Reduced Root Biomass Research Articles

Evaluation of forage resources under poorly drained soils for dairy systems

Alfalfa is crucial for dairy farms, but its potential production and persistence can be hindered by waterlogging, poorly drained soils, and high-water tables. The objectives of this study were (a) to evaluate herbage mas and quality of different forage species on poorly drained soils, and (b) to evaluate root biomass accumulation and their impacts on soil physical properties. The study was conducted in Santa Fe, Argentina, on an Aquic Argiudoll. Four treatments were established in March 2017: Alfalfa (control), Fescue, Annual (Ryegrass and Sorghum rotation regime), and Mixture (a mixture of Brome, Chicory, Red clover, and White clover). Aboveground herbage mass and nutritive quality were analyzed frequently, while roots and soil samples were collected after 2 years for further analysis. Root biomass was significantly higher (p < 0.05) in Annual and Mixture pastures compared to Alfalfa and Fescue. Lower root biomass in Alfalfa was attributed to temporary waterlogging and low plant density. Fescue exhibited reduced root biomass due to higher bulk density and lower soil porosity. Soil bulk density was lowest in Mixture, and no significant differences in soil penetration resistance were found among treatments (p > 0.05). There are alternatives to alfalfa with high production and quality that ensure a good economic return to farmers. The choice of forages for its root biomass accumulation has effects on the physics of the soil that ultimately modify the water dynamics. These findings have implications for sustainable forage management strategies, particularly in areas prone to waterlogging and poorly drained soils.

Exogenous protectants alleviate ozone stress in Trifolium repens: Impacts on plant growth and endophytic fungi

Industrialization-driven surface ozone (O3) pollution significantly impairs plant growth. This study evaluates the effectiveness of exogenous protectants [3 mg L⁻1 abscisic acid (ABA), 400 mg L⁻1 ethylenediurea (EDU), and 80 mg L⁻1 spermidine (Spd)] on Trifolium repens subjected to O3 stress in open-top chambers, focusing on plant growth and dynamics of culturable endophytic fungal communities. Results indicate that O3 exposure adversely affects photosynthesis, reducing root biomass and altering root structure, which further impacts the ability of plant to absorb essential nutrients such as potassium (K), magnesium (Mg), and zinc (Zn). Conversely, the application of ABA, EDU, and Spd significantly enhanced total biomass and chlorophyll content in T. repens. Specifically, ABA and Spd significantly improved root length, root surface area, and root volume, while EDU effectively reduced leaves' malondialdehyde levels, indicating decreased oxidative stress. Moreover, ABA and Spd treatments significantly increased leaf endophytic fungal diversity, while root fungal abundance declined. The relative abundance of Alternaria in leaves was substantially reduced by these treatments, which correlated with enhanced chlorophyll content and photosynthesis. Concurrently, EDU and Spd treatments increased the abundance of Plectosphaerella, enhance the absorption of K, Ca, and Mg. In roots, ABA treatment increased the abundance of Paecilomyces, while Spd treatment enhanced the presence of Stemphylium, linked to improved nitrogen (N), phosphorus (P), and K uptake. These findings suggest that specific symbiotic fungi mitigate O3-induced stress by enhancing nutrient absorption, promoting growth. This study highlights the potential of exogenous protectants to enhance plant resilience against O3 pollution through modulating interactions with endophytic fungal communities.

Growth and Biomass Distribution in Cocoa Varieties under Different Nitrogen Regimes

Among the 17 vital plant nutrients, nitrogen (N) is crucial in crop production. It extensively enhances the growth and biomass production of plants by improving photosynthesis and protein synthesis. To study the impact of three different N levels (40, 80, and 120 ppm) on the growth and biomass production of eight cocoa varieties, a hydroponic experiment was carried out at ICAR-CPCRI, Regional Station, Vittal. The results showed that increasing N concentration significantly boosted growth and biomass production. Among the different varieties, VTLCH-1 exhibited the highest plant height, maximum number of leaves, greater stem diameter, and the highest total fresh biomass with the application of 120 ppm nitrogen. Biomass partitioning analysis revealed that higher N levels increased leaf and stem biomass while reducing root biomass, leading to a higher shoot-to-root ratio. This indicates that N application influences the biomass production and distribution in the plant.

Evaluation of the Effectiveness of Innovative Sorbents in Restoring Enzymatic Activity of Soil Contaminated with Bisphenol A (BPA).

As part of the multifaceted strategies developed to shape the common environmental policy, considerable attention is now being paid to assessing the degree of environmental degradation in soil under xenobiotic pressure. Bisphenol A (BPA) has only been marginally investigated in this ecosystem context. Therefore, research was carried out to determine the biochemical properties of soils contaminated with BPA at two levels of contamination: 500 mg and 1000 mg BPA kg-1 d.m. of soil. Reliable biochemical indicators of soil changes, whose activity was determined in the pot experiment conducted, were used: dehydrogenases, catalase, urease, acid phosphatase, alkaline phosphatase, arylsulfatase, and β-glucosidase. Using the definition of soil health as the ability to promote plant growth, the influence of BPA on the growth and development of Zea mays, a plant used for energy production, was also tested. As well as the biomass of aerial parts and roots, the leaf greenness index (SPAD) of Zea mays was also assessed. A key aspect of the research was to identify those of the six remediating substances-molecular sieve, zeolite, sepiolite, starch, grass compost, and fermented bark-whose use could become common practice in both environmental protection and agriculture. Exposure to BPA revealed the highest sensitivity of dehydrogenases, urease, and acid phosphatase and the lowest sensitivity of alkaline phosphatase and catalase to this phenolic compound. The enzyme response generated a reduction in the biochemical fertility index (BA21) of 64% (500 mg BPA) and 70% (1000 mg BPA kg-1 d.m. of soil). The toxicity of BPA led to a drastic reduction in root biomass and consequently in the aerial parts of Zea mays. Compost and molecular sieve proved to be the most effective in mitigating the negative effect of the xenobiotic on the parameters discussed. The results obtained are the first research step in the search for further substances with bioremediation potential against both soil and plants under BPA pressure.

Biochar Application Improved Sludge-Amended Landscape Soil Fertility Index but with No Added Benefit in Plant Growth

Co-application of sewage sludge (SS) with biochar in landscape/forestry soil is a common strategy for enhancing soil fertility and reducing the bioavailability of potential toxic elements (PTEs) derived from SS, such as Cd, Pb, Cu, Zn, and Ni. However, due to variability of biochar quality and uncertainties in responses of different plant species, whether the co-application benefits the landscape/forestry plant system remains elusive. Here, we tested the effectiveness of three types of biochar (SS-derived biochar (SB), rice straw-derived biochar (RB), and litter-derived biochar (LB)), which were added to soil amended with SS at 50% (w/w) at rates of 1.5%, 3%, and 4.5% as growth media for the landscape plant Aglaonema modestum (A. modestum). We analyzed the substrate’s physicochemical properties and assessed the alleviation of phytotoxicity by biochar application. A significant increase in the fertility index of substrate was observed in all the treatments with biochar addition. The addition of biochar reduced the potential mobility of PTEs while increasing their residual fraction in media. Nonetheless, it has been found that the addition of biochar has ineffective or even negative effects on A. modestum growth (height, biomass, root length) and nutrient absorption. Importantly, the reduction in root biomass and the increased activity of root antioxidant enzymes (SOD, POD, CAT, and MDA) indicate contamination stress of biochar on the roots of A. modestum. Toxic elements of concern—namely Cu, Cd, and Pb—were not significantly higher in tissues of A. modestum saplings planted in biochar-SS-amended soil. However, elevated levels of other elements that may pose toxicity concerns, such as Ni and Zn, increased in tissues at high biochar dosages. Based on the Entropy–Weight TOPSIS method, it was further confirmed that compared to the treatment without biochar, all treatments except for 3.0% LB application resulted in poorer A. modestum comprehensive growth. Our results emphasize the need for detailed research on the response of specific plants to biochar in specific environments, including plant adaptability and the unexplored toxicity of biochar, to understand the large variations and mechanisms behind these ineffective or negative effects before the large-scale co-utilization of SS and biochar in landscape/forestry soils.

Molecular Identification and Pathogenicity of Fusarium Species Associated with Wood Canker, Root and Basal Rot in Turkish Grapevine Nurseries.

Fusarium species are agriculturally important fungi with a broad host range and can be found as endophytic, pathogenic, or opportunistic parasites in many crop plants. This study aimed to identify Fusarium species in bare-rooted, dormant plants in Turkish grapevine nurseries using molecular identification methods and assess their pathogenicity. Asymptomatic dormant plants were sampled from grapevine nurseries (43) in different regions of the country, and fungi were isolated from plant roots and internal basal tissues. The Fusarium strains were identified by performing gene sequencing (TEF1-α, RPB2) and phylogenetic analyses. Pathogenicity tests were carried out by inoculating mycelial agar pieces of strains onto the stem or conidial suspensions into the rhizosphere of vines (1103 Paulsen rootstock). Laboratory tests revealed that Fusarium species were highly prevalent in Turkish grapevine nurseries (41 out of 43). Gene sequencing and phylogenetic analyses unraveled that 12 Fusarium species (F. annulatum, F. brachygibbosum, F. clavum, F. curvatum, F. falciforme, F. fredkrugeri, F. glycines, F. nanum, F. nematophilum, F. nirenbergiae, F. solani, and Fusarium spp.) existed in the ready-to-sale plants. Some of these species (F. annulatum, F. curvatum and F. nirenbergiae) consistently caused wood necrosis of seedling stems, rotting of the basal zone and roots, and reduced root biomass. Although the other nine species also caused some root rot and root reduction, their virulence was not as severe as the pathogenic ones, and they were considered opportunistic parasites or endophytic species. This study suggests that Fusarium species might play an important role in root-basal rot, wood canker symptoms, and young vine decline in Turkish grapevine nurseries and that these species need to be considered for healthy seedling production.

Light Intensity: A Key Ecological Factor in Determining the Growth of Pseudolarix amabilis Seedlings

The notable absence of juvenile Pseudolarix amabilis trees in forest understories suggests their vulnerability to ecological niche competition, leading to limited survival prospects. This study examines the key factors limiting the growth of P. amabilis seedlings by investigating the effects of five ecological factors: light intensity, rainfall, groundwater level, soil type, and type of fertilization, on the growth of one-year-old P. amabilis seedlings. Our results demonstrate that increasing the light intensity promotes plant growth by augmenting the leaf count, leaf biomass, plant height, stem biomass, root biomass, and total biomass. Further analysis reveals that increased light intensity influences biomass allocation, reducing the specific leaf area and leaf–stem biomass ratio, and favoring root and stem growth over leaf investment. Rainfall, groundwater level, fertilization type, and rhizosphere soil type primarily influence root growth by impacting the soil’s physicochemical properties. Specifically, rising groundwater levels lower the soil temperature and increase the soil moisture, total potassium content, and soil pH, leading to reductions in root biomass, plant height, net height increment, leaf number, and total biomass. When groundwater levels reach 21 cm and 28 cm, submerging the surface soil layer, root biomass decreases by 1.6 g/plant (−51.6%) and 2.3 g/plant (−74.2%), respectively. Further analysis reveals a gradual decrease in the root–shoot ratio above the 14 cm groundwater level, while the specific leaf area and leaf–stem biomass ratio remains unaffected, indicating stronger belowground root stress compared to aboveground stem and leaf components. The results highlight light intensity as the key ecological factor determining the growth of P. amabilis seedlings. These findings underscore the importance of considering light intensity in the management of natural stands, the cultivation of artificial forests, and the nursery cultivation of endangered P. amabilis.

Integrated small RNA, transcriptome and physiological approaches provide insight into Taxodium hybrid 'Zhongshanshan' roots in acclimation to prolonged flooding.

Although Taxodium hybrid 'Zhongshanshan' 406 (Taxodium mucronatum Tenore×Taxodium distichum; Taxodium 406) is an extremely flooding-tolerant woody plant, the physiological and molecular mechanisms underlying acclimation of its roots to long-term flooding remain largely unknown. Thus, we exposed saplings of Taxodium 406 to either non-flooding (control) or flooding for 2months. Flooding resulted in reduced root biomass, which is in line with lower concentrations of citrate, α-ketoglutaric acid, fumaric acid, malic acid and adenosine triphosphate (ATP) in Taxodium 406 roots. Flooding led to elevated activities of pyruvate decarboxylase, alcohol dehydrogenase and lactate dehydrogenase, which is consistent with higher lactate concentration in the roots of Taxodium 406. Flooding brought about stimulated activities of superoxide dismutase and catalase and elevated reduced glutathione (GSH) concentration and GSH/oxidized glutathione, which is in agreement with reduced concentrations of O2- and H2O2 in Taxodium 406 roots. The levels of starch, soluble protein, indole-3-acetic acid, gibberellin A4 and jasmonate were decreased, whereas the concentrations of glucose, total non-structural carbohydrates, most amino acids and 1-aminocyclopropane-1-carboxylate (ACC) were improved in the roots of flooding-treated Taxodium 406. Underlying these changes in growth and physiological characteristics, 12,420 mRNAs and 42 miRNAs were significantly differentially expressed, and 886 miRNA-mRNA pairs were identified in the roots of flooding-exposed Taxodium 406. For instance, 1-aminocyclopropane-1-carboxylate synthase 8 (ACS8) was a target of Th-miR162-3p and 1-aminocyclopropane-1-carboxylate oxidase 4 (ACO4) was a target of Th-miR166i, and the downregulation of Th-miR162-3p and Th-miR166i results in the upregulation of ACS8 and ACO4, probably bringing about higher ACC content in flooding-treated roots. Overall, these results indicate that differentially expressed mRNA and miRNAs are involved in regulating tricarboxylic acid cycle, ATP production, fermentation, and metabolism of carbohydrates, amino acids and phytohormones, as well as reactive oxygen species detoxification of Taxodium 406 roots. These processes play pivotal roles in acclimation to flooding stress. These results will improve our understanding of the molecular and physiological bases underlying woody plant flooding acclimation and provide valuable insights into breeding-flooding tolerant trees.

Nitrogen deposition suppresses soil respiration by reducing global belowground activity

Soil respiration (Rs) indicates below-ground biological activities. Previous studies have suggested that higher nitrogen (N) deposition due to human activities exerts an increasingly negative effect on Rs. However, the mechanisms underlying this negative effect remain highly uncertain on a global scale. Using a global dataset of 262 N addition experiments, here we show the overall N addition effects on Rs changed from positive to negative with increasing N addition rate and duration. By constructing a structural equation model (SEM) that explained 41 % variation in the responses of Rs to N addition, we revealed that Rs under increasing N addition was simultaneously associated with decreases in soil pH, root biomass and microbial biomass, with the strongest influence by root biomass. Decreasing soil pH had cascading effects on root and microbial biomass, while N-addition-induced root biomass reduction further manifested a decrease in microbial biomass. Across global variations in the environment, lower background soil pH amplified the negative impacts of N addition on root and microbial biomass, which consequently exhilarated the negative impact of high N on Rs. Our results highlight that predicting the response of belowground biological activities to global changes is complex with the essence of integrative understanding for the multivariate pathways through soil physical properties, plants and microorganisms.

Impact of low light intensity on biomass partitioning and genetic diversity in a chickpea mapping population.

With recent climatic changes, the reduced access to solar radiation has become an emerging threat to chickpeas' drought tolerance capacity under rainfed conditions. This study was conducted to assess, and understand the effects of reduced light intensity and quality on plant morphology, root development, and identifying resistant sources from a Sonali/PBA Slasher mapping population. We evaluated 180 genotypes, including recombinant inbred lines (RILs), parents, and commercial checks, using a split-block design with natural and low light treatments. Low light conditions, created by covering one of the two benches inside two growth chambers with a mosquito net, reduced natural light availability by approximately 70%. Light measurements encompassed photosynthetic photon flux density, as well as red, and far-red light readings taken at various stages of the experiment. The data, collected from plumule emergence to anthesis initiation, encompassed various indices relevant to root, shoot, and carbon gain (biomass). Statistical analysis examined variance, treatment effects, heritability, correlations, and principal components (PCs). Results demonstrated significant reductions in root biomass, shoot biomass, root/shoot ratio, and plant total dry biomass under suboptimal light conditions by 52.8%, 28.2%, 36.3%, and 38.4%, respectively. Plants also exhibited delayed progress, taking 9.2% longer to produce their first floral buds, and 19.2% longer to commence anthesis, accompanied by a 33.4% increase in internodal lengths. A significant genotype-by-environment interaction highlighted differing genotypic responses, particularly in traits with high heritability (> 77.0%), such as days to anthesis, days to first floral bud, plant height, and nodes per plant. These traits showed significant associations with drought tolerance indicators, like root, shoot, and plant total dry biomass. Genetic diversity, as depicted in a genotype-by-trait biplot, revealed contributions to PC1 and PC2 coefficients, allowing discrimination of low-light-tolerant RILs, such as 1_52, 1_73, 1_64, 1_245, 1_103, 1_248, and 1_269, with valuable variations in traits of interest. These RILs could be used to breed desirable chickpea cultivars for sustainable production under water-limited conditions. This study concludes that low light stress disrupts the balance between root and shoot morphology, diverting photosynthates to vegetative structures at the expense of root development. Our findings contribute to a better understanding of biomass partitioning under limited-light conditions, and inform breeding strategies for improved drought tolerance in chickpeas.

Alone as effective as together: AMF and Trichoderma inoculation boost maize performance but differentially shape soil and rhizosphere microbiota

AbstractIntroductionInoculation of plants with beneficial microorganisms may improve plant performance yet suffers from efficacy variability. A solution might be the combined application of different inoculants as consortium. The objective of the present study was to evaluate the effects of single or combined inoculation of Trichoderma harzianum, strain TGFG411, and a consortium of arbuscular mycorrhizal fungi (AMF) on plant growth, and native microbial communities (here bacteria/archaea, fungi and AMF) in root‐associated soil (RAS) and rhizosphere (RH), that is, soil loosely or tightly attached to the roots, respectively.Materials and MethodsA greenhouse experiment was carried out with non‐sterile agricultural soil and the model crop maize, which was single inoculated with either TGFG411 or AMF or received a combined inoculation of TGFG411 + AMF. Control plants received only water. Seven weeks after the second AMF inoculation, the plant growth promotion capacity of the inoculants was measured based on shoot and root parameters. Furthermore, RAS and RH microbiota (fungi including AMF, bacteria and archaea) were assessed via a combination of different cultivation‐dependent, microscopic and DNA‐based methods.ResultsAfter 7 weeks of maize growth, both single and combined inoculation of AMF and TGFG411 enhanced shoot dry weight and led to a significant reduction in root biomass. The TGFG411 strain successfully established in the soil. However, no definite evidence for the establishment of the inoculated AMF was found. Single or combined inoculation of TGFG411 and AMF modified the composition of total bacterial in the RH, whereas modulated total fungal communities in the RAS.ConclusionThe combined inoculation did not result in a significant improvement of plant performance compared with single inoculation likely due to optimal nutrient supply. However, samples receiving the combined inoculation exhibited a distinct modulation of the native RAS/RH microbiota, which may influence the inoculant efficacy under less favourable conditions.

Root-shoot ratio and SOD activity are associated with the sensitivity of common bean seedlings to NaCl salinization

The response of two common bean (Phaseolus vulgaris) varieties with different sensitivities to salinity (Montalbán: sensitive; I-193: moderately sensitive) was studied to determine some phytometric and physiological characteristics that could be associated with their differential sensitivities. Plants were sown in a greenhouse during the seedling stage and irrigated with a nutrient solution to which NaCl of 60 mol m−3 was added, while a control group was maintained in parallel. In Montalban, salinity caused a significant reduction in root biomass while shoot biomass and leaf area decreased with salt stress in both genotypes. The root/shoot ratio slightly increased in I.193 and decreased in Montalban salinized plants. Chlorophyll content increased with salinity in both genotypes. The presence of O2·- (superoxide radicle) in root apex decreased under the saline condition which did not occur in the case of H2O2. Superoxide dismutase (SOD) activity increased in roots and primary leaves under salt stress to a greater extent in I-193 than in Montalban. Four SOD isoenzymes were detected, one MnSOD, one FeSOD, and two Cu/ZnSOD, but their expression varied according to the variety. Catalase (CAT) activity increased only in the roots of stressed Montalban plants. These results suggest that root/shoot ratio and SOD enzyme activity are related to the lower salt sensitivity shown by I-193.

Responses of the arbuscular mycorrhizal fungi community to warming coupled with increased drought in an arid desert region

Warming coupled with precipitation changes induced by climate change profoundly affect desert ecosystem functions in global drylands. Arbuscular mycorrhizal fungi (AMF) play a crucial role in such ecosystems by regulating energy and nutrient exchange. However, little is known about how AMF communities respond to warming coupled with reduced precipitation (W + RP). We evaluated the impacts of 0.5 °C and 1.5 °C increase in temperature coupled with 5 % and 8 % reductions in total annual precipitation (0.5 °C W + 5 % RP, 1.5 °C W + 8 % RP) on AMF communities and the main ecological processes structuring AMF community assemblies in the rhizosphere soil of typical winter annual plants in the Tengger Desert, northwest China. The results showed that warming coupled with reduced precipitation could significantly alter the composition, abundance, and diversity of AMF communities. Both AMF biomass and AMF diversity increased in the 0.5 °C W + 5 % RP treatment but decreased in the 1.5 °C W + 8 % RP treatment. The 1.5 °C W + 8 % RP treatment significantly reduced root biomass and the AMF colonization rate but increased the specific root length, indicating a trade-off between fine roots and their symbiotic AMF. The AMF community was phylogenetically random in the 0.5 °C W + 5 % RP treatment but appeared clustered in the 1.5 °C W + 8 % RP treatment, implying that more pronounced warming coupled with reduced precipitation can promote the deterministic assembly of the AMF community. We provide a conceptual framework for comprehending the mechanisms underlying the effects of warming coupled with reduced precipitation on AMF communities, incorporating biological and geochemical processes. Overall, the findings of this study suggest that AMF abundance and diversity and the main ecological processes driving AMF assemblages respond differently to more pronounced compared to less intensive warming coupled with reduced precipitation. Importantly, higher warming coupled with a reduction in precipitation reduced plant dependence on AMF and resulted in stronger environmental filtration by significantly reducing soil water content.

Linking soil physical quality to shoot and root biomass production in scenarios of sugarcane straw removal

Understanding how sugarcane straw removal affects soil physical attributes and root development over successive cultivation years is critical for sustainable straw-based bioenergy production. The aim of this study was to evaluate the effects of straw removal on soil physical quality and its relationship with sugarcane root development and crop yield in soils with contrasting textures. Three straw removal rates corresponding to total removal (TR), moderate removal (MR), and no removal (NR) were arranged in a randomized block design with four replicates. Soil was sampled at depths of 0–0.10, 0.10–0.20, and 0.20–0.40 m to determine soil bulk density, macro- and microporosity, soil penetration resistance, and carbon stock. Annual assessments of sugarcane root and stalk dry biomass were conducted. Overall, excessive straw removal rates were detrimental to soil porosity, C stock, and increased bulk density in the surface layer over successive years compared to moderate and no removal rates. Higher soil penetration resistance levels were observed under total removal, reaching values of 2.6 MPa in the 0–0.10 m layer in both soils. Average reductions in root biomass of 23–33% were verified at moderate and total removal rates in both soils, which affected sugarcane stalk yield, with maximum losses of 24% over crop cycles in the clayey soil. In the sandy loam soil, increases in soil C were correlated with reduced soil penetration resistance, which positively influenced root biomass production. Soil compaction over the years was particularly detrimental in the clayey soil, where the biomass production performance of sugarcane roots and stalk yield decreased in response to increased soil bulk density. Our results suggest that reductions in root biomass may occur in response to straw removal, as well as the loss of soil physical quality induced by soil compaction, with negative effects on C accumulation and soil resistance to root penetration.

Nitrogen availability affects the responses of marsh grass and sedge plants (Phragmites australis and Bolboschoenus planiculmis) to flooding time

Flooding time and external nitrogen (N) input have been projected to be the main threats to marsh ecosystems in the scenario of more intense flooding events and N deposition. How flooding and N addition experienced at different growth stages interact in determining phenotypic change remains scarce. We established a controlled experiment (3 flooding time treatments x 5 N addition levels) using two herbaceous marsh species (Phragmites australis and Bolboschoenus planiculmis) to assess the responses of six key traits to environmental changes and the indication of plant performance. Early flooding reduced plant height and aboveground biomass of P. australis and below/aboveground biomass ratio of B. planiculmis and increased below/aboveground biomass ratio of P. australis and root biomass of B. planiculmis, whereas late flooding reduced root biomass of P. australis and ramet number and aboveground biomass of B. planiculmis. The combination of flooding and high N (16 and 32 g N m−2) exerted negative effects on ramet number of both plant species. The interaction of early flooding and low-medium N (8 and 16 g N m−2) inhibited clonal/belowground biomass ratio of both plant species. The combination of early flooding and low N (0, 4 and 8 g N m−2) promoted root biomass and below/aboveground biomass ratio of P. australis. Ramet number, plant height, and root biomass explained 80–90 % of aboveground biomass variation of both plant species, and the contribution of ramet number was greater than that of the other two traits. These results highlight that the influence of flooding time and external N input on the performance of marsh plants depends on species identity. Meanwhile, the ramet number-plant height-root biomass (RHR) strategy is supposed to be the adaptation strategy of wetland clonal plants to environmental changes, and clonal reproductive traits should be incorporated into vegetation dynamics models for marsh plants.

Influence of Incremental Short Term Salt Stress at the Seedling Stage on Root Plasticity, Shoot Thermal Profile and Ion Homeostasis in Contrasting Wheat Genotypes

Understanding the component traits determining salt stress tolerance is a major breeding target in wheat. The lack of genetic resources suited to salt-affected regions and the complexity of the traits involved impede progress in breeding salt-tolerant wheat varieties. This study was conducted with four bread wheats, namely (Triticum aestivum) Kharchia-65 (K-65), BT-Schomburgk (BTS), HD-2687, and HD-3298. Treatments were imposed on plants with varying electrical conductivity (control, 5 dS m−1, 10 dS m−1, and 15 dS m−1) with a combination of three different salts NaCl, CaCl2·2H2O, and Na2SO4. We evaluated variations in root system architecture, canopy temperature (depicted as a thermal image), reactive oxygen species (ROS) homeostasis, and leaf stomatal density in response to incremental doses of salt stress in a hydroponic experiment. As the plants were sampled after short-term exposure to stress (within 3 weeks of stress imposition), the plants were expected to be in a quiescent state. Due to the osmotic effect, the growth of the plants was compromised, and the associated decrease in stomatal conductance increased the canopy temperature. ROS accumulation and antioxidant enzyme activity did not follow a definite pattern. The antioxidant system’s tolerance to ROS comes into action much later in the tolerance mechanism. That could probably be the reason behind the varied response in ROS accumulation and antioxidant enzymes after short-term exposure to salt stress. Thermal images could effectively differentiate between salt-tolerant (K65) and sensitive (HD2687) genotypes. The variation in Na+/K+ ratio also suggested a genotypic variation in salt tolerance. The genotypes of K-65 maintained a better root system, while HD2687 showed severe reduction in root biomass and other root traits under salt stress. The PCA data also point out genotypic variation in lateral and main root traits in response to different salt stress levels. For salt tolerance in wheat, the main contributing root traits were total root length, total surface area, total root volume, tips, and other main, lateral root traits. The idea of differential control of RSA dynamics is novel and can be further explored to understand natural variation in salt stress tolerance.

First Report of Root Rot Caused by Ilyonectria robusta in the Medicinal Herb Aconitum carmichaelii in China.

Aconitum carmichaelii Debeaux is used as a traditional Chinese medicine with antiarrhythmic, antiinflammatory and other pharmacological functions. It is widely cultivated in China. According to our survey, about 60% of A. carmichaelii in Qingchuan, Sichuan, suffered from root rot, reducing yields by 30% in the past five years. Symptomatic plants exhibited stunted growth, dark brown roots, reduced root biomass, and fewer root hairs. The disease caused root rot and plant death in 50% of the infected plants. In October 2019, ten symptomatic 6-month-old plants were collected from fields in Qingchuan. Diseased pieces of the roots were surface sterilized with sodium hypochlorite solution (2%), rinsed three times in sterile water, plated on potato dextrose agar (PDA), and incubated at 25°C in the dark. Six single-spore isolates of a Cylindrocarpon-like anamorp were obtained. The colonies on PDA were 35 to 37 mm diam after seven days with regular margins. The plates were covered with felty aerial mycelium, white to buff, and the reverse side chestnut near center with a ochre to yellowish leading edge. On spezieller nährstoffarmer agar (SNA), macroconidia were 1 to 3 septate, straight or slightly curved, cylindrical, with rounded ends, and varied in size: 1-septate 15.1 to 33.5 × 3.7 to 7.3 μm (n=250), 2-septate 16.5 to 48.5 × 3.7 to 7.6 μm (n=85), and 3-septate 22.0 to 50.6 × 4.9 to 7.4 μm (n=115). Microconidia were ellipsoid to ovoid, and 0 to 1 septate; aseptate spores were 4.5 to 16.8 × 1.6 to 4.9 μm (n=200), and 1-septate spores were 7.4 to 20.0 × 2.4 to 5.1 μm (n=200). The chlamydospores were brown, thick-walled, globose to subglobose, 7.9 to 15.9 μm (n=50). The morphology of these isolates was consistent with the previous description of Ilyonectria robusta (Cabral et al. 2012). Isolate QW1901 was characterized by sequencing the ITS, TUB, H3, and tef1α loci using previously reported primer pairs: ITS1/ITS4 (White et al. 1990), T1/Bt-2b (O'Donnell and Cigelnik 1997), CYLH3F/CYLH3R (Crous et al. 2004), and EF1/EF2 (O'Donnell et al. 1998). A Blastn search of the sequences of ITS, TUB, H3, and tef1α showed that QW1901 shared 99.26, 97.89, 97.79, and 99.17 % identities, respectively, with the ex-type strain of I. robusta (CBS308.35). The ITS, TUB, H3, and tef1α sequences were deposited in GenBank under accession nos. MW534715, and MW880180 to MW880182, respectively. A phylogenetic tree was constructed from a neighbor-joining analysis on the alignment of the combined ITS, TUB, H3, and tef1α sequence. QW1901 was clustered with the ex-type strain of I. robusta. To confirm the pathogenicity of I. robusta, bare roots of healthy 6-month-old A. carmichaelii were inoculated with mycelial plugs of 7-day-old QW1901 colonies selected randomly (Lu et al. 2015). Five needle-wound lateral roots and five intact roots were inoculated as replicates with pathogen-free agar plugs as a control. Then, all plants were grown in sterile soil in a growth chamber at 20±1°C and watered regularly. Pathogenicity assays were repeated twice. After 20 days of cultivation, infected plants exhibited symptoms similar to those observed in the field. All control plants remained asymptomatic. Sequencing confirmed the re-isolation of I. robusta from the inoculated plants, satisfying Koch's hypothesis. Ilyonectria robusta has been reported to cause root rot of plants such as Codonopsis tangshen and Panax ginseng ( Lu et al. 2015; Zheng et al. 2021), and has also been reported to be isolated from Aconitum kongboense in China (Wang et al. 2015). However, this is the first report of the pathogen causing root rot of A. carmichaelii. Management measures, such as growing disease-free seedlings in sterile soil, should be used to minimize the risk of this pathogen.

Black foot in nursery grapevines in Uruguay caused by Dactylonectria and Ilyonectria

Black foot is a serious soilborne fungal disease causing decline of young grapevines. Affected plants show brown to dark streaks developing from the rootstock bases, wood necroses at trunk bases, sunken necrotic lesions on roots, and reduced root biomass. Several fungi, commonly known as Cylindrocarpon-like asexual morphs, have been associated with black foot. Nursery vines are infected during rooting in propagation processes, which is important for dissemination of the pathogens. Species associated with black foot in nursery vines produced in Uruguay were characterized by molecular, phenotypical and pathogenicity studies. From 2017 to 2019, 181 rooted vines grafted onto ‘1103P’, ‘SO4’, ‘101-14’, ‘3309C’ or ‘Gravesac’ rootstocks were sampled, and 71 Cylindrocarpon-like fungal isolates were recovered from rootstock tissues (basal ends and roots). Based on multi-gene phylogenetic analyses of HIS3, TEF and TUB2, and supported by phenotypical characterization, five species of Dactylonectria and Ilyonoectria were identified, with D. macrodidyma being the most prevalent followed by D. novozelandica, D. torresensis, D. palmicola and I. liriodendri. Four Ilyonectria isolates could not be identified to species level. Isolate pathogenicity was assessed using healthy rooted ‘Gravesac’ plants. After three months, isolates of all species infected the plants, causing necrotic lesions on roots and reducing root biomass. On average, 39% of ready-to-plant nursery vines were affected by black foot, emphasizing the need to develop integrated management to reduce black foot incidence in Uruguayan grapevine nurseries, based on studies under local conditions.

Differential sensitivity of above- and belowground plant biomass to drought and defoliation in temperate grasslands

Multi-year droughts combined with other stressors such as defoliation are likely to have substantial ecological impacts. However, grasslands vary significantly in their response to drought and defoliation, and interpretations rarely address the importance of roots despite evidence showing roots are likely to respond differently to drought and defoliation than shoots. Here, we conducted a three-year manipulative experiment, combining a reduction in rainfall treatment (drought, 45% of ambient) with each of a time-of-defoliation (early vs. late) and an intensity-of-defoliation (none, light, heavy) treatment at seven temperate grassland sites to test three a priori hypotheses: 1) defoliation early relative to late in the season would exacerbate drought impacts on aboveground net primary productivity (ANPP) and root biomass; 2) ANPP and root biomass would progressively decrease with increasing intensity of defoliation early in the growing season under drought; 3) drought and defoliation effects on ANPP and root biomass would vary along a gradient of long-term mean annual precipitation of study sites. Across all seven sites, the combined effects of drought and defoliation led to greater changes in root biomass than ANPP. Under drought conditions specifically, defoliation early in the growing season reduced root biomass, but not ANPP, compared to defoliation late in the growing season. The decline in root biomass under drought was more substantial when the intensity of early-season defoliation increased from none to heavy. Furthermore, variation in the timing and intensity of defoliation altered root biomass more in mesic than arid grasslands, while their effects on ANPP remained unchanged across the seven sites. These results indicate that root systems may be more responsive than ANPP to simultaneous drought and defoliation, and could lead to long-term changes in plant productivity.

Field traffic-induced soil compaction under moderate machine-field conditions affects soil properties and maize yield on sandy loam soil.

Soil compaction due to field trafficking involves a complex interplay of machine-soil properties. In contrast to previous studies simulating worst field scenarios, this two-year field experiment investigated the effects of traffic-induced compaction involving moderate machine operational specifications (axle load, 3.16 Mg; mean ground contact pressure, 77.5 kPa) and lower field moisture contents (< field capacity) at the time of trafficking on soil physical properties, spatial root distribution, and corresponding maize growth and grain yield in sandy loam soil. Two compaction levels, i.e. two (C2) and six (C6) vehicle passes, were compared with a control (C0). Two maize (Zea mays L.) cultivars, i.e. ZD-958 and XY-335, were used. Results showed topsoil (< 30cm) compaction with increases in bulk density (BD) and penetration resistance (PR) up to 16.42% and 127.76%, respectively, in the 10-20cm soil layer in 2017. Field trafficking resulted in a shallower and stronger hardpan. An increased number of traffic passes (C6) aggravated the effects, and the carryover effect was found. Higher BD and PR impaired root proliferation in deeper layers of topsoil (10-30cm) and promoted shallow horizontal root distribution. However, XY-335, compared with ZD-958, showed deeper root distribution under compaction. Compaction-induced reductions in root biomass and length densities were respectively up to 41% and 36% in 10-20cm and 58% and 42% in the 20-30cm soil layer. Consequent yield penalties (7.6%-15.5%) underscore the detriments of compaction, even only in topsoil. In crux, despite their low magnitude, the negative impacts of field trafficking under moderate machine-field conditions after just two years of annual trafficking foreground the challenge of soil compaction.