ROOT PENETRATION INDEX 3, a major quantitative trait locus (QTL) associated with root system penetrability in Arabidopsis.

Soil mechanical impedance precludes root penetration, confining root system development to shallow soil horizons where mobile nutrients are scarce. Using a two-phase-agar system, we characterized Arabidopsis thaliana responses to low and high mechanical impedance at three root penetration stages. We found that seedlings whose roots fail to penetrate agar barriers show drastic changes in shoot and root morphology, while those capable of penetrating have only minor morphological effects. The assessment of 21 Arabidopsis accessions revealed that primary root penetrability (PRP) varies widely among accessions. To search for quantitative trait loci (QTLs) associated to root system penetrability, we evaluated a recombinant inbred population (RIL) derived from Landsberg erecta (Ler-0, with a high PRP) and Shahdara (Sha, with a low PRP) accessions. QTL analysis revealed a major-effect QTL localized in chromosome 3 (q-RPI3), which accounted for 29.98% (LOD = 8.82) of the total phenotypic variation. Employing an introgression line (IL-321), with a homozygous q-RPI3 region from Sha in the Ler-0 genetic background, we demonstrated that q-RPI3 plays a crucial role in root penetrability. This multiscale study revels new insights into root plasticity during the penetration process in hard agar layers, natural variation and genetic architecture behind primary root penetrability in Arabidopsis.

The ectomycorrhizal basidiomycete Laccaria bicolor releases a GH28 polygalacturonase that plays a key role in symbiosis establishment

In ectomycorrhiza, root penetration and colonization of the intercellular space by symbiotic hyphae is thought to rely on the mechanical force that results from hyphal tip growth, enhanced by the activity of secreted cell-wall-degrading enzymes. Here, we characterize the biochemical properties of the symbiosis-induced polygalacturonase LbGH28A from the ectomycorrhizal fungus Laccaria bicolor. The transcriptional regulation of LbGH28A was measured by qPCR. The biological relevance of LbGH28A was confirmed by generating RNAi-silenced LbGH28A mutants. We localized the LbGH28A protein by immunofluorescence confocal and immunogold cytochemical microscopy in poplar ectomycorrhizal roots. qPCR confirmed the induced expression of LbGH28A during ectomycorrhiza formation. L. bicolor RNAi mutants have a lower ability to establish ectomycorrhiza confirming the key role of this enzyme in symbiosis. The purified recombinant LbGH28A has its highest activity towards pectin and polygalacturonic acid. In situ localization of LbGH28A indicates that this endopolygalacturonase is located in both fungal and plant cell walls at the symbiotic hyphal front. The present findings suggest that the symbiosis-induced pectinase LbGH28A is involved in the Hartig net formation and is an important determinant for successful symbiotic colonization.

Parametric Optimization of the GMAW Welding Process in Thin Thickness of Austenitic Stainless Steel by Taguchi Method

In the present work, an analysis of different welding parameters was carried out on the welding of stainless-steel thin thickness tubes by the Gas Metal Arc Welding (GMAW) process. The influence of three main parameters, welding voltage, movement angle, and welding current in the quality of the welds, was studied through a specifically designed experimental process based on the establishment of three different levels of values for each of these parameters. Weld quality is evaluated using destructive testing (macrographic analysis). Specifically, the width and root penetration of the weld bead were measured; however, some samples have been disregarded due to welding defects outside the permissible range or caused by excessive melting of the base metals. Data are interpreted, discussed, and analyzed using the Taguchi method and ANOVA analysis. From the analysis of variance, it was possible to identify the most influential parameter, the welding voltage, with a contribution of 43.55% for the welding penetration and 75.26% for the bead width, which should be considered in the designs of automatic welding processes to improve the quality of final welds.

Evaluation and GWAS of radicle gravitropic response in a core rice germplasm population

Aims Since gravitropism is one of the primary determinants of root development, facilitating root penetration into soil and subsequent absorption of water and nutrients, we studied this response in rice. Methods The gravitropism of 226 Chinese rice micro-core accessions and drought-resistant core accessions were assessed through the modified gravity-bending experiment and genome-wide association analysis (GWAS) was used to map the associated QTLs. Results The average value of gravitropic response speed of seminal roots was 41.05°/h, ranging from 16.77°/h to 62.83°/h. The gravity response speed of Indica (42.49°/h) was significantly (P < 0.002) higher than Japonica (39.71°/h) subspecies. The gravitational response speed of seminal roots was significantly positively correlated with the number of deep roots (r = 0.16), the growth speed of seminal roots (r = 0.21) and the drought resistance coefficient (r = 0.14). Conclusions In total, 3 QTLs (quantitative traits) associated with gravitropic response speed were identified on chromosome 4, 11 and 12. There are some known QTLs relating to roots traits and drought resistance located nearby the QTLs identified here, which confirms the close relationship between radicle gravitropism and the drought resistance. From within these intervals, 5 candidate genes were screened and verified by qPCR in a few rice varieties with extreme phenotypic values, demonstrating that gene LOC_Os12g29350 may regulate gravitropism negatively. This may be a promising candidate to be confirmed in further studies.

Numerical and Experimental Investigations of Fracture Behaviour of Welded Joints with Multiple Defects

Current standards related to welded joint defects (EN ISO 5817) only consider individual cases (i.e., single defect in a welded joint). The question remains about the behaviour of a welded joint in the simultaneous presence of several different types of defects, so-called multiple defects, which is the topic of this research. The main focus is on defects most commonly encountered in practice, such as linear misalignments, undercuts, incomplete root penetration, and excess weld metal. The welding procedure used in this case was metal active gas welding, a common technique when it comes to welding low-alloy low-carbon steels, including those used for pressure equipment. Different combinations of these defects were deliberately made in welded plates and tested in a standard way on a tensile machine, along with numerical simulations using the finite element method (FEM), based on real geometries. The goal was to predict the behaviour in terms of stress concentrations caused by geometry and affected by multiple defects and material heterogeneity. Numerical and experimental results were in good agreement, but only after some modifications of numerical models. The obtained stress values in the models ranged from noticeably lower than the yield stress of the used materials to slightly higher than it, suggesting that some defect combinations resulted in plastic strain, whereas other models remained in the elastic area. The stress–strain diagram obtained for the first group (misalignment, undercut, and excess root penetration) shows significantly less plasticity. Its yield stress is very close to its ultimate tensile strength, which in turn is noticeably lower compared with the other three groups. This suggests that welded joints with misalignment and incomplete root penetration are indeed the weakest of the four groups either due to the combination of the present defects or perhaps because of an additional unseen internal defect. From the other three diagrams, it can be concluded that the test specimens show very similar behaviour with nearly identical ultimate tensile strengths and considerable plasticity. The diagrams shows the most prominent yielding, with an easily distinguishable difference between the elastic and plastic regions. The diagrams are the most similar, having the same strain of around 9% and with a less obvious yield stress limit.

Influences of Weaving Parameters on Dynamic Characteristics and Stability Control of the Droplet Transfer in Arc-Weaving P-GMAW Process

The dynamic characteristics of droplet transfer is extremely complicated with the combined effects of gravity force and weaving motion during the weaving vertical-up welding on thick plate. In this paper, we firstly observed the droplet transfer behavior under various weaving parameters with high-speed photography and electrical signals during pulsed gas metal arc welding (P-GMAW). Then we investigated the influences of different weaving parameters on the arc shape and molten pool as well as droplet characteristics. By establishing a novel weaving-force model based on static-force balance theory (SFBT), we further revealed the drop transfer mechanism in weaving P-GMAW process. Extensive experimental results demonstrated that the suitable weaving parameters could effectively improve the droplet transfer stability and suppress welding defects including incomplete root penetration and lack of sidewall fusion. The findings of this paper will provide a basis for enhancing the welding process stability and obtaining a high-quality weld joint.

Topsoil Moisture Depletion and Recharge below Young Norway Spruce, White Birch and Treeless Gaps at a Mountain-Summit Site

Background and Objectives: Mineral topsoil moisture is a very important component of the hydrological balance in forests. The moisture is closely related to the forest type, its woody species composition, stand age, and structure through interception and evapotranspiration. We aimed to investigate the topsoil moisture response to precipitation in three treatments: under young Norway spruce, white birch, and a grass-dominated treeless gap at an acidic mountain site in the Jizerské hory Mts., Czech Republic. The study was conducted in 18- to 21-year-old stands during four growing seasons. Materials and Methods: The analyzed parameters were: rainfall amounts measured by an on-site automated station, root penetration using a root auger, and soil moisture measured continuously using electric sensors, as well as derived parameters such as interception. Results and Conclusions: Even within small patches of the three treatments, soil water content was found to be higher under the gap vegetation compared to both tree species. In addition, the topsoil under spruce was significantly more saturated than under birch. The average growing-season interception capacity of birch, spruce, and the gap treatment ranged from 1.4 to 2.2 mm, 2.1 to 2.6 mm, and 1.2 to 2.2 mm, respectively. Soil moisture mostly decreased during periods of flushing and stabilized during the transitions from the growing to the dormant seasons. The seasonal effects were particularly obvious under the birch stand. The crucial factors decreasing topsoil water content under birch included both rooting depth and density, which may predispose preferential pathways for water infiltration. This validated white birch’s capability to decrease topsoil water content, which can be beneficial at secondary-waterlogged sites.

Increasing root penetration into a different environment is more important than improving rooting depth

Deep rooting is often thought as a promising phenotype for resource extraction, but on soils with constraints, desired rooting depth was rarely observed. We hypothesised that if the genetic effect on root growth and rooting depth were separated from other effects, the determinants of root growth and rooting depth could be quantified. The conventional core-breaking method was used to measure root growth of wheat at two sites in two successive years under rain fed conditions. The Bayesian hierarchical nonlinear mixed models (HNLMMs) were employed to estimate root distribution, heritability and rooting depth. We found that root penetration from the non-sodic top to the sodic subsoil was most critical in determining rooting depth. Our study indicates that focusing on root-soil interaction at the transition layer where soil constraints start to emerge would lead to a more effective solution to develop resilient roots. Our work not only serves as a guide for selecting genotypes in pot trials, but also provides a theoretical support to breed advance crops with better soil adaptation.

An Acceptance Analysis of Subsoil Amelioration Amongst Agricultural Actors in Two Regions in Germany

The subsoil, commonly defined as horizons below the working depth of 30 cm, often receives little attention in farming practice. Yet plants extract between 10 and 80% of their nutrient and water requirements from the subsoil. Recent research indicates that subsoil amelioration measures, which enhance water storage capacity, root penetration and microbial activity, could contribute to stabilizing yields in times of drought. Therefore, we investigated farmers' and other soil experts' perceptions of subsoil amelioration as an approach to adapt to climate change as well as the factors that influence their willingness to adopt specific measures to improve the subsoil. We applied the Q-method combined with focus groups in two case study regions in Germany. Two subsoil amelioration techniques were considered: (1) Deep loosening combined with the incorporation of compost into deep soil layers (30–60 cm) and (2) the cultivation of alfalfa as deep-rooting pre-crop. Our results show three distinct views on subsoil amelioration, which we termed as the “pioneers,” the “skeptics,” and the “ecologists.” While the pioneers were open toward applying deep loosening combined with incorporation of compost into the subsoil, the skeptics had concerns about the method and perceived it as hardly feasible in practice, and the ecologists clearly preferred biological approaches such as alfalfa cultivation. Despite the different views, all three perspectives view subsoil amelioration as a useful approach to adapt to changing climate conditions. In conclusion, we identified a number of factors that influence the willingness to implement specific techniques to improve the subsoil: economic and farm-level considerations, awareness of subsoil functions, environmental awareness, individual norms and beliefs as well as risk perception. We recommend considering these factors in the design of a policy framework that promotes subsoil amelioration in Germany. Our findings could be of relevance for agricultural systems around the world, which are prone to drought risk.