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.
Intercropping is a farming practice involving two or more crop species, or genotypes, growing together and coexisting for a time. On the fringes of modern intensive agriculture, intercropping is ...important in many subsistence or low‐input/resource‐limited agricultural systems. By allowing genuine yield gains without increased inputs, or greater stability of yield with decreased inputs, intercropping could be one route to delivering ‘sustainable intensification’. We discuss how recent knowledge from agronomy, plant physiology and ecology can be combined with the aim of improving intercropping systems. Recent advances in agronomy and plant physiology include better understanding of the mechanisms of interactions between crop genotypes and species – for example, enhanced resource availability through niche complementarity. Ecological advances include better understanding of the context‐dependency of interactions, the mechanisms behind disease and pest avoidance, the links between above‐ and below‐ground systems, and the role of microtopographic variation in coexistence. This improved understanding can guide approaches for improving intercropping systems, including breeding crops for intercropping. Although such advances can help to improve intercropping systems, we suggest that other topics also need addressing. These include better assessment of the wider benefits of intercropping in terms of multiple ecosystem services, collaboration with agricultural engineering, and more effective interdisciplinary research.
Great potential exists to harness plant traits at the root–soil interface, mainly rhizodeposition and root hairs, to ‘build’ soils with better structure that can trap more carbon and resources, ...resist climate stresses, and promote a healthy microbiome. These traits appear to have been preserved in modern crop varieties, but scope exists to improve them further because they vary considerably between genotypes and respond to environmental conditions. From emerging evidence, rhizodeposition can act as a disperser, aggregator, and/or hydrogel in soil, and root hairs expand rhizosheath size. Future research should explore impacts of selecting these traits on plants and soils concurrently, expanding from model plants to commercial genotypes, and observing whether impacts currently limited to glasshouse studies occur in the field.
Root hairs and rhizodeposits are root traits that vary between plant species and crop genotypes and have a large impact on both plants and soils.Targeting these traits may benefit both plants and soil, improving food and environmental security at the same time. Soils may store more carbon (greenhouse gas mitigation), trap more water (drought tolerance) and nutrients, and resist erosion.From limited research, rhizosheath size has been maintained or improved in modern crop varieties, but potential exists to increase it further. Whether this will lead to improved yield or soil properties, however, requires greater field testing to verify.Laboratory and glasshouse research using root trait ideotypes has found marked impacts on soil biophysical properties. Rhizodeposits vary in behaviour between species from hydrogels to surfactants, and as soil dispersers (miners) or aggregators (builders).
Microplastics (MiPs) can potentially influence soil structural stability, with impacts likely dependent on their chemistry, concentration, size, and degradation in soil. This study used high-energy ...moisture characteristics (HEMC; water retention at matric suctions from 0 to 50 hPa) to quantify the effects of these MiP properties on soil structure stabiltiy. The HEMCs of soil samples contaminated with polypropylene (PP) or polyethylene (PE) were measured and modelled. Greater MiP concentrations (2 % and 7 % w w−1) increased the volume of drainable pores (VDP). At smaller MiP concentrations (0.5 % and 1 % w w−1), larger MiP fibres (3 and 5 mm) exhibited higher VDP values compared to a smaller size (1.6 mm) across a range of concentrations. Both PE and PP MiPs increased the modal matric suction (hmodal). The impacts on VDP and hmodal were more pronounced for fast than slow wetting, likely due to MiPs fibres entangling around soil aggregates, and MiPs pores filling after aggregate slaking, respectively. Soil structural index (SI) and stability ratio (SR) values increased following MiP incorporation. Our findings revealed the detrimental impacts of MiPs on soil aggregates and pores, demonstrating that MiPs significantly influence HEMC parameters due to combined impacts on structure stability and pore distribution.
Microplastics have emerged as a major anthropogenic hazardous material in the soil environment, with secondary impacts on soil structure and aggregate stability. Our study indicates that MiPs alter water retention, pore distribution, and soil hydraulic properties, affecting soil’s ability to retain and supply water. The introduction of MiPs leads to the destruction of soil aggregates and pores, compromising soil health and productivity. By characterising structural stability and pore structure dynamics using HEMC, this study highlights the sensitivity of MiP impacts, emphasizing the need for comprehensive assessment and strategies to preserve soil ecosystem functioning in the face of increasing MiP pollution.
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•Microplastics (MiPs) added artificial pores, boosting soil specific water capacity.•Soil water retention increased more with smaller than larger MiPs.•MiPs can have detrimental effects on soil aggregate stability during slow wetting.•Under fast wetting, MiPs improve soil aggregate stability by decreasing slaking.•Pores and high-energy moisture characteristics were affected by MiP concentration.
Aims
Crop genotypes may respond differently to various physical soil conditions. The objective of this study was to investigate the responses of the root architectures of two maize cultivars ...(Zhengdan958 and Denghai605) to various soil compaction and moisture conditions.
Methods
Two compaction levels (1.3 g cm
− 3
and 1.6 g cm
− 3
) and two moisture conditions (60% and 80% field capacity) were investigated to determine their impact on root growth. The root architectures of maize seedlings were assessed via X-ray computed tomography (CT). Soil penetration resistance, above-ground biomass and root biomass values were also determined.
Results
Soil moisture had significant effects on root biomass, above-ground biomass, the ratio of root biomass to above-ground biomass, and all root traits except for root volume. Soil compaction reduced root surface area and total root length of Zhengdan958 at 80% field capacity but not at 60% field capacity. However, soil compaction had little impact on root traits of Denghai605 at both moisture levels. Zhengdan958 had larger root volume, total root length, root diameter, root biomass and above-ground biomass than Denghai605 under noncompacted conditions. The ratio of root biomass to above-ground biomass was greater for Zhengdan958 than Denghai605 at the noncompacted and 60% field capacity conditions.
Conclusions
High moisture content has negative effects on root traits in compacted soil. The response of root architectures to soil compaction was more sensitive in Zhengdan958 than Denghai605. Zhengdan958 showed greater growth performance than Denghai605 under noncompacted conditions, and the drought tolerance of Zhengdan958 was greater than that of Denghai605.
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.
Carbon exchange across the soil–atmosphere interface has major implications for environmental change, but a consensus on the effect of temperature on soil organic matter (SOM) mineralisation remains ...elusive. In this study we investigated the temperature sensitivities of basal respiration (partitioned into recent and older SOM sources) and of additional SOM mineralisation associated with the addition of labile C to soil (priming effects). Soil samples were incubated at 15, 20, 25 and 30 °C, and following a 14 day stabilisation period, daily amendments of 13C-enriched glucose (0.2 mg g−1 soil) were applied (control treatments received water only). Soils were collected where C4 maize had recently been cultivated across fields which were historically planted with C3 spring barley. This enabled basal SOM mineralisation to be partitioned into recent (<4 years) and older SOM sources using natural abundance (C3/C4) δ13C signatures of soil CO2 efflux. Priming was quantified as the change in SOM-derived soil CO2 efflux in glucose-amended, relative to control soils, with apparent priming accounted for by δ13C analyses of the soil microbial biomass. Basal soil respiration was positively correlated with temperature (Q10 = 1.6), with increased mineralisation of older SOM entirely responsible for this effect (Q10 = 2.7). Glucose addition resulted in positive priming of SOM mineralisation at each temperature, but the absolute magnitude of this response was not affected by temperature. The results demonstrate that soil respiration conflates CO2 produced by a number of SOM mineralisation processes, each of which displayed distinct temperature sensitivities. Therefore, accurate prediction of SOM sensitivity to rising global temperatures and their inherent variations are required. This will be particularly the case for priming processes, where their magnitude may be most dependent on indirect effects of temperature on plant inputs to soil.
•Temperature treatments of 15, 20, 25 and 30 °C were applied to soils.•Additions of 13C enriched glucose induced real, positive priming effects.•Recalcitrant and labile carbon turnover showed separate temperature responses.•Priming was not sensitive to temperature changes.
Nitrate accumulated deep (>100 cm) in the regolith (soil and saprolite) threatens groundwater quality, but most studies focus only on nitrate nearer the surface (<100 cm). Surface soil management ...versus regolith interactions affect deep nitrate leaching, but their combined impact remains unclear. This study measured how deep nitrate accumulation was affected by crop practices including orchard/cropland planting years, regolith structure, and soil properties in highly weathered subtropical red soils. Deep nitrate storage varied from 43.6 to 1116.3 kg ha–1. Regolith thickness was positively correlated with nitrate storage (R 2 = 0.43, p < 0.05). Reticulated red clay (110–838 cm) had 81% of the accumulated nitrate and overlapped with 79% of the nitrate accumulation layer. All of the nitrate accumulation parameters (except for peak depth (PD)) generally increased with the planting years. The difference in peak nitrate concentration (9.0–20.0 mg kg–1) with planting year gradient (3–58 years) varied by 2.2 times, and the difference in nitrate storage (43.6–425.7 kg ha–1) varied by 9.8 times. Texture and pH explain 41.6% of the variation in nitrate concentration. As soil management practices interact with deeper regolith to control the spatial pattern of nitrate accumulation, vulnerable regions could be identified to avoid high accumulation.
The interface between plants' roots and soil is strongly affected by rhizodeposits, especially mucilage, that change mechanical and hydrological behaviour. In addition to impacts to aggregation, ...water capture and root penetration, rhizodeposits may also affect the pull‐out resistance of plant roots. Due to the complex architecture of plant roots and an inability to restrict rhizodeposit production, this study used a simplified system of wooden skewers to simulate roots and chia seed mucilage as a model to simulate rhizodeposit compounds. Pull‐out tests were then carried out to measure the impacts of mucilage, and one (WD1) or two (WD2) cycles of wetting and drying of soils. Using a mechanical test frame, the maximum pull‐out resistance (Fmax) and pull‐out displacement (dL) were recorded, allowing for pull‐out energy (E), average pull‐out force (F¯$$ \overline{F} $$) and bond strength (τmax) to be calculated. The results showed that all pull‐out parameters of the samples with added rhizodeposit compounds tended to decrease between WD1 and WD2, but they were still significantly greater than without the added mucilage. The model rhizodeposit increased all pull‐out parameters by a minimum of 30%. With an additional wet–dry cycle, the mucilage tended to cause a decline in pull‐out parameters relative to a single wet‐dry cycle. This suggests mucilages could enhance the mechanical resistance of roots to pull‐out, but resistance decreases over time with cycles of wetting and drying. To conclude, an important role of mucilage is pull‐out resistance, which has relevance to plant anchorage and root reinforcement of soils.
Surface tension was measured for aqueous solutions of dl-malic acid, l-glutamine, l-serine, l-proline, l-methionine, l-valine, and l-lactic acid as a function of concentration using a Du Noüy ring ...over a temperature range between 298 and 328 K at 101 kPa atmospheric pressure. Surface tensions of several concentrations of each organic acid were measured to develop four isotherms with a temperature ramp of 10 K starting from 298 K. Cohesive forces between molecules were weakened by temperature rise, resulting in decreased surface tension. Mass concentration and temperature effects on surface tension were reflected by the slopes of the relationships between surface tension and either mass concentration or temperature, respectively. In this study, l-serine and l-glutamine showed hydrophilic behavior, while l-proline, l-methionine, dl-malic acid, l-valine, and l-lactic acid had hydrophobic behavior. For all acids studied here, increased temperature caused decreased surface tension of aqueous solutions of solute.
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