiments. The wild L. serriola is therefore a potential source of agriculturally important alleles to optimize resource acquisition by cultivated lettuce, thereby minimizing water and fertilizer inputs and ultimately enhancing water quality. Received: 25 February 2000 / Accepted: 31 March 2000     

植物根构型特性与磷吸收效率

植物根构型,即根系在生长介质中的空间造型和分布,与磷吸收效率密切相关;认识植物根构型,可为植物磷效率的遗传改良提供依据。长期以来,人们试图定量描述植物根构型,确立一个能客观全面地描述根系三维立体构型的综合指标。试验指出,植物主要通过向地性变化和根冠之间的碳源分配来改变根构型,从而影响磷吸收效率;根系向地性变化可由缺磷等因素所诱导,且存在着一定的遗传变异性。有证据表明,根构型对低磷胁迫的适应性变化是     

根系分泌物国际研究态势分析

近几十年来,根系分泌物及其在生态学中的应用研究取得了很大的进展,植物根系分泌物尤其是森林植被的根系分泌物在生态恢复重建过程中的作用和功能受到越来越多的重视。本文以SCIE、CPCIS、CCR、IC等数据库为统计分析源,检索并分析了数据库中关于根系分泌物的研究论文（论文、会议论文和综述）产出,利用Thomson Data Analyzer（TDA）分析工具和Aureka分析平台进行数据挖掘。分析表明,该研究涉及多个学科领域,近年来在植物与土壤等学科领域的论文数量最多,而在国家分布的主题领域,美国在该领域的论文产出量最高,为全部论文产出的28.93%,基金资助情况方面,以美国国家科学基金会、中国国家基金委为植物根系分泌物研究的主要资助机构。另外从主题词分布、年度研究主题变化等文献计量学的角度进行了统计分析,以揭示国际国内关于植物尤其是林木（区别于作物）根系分泌物研究的发展现状和态势。     

Root architecture and wind-firmness of mature Pinus pinaster

This study aims to link three-dimensional coarse root architecture to tree stability in mature timber trees with an average of 1-m rooting depth. Undamaged and uprooted trees were sampled in a stand damaged by a storm. Root architecture was measured by three-dimensional (3-D) digitizing. The distribution of root volume by root type and in wind-oriented sectors was analysed. Mature Pinus pinaster root systems were organized in a rigid 'cage' composed of a taproot, the zone of rapid taper of horizontal surface roots and numerous sinkers and deep roots, imprisoning a large mass of soil and guyed by long horizontal surface roots. Key compartments for stability exhibited strong selective leeward or windward reinforcement. Uprooted trees showed a lower cage volume, a larger proportion of oblique and intermediate depth horizontal roots and less wind-oriented root reinforcement. Pinus pinaster stability on moderately deep soils is optimized through a typical rooting pattern and a considerable structural adaptation to the prevailing wind and soil profile.     

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.     

Exploring the interacting effect of soil texture and bulk density on root system development in tomato (Solanum lycopersicum L.)

Knowledge of the responses of root systems in horizoned heterogeneous soil is vital to optimise uptake of water and nutrients to maximise crop productivity. We explored the interacting effects of soil bulk density and texture on the development of root systems in tomato.Two main techniques were employed, X-ray micro-Computed Tomography (μCT), to provide non-destructive, three-dimensional (3D) images of root systems in situ and destructive root washing followed by WinRHIZO^® scanning. Solanum lycopersicum L. cv. Ailsa Craig plants were grown in soil columns for 10 days to measure the effect of soil compaction on selected root traits. Treatments included bulk density (1.2–1.6 Mg m⁻³), soil texture (loamy sand and clay loam) and the effects of layering.The effect of bulk density on root growth was greatest 3 days after transplanting (DAT) in both soil types. The effect of soil texture was not apparent at this stage, but was significant at 10 DAT for most root and shoot variables. The influence of bulk density differed between soil types as increasing compaction promoted plant growth in clay loam but retarded root growth in loamy sand.We observed that at 3 DAT root growth is primarily influenced by bulk density but by 10 DAT a switch in the processes regulating root growth occurs and the texture of the soil becomes very influential. Future investigations of root growth must consider soil physical properties individually and at specific time points, as their importance changes as the root system becomes established. Here we have demonstrated both positive and negative impacts across a wide range of bulk density treatments in different soil textures on root growth. This illustrates the importance of understanding the complex nature of root–soil interactions, especially for agricultural practices such as seedbed preparation.     

Frequent fires alter tree architecture and impair reproduction of a common fire‐tolerant savanna tree

• Several Cerrado tree species have traits and structures that protect from fires. The effectiveness of a trait depends on the fire regime, especially the frequency. We used Vochysia elliptica, a common Cerrado tree, as a model to test whether different fire frequencies alter crown architecture and flower, fruit and seed production.
• We analysed the effect of fire on the production of inflorescences, fruits and seeds, as well as seed germination and tree architecture of 20 trees in each of three plots of a long‐term ecological experiment managed with different fire regimes: burned every 2 years (B), burned every 4 years (Q) in mid‐dry season and an area protected from fire (C).
• We found a large negative effect of fire frequency on crown architecture and on flower and fruit production. Trees in C and Q had significantly more main branches and a larger crown area than trees in B. At its peak, a tree in C was expected to produce 2.4 times more inflorescences than Q, and 15.5 times more than B, with similar magnitudes for fruits. Sixty per cent of trees in B and 10% in Q produced no fruits.
• The differences in architecture might explain the reduction in sexual reproduction due to a smaller physical space to produce flowers at the branch apices. Resource limitation due to plant investment to replace burned vegetative parts may also decrease sexual reproduction. Our results indicate potentially severe consequences of high fire frequencies for population dynamics and species persistence in Cerrado communities.