Contrasting Root Architecture Research Articles

Cover crop influence on pore size distribution and biopore dynamics: Enumerating root and soil faunal effects.

Pore structure is a key determinant of soil functioning, and both root growth and activity of soil fauna are modified by and interact with pore structure in multiple ways. Cover cropping is a rapidly growing popular strategy for improving agricultural sustainability, including improvements in pore structure. However, since cover crop species encompass a variety of contrasting root architectures, they can have disparate effects on formation of soil pores and their characteristics, thus on the pore structure formation. Moreover, utilization of the existing pore systems and its modification by new root growth, in conjunction with soil fauna activity, can also vary by cover crop species, affecting the dynamics of biopores (creation and demolition). The objectives of this study were (i) to quantify the influence of 5 cover crop species on formation and size distribution of soil macropores (>36 μm Ø); (ii) to explore the changes in the originally developed pore architecture after an additional season of cover crop growth; and (iii) to assess the relative contributions of plant roots and soil fauna to fate and modifications of biopores. Intact soil cores were taken from 5 to 10 cm depth after one season of cover crop growth, followed by X-ray computed micro-tomography (CT) characterization, and then, the cores were reburied for a second root growing period of cover crops to explore subsequent changes in pore characteristics with the second CT scanning.Our data suggest that interactions of soil fauna and roots with pore structure changed over time. While in the first season, large biopores were created at the expense of small pores, in the second year these biopores were reused or destroyed by the creation of new ones through earthworm activities and large root growth. In addition, the creation of large biopores (>0.5 mm) increased total macroporosity. During the second root growing period, these large sized macropores, however, are reduced in size again through the action of soil fauna smaller than earthworms, suggesting a highly dynamic equilibrium. Different effects of cover crops on pore structure mainly arise from their differences in root volume, mean diameter as well as their reuse of existing macropores.

Dynamics of localised nitrogen supply and relevance for root growth of Vicia faba (\u2018Fuego\u2019) and Hordeum vulgare (\u2018Marthe\u2019) in soil

Root growth responds to local differences in N-form and concentration. This is known for artificial systems and assumed to be valid in soil. The purpose of this study is to challenge this assumption for soil mesocosms locally supplied with urea with and without nitrification inhibitor. Soil column experiments with Vicia faba (‘Fuego’) and Hordeum vulgare (‘Marthe’) were performed to investigate soil solution chemistry and root growth response of these two species with contrasting root architectures to the different N-supply simultaneously. Root growth was analysed over time and separately for the fertiliser layer and the areas above and below with X-ray CT (via region growing) and WinRHIZO. Additionally, NO3− and NH4+ in soil and soil solution were analysed. In Vicia faba, no pronounced differences were observed, although CT analysis indicated different root soil exploration for high NH4+. In Hordeum vulgare, high NO3− inhibited lateral root growth while high NH4+ stimulated the formation of first order laterals. The growth response to locally distributed N-forms in soil is species specific and less pronounced than in artificial systems. The combination of soil solution studies and non-invasive imaging of root growth can substantially improve the mechanistic understanding of root responses to different N-forms in soil.

Genetic and phenotypic associations between root architecture, arbuscular mycorrhizal fungi colonisation and low phosphate tolerance in strawberry (Fragaria \xd7 ananassa)

BackgroundPhosphate is an essential plant macronutrient required to achieve maximum crop yield. Roots are able to uptake soil phosphate from the immediate root area, thus creating a nutrient depletion zone. Many plants are able to exploit phosphate from beyond this root nutrient depletion zone through symbiotic association with Arbuscular Mycorrhizal Fungi (AMF). Here we characterise the relationship between root architecture, AMF association and low phosphate tolerance in strawberries. The contrasting root architecture in the parental strawberry cultivars ‘Redgauntlet’ and ‘Hapil’ was studied through a mapping population of 168 progeny. Low phosphate tolerance and AMF association was quantified for each genotype to allow assessment of the phenotypic and genotypic relationships between traits.ResultsA “phosphate scavenging” root phenotype where individuals exhibit a high proportion of surface lateral roots was associated with a reduction in root system size across genotypes. A genetic correlation between “root system size” traits was observed with a network of pleiotropic QTL found to represent five “root system size” traits. By contrast, average root diameter and the distribution of roots appeared to be under two discrete methods of genetic control. A total of 18 QTL were associated with plant traits, 4 of which were associated with solidity that explained 46% of the observed variation. Investigations into the relationship between AMF association and root architecture found that a higher root density was associated with greater AMF colonisation across genotypes. However, no phenotypic correlation or genotypic association was found between low phosphate tolerance and the propensity for AMF association, nor root architectural traits when plants are grown under optimal nutrient conditions.ConclusionsUnderstanding the genetic relationships underpinning phosphate capture can inform the breeding of strawberry varieties with better nutrient use efficiency. Solid root systems were associated with greater AMF colonisation. However, low P-tolerance was not phenotypically or genotypically associated with root architecture traits in strawberry plants. Furthermore, a trade-off was observed between root system size and root architecture type, highlighting the energetic costs associated with a “phosphate scavenging” root architecture.

Cover crop species have contrasting influence upon soil structural genesis and microbial community phenotype

Cover crops (plants grown in an agricultural rotation between cash crops) can significantly improve soil quality via sequestering carbon, retaining nutrients, decreasing soil erosion, and maintaining belowground biodiversity. However, little is known about the effects of such plants upon soil structure. The aim of the study was to assess the impact of four species typically used as cover crops and which have contrasting root architecture (viz. clover, black oat, phacelia, tillage radish) on soil structural genesis and the associated modification of microbial community structure in a clay soil. The four plant species were grown in a replicated pot experiment with sieved soil (<2 mm), with unplanted soil as control for 8 weeks. X-ray Computed Tomography was used to quantify the formation of pore networks in 3D and phospholipid fatty acid analysis was performed to characterise the microbial community phenotype. Black oats developed a greater soil-pore connectivity than the other species throughout the growth period, whereas phacelia decreased both the porosity and pore-connectivity. The microbial community phenotype under phacelia was notably different from the other species, with a greater proportion of fungal markers. Thus, different plant species have differential effects upon soil structural genesis and microbial community phenotype, which provides evidence that certain species may be more suitable as cover crops in terms of soil structural conditioning depending upon specific contexts.

Does woody species with contrasting root architecture require different container size in nursery?

Small containers used in seedlings production of tree species with different root architecture can result in serious constraints for root growth and unsuitable plant quality, with potential impacts on field performance. We compare responses of root morphology to changes in container size and shape in both deep-rooting (Acacia caven) and shallow-rooting (Baccharis linearis) species, both commonly used in active restoration plans in central Chile. For both species, seedlings were cultivated in four different PVC container-types varying in size (440 mL and 880 mL) and shape ([10, 20, 35, and 45] cm in length), and a control treatment that consists in the commonly container-type used in Chilean nurseries (440 mL black polyethylene bag). Seedlings were cultivated for one growing season under controlled conditions and a set of above- and belowground morphological parameters were evaluated. A second short experiment was performed afterwards to evaluate potential seedling quality through the root growth potential (RGP) test. Results showed that an increase in container volume differently affected morphological parameters of A. caven and B. linearis seedlings. The control treatment had high presence of spiral roots for the deep-rooting species, restricting normal root growth. For both species, elongated containers (&gt;35 cm) produced seedlings with smaller shoots with longer root systems and without deformations in the taproot or main root. Elongated containers also restarted growth of new roots more deeply in the container as result of the RGP test. We concluded that contrasting root architecture of native species require different container size in nursery to promote an adequate root development and growth.

Dissecting root trait variability in maize genotypes using the semi-hydroponic phenotyping platform

The production of maize (Zea mays L.) is restricted by various edaphic stresses, including drought and low-fertility soil. Searching for genotypes with optimal root traits is a promising practice when breeding for improved adaptation to abiotic stress and resource-use efficiency. Using an established semi-hydroponic phenotyping technique, we assessed root trait variability across 174 maize genotypes including 113 cultivars and 11 breeding lines from northern China and 50 Serbian hybrids. Large variation in root architecture traits was observed among the tested genotypes 28 days after transplanting. Sixteen of the characterized traits had coefficients of variation greater than 0.25, especially local root traits. Root traits including total root length, root length at various depths, total shoot mass and nodal root angle, should be considered in maize breeding programs. Genotype ranking data based on a composite score was used to assist in the selection of genotypes with contrasting root architecture traits for future studies. This study identified genotypic variation in root architecture traits in a diverse genotypes of maize. The outcomes of this study could form a basis for maize breeding programs aimed at producing maize cultivars for improved adaptation to target environments.

Copper oxide nanoparticle effects on root growth and hydraulic conductivity of two vegetable crops

Root growth and water transport were evaluated for two vegetable crops of contrasting root architecture (lettuce, carrot) exposed to copper oxide nanoparticles (CuO NPs). 10-day seedling root growth assays were evaluated for 16 nanometer (nm) diameter CuO NP and CuCl2 control (0.8 – 798.9 mg Cu L-1). In a separate experiment, hydraulic conductivity (Kh) of root systems not previously exposed to NP was tested using 16 and 45 nm CuO NP (798.9 mg Cu L-1) relative to CuO NP-free controls, and xylem sap was assessed by TEM-EDS for presence of CuO NPs. 16 nm CuO NP produced dose-dependent increases in root diameter for lettuce (+52%) and carrot (+26%) seedlings, whereas CuCl2 did not affect (lettuce) or marginally increased (carrot) root diameter. Root Kh was similarly reduced by 16 and 45 nm CuO NPs for lettuce (-46%) but not for carrot, and no Cu was identified by TEM-EDS in xylem sap. Adverse effects of CuO NPs on root physiology and function in the early stages of growth of two key food crops are not necessarily due to Cu2+ toxicity and can be specific to crop species. In addition to triggering root thickening, reduction of root Kh signifies that CuO NPs can compromise root water transport and thus crop performance.

An image processing and analysis tool for identifying and analysing complex plant root systems in 3D soil using non-destructive analysis: Root1.

The objective of this study was to develop a flexible and free image processing and analysis solution, based on the Public Domain ImageJ platform, for the segmentation and analysis of complex biological plant root systems in soil from x-ray tomography 3D images. Contrasting root architectures from wheat, barley and chickpea root systems were grown in soil and scanned using a high resolution micro-tomography system. A macro (Root1) was developed that reliably identified with good to high accuracy complex root systems (10% overestimation for chickpea, 1% underestimation for wheat, 8% underestimation for barley) and provided analysis of root length and angle. In-built flexibility allowed the user interaction to (a) amend any aspect of the macro to account for specific user preferences, and (b) take account of computational limitations of the platform. The platform is free, flexible and accurate in analysing root system metrics.

Phosphorus starvation boosts carboxylate secretion in P-deficient genotypes of Lupinus angustifolius with contrasting root structure

Lupinus angustifolius L. (narrow-leafed lupin) is an important grain legume crop for the stockfeed industry in Australia. This species does not form cluster roots regardless of phosphorus (P) nutrition. We hypothesise that this species may have adaptive strategies for achieving critical P uptake in low-P environments by altering shoot growth and root architecture and secreting carboxylates from roots. Three wild genotypes of L. angustifolius with contrasting root architecture were selected to investigate the influence of P starvation on root growth and rhizosphere carboxylate exudation and their relationship with P acquisition. Plants were grown in sterilised loamy soil supplied with zero, low (50 μm) or optimal (400 μm) P for 6 weeks. All genotypes showed a significant response in shoot and root development to varying P supply. At P deficit (zero and low P), root systems were smaller and had fewer branches than did roots at optimal P. The amount of total carboxylates in the rhizosphere extracts ranged from 3.4 to 17.3 μmol g–1 dry root. The total carboxylates comprised primarily citrate (61–78% in various P treatments), followed by malate and acetate. Genotype #085 (large root system with deep lateral roots) exuded the greatest amount of total carboxylates to the rhizosphere for each P treatment, followed by #016 (medium root system with good branched lateral roots) and #044 (small root system with short and sparse lateral roots). All genotypes in the low-P treatment significantly enhanced exudation of carboxylates, whereas no significant increase in carboxylate exudation was observed in the zero-P treatment. Small-rooted genotypes had higher P concentration than the medium- and large-rooted genotypes, although larger plants accumulated higher total P content. Large-rooted genotypes increased shoot P utilisation efficiency in response to P starvation. This study showed that narrow-leafed lupin genotypes differing in root architecture differed in carboxylate exudation and P uptake. Our finding suggested that for L. angustifolius there is a minimum plant P concentration below which carboxylate exudation is not enhanced despite severe P deficiency. The outcomes of this study enhance our understanding of P acquisition strategies in L. angustifolius genotypes, which can be used for the selection of P-efficient genotypes for cropping systems.

When do arbuscular mycorrhizal fungi protect plant roots from pathogens?

Arbuscular mycorrhizal (AM) fungi are mainly thought to facilitate phosphorus uptake in plants, but they can also perform several other functions that are equally beneficial. Our recent study sheds light on the factors determining one such function, enhanced plant protection from root pathogens. Root infection by the fungal pathogen Fusarium oxysporum was determined by both plant susceptibility and the ability of an AM fungal partner to suppress the pathogen. The non-susceptible plant species (Allium cepa) had limited F. oxysporum infection even without AM fungi. In contrast, the susceptible plant species (Setaria glauca) was heavily infected and only AM fungi in the family Glomeraceae limited pathogen abundance. Plant susceptibility to pathogens was likely determined by contrasting root architectures between plants, with the simple rooted plant (A. cepa) presenting fewer sites for infection.AM fungal colonization, however, was not limited in the same way in part because plants with fewer, simple roots are more mycorrhizal dependent. Protection only by Glomus species also indicates that whatever the mechanism(s) of this function, it responds to AM fungal families differently. While poor at pathogen protection, AM fungal species in the family Gigasporaceae most benefited the growth of the simple rooted plant species. Our research indicates that plant trait differences, such as root architecture can determine how important each mycorrhizal function is to plant growth but the ability to provide these functions differs among AM fungi.

Multiple stress response and belowground competition in multilines of common bean ( Phaseolus vulgaris L.)

Multilines (genetic mixtures) composed of genotypes of contrasting root architecture were hypothesized to show improved growth and productivity in comparison with genetic monocultures in conditions of multiple edaphic stresses. To test this hypothesis, three multilines of common bean ( Phaseolus vulgaris L.), each composed of two recombinant inbred lines having contrasting root architecture in previous studies, were evaluated at seven sites in Honduras with varying soil phosphorus and moisture availability. Molecular markers were used to quantify the presence of each genotype in both root and seed-yield samples. Root growth in competition was dependent on both soil treatment and genotype. In one of the multilines, the root zone was dominated by one genotype, especially in the high-P treatment. In contrast, the root zone of another multiline had equal representation from both genotypes. These results show that response to belowground competition can differ among genotypes of the same species. No tradeoff between root growth and plant performance (yield or shoot biomass) was observed. Contrary to expected results, profiles of root distribution did not differ significantly in the environments tested in this study. As a result, differences in uptake of resources (phosphorus and water) in divergent soil domains and yield advantage of multilines were observed in only a small number of cases. Multilines did not create any yield penalty. Future work with genotypes that are more contrasting in root architecture is necessary to assess this strategy for use by resource-poor farmers.

Phosphorus runoff from a phosphorus deficient soil under common bean (Phaseolus vulgaris L.) and soybean (Glycine max L.) genotypes with contrasting root architecture

The selection and breeding of crop genotypes with root traits that improve soil resource extraction is a promising avenue to improved nutrient and water use efficiency in low-input farming systems. Such genotypes may accelerate nutrient extraction (“nutrient mining”), but may also reduce nutrient loss via soil erosion by producing greater shoot biomass and by direct effects of root traits on aggregate formation and water infiltration. Little is known about the effects of root architecture on phosphorus (P) runoff and soil erosion, and the relative importance of root and shoot traits on runoff P loss has not been determined. Four genotypes of common bean (Phaseolus vulgaris L.) and two genotypes of soybean (Glycine max) selected for contrasting root architecture were grown in a low P soil (Aquic Fragiudult, <20 mg kg−1 Mehlich-3 P, 3% slope) and subjected to rainfall-runoff experiments with and without shoot removal. Plots with intact shoots had significantly lower runoff volumes (1.3–7.6 mm) and total P loads in runoff (0.005–0.32 kg ha−1) than plots with shoots removed (7.0–16.8 mm; 0.025–1.95 kg ha−1). Dissolved reactive P leached from plant material did not contribute significantly to P loss in runoff. Total root length acquired from soil cores differed significantly among genotypes. Root length densities in the upper 15 cm of soil mid-way between rows were less than 4.0 cm cm−3 and variation in root length density was not correlated with runoff or P loss. Root length density also did not affect rainfall infiltration or surface runoff volume. We conclude that for annual dicotyledonous crops such as bean and soybean with relatively low root length densities, root traits have little direct effect on soil erosion.

Root Gravitropism and Below-ground Competition among Neighbouring Plants: A Modelling Approach

Competition for nutrients among neighbouring roots occurs when their individual depletion volumes overlap, causing a reduction in nutrient uptake. By exploring different spatial niches, plants with contrasting root architecture may reduce the extent of competition among neighbouring root systems. The main objectives of this study were: (1) to evaluate the impact of root architecture on competition for phosphorus among neighbouring plants; and (2) to compare the magnitude of competition among roots of the same plant vs. roots of neighbouring plants. SimRoot, a dynamic geometric model, was used to simulate common bean root growth and to compare the overlap of depletion volumes. By varying the gravitropism of basal roots, we simulated three distinct root architectures: shallow, intermediate and deep, corresponding to observed genetic variation for root architecture in this species. Combinations of roots having the same architecture resulted in more intense inter-plant competition. Among them, the deep-deep combination had the most intense competition. Competition between deep root systems and shallow root systems was only half that of deep root systems competing with other deep root systems. Inter-plant root competition increased as soil diffusivity increased and the distance among plants decreased. In heterogeneous soils, co-localization of soil resources and roots was more important in determining resource uptake than inter-plant root competition. Competition among roots of the same plant was three- to five-times greater than competition among roots of neighbouring plants. Genetic variation for root architecture in common bean may be related to adaptation to diverse competitive environments.

Fractal geometry of root systems: Field observations of contrasting genotypes of common bean ( Phaseolus vulgaris L.) grown under different phosphorus regimes

Root growth and architecture are important for phosphorus acquisition due to the relative immobility of P in the soil. Fractal geometry is a potential new approach to the analysis of root architecture. Substantial genetic variation in root growth and architecture has been observed in common bean. Common bean (Phaseolus vulgaris L.) genotypes with contrasting root architecture were grown under moderate and low P conditions in a field experiment. Linear and planar fractal dimension were measured by tracing root intercepts with vertical planes. Linear fractal dimension increased over time in efficient genotypes, but remained fairly constant over time in inefficient genotypes. Planar fractal dimension increased over time for all genotypes, but was higher in efficient than inefficient genotypes at the end of the experiment. Planar fractal dimension of medium P plants was found to correlate with shoot P content indicating fractal dimension to be a possible indicator for root P uptake. The increasing fractal dimension over time indicates that fractal analysis is a sensitive measure of root branching intensity. A less destructive method for acquisition of data that allows for continuous analysis of fractal geometry and thereby screening for more P efficient genotypes in the field is suggested. This method will allow the researcher to conduct fractal analysis and still complete field trials with final yield evaluation.