Root Distribution

Currently used in many countries in the world, vetiver grass (Vetiveria zizanioides) applications include soil and water conservation systems in agricultural environment, slope stabilization, mine rehabilitation, contaminated soil and saline land remediation, as well as wastewater treatment. The root system morphology of vetiver was investigated in a small plantation growing on abandoned marl terraces in southern Spain. Root distribution with depth, laterally from the plant, as well as root parameters such as root diameter and tensile strength were also investigated. The profile wall method combined with the block excavation showed that the vetiver grass grows numerous positively gravitropic roots of more or less uniform diameter. These were generally distributed in the uppermost soil horizon closer to the culm base. In situ shear test on blocks of soil permeated with vetiver roots were carried out and showed a greater shear strength resistance than the samples of non vegetated soil. The root reinforcement measured in situ was comparable to the one predicted by the perpendicular root reinforcement model. The stability of a modelled terraced slope planted with vetiver was marginally greater than the one of a nonvegetated slope. A local instability on one terrace can have a detrimental effect on the overall stability of the terraced slope.

1) to investigate the spatial distribution of fine roots and its correlation with selected soil properties on an artificial ecosystem dominated by woody vegetation species, and (2) to compare the root distribution to that predicted using a global model for natural ecosystems. Root diameter distribution (≤5 mm), root biomass density (RBD), root length density (RLD), soil pH, soil electrical conductivity and dry soil bulk density were measured on soil core samples (217) collected from a trench wall using a 20×20-cm grid sampling. Approximately 90% of the RBD (mean ± standard error: 0.27±0.027 kg m −3 ) and RLD (1.57±0.023 cm cm −3 ) occurred in the top 40 cm, decreasing exponentially to a maximum rooting depth of 150 cm. RBD exhibited a vertical spatial structure associated with soil pH (p<0.05; r 2 = 0.48), and a random lateral distribution. Coefficients of variation (CV) of RBD were high irrespective of orientation (vertical: 79-200%, lateral: 50-236%). The root extinction parameter β (0.944) for the global model was lower (p<0.05) than that of woodlands (β= 0.964-0.976), indicating a shallow root distribution resembling that of grasslands (β=0.943). The superficial root distribution indicated subsoil chemical constraints to root growth, while high lateral variability was attributed to sparse vegetation. The findings stress the need to account for both vertical and lateral variability of roots for accurate modelling of water use and productivity on certain artificial ecosystems with sparse vegetation.

Understanding and predicting ecosystem functioning (e.g., carbon and water fluxes) and the role of soils in carbon storage requires an accurate assessment of plant rooting distributions. Here, in a comprehensive literature synthesis, we analyze rooting patterns for terrestrial biomes and compare distributions for various plant functional groups. We compiled a database of 250 root studies, subdividing suitable results into 11 biorues, and fitted the depth coefficient 1~ to the data for each biome (Gale and Grigal 1987). ~ is a simple numerical index of rooting distribution based on the asymptotic equation Y = 1-~ a, where d = depth and Y = the proportion of roots from the surface to depth d. High values of [3 correspond to a greater proportion of roots with depth. Tundra, boreal forest, and temperate grasslands showed the shallowest rooting profiles ([3 = 0.913, 0.943, and 0.943, respectively), with 80-90% of roots in the top 30 cm of soil; deserts and temperate coniferous forests showed the deepest profiles ([3 = 0.975 and 0.976, respectively) and had only 50% of their roots in the upper 30 cm. Standing root biomass varied by over an order of magnitude across biomes, from approximately 0.2 to 5 kg m -2. Tropical evergreen forests had the highest root biomass (5 kg m-2), but other forest biomes and sclerophyllous shrublands were of similar magnitude. Root biomass for croplands, deserts, tundra and grasslands was below 1.5 kg m -2. Root/shoot (R/S) ratios were highest for tundra, grasslands, and cold deserts (ranging from 4 to 7); forest ecosystems and croplands had the lowest R/S ratios (approximately 0.1 to 0.5). Comparing data across biomes for plant functional groups, grasses had 44% of their roots in the top 10 cm of soil ([3 = 0.952), while shrubs had only 21% in the same depth increment ([3 = 0.978). The rooting distribution of all temperate and tropical trees was ~ = 0.970 with 26% of roots in the top 10 cm and 60% in the top 30 cm. Overall, the globally averaged root distribution for all ecosystems was ~ = 0.966 (r 2 = 0.89) with approximately 30%, 50%, and 75% of roots in the top 10 cm, 20 cm, and 40 cm, respectively. We discuss the merits and possible shortcomings of our analysis in the context of root biomass and root functioning.

____________________________________________________________________________________________________________________________________________________________________________ Chopart JL, Sine B, Dao A, Muller B 2008. Root orientation of four sorghum cultivars: application to estimate root length density from root counts in soil profiles. Plant Root 2: 67-75. doi:10.3117/plantroot.2.67 Copyrights 2008, Plant Root (JSRR), www.plantroot.org O Or ri ig gi in na al l r re es se ea ar rc ch h a ar rt ti ic cl le e Abstract:

In Mediterranean environments, gully erosion is responsible for large soil losses. It has since long been recognized that slopes under vegetation are much more resistant to soil erosion processes compared to bare soils and improve slope stability. Planting or preserving vegetation in areas vulnerable to erosion is therefore considered to be a very effective soil erosion control measure. Re-vegetation strategies for erosion control rely in most cases on the effects of the above-ground biomass in reducing water erosion rates, whereas the role of the below-ground biomass is often neglected or underestimated. While the above-ground biomass can temporally disappear in semi-arid environments, roots may still be present underground and play an important role in protecting the topsoil from being eroded. In order to evaluate the potential of plant species growing in Mediterranean environments to prevent shallow mass movements on gully or terrace walls, the root reinforcement effect of 25 typical Mediterranean matorral species (i.e. shrubs, grasses herbs, small trees) was assessed, using the simple perpendicular model of Wu et al. (Can Geotech J 16:19-33, 1979). As little information is available on Mediterranean plant root characteristics, root distribution data were collected in SE-Spain and root tensile strength tests were conducted in the laboratory. The power root tensile strength-root diameter relationships depend on plant species. The results show that the shrubs Salsola genistoides Juss. Ex Poir. and Atriplex halimus L. have the strongest roots, followed by the grass Brachypodium retusum (Pers.) Beauv. The shrubs Nerium oleander L. and the grass Avenula bromoides (Gouan) H. Scholz have the weakest roots in tension. Root area ratio for the 0-0.1 m topsoil ranges from 0.08% for the grass Piptatherum miliaceum (L.) Coss to 0.8% for the tree Tamarix canariensis Willd. The rush Juncus acutus L. provides the maximum soil reinforcement to the topsoil by its roots (i.e. 304 kPa). Grasses also increase soil shear strength significantly (up to 244 kPa in the 0-0.1 m topsoil for Brachypodium retusum (Pers.) Beauv.). The shrubs Retama sphaerocarpa (L.) Boiss. and Anthyllis cytisoides L. are increasing soil shear strength to a large extent as well (up to 134 and 160 kPa respectively in the 0-0.10 m Plant Soil (

This review summarises current knowledge on root interactions in agroforestry systems, discussing cases from temperate and tropical ecosystems and drawing on experiences from natural plant communities where data from agroforestry systems are lacking. There is an inherent conflict in agroforestry between expected favourable effects of tree root systems, e.g. on soil fertility and nutrient cycling, and competition between tree and crop roots. Root management attempts to optimise root functions and to stimulate facilitative and complementary interactions. It makes use of the plasticity of root systems to respond to environmental factors, including other root systems, with altered growth and physiology. Root management tools include species selection, spacing, nutrient distribution, and shoot pruning, among others. Root distribution determines potential zones of root interactions in the soil, but are also a result of such interactions. Plants tend to avoid excessive root competition both at the root system level and at the single-root level by spatial segregation. As a consequence, associated plant species develop vertically stratified root systems under certain conditions, leading to complementarity in the use of soil resources. Parameters of root competitiveness, such as root length density, mycorrhization and flexibility in response to water and nutrient patches in the soil, have to be considered for predicting the outcome of interspecific root interactions. The patterns of root activity around individual plants differ between species; knowing these may help to avoid excessive competition and unproductive nutrient losses in agroforestry systems through suitable spacing and fertiliser placement. The possibility of alleviating root competition by supplying limiting growth factors is critically assessed. A wide range of physical, chemical and biological interactions occurs not only in spatial agroforestry, but also in rotational systems. In a final part, the reviewed information is applied to different types of agroforestry systems: associations of trees with annual crops; associations of trees with grasses or perennial fodder and cover crops; associations of different tree and shrub species; and improved fallows.

An integrated approach has been used to analyse the water relations of three Mediterranean species, A. unedo L., Q. ilex L. and P. latifolia L. co-occurring in a coastal dune ecosystem. The approach considered leaf level gas exchange, sap flow measurements and structural adaptations between 15 May and 31 July 2007, and was necessary to 5 15 23.9±1.2 (May) to 15.2±1.5 (July), as a response to drought. A. unedo also underwent an almost stepwise loss on hydraulic conductivity, such a loss didn't occur for Q. ilex, while P. latifolia was able to slightly increase hydraulic conductivity, showing how different plant compartments coordinate differently between species as a response to drought. Such different coordination affects the gas exchange between vegetation and 20 the atmosphere, and has implications for the response of the Mediterranean coastal dune ecosystems to climate change.

Although changes in depth to groundwater occur naturally, anthropogenic alterations may exacerbate these fluctuations and, thus, affect vegetation reliant on groundwater. These effects include changes in physiology, structure, and community dynamics, particularly in arid regions where groundwater can be an important water source for many plants. To properly manage ecosystems subject to changes in depth to groundwater, plant responses to both rising and falling groundwater tables must be understood. However, most research has focused exclusively on riparian ecosystems, ignoring regions where groundwater is avail-able to a wider range of species. Here, we review responses of riparian and other species to changes in groundwater levels in arid environments. Although decreasing water tables often result in plant water stress and reduced live biomass, the converse is not necessarily true for rising water tables. Initially, rising water tables kill flooded roots because most species cannot tolerate the associated low oxygen levels. Thus, flooded plants can also experience water stress. Ultimately, individual species responses to either scenario depend on drought and flooding tolerance and the change in root system size and water uptake capacity. However, additional environmental and biological factors can play important roles in the severity of vegetation response to altered groundwater tables. Using the reviewed information, we created two conceptual models to highlight vegetation dynamics in areas with groundwater fluctuations. These models use flow charts to identify key vegetation and ecosystem properties and their responses to changes in groundwater tables to predict community responses. We then incorporated key concepts from these models into EDYS, a comprehensive ecosystem model, to highlight the potential complexity of predicting community change under different fluctuating groundwater scenarios. Such models provide a valuable tool for managing vegetation and groundwater use in areas where groundwater is important to both plants and humans, particularly in the context of climate change.

Many soil physical properties and crop yield are affected by compaction and tillage systems. The effect of three different factors, i.e. tillage treatments (no-tillage, chisel plowing, and moldboard plowing), axle load (6 and 16 t/axle vehicle), and tire inflation pressure (120 and 350 kPa inflation pressures) on okra (Abelmoschus esculentus) root density and soil physical properties (bulk density and cone penetration resistance) was studied. This study was initiated in April 2000 on a loam soil (42% sand, 36% silt, 22% clay) at an experimental farm in Irbid, a district in the northern part of Jordan. Response to the above factors was measured down to 48 cm. Axle load and tire inflation pressure caused an increase in bulk density (BD) and cone penetration (CI) resistance from the soil surface down to 48 cm. The loaded vehicle with 350 kPa tire inflation pressure on no-tillage plots had the greatest effect soil physical properties measured while the unloaded vehicle with 120 kPa tire inflation pressure on chisel-plowed plots had the least effect. Plants in the no-tillage and moldboard-plowed treatments had a higher concentration of roots near the base of the plant compared to the plants in the chisel-plowed treatment.

Biodiversity eVects on ecosystem functioning in forests have only recently attracted increasing attention. The vast majority of studies in forests have focused on above-ground responses to diVerences in tree species diversity, while systematic analyses of the eVects of biodiversity on root systems are virtually non-existent. By investigating the Wne root systems in 12 temperate deciduous forest stands in Central Europe, we tested the hypotheses that (1) stand Wne root biomass increases with tree diversity, and (2) 'below-ground overyielding' of species-rich stands in terms of Wne root biomass is the consequence of spatial niche segregation of the roots of diVerent species. The selected stands represent a gradient in tree species diversity on similar bedrock from almost pure beech forests to mediumdiverse forests built by beech, ash, and lime, and highlydiverse stands dominated by beech, ash, lime, maple, and hornbeam. We investigated Wne root biomass and necromass at 24 proWles per stand and analyzed species diVerences in Wne root morphology by microscopic analysis. Fine root biomass ranged from 440 to 480 g m ¡2 in the species-poor to species-rich stands, with 63-77% being concentrated in the upper 20 cm of the soil. In contradiction to our two hypotheses, the diVerences in tree species diversity aVected neither stand Wne root biomass nor vertical root distribution patterns. Fine root morphology showed marked distinctions between species, but these root morphological diVerences did not lead to signiWcant diVerences in Wne root surface area or root tip number on a stand area basis. Moreover, diVerences in species composition of the stands did not alter Wne root morphology of the species. We conclude that 'below-ground overyielding' in terms of Wne root biomass does not occur in the species-rich stands, which is most likely caused by the absence of signiWcant spatial segregation of the root systems of these late-successional species.

Spaced poplar (Populus spp.) trees are used widely in New Zealand for soil conservation on erodible pastoral hill country. Their root distribution in this environment, and factors that affect it, are poorly understood. Robust recommendations on effective tree spacing depend on knowledge of root systems. This study determined the effect of tree density, position between trees, and soil depth (0–90 cm)

Root distribution of the wild jack tree (Artocarpus hirsutus) was determined by selective placement of 32p at various depths and lateral distances from the tree, in Kerala, India. In eight-and-a-half-year-old trees growing on a lateritic site, absorption of 32p from a lateral distance of 75 cm and 30 cm depth was much greater than from 150 and 225 cm lateral distance and 60 and 90 cm depth. Root activity declined with increasing depth and lateral distance. Most of the physiologically active roots were concentrated within a radius of 75 cm and 30 cm depth, although the tap root might reach even deeper. Possibly, surface accumulation of feeder roots may cause considerable overlap of the tree and crop root zones in intercropping situations. However, as the tree roots seldom extend beyond 2.25 m laterally from the trunk, the effect of overlapping root zones and the associated competitive effects may not be a serious problem for intercropping during the first few years (< 10 years after planting) of tree growth.

The grapevine plays a very important role in the economic, social and cultural sectors of many regions; however vineyards are often grown in regions under stressful conditions and thus they are vulnerable to climate change. The objective of this research was to investigate the effect of partial root-zone drying (PRD) irrigation on vine water relations, vegetative growth, plant microclimate, berry composition and yield components, compared to conventional deficit irrigation (DI, 50% ETc), full irrigation (FI, 100% of ETc) and non-irrigated vines (NI). The study was undertaken in mature ‘Moscatel’ grapevines (Vitis vinifera L.) grown in Pegões, South of Portugal. Compared to the other irrigated treatments, PRD vines showed a better microclimate at the cluster zone with higher incident photosynthetic photon flux density (PPFD). Within the more open canopies of NI and PRD treatments, berry temperatures were higher than those of denser ones (DI and FI). Compared to the conventional irrigation technique the better microclimate observed in PRD vines was a consequence of a reduction in vine growth, where lower values of leaf layer number, leaf area, canopy wideness, water shoots and shoot weight were observed. In PRD vines we observed a tendency to a development of a deeper root system, while DI and FI showed a more homogeneous root distribution throughout the different soil layers. PRD showed an improvement in berry quality with higher values of flavour precursors, and total phenols concentration without any significant yield reduction compared to DI and FI.

Soil compaction influences crop growth, movement of water and chemicals in numerous ways. Mathematical modelling contributes to better understanding of the complex and variable effects. This paper reviews models for simulating topsoil and subsoil compaction effects. The need for including both topsoil and subsoil compaction results from still increasing compactive effect of vehicular pressure which penetrates more and more into the subsoil and which is very persistent. The models vary widely in their conceptual approach, degree of complexity, input parameters and output presentation. Mechanistic and deterministic models were most frequently used. To characterise soil compactness, the models use bulk density and/or penetration resistance and water content data. In most models root growth is predicted as a function of mechanical impedance and water status of soil and crop yield-from interactions of soil water and plant transpiration and assimilation. Models for predicting movement of water and chemicals are based on the Darcy/Richards one-dimensional flow equation. The effect of soil compaction is considered by changing hydraulic conductivity, water retention and root growth. The models available allow assessment of the effects of topsoil and subsoil compaction on crop yield, vertical root distribution, chemical movement and soil erosion. The performance of some models was improved by considering macro-porosity and strength discontinuity (spatial and temporal variability of material parameters). Scarcity of experimental data on the heterogeneity is a constraint in modelling the effects of soil compaction. Suitability of most models was determined under given site conditions. Few of the models (i.e. SIBIL and SIMWASER) were found to be satisfactory in modelling the effect of soil compaction on soil water dynamics and crop growth under different climate and soil conditions.

Compared to agricultural lands, forests are complex ecosystems as they can involve diverse plant species associations, several vegetative strata (overstorey, shrubs, herbaceous and other annual plant layer) and multi-layered soil profiles (forest floor, hemi-organic and mineral layers). A high degree of variability is thus generally observed in radionuclide transfers and redistribution patterns in contaminated forests. In the long term, the soil compartment represents the major reservoir of radionuclides which can give rise to long-term plant and hence food contamination. For practical reasons, the contamination of various specific forest products has commonly been quantified using the aggregated transfer factor (T ag in m 2 kg À1 ) which integrates various environmental parameters including soil and plant type, root distribution as well as nature and vertical distribution of the deposits. Long lasting availability of some radionuclides was shown to be the source of much higher transfer in forest ecosystems than in agricultural lands. This study aimed at reviewing the most relevant quantitative information on radionuclide transfers to forest biota including trees, understorey vegetation, mushrooms, berries and game animals. For both radiocaesium and radiostrontium in trees, the order of magnitude of mean T ag values was 10 À3 m 2 kg À1 (dry weight). Tree foliage was usually 2-12 times more contaminated than trunk wood. Maximum contamination of tree components with radiocaesium was associated with (semi-)hydromorphic areas with thick humus layers. The transfer of radionuclides to mushrooms and berries is high, in comparison with foodstuffs grown in agricultural systems. Concerning caesium uptake by mushrooms, the transfer is characterized by a very large variability of T ag , from 10 À3 to 10 1 m 2 kg À1 (dry weight). For berries, typical values are around 0.01-0.1 m 2 kg À1 (dry weight). Transfer of radioactive caesium to game animals and reindeer and the rate of activity reduction, quantified as an ecological half-life, reflect the soil and pasture conditions at individual locations. Forests in temperate and boreal regions differ with respect to soil type and vegetation, and a faster decline of muscle activity concentrations in deer occurs in the temperate zone. However, in wild boar the caesium activity concentration shows no decline because of its special feeding habits. In the late phase, i.e. at least a few months since the external radionuclide contamination on feed plants has been removed, a T ag value of 0.01 m 2 kg À1 (fresh weight) is common for 137 Cs in the muscles of adult moose and terrestrial birds living in boreal forests, and 0.03 m 2 kg À1 (fresh weight) for arctic hare. Radiocaesium concentrations in reindeer muscle in winter may exceed the summer content by a factor of more than two, the mean T ag values for winter ranging from 0.02 to 0.8 m 2 kg À1 (fresh weight), and in summer from 0.04 to 0.4 m 2 kg À1 . The highest values are found in the year of initial contamination, followed by a gradual reduction. In waterfowl a relatively fast decline in uptake of 137 Cs has been found, with T ag values changing from 0.01 to 0.002 m 2 kg À1 (fresh weight) in the three years after the contaminating event, the rate being determined by the dynamics of 137 Cs in aquatic ecosystems.

A growth analysis study involving monthly excavation of Dioscorea esculenta plants revealed that the root system developed fully in the period before tuber initiation, and extended radially for a distance between 2.3 and 4.3 m. Primary roots initially remained in the top 10 cm of the soil profile, but descended to approximately 30 cm near their full extension. Tuber number increased from initiation around 21 weeks after planting (WAP) until maximum vine growth was reached around 33 WAP, but tuber dry weight continued to increase throughout the senescence period of the vine, to 45 WAP. Tubers lost dry matter but not fresh weight during dormancy in the soil, to 55 WAP. The results indicate that a distance of at least 4.5 m is required to separate experimental fertilizer treatments, and that post-establishment burial of fertilizers around the mound or ridge risks damage to roots near their base, while inter-row application is accessible to roots and may be preferable.

The influence of several regulated deficit irrigation (RDI) strategies under subsurface drip irrigation (SDI) conditions on water relations and gas exchange activity was analysed during a four year period for mature trees of a local variety of almond (Prunus dulcis (Mill.) D.A. Webb, cv. Cartagenera), in a commercial plantation in the district of Aljorra, Murcia (Southern Spain). Five treatments were applied: T1 (surface drip), which was irrigated at 100% ETc (crop evapotranspiration) for the full season, applying 603 mm per year; T2 (surface drip), irrigated at 100% ETc, except during the kernel-filling stage (from early June to early August), when 20% ETc was applied; T3 (SDI), equal to T2, but in subsurface drip irrigation; T4 (SDI), irrigated at 100% ETc, except during kernel-filling (20% ETc) and post-harvest (75% ETc); T5 (SDI), equal to T4, but a greater reduction of post-harvest irrigation (50% ETc). The severity of water stress was characterised by measurements of soil water content (θ v), predawn leaf water potential (pd), osmotic potential (π), relative water content (RWC), and gas exchange rates. Under stress (during the kernel-filling stage) and non-stress conditions (during active growth and post-harvest periods) in treatments T2, T3 and T4 there were not significant differences in the soil water content, nor in the plant water status and gas exchange parameters measured. Only T5 (SDI) showed a significant reduction in gas exchange activity at the end of the kernel-filling stage (point of maximum stress). This response was closely correlated with the severity of the stress reached. Minimum values of pd reached in this period were −2.37 MPa in T2, −2.26 MPa in T3, −1.95 MPa in T4 and −2.52 MPa in T5. Maximum reductions in photosynthesis rate (A), with regard to the control, were 64%, 61%, 58% and 75%, respectively. Reductions in A, E and stomatal conductance (g s) in response to severe water stress were reversible. Although soil and plant water status recovered rapidly when trees were irrigated post-harvest, gas exchange activity (g s , E and A) recovered more slowly in all treatments. T5 showed a recovery of soil water status that was slower and incomplete compared to the other treatments, postharvest (early August-early September), although gas exchange activity was not affected in this period. These results indicate that these RDI strategies, with a severe irrigation deprivation during kernel-filling (20% ETc), and a recovery post-harvest at 75% ETc or up to 50% ETc under SDI, can be adequate in this orchard under semiarid conditions, due to a higher water application efficiency of this irrigation system, saving between 220-273 mm year −1 irrigation water.

Background and aims Plant roots provide mechanical cohesion (c r ) to soil on slopes which are prone to shallow landslides. c r varies in heterogeneous natural forests due to the spatial, inter-and intra-annual dynamics of root demography. Characterizing root initiation density and mortality, as well as how root growth is influenced by abiotic and biotic factors is essential for exploring a root system's capacity to reinforce soil. Methods In this study, root demography data were monitored using field rhizotrons during 1.5 years in two naturally regenerated mixed forests in the French Alps. These forests are composed of trees growing in groups (tree islands) with large gaps between the islands. Three categories of driving variables were measured: (i) spatial factors: altitude (1,400 m, 1,700 m), ecological patch (gap, tree island), soil depth (0.0-1.0 m divided into five layers of 0.2 m); (ii) temporal factors: month (12 months from ); (iii) biological factors: root diameter classes (]0, 1] mm, ]1, 2] mm, ]2, 5] mm (according to the international standard ISO 31-11, ]x, y] denotes a left half-open interval from x (excluded) to y (included)). Two types of two-part models, a Hurdle model (H) and a Zero-inflated model (ZI) were used to fit root data with a high zero population, i.e. if root initiation or mortality was zero during a given time period, or if roots were not present at all points throughout a soil profile. Results Root initiation quantity decreased with increasing soil depth, as well as being lower in tree islands. Both soil depth and ecological patch interacted strongly with altitude. Root dynamics were significantly less active with a lower net production and c r increment in winter and spring than in

We analysed the abundance, spatial distribution and soil contact of wheat roots in dense, structured subsoil to determine whether incomplete extraction of subsoil water was due to root system limitations. Intact soil cores were collected to 1.6 m below wheat crops at maturity on a red Kandosol in southern Australia. Wheat roots, remnant roots, soil pores and root-soil contact were quantified at fresh breaks in the soil cores. In surface soil layers (<0.6 m) 30-40% of roots were clumped within pores and cracks in the soil, increasing to 85-100% in the subsoil (>0.6 m), where 44% of roots were in pores with at least three other roots. Most pores contained no roots, with occupancy declining from 20% in surface layers to 5% in subsoil. Wheat roots clumped into pores contacted the surrounding soil via numerous root hairs, whereas roots in cracks were appressed to the soil surface and had very few root hairs. Calculations assuming good root-soil contact indicated that root density was sufficient to extract available subsoil water, suggesting that uptake is constrained at the root-soil interface. To increase extraction of subsoil water, genetic targets could include increasing root-soil contact with denser root hairs, and increasing root proliferation to utilize existing soil pores.

For more than a century, scientists have considered whether mixtures of tree species may differ in nutrition and yield relative to monocultures. We review the empirical evidence on the nutritional interactions of tree species in mixtures, including information on foliar nutrition, soil nutrient supply, rates of nutrient input, and patterns of root distribution. Linear effects were most common, with mixtures intermediate in value between monocultures. In some cases, values for mixtures were lower than expected, indicating an antagonistic interaction. A few cases that included nitrogenfixing species showed a synergistic interaction, with mixtures showing higher values than monocultures. Nutrient concentrations in foliage of Sitka spruce (Picea sitchensis (Bong.) Carrière) were improved in mixtures with other conifers in three studies, in contrast to four studies with mixtures of various conifers and hardwoods that showed no effect of mixtures on foliage nutrient concentrations. Mixtures that combine species with and without the ability to fix atmospheric nitrogen have shown a full range of foliar responses from decreases to increases in phosphorus, to increases in nitrogen, to no effect of mixtures. Rates of litter decomposition usually showed no effect of species mixtures, but a few cases demonstrated both increases and decreases in decomposition relative to monocultures. Pools of soil nutrients generally did not differ between mixtures and monocultures. Root distributions in mixtures of Norway spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) were altered in mixtures; compared with monocultures, spruce rooted more shallowly in mixtures with beech, and beech rooted more deeply in mixtures with spruce. General conclusions are limited by the small number of studies that directly addressed mixed-species effects in forests, and the wide variety of observed interactions. Further research would be particularly helpful in identifying situations where nonlinear interactions may develop, including the species and site conditions that promote nonlinear interactions. Neighborhood methods, which analyze the relationship between stand composition and nutritional properties on a small spatial scale, offer great potential for exploring nutritional effects in mixed-species stands.

In a field study on bamboo (Bambusa arundinacea (Retz.) Willd.) hedgerow systems of Kerala, we tested the following three hypotheses: (1) Effective root foraging space is a function of crown spread, (2) Proximity of trees depress lateral spread of roots in mixed species systems and (3) The closer the trees are located the greater will be the subsoil root activity which in turn facilitates active absorption of nutrients from deeper layers of the soil profile. Root distribution of boundary planted bamboo and root competition with associated trees in two binary mixtures, teak (Tectona grandis)-bamboo and Malabar white pine (Vateria indica)-bamboo, were evaluated using modified logarithmic spiral trenching and 32 P soil injection techniques respectively. Excavation studies indicate that rooting intensity declined linearly with increasing lateral distance. Larger clumps manifested wider foraging zones. Eighty three per cent of the large clumps (> 4.0 m dia.) extended roots beyond 8 m while only 33% of the small (< 2.5 m dia.) clumps extended roots up to 8 m. Highest root counts were found in the 10-20 cm layer with nearly 30% of total roots. Although nearness of bamboo clumps depressed root activity of teak and Vateria in the surface layers of the soil profile, root activity in the deeper layers was stimulated. 32 P recovery was higher when applied at 50-cm depth than at 25-cm depth implying the safety net role of tree roots for leached down nutrients. Inter specific root competition can be regulated by planting crops 8-9 m away from the bamboo clumps and/or by canopy reduction treatments.

Previous studies relating root systems and drought tolerance in oil palm focused mainly on biomass. Yet, total root length (TRL), total root surface area (TRS), and root distribution in the soil better determine water uptake. These morphological traits were studied on 3 oil palm genotypes displaying a contrasting drought tolerance. A new concept of potential root water extraction ratio (PRER)

We compared the belowground biomass (BGB)/aboveground biomass (AGB) ratio and the vertical root distribution of 40-year-old Pinus radiata D. Don fertilized with 0 or 90 kg P·ha -1 at planting. Root biomass was determined by a combination of coring (fine roots, φ < 2 mm; small roots, 2 ≤ φ < 15 mm) and excavation (coarse roots, φ ≥ 5 mm). Stand-level AGB and coarse root biomass (CRB) were estimated with the use of allometric relations. After 40 years, AGB and CRB of P-fertilized trees were 4.5 times those of unfertilized trees, indicating that CRB scaled isometrically with AGB independently of P supply. By contrast, P fertilization increased the fine and small root biomass (FSRB) pool by only 50%. As a result, the scaling of FSRB to AGB was dependent on P supply. The differential response of the FSRB to P fertilization caused the overall BGB/AGB ratio to decrease from 0.29 in control plots to 0.20 in P-fertilized plots. Phosphorus fertilization also altered the vertical distribution of fine root biomass (FRB). For example, the proportion of FRB in the top 15 cm increased from 41% to 52% with P fertilization. Collectively, the results showed that P added early in the growth phase had a persistent effect on the BGB/AGB ratio in P. radiata. This was primarily brought about by altered biomass partitioning to the nutrient-acquiring FSRB pool.

Most trickle irrigation in the world is surface drip yet subsurface drip irrigation (SDI) can substantially improve irrigation water use efficiency (IWUE) by minimizing evaporative loss and maximizing capture of in-season rainfall by the soil profile. However, SDI emitters are placed at depths, and in many soil types sustained wetting fronts are created that lead to hypoxia of the rhizosphere, which is detrimental to effective plant functioning. Oxygation (aerated irrigation water) can ameliorate hypoxia of SDI crops and realize the full benefit of SDI systems. Oxygation effects on yield, WUE and rooting patterns of soybean, chickpeas, and pumpkin in glasshouse and field trials with SDI at different emitter depths (5, 15, 25, and 35 cm) were evaluated. The effect of oxygation was prominent with increasing emitter depths due to the alleviation of hypoxia. The effect of oxygation on yield in the shallow-rooted crop vegetable soybean was greatest (+43%), and moderate on medium (chickpea +11%) and deep-rooted crops (pumpkin +15%). Oxygation invariably increased season-long WUE (WUEsl) for fruit and biomass yield and instantaneous leaf transpiration rate. In general, the beneficial effects of oxygation at greater SDI depth on a heavy clay soil were mediated through greater root activity, as observed by general increase in root weight, root length density, and soil respiration in the trialed species. Our data show increased moisture content at depth with a lower soil oxygen concentration causing hypoxia. Oxygation offsets to a degree the negative effect of deep emitter placement on yield and WUE of SDI crops.

This literature review presents information about the role of tree root systems for the functioning of agroforestry associations and rotations and attempts to identify root-related criteria for the selection of agroforestry tree species and the design of agroforestry systems. Tree roots are expected to enrich soil with organic matter, feed soil biomass, reduce nutrient leaching, recycle nutrients from the subsoil below the crop rooting zone and improve soil physical properties, among other functions. On the other hand, they can depress crop yields in tree-crop associations through root competition. After a brief review of favourable tree root effects in agroforestry, four strategies are discussed as potential solutions to the dilemma of the simultaneous occurrence of desirable and undesirable tree root functions: 1) the selection of tree species with low root competitiveness, eventually supplemented by shoot pruning; 2) the identification of trees with a root distribution complementary to that of the crops; 3) the reduction of tree root length density by trenching or tillage; and 4) the use of agroforestry rotations instead of tree-crop associations. The potential and limitations of these strategies are discussed, and deficits in current understanding of tree root ecology in agroforestry are identified. In addition to the selection of tree species and provenances according to root-related criteria, the development of management techniques that allow the manipulation of tree root systems to maximize benefit and minimize competition are proposed as important tasks for future agroforestry research.

Ground-penetrating radar has been used to detect and map tree roots using surface-based antennas in reflection mode. On amenable soils these methods can accurately detect lateral tree roots. In some tree species (e.g. Pinus taeda, Pinus palustris), vertically orientated tap roots directly beneath the tree, comprise most of the root mass. It is difficult if not impossible to vertically delineate these roots with surface-based radars. To address this problem, a collaborative project between the USDA Forest Service, Southern Research Station, Radarteam AB and the Swedish University of Agricultural Sciences (SLU), was undertaken in August 2003 to assess the potential of high-frequency borehole radar to detect vertical, near-surface reflectors (0-2 m) resulting from tree roots. A set of controlled experiments on buried logs were used to test the efficacy of crosshole and borehole to surface travel time data to model near surface woody targets with tomography. Using these results, five Pinus sylvestris trees were scanned with borehole to surface radar and tomograms of their root systems were created. Three of the five tomograms compared favorably with root distribution maps made using destructively sampled data. However, the other two trees were misinterpreted, one was sharply underestimated, the other overestimated. This is the first report of using borehole radar to study vertical tree roots. Crosshole tomography provided excellent information on the depth of tree roots, but was less useful for imaging near surface features. Borehole to surface measures provided the best information on the near surface, where the bulk of roots are found . The technique has promise in forest research, but the development of new high-frequency borehole antennas, and forward modeling software that allows concurrent processing of travel-time and amplitude data is necessary to further this research.

Background: Plants interact with each other, nutrients, and microbial communities in soils through extensive root networks. Understanding these below ground interactions has been difficult in natural systems, particularly those with high plant species diversity where morphological identification of fine roots is difficult. We combine DNA-based root identification with a DNA barcode database and above ground stem locations in a floristically diverse lowland tropical wet forest on Barro Colorado Island, Panama, where all trees and lianas .1 cm diameter have been mapped to investigate richness patterns below ground and model rooting distributions.

The root distribution of Commiphora pyracanthoides
Engl., a potential encroaching woody species in the
sweet bushveld areas of the Northern Province, South
Africa, was studied at the Mara Agricultural
Development Centre. The root system of ten
C. pyracanthoides shrubs consisted of a taproot system
supported by a well developed fleshy secondary root
system. Minimum branching of secondary roots
occurred, resulting in the absence of tertiary and feeder
roots. Weak relationships existed between root
distribution, plant height and canopy diameter, but
subjectively estimated, secondary roots extended
horizontally at an average depth of 15 -20 cm to a
distance of more or less 1-1.5 times the canopy
diameter and 1.5-2 times tree height. It is proposed
that the correct placement of soil-applied arboricides
and/or absorption mechanisms may be critical for
effective chemical control of C. pyracanthoides

Slope stability models traditionally use simple indicators of root system structure and strength when vegetation is included as a factor. However, additional root system traits should be considered when managing vegetated slopes to avoid shallow substrate mass movement. Traits including root distribution, length, orientation and diameter are recognized as influencing soil fixation, but do not consider the spatial and temporal dimensions of roots within a system. Thick roots act like soil nails on slopes and the spatial position of these thick roots determines the arrangement of the associated thin roots. Thin roots act in tension during failure on slopes and if they traverse the potential shear zone, provide a major contribution in protecting against landslides. We discuss how root traits change depending on ontogeny and climate, how traits are affected by the local soil environment and the types of plastic responses expressed by the plant. How a landslide engineer can use this information when considering slope stability and management strategies is discussed, along with perspectives for future research. This review encompasses many ideas, data and concepts presented at the Second International Conference 'Ground Bio-and Eco-engineering: The Use of Vegetation to Improve Slope Stability-ICGBE2' held at Beijing, China, 14-18 July 2008. Several papers from this conference are published in this edition of Plant and Soil.

Models of tree-soil-crop interactions in agroforestry should maintain a balance between dynamic processes and spatial patterns of interactions for common resources. We give an outline and discuss major assumptions underlying the WaNuLCAS model of water, nitrogen and light interactions in agroforestry systems. The model was developed to deal with a wide range of agroforestry systems: hedgerow intercropping on flat or sloping land, fallow-crop mosaics or isolated trees in parklands, with minimum parameter adjustments. Examples are presented for simulation runs of hedgerow intercropping systems at different hedgerow spacings and pruning regimes, a test of the safety-net function of deep tree roots, lateral interactions in crop-fallow mosaics and a first exploration for parkland systems with a circular geometry.

Root distribution pattern and competitiveness of bamboo (Bambusa arundinacea (Retz.) Willd.) for below ground resources in mixed species systems were evaluated using logarithmic spiral trenching and 32 P soil injection techniques respectively. Excavation studies indicated that rooting intensity in different soil horizons declined either exponentiallyor quadraticallywith increasing lateral distance from the bamboo clump. Surface horizon (0-10 cm) of the soil pro le showed the least bamboo rooting intensity. It was highest in the 10-20 cm soil layer with nearly 27% of the total roots. Clump size is another important determinant of bamboo rooting intensity. Smaller bamboo crowns/ clumps showed the lowest rooting intensity, when measured at 5 m and 7.5 m lateral distances and increased linearly with increasing crown radius. Implicit in this is the potential for management practices to regulate competition in mixed species systems through controlling clump size/ crown expansion. Our results also showed that 32 P uptake by bamboo in binary combinations involving teak (Tectona grandis) and vateria (Vateria indica) was proportional to bamboo rooting intensity, when the 32 P label was applied to the dicot trees. Root competitiveness in polycultural systems involving bamboo, therefore, is a function of the proximity of bamboo to the associated tree/ crop, which in turn, decides the bamboo rooting intensity.

Inoculation of large-scale plant root culture reactors can be carried out by briefly homogenizing bulk root tissue, followed by aseptic transfer as a slurry to the reactor. Uniform root distribution can be achieved in bioreactors by entrapment of the growing root inoculum onto process packing elements (e.g. distillation packings), randomly distributed within the reactor, in a bubble column operation. These two techniques have been successfully used to inoculate a 14 L pilot-scale reactor which is subsequently operated as a trickle bed reactor.

Clonal Eucalyptus plantations in the Pointe-Noire region have been established on sandy and nutrient poor soils, and carry potential risk of depleting water and nutrient. To assess these risks, water and nutrient budgets should be calculated. However, the accuracy of hydrological models is strongly dependent on a realistic description of root distribution in soil. The spatial distribution of root systems in a chronosequence of clonal stands was then studied, using root intersect counting. The stands were 3 months, 6 months, 1 year, 2 years and 9 years old. For each stand we studied three vertical profiles perpendicular to the planting row at different spacing from a representative tree. The profiles were divided into square grid cells of 25 cm 2 , and the number of roots belonging to three diameter classes (between 0.1 and 1, 1 and 10 mm, and over 10 mm) were counted in each grid cell. The profiles were 2.50 m wide (half the distance between the planting rows) and 3 m deep, except for the two youngest stands (1.5 m deep). Spatial statistical analyses and analysis of variance were carried out to describe root distributions and their spatial and temporal changes. We observed that: (J.-P. Bouillet).

In the province of Québec, Canada, the majority of planted jack pine (Pinus banksiana Lamb.) seedlings are produced in rigid wall containers. More than 95% of them exhibit deformations of the root system which may induce stem instability. Studies of the root architecture of planted jack pine have been limited to a 30cm radius from the stem, as barely any studies have been devoted to naturally regenerated stands. Moreover, only a few researches have focused on temporal evolution of root systems. The aim of the present study was to characterize the architectural, spatial, and temporal development of jack pine roots in natural and planted stands. Study sites were located in the continuous boreal forest of Quebec. The plantation was done in 1987, so that the trees were 15 years old at the time of sampling. Trees from natural stand had regenerated after a fire in 1983 and were 13–16 years old. The root systems of 14 jack pine trees per site were manually excavated up to a &lt;5mm diameter, without regard to their distance from the stem. The number, length, diameter, and the spatial and temporal development of roots were analyzed according to three scales of root architecture: the root system, axes, and segments. Overall, the numbers and lengths of roots were higher with planted pines. However, naturally regenerated trees displayed a better distribution of their roots around the stem and at depth, combined with more rapid length growth during the first years. In natural stands, all the trees had a taproot and 30% of the main roots originated at a depth of more than 20cm, and they are regularly distributed around the stems. Planted trees did not present a taproot and 97% of the main roots originated in the first 20cm beneath the soil surface. Moreover, 50% of root length was located in one-third of the area surrounding the stems, an area that corresponded to the furrow. Finally, the annual development of lateral roots in planted stand displayed a 5-year delay when compared with natural stand, which also affected maximum growth length and development of the branching pattern. Root distribution and temporal development are known to play a major role in the stability of aerial parts. Seedling production methods, container type, site preparation and planting techniques need to be examined in greater detail in order to assess their effect throughout the development of the root system. It is necessary to compare different sylvicultural practices and with natural/planted stands to gain a clearer understanding of this problem.

Grape (Vitis vinifera L.) yield and its quality are dependent of the status of the root system. Root distribution information is also valuable for soil and water management. An analysis of methods to evaluate the root distribution of grapevines for both, drip and microsprinkler irrigation in a Typic Acrustox is presented for the table grape cv. Italia grafted on the rootstock IAC-313, in northeastern Brazil. Measured root parameters using the monolith method were root dry weight (Dw) and root length density (Lv), while root area (Ap) was estimated using the soil profile method in combination with digital image analysis. For both irrigation systems, roots were present to the 1 m soil depth and extended laterally to 1 m distance from the trunk, but grapevines irrigated by microsprinkler showed greater root presence as the distance from the trunk increased. Values of Ap were reasonably well correlated to Dw and Lv. However, correlation values were higher when fractional root distributi...