In this paper, we provide direct evidence of the importance of root hairs on pore structure development at the root–soil interface during the early stage of crop establishment.
This was achieved by ...use of high-resolution (c. 5 μm) synchrotron radiation computed tomography (SRCT) to visualise both the structure of root hairs and the soil pore structure in plant–soil microcosms. Two contrasting genotypes of barley (Hordeum vulgare), with and without root hairs, were grown for 8d in microcosms packed with sandy loam soil at 1.2 g cm−3 dry bulk density. Root hairs were visualised within air-filled pore spaces, but not in the fine-textured soil regions.
We found that the genotype with root hairs significantly altered the porosity and connectivity of the detectable pore space (> 5 μm) in the rhizosphere, as compared with the no-hair mutants. Both genotypes showed decreasing pore space between 0.8 and 0.1mm from the root surface. Interestingly the root-hair-bearing genotype had a significantly greater soil pore volume-fraction at the root–soil interface.
Effects of pore structure on diffusion and permeability were estimated to be functionally insignificant under saturated conditions when simulated using image-based modelling.
Aims
The rhizosheath is defined as the weight of soil adhering strongly to roots on excavation, and current interest in this trait as a potential tolerance mechanism to abiotic stress has prompted us ...to explore the extent of its occurrence throughout the angiosperm phylogeny.
Methods
Here we describe a robust, novel method which was used to screen species for the presence/absence and strength of a rhizosheath. We correlate the latter with root hair length to provide insight into some of the factors affecting its formation. We go on to compare experimental data with previous observations in the literature.
Results
Results of a glasshouse screen demonstrate that rhizosheaths exist in species from many angiosperm orders, and the frequency of their occurrence and their strength and size are related. No correlation between root hair length and rhizosheath size was found, except when root hairs were extremely short, but the presence of root hairs was required for rhizosheath formation.
Conclusions
The rhizosheath is present in species from many angiosperm orders. Potential to enhance the trait is likely to exist in a range of crop species and could help contribute to future agricultural sustainability.
Root hairs are a key trait for improving the acquisition of phosphorus (P) by plants. However, it is not known whether root hairs provide significant advantage for plant growth under combined soil ...stresses, particularly under conditions that are known to restrict root hair initiation or elongation (e.g. compacted or high-strength soils). To investigate this, the root growth and P uptake of root hair genotypes of barley, Hordeum vulgare L. (i.e. genotypes with and without root hairs), were assessed under combinations of P deficiency and high soil strength. Genotypes with root hairs were found to have an advantage for root penetration into high-strength layers relative to root hairless genotypes. In P-deficient soils, despite a 20% reduction in root hair length under high-strength conditions, genotypes with root hairs were also found to have an advantage for P uptake. However, in fertilized soils, root hairs conferred an advantage for P uptake in low-strength soil but not in high-strength soil. Improved root–soil contact, coupled with an increased supply of P to the root, may decrease the value of root hairs for P acquisition in high-strength, high-P soils. Nevertheless, this work demonstrates that root hairs are a valuable trait for plant growth and nutrient acquisition under combined soil stresses. Selecting plants with superior root hair traits is important for improving P uptake efficiency and hence the sustainability of agricultural systems.
Active and adaptive plasticity in a changing climate Brooker, Rob; Brown, Lawrie K.; George, Timothy S. ...
Trends in plant science,
July 2022, 2022-Jul, 2022-07-00, 20220701, Letnik:
27, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Better understanding of the mechanistic basis of plant plasticity will enhance efforts to breed crops resilient to predicted climate change. However, complexity in plasticity’s conceptualisation and ...measurement may hinder fruitful crossover of concepts between disciplines that would enable such advances. We argue active adaptive plasticity is particularly important in shaping the fitness of wild plants, representing the first line of a plant’s defence to environmental change. Here, we define how this concept may be applied to crop breeding, suggest appropriate approaches to measure it in crops, and propose a refocussing on active adaptive plasticity to enhance crop resilience. We also discuss how the same concept may have wider utility, such as in ex situ plant conservation and reintroductions.
Increasing environmental uncertainty is focussing research interest on plant plasticity. But despite calls for plasticity concepts to be adopted in crop breeding, this does not appear to have happened.Plasticity is a broad and multifaceted concept, making it potentially difficult to identify those aspects of previous research most relevant to the crop breeding context.Given the challenges posed by climate change and the different evolutionary contexts in natural and crop systems, we identify active adaptive plasticity as a key issue for further investigation by crop breeders.We outline and illustrate the experimental and statistical analytical approaches necessary to begin to assess active adaptive plasticity, and we highlight benefits that might arise in other fields from a fuller understanding of the role and regulation of this aspect of plasticity.
There is an urgent need for simple rapid screens of root traits that improve the acquisition of nutrients and water. Temperate cereals produce rhizosheaths of variable weight, a trait first noted on ...desert species sampled by Tansley over 100 yr ago. This trait is almost certainly important in tolerance to abiotic stress. Here, we screened association genetics populations of barley for rhizosheath weight and derived quantitative trait loci (QTLs) and candidate genes. We assessed whether rhizosheath weight was correlated with plant performance and phosphate uptake under combined drought and phosphorus deficiency. Rhizosheath weight was investigated in relation to root hair length, and under both laboratory and field conditions. Our data demonstrated that rhizosheath weight was correlated with phosphate uptake under dry conditions and that the differences in rhizosheath weight between genotypes were maintained in the field. Rhizosheath weight also varied significantly within barley populations, was correlated with root hair length and was associated with a genetic locus (QTL) on chromosome 2H. Putative candidate genes were identified. Rhizosheath weight is easy and rapid to measure, and is associated with relatively high heritability. The breeding of cereal genotypes for beneficial rhizosheath characteristics is achievable and could contribute to agricultural sustainability in nutrient‐ and water‐stressed environments.
Micronutrient deficiency in cereals is a problem of global significance, severely reducing grain yield and quality in marginal soils. Ancient landraces represent, through hundreds of years of local ...adaptation to adverse soil conditions, a unique reservoir of genes and unexplored traits for enhancing yield and abiotic stress tolerance. Here we explored and compared the genetic variation in a population of Northern European barley landraces and modern elite varieties, and their tolerance to manganese (Mn) limitation.
A total of 135 barley accessions were genotyped and the genetic diversity was explored using Neighbor-Joining clustering. Based on this analysis, a sub-population of genetically diverse landraces and modern elite control lines were evaluated phenotypically for their ability to cope with Mn-deficient conditions, across three different environments increasing in complexity from hydroponics through pot experiments to regional field trials.
Genetically a group of Scottish barley landraces (Bere barley) were found to cluster according to their island of origin, and accessions adapted to distinct biogeographical zones with reduced soil fertility had particularly larger Mn, but also zinc (Zn) and copper (Cu) concentrations in the shoot. Strikingly, when grown in an alkaline sandy soil in the field, the locally adapted landraces demonstrated an exceptional ability to acquire and translocate Mn to developing leaves, maintain photosynthesis and generate robust grain yields, whereas modern elite varieties totally failed to complete their life cycle.
Our results highlight the importance of gene pools of local adaptation and the value of ancient landrace material to identify and characterize genes that control nutrient use efficiency traits in adverse environments to raise future crop production and improve agricultural sustainability in marginal soils. We propose and discuss a model summarizing the physiological mechanisms involved in the complex trait of tolerance to Mn limitation.
Growers need to produce increased crop yield to use resources more effectively and be resilient to abiotic stress and changing climates; however, current approaches are leading to maladaptation to ...stress.Bottlenecks in the selection of barley varieties have resulted in a reduction of genetic diversity that is obstructive to climate-smart agriculture.To reverse genetic erosion and identify novel sources of variation, we are re-examining and reintroducing crop landraces.Landscape genomics can add a new dimension by modelling potential adaptive responses to a specific environment or global climate change.In a conceptual model, we outline a targeted breeding programme connecting old cultivar collections with state-of-the-art gene discovery and phenotyping, necessary to provide new resources for future needs.
Future crops need to be sustainable in the face of climate change. Modern barley varieties have been bred for high productivity and quality; however, they have suffered considerable genetic erosion, losing crucial genetic diversity. This renders modern cultivars vulnerable to climate change and stressful environments. We highlight the potential to tailor crops to a specific environment by utilising diversity inherent in an adapted landrace population. Tapping into natural biodiversity, while incorporating information about local environmental and climatic conditions, allows targeting of key traits and genotypes, enabling crop production in marginal soils. We outline future directions for the utilisation of genetic resources maintained in landrace collections to support sustainable agriculture through germplasm development via the use of genomics technologies and big data.
• Soil adjacent to roots has distinct structural and physical properties from bulk soil, affecting water and solute acquisition by plants. Detailed knowledge on how root activity and traits such as ...root hairs affect the three-dimensional pore structure at a fine scale is scarce and often contradictory.
• Roots of hairless barley (Hordeum vulgare L. cv Optic) mutant (NRH) and its wildtype (WT) parent were grown in tubes of sieved (<250 μm) sandy loam soil under two different water regimes. The tubes were scanned by synchrotron-based X-ray computed tomography to visualise pore structure at the soil–root interface. Pore volume fraction and pore size distribution were analysed vs distance within 1 mm of the root surface.
• Less dense packing of particles at the root surface was hypothesised to cause the observed increased pore volume fraction immediately next to the epidermis. The pore size distribution was narrower due to a decreased fraction of larger pores. There were no statistically significant differences in pore structure between genotypes or moisture conditions.
• A model is proposed that describes the variation in porosity near roots taking into account soil compaction and the surface effect at the root surface.
Aims Intercropping can improve plant yields and soil phosphorus (P) use efficiency. This study compares inter- and intra-species intercropping, and determines whether P uptake and shoot biomass ...accumulation in intercrops are affected by soil P availability. Methods Four barley cultivars (Hordeum vulgare L.) and three legume species (Trifolium subterreneum, Ornithopus sativus and Medicago truncatula) were selected on the basis of their contrasting root exudation and morphological responses to P deficiency. Monocultures and barley-barley and barley-legume intercrops were grown for 6 weeks in a pot trial at very limiting, slightly limiting and excess available soil P. Aboveground biomass and shoot P were measured. Results Barley-legume intercrops had 10–70% greater P accumulation and 0–40% greater biomass than monocultures, with the greatest gains occurring at or below the sub-critical P requirement for barley. No benefit of barley-barley intercropping was observed. The plant combination had no significant effect on biomass and P uptake observed in intercropped treatments. Conclusions Barley-legume intercropping shows promise for sustainable production systems, especially at low soil P. Gains in biomass and P uptake come from inter- rather than intra-species intercropping, indicating that plant diversity resulted in decreased competition between plants for P.
Key message
Characterisation and genetic mapping of a key gene defining root morphology in bread wheat.
Root morphology is central to plants for the efficient uptake up of soil water and mineral ...nutrients. Here we describe a conditional mutant of hexaploid wheat (
Triticum aestivum
L.) that when grown in soil with high Ca
2+
develops a larger rhizosheath accompanied with shorter roots than the wild type. In wheat, rhizosheath size is a reliable surrogate for root hair length and this was verified in the mutant which possessed longer root hairs than the wild type when grown in high Ca
2+
soil. We named the mutant
Stumpy
and showed it to be due to a single semi-dominant mutation. The short root phenotype at high Ca
2+
was due to reduced cellular elongation which might also explain the long root hair phenotype. Analysis of root cell walls showed that the polysaccharide composition of
Stumpy
roots is remodelled when grown at non-permissive (high) Ca
2+
concentrations. The mutation mapped to chromosome 7B and sequencing of the 7B chromosomes in both wild type and
Stumpy
identified a candidate gene underlying the
Stumpy
mutation. As part of the process to determine whether the candidate gene was causative, we identified wheat lines in a Cadenza TILLING population with large rhizosheaths but accompanied with normal root length. This finding illustrates the potential of manipulating the gene to disconnect root length from root hair length as a means of developing wheat lines with improved efficiency of nutrient and water uptake. The
Stumpy
mutant will be valuable for understanding the mechanisms that regulate root morphology in wheat.
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