Root growth and distribution of two short-season rice genotypes

Root growth dynamics of lowland rice (Oryza sativa L.) throughout the growing season are poorly understood. A field experiment was conducted in 1987 to compare root growth and distribution of two rice genotypes at two Arkansas locations on soils with different physical and chemical properties. Two genotypes, Bond and an experimental line (RU8701084), were grown on a Captina silt loam (Typic Fragiudults) at Fayetteville, AR, and on a Crowley silt loam (Typic Albaqualfs) near Stuttgart, Ar. Plots contained minirhizotrons oriented at a 45° angle and extended 55 cm (Captina) and 40 cm (Crowley) vertical to the soil surface. Root measurements were taken several times during the season at specific growth stages. Plant height and tiller number were taken at 9 dates at Fayetteville up to physiological maturity. In general, root length (RL) and root length density (RLD) were greater on the Captina soil. Genotypes at both locations reached maximum root growth rates between active tillering and panicle initiation (PI) and maximum RL by early reproduction. Total RL were similar between genotypes on the Captina. However on the Crowley, the mean RL for Bond between the period of early booting and flood removal was an average of 54% greater than for RU8701084. During early reproductive growth at both locations RL plateaued, but then declined during the grain filling process. There was a trend for RU8701084 to contain a greater percentage of its total RL in the top 20 and 10 cm of soil on the Captina and Crowley, respectively, while Bond tended to be a deeper rooted genotype. Bond had a greater RLD at the 20–30 cm depth increment on the Crowley, which contributed to the greater RL. Less than 15% of the total RL of either genotype was measured below 30 cm on the Crowley. In contrast, nearly 25% of the total RL was found at the 30–40 cm depth increment on the Captina. Results showed that rice root growth varied between soils, that root distribution patterns differed between genotypes, and that patterns of root growth changed with changes in plant development.     

Nutrient uptake relationship to root characteristics of rice

Data on root parameters and distribution are important for an improved understanding of the factors influencing nutrient uptake by a crop. Therefore, a study was conducted on a Crowley silt loam at the Rice Research and Extension Center near Stuttgart, Arkansas to measure root growth and N, P and K uptake by three rice (Oryza sativa L.) cultivars at active tillering (36 days after emergence (DAE)), maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Soil-root core samples were taken to a depth of 40 cm after plant samples were removed, sectioned into 5 cm intervals, roots were washed from soil and root lengths, dry weights and radii were measured. Root parameters were significantly affected by the soil depth × growth stage interaction. In addition, only root radius was affected by cultivar. At the 0- to 5-cm soil depth, root length density ranged from 38 to 93 cm cm^-3 throughout the growing season and decreased with depth to about 2 cm cm^-3 in the 35- to 40-cm depth increment. The increase in root length measured with each succeeding growth stage in each soil horizon also resulted in increased root surface area, hence providing more exposed area for nutrient uptake. About 90% of the total root length was found in the 0- to 20-cm soil depth throughout the season. Average root radius measured in the 0- to 5-cm and 35- to 40-cm depth increments ranged from 0.012 to 0.013 cm and 0.004 to 0.005 cm, respectively throughout the season. Total nutrient uptake by rice differed among cultivars only during vegetative growth. Differences in total nutrient uptake among the cultivars in the field appear to be related to absorption kinetics of the cultivars measured in a growth chamber study. Published with permission of the Arkansas Agricultural Experiment Station.     

Root length density and water uptake distributions of winter wheat under sub-irrigation

As the critical information to study flow transport in soil–plant systems, root distributions and root-water-uptake (RWU) patterns have been studied extensively. However, most root distribution data in the past were collected under surface irrigation. Less research has been conducted to characterize root distributions under sub-irrigation. The objectives of this study were to (1) test if the generalized function of normalized root length density (NRLD) in the literature was applicable to root distributions of winter wheat under natural sub-irrigation, which provides water from subsurface by capillary rise from the water table, and (2) estimate RWU distributions of winter wheat under natural sub-irrigation. Column experiments were conducted to study the distributions of root length density (RLD) and RWU of winter wheat (Triticum aestivum L. cv. Nongda 189) during a growing period of 57 days from planting to tillering stages under surface irrigation and natural sub-irrigation. Data of root distributions and soil water content were collected in the experiments with different treatments of irrigation levels. Results showed that the RLD distributions of winter wheat under both surface irrigation and natural sub-irrigation were of similar patterns. The NRLD distributions under sub-irrigation were adequately characterized by the generalized function. An inverse method was employed to estimate the average RWU rate distributions of winter wheat. In addition, based on the potential RWU coefficient and the NRLD function, a simple approach was developed to predict RWU rates at different depths. The predicted RWU rates had a good agreement with the estimated RWU rate distributions using the inverse method.Section editor: R. E. Munns     

Quantifying relationships between rooting traits and water uptake under drought in Mediterranean barley and durum wheat

In Mediterranean regions drought is the major factor limiting spring barley and durum wheat grain yields. This study aimed to compare spring barley and durum wheat root and shoot responses to drought and quantify relationships between root traits and water uptake under terminal drought.One spring barley(Hordeum vulgare L. cv. Rum) and two durum wheat Mediterranean cultivars(Triticum turgidum L. var durum cvs Hourani and Karim) were examined in soil‐column experiments under well watered and drought conditions. Root system architecture traits, water uptake, and plant growth were measured. Barley aerial biomass and grain yields were higher than for durum wheat cultivars in well watered conditions. Drought decreased grain yield more for barley(47%) than durum wheat(30%, Hourani). Root‐to‐shoot dry matter ratio increased for durum wheat under drought but not for barley, and root weight increased for wheat in response todrought but decreased for barley. The critical root length density(RLD) and root volume density(RVD) for 90% available water capture for wheat were similar to(cv. Hourani) or lower than(cv. Karim) for barley depending on wheat cultivar. For both species, RVD accounted for a slightly higher proportion of phenotypic variation in water uptake under drought than RLD.     

Quantifying relationships between rooting traits and water uptake under drought in Mediterranean barley and durum wheat

In Mediterranean regions drought is the major factor limiting spring barley and durum wheat grain yields. This study aimed to compare spring barley and durum wheat root and shoot responses to drought and quantify relationships between root traits and water uptake under terminal drought.One spring barley（Hordeum vulgare L. cv. Rum） and two durum wheat Mediterranean cultivars（Triticum turgidum L. var durum cvs Hourani and Karim） were examined in soil‐column experiments under well watered and drought conditions. Root system architecture traits, water uptake, and plant growth were measured. Barley aerial biomass and grain yields were higher than for durum wheat cultivars in well watered conditions. Drought decreased grain yield more for barley（47%） than durum wheat（30%, Hourani）. Root‐to‐shoot dry matter ratio increased for durum wheat under drought but not for barley, and root weight increased for wheat in response todrought but decreased for barley. The critical root length density（RLD） and root volume density（RVD） for 90% available water capture for wheat were similar to（cv. Hourani） or lower than（cv. Karim） for barley depending on wheat cultivar. For both species, RVD accounted for a slightly higher proportion of phenotypic variation in water uptake under drought than RLD.     

A procedure for determining average root length density in row crops by single-site augering

A simplified procedure has been formulated and tested for determining average root length density (RLD) by auger sampling at a single site in wheat, corn and mustard. It involves the determination of horizontal root distribution in the representative half of the unit soil strip (distance from base of plant to mid-point in the rows) by excavating small monolith segments in the top soil layer. Average RLD is computed by dividing the integral of polynomial function fitted to the horizontal root distribution (in the unit soil strip) with its length. The average RLD, thus, obtained is interpolated on the curve between root length density and horizontal distance from the plant base (d) in the representative half of the unit soil strip. Root length density determined by centering 5 cm diameter auger at the interpolated d gave minimum deviation from the average RLD of that layer compared to the other possible single site sampling schemes with same-sized auger. These results indicate that for row crops, the best centre for single-site augering is about one-third of distance from the plant base to mid-way between the two rows.     

Root distribution and water uptake patterns of corn under surface and subsurface drip irrigation

Information on root distribution and uptake patterns is useful to better understand crop responses to irrigation and fertigation, especially with the limited wetted soil volumes which develop under drip irrigation. Plant water uptake patterns play an important role in the success of drip irrigation system design and management. Here the root systems of corn were characterized by their length density (RLD) and root water uptake (RWU). Comparisons were made between the spatial patterns of corn RWU and RLD under surface and subsurface drip irrigation in a silt loam soil, considering a drip line on a crop row and between crop rows. Water uptake distribution was measured with an array of TDR probes at high spatial and temporal resolution. Root length density was measured by sampling soil cores on a grid centered on crop row. Roots were separated and an estimation of root geometrical attributes was made using two different image analysis programs. Comparisons of these programs yielded nearly identical estimates of RLD. The spatial patterns of RWU and RLD distributions, respectively normalized to the total uptake and root length, were generally similar only for drip line on a crop row, but with some local variations between the two measures. Both RLD and RWU were adequately fitted with parametric models based on semi-lognormal and normal Gaussian bivariate density functions (Coelho and Or, 1996; Soil Sci. Soc. Am. J. 60, 1039–1049).     

Iron plaque formation and its effect on arsenic uptake by different genotypes of paddy rice

Background and aims

Iron plaque on roots has been hypothesized to be an effective restraint on the uptake of arsenic (As) by rice plants. Evaluating the formation of iron plaque and its effect on As uptake by various rice cultivars is valuable because selecting low As uptake rice cultivars results in reduced risks associated with rice consumption. This study examines iron plaque formation and its effect on As uptake by different genotypes of rice cultivars.

Methods

Hydroponic cultures were conducted in phytotron at day 25/night 20°C and the rice seedlings in fifth-leaf age were treated with Fe (II) at the levels of 0 and 100 mg L^?1 in the Kimura B nutrient solutions for 14 days. The amount of iron plaque formation of 28 rice cultivars was determined by using the DCB extractable Fe of roots. Four cultivars representing high and low iron plaque formation capability, from indica and japonica respectively, were selected out of the 28 cultivars and processed for Fe and As treatments. After Fe treatments for 4 days, the seedlings were fed with As (III) at levels of 0, 0.5, and 1 mg L^?1 for another 10 days. We were thus able to determine the amounts of iron plaque formation and the As content in iron plaque, roots, and shoots of the four tested cultivars.

Results

Iron plaque formation capability differed among tested twenty-eight rice cultivars. Feeding As to four tested cultivars enhanced iron plaque formation on roots; the As uptake by roots and shoots was decreased by the addition of Fe. Both the retention of As on iron plaque and the decrease of As uptake by the addition of Fe varied among tested cultivars and were not correlated with the iron plaque formation capability.

Conclusions

Iron plaque can sequestrate As on the roots and reduce rice’s As uptake. However, other factors also influence the As uptake, namely the differences in binding affinity of iron plaque to As, the existent As species in the rhizosphere, and the uptake capability of various As species by rice plants. These factors should also be considered when selecting low As uptake rice cultivars.     

Effects of water supply on root traits and biological yield of Durum (Triticum durum Desf.) and Khorasan (Triticum turanicum Jakubz) wheat

The ability of a plant to change its root characteristics to increase the acquisition of soil water is an important adaptation mechanism to water limitation. In this regard, a field study was carried out in the Pannonian region of eastern Austria with two tetraploid wheat genotypes, i.e. Durum (Triticum durum Desf.) and Khorasan (Triticum turanicum Jakubz), during a comparatively wetter and drier year, i.e. 2008 and 2009, respectively. The genotypes showed significant differences in average root diameter and fine root length. All root traits varied with soil depth. The highest root length density and root biomass were observed with Khorasan wheat in 0–10 cm soil depth. Durum wheat showed a stronger response in fine roots to water availability and produced more fine roots in the moist year. Electric root capacitance was higher with Khorasan wheat. Durum showed higher biological yield stability across years with different precipitation with respect to above- and belowground biomass. It produced more leaf area under humid conditions. Khorasan allocated more assimilates to belowground organs in dry conditions, but without positive effect on aboveground biomass.     

Effect of irrigation frequency on root water uptake in sugar beet

A 2-year trial was performed on autumn-sown sugar beet grown in pots in order to study the influence of irrigation frequency on the water used by plants along the soil profile. The outdoor pots, containing one plant each, were 1.3 m high and had circular openings, through which Time Domain Reflectometry (TDR) apparatus wave guides could be inserted. Three irrigation intervals were compared and plants were watered whenever the soil layer explored by roots had lost 30% (SWD₁), 50% (SWD₂) and 70% (SWD₃) of the total available water (TAW). During the irrigation season, the water extracted by the plants from each layer along the soil profile (RWU) was determined by monitoring volumetric soil moisture content (), by TDR. At harvest time, root length density (RLD) along the soil profile was assessed using the Tennant method. The applied irrigation frequencies significantly affected the RWU. With the SWD₃ protocol, irrigation was at longer irrigation intervals (9 days) and watering volumes were as high as 84 mm. In this treatment, the plants lost almost 60% of total water from the lower soil layer (0.6–1.0 m). In treatment SWD₁, the irrigation interval was very short (3 days), and water extraction from 0.0–0.6 m soil depth was 92.0%. In the intermediate treatment, the irrigation interval was 5.5 days and a more uniform water depletion was observed along the root zone, approximately equal between the 0–0.6 and 0.6–1.0 m soil layer. Water extraction of sugar beet plants at the deeper soil layers in response to long irrigation intervals was related to an increase in water uptake efficiency of the deeper younger roots and not to an increase in root length density, which, on the contrary, decreased. This morpho-physiological acclimatization to progressive soil water deficit was coupled with an increase of the root/shoot ratio.     

Root length and biomass losses during sample preparation with different screen mesh sizes

Data are presented on the differences in root length density (RLD), dry matter (DM), and root diameter values determined on wheat and faba bean using sieves of different mesh size to separate roots from soil during sample preparation. Screens with 0.2, 1, and 2 mm (0.04, 1, and 4 mm²) aperture were used. Roots collected on the 2-mm sieve represented on average 55% of the weight and only 10% of the total length collected using a 0.2-mm sieve. With a 1-mm sieve 75% of weight was retained, but only 34% of the length. In the 0–20 cm soil layer average RLD and DM values ranged between 1.3 and 2.5 cm cm^-3 and 215 and 136 g m^-2 for faba bean and wheat respectively with 2 mm screens and 14.6 and 18.1 cm cm^-3 and 313 and 202 g m^-2 with 0.2 mm sieves. RLD was more affected than weight since losses from coarse screens were largely due to fine root fractions, although the 1-and 2-mm screens retained a small amount of fine roots that were long or attached to main structures. Variability was higher for measurements on coarser screens. The use of screens much coarser than the diameter of fine roots is not recommended for the study of surface-related phenomena in which root length quantification is necessary, while it may be acceptable for gross comparisons of root weight and spatial extent.     

Potassium uptake by plants,as characterized by root density,species and K/Rb ratio

Summary A small fraction of the plant K requirement is attained by root interception. The bulk of K has to be transported to the growing roots by mass-flow and diffusion in which diffusion mechanism plays the major role. Studies were undertaken to evaluate soil and plant parameters that might have influence on K supply mechanisms in soil and on plant uptake of K. Increasing wheat plant density led to competition for K absorption and resulted in lower K uptake by plant. In high plant density treatment, about 60% of the K requirement was met by diffusion process whereas in low plant density treatment mass-flow contributed most of the K demand. Solution diffusion and mass-flow were the major mechanisms of K supply to wheat roots. The mechanism of K supply to wheat root was compared with corn and onion. The major mechanism of K supply to corn and onion roots was exchange and solution diffusion. The mechanism of K supply to different crop species is attributable to differences in the K requirements, water flux rates and to the differences in root parameters.     

Analysis of root images from auger sampling with a fast procedure: a case of application to sugar beet

Manual line-intersect methods for estimating root length are being progressively replaced by faster and more accurate image analysis procedures. These methods even allow the estimation of some more root parameters (e.g., diameter), but still require preliminary labour-intensive operations. Through a task-specific macro function written in a general-purpose image analysis programme (KS 300 – Zeiss), the processing time of root images was greatly reduced with respect to skeletonisation methods by using a high-precision algorithm (Fibrelength). This has been previously proposed by other authors, and estimates length as a function of perimeter and area of the digital image of roots. One-bit binary images were acquired, aiming at large savings in computer memory, and automatic discrimination of roots against extraneous objects based on their elongation index (perimeter²/area), was performed successfully. Of four tested spatial resolutions (2.9, 5.9, 8.8, 11.8 pixel mm^–1), in clean samples good accuracy in root length estimation was achieved at 11.8 pixel mm^–1, up to a root density of 5 cm cm^–2 on the scanner bed. This resolution is theoretically suitable for representing roots at least 85 m wide. When dealing with uncleaned samples, a thick layer of water was useful in speeding up spreading of roots on the scanner bed and avoiding underestimation of their length due to overlaps with organic debris. A set of fibrous root samples of sugar beet (Beta vulgaris var. saccharifera L.) collected at harvest over two years at Legnaro (NE Italy) was analysed by applying the above procedure. Fertilisation with 100 kg ha^–1 of nitrogen led to higher RLD (root length density in soil) in shallow layers with respect to unfertilised controls, whereas thicker roots were found deeper than 80 cm of soil without nitrogen.     

Root distribution and interactions between intercropped species

Even though ecologists and agronomists have considered the spatial root distribution of plants to be important for interspecific interactions in natural and agricultural ecosystems, few experimental studies have quantified patterns of root distribution dynamics and their impacts on interspecific interactions. A field experiment was conducted to investigate the relationship between root distribution and interspecific interactions between intercropped plants. Roots were sampled twice by auger and twice by the monolith method in wheat (Triticum aestivum L.)/maize (Zea mays L.) and faba bean (Vicia faba L.)/maize intercropping and in sole wheat, maize, and faba bean up to 100 cm depth in the soil profile. The results showed that the roots of intercropped wheat spread under maize plants, and had much greater root length density (RLD) at all soil depths than sole wheat. The roots of maize intercropped with wheat were limited laterally, but had a greater RLD than sole-cropped maize. The RLD of maize intercropped with faba bean at different soil depths was influenced by intercropping to a smaller extent compared to maize intercropped with wheat. Faba bean had a relatively shallow root distribution, and the roots of intercropped maize spread underneath them. The results support the hypotheses that the overyielding of species showing benefit in the asymmetric interspecific facilitation results from greater lateral deployment of roots and increased RLD, and that compatibility of the spatial root distribution of intercropped species contributes to symmetric interspecific facilitation in the faba bean/maize intercropping. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Spatial distribution of roots of pearl millet on sandy soils of Niger

Root sampling in crop stands of low planting density requires reliable information on horizontal distribution of roots. This applies particularly to pearl millet in the Sahel, which is sown at a rate of less than two pockets of seed per m². The objective of this study was to investigate the spatial variability of root length density (RLD) among sampling positions in an improved management system with ridging and under traditional sowing. RLD between ridges (bR) was lower compared to sampling positions within ridges (wR) at soil depth layers from 0 to 80 cm soil depth. We found a highly significant, positive correlation between the sum of the root length (RL) of four sampling dates (tillering, booting, flowering, and maturity) with shoot dry mass (SDM) at maturity. The square of the correlation coefficient was highest when calculation of RL was based on RLD at all four sampling positions. While SDM exhibited significant differences among three pearl millet varieties, sole root sampling wR at a lateral distance of 60 cm relative to the pocket would not allow for the detection of varietal differences in RL, while all other sampling positions did. The correlation between RL and SDM was considerably improved if information of RLD bR was included. Under traditional sowing, RLD directly under the plant was lower compared to sampling positions at lateral distance 25 and 50 cm from the centre of the pocket, but this effect of sampling position was not significant. RLD estimates within deeper soil layers were not systematically affected by direction and lateral distance. To obtain accurate information about depth of rooting and RL under traditional sowing, samples should be taken from lateral distances between 20 and 40 cm from the pocket centre.     

Soil physical behaviour and crop responses to tillage in lowland rice soils of varying clay content

The influence of various tillage methods on two wetland rice soils in the Philippines is reported. The soils differed principally in clay content, 38% for the clay loam (clayey, mixed isohyperthermic Entic Hapludoll) while 56% for the clay (clayey, mixed noncalcareous, isohyperthermic Andaqueptic Haplaquoll). This had a marked effect on their response to tillage and varying water regime. The clay soil, under field conditions, showed little change in pore size distribution or soil water behaviour with different tillage methods. Crop (Rice, Oryza sativa L., var. IR20) yields were unaffected by tillage.In contrast, tillage effects were very marked in the clay loam soil, which consisted of a greenhouse and a field trial. In the greenhouse, which experienced severe dry periods, wet tillage not only increased the moisture retentivity but also the soil impedance at soil matric potential ()<–0.01 MPa. Seasonal average was <–1 MPa. Root length density decreased by 39% with dry tillage and by 56% with wet tillage compared with zero tillage. Grain yield however, did not vary with soil treatment. In the field, which experienced moderate dry spells, varied between –0.13 and –0.48 MPa. Root length density was significantly reduced at soil impedance >0.75 MPa. Wet tillage increased soil moisture storage which minimized the soil impedance during the dry cycle more effectively than did dry tillage. The crop performed best under wet tillage and least under zero tillage. Wet tillage in this soil was more effective under moderate than under severe water stress conditions.     

Appearance of bulges on maize roots as affected by 6-benzylaminopurine and α-naphthylacetic acid

The thickening that appeared on maize roots under the influence of 6-benzylaminopurine and α-naphthylacetic acid (concentration 10⁻⁵, 10⁻⁶, 10⁻⁷ and 10⁻⁸ M) were analysed. The changes in length and width of maize roots at the edge of elongation zone after 24,48 and 72 h of treatment were studied. The growth in length of cells at the edge of elongation zone stopped abruptly but the growth in width slowly continued. So, the growth of cells in length and width under the influence of growth regulators was not simultaneous. They had distinct time limits.     

杀灭土壤中线虫对小麦生长和吸收N、P的影响

盆栽条件下研究了施用杀线剂(克线磷,67mg·kg^-1干土)和干热(105℃,2h)两种杀线措施对小麦生长和N、P养分吸收的影响。杀线剂对土壤中线虫的平均杀灭率约为80%, 干热处理的杀灭率为100%. 在杀线剂处理中,苗期至抽穗期小麦生物量、拔节期至成熟期植株含N量、全生育期植株吸N量以及抽穗和成熟期吸P量均显着低于对照。土壤干热处理后抽穗和成熟期小麦的生物量、含N量及N、P吸收量也比对照显着降低。两种杀线处理植株地上部生物量和N、P吸收量与相应处理全株变化趋势基本一致。但杀灭线虫对植株含P量影响较小。分析杀线虫后小麦生长和养分吸收受抑主要与土壤有机氮的矿化作用减弱、微生物活动产生的植物生长促进物质降低有关     

Phytoremediation of arsenic contaminated soil by Pteris vittata L. II. Effect on arsenic uptake and rice yield

A greenhouse experiment evaluated the effect of phytoextraction of arsenic from a contaminated soil by Chinese Brake Fern (Pteris vittata L.) and its subsequent effects on growth and uptake of arsenic by rice (Oryza sativa L.) crop. Pteris vittata was grown for one or two growing cycles of four months each with two phosphate sources, using single super phosphate (SSP) and di-ammonium phosphate (DAP). Rice was grown on phytoextracted soils followed by measurements of biomass yield (grain, straw, and root), arsenic concentration and, uptake by individual plant parts. The biomass yield (grain, straw and rice) of rice was highest in soil phytoextracted with Pteris vittata grown for two cycles and fertilized with diammonium phosphate (DAP). Total arsenic uptake in contaminated soil ranged from 8.2 to 16.9 mg pot(-1) in first growing cycle and 5.5 to 12.0 mg pot(-1) in second growing cycle of Pteris vittata. There was thus a mean reduction of 52% in arsenic content of rice grain after two growing cycle of Pteris vittata and 29% after the one growing cycle. The phytoextraction of arsenic contaminated soil by Pteris vittata was beneficial for growing rice resulted in decreased arsenic content in rice grain of <1 ppm. There was a mean improvement in rice grain yield 14% after two growing cycle and 8% after the one growing cycle of brake fern.