Specific Root Length Research Articles

Topsoil Hardening: Effects on Soybean Root Architecture and Water Extraction Patterns

Topsoil hardening is one of the major causes of poor root growth although its effects on subsoil roots are still not well-known. Our aim was to examine the effects of topsoil hardening on the growth and functioning of shallow and deep roots of soybean plants. Two rain shelter experiments were conducted in two consecutive years. Plants were grown in topsoil monoliths (0–20 cm) with low (LR) or high mechanical resistance (HR), extracted from adjacent no-tillage cropping fields, and placed above 180 cm-high containers filled with a sandy loam soil. The effects of topsoil hardening were largely regulated by the level of water stress. In stressed plants, HR conditions reduced total aboveground biomass (up to 13%), total root biomass, root length density, and root surface area (up to 23, 38, and 37% respectively). Mechanical impedances reduced root biomass and length in both shallow (0–20 cm) and very deep layers (+ 160 cm). No changes were observed in specific root length or specific surface area. Plants growing in HR topsoils showed lower total water extraction but greater specific water uptake rates (29–47% higher in year 1 and 2 respectively). No clear architectural (i.e., root density) or morphological (i.e., specific root length/area) responses of enhanced root foraging capacity were observed in subsoil roots. However, soybean root system responded through functional mechanisms (i.e., specific water uptake) which partially attenuated the negative effects of mechanical impedances.

Two dimensional in-vitro phenotyping of root system architecture using Poly Ethylene Glycol in backcross inbred lines harboring drought tolerant QTLs of rice (Oryza sativa L.)

The present investigation was made to validate the effect and expression of multiple drought QTLs from Apo in the background of high yielding drought susceptible variety IR 64 under two dimensional in-vitro root architecture studies. The genotype CB 229 (DTY2.2, DTY3.1 and DTY8.1) recorded a higher network bushiness, network width, specific root length and network distribution of roots under PEG treatment (stress) and in network area CB 193-3 outperformed than CB 229. This clearly shows that introgression of multiple drought QTLs in various combination in the same genetic background enhances different level of expression of QTLs and tolerance to varied intensity of drought. Under field screening for drought, CB 229 out performed in both spikelet fertility percentage and yield than the remaining BILs. The traits viz., major ellipse axis, maximum number of roots, network bushiness, specific root length, network convex area and network width are positively correlated with spikelet fertility percentage and single plant yield under drought experiment. Principal component analysis accounted for 78.47 per cent of variability among root traits in PC1 and was loaded with all the traits observed under in-vitro condition. Hence, an understanding on complex nature of QTL expression associated with root system architecture under in-vitro stress in rice may help the breeder to develop new cultivars with enhanced level of tolerance against water limited situations in near future.

Soil environment and growth adaptation strategies of Amorpha fruticosa as affected by mulching in a moderately saline wasteland

AbstractUnderstanding the growth adaptive strategies of Amorpha fruticosa in response to the changes of saline soil environment under different mulch types (plastic mulch [PM]; sand mulch [SM]; rice straw mulch [RSM]; and control with non‐mulching [CK]) is very important, as this determines afforestation success in a moderately saline soil. The species' soil microenvironments, fine root traits, and biomass allocation patterns were investigated in 2016 and 2017. Compared to CK, electrical conductivity of saturated paste extracts (ECe) reduced significantly under the mulching treatments especially under PM. Both PM and SM effectively increased soil temperature (Tsoil) and available nitrogen (AN), but reduced soil organic carbon (SOC) in 2016; while RSM increased soil nutrients, but reduced Tsoil. The A. fruticosa under RSM (following PM and SM) invested more biomass, to shoots relative to roots, to coarse roots relative to fine roots, and to stems and leaves at the expense of coarse roots and fine roots from 2016 to 2017, as its saline soil environment especially the low Tsoil improved. In both years, the fine roots of A. fruticosa under PM employed exploitation potential or ‘extensive strategy’ (fine root mass density; fine root length density) more successfully at the 0–40 cm, while the fine roots under CK used higher exploitation efficiency or ‘intensive strategy’ (specific root length; and specific root area). The indicators of intensive strategy at the 40–60 cm were higher under PM than SM and RSM. Therefore, PM will better help A. fruticosa adapt to the harsh soil environment during afforestation in a moderately saline wasteland.

An invasive plant experiences greater benefits of root morphology from enhancing nutrient competition associated with arbuscular mycorrhizae in karst soil than a native plant.

The Eupatorium adenophorum have widespread invaded the karst ecosystem of southwest China and threatened the regional native community stability. Arbuscular mycorrhizae (AM) plays an important role in promoting growth for host plants via root external mycelia. However, whether AM regulates plant root traits underlying competition between invasive and native species via mycorrhizal networks in karst habitats, remains unclear. An experiment was conducted in a microcosm composed of two planting compartments flanking a competition compartment. The invasive E. adenophorum and native Artemisia annua were each placed in one of the two planting compartments with or without Glomus etunicatum fungus. The nutrient access treatments included the competitive utilization (Cu), single utilization (Su) and non-utilization (Nu) by using different nylon meshes allowed or prevented mycelium passing to acquire nutrients from the competition compartment. Root traits and nutrients of the two species were analyzed. The results showed that AM fungi had differential effects on root traits and nutrients of E. adenophorum and A. annua seedlings, which increased dry weight, length, surface area, volume, tips and branching points in roots, specific root length and volume, root nitrogen (N) and phosphorus (P) contents under Cu, Su and Nu treatments. AM fungus was also associated with decreases in the average diameter for both species. Under the Cu treatment, E. adenophorum had significantly greater length, surface area, volume, tips and branching points of roots, specific root traits, and root N and P than A. annua. AM fungi changed root phenotypes and nutrient uptake for both invasive and native plant species via interconnected mycorrhizal networks. Overall, our results suggest that through mycorrhizal networks, the invasive plant experiences greater benefits than the native plant in the nutrient competition, which fosters root morphological developments in karst soil.

Integrating Amendment and Liquid Fertilizer for Aided-Phytostabilization and Its Impacts on Soil Microbiological Properties in Arsenic-Contaminated Soil

Indiscriminate overuse of liquid fertilizer and arsenic (As) contaminated soil by abandoned mines is one of the important environmental issues in Korea. This study was carried out to solve these two problems. Amendments (limestone, red mud and acid mine drainage sludge), liquid fertilizer and plant vegetation (Hairy vetch; Vicia villosa Roth) were simultaneously treated. Some soil chemical properties (pH, dissolved organic carbon, inorganic nitrogen content, and bioavailable As), soil respiration and enzyme activity (urease activity and dehydrogenase activity) were determined for chemical and biological assessment. Amendments decreased bioavailable As in soil, and acid mine drainage sludge had the best reduction efficiency in alkali soil. Liquid fertilizer affects not only soil chemical properties but also biological properties. Through multiple regression analysis, the rhizosphere effect through plant cultivation using specific root length index was reflected in the result of soil microbial and enzyme activity. In the reclamation of As-contaminated soil, the synergistic effect of multiple treatments could be confirmed. In particular, biological assessment indicators could be useful when evaluating the complex treatment of various restoration techniques, including the phytoremediation method. Based on these results, a long-term follow-up study on the field scale will be possible.

C4 photosynthesis and the economic spectra of leaf and root traits independently influence growth rates in grasses

Abstract Photosynthetic pathway is an important cause of growth rate variation between species such that the enhanced carbon uptake of C4 species leads to faster growth than their C3 counterparts. Leaf traits that promote rapid resource acquisition may further enhance the growth capacity of C4 species. However, how root economic traits interact with leaf traits, and the different growth strategies adopted by plants with C3 and C4 photosynthetic pathways is unclear. Plant economic traits could interact with, or act independently of, photosynthetic pathway in influencing growth rate, or C3 and C4 species could segregate out along a common growth rate–trait relationship. We measured leaf and root traits on 100+ grass species grown from seeds in a controlled, common environment to compare with relative growth rates (RGR) during the initial phase of rapid growth, controlling for phylogeny and allometric effects. Photosynthetic pathway acts independently to leaf and root functional traits in causing fast growth. Using C4 photosynthesis, plants can achieve faster growth than their C3 counterparts (by an average 0.04 g g−1 day−1) for a given suite of functional trait values, with lower investments of leaf and root nitrogen. Leaf and root traits had an additive effect on RGR, with plants achieving fast growth by possessing resource‐acquisitive leaf traits (high specific leaf area and low leaf dry matter content) or root traits (high specific root length and area, and low root diameter), but having both leads to an even faster growth rate (by up to 0.06 g g−1 day−1). C4 photosynthesis can provide a greater relative increase in RGR for plants with a ‘slow’ ecological strategy than in those with fast growth. However, above‐ground and below‐ground strategies are not coordinated so that species can have any combination of ‘slow’ or ‘fast’ leaf and root traits. Synthesis. C4 photosynthesis increases growth rate for a given combination of economic traits, and significantly alters plant nitrogen economy in the leaves and roots. However, leaf and root economic traits act independently to further enhance growth. The fast growth of C4 grasses promotes a competitive advantage under hot, sunny conditions.

Can salicylic acid modulate biochemical, physiological and population alterations in a macrophyte species under chemical stress by diclofenac?

Salicylic acid (SA) is a pharmaceutical drug that may exert toxic effects by its own; however, simultaneous exposure of plants to SA and to other substances, often results in the significant changes in the patterns of toxic response/resistance to these other sources of chemical stress. Thus, the aim of this work was to investigate the capacity of SA of modulating Lemna minor responses co-exposed to the pharmaceutical drug, diclofenac - DCF. To attain this objective, L. minor was exposed for 7 days, to DCF alone, and to combinations of DCF with SA. After exposure, biochemical, physiological and population endpoints were analyzed as follows: catalase (CAT) and glutathione S-transferases (GSTs) activities, pigments content (chlorophyll a (Chl a), b (Chl b) and total (TChl), carotenoids (Car) and [Chl a]/[Chl b] and [TChl]/[Car] ratios), and growth specific rate, fresh weight and root length. Single exposures to DCF were capable of causing effects in all analyzed endpoints. However, co-exposure of DCF with SA partially reverted these effects. Finally, we may suggest that SA is capable to prevent the toxicity of DCF in macrophytes, by modulating the toxic response of exposed plants.

Weak latitudinal gradients in insect herbivory for dominant rangeland grasses of North America.

Patterns of insect herbivory may follow predictable geographical gradients, with greater herbivory at low latitudes. However, biogeographic studies of insect herbivory often do not account for multiple abiotic factors (e.g., precipitation and soil nutrients) that could underlie gradients. We tested for latitudinal clines in insect herbivory as well as climatic, edaphic, and trait‐based drivers of herbivory. We quantified herbivory on five dominant grass species over 23 sites across the Great Plains, USA. We examined the importance of climate, edaphic factors, and traits as correlates of herbivory. Herbivory increased at low latitudes when all grass species were analyzed together and for two grass species individually, while two other grasses trended in this direction. Higher precipitation was related to more herbivory for two species but less herbivory for a different species, while higher specific root length was related to more herbivory for one species and less herbivory for a different species. Taken together, results highlight that climate and trait‐based correlates of herbivory can be highly contextual and species‐specific. Patterns of insect herbivory on dominant grasses support the hypothesis that herbivory increases toward lower latitudes, though weakly, and indicates that climate change may have species‐specific effects on plant–herbivore interactions.

Root proliferation and phosphorus acquisition in response to stratification of soil phosphorus by two contrasting Trifolium subterraneum cultivars

Phosphorus (P) is usually stratified in the topsoil layer under pasture, due to the broadcast application of fertiliser, excreta and leaf-litter deposition on the soil surface, and minimal soil disturbance. The objective of this study was to investigate root proliferation and P acquisition in response to P stratification by comparing two Trifolium subterraneum cultivars with contrasting root morphologies. Clover micro-swards were grown with deficient, constrained and sufficient P supplied in a topsoil layer overlying a P-deficient subsoil that mimicked the stratification of P that occurs under pasture. Phosphorus labelled with 33P- and 32P-radioisotope tracer was mixed throughout the topsoil and subsoil layers, respectively. The shoot yield and total plant P uptake of the cultivars increased in response to increased topsoil P supply. The length of roots produced by the cultivars was equivalent in each of the P treatments, although the specific root length achieved by the cultivars was substantially different. In the P-constrained and P-sufficient treatments, ~91% and ~ 99% of total plant P was acquired by topsoil roots, respectively. In contrast, subsoil roots acquired 60–74% of total plant P in the P-deficient treatment. Topsoil roots were most important for P acquisition when P was highly stratified, whereas subsoil roots contributed to P acquisition when P was uniformly distributed throughout the P-deficient soil profile. Selection for prolific nutrient-foraging roots, in conjunction with plasticity for subsoil exploration, may improve the P-acquisition efficiency of T. subterraneum genotypes and confer adaptability across a range of soil-P environments.

Traits of dominant species and soil properties co-regulate soil microbial communities across land restoration types in a subtropical plateau region of Southwest China

Soil microbial community is essential for maintaining and improving ecosystem functioning in ecological restoration practice and is intimately linked with the plant community. However, little is known on how soil microbial communities respond to the functional characteristics of plant communities. Here we investigated the changes in plant community functional attributes, soil properties, and soil microbial community characteristics of four land restoration (vegetation) types in a subtropical plateau region. The relative contributions of soil abiotic properties and plant community functional attributes to variation in microbial community composition and function were then assessed. We found that plant community attributes, soil properties, and the soil microbial communities differed significantly among land restoration types, and the plant functional traits of dominant species and soil properties jointly determined soil microbial community structure and functions. Specifically, soil microbial community structure was significantly linked to the community-weighted mean (CWM) of plant functional traits, soil water content, and soil organic carbon. Soil microbial carbon-metabolic functions were tightly correlated with the CWM of leaf dry matter content, specific leaf area, and specific root length. Variance partitioning also revealed that the CWM of plant functional traits and soil variables cooperatively explained 67% and 64% variation in soil microbial community structure and carbon-metabolic functions. Meanwhile, significant correlations were found between variation in microbial community composition and carbon-metabolic functions. In conclusion, our observations demonstrate that soil microbial community characteristics were governed by dominant species in plant communities across land restoration types, mainly due to differences in plant functional traits and soil resource driven by plant traits.

Optimizing the choice of service crops in vineyards to achieve both runoff mitigation and water provisioning for grapevine: a trait-based approach

Aims : In vineyards, service crops may increase water infiltration and positively contribute to soil water refilling, but may also increase the risk of competition for water with grapevines which could impair grape yield over several years. This study aimed to test the relationships between service crop functional traits and two related services of major interest in viticulture: runoff control and water provisioning. Methods: We measured the water stock, the cover rate, along with above- and belowground functional markers of 38 plant communities after a winter growing season in an experimental vineyard, to assess relationships between service crop functional markers, runoff control and water provisioning. Results: Both aboveground and belowground functional markers were significant predictors of service provision at the community level. The plant aboveground dry matter content was positively related to soil water stocks and negatively related to the cover rate of the communities, while the specific leaf area (SLA) was positively related to the cover rate. The rooting depth and morphological root traits (specific root length and very fine root fraction) were negatively related with the soil water stock. Moreover, these results agree with ecological theories about the relationships between plant functional markers, plant ecological strategies and resources use. Conclusions: The identification of functional markers related to service provision may help us to select species or communities service crops that could perform interesting trade-offs between multiple services due to a suited combination of related markers, and provide insights for plant selection in order to breed plant varieties and cultivars with the aim of providing agroecosystem services.

Root proliferation in response to P stress and space: implications for the study of root acclimation to low P supply and P acquisition efficiency

The experiment was conducted to understand how root morphological traits contributed to the contrasting P-acquisition efficiencies of two Trifolium subterraneum cultivars. Phosphorus acquisition, root length proliferation and root acclimation to P deficiency were investigated by varying the P supply (20–300 mg P kg−1) and planting density (1–12 plants pot−1) of clover micro-swards. The shoot yield of both cultivars increased in response to increased P supply and increased planting density. Higher planting densities increased shoot yield by reducing the time to leaf canopy closure. In P-deficient soil, the ‘less P-efficient’ cultivar acquired less P and yielded relatively poorly compared with the ‘more P-efficient’ cultivar when planting density was low (<6 plants pot−1). However, the P acquisition and yields of the cultivars were equivalent when planting density was high (~6–12 plants pot−1). Both cultivars proliferated nutrient-foraging roots in response to P limitation and space (i.e. lower planting densities). However, the proliferation responses of the cultivars differed, particularly in response to space. Differential proliferation responses, combined with differences in specific root length, explained how the cultivars differed in P-acquisition efficiency. The results indicate that inappropriate cultural conditions (e.g. planting densities) may confound attempts to define P-efficient root traits and to identify genotypes with improved P-acquisition efficiency.

Below-ground determinants and ecological implications of shrub species' degree of isohydry in subtropical pine plantations.

The degree of plant iso/anisohydry is a popular framework for characterising species-specific drought responses. However, we know little about associations between below-ground and above-ground hydraulic traits as well as the broader ecological implications of this framework. For 24 understory shrub species in seasonally dry subtropical coniferous plantations, we investigated contributions of the degree of isohydry to species' resource economy strategies, abundance, and importance value, and quantified the hydraulic conductance (Kh ) of above-ground and below-ground organs, magnitude of deep water acquisition (WAdeep ), shallow absorptive root traits (diameter, specific root length, tissue density), and resource-use efficiencies (Amax , maximum photosynthesis rate; PNUE, photosynthetic nitrogen-use efficiency). The extreme isohydric understory species had lower wood density (a proxy for higher growth rates) because their higher WAdeep and whole-plant Kh allowed higher Amax and PNUE, and thus did not necessarily show lower abundance and importance values. Although species' Kh was coordinated with their water foraging capacity in shallow soil, the more acquisitive deep roots were more crucial than shallow roots in shaping species' extreme isohydric behaviour. Our results provide new insights into the mechanisms through which below-ground hydraulic traits, especially those of deep roots, determine species' degree of isohydry and economic strategies.

Climate and soil nutrients differentially drive multidimensional fine root traits in ectomycorrhizal‐dominated alpine coniferous forests

Abstract Fine root traits vary greatly with environmental changes, but the understanding of root trait variation and its drivers is limited over broad geographical scales, especially for ectomycorrhizal (ECM)‐dominated conifers in alpine forests. Herein, the covariation patterns of and environmental controls for fine root traits among ECM‐dominated conifers were examined to test whether and how climate and soil nutrients differentially affect fine root trait variations. Eight traits of first‐ and second‐order roots were measured, that is, root diameter (RD), specific root length (SRL), branching intensity (BRI), root tissue density (RTD), mycorrhizal colonization rate (MCR) and concentrations of carbon (C), nitrogen (N) and phosphorus (P), across 76 alpine coniferous populations on the eastern Tibetan Plateau, China. Our results showed that variations of the fine root traits fell into two major dimensions: the first dimension (32.39% of the total variance) was mainly represented by RD and SRL, potentially conveying a trade‐off between root life span and efficiency of resource foraging; the second dimension (23.70% of the variance) represented coordinated variation for root nutrients (i.e. N and P) and RTD, which depicts the conservation‐acquisition trade‐off in resource uptake, that is, root economic spectrum. Variations in RD and SRL were mainly driven by climatic variables, characterized by a significant increase in RD and a decrease in SRL with increasing mean annual precipitation. In contrast, variations in fine root nutrients (i.e. N and P) and RTD were primarily driven by soil fertility, showing a significant increase in root N and P concentrations but a decrease in RTD with increasing soil resource levels. Synthesis. Our study clearly shows two distinct dimensions of the variation of fine root traits in ECM‐dominated alpine coniferous forests, providing further evidence of the inherent multidimensionality of root traits. Moreover, our findings highlight different roles of climatic and soil variables in driving the variation of fine root traits, potentially leading to the multidimensionality of root traits. This study provides new insights for understanding and predicting shifts in plant belowground strategies in climate‐sensitive alpine forests world‐wide.

Root nitrogen acquisition strategy of trees and understory species in a subtropical pine plantation in southern China

Nitrogen (N) is considered as a major factor that limits plant growth and metabolism, and absorptive roots play a critical role in plant resource acquisition. However, little is known about the roles of mycorrhizal colonization, and morphological and architectural traits of absorptive roots in N uptake rates. We examined the uptake rates for ammonium ( $${\text{NH}}_{4}^{ + }$$ ), nitrate ( $${\text{NO}}_{3}^{ - }$$ ) and glycine using a 15N isotope tracer technique and measured mycorrhizal colonization rates and functional traits (morphology, architecture and chemistry) of absorptive roots in a subtropical plantation during the growing season. Results showed that trees, shrubs and herbs all preferred to take up $${\text{NH}}_{4}^{ + }$$ over $${\text{NO}}_{3}^{ - }$$ and glycine, likely due to the dominant available N form in native soils. Species coexisting in the subtropical plantation did not show chemical niche differentiation, but there was a temporal niche separation in N acquisition across plant species. Absorptive roots with higher mycorrhizal colonization rates exhibited higher N uptake rates than those with lower colonization. In May, morphological traits (diameter and root tissue density) seemed playing important roles in N acquisition on that the absorptive roots with larger diameter and shorter specific root length (SRL) showed higher uptake rates for $${\text{NH}}_{4}^{ + }$$ , $${\text{NO}}_{3}^{ - }$$ , and glycine than those with smaller diameter and longer SRL. While in August, the architectural traits of root branching might be essential to enhance nutrient absorption on that the absorptive roots with intensive branching exhibited higher N uptake rates than those with less branching. Our findings suggested that plant species may evolve effective N acquisition strategies integrated mycorrhizal symbiosis, and root morphological and architectural traits over a temporal scale to acclimate to the changing environments.

Main Root Adaptations in Pepper Germplasm (Capsicum spp.) to Phosphorus Low-Input Conditions

Agriculture will face many challenges regarding food security and sustainability. Improving phosphorus use efficiency is of paramount importance to face the needs of a growing population while decreasing the toll on the environment. Pepper (Capsicum spp.) is widely cultivated around the world; hence, any breakthrough in this field would have a major impact in agricultural systems. Herein, the response to phosphorus low-input conditions is reported for 25 pepper accessions regarding phosphorus use efficiency, biomass and root traits. Results suggest a differential response from different plant organs to phosphorus starvation. Roots presented the lowest phosphorus levels, possibly due to mobilizations towards above-ground organs. Accessions showed a wide range of variability regarding efficiency parameters, offering the possibility of selecting materials for different inputs. Accessions bol_144 and fra_DLL showed an interesting phosphorus efficiency ratio under low-input conditions, whereas mex_scm and sp_piq showed high phosphorus uptake efficiency and mex_pas and sp_bola the highest values for phosphorus use efficiency. Phosphorus low-input conditions favored root instead of aerial growth, enabling increases of root total length, proportion of root length dedicated to fine roots and root specific length while decreasing roots’ average diameter. Positive correlation was found between fine roots and phosphorus efficiency parameters, reinforcing the importance of this adaptation to biomass yield under low-input conditions. This work provides relevant first insights into pepper’s response to phosphorus low-input conditions.

Contrasting patterns in biomass allocation, root morphology and mycorrhizal symbiosis for phosphorus acquisition among 20 chickpea genotypes with different amounts of rhizosheath carboxylates

Abstract Adjustments in root biomass allocation, root morphology, carboxylate exudation and mycorrhizal symbiosis are well‐known strategies for plants to cope with phosphorus (P) deficiency. Large genotypic variation in these functional traits has been demonstrated within numerous species. Yet, whether these functional traits are coordinated differently among genotypes of a species to enhance P acquisition remains unknown. We characterized 11 root functional traits associated with P acquisition in 20 chickpea genotypes with contrasting amounts of rhizosheath carboxylates, grown in a glasshouse with severely limiting insoluble (10 mg/kg FePO4), moderately limiting soluble (10 mg/kg KH2PO4) and adequate (50 mg/kg KH2PO4) P supply. Substantial variation was found among genotypes in root functional traits associated with P acquisition. Genotypes with a large amount of carboxylates (HRC) had thinner roots, and a lower root mass fraction and root mass density (RMD), but higher specific root length (SRL) and colonization by arbuscular mycorrhizal fungi (AMF) than genotypes with a small amount of rhizosheath carboxylates. In response to soil P availability, chickpea genotypes showed large plasticity in root biomass allocation, rhizosheath pH, carboxylate amount and colonization by AMF, but a limited response in most root morphological traits (i.e. mean root diameter, RMD and SRL). Shoot P content was strongly correlated with different root functional traits in the three P treatments. Our findings suggest a range of predictable relationships between root functional traits among chickpea genotypes; those with HRC tended to have relatively thinner roots with lower cost of root construction, while allocating more resources to carboxylate exudation and colonization by AMF. The shift in the relationships between shoot P content and root functional traits indicates that root traits and/or trait combinations in chickpea vary in a manner that enhances P acquisition under specific soil P conditions (i.e. P sources/levels). Such knowledge provides valuable information for chickpea genotype breeding and our understanding of evolution of traits with improved root/rhizosphere functioning. A free Plain Language Summary can be found within the Supporting Information of this article.

Phenotypic variability in bread wheat root systems at the early vegetative stage

BackgroundUnderstanding root system morphology in bread wheat is critical for identifying root traits to breed cultivars with improved resource uptake and better adaptation to adverse environments. Variability in root morphological traits at early vegetative stages was examined among 184 bread wheat genotypes originating from 37 countries grown in a semi-hydroponic phenotyping system.ResultsAt the onset of tillering (Z2.1, 35 days after transplanting), plants had up to 42 cm in shoot height and 158 cm long in root depth. Phenotypic variation existed for both shoot and root traits, with a maximal 4.3-fold difference in total root length and 5-fold difference in root dry mass among the 184 genotypes. Of the 41 measured traits, 24 root traits and four shoot traits had larger coefficients of variation (CV ≥ 0.25). Strong positive correlations were identified for some key root traits (i.e., root mass, root length, and these parameters at different depths) and shoot traits (i.e., shoot mass and tiller number) (P ≤ 0.05). The selected 25 global traits (at whole-plant level) contributed to one of the five principal components (eigenvalues> 1) capturing 83.0% of the total variability across genotypes. Agglomerative hierarchical clustering analysis separated the 184 genotypes into four (at a rescaled distance of 15) or seven (at a rescaled distance of 10) major groups based on the same set of root traits. Strong relationships between performance traits (dry mass) with several functional traits such as specific root length, root length intensity and root tissue density suggest their linkage to plant growth and fitness strategies.ConclusionsLarge phenotypic variability in root system morphology in wheat genotypes was observed at the tillering stage using established semi-hydroponic phenotyping techniques. Phenotypic differences in and trait correlations among some interesting root traits may be considered for breeding wheat cultivars with efficient water acquisition and better adaptation to abiotic stress.

Influence of fine root traits on in situ exudation rates in four conifers from different mycorrhizal associations.

Plant roots can exude organic compounds into the soil that are useful for plant survival because they can degrade microorganisms around the roots and enhance allelopathy against other plant invasions. We developed a method to collect carbon (C) exudation on a small scale from tree fine roots by C-free filter traps. We quantified total C through root exudation in four conifers from different microbial symbiotic groups (ectomycorrhiza (ECM) and arbuscular mycorrhiza (AM)) in a cool-temperate forest in Japan. We determined the relationship of mass-based exudation rate from three diameter classes (<0.5, 0.5-1.0, and 1.0-2.5mm) of the intact root system with root traits such as morphological traits including root diameter, specific root length (SRL), specific root area (SRA), root tissue density (RTD) and chemical traits including root nitrogen (N) content and C/N. Across species, the mass-based root exudation rate was found to correlate with diameter, SRA, RTD, N and C/N. When comparing mycorrhizal types, there were significant relationships between the exudation and diameter, SRL, SRA, root N and C/N in ECM species; however, these were not significant in AM species. Our results show that relationships between in situ root exudation and every measured trait of morphology and chemistry were strongly driven by ECM roots and not by AM roots. These differences might explain the fact that ECM roots in this study potentially covaried by optimizing the exudation and root morphology in forest trees, while exudation in AM roots did not change with changes in root morphology. In addition, the contrasting results may be attributable to the effect of degree and position of ECM and AM colonization in fine root system. Differences in fine root exudation relationships to root morphology for the two types of mycorrhizae will help us better understand the underlying mechanisms of belowground C allocation in forest ecosystems.

Adaptive changes in root morphological traits of Gramineae and Leguminosae seedlings in the ecological restoration of the semiarid region of northwest China

AbstractGramineae and Leguminosae forages are widely grown in the semiarid region of northwest China. To understand the changes in root morphology in forage seedlings under drought stress, a nursery experiment was conducted with and without water stress using four Gramineae species (Bromus inermis, Agropyron mongolicum, Lolium perenne, and Bothriochloa ischaemum) and four Leguminosae species (Lespedeza bicolor, Medicago sativa, Astragalus adsurgens and Melilotus suaveolens). The forages were grown in rhizoboxes under drought stress (15% polyethylene glycol stress) and well‐watered (85% of field capacity) conditions. The results showed that the root length, root area, and specific root length of the Gramineae species were higher than those of the Leguminosae species at the 30–60 cm soil depth. The fine roots of eight species in the 0~0.5 mm diameter class had the largest total root length and total root area, and the total root volume and root tips in the 0.5~1.0 mm diameter class were the highest. Based on the subordinate function method results, B. inermis had the highest comprehensive score, while M. suaveolens had the lowest. Our results implied that Gramineae seedlings distributed more roots than Leguminosae seedlings in the 30–60 cm soil layer under drought stress. Under drought stress, fine roots in the 0~0.5 mm and 0.5~1.0 mm diameter classes were the main organs sustaining the growth of the eight species when suffered drought stress. Among the eight species, B. inermis had the strongest drought tolerance and could act as an optimal ecological restoration forage in the semiarid region of northwest China.