Root System Traits Research Articles

Implications of tolerance to iron toxicity on root system architecture changes in rice (Oryza sativa L.)

IntroductionToxicity due to excess soil iron (Fe) is a significant concern for rice cultivation in lowland areas with acidic soils. Toxic levels of Fe adversely affect plant growth by disrupting the absorption of essential macronutrients, and by causing cellular damage. To understand the responses to excess Fe, particularly on seedling root system, this study evaluated rice genotypes under varying Fe levels.MethodsSixteen diverse rice genotypes were hydroponically screened under induced Fe levels, ranging from normal to excess. Morphological and root system characteristics were observed. The onset of leaf bronzing was monitored to identify the toxic response to the excess Fe. Additionally, agronomic and root characteristics were measured to classify genotypes into tolerant and sensitive categories by computing a response stability index.ResultsOur results revealed that 460 ppm of Fe in the nutrient solution served as a critical threshold for screening genotypes during the seedling stage. Fe toxicity significantly affected root system traits, emphasizing the consequential impact on aerial biomass and nutrient deprivation. To classify genotypes into tolerant and sensitive categories, leaf bronzing score was used as a major indicator of Fe stress. However, the response stability index provided a robust basis for classification for the growth performance. Apart from the established tolerant varieties, we could identify a previously unrecognized tolerant variety, ILS 12–5 in this study. Some of the popular mega varieties, including BPT 5204 and Pusa 44, were found to be highly sensitive.DiscussionOur findings suggest that root system damage, particularly in root length, surface area, and root volume, is the key factor contributing to the sensitivity responses under Fe toxicity. Tolerant genotypes were found to retain more healthy roots than the sensitive ones. Fe exclusion, by reducing Fe2+ uptake, may be a major mechanism for tolerance among these genotypes. Further field evaluations are necessary to confirm the behavior of identified tolerant and sensitive lines under natural conditions. Insights from the study provide potential scope for enhancement of tolerance through breeding programs as well as throw light on the role root system in conferring tolerance.

Soil compaction development facilitated the decadal improvement of the root system architecture and rhizosheath soil traits of soybean in the North China Plain

Machinery agriculture has increased crop yield but induced soil compaction worldwide in the last decades. The crop yield increase is partly attributed to high-yielding crop breeding, but the effects of emerging soil compaction on the selection of root system traits and its impact on yield increase remain unclear. The objectives of this study were 1) to identify the effects of soil compaction on grain yield and root system architecture and rhizosheath soil traits of soybean (Glycine max (L.) Merr.) at the full-bloom stage, 2) to understand whether and how the development of soil compaction affected the selection of merit root and rhizosheath soil traits through crop breeding and contributed to soybean grain yield increase. Thirty-four most popular soybean cultivars released before and after the wide use of agricultural machinery in the North China Plain were grown in the fields without (NOM) and with (COM) applied soil compaction in 2017 and 2018. The phenotypes of root system, including rhizosheath soil, of soybean, were separated by soil compaction and cultivar release period, confirming the development of soil compaction and its impacts on the co-development of rhizosheaths with the root system of soybean. The correlation with the year of release of the cultivar demonstrated that 21 out of the 24 measured traits were selected by crop breeding. Multivariate analysis of the variance demonstrated that the selection of thinner hypocotyl, more root tips, and denser rhizosheath soil were relevant to the soil compaction development. The selection of shorter plant height, larger root biomass and area, thinner root tip, thicker taproot, and rhizosheath soil mass were likely relevant to the experimental year factor caused by drought or its associated change in nutrient availability. Most of the selected traits increased the resistance or the resilience to soil compaction and nine of them correlated with the grain yield of cultivars released at different periods. These results for the first time suggested that crop breeding increased grain yield partly by increasing the resistance and resilience to soil compaction. Soil compaction could be considered in a future breeding program design to increase crop breeding efficiency by selecting resistant and resilient root traits.

Root traits correlated with soybean yield in a subtropical region

Root system plays a crucial role in plants’ anchoring, water and nutrients acquisition and storage of carbohydrates. While it is understood that root system traits contribute to crop yield, little is known about the particular effects of root morphology over crop yield, even on major crops such as soybean (Glycine max). The objective of this study was to investigate if distinct soybean grain yield plants, grown at different sites, displayed differences in their root system morphology. This distinct traits in the root system should be responsible to the differences of yield, thus, showing which traits should be followed in breeding programs to develop higher yield cultivars. The soybean cultivar DM 5958 RSF IPRO was sowing in a randomized complete block design experiment. Treatments comprised three cultivation sites and five soybean grain yield classes. Plant emergence and root system morphology attributes were evaluated. Results showed that late emergence negatively influenced root development. A huge difference among sites over very thin (89%) and thin (85%) roots was found in the high yield class, and since the plants have similar yield, it appeared that the thin and very thin roots length have no impact on the yield, being influenced mostly by the environment. Forks and tips roots didn’t show a pattern. In contrast, roots volume only showed a 22% reduction, demonstrating to be less influenced by the environment, resulting in a greater correlation with the grain yield. Thus identified as the main attribute to be explored when seeking to select new soybean cultivars.

Plasticity of root hair and rhizosheath traits and their relationship to phosphorus uptake in sorghum.

Sorghum is an essential crop for resilient and adaptive responses to climate change. The root systems of crop plants significantly contribute to the tolerance of abiotic stresses. There is little information on sorghum genotypes' root systems and plasticity to external P supply. In this paper, we investigated the variations in root systems, as well as the responses, trait relationships, and plasticity of two sorghum genotypes (Naga Red and Naga White), popularly grown in Ghana, to five external P concentrations ([P]ext): 0, 100, 200, 300, and 400 mg P kg-1 soil. Sorghum plants were grown in greenhouse pots and harvested for root trait measurements at the five-leaf and growing point differentiation (GPD) developmental stages. The plants were responsive to [P]ext and formed rhizosheaths. The two genotypes showed similar characteristics for most of the traits measured but differed significantly in total and lateral root lengths in favor of the red genotype. For example, at the five-leaf growth stage, the lateral root length of the red and white genotypes was 22.8 and 16.2cm, respectively, but 124 and 88.9cm, at the GPD stage. The responses and plasticity of the root system traits, including rhizosheath, to [P]ext were more prominent, positive, and linear at the five-leaf stage than at the GPD growth stage. At the five-leaf growth stage, total root length increased by about 2.5-fold with increasing [P]ext compared to the unamended soil. At the GPD stage, however, total root length decreased by about 1.83-fold as [P]ext increased compared to the unamended soil. Specific rhizosheath weight correlated with RHD, albeit weakly, and together explained up to 59% of the variation in tissue P. Root hair density was more responsive to P supply than root hair length and showed a similar total and lateral root length pattern. Most desirable responses to P occurred at a rate of 200-300 mg P kg-1 soil. It is concluded that sorghum would form rhizosheath, and [P]ext could be critical for the early vigorous growth of sorghum's responsive root and shoot traits. Beyond the early days of development, additional P application might be necessary to sustain the responses and plasticity observed during the early growth period, but this requires further investigation, potentially under field conditions.

Essential oil-grafted copper nanoparticles as a potential next-generation fungicide for holistic disease management in maize.

Sustainable food production is necessary to meet the demand of the incessantly growing human population. Phytopathogens pose a major constraint in food production, and the use of conventional fungicides to manage them is under the purview of criticism due to their numerous setbacks. In the present study, essential oil-grafted copper nanoparticles (EGC) were generated, characterized, and evaluated against the maize fungal pathogens, viz., Bipolaris maydis, Rhizoctonia solani f. sp. sasakii, Macrophomina phaseolina, Fusarium verticillioides, and Sclerotium rolfsii. The ED50 for the fungi under study ranged from 43 to 56 μg ml-1, and a significant inhibition was observed at a low dose of 20 μg ml-1 under in vitro conditions. Under net house conditions, seed treatment + foliar spray at 250 and 500 mg L-1 of EGC performed remarkably against maydis leaf blight (MLB), with reduced percent disease index (PDI) by 27.116 and 25.292%, respectively, in two Kharif seasons (May-Sep, 2021, 2022). The activity of enzymatic antioxidants, viz., β-1, 3-glucanase, PAL, POX, and PPO, and a non-enzymatic antioxidant (total phenolics) was increased in treated maize plants, indicating host defense was triggered. The optimum concentrations of EGC (250 mg L-1 and 500 mg L-1) exhibited improved physiological characteristics such as photosynthetic activity, shoot biomass, plant height, germination percentage, vigor index, and root system traits. However, higher concentrations of 1,000 mg L-1 rendered phytotoxicity, reducing growth, biomass, and copper bioaccumulation to high toxic levels, mainly in the foliar-sprayed maize leaves. In addition, EGC and copper nanoparticles (CuNPs) at 1,000 mg L-1 reduced the absorption and concentration of manganese and zinc indicating a negative correlation between Cu and Mn/Zn. Our study proposes that the CuNPs combined with EO (Clove oil) exhibit astounding synergistic efficacy against maize fungal pathogens and optimized concentrations can be used as an alternative to commercial fungicides without any serious impact on environmental health.

Quantifying root-induced soil strength, measured as soil penetration resistance, from different crop plants and soil types

A common soil mechanical property for assessing soil strength is soil penetration resistance (PR) or soil cone index (CI), which is related to the undrained shear strength of saturated and cohesive soil. Plant roots can increase soil strength, but physical conditions may confound this. Pot experiments were conducted using 70 cm soil columns, three soil types (beach sand, erosion-prone soil, and two typical arable soils), and four crop plants (maize, sorghum, Napier, and vetiver grass). We tested the hypothesis that plant roots impact soil strength, measured as soil PR, and the induced soil strength differs based on plant species. The CI and root system architecture (RSA) traits were measured. Napier grass grown in arable soils recorded higher total biomass. Together with maize, Napier grass had a more significant root length density, particularly at 25–40 cm depth. The CI increased with increasing depth, with a 57–99% increase in CI in the bottom layer compared to the top layer of the soil column. The overall CI of soils grown to Napier grass (2.0 and 2.3 MPa) and maize (1.7 and 2.2 MPa) were similar, but both were higher than the soils cultivated with the other crop plants and unplanted control. The overall CI of the SEA sand of ∼2.0 MPa was 36%, higher than that for the arable soils. Soil moisture content did not significantly increase CI, but the interaction of soil bulk density and root system traits could be implicated in increased CI of root-permeated soils. It is concluded that (i) roots growing in arable soils can increase CI and hence soil strength, possibly due to the binding effect of root systems, even when the transpiration effect of plants on soil moisture is low; (ii) crop plants contribute differently to soil strength, and (iii) Napier grass could offer a rapid growth and establishment option when considering plants for soil reinforcement and stability.

Counteracting action of Bacillus stratosphericus and Staphylococcus succinus strains against deleterious salt effects on Zea mays L.

The salinization of soil is the process of progressive accumulation of salts such as sulfates, sodium, or chlorides into the soil. The increased level of salt has significant effects on glycophyte plants, such as rice, maize, and wheat, which are staple foods for the world's population. Consequently, it is important to develop biotechnologies that improve crops and clean up the soil. Among other remediation methods, there is an environmentally friendly approach to ameliorate the cultivation of glycophyte plants in saline soil, namely, the use of microorganisms tolerant to salt with growth-promoting features. Plant growth-promoting rhizobacteria (PGPR) can improve plant growth by colonizing their roots and playing a vital role in helping plants to establish and grow in nutrient-deficient conditions. Our research aimed to test in vivo halotolerant PGPR, isolated and characterized in vitro in a previous study conducted in our laboratory, inoculating them on maize seedlings to improve their growth in the presence of sodium chloride. The bacterial inoculation was performed using the seed-coating method, and the produced effects were evaluated by morphometric analysis, quantization of ion contents (sodium, potassium), produced biomass, both for epigeal (shoot) and hypogeal (root) organs, and by measuring salt-induced oxidative damage. The results showed an increase in biomass and sodium tolerance and even a reduction of oxidative stress in seedlings pretreated with a PGPR bacterial consortium (Staphylococcus succinus + Bacillus stratosphericus) over the control. Moreover, we observed that salt reduces growth and alters root system traits of maize seedlings, while bacterial treatment improves plant growth and partially restores the root architecture system in saline stress conditions. Therefore, the PGPR seed-coating or seedling treatment could be an effective strategy to enhance sustainable agriculture in saline soils due to the protection of the plants from their inhibitory effect.

Distinctive root system adaptation of ploidy wheats to water stress: A cue to yield enhancement

AbstractGiven the worldwide effort to improve crop drought resistance, it is crucial to understand the mechanisms of root system adaptation of ploidy wheat to water‐deficient environments. A meta‐analysis was performed to examine the changes in root system mechanisms under drought conditions. Data used in the analysis were drawn from 192 papers, taking into account wheat ploidy levels as well as pot and field studies. The results illustrated that water stress reduced grain yield and aboveground biomass to a greater extent in diploid and tetraploid compared with hexaploid genotypes. In contrast, drought reduced root biomass, root surface area and root volume more in hexaploid than in diploid and tetraploid wheat. Under water‐limited conditions, diploid and tetraploid genotypes exhibited greater root biomass and root length densities in the topsoil. Hexaploid genotypes greatly reduced root biomass and root length density in the topsoil and maintained higher root biomass and root length density in subsoil. These genotypes also showed smaller root diameter and xylem centre vessel diameter under drought conditions. The analysis revealed that grain yield was negatively correlated with topsoil root biomass and root length density, root volume, root diameter and xylem centre vessel, but positively correlated with subsoil root mass, root length density and root vigour. The study demonstrated that domestication and selection pressures of ploidy wheat have altered wheat root system traits while improving grain yield. Greater root mass and root length densities in the subsoil facilitate access to soil moisture from deep layers, contributing to high yields in drought environments.

Effective drought mitigation by rhizobacteria consortium in wheat field trials

To evaluate the drought mitigation on the yield and morpho-physiological traits of wheat by plant growth-promoting bacteria (PGPB), a two-year factorial split-plot field experiment was conducted based on a randomized complete block design. The factors were three levels of normal, moderate, and severe stress, and two levels of control and inoculated bacteria (Azotobacter, Azospirillum, Microbacterium, and Pseudomonas). The results indicated that drought stress negatively affected the morpho-physiological traits of wheat. An increase in oxidative stress and lipid peroxidation reduced wheat chlorophyll content and grain yield (GY) by 18% and 49%, respectively. Moreover, wheat root system traits, including root biomass, volume, surface area, and length density decreased significantly under drought stress. The inoculation of PGPB significantly increased the biomass, volume, and surface area of wheat roots by 48%, 31%, and 18.5%, respectively. An improved root system in the inoculated treatment with an increase in the relative leaf water content and a decrease in oxidative stress could increase leaf chlorophyll content. The PGPB inoculation significantly elevated wheat GY under normal and stress conditions, with the highest yield increase at the moderate stress level (12%). At the high stress level, however, bacterial inoculation did not significantly influence wheat yield. Altogether, the inoculation of bacteria with various growth-stimulating traits improved the morphological, physiological, and metabolic traits of wheat under drought stress, ultimately increasing wheat GY in real field conditions.

Phenotypic Diversity of Seminal Root Traits in Bread Wheat Germplasm from Different Origins.

Bread wheat (Triticum aestivum L.) is a major staple crop, and more adapted varieties are needed to ensure productivity under unpredictable stress scenarios resulting from climate changes. In the development of new genotypes, root system traits are essential since roots have a key function in water and nutrient uptake, and root architecture determines the plant's ability to spatially explore the soil resources. Genetic variation in wheat root system may be assessed at the early stages of development. This study evaluates in vitro and at the seedling stage, the genetic diversity of root growth angle (RGA), seminal root number (SRN), and radicle length (RadL) in 30 bread wheat genotypes from different origins and belonging to distinct evolutive or breeding groups. SRN and RadL were analyzed at 1, 2, 3 and 6 days after sowing (DAS) and RGA was measured through the angle between the first pair of seminal roots. A large variability was found in RGA values that ranged from 63° to 122°. Although differences were found between genotypes within the same groups, the narrower angles tended to occur among landraces, while the higher RGA values were observed in advanced lines and Australian varieties. Differences were also observed as regards the SRN (1.0-3.0, 2.7-4.7, 3.2-5.0 and 4.4-6.3 at 1, 2, 3 and 6 DAS, respectively) and RadL (0.1-1.5, 2.1-5.0, 4.0-7.5 and 5.1-13.7 cm at 1, 2, 3 and 6 DAS, respectively). Genetic variability in root traits at seedling stage allows more rapid selection of genotypes better adapted to environmental and soil constraints, necessary to Portuguese Wheat Breeding Program. It will also contribute to the definition of wheat ideotypes with improved performance under Mediterranean climate conditions.

All Are in a Drought, but Some Stand Out: Multivariate Analysis in the Selection of Agronomic Efficient Popcorn Genotypes

The search for productive germplasm adapted to adverse conditions is an important action to mitigate the harmful effects of climate change. The aim was to identify the yield potential of 50 popcorn inbred lines grown in field conditions, in two crop seasons (CS), and under contrasting water conditions (WC). Morphoagronomic, physiological, and root system traits were evaluated. Joint and individual analyses of variance were performed, in addition to the multivariate GT bip-lot analysis. Expressive reductions between WC were observed in 100-grain weight (100 GW), popping expansion (PE), grain yield (GY), expanded popcorn volume per ha (EPV), row number per ear (RNE), plant height (PH), relative chlorophyll content (SPAD), and nitrogen balance index (NBI). It was found that the SPAD, 100 GW, GY, PE, and grain number per ear (GNE) traits had the most significant impact on the selection of genotypes. Regardless of WC and CS, the ideal lines were L294 and L688 for PE; L691 and L480 for GY; and L291 and L292 for both traits. SPAD, 100 GW, and GNE can contribute to the indirect selection. Our work contributes to understanding the damage caused by drought and the integration of traits for the indirect selection of drought-tolerant popcorn genotypes.

Multipronged Phenotyping Approaches to Characterize Sugarcane Root Systems.

Roots are the primary conductors of water and nutrients and play a vital role in sustaining growth and yield under stressful environments. The study of plant roots poses methodological difficulties in in situ assessment and sampling, which is especially true for sugarcane (Saccharum spp.). Traditional methods during the 1920s documented the genotypic variation in sugarcane root systems, after which few studies were reported on sugarcane root traits per se until recently. In addition to morphology, rhizosphere characteristics, including allelopathic effects and/or affinity for microbial symbiosis, determine plant establishment and survival. Ultimately, root systems define the above-ground productivity of sugarcane. With the impetus for climate-resilient varieties, it is becoming more relevant to explore and utilize the variability in root system traits of sugarcane. This paper describes multipronged approaches for sugarcane root phenotyping, including field excavation by trench sampling, the use of a root core sampler, raised platforms for root sampling, and raising plants under hydroponic culture, employed by a team of scientists at the Indian Council of Agricultural Research-Sugarcane Breeding Institute (ICAR-SBI). Field excavation by trench sampling is imperative to assess the plant roots in their natural growing environment. The use of raised platforms simulating field conditions and a root core sampler are alternative approaches, with a considerable reduction in time, uniform sample size, and less loss of root material. Hydroponic plant culture allows the study of morphology, anatomical features, and rhizosphere biology, including the exudation of organic compounds and microbial interactions. Data generated from different experiments using diverse sampling methods add to the wealth of information on the root system traits of sugarcane.

Fine root hydraulic conductivity relates to root functional traits in four coniferous species

Tree fine roots (<2 mm in diameter) are the primary organs for water acquisition from soil, yet how root traits contribute to water uptake under field conditions is not well established. In this study, we quantified the relationship between root water uptake and root functional traits in natural coniferous forests. In cool-temperate coniferous forests, we directly measured in situ hydraulic conductivity (Lp; m3 m−2 s−1 MPa−1) of fine root using a pressure chamber method. We also examined the relationship between the Lp of the intact root segments and root traits, such as morphological traits, including root diameter and tissue density, and chemical traits, such as root N content, particularly at the interspecific level. The Lp of fine root segments differed significantly among species. Fine root Lp was positively correlated with root tissue density and negatively correlated with root diameter and N content across species, suggesting it is related to actual water movement within trees. Our results show that the Lp of fine root systems in the forest field reflects and originates from both water resistance in transportation and absorption, especially a water transport rather than an absorption function. We highlight that the linkage between in situ Lp and the fine root system traits enable understanding of the complex functional balance characterizing the overall hydraulic uptake and transport capacity of water resources from the soil through exploitative root foraging.

Genetic Control of the Root System Traits in Oilseed Rape Under Contrasting Phosphate Supply Conditions by Genome-wide Association Study

Genetic Control of the Root System Traits in Oilseed Rape Under Contrasting Phosphate Supply Conditions by Genome-wide Association Study

Root System Traits and Mechanical Properties of Three Shrub Species: Implications for the Structural Stability of the Ecological Slope

The purpose of this paper is to find the shrub species more suitable to enhance the structural stability of the ecological slope in the study area. Through the investigation, we found three common shrubs, there are Amorpha fruticosa Linn. (AFL), Syringa oblata Lindl. (SOL) and Forsythio mandshurica Uyeki. (FMU). In this study, the root system traits and mechanical properties were characterized and described using reliable experimental approaches. The results shown the root withdrawal force was proportional to diameter (from 0.6-6 mm). The mean specific root length, individual length, surface area, and mean diameter of fine roots in different slopes were higher for AFL and SOL than for FMU, especially for high root orders. Although previous studies have focused on the relevant content, the reinforcement ability of different shrubs is rarely quantitatively compared under the same road conditions. Moreover, the morphology traits of the fine root were considered in this study. These results suggested that the root system traits and mechanical properties of AFL would enable more effective consolidated slopes structure than SOL and FMU, revealing that planting AFL might be a better way for enhancing ecological slope structure stability.

Phenotyping Complex Plant Structures with a Large Format Industrial Scale High-Resolution X-Ray Tomography Instrument.

Phenotyping specific plant traits is difficult when the samples to be measured are architecturally complex. Inflorescence and root system traits are of great biological interest, but these structures present unique phenotyping challenges due to their often complicated and three-dimensional (3D) forms. We describe how a large industrial scale X-ray tomography (XRT) instrument can be used to scan architecturally complex plant structures for the goal of rapid and accurate measurement of traits that are otherwise cumbersome or not possible to capture by other means. The combination of a large imaging cabinet that can accommodate a wide range of sample size geometries and a variable microfocus reflection X-ray source allows noninvasive X-ray imaging and 3D volume generation of diverse sample types. Specific sample fixturing (mounting) and scanning conditions are presented. These techniques can be moderate to high throughput and still provide unprecedented levels of accuracy and information content in the 3D volume data they generate.

Root hair and rhizosheath traits contribute to genetic variation and phosphorus use efficiency in cowpea (Vigna unguiculata (L.) Walp)

Rhizosheaths are soil particles that bind to the surface of plant roots after excavation. Rhizosheaths can indicate root hair length and are essential for the uptake of soil resources. Cowpea is a key legume crop for Africa's food security, livelihood, and agroecosystem sustainability. Still, genetic variation in rhizosheaths and root hair traits in cowpea and their impact on phosphorus (P) uptake have not been tested. Here, 60 cowpea genotypes were grown to assess genotypic variations in root hair, rhizosheath, and other root system traits. Subsequently, 20 genotypes were selected to evaluate variations in trait responses to varying rates of external P application ([P]ext). Root hair traits were positively related to rhizosheath dry weight, and this showed significant genotypic variation (p < 0.001), with more than 2.5-fold variation. Root hair length and density were 0.111 cm and 0.329 roots cm−2, respectively, with 54.3% and 59.1% differences between their lowest and highest values. Shoot biomass, specific rhizosheath weight, and root hair length were the top contributors to the genotypic variations. The main effect of [P]ext was highly significant, with plants producing more biomass at higher [P]ext but root hair length increased at low [P]ext. This paper contributes seminal information on variations in root hair and rhizosheath formation with P uptake and the potential for using this information in cowpea improvement for adaptation to rhizospheric stresses.

Anatomical and morphological traits of the okra root system and the growing practice in plastic-covered greenhouses

The article presents studies of the anatomical and morphological traits of the okra root system and elements of the okra growing practice in plastic-covered greenhouses. The studies were carried out in 2018–2020 on the territory of the Educational and Scientific Production Center “Vegetable Experimental Station named after V. I. Edelstein”, Federal State Budgetary Educational Institution of Higher Education Russian State Agrarian University – Moscow Timiryazev Agricultural Academy. The two ways of formation were studied (1 and 2 stems). As a result of the research, the anatomical and morphological traits of the okra root system were clarified, the highest yield of okra fruits of the Lady’s Finger variety was established when plants were formed in two shoots. To obtain the highest yield of fruits, we recommend growing the Lady’s Finger variety, forming plants in 2 shoots, while the yield is 1.6 kg/m2, which is 0.2 kg/m2 higher than the yield of this variety obtained when plants were formed in 1 shoot.

Interactions among rooting traits for deep water and nitrogen uptake in upland and lowland ecotypes of switchgrass (Panicum virgatum L.).

The response of plant growth and development to nutrient and water availability is an important adaptation for abiotic stress tolerance. Roots need to intercept both passing nutrients and water while foraging into new soil layers for further resources. Substantial amounts of nitrate can be lost in the field when leaching into groundwater, yet very little is known about how deep rooting affects this process. Here, we phenotyped root system traits and deep 15N nitrate capture across 1.5 m vertical profiles of solid media using tall mesocosms in switchgrass (Panicum virgatum L.), a promising cellulosic bioenergy feedstock. Root and shoot biomass traits, photosynthesis and respiration measures, and nutrient uptake and accumulation traits were quantified in response to a water and nitrate stress factorial experiment for switchgrass upland (VS16) and lowland (AP13) ecotypes. The two switchgrass ecotypes shared common plastic abiotic responses to nitrogen (N) and water availability, and yet had substantial genotypic variation for root and shoot traits. A significant interaction between N and water stress combination treatments for axial and lateral root traits represents a complex and shared root development strategy for stress mitigation. Deep root growth and 15N capture were found to be closely linked to aboveground growth. Together, these results represent the wide genetic pool of switchgrass and show that deep rooting promotes nitrate capture, plant productivity, and sustainability.

Plastic response of Medicago sativa L. root system traits and cold resistance to simulated rainfall events.

Climate change (rainfall events and global warming) affects the survival of alfalfa (Medicago sativa L.) in winter. Appropriate water management can quickly reduce the mortality of alfalfa during winter. To determine how changes in water affect the cold resistance of alfalfa, we explored the root system traits under different rainfall events and the effects on cold resistance in three alfalfa cultivars. These were exposed to three simulated rainfall events (SRE) × two phases in a randomized complete block design with six replications. The three cultivars were WL168, WL353 and WL440, and the three SRE were irrigation once every second day (D2), every four days (D4) and every eight days (D8). There were two phases: before cold acclimation and after cold acclimation. Our results demonstrated that a period of exposure to low temperature was required for alfalfa to achieve maximum cold resistance. The root system tended toward herringbone branching under D8, compared with D2 and D4, and demonstrated greater root biomass, crown diameter, root volume, average link length and topological index. Nevertheless, D8 had less lateral root length, root surface area, specific root length, root forks and fractal dimensions. Greater root biomass and topological index were beneficial to cold resistance in alfalfa, while more lateral roots and root forks inhibited its ability to survive winter. Alfalfa roots had higher proline, soluble sugar and starch content in D8 than in D2 and D4. In contrast, there was lower malondialdehyde in D8, indicating that alfalfa had better cold resistance following a longer irrigation interval before winter. After examining root biomass, root system traits and physiological indexes we concluded that WL168 exhibited stronger cold resistance. Our results contribute to greater understanding of root and cold stress, consequently providing references for selection of cultivars and field water management to improve cold resistance of alfalfa in the context of changes in rainfall patterns.