Spatial Distribution Of Roots Research Articles

Relationships between soil structure, root distribution and water uptake of chickpea ( Cicer arietinum L.). Plant growth and water distribution

Root clustering as a consequence of soil compaction has been hypothesised as a cause of reduction in both water uptake and growth of plants. On the basis of such a hypothesis models of water uptake that take root spatial arrangement into account have been proposed. Data to validate such models are scarce, particularly for leguminosae. This research was conducted on chickpea with the aim of studying the spatial distribution of roots and water in growth media of different degrees of compaction. Chickpea var. Sultano was grown in pots containing silty-clay soil with aggregates of <0.5 cm in diameter for treatment TF (fine soil), and fine soil + a large clod (representing 30–33% of the total soil dry weight) for treatment TF+Z. Each pot was brought to field capacity and covered with mulch to avoid evaporation losses. Plants were grown on stored water. The treatment with homogeneous soil (TF) showed a higher above-and below-ground growth and water uptake compared with those of TF+Z. A hyperbolic relation was found between root density and soil resistance penetration. Roots were distributed quite homogeneously in the fine soil of both treatments, but they colonised only the outer parts of the clods. At the end of the experiment treatment TF+Z showed unextracted water in the clods. The spatial distribution of roots and the plant ability to take up water were strongly affected by soil structural conditions.

Productivity, microclimate and water use in Grevillea robusta-based agroforestry systems on hillslopes in semi-arid Kenya

This paper describes a multi-disciplinary project to examine the changing interactions between trees and crops as the trees in semi-arid agroforestry systems establish and mature; the project is one of the most detailed and highly instrumented long-term studies of tree and crop growth, system performance, resource capture, hydrology and microclimate ever carried out within an agroforestry context. Its primary objective was to compile a comprehensive experimental database to improve the mechanistic understanding of tree/crop interactions and support the development and validation of process-based simulation models describing resource capture and tree and crop growth in semi-arid agroforestry systems. Grevillea robusta A. Cunn. (grevillea) trees were grown as mono-cultures or in mixtures with cowpea ( Vigna unguiculata L.) or maize ( Zea mays L.) over a 68-month period. Allometric approaches were used to determine seasonal and annual growth increments for leaf area and leaf, branch and trunk biomass in grevillea. Crop performance was examined during each growing season, while the spatial distribution of tree and crop roots was established during the latter stages of the experiment using coring and mini-rhizotron approaches. Detailed hydrological studies examined effects on the soil water balance and its components (precipitation, interception, runoff and soil moisture status); equivalent measurements of spatial and temporal variation in microclimatic conditions allowed the mechanistic basis for beneficial and detrimental effects on understorey crops and the influence of proximity to trees on crop performance to be examined. Transpiration by grevillea and water movement through lateral and tap roots were measured using sap flow methodology, and light interception by the tree and crop canopies was routinely determined. This multi-disciplinary study has provided a detailed understanding of the changing patterns of resource capture by trees and crops as agroforestry systems mature. This paper provides an overview of the underlying rationale, experimental design and core measurements, outlines key results and conclusions, and draws the attention of readers to further papers providing more detailed consideration of specific aspects of the study.

Biomass of Fine and Small Roots in Two Japanese Black Pine Stands of Different Ages

The biomass and the spatial distribution of fine and small roots were studied in two Japanese black pine (Pinus thunbergii Parl.) stands growing on a sandy soil. More biomass of fine and small roots was found in the 17-year-old than in the 40-year-old stand. There were 62 g m−2 of fine roots and 56 g m−2 of small roots in the older stand, which represented mean values of 608 g for fine and 552 g for small roots per tree, respectively. In the younger stand, a total of 85 g m−2 of fine roots and 66 g m−2 of small roots were determined, representing a mean of 238 g for fine and 186 g for small roots per tree, respectively. Fine and small root biomasses decreased linearly with a soil depth of 0–50 cm in the older stand. In the younger stand, the fine and small roots developed only up to a depth of 30 cm. Horizontal distributions (with regard to distance from a tree) of both root groups were homogeneous. A positive correlation in the amount of biomass of fine and small roots per m2 relative to tree size was found. Fine and small root biomasses increased consistently from April to July in both stands. The results also indicated earlier growth activity of the fine roots than small roots at the beginning of the growing season. The seasonal increases in fine and small root biomasses were slightly higher in the younger stand than the older stand.

The Distribution of Wheat and Maize Roots as Influenced by Biopores in a Subsoil of the Kanto Loam Type

Biopores are tubular soil macropores left by plant roots after their decay or burrowed by soil animals, which provide channels for deep rooting and improve crop access to water and nutrients. The density oi biopores, number of biopores per unit area, and proportion of biopores occupied by roots were measured on horizontal soil profiles at 30, 50, and 70 cm in depth in a fine-texture subsoil of Andosol (Light clay, a volcanic ash of the Kanto loam type) at the mature stage of wheat and maize. Images of 0,1 mm resolution from the pictures of cleaned profile surfaces were examined on a computer display. Dark spots with a circular and smooth boundary were regarded as biopores. The density of biopores larger than 1 mm in diameter ranged from 500 to 2,000 m–2. The percentage of biopores occupied by roots was more than 30% of biopores larger than 1 mm and increased with depth. Roots were accumulated in biopores. The proportion of biopores (> 1 mm) with roots increased with depth. It was 28-35% in the wheat plot and 14-20% in the maize plot. This suggested that thinner wheat roots easily entered a biopore and remained in it. The possible influence of biopores on the spatial distribution of roots was discussed.

Efecto de una plantación de Pinus radiata en la distribución espacial del contenido de agua del suelo

The effect of a 15-year-old Pinus radiata plantation, with a density of 460 trees/ha, on spatial and temporal soil water content was determined in the area of Collipulli, IX Region of Chile Precipitation, interception loss, temporal and spatial variation of the soil-water-content and the spatial distribution of active roots up to a depth of three meters were measured. The results were compared with those from a natural Agrostis-Holcus meadow in the same area. The total amount of active roots was 37.2 t/ha of dry matter for Pinus radiata and 9.5 t/ha for the meadow. Most roots were found in the first 50 cm of soil for both sites. Horizontal distribution of the roots was more homogeneous in the meadow, whereas in the forest a higher concentration of roots was found near the trees. The maximum depth reached by roots in the forest was 2.5 m, whereas in the meadow they reached only 1.1 m. In the forest plantation, the horizontal distribution of the soil water content was more uneven, as a result of the canopy interception and the heterogeneous distribution of the roots. The evapotranspiration effect on the soil water content exceeded 3 m of depth under the forest, but in contrast, was up to 150 cm in the meadow.

Root zone solute dynamics under drip irrigation: A review

Infiltration and subsequent distribution of water and solutes under cropped conditions is strongly dependent on the irrigation method, soil type, crop root distribution, and uptake patterns and rates of water and solutes. This review discusses aspects of soil water and solute dynamics as affected by the irrigation and fertigation methods, in the presence of active plant uptake of water and solutes. Fertigation with poor quality water can lead to accumulation of salts in the root zone to toxic levels, potentially causing deterioration of soil hydraulic and physical properties. The high frequency of application under drip irrigation enables maintenance of salts at tolerable levels within the rooting zone. Plant roots play a major role in soil water and solute dynamics by modifying the water and solute uptake patterns in the rooting zone. Modeling of root uptake of water and solutes is commonly based on incorporating spatial root distribution and root length or density. Other models attempt to construct root architecture. Corn uptake rate and pattern of nitrate nitrogen was determined from field studies of nitrate dynamics under drip irrigation using TDR monitoring. The determined nitrate nitrogen uptake rates are within literature values for corn.

X-ray computed tomography to quantify tree rooting spatial distributions

Poor root development due to constraining soil conditions could be an important factor influencing health of urban trees. Therefore, there is a need for efficient techniques to analyze the spatial distribution of tree roots. An analytical procedure for describing tree rooting patterns from X-ray computed tomography (CT) data is described and illustrated. Large irregularly shaped specimens of undisturbed sandy soil were sampled from various positions around the base of trees using field impregnation with epoxy resin, to stabilize the cohesionless soil. Cores approximately 200 mm in diameter by 500 mm in height were extracted from these specimens. These large core samples were scanned with a medical X-ray CT device, and contiguous images of soil slices (2 mm thick) were thus produced. X-ray CT images are regarded as regularly-spaced sections through the soil although they are not actual 2D sections but matrices of voxels ∼0.5 mm×0.5 mm×2 mm. The images were used to generate the equivalent of horizontal root contact maps from which three-dimensional objects, assumed to be roots, were reconstructed. The resulting connected objects were used to derive indices of the spatial organization of roots, namely: root length distribution, root length density, root growth angle distribution, root spatial distribution, and branching intensity. The successive steps of the method, from sampling to generation of indices of tree root organization, are illustrated through a case study examining rooting patterns of valuable urban trees.

The effects of free‐air CO2 enrichment and soil water availability on spatial and seasonal patterns of wheat root growth

Abstract Spring wheat [ Triticum aestivum (L). cv. Yecora Rojo] was grown from December 1992 to May 1993 under two atmospheric CO2 concentrations, 550 μmol mol–1 for high‐CO2 plots, and 370 μmol mol–1 for control plots, using a Free‐Air CO2 Enrichment (FACE) apparatus. In addition to the two levels of atmospheric CO2, there were ample and limiting levels of water supply through a subsurface trip irrigation system in a strip, split‐plot design. In order to examine the temporal and spatial root distribution, root cores were extracted at six growth stages during the season at in‐row and inter‐row positions using a soil core device (86 mm ID, 1.0 m length). Such information would help determine whether and to what extent root morphology is changed by alteration of two important factors, atmospheric CO2 and soil water, in this agricultural ecosystem.Wheat root growth increased under elevated CO2 conditions during all observed developmental stages. A maximum of 37% increase in total root dry mass in the FACE vs. Control plots was observed during the period of stem elongation. Greater root growth rates were calculated due to CO2 enhancement until anthesis. During the early vegetative growth, root dry mass of the inter‐row space was significantly higher for FACE than for Control treatments suggesting that elevated CO2 promoted the production of first‐order lateral roots per main axis. Then, during the reproductive period of growth, more branching of lateral roots in the FACE treatment occurred due to water stress. Significant higher root dry mass was measured in the inter‐row space of the FACE plots where soil water supply was limiting. These sequential responses in root growth and morphology to elevated CO2 and reduced soil water supports the hypothesis that plants grown in a high‐CO2 environment may better compensate soil‐water‐stress conditions.

Macropore sheath: quantification of plant root and soil macropore association

Plants require roots to supply water, nutrients and oxygen for growth. The spatial distribution of roots in relation to the macropore structure of the soil in which they are growing influences how effective they are at accessing these resources. A method for quantifying root-macropore associations from horizontal soil sections is illustrated using two black vertisols from the Darling Downs, Queensland, Australia. Two-dimensional digital images were obtained of the macropore structure and root distribution for an area 55 x 55 mm at a resolution of 64 mu m. The spatial distribution of roots was quantified over a range of distances using the K-function. In all specimens, roots were shown to be clustered at short distances (1-10 mm) becoming more random at longer distances. Root location in relation to macropores was estimated using the function describing the distance of each root to the nearest macropore. From this function, a summary variable, termed the macropore sheath, was defined. The macropore sheath is the distance from macropores within which 80% of roots are located. Measured root locations were compared to random simulations of root distribution to establish if there was a preferential association between roots and macropores. More roots were found in and around macropores than expected at random.

Root System Morphology of Pepper and Melon at Harvest Stage Grown with Drip Irrigation under Desert Conditions in Baja California, Mexico.

メキシコ合衆国バハ・カリフォルニア州のゲレロ・ネグロにおいて, 日本政府とメキシコ政府の共同事業としてメキシコ沙漠地域農業開発プロジェクト(以下, プロジェクト)が実施されている.プロジェクトの目的は, 沙漠地域において点滴灌漑を用いて野菜および果樹を栽培するための技術の開発および移転にある.この目的を十分に達成するために, プロジェクトで最も重要な作物であるトウガラシとメロンの根系の形態を, 収穫期に調査した.その結果, 露地栽培のトウガラシの場合は, 根長密度が土壌表面から深くなるにつれて緩やかに減少し, 深さ20cm以下で急激に小さくなっていたが, 条直下と条間の根長密度の差は小さかった.畝立マルチ栽培のメロンの場合は, 畝の中の根長密度がかなり大きく, 畝の外では小さかった.主根から形成された側根には, 線虫の被害と考えられる多数のコブが認められた.次に, 根系形態に及ぼす点滴灌漑の影響を検討するため, 点滴チューブが配置された側と反対側における根長密度を比較した。その結果, トウガラシでは, 条の左右のいくつかの地点で, 根長密度に統計的に有意な差が認められた.一方, メロンではどの地点についても有意な差は認められなかったが, 根長密度の分布が部分的に非対称であった.以上のような根系分布の非対称性は, 点滴チューブの有無によるものと考えられる.なお, 予備調査の結果, 根長密度が高い部分で側根の形成が発達していること, とくに側根が長いことが示唆された.

Comparison of root distributions of species in North American grasslands using GIS

Abstract. We quantified the spatial distribution of roots of individual plants using detailed drawings from the literature of species of grasses, forbs, and shrubs in the Central Great Plains grasslands of North America. We scanned each two‐dimensional drawing electronically and used ARC/INFO, a Geographic Information System, to calculate root length (cm) and density (cm root length/cm soil) with depth in the soil profile. We then selected one of three mathematical models that best fit the data, and classified each species as either shallow‐, medium‐ or deep‐rooted. 66 root drawings from 55 species were evaluated. Most plants were shallow‐rooted with largest root densities occurring at depths &lt; 20 cm; most maximum rooting depths were &gt; 1m. Grasses had the shallowest maximum depth and shrubs the deepest. Deep‐rooted forbs had the smallest root densities by depth. Most plants had two sections to their distribution of root density: an initial increase from the soil surface followed by a decrease in density with increasing depth. Our results suggest that the abundance and importance of different species and growth forms in North American grasslands is related to similarities and differences in the spatial distributions of their root systems. Our approach provides quantitative information on root distributions to be used for comparisons among species, and in simulation modeling analyses that could not be done with conventional methods that are qualitative in nature.

Modelling and simulation of the architecture and development of the oil-palm (Elaeis guineensis Jacq.) root system : II. Estimation of root parameters using the RACINES postprocessor

A stochastic model of oil-palm (Elaeis guineensis Jacq.) root system architecture and development has been developed. This model enabled us to create 3-D numerical models of complete root systems by simulation. The application of a postprocessor software, called "RACINES", to these 3-D numerical models, provided an estimation of some parameters of plant root systems. The objective of this paper is to present oil-palm root characteristics as possible outputs of the application of this RACINES software. The outputs described in this article cover (i) spatial distribution of roots under plantation conditions, (ii) the estimation and distribution of total root biomass, per root type or per soil horizon and (iii) the location and quantification of absorbent surfaces. The computing techniques used were based on voxellization of space and creation of 3-D virtual sceneries exactly reproducing observed planting designs. By comparing the results of observations and simulations for spatial distribution (by trench wall density maps) and root biomasses (by real and virtual sampling) we were able to carry out additional numerical validations of the model. (Resume d'auteur)

Modelling and simulation of the architecture and development of the oil-palm (Elaeis guineensis Jacq.) root system. I. The model

A stochastic model of oil-palm (Elaeis guineensis Jacq.) root system architecture and development has been developed. This model enabled us to create 3-D numerical models of complete root systems by simulation. The application of a postprocessor software, called “RACINES”, to these 3-D numerical models, provided an estimation of some parameters of plant root systems. The objective of this paper is to present oil-palm root characteristics as possible outputs of the application of this RACINES software. The outputs described in this article cover (i) spatial distribution of roots under plantation conditions, (ii) the estimation and distribution of total root biomass, per root type or per soil horizon and (iii) the location and quantification of absorbent surfaces. The computing techniques used were based on voxellization of space and creation of 3-D virtual sceneries exactly reproducing observed planting designs. By comparing the results of observations and simulations for spatial distribution (by trench wall density maps) and root biomasses (by real and virtual sampling) we were able to carry out additional numerical validations of the model.

Influence of spatial root distribution, organic nitrogen mineralization and fertilizer application on soil interlayer ammonium

Influence of spatial root distribution, organic nitrogen mineralization and fertilizer application on soil interlayer ammonium

Influence of spatial root distribution, organic nitrogen mineralization and fertilizer application on soil interlayer ammonium

The amount of interlayer NH 4 + -N and net mineralization of organic N were measured at periodic intervals, over a period of 10 months, in soil samples collected from a peach orchard which had been subjected to different rates of N fertilizer application. Two different groups of soil samples, designated sampling 1 and sampling 2 were collected. Soils of sampling 1 were collected from sites where the soil was heavily penetrated by tree roots and those of sampling 2 were collected from sites where the soil remained free from tree roots. In sampling 1, during the 10-month period, the concentration of interlayer NH 4 + -N showed significant variations, while in sampling 2 no significant variation was found. In sampling 1 the amount of NH 4 + -N released from the interlayers of the clay minerals were not influenced by the N fertilizer application rate. Changes in the interlayer NH 4 + -N concentrations were related to variation in net N mineralization and immobilization rates as well as to plant uptake N. It is concluded that, in our experiment, the dynamics of interlayer NH 4 + -N in soil were influenced by the spatial distribution of the tree roots and organic N mineralization, while N application influenced seasonal variation but not the total interlayer NH 4 + -N released during the experiment.

A comparison of soil core sampling and minirhizotrons to quantify root development of field-grown potatoes

Root growth of potato (Solanum tuberosum L.) is sensitive to soil conditions. A reduced root system size can result in reduced uptake of water and/or nutrients, leading to impaired crop growth. To understand the mechanisms by which soil conditions affect crop growth, study of temporal and spatial development of roots is required. In field experiments, effects of soil temperature, soil compaction and potato cyst nematodes (Globodera pallida) on root growth of potato cultivars were studied using two methods: core sampling and vertically oriented minirhizotrons. Minirhizotrons showed relatively more roots in deeper soil layers than core sampling, probably because of preferential root growth along the tube. Spatial distribution of roots should therefore be analysed by core sampling. To eliminate differences in spatial distribution, total root systems as measured by both methods were compared. Nematodes, cultivars and time did not affect the relationship between both methods. Soil compaction, however, affected it because of a strong response of root length in bulk soil and small differences in root number against the minirhizotron, suggesting that soil coring has to be used to study effects of different bulk densities. With both methods, sequential measurements of roots give the net effect of root growth and decay. Data on root turnover can only be obtained with minirhizotrons by comparing video recordings of different dates. Other information obtained with minirhizotrons is the average orientation of roots. Moreover, the minirhizotron method has the advantage of demanding less labour.

Evaluation in field conditions of a three-dimensional architectural model of the maize root system: Comparison of simulated and observed horizontal root maps

Most existing water and nutrient uptake models are based on the assumption that roots are evenly distributed in the soil volume. This assumption is not realistic for field conditions, and significantly alters water or nutrient uptake calculations. Therefore, development of models of root system growth that account for the spatial distribution of roots is necessary.

Grass barriers in cassava hillside cultivation: Rooting patterns and root growth dynamics

Living grass barriers can effectively reduce soil erosion on hillsides under cassava [ Manihot esculenta Crantz]. Competition below ground in barrier-crop systems is, however, poorly understood. The objectives of this study were, therefore, (i) to describe rooting patterns and spatial root distribution of cassava and of grasses commonly used as live barriers in soil conservation, and (ii) to determine root growth dynamics over time, using direct observation and quantitative methods. Field research was carried out near Santander de Quilichao, Colombia, on a Typic Dystropept soil where average annual precipitation is 1799 mm. Single 20-m rows of vetiver grass [ Vetiveria zizanioides (L.) Nash], lemon grass [ Cymbopogon citratus (DC. ex Nees) Stapf] and guatemala grass [ Tripsacum andersonii J.R. Gray] were grown on a 13% slope. Cassava was planted in rows on either side of the grass barriers. Observation pits were dug in the cassava-grass plots and perspex sheets fitted closely to exposed walls. These pits allowed periodic tracing of roots. Root length was recorded in metres either per total of an exposed surface measuring 0.8 (depth) and 1.2 m (width) or measuring 0.2 (depth) × 1.2 m (width). Because of their vertical growth and their weak tendency to branch, the roots of vetiver grass rarely mixed with cassava roots, signifying a largely separate soil exploration by the two plants. In contrast, the profuse vertical and horizontal spread of guatemala grass and cassava roots indicated a joint exploration of soil volume. The cassava-lemon grass system revealed an intermediate pattern. The longest roots per exposed area of 0.2 × 1.2 m were observed for cassava growing on both sides of the vetiver grass barrier, and increasing from 6.0 m in the 0–20 cm profile segment to 7.3 m in the 20–40 cm segment. In contrast, roots of cassava with guatemala grass shortened from 5.4 m in the uppermost profile segment to 3.6 m in the 20–40 cm segment. Vetiver grass exhibited the slowest and steadiest root growth and guatemala grass the fastest. Final total root lengths obtained from the entire exposed soil profile were 7 m for vetiver grass, 16 m for guatemala grass and 17 m for lemon grass. Cassava root growth was very slow initially, but increased 25–28 weeks after grass planting when grass root growth temporarily slowed down as a result of cutback. Final total cassava root lengths obtained from the exposed soil profile were 17, 10 and 10 m in association with the three grasses, respectively. The differences in rooting pattern, root growth dynamics and final root lengths suggest that different degrees of root interaction may have occurred, with possible consequences for soil exploration, and nutrient and water uptake.

Spatial Distribution of Roots in Sweetgum and Loblolly Pine Monocultures and Relations with Above-Ground Biomass and Soil Nutrients

Models of plant-plant interactions often assume that root systems are symmetrically arranged around individual plants and, therefore, below-ground competition intensity is a function of inter-plant distance. To explore this assumption, we measured three-dimensional distributions (horizontal and vertical dimensions) of roots in one plot each of a 3-year-old Sweetgum Sprout (root-stock : 4 years) and 3-year-old Loblolly Pine monoculture. In each plot, 0.5 m grids were set and all roots in each 0.25 m 2 section (horizontal dimensions) were washed from the soil in four horizons (vertical dimension) down to a total depth of 60 cm. Fine-root biomass summed across the vertical dimension was not correlated with local above-ground biomass, an indication that distance-dependent patterns of root distribution were not strong, at least in the scale of this study. Three-dimensional fine root density was, however, correlated with levels of soil P and K but not soil N or organic matter. Compared to a null model of symmetrical horizontal root distribution, actual root systems of individual plants appeared to avoid inter-plant overlap. Compared with Loblolly Pine, Sweetgum root systems were less concentrated in the upper 10 cm and more symmetric overall. We propose that distance-dependent patterns of below-ground plant-plant interactions will be diminished by the tendency for roots to forage for nutrients and avoid overlap with roots of other plants, and by differences among species in root system behaviour.

Distribution of soil invertase in relation to the root systems ofPicea sitchensis (Bong.) Carr. andAcer pseudoplatanus L. during development of young plants

A method is described for sampling rhizosphere soil under newly establishedPicea sitchensis andAcer pseudoplatanus. The technique involves taking soil samples to a depth of 150 mm at 100 mm intervals along transects, each 45° from its neighbour, radiating from the base of the stem. Invertase activities were measured in the soil samples and compared to their activities in fallow and rhizosphere soils. When the field soil was dry, the tree root systems were carefully excavated to retain as many fine roots as possible. The distribution of the soil invertase was matched to the spatial distribution of the roots showing the precise position of the rhizosphere relative to the initial ‘blind’ soil sampling. Statistics were applied to derive equations for calculating the percentage enzyme activity relative to that found in rhizosphere soil at various locations radiating from the base of the stem. This information was subsequently applied to soil sampled under trees of the same age as those excavated to give a non-destructive method for sampling rhizosphere soil routinely from under a large number of trees.