Root Growth Patterns Research Articles

Root growth dynamic and plant performance of nectarine trees amended with biochar and compost

A 2-year experiment was carried out outdoor on 1-year-old nectarine trees (Big Top grafted on Adesoto 101 Puebla (P. insititia) grown in large (˜0.5 m3) pots filled with a sandy and poorly fertile soil in which, with 4 replicates, the following soil-applied amendment strategies were compared: a) unamended control; b) biochar (16.4 g kg−1 (d.w.)); c) compost (40.0 g kg−1 (d.w.)) and d) biochar mixed with compost, at the same rates of the previous two strategies. Only the first two strategies received mineral fertilizers. We monitored root growth dynamic and assessed tree growth, nutritional status, leaf photosynthetic rate, yield, fruit quality, tree architecture and tree biomass partitioning. Our findings demonstrate that benefits on soil properties and tree growth were mainly attributable to the addition of compost and, to a less extent, by biochar alone (mostly without significant effects), indicating that perennial agro-ecosystems may not immediately respond to biochar application. Strategies influenced root physiology rather than morphology or biomass, as a possible adaptation to the changed growing conditions. However, root growth pattern did not reflect the aboveground tree performance. Compost extended root lifespan and increased photosynthetic leaf efficiency, while biochar reduced root survivorship and increased root turnover, signifying that amendment strategies modify C fixation and alter C budget partitioning within tree organs. The PCA analysis suggests that biochar-induced benefits on tree yield could presumably occur over time. Tree physiology and performance were not outperformed by the mixture of the two amendments, likely because compost hindered potential synergism with biochar. While we conclude that the contemporaneous addition of biochar and compost may not always reflect additive responses on plant performance, we speculate that these matrices can be conveniently combined in the sustainable management of nectarine trees with the aim to replace mineral inputs, preserve soil fertility and fight climate changes.

Lateral Roots: Random Diversity in Adversity.

Lateral roots are essential for soil foraging and uptake of minerals and water. They feature a large morphological diversity that results from divergent primordia or root growth and development patterns. Besides a structured diversity, resulting from the hierarchical and developmental organization of root systems, there exists a random diversity, occurring between roots of similar age, of the same hierarchical order, and exposed to uniform conditions. The physiological bases and functional consequences of this random diversity are largely ignored. Here we review the evidence for such random diversity throughout the plant kingdom, present innovative approaches based on statistical modeling to account for such diversity, and set the list of its potential benefits in front of a variable and unpredictable soil environment.

Nitrosative stress-mediated inhibition of OsDHODH1 gene expression suggests roots growth reduction in rice (Oryza sativa L.).

This study monitored the transcriptional response of OsDHODH1 under nitrosative stress conditions relative to the transcripts accumulations for the core mitochondrial cytochrome c oxidase1 (CcOX1) subunit, nuclear CcOX subunits 5b and 5c, two rice nitrate reductases (OsNIA1 and OsNIA2), and nitric oxide excess 1 (OsNOE1) genes. Our findings reveal that short-term exposure of rice seedlings to 1mM SNP (Nitric oxide donor) applied exogenously for 1h resulted in significant down-regulation of OsDHODH1 expression in all rice cultivars. In addition, the transcriptional patterns for the CcOX subunits, which are known to have a high affinity for nitric oxide, showed that the core catalytic subunit (OsCcOX1) and the nuclear subunit (OsCcOX5b) were up-regulated, while the nuclear subunit (OsCcOX5c) gene expression was suppressed. OsGSNOR1 expression was enhanced or decreased concomitant with a decrease or increase in SNO accumulation, particularly at the basal level. Moreover, high OsNIA1 expression was consistent with impaired root development, whereas low transcript accumulation matched a balanced root-growth pattern. This suggests that OsNIA1 expression would prevail over OsNIA2 expression under nitrosative stress response in rice. The level of malondialdehyde (MDA) content increased with the increase in SNP concentration, translating enhanced oxidative damage to the cell. We also observed increased catalase activity in response to 5mM SNP suggesting that potential cross-talk exist between nitrosative and oxidative stress. These results collectively suggest a possible role of OsDHODH1 and OsCcOX5b role in plant root growth during nitrosative stress responses.

Genome-wide analysis of magnesium transporter genes in Solanum lycopersicum

Magnesium (Mg) is an important micronutrient for various physiological processes in plants. In this study, putative Magnesium Transporter (MGT) genes have been identified in Solanum lycopersicum, Solanum tuberosum, Brachypodium distachyon, Fagaria vesca, Brassica juncea and were classified into 5 distinct groups based on their sequence homology. MGT genes are very diverse and possess very low sequence identity within its family. However, the Gly-Met-Asn (GMN) signature motif is present in most of the genes which are believed to be essential for Mg2+ recognition. In S. lycopersicum, different physiological root growth pattern was observed in both Mg excess and deficient conditions. Quantitative RT-PCR gene expression study shows that most of the SlMGT genes were upregulated in response to Mg deficient condition.

Temporal genetic patterns of root growth in Brassica napus L. revealed by a low-cost, high-efficiency hydroponic system.

Application of a low-cost and high-efficiency hydroponic system in a rapeseed population verified two types of genetic factors ("persistent" and "stage-specific") that control root development. The root system is a vital plant component for nutrient and water acquisition and is targeted to enhance plant productivity. Genetic dissection of the root system generally focuses on a single stage, but roots grow continuously during plant development. To reveal the temporal genetic patterns of root development, we measured nine root-related traits in a rapeseed recombinant inbred line population at six continuous stages during vegetative growth, using a modified hydroponic system with low-cost and high-efficiency features that could synchronize plant growth under controlled conditions. Phenotypic correlation and growth dynamic analysis suggested the existence of two types of genetic factors ("persistent" and "stage-specific") that control root development. Dynamic (unconditional and conditional) quantitative trait loci (QTL) mapping detected 28 stage-specific and 23 persistent QTLs related to root growth. Among them, 13 early stage-specific, 19 persistent and 8 later stage-specific QTLs were detected at 7 DAS (days after sowing), 16 DAS and 5 EL (expanding leaf stage), respectively, providing efficient and adaptable stages for QTL identification. The effective prediction of biomass accumulation using root morphological traits (up to 96.6% or 92.64% at a specific stage or the final stage, respectively) verified that root growth allocation with maximum root uptake area facilitated biomass accumulation. Furthermore, marker-assistant selection, which combined the "persistent" and "stage-specific" QTLs, proved their effectiveness for root improvement with an excellent uptake area. Our results highlight the potential of high-throughput and precise phenotyping to assess the dynamic genetics of root growth and provide new insights into ideotype root system-based biomass breeding.

Root morphology and seedling growth of three tree species in southern China in response to homogeneous and heterogeneous phosphorus supplies

Trees adjust their root morphological characteristics to respond heterogeneous phosphorus conditions, and root length and root-to-shoot ratio will increase to improve phosphorus nutrient absorption in heterogeneous phosphorus soils. This study examined the responses of root morphology and seedling growth to homogeneous and heterogeneous phosphorus (P) supplies in three major tree species (Cunninghamia lanceolata, Pinus massoniana, and Phoebe zhennan) in southern China. Pot experiments including two homo-P and five hetero-P supplies with different P dosage levels were conducted across three species. Root length, root average diameter, root biomass, aboveground biomass, root-to-shoot ratio, P accumulation, P-efficiency ratio, and increments in height and diameter of seedlings were quantified. Roots of the three species showed symmetric and asymmetric growth in response to homo-P and hetero-P supplies, respectively. The root biomass and average diameter were greater in the P-rich patch than in the P-poor patch, and roots in the P-poor patch were thinner and longer than their opposite counterparts. The root length and biomass were higher in hetero-P treatments than in homo-P treatments at an equivalent P dosage. The heterogeneity magnitude was negatively correlated with the aboveground biomass and positively correlated with the root biomass and root-to-shoot ratio. The P-efficiency ratio was negatively correlated with the dose of added P. The growth responses include a comprehensive adjustment in the root morphology and root-to-shoot ratio. The root growth pattern can change to adapt to lower P availability in soil, and the root-to-shoot ratio will increase to optimize nutrient partitioning and improve P-nutrient absorption in hetero-P soils.

Seasonal Patterns of Root Production with Water and Nitrogen Additions Across Three Dryland Ecosystems

Root production is known to contribute at least 50% of total net primary production in dryland ecosystems, yet few studies have addressed seasonal dynamics of root production or the belowground response to altered resource availability. We aimed to identify how root production varies across three dryland ecosystems dominated by different plant functional types: the shortgrass steppe, dominated by C4 perennial bunchgrasses, the northern mixed-grass prairie, co-dominated by perennial C3 and C4 grasses, and the sagebrush steppe, dominated by a perennial shrub with an understory of C3 and C4 grasses and forbs. We also sought to determine how root production changes throughout a growing season for these three systems, and how it responds to increased water and nitrogen availability. We used root ingrowth cores to monitor root production in 6-week intervals between June 1 and October 5, 2017, and with water and nitrogen additions in shortgrass steppe, mixed-grass prairie, and sagebrush steppe in the western Great Plains of the United States. We found that the northern mixed-grass prairie had the highest total root production during our sampling period, and that seasonal patterns of root growth varied significantly across the dryland types, with root growth greatest during the middle of the growing season at the sagebrush steppe and greatest during the end of the growing season at the northern mixed-grass prairie. As expected, belowground root production was about half aboveground production in all sites. Root production responded less to water and nitrogen addition than did aboveground production.

Priming winter wheat seeds with the bacterial quorum sensing signal N-hexanoyl-L-homoserine lactone (C6-HSL) shows potential to improve plant growth and seed yield.

Several model plants are known to respond to bacterial quorum sensing molecules with altered root growth and gene expression patterns and induced resistance to plant pathogens. These compounds may represent novel elicitors that could be applied as seed primers to enhance cereal crop resistance to pathogens and abiotic stress and to improve yields. We investigated whether the acyl-homoserine lactone N-hexanoyl-L-homoserine lactone (C6-HSL) impacted winter wheat (Triticum aestivum L.) seed germination, plant development and productivity, using two Ukrainian varieties, Volodarka and Yatran 60, in both in vitro experiments and field trials. In vitro germination experiments indicated that C6-HSL seed priming had a small but significant positive impact on germination levels (1.2x increase, p < 0.0001), coleoptile and radicle development (1.4x increase, p < 0.0001). Field trials over two growing seasons (2015–16 and 2016–17) also demonstrated significant improvements in biomass at the tillering stage (1.4x increase, p < 0.0001), and crop structure and productivity at maturity including grain yield (1.4–1.5x increase, p < 0.0007) and quality (1.3x increase in good grain, p < 0.0001). In some cases variety effects were observed (p ≤ 0.05) suggesting that the effect of C6-HSL seed priming might depend on plant genetics, and some benefits of priming were also evident in F1 plants grown from seeds collected the previous season (p ≤ 0.05). These field-scale findings suggest that bacterial acyl-homoserine lactones such as C6-HSL could be used to improve cereal crop growth and yield and reduce reliance on fungicides and fertilisers to combat pathogens and stress.

Diurnal dynamics of fine root growth in grapevines

Fine roots can grow more rapidly at certain points during the day depending on species and environmental conditions. The grapevine is a large perennial that has an extensive below-ground structural system; however its diurnal root growth pattern has received little attention. The aim of this study was to characterize the diurnal fine root growth dynamics of four grapevine genotypes and to assess the impact of soil temperature on this growth. One-year-old vines of Shiraz (Vitis vinifera), and the rootstocks Ramsey (V. champinii), 140 Ruggeri (V. berlandieri x V. rupestris) and Schwarzmann (V. rupestris x V. riparia) were grown in tapered rectangular pots with transparent acrylic windows to assess diurnal root growth dynamics using sequential image acquisition with a high resolution scanner. All four genotypes displayed a pronounced diurnal root growth pattern that positively followed daily soil temperature fluctuations. Maximum growth rates did not differ between the genotypes and were highest in the afternoon, declined through the night and reached a minimum the next morning. While diurnal root growth rates were influenced by soil temperature, this was not the only factor as evidenced by an extensive range of growth rates between the individual roots of a plant even when exposed to optimal temperatures. It is argued here that other environmental and endogenous factors will likely have an influence on the maximum rate of growth.

Root growth and development do not directly relate to shoot morphogenetic strategies in temperate forage legumes

Little is yet known about the component traits that control the deployment of root architecture in most grassland species. The aim of this study was to compare patterns of root growth in contrasting forage legumes and to analyse their dependency to shoot development. The parameters of a dynamic simulation model were identified for seven contrasting species in a series of greenhouse experiments in order to characterize root elongation, root branching and taproot growth. The model allowed us to explore the interactions between root development and whole plant growth. Most of the root morphogenetic parameters studied displayed significant inter-specific variability. Several traits appeared to be correlated, indicating a close association between extreme root tip diameters, the branching ability of roots and their maximal elongation rate. The species differed along two PCA axes which accounted respectively for the branching ability of fine roots and taproot development. Quite remarkably, the group of species identified for root development did not coincide with those previously identified for shoots, suggesting a degree of independence between the morphogenetic traits that control shoot and root architecture. However, both plant parts remained tightly linked through the trophic relationship represented by root biomass allocation. Our results suggest that the concomitant analysis of root and shoot development is necessary to properly decipher rooting strategies in forage legumes.

Evaluation of AquaCrop model simulations of cotton growth under deficit irrigation with an emphasis on root growth and water extraction patterns

One of the most vital parameters for the robust crop growth models’ performance is the crops’ root growth pattern. However, its reference measurement methods are laborious, destructive and costly. In this paper we determined the root growth pattern of cotton (Gossypium hirsutum) in the 50 to 100 cm top-soil layer using soil water content measurements from the cotton cultivating seasons of 2015 and 2016 in Northern Greece. The estimated root growth pattern along with canopy cover, biomass, soil water content and final seed cotton yield measurements were then used to evaluate the capability of the FAO AquaCrop model to simulate a deficit irrigated cotton, cultivated under real farming conditions. To do so, a number of existing cotton crop files from the literature were tested. The results showed that the estimated root growth patterns were almost the same in 2015 and 2016 exhibiting root growing rates equal to 1.7 and 2 cm/d, respectively. When the model was run in growing degree days mode, it simulated root growth pattern, canopy cover, biomass and soil water content with fair accuracy for all the proposed crop files (R2 ≥ 0.93, modeling efficiency ≥ 0.91), but the seed cotton yield was simulated adequately only when the AquaCrop’s library file was used. In calendar days mode the model failed to simulate root growth pattern satisfactorily, but the simulation of canopy cover, biomass and soil water content was fair (R2 ≥ 0.75, model efficiency ≥ 0.72). Lastly, the seed cotton yield in the calendar days mode was once again simulated accurately only when the model’s default crop file was used.

Root architecture and its relation with the growth characteristics of three planted Shorea species (Dipterocarpaceae)

Root and its architecture are important for trees to support their growth and development. However, there have been still few reports on tree roots architecture of important tropical forest tree species such as Shorea species. In this study, the differences of root architecture formation and the relation of root architecture and phenotype (growth) characteristics, including Index of Roots Anchoring (IRA) and Index of Roots Binding (IRB) of S. stenoptera, S. palembanica, and S. leprosula in Gunung Walat Education Forest were examined through root growth patterns, root morphology, and root growth variables. The results showed that the root growth patterns and the root morphology of three species were similar, which were classified into Champagnat group model with monopodial typical growth and tended to form orthotrophic branching. The total of root length significantly influenced tree height and trunk volume, while the depth root significantly influenced tree height and the crown diameter. The IRA values of S. stenoptera dan S. palembanica were categorized into medium group, while S. leprosula belonged to high group, suggesting that S. leprosula has a strong root anchorage compared to other two species. The IRB values of three Shorea species were categorized into low group, indicating low root binding ability in soil.

OsARD4 encoding an acireductone dioxygenase improves root architecture in rice by promoting development of secondary roots

This study was aimed at unravelling the molecular basis of root growth behavior in a drought-tolerant upland rice genotype, Nootripathu. Root tips of Nootripathu were found to possess shorter root caps and a greater number of dividing cells, favoring faster elongation compared to shallow-rooted IR20. Width and length of cortical cells in the roots of rapidly growing Nootripathu were found to be two to three times higher than IR20. Evaluation of shallow-rooted IR20, deep-rooted Nootripathu and their Recombinant Inbred Lines (RILs) for root characteristics revealed the presence of genetic variation for root traits among RILs. 2D-PAGE analysis of proteins in roots of IR20, Nootripathu and bulks of extreme RILs differing in root traits resulted in the identification of proteins co-segregating with root growth behavior and co-localized with QTLs for root traits. A putative candidate gene, OsARD4, encoding an “acireductone dioxygenase” was validated for its role in modulating the root growth pattern through genetic transformation. Transgenic ASD16 rice plants engineered for the overexpression of OsARD4 exhibited root growth characteristics similar to those of Nootripathu, including faster radical emergence, more rapid elongation of primary roots, early initiation of crown/lateral roots, and higher root biomass than the non-transgenic plants.

Root distribution patterns of reticulatus and inodorus melon (Cucumis melo L.) under subsurface deficit irrigation

Information on root growth patterns is crucial to understand cultivar adaptations to deficit irrigation, particularly for subsurface drip-irrigated crops, where root systems are more confined than furrow or sprinkler systems. A 2-year field experiment evaluated the effect of deficit irrigation (50% vs. 100% crop evapotranspiration, ETc) on root growth of melon (Cucumis melo L.) cultivars (Mission, Da Vinci, and Super Nectar) on a mollisol soil in southwestern Texas, USA. Root length intensity (La; mm cm−2), and root length density (RLD; cm cm−3) were measured at different growth stages using the minirhizotron and soil core methods, respectively. A higher La was recorded in 2012 than in 2011 (3.71 mm cm−2 vs. 0.50 mm cm−2), due to differences in temporal distribution of rainfall between years. Overall, deficit irrigation increased La as compared to 100% ETc, but significant effects occurred at depth (> 40 cm below the soil surface and > 25 cm below the subsurface drip tape). In 2012, moderate water deficit promoted deep root growth at the fruit setting stage but not in 2011, while root growth responses to cumulative deficit varied with cultivar. In 2012, deficit irrigation enhanced root growth in cv. Mission (cantaloupe; reticulatus) throughout the season, it was maintained in cv. Da Vinci (Tuscan; reticulatus), while it decreased in cv. Super Nectar (honeydew; inodorus) at the final harvest stage. Thus, the reticulatus melon cvs. Mission and Da Vinci can better adjust to moderate water-deficit conditions as compared to the inodorus melon cv. Super Nectar. Minirhizotron data provided useful information on root growth dynamics in deeper soil layers in a non-destructive way, which makes it a valuable tool in screening cultivars for water deficit adaptation.

Quantification of Root Growth Patterns From the Soil Perspective via Root Distance Models.

The rhizosphere, the fraction of soil altered by plant roots, is a dynamic domain that rapidly changes during plant growth. Traditional approaches to quantify root growth patterns are very limited in estimating this transient extent of the rhizosphere. In this paper we advocate the analysis of root growth patterns from the soil perspective. This change of perspective addresses more directly how certain root system architectures facilitate the exploration of soil. For the first time, we propose a parsimonious root distance model with only four parameters which is able to describe root growth patterns throughout all stages in the first 3 weeks of growth of Vicia faba measured with X-ray computed tomography. From these models, which are fitted to the frequency distribution of root distances in soil, it is possible to estimate the rhizosphere volume, i.e., the volume fraction of soil explored by roots, and adapt it to specific interaction distances for water uptake, rhizodeposition, etc. Through 3D time-lapse imaging and image registration it is possible to estimate root age dependent rhizosphere volumes, i.e., volumes specific for certain root age classes. These root distance models are a useful abstraction of complex root growth patterns that provide complementary information on root system architecture unaddressed by traditional root system analysis, which is helpful to constrain dynamic root growth models to achieve more realistic results.

Optimal layout method of distributed locking device of satellite based on plant root growth theory

The method of determining the optimal direction of satellite locking point is extended from the mechanical stability principle of plant roots growth under external loads. The method of topological optimization of the number and location of satellite locking units was proposed based on the adventitious root growth pattern of monocotyledons. Inspired by the fibrous root growth rhythm, the method for topological optimization of the effective contact interface shape of the satellite locking units is presented. A satellite finite element model and three-dimensional spring support model are established to lay the foundation for system frequency analysis. Parallel algorithm is used to optimize the position of the main locking points. One-dimensional search method is adopted to select the growth positions of the secondary locking points with the goal of maximizing fundamental frequency of the system. The relationship between the locking stiffness and system fundamental frequency is explored. Finally, the optimization results of this method are compared with those of conventional methods; the comparison demonstrated that the fundamental frequency of the locking system is significantly enhanced by the proposed method.

RhizoChamber-Monitor: a robotic platform and software enabling characterization of root growth

BackgroundIn order to efficiently determine genotypic differences in rooting patterns of crops, novel hardware and software are needed simultaneously to characterize dynamics of root development.ResultsWe describe a prototype robotic monitoring platform—the RhizoChamber-Monitor for analyzing growth patterns of plant roots automatically. The RhizoChamber-Monitor comprises an automatic imaging system for acquiring sequential images of roots which grow on a cloth substrate in custom rhizoboxes, an automatic irrigation system and a flexible shading arrangement. A customized image processing software was developed to analyze the spatio-temporal dynamics of root growth from time-course images of multiple plants. This software can quantify overall growth of roots and extract detailed growth traits (e.g. dynamics of length and diameter) of primary roots and of individual lateral roots automatically. It can also identify local growth traits of lateral roots (pseudo-mean-length and pseudo-maximum-length) semi-automatically. Two cotton genotypes were used to test both the physical platform and the analysis software.ConclusionsThe combination of hardware and software is expected to facilitate quantification of root geometry and its spatio-temporal growth patterns, and therefore to provide opportunities for high-throughput root phenotyping in support of crop breeding to optimize root architecture.

A comparison of lateral root patterning among dicot and monocot plants

Lateral root branching along the primary root involves complex gene regulatory networks in model plant Arabidopsis. However, it is largely unclarified whether different plant species share a common mechanism to pattern the lateral root along the primary axis. In this study, we assessed the development pattern of lateral root among several dicot and monocot plants, including Arabidopsis, tomato, Medicago, Nicotiana, rice, and ryegrass by using an agar-gel culture system. Our results reveal a regular-spaced distribution pattern of lateral roots along the primary root axis of both dicot and monocot plants. Meanwhile, the root patterning is tightly controlled by root bending and the plant hormone auxin. However, nitrogen and phosphate starvations trigger distinguished root growth patterns among different plant species. Our studies strongly suggest a partially shared signaling pathway underlying root patterning of various plant species, and also provide a foundation for further identification of genes associated with root development.

Seasonal dynamics of water and nutrient fluxes in an agricultural peatland

AbstractThe American cranberry (Vaccinium macrocarpon Ait.) is an important part of the cultural heritage and economy of Southeastern Massachusetts, yet water quality concerns and wetland protection laws challenge its commercial production. Here, we report inputs and outputs of water, nitrogen (N), and phosphorus (P) for a 2.12‐ha cranberry bed over a 2‐year period from 2013 to 2015. Water‐budget analysis indicated that precipitation contributed 40%, floodwater 37%, irrigation 15%, and groundwater 8% of water inputs to the cranberry bed. Minor annual variation in surface water discharge (~90 mm·year−1 or 3%) contrasted with large decreases in net (= outputs − inputs) nutrient export, from 16.2 to 9.1 kg N·ha−1·year−1 for total (dissolved + suspended particulate) nitrogen (TN) and from 3.34 to 1.47 kg P·ha−1·year−1 for total phosphorus (TP) between Years 1 and 2. Annual variation in net TN and TP export was tied to decreases in spring and summer nutrient export and controlled by the combined effects of fertilizer management, soil biogeochemistry, and hydrology. The relatively high spring TN export in Year 1 was associated with coincident increases in soil temperature and rainfall. A second factor was the timing of fertilizer application, which occurred 1 day prior to a major summer storm (i.e., third largest daily rainfall since 1926) and was responsible for up to 15% and 9% of the Year 1 TN and TP export, respectively. Nutrient budgets, which balanced water and fertilizer inputs with water, fruit, and vegetative outputs, were consistent with the burial of 21.6 kg N·ha−1·year−1 and 7.27 kg P·ha−1·year−1. Field measurements indicated that burial would increase TN and TP in the shallow (0–5 cm) rooting zone by 14% and 6%, respectively, which seemed plausible based on the relatively young age of the bed (4–5 years) and new root growth patterns in Vaccinium plants.

Frontiers in root ecology: recent advances and future challenges

Background and aims: Plant phenology is a sensitive indicator of plant response to climate change. Observations of phenological events belowground for most ecosystems are difficult to obtain and very little is known about the relationship between tree shoot and root phenology. We examined the influence of environmental factors on fine root production and mortality in relation with shoot phenology in hybrid walnut trees (Juglans sp.) growing in three different climates (oceanic, continental and Mediterranean) along a latitudinal gradient in France. Methods : Eight rhizotrons were installed at each site for 21 months to monitor tree root dynamics. Root elongation rate (RER), root initiation quantity (RIQ) and root mortality quantity (RMQ) were recorded frequently using a scanner and time-lapse camera. Leaf phenology and stem radial growth were also measured. Fine roots were classified by topological order and 0–1 mm, 1–2 mm and 2–5 mm diameter classes and fine root longevity and risk of mortality were calculated during different periods over the year. Results : Root growth was not synchronous with leaf phenology in any climate or either year, but was synchronous with stem growth during the late growing season. A distinct bimodal pattern of root growth was observed during the aerial growing season. Mean RER was driven by soil temperature measured in the month preceding root growth in the oceanic climate site only. However, mean RER was significantly correlated with mean soil water potential measured in the month preceding root growth at both Mediterranean (positive relationship) and oceanic (negative relationship) sites. Mean RIQ was significantly higher at both continental and Mediterranean sites compared to the oceanic site. Soil temperature was a driver of mean RIQ during the late growing season at continental and Mediterranean sites only. Mean RMQ increased significantly with decreasing soil water potential during the late aerial growing season at the continental site only. Mean root longevity at the continental site was significantly greater than for roots at the oceanic and Mediterranean sites. Roots in the 0–1 mm and 1–2 mm diameter classes lived for significantly shorter periods compared to those in the 2–5 mm diameter class. First order roots (i.e. the primary or parents roots) lived longer than lateral branch roots at the Mediterranean site only and first order roots in the 0–1 mm diameter class had 44.5% less risk of mortality than that of lateral roots for the same class of diameter. Conclusions: We conclude that factors driving root RER were not the same between climates. Soil temperature was the best predictor of root initiation at continental and Mediterranean sites only, but drivers of root mortality remained largely undetermined