Root Growth Dynamics Research Articles

The Cyclic Nucleotide-Gated Channel CNGC14 Regulates Root Gravitropism in Arabidopsis thaliana

In plant roots, auxin inhibits cell expansion, and an increase in cellular auxin levels on the lower flanks of gravistimulated roots suppresses growth and thereby causes downward bending. These fundamental features of root growth responses to auxin were first described over 80 years ago, but our understanding of the underlying molecular mechanisms has remained scant. Here, we report that CYCLIC NUCLEOTIDE-GATED CHANNEL 14 (CNGC14) is essential for the earliest phase of auxin-induced ion signaling and growth inhibition in Arabidopsis roots. Using a fluorescence-imaging-based genetic screen, we found that cngc14 mutants exhibit a complete loss of rapid Ca(2+) and pH signaling in response to auxin treatment. Similarly impaired ion signaling was observed upon gravistimulation. We further developed a kinematic analysis approach to study dynamic root growth responses to auxin at high spatiotemporal resolution. These analyses revealed that auxin-induced growth inhibition and gravitropic bending are significantly delayed in cngc14 compared to wild-type roots, where auxin suppresses cell expansion within 1 min of treatment. Finally, we demonstrate that auxin-induced cytosolic Ca(2+) changes are required for rapid growth inhibition. Our results support a direct role for CNGC14-dependent Ca(2+) signaling in regulating the early posttranscriptional phase of auxin growth responses in Arabidopsis roots.

Spring root-zone temperature regulates root growth, nutrient uptake and shoot growth dynamics in grapevines

Background and Aims Environmental factors such as root-zone temperature can influence plant development. Linkages between spring soil temperature, carbohydrate reserve mobilisation, nutrient uptake and nitrogen partitioning were investigated in Shiraz grapevines to gain better understanding of how this abiotic factor can alter root and canopy development. Methods and Results Plants were exposed to a cool, an ambient or a warm root-zone temperature over a 9-week period from budburst. Root starch mobilisation was correlated to the sum of cumulative heat units absorbed by the soil (soil growing degree days, GDDsoil) and this contributed to greater fine root density and extent of root branching. Most macronutrients, including N, accumulated to greater concentration in the leaves of vines exposed to the warm root-zones. Patterns of 15N accumulation indicated that despite greater fertiliser-N uptake in the warm root-zone treatment, most of the N that accumulated in the shoots was the result of N reserve mobilisation. Warmed root-zones resulted in plants with accelerated leaf emergence, extended internodes and elongated shoots with larger leaves. Plant leaf area and shoot dry mass were both positively correlated to GDDsoil, but inversely correlated to root starch concentration, indicating a link between root carbohydrate reserve mobilisation and shoot growth. Conclusions Warm soils stimulated root starch and N mobilisation, root growth and primary nutrient uptake with further consequences on canopy growth and altered N partitioning among the plant components. Significance of the Study Following winter dormancy, GDDsoil can thus be used to model above- and below-ground plant growth responses in the grapevine.

Root growth dynamics inside and outside of soil biopores as affected by crop sequence determined with the profile wall method

Taprooting crop species are capable of creating soil biopores (>2 mm in diameter) in the subsoil due to their large root size and deep-rooting habit. The aim of this study was to quantify root growth dynamics of wheat in the subsoil during its complete growth season as affected by crop sequence. Temporal observation on root length (km m−2) of wheat inside and outside of biopores at four growth stages (tillering, booting, anthesis, and milk) was conducted by using the profile wall method under the two crop sequence treatments involving two precrops, viz., chicory and tall fescue. Frequency of biopore presence measured on vertical profile walls depended on the choice of precrops in which chicory precrop resulted in higher frequency (2.3 %) compared with tall fescue (1.5 %). Root length of wheat measured inside biopores was significantly higher when grown after chicory (0.024 km m−2) in comparison to tall fescue (0.006 km m−2). On average, root length outside biopores after growing chicory was 45.9 % higher than tall fescue until the stage of anthesis. We conclude that at the site under study biopores as pathways for rapid root growth into deeper soil layers allow roots to re-enter and explore the subsoil. Thus, cereals cultivated in rotation with taprooted crops can draw benefit from enhanced uptake of water and nutrients from deeper soil layers during early growth stages. Model simulations with various abiotic and biotic factors will be helpful to reveal the direct evidence of biopore-root-shoot relationship in the future.

Investigation of Water Dynamics and the Effect of Evapotranspiration on Grain Yield of Rainfed Wheat and Barley under a Mediterranean Environment: A Modelling Approach.

Agro-hydrological models have increasingly become useful and powerful tools in optimizing water and fertilizer application, and in studying the environmental consequences. Accurate prediction of water dynamics in such models is essential for models to produce reasonable results. In this study, detailed simulations were performed for water dynamics of rainfed winter wheat and barley grown under a Mediterranean climate over a 10-year period. The model employed (Yang et al., 2009. J. Hydrol., 370, 177-190) uses easily available agronomic data, and takes into consideration of all key soil and plant processes in controlling water dynamics in the soil-crop system, including the dynamics of root growth. The water requirement for crop growth was calculated according to the FAO56, and the soil hydraulic properties were estimated using peto-transfer functions (PTFs) based on soil physical properties and soil organic matter content. Results show that the simulated values of soil water content at the depths of 15, 45 and 75 cm agreed with the measurements well with the root of the mean squared errors of 0.027 cm3 cm-3 and the model agreement index of 0.875. The simulated seasonal evapotranspiration (ET) ranged from 208 to 388 mm, and grain yield was found to correlate with the simulated seasonal ET in a linear manner within the studied ET range. The simulated rates of grain yield increase were 17.3 and 23.7 kg ha-l for every mm of water evapotranspired for wheat and barley, respectively. The good agreement of soil water content between measurement and simulation and the simulated relationships between grain yield and seasonal ET supported by the data in the literature indicates that the model performed well in modelling water dynamics for the studied soil-crop system, and therefore has the potential to be applied reliably and widely in precision agriculture. Finally, a two-staged approach using inverse modelling techniques to further improve model performance was discussed.

Root growth dynamics linked to above-ground growth in walnut (Juglans regia).

Examination of plant growth below ground is relatively scant compared with that above ground, and is needed to understand whole-plant responses to the environment. This study examines whether the seasonal timing of fine root growth and the spatial distribution of this growth through the soil profile varies in response to canopy manipulation and soil temperature. Plasticity in the seasonal timing and vertical distribution of root production in response to canopy and soil water manipulation was analysed in field-grown walnut (Juglans regia 'Chandler') using minirhizotron techniques. Root production in walnuts followed a unimodal curve, with one marked flush of root growth starting in mid-May, with a peak in mid-June. Root production declined later in the season, corresponding to increased soil temperature, as well as to the period of major carbohydrate allocation to reproduction. Canopy and soil moisture manipulation did not influence the timing of root production, but did influence the vertical distribution of roots through the soil profile. Water deficit appeared to promote root production in deeper soil layers for mining soil water. Canopy removal appeared to promote shallow root production. The findings of this study add to growing evidence that root growth in many ecosystems follows a unimodal curve with one marked flush of root growth in coordination with the initial leaf flush of the season. Root vertical distribution appeared to have greater plasticity than timing of root production in this system, with temperature and/or carbohydrate competition constraining the timing of root growth. Effects on root distribution can have serious impacts on trees, with shallow rooting having negative impacts in years with limited soil water or positive impacts in years with wet springs, and deep rooting having positive impacts on soil water mining from deeper soil layers but negative impacts in years with wet springs.

Fine root lifespan dynamics in four sour cherry (Prunus cerasus) cultivars grown in Central Poland using the minirhizotron technique

Sour cherry (Prunus cerasus L.) is one of the most important fruit crops in Poland. There are many varieties cultivated in orchards, but only a few of them play an important role in commercial production. These few varieties have been the object of numerous studies focused on practical aspects like growth performance, yielding, or resistance to diseases. Recently more belowground research has been carried out in pomological plants using the minirhizotron research allowing to observe roots in short and long term experiments. There have been very few studies concerning root growth dynamics of sour cherry cultivars. Here we studied the influence of four major factors on root growth: the cultivar, root diameter, soil depth, and season on the survivorship of fine roots. We used the minirhizotron technique (MR) to examine fine roots dynamics of four sour cherry cultivars grafted on the Mahaleb rootstock, grown in an experimental orchard in Central Poland. The results revealed that the greatest impact on root survivorship was exerted by root diameter, depth of root formation and the season, whereas cultivars had no obvious influence. The finest roots (with a diameter 0.75mm) and roots formed at a depth of more than 50 cm below the soil surface have the longest survivorship. The season of root growth has little impact on root survivorship, but has a big influence on the number of the roots formed. There is no impact of the cultivar on the differences in observed roots survivorship.

Multi-scale Phenotyping of West-European and South-African Maize Hybrids with Contrasting Drought Sensitivity

The urgent need of breeding more drought tolerant crops in order to meet the future needs of the growing world population, requires better understanding of the drought adaptation mechanisms. Phenotyping remains one of the main factors limiting breeding advance.By using a novel non-invasive root and shoot phenotyping system, we were able to link root and shoot phenotype and study their detailed development in time. Kinematic analysis provided the cellular basis of the observed differences in leaf growth.In this study, a set of commercial hybrid maize lines with contrasting drought sensitivity from West-Europe and South-Africa, together with the reference inbred line B73 were subjected to control and severe drought conditions in a glasshouse experiment in order to perform an extensive phenotyping of shoot and root growth.We showed that drought tolerance could be directly linked to advanced leaf and root growth dynamics and increased photosynthetic rates. At the cellular level, growth rate differences were mainly correlated with cell division rate. The typical ideotype of a drought tolerant line has fast growing shoot and root, and keeps its photosynthesis rate at a relatively high level even during wilting.

In Situ Visualization and Quantification of Three‐Dimensional Root System Architecture and Growth Using X‐Ray Computed Tomography

Root system architecture and associated root–soil interactions exhibit large changes over time. Nondestructive methods for the quantification of root systems and their temporal development are needed to improve our understanding of root activity in natural soils. X‐ray computed tomography (X‐ray CT) was used to visualize and quantify growth of a single Vicia faba L. root system during a drying period. The plant was grown under controlled conditions in a sandy soil mixture and imaged every second day. Minkowski functionals and Euclidean distance transform were used to quantify root architectural traits. We were able to image the root system with water content decreasing from 29.6 to 6.75%. Root length was slightly underestimated compared with destructive measurements. Based on repeated measurements over time it was possible to quantify the dynamics of root growth and the demography of roots along soil depth. Measurement of Euclidean distances from any point within the soil to the nearest root surface yielded a frequency distribution of travel distances for water and nutrients towards roots. Our results demonstrate that a meaningful quantitative characterization of root systems and their temporal dynamics is possible.

Effect of water table fluctuations on phreatophytic root distribution

The vertical root distribution of riparian vegetation plays a relevant role in soil water balance, in the partition of water fluxes into evaporation and transpiration, in the biogeochemistry of hyporheic corridors, in river morphodynamics evolution, and in bioengineering applications. The aim of this work is to assess the effect of the stochastic variability of the river level on the root distribution of phreatophytic plants. A function describing the vertical root profile has been analytically obtained by coupling a white shot noise representation of the river level variability to a description of the dynamics of root growth and decay. The root profile depends on easily determined parameters, linked to stream dynamics, vegetation and soil characteristics. The riparian vegetation of a river characterized by a high variability turns out to have a rooting system spread over larger depths, but with shallower mean root depths. In contrast, a lower river variability determines root profiles with higher mean root depths.

Galactoglucomannan oligosaccharides alleviate cadmium stress in Arabidopsis

Our study focused on the mediatory role of galactoglucomannan oligosaccharides (GGMOs) in plant protection against cadmium stress, examined mainly on the primary root growth of Arabidopsis thaliana. The application of GGMOs diminished the negative effect of cadmium on root length, root growth dynamics and also on photosynthetic pigment content. We tested the hypothesis that the effect of GGMOs is associated with decreased cadmium accumulation or its modified distribution. Cadmium distribution was observed chronologically from the first day of plant culture and depended on the duration of cadmium treatment. First, cadmium was stored in the root and hypocotyl and later transported by xylem to the leaves and stored there in trichomes. The protective effect of GGMOs was not based on modified cadmium distribution or its decreased accumulation. In cadmium and GGMOs+cadmium-treated plants, the formation of suberin lamellae was shifted closer to the root apex compared to the control and GGMOs. No significant changes between cadmium and GGMOs+cadmium variants in suberin lamellae development corresponded with any differences in cadmium uptake. GGMOs also stimulated Arabidopsis root growth under non-stress conditions. In this case, suberin lamellae were developed more distantly from the root apex in comparison with the control. Faster solute and water transport could explain the faster plant growth induced by GGMOs. Our results suggest that, in cadmium-stressed plants, GGMOs' protective action is associated with the response at the metabolic level.

A scanner system for high-resolution quantification of variation in root growth dynamics of Brassica rapa genotypes.

The potential exists to breed for root system architectures that optimize resource acquisition. However, this requires the ability to screen root system development quantitatively, with high resolution, in as natural an environment as possible, with high throughput. This paper describes the construction of a low-cost, high-resolution root phenotyping platform, requiring no sophisticated equipment and adaptable to most laboratory and glasshouse environments, and its application to quantify environmental and temporal variation in root traits between genotypes of Brassica rapa L. Plants were supplied with a complete nutrient solution through the wick of a germination paper. Images of root systems were acquired without manual intervention, over extended periods, using multiple scanners controlled by customized software. Mixed-effects models were used to describe the sources of variation in root traits contributing to root system architecture estimated from digital images. It was calculated that between one and 43 replicates would be required to detect a significant difference (95% CI 50% difference between traits). Broad-sense heritability was highest for shoot biomass traits (>0.60), intermediate (0.25–0.60) for the length and diameter of primary roots and lateral root branching density on the primary root, and lower (<0.25) for other root traits. Models demonstrate that root traits show temporal variations of various types. The phenotyping platform described here can be used to quantify environmental and temporal variation in traits contributing to root system architecture in B. rapa and can be extended to screen the large populations required for breeding for efficient resource acquisition.

Incorporating dynamic root growth enhances the performance of Noah-MP at two contrasting winter wheat field sites

Interactions between the soil, the vegetation, and the atmospheric boundary layer require close attention when predicting water fluxes in the hydrogeosystem, agricultural systems, weather, and climate. However, land-surface schemes used in large-scale models continue to show deficiencies in consistently simulating fluxes of water and energy from the subsurface through vegetation layers to the atmosphere. In this study, the multiphysics version of the Noah land-surface model (Noah-MP) was used to identify the processes, which are most crucial for a simultaneous simulation of water and heat fluxes between land surface and the lower atmosphere. Comprehensive field data sets of latent and sensible heat fluxes, ground heat flux, soil moisture, and leaf area index from two contrasting field sites in South-West Germany are used to assess the accuracy of simulations. It is shown that an adequate representation of vegetation-related processes is the most important control for a consistent simulation of energy and water fluxes in the soil-plant-atmosphere system. In particular, using a newly implemented submodule to simulate root growth dynamics has enhanced the performance of Noah-MP. We conclude that further advances in the representation of leaf area dynamics and root/soil moisture interactions are the most promising starting points for improving the simulation of feedbacks between the subsoil, land surface and atmosphere in fully coupled hydrological and atmospheric models.

Spring barley shows dynamic compensatory root and shoot growth responses when exposed to localised soil compaction and fertilisation.

The impact of heterogeneous soil compaction in combination with nutrient availability on root system architecture and root growth dynamics has scarcely been investigated. We quantified changes of barley (Hordeum vulgare L.) root and shoot growth during the first 3 weeks of growth in a controlled-environment chamber. Vertically divided split-root rhizotrons were filled either uniformly with loose or compacted peat, or heterogeneously with loose peat in one compartment and compacted peat in the other. We investigated the following questions. (a) Can growth processes affected by soil compaction be mimicked in our system? (b) Do plants show compensatory growth effects when exposed to heterogeneous soil compaction? (c) Does localised fertiliser application affect root systems' responses to compaction? We observed compensatory effects regarding root system architecture and root growth dynamics due to vertically heterogeneous soil compaction. Roots grew deeper and lateral roots emerged earlier in the loose compartment of the split-root treatment compared with uniform treatments. When fertiliser was applied only via the compacted compartment in the split-root treatment, more lateral roots were initiated in the compacted compartment and lateral root formation started a few days earlier than in the uniform treatments. Consequently, the first days after exposure to heterogeneous soil conditions are critical for the analysis of underlying physiological responses.

Physiological responses to humic substances as plant growth promoter

Humic substances (HS) have been widely recognized as a plant growth promoter mainly by changes on root architecture and growth dynamics, which result in increased root size, branching and/or greater density of root hair with larger surface area. Stimulation of the H+-ATPase activity in cell membrane suggests that modifications brought about by HS are not only restricted to root structure, but are also extended to the major biochemical pathways since the driving force for most nutrient uptake is the electrochemical gradient across the plasma membrane. Changes on root exudation profile, as well as primary and secondary metabolism were also observed, though strongly dependent on environment conditions, type of plant and its ontogeny. Proteomics and genomic approaches with diverse plant species subjected to HS treatment had often shown controversial patterns of protein and gene expression. This is a clear indication that HS effects of plants are complex and involve non-linear, cross-interrelated and dynamic processes that need be treated with an interdisciplinary view. Being the humic associations recalcitrant to microbiological attack, their use as vehicle to introduce beneficial selected microorganisms to crops has been proposed. This represents a perspective for a sort of new biofertilizer designed for a sustainable agriculture, whereby plants treated with HS become more susceptible to interact with bioinoculants, while HS may concomitantly modify the structure/activity of the microbial community in the rhizosphere compartment. An enhanced knowledge of the effects on plants physiology and biochemistry and interaction with rhizosphere and endophytic microbes should lead to achieve increased crop productivity through a better use of HS inputs in Agriculture.

Root growth of perennials in vertical growing media for use in green walls

The vertical orientation of green walls causes a risk of uneven water distribution within the growing medium, and thereby stress on the plant roots. Therefore it was studied how the root and top growth of different species were affected by the water holding characteristics of the growing media.Five species of hardy perennials (Campanula poscharskyana ‘Stella’, Fragaria vesca ‘Småland’, Geranium sanguineum ‘Max Frei’, Sesleria heufleriana and Veronica officinalis ‘Allgrün’) were grown in 3 types of growing media (coir and 2 of rockwool) in vertical boxes under greenhouse conditions. Root distribution was registered over 52 days and the activity of individual root systems was studied via 15N uptake and plant parameters were measured. The water holding characteristics of the growing media was determined on a sandbox.From day 21 and throughout the experiment, the plants growing in the coir medium showed stronger root growth compared to the two rockwool media. From day 28 onwards, there was also a difference between the two rockwool media, with a higher root frequency in the less dense medium. This pattern was consistent for all species, even if they showed different root growth dynamics. Fragaria, Geranium and Veronica showed steadily increasing root growth throughout the experiment, whereas Campanula started slow, but showed a strong root growth towards the end of the experiment. Sesleria showed little root growth throughout the experiment. Dry weight and root activity measured as 15N uptake was higher for plants grown in coir than rockwool. The coir medium showed a more gradual water release with increasing tension than either of the rockwool media, corresponding to the water content measured locally in the boxes.The results confirmed that the growing media affect root and aboveground plant growth. This is consistent with the differences in water retention, as the more even vertical water distribution in the coir medium resulted in stronger growth compared to the rockwool media. The five species showed different root growth dynamics and different abilities to grow in the different media, and 15N uptake showed that low root growth in the rockwool media also resulted in low root uptake activity.

Localised ABA signalling mediates root growth plasticity

Two recent reports show that cellular abscisic acid (ABA) signalling, together with other phytohormone signalling pathways, is crucial for salt-regulated root growth dynamics. Here we discuss these findings and place them in a broader framework on how cellular hormone signalling regulates root growth plasticity in response to environmental cues.

APPLICATION OF THE MINIRHIZOTRON TECHNIQUE TO STUDYING THE ROOTS OF FRUIT PLANTS

Minirhizotron, a non-destructive technique is based on the application of transparent tubes, located in plant’s root zone. This method has been known since the beginning of 20 th century and is used for plant root’s observations, especially in forest trees (Scots pine, Norway spruce, silver fir, birch), steppe grasses, vegetables and cereals. Minirhizotron technique is also applicable to pomological plants observations, mostly apples, but many others orchard species were observed with this method last years. The study of root growth dynamics in fruit plants using the non-destructive, minirhizotron method is conducted in the Pomological Orchard in Skierniewice. The objects of the observations are the roots of: apple trees cultivar. ‘Gold Milenium’, blackcurrant bushes cultivar ‘Tiben’ and sweet cherry cultivar ‘Vanda’. The observations were carried out monthly over a period of from March to November.

The Allium test: injection of test compounds into the bulb

We developed three methods for injecting substances into the bulb of Allium: (1) direct injection, (2) injection through the open space in the bulb after the removal of the upper half of the bulb, and (3) through a special “tunnel” cut in the bulb. Water (control) and solutions of methotrexate and copper sulfate were injected into bulbs and the dynamics of root growth were measured. We found that 2.2 mM methotrexate and 100 mM copper sulfate inhibit root growth. Injection through the “tunnel” was the most effective method. Cytological analysis showed that methotrexate inhibited mitotic activity completely in the root apical meristem and copper sulfate induced swelling of cells in the root meristem.

Dynamics of Plant Root Growth under Increased Atmospheric Carbon Dioxide

Plant growth is influenced by above‐ and belowground environmental conditions and increasing atmospheric carbon dioxide (CO2) concentrations enhances growth and yield of most agricultural crops. This review covers current knowledge on the impact of increasing CO2concentration on root dynamics of plants in terms of growth, root/shoot (R/S) ratio, root biomass, root length, root longevity, root mortality, root distribution, root branching, root quality, and the response of these root parameters to management practices including soil water and nutrients. The effects of CO2concentration on R/S ratio are contradictory due to complexity in accurate underground biomass estimation under diverse crops and conditions. Roots become more numerous, longer, thicker, and faster growing in crops exposed to high CO2with increased root length in many plant species. Branching and extension of roots under elevated CO2may lead to altered root architecture and ability of roots to acquire water and nutrients from the soil profile with exploration of the soil volume. Root turnover is important to the global C budget as well as to nutrient cycling in ecosystems and individual plants. Agricultural management practices have a greater impact on root growth than rising atmospheric CO2since management practices influence soil physical, chemical, and biological properties of soil, consequently affects root growth dynamics in the belowground. Less understood are the interactive effects of elevated CO2and management practices including drought on root dynamics, fine‐root production, and water‐nutrient use efficiency, and the contribution of these processes to plant growth in water and nutrients limited environments.

Which processes drive fine root elongation in a natural mountain forest ecosystem?

Background: Quantifying the dynamics of root growth is vital when characterising the role of vegetation in carbon cycling. Aims: We examined the temporal dynamics of root growth and responses to spatial (altitude, forest patchiness and soil depth) and biological factors (root diameter and root topology) in mid-montane and upper montane coniferous forest ecosystems. Methods: Using rhizotrons, two indicators were investigated: occurrence, i.e. the proportion of roots which had elongated since the previous measurement of root elongation (%), and daily root elongation speed (mm d−1) once the elongation occurred. Results: Spatial factors had a limited effect on root growth. Roots in the same diameter class possessed different elongation speeds and this was related to topological ranking, reflecting a disparity in physiological activity. Temporally, the occurrence of root elongation reached a peak in May–October (up to 90%) and sharply dropped after October 2010. The maximum root elongation speed (mean: 3.0 mm d−1) was measured in July–August. Root growth was the most inactive in February 2011 but some roots still exhibited positive elongation speeds (mean: 0.5 mm d−1). Occurrence and speed of elongation reacted differently with regard to environmental and biological factors. Conclusions: Temporal and biological factors contributed more towards explaining the variability of root growth than spatial factors. In future studies, both occurrence and speed of elongation should be used to characterise root growth.