Root-free Soil Research Articles

Beyond the rootzone: Unveiling soil property and biota gradients around plants

Although the effects of plants on soil properties are well known, the effects of distance from plant roots to root-free soil on soil properties and associated soil organisms are much less studied. Previous research on the effects of distance from a plant explored specific soil organisms and properties, however, comparative studies across a wide range of plant-associated organisms and multiple model systems are lacking.We conducted a controlled greenhouse experiment using soil from two contrasting habitats. Within each soil type, we cultivated two plant species, individually and in combination, studying soil organisms and properties in the root centre, the root periphery, and the root-free zones.We showed that the distance from the cultivated plant (representing decreasing amount of plant roots) had a significant impact on the abiotic properties of the soil (pH and available P and N) and also on the composition of the fungal, bacterial, and nematode communities. The specific patterns, however, did not always match our expectations. For example, there was no significant relationship between the abundance of fungal pathogens and the distance from the cultivated plant compared to a strong decrease in the abundance of arbuscular mycorrhizal fungi. Changes in soil chemistry along the distance from the cultivated plant were probably one of the important drivers that affected bacterial communities. The abundance of nematodes also decreased with distance from the cultivated plant, and the rate of their responses reflected the distribution of their food sources.The patterns of soil changes along the gradient from plant to root-free soil were largely similar in two contrasting soil types and four plant species or their mixtures. This suggests that our results can be generalised to other systems and contribute to a better understanding of the mechanisms of soil legacy formation.

Influences of root fragments on soil thermal property measurements with heat pulse method

Heat pulse (HP) method has been widely applied for measuring thermal properties, heat fluxes, and soil–water evaporation for near-surface soil layers. In topsoil layers, the presence of roots violates the underlying assumption of HP method that the soil under test is homogeneous. In this study, numerical and laboratory experiments were conducted to test the influence of root fragments on soil thermal property measurement with HP sensors. Soybean root fragments, with a water content of about 0.74 m3 m−3 and diameters ranging from 0.5 to 4 mm, were carefully repacked into soil samples that were used for HP measurements. Results showed that the effects of roots on soil thermal property measurements depended on root size, root location and directions relative to the heater probe, and the thermal property differences between soil sample and root. Roots showed negligible influence on heat pulse data when the root fragments were positioned outside the HP measurement region (more than probe space away from heater probe), or root diameters (d) were less than 1 mm, or in oven-dried soil samples. On relatively wet soils (i.e., with water content of 0.05–0.25 m3 m−3), when root fragments were located in between the heater and sensing probes (parallel to the probe planes), (1) the heat capacity (C) and thermal conductivity (λ) differences between root-free soil and root-soil mixture increased proportionally with d increased from 1 mm to 4 mm; (2) the differences in absolute values of C and λ between the root-free soil and soil-root mixture were highly dependent on soil water content. The errors in soil C and λ estimates were larger when the root fragment was parallel with than perpendicular to or inclined 45 degrees to the probe plane, and the error overall decreased with a smaller ρb and sand fraction. When the root fragments were positioned within the HP measurement region, or d were larger than 1 mm, or in relatively wet soil samples, it is important to consider root effect when interpreting HP signals.

Mycorrhizal fungi-mediated uptake of tree-derived nutrients by crops – the role of tree-maintained versus crop-associated fungal mycelia

Arbuscular mycorrhizal (AM) fungi translocate nutrients within agroforestry systems but the role of common mycorrhizal fungal networks (CMNs) is unclear. We compared AM fungi-mediated nutrient transfer from mango versus faidherbia trees to maize plants to understand how to foster the AM symbiosis for enhanced agroecosystem sustainability. In mesocosms we applied 15N and 33P tracers via tree stem injection or root-free soil labeling compartments to test tree-to-maize versus soil-to-maize nutrient transfer via AM fungi. Maize plants grew in large in-growth cores with intact versus broken mycelia. Soil-to-maize transfer was assessed with and without trees to compare nutrient transfer via tree-maintained AM fungi i.e. CMNs versus maize-associated AM fungi. Tracer application via stem injection neither corroborated nor falsified our hypothesis of tree-to-maize nitrogen and phosphorus transfer. Soil-to-maize nutrient transfer occurred but was not enhanced by the presence of mango or faidherbia trees. Competition with maize plants for nitrogen but not phosphorus was greater with mango than faidherbia trees. Results from our experimental set-up provide neither evidence nor disproval for CMNs between two-year-old trees and ten-week-old maize plants. In the absence of trees and tree-maintained AM fungal mycelia maize plants developed their own AM fungal mycelia that mediated uptake of nutrients from beyond the maize plants’ rooting zones.

Response of bacterial communities to the application of sewage sludge biochar and Penicillium aculeatum in rhizosphere and bulk soil of wheat

The application of sewage sludge biochar (SSB) in agriculture is a promising solution for detoxifying and recycling the nutrient-rich sludge. However, knowledge is required on how SSB alone or in combination with biofertilizers influences the soil microbial communities. This work used a wheat pot experiment with a root free soil compartment to study effects of SSB and the phosphate-solubilizing Penicillium aculeatum on bacterial communities in wheat rhizosphere and bulk soil. Treatments were applied only to the root free soil compartment. Analysis by 16S rRNA gene amplicon sequencing showed that SSB increased the alpha diversity and induced taxon-specific shifts. These shifts occurred in both rhizosphere and bulk soil, and they were dominated by increased relative abundance of Gemmatimonadetes and Chloroflexi which were primarily explained by increases in soil P availability and soil pH, respectively. Application of P. aculeatum had smaller effects on bacterial communities and these effects occurred mainly in rhizosphere soil and were probably related to unidentified interactive rhizosphere processes. The combined application of SSB and P. aculeatum did not reveal any additive effects on the bacterial communities as compared to the sole application of SSB. Due to the different treatment effects on rhizosphere and bulk soil communities, the analysis of both soil compartments will provide a better understanding of interactions between biochar, soil, bacteria and plants.

An arbuscular mycorrhizal fungus alters soil water retention and hydraulic conductivity in a soil texture specific way

Arbuscular mycorrhizal fungi (AMF) alter plant water relations and contribute to soil structure. Although soil hydraulic properties depend on soil structure and may limit plant water uptake, little is known about how AMF influence soil water retention (the relation between the soil water content and soil water potential) and hydraulic conductivity in different soils. Instead, these soil hydraulic properties often are considered to be independent of AMF presence in experiments. We asked if this assumption holds true for both sand and loam. We grew maize plants either inoculated with Rhizophagus irregularis or with autoclaved inoculum in pots filled with quartz sand or loam soil until extraradical spread of the fungus throughout the pots was achieved. Each pot contained a hyphal compartment made of a soil sampling core (250 cm3) covered with a 20-µm nylon mesh to encourage fungus ingrowth but to exclude root ingrowth. We measured soil water retention and unsaturated hydraulic conductivity in these undisturbed root-free soil volumes. We observed that in loam harboring the mycorrhizal fungus, the soil water retention decreased, while in sand, it increased without detectable changes in the soil bulk density. The effects of the fungus on the soil water potential were strongest at low soil water contents in both soils. As a consequence of the altered water potentials in soils with the mycorrhizal fungus, soil hydraulic conductivity increased in loam but decreased in sand after fungus ingrowth. We conclude that in our study, the mycorrhizal fungus acted as a soil conditioner even distant from roots, which encouraged drainage in loams prone to sogginess but enhanced water storage in sands prone to quick desiccation. We recommend considering soil hydraulic properties as being dynamic in future studies on water relations of mycorrhizal plants.

The effect of chamber placement site on N2O emission under different fertilizer regimes from maize field

Static chamber method has been used to monitor greenhouse gas (GHG) emission from agricultural soils. When monitoring GHG emission in rice or wheat systems, all the plant stems can be covered in the top chamber. Under this situation, both nitrous oxide (N2O) emission from the root free soils and the root area soils can be estimated. However, in maize field, most of the studies placed the chamber within the maize row due to the difficulty to cover the whole maize stalk. N2O emission from the root area was not estimated since the majority of maize roots were excluded in the chamber. This may lead to a under estimation of global N2O emission from maize cultivation. To evaluate the spatial variability of N2O emission from maize field, a two-year field experiment was conducted. N2O emissions from three sampling sites including inter-rows, within-rows and root area were monitored under five different fertilization regimes. Results showed that chamber placement site had a significant effect on the N2O emission during the maize growing season. Placing the chamber in inter-rows either overestimated or underestimated N2O emission. In 2018, N2O emission rate in the inter-rows was 69 % higher than the root area on average of the five treatments; whereas, in 2020, N2O emission rate in the inter-rows was 2.5 times lower than the root area. N fertilization regimes had a significant effect on N2O emission. On average of chamber sites, N2O emission under N fertilizer broadcasting was around 2 times lower compared to nest-applied. The highest N2O emission rate was observed when both basal and dressing N fertilizer were applied in a nest, which was 1.1–3.2 times higher than the other N fertilizer placement regimes. The N2O emission rate from the within-rows was close to the average value of the three sampling sites. Our results suggested that placing chamber in the center of two neighboring maize plants could represent the average area-scaled N2O emission in maize field.

Response of soil aggregate stability and rill erodibility to soil electric field

Soil electric field (E0) might have strong effects on rill erosion, and it is in turn largely affected by root growth. This study aimed to quantify the ability of roots to predict E0 and elucidate the effects of E0 on the mean weighted diameter of soil aggregates (MWD) and rill erodibility (Kr). Samples were collected from three typical areas in the Loess Plateau of China, and each area had two typical grasslands. Soil detachment rates were measured using a hydraulic flume under five discharges (0.1, 0.2, 0.3, 0.4, and 0.6 L s−1) on a slope of 15°. The results indicated that plant roots negatively contributed to E0. The mean E0 of grasslands (rooted soil) was lower by 3.27 times compared with that of fallow lands (root-free soil). With significant correlation (P < 0.05), root length density (RLD) and root surface area density (RSAD) were found to be suitable parameters for predicting E0, which decreased exponentially with RLD (R2 = 0.306) and RSAD (R2 = 0.381). In addition, E0 strongly affected MWD and Kr by influencing soil repulsive forces. E0 was negatively correlated to MWD (logarithmic function, R2 = 0.96), but positively correlated to Kr (linear function, R2 = 0.88). Our results provide new insight into the mechanism of rill erosion considering plant roots.

Effect of different organic wastes on biological properties of maize (Zea Mays Indendata) rhizosphere

This study was carried in order to determine the effects different various organic wastes (tobacco prodction waste, wheat straw, tea waste and hazelnut husk) under greenhause conditions on biological properties (microbial biomass C, basal soil respiration, dehydrogenase activity, urease activity and arlysulphatase activity) in clay-loam soil and rhizosphere (Zea mays indandata) soil of maize plant. The organic wastes were thoroughly mixed with the soil at a rate equivalent to 50 g kg-1 on air-dried weight basis. Experimental desing was randomized plot desing with there replications in greenhause. The moisture content in soil was mantained around 60 % of maximum water holding capacity by weighing the pots everday. Changes in the biological properties were determined in the soil and rhizosphere (Zea mays indendata) samples and root free soil taken in 15, 30, 45, 60, 75 and 90 days after the experiment was conducted. At the end of experiment, all organic waste added soil increased biological properties of soil in comparison with the control (P<0.01) at all experimental periods. Moreover, biological properties in rhizosphere soil were higher than in root free soil at all organic waste application (P<0.01). Increased of organic wastes on soil biological properties had different trend (P<0.01), the most increases in the biological properties in the soil treated with tea wastes and tobacco production waste with supplying of low initial C/N ratio compared to other organic wastes.

The effect of tillage and no-tillage system on culturable fungal communities in the rhizosphere and soil of two spelt cultivars

A return to old species cultivated in the past, especially those with high health-promoting and nutritional values, such as spelt (Triticum aestivum ssp. spelta) is being increasingly observed. In addition, due to the increasing use of soil protective cultivation systems in recent years, such as no-tillage cultivation or direct sowing, the aim of the study was to assess the mycobiota of spelt rhizosphere and root-free soil, determine the ratio of potentially pathogenic to antagonistic fungi and assess the impact of cultivation systems on the frequency and biodiversity of fungi. The frequency and species composition were examined in 3-years cultivation of two spelt cultivars. The total number of rhizosphere fungi was significantly higher in the no-tillage system and under the spelt cultivar Franckenkorn compared to the tillage system and the cultivar Badengold. The species richness of the analyzed experimental variants was similar. The dominant group of fungi was the order Hypocreales (Ascomycota). Ninety-five percent of the fungal population from the rhizosphere and 88% of fungi from root-free soil belonged to rare (1–5%) or sporadic species (<1%). Taxa with higher frequency (>5%) in the rhizosphere included: Clonostachys, Gibellulopsis, Rhizopus and Sarocladium, Mortierella, Mucor, Penicillium, Sarocladium and Trichoderma. The cultivation system and plant cultivar affected the occurrence and distribution of fungal populations in the rhizosphere and root-free soil. The similarity of species composition of fungal communities in the rhizosphere and root-free soil was low, while taking into account species frequency, their diversity was high. The ratio of antagonistic to potentially phytopathogenic fungi of spelt rhizosphere deteriorated in the 2nd and 3rd year of wheat cultivation.

Do local-scale context dependencies shape how ectomycorrhizal fungal diversity structures with reduced or sustained experimental N addition?

Atmospheric nitrogen (N) pollution visibly and rapidly changes forest systems, for example impacting the diversity of forest ectomycorrhizal (EcM) fungi. EcM fungi are measurable by components that vary in longevity, hence, reflecting different temporal scales of presence: EcM root-tips are viable for, at most, a couple growing seasons, compared to fungal structures that may persist in soil as DNA for decades or longer. In-growth mesh bags, in contrast, typically capture a single growing season of hyphal growth. The different components might portray different diversity responses by EcM fungi to large-scale N pollution, as well as any subsequent reductions from improved environmental standards. Within an established oak forest study system, we examined the impact of sustained and recently reduced experimental N addition on EcM fungal diversity and composition, measured in three main fungal components (root-free soil, root-tips, and mesh bag hyphae). We hypothesized that elevated soil N would reduce EcM fungal diversity, and that composition would change, but with differences among fungal components related to the temporal longevity of the components. Our expectations were largely met, in that richness primarily declined with increased soil N, and all trends were most pronounced with the soil EcM fungi (the only component potentially reflective of long-term fungal presence). We discovered that abatement of the experimental N treatment did not revert fungal trends to those of the same-site plots with ambient N treatment. Instead, the stochastic nature of local-scale disturbances, related to invasive earthworms and forest stand dynamics, likely impacted N levels and, thus, EcM fungal trends. Due to the context-dependency of localized disturbance(s), assessing the effects of reduced large-scale N deposition on EcM fungi can prove to be challenging.

An experimental setup to prepare root-free mycorrhizal soil specimen for hydraulic conductivity measurement

An experimental setup to prepare root-free mycorrhizal soil specimen for hydraulic conductivity measurement

Organic carbon from graminoid roots as a driver of fermentation in a fen.

Fen Schlöppnerbrunnen is a moderately acidic methane-emitting peatland overgrown by Molinia caerulea and other wetland graminoids (e.g. Carex rostrata). Recently, the accumulation of H2, an indicator for fermentation, was observed with anoxically incubated C. rostrata roots but not with root-free fen soil. Based on this finding, we hypothesized that root-derived organic carbon has a higher capacity to promote fermentation processes than peat organic carbon from root-free fen soil. To address this hypothesis, C. rostrata and M. caerulea roots were anoxically incubated with or without fen soil and the product profiles of root treatments were compared with those of root-free soil treatments. Ethanol, acetate, propionate, butyrate, H2 and CO2 accumulated in root treatments and collective amounts of carbon in accumulating products were 20-200 times higher than those in root-free soil treatments, in which mainly CO2 accumulated. Analyses of 16S rRNA and 16S rRNA gene sequences revealed that Clostridium, Propionispira and Rahnella, representatives of butyrate, propionate and mixed acid fermenters, respectively, were relatively enriched in root treatments. In contrast, differences of the microbial community before and after incubation were marginal in root-free soil treatments. Collectively, these findings supported the assumed stimulatory effect of root-derived organic carbon on fen fermenters.

Long-term measurements in a mixed-grass prairie reveal a change in soil organic carbon recalcitrance and its environmental sensitivity under warming.

Soil respiration, the major pathway for ecosystem carbon (C) loss, has the potential to enter a positive feedback loop with the atmospheric CO2 due to climate warming. For reliable projections of climate-carbon feedbacks, accurate quantification of soil respiration and identification of mechanisms that control its variability are essential. Process-based models simulate soil respiration as functions of belowground C input, organic matter quality, and sensitivity to environmental conditions. However, evaluation and calibration of process-based models against the long-term in situ measurements are rare. Here, we evaluate the performance of the Terrestrial ECOsystem (TECO) model in simulating total and heterotrophic soil respiration measured during a 16-year warming experiment in a mixed-grass prairie; calibrate model parameters against these and other measurements collected during the experiment; and explore whether the mechanisms of C dynamics have changed over the years. Calibrating model parameters against observations of individual years substantially improved model performance in comparison to pre-calibration simulations, explaining 79-86% of variability in observed soil respiration. Interannual variation of the calibrated model parameters indicated increasing recalcitrance of soil C and changing environmental sensitivity of microbes. Overall, we found that (1) soil organic C became more recalcitrant in intact soil compared to root-free soil; (2) warming offset the effects of increasing C recalcitrance in intact soil and changed microbial sensitivity to moisture conditions. These findings indicate that soil respiration may decrease in the future due to C quality, but this decrease may be offset by warming-induced changes in C cycling mechanisms and their responses to moisture conditions.

COMPARATIVE DISSIPATION OF ANTHRACENE AND PHENANTHRENE IN A PRISTINE TYPIC HAPLUDOLL SOIL

Polycyclic aromatic hydrocarbons (PAHs) are of great environmental concern due to their widespread occurrence and persistence. Anthracene and phenanthrene (C14H10) are two priority pollutants that are found in high concentrations in PAHs-contaminated surface soils. The objective of this study was to analyze the capability of endogenous soil microorganisms of a pristine soil of the Pampas region, Argentina, to dissipate two isomers: anthracene and phenanthrene. Nutrient availability and the effects of ryegrass (Lolium perenne L.) on these PAHs´ dissipation were also evaluated. After 100 days, both contaminants were significantly degraded in root-free soils by autochthonous microorganisms. L. perenne significantly enhanced microbial degradation. The dissipation of both pollutants in the rhizosphere was accompanied by higher values of total bacteria counts at the end of the experimental period. No biostimulation effect was observed. In all cases, the dissipation of phenanthrene was significantly higher than anthracene. These results point to the important role of indigenous PAH degrading microorganisms, even present in a non-polluted soil.

Core-labelling technique (CLT): a novel combination of the ingrowth-core method and tracer technique for deep root study

BackgroundIngrowth-core method is a useful tool to determine fine root growth of standing crops by inserting root-free soil in mesh-bags for certain period of time. However, the root density observed by the method does not directly explain the nutrient uptake potential of crop plants as it varies over soil depth and incubation time. We have inserted an access-tube up to 4.2 m of soil depth with openings directly under crop plants, through which ingrowth-cores containing labelled soil with nutrient tracers were installed, called core-labelling technique (CLT). The main advantage of CLT would be its capacity to determine both root density and root activity from the same crop plants in deep soil layers. We tested the validity of the new method using a model crop species, alfalfa (Medicago sativa) against three depth-levels (1.0, 2.5 and 4.2 m), three sampling spots with varying distance (0–0.36, 0.36–0.72 and > 5 m from core-labelled spot), two sampling times (week 4 and 8), and two plant parts (young and old leaves) under two field experiments (spring and autumn).ResultsUsing CLT, we were able to observe both deep root growth and root activity up to 4.2 m of soil depth. Tracer concentrations revealed that there was no sign of tracer-leakage to adjacent areas which is considered to be advantageous over the generic tracer-injection. Root activity increased with longer incubation period and tracer concentrations were higher in younger leaves only for anionic tracers.ConclusionsOur results indicate that CLT can lead to a comprehensive deep root study aiming at measuring both deep root growth and root activity from the same plants. Once produced and installed, the access-tubes and ingrowth-cores can be used for a long-term period, which reduces the workload and cost for the research. Therefore, CLT has a wide range of potential applications to the research involving roots in deep soil layers, which requires further confirmation by future experiments.

Nitrogen Fixation and Resorption Efficiency Differences Among Twelve Upland and Lowland Switchgrass Cultivars

In nitrogen (N)-limited terrestrial ecosystems, plants employ various strategies to acquire and conserve N, including translocation of N in perennial tissues and stimulation of N fixation in roots and soils. Switchgrass (Panicum virgatum) is a genotypically and phenotypically diverse perennial grass with two distinct ecotypes (lowland and upland) and numerous genotypes. It grows well in low-N soils, likely because of its ability to translocate N and to associate with N-fixing microbes, but little is known about variation in these traits among cultivars or even ecotypes. We measured N translocation, N fixation potential in roots and soils, soil net N mineralization, soil net nitrification, and biomass yields in 12 switchgrass cultivars grown in a replicated block experiment in southwestern Michigan, United States. Lowland cultivars had higher yields, rates of N translocation, soil net N mineralization, and N fixation potentials on washed, nonsterile roots, while upland cultivars exhibited higher N fixation potentials in root-free soil. N resorption efficiencies averaged 53 ± 5% (± standard error) for lowland versus 29 ± 3% for upland cultivars. Additionally, there were significant among-cultivar differences for all response variables except mineralization and nitrification, with differences likely explained by cultivar-specific physiologies and microbial communities. The ideal cultivar for biofuels is one that can maintain high yields with minimal fertilizer addition, and there appear to be several cultivars that meet these criteria. In addition, results suggest substantial N cycle differences among cultivars that might be exploited by breeders to create new or improved high-yielding, N-conserving switchgrass lines.

Root effects on the temperature sensitivity of soil respiration depend on climatic condition and ecosystem type

Root activity may alter the temperature sensitivity (Q10) of soil respiration. However, we lack a comprehensive understanding of root effects on Q10 across different climatic regions and ecosystem types. Here, we conducted a global synthesis of 87 observations of Q10 values of soil respiration and its components from 40 published studies. We found that roots significantly enhanced Q10 of soil respiration because root and rhizosphere respiration was more temperature-sensitive than the respiration of root-free soil, especially in cold regions (mean annual temperature <10 °C). Moreover, roots significantly enhanced Q10 of soil respiration in grassland and cropland but not in forest ecosystems. Overall, our results suggest that the positive effects of roots on Q10 largely depend on climatic condition and ecosystem type, and are potentially useful for parameterizing and benchmarking biogeochemical and Earth system models.

How does root biodegradation after plant felling change root reinforcement to soil?

Previous studies have shown that root reinforcement provided by trees could decrease over time after stem cutting. The short-term changes in root mechanical and structural traits associated with root reinforcement after stem cutting have not been fully studied. We aimed to quantify the temporal changes in root mechanical and structural traits following stem cutting, and to identify the major drivers of root reinforcement deterioration. At six elapsed times (zero, one, three, six, nine, and twelve months) after stem cutting of the species Symplocos setchuensis Brand, we measured shear strength for both rooted and root free soils, root failure modes, root mechanical traits (tensile strength, Young’s modulus, and tensile strain) and structural traits (cellulose, hemicellulose and lignin contents). Both root mechanical and structural traits significantly differed as a function of root diameter and time after stem cutting. Tensile strength decreased 19.7% while Young’s modulus decreased 46.9% twelve months after stem cutting. Hemicellulose content showed the greatest decrease (45.3%) among the structural traits. The relative reduction in magnitude was higher for fine roots than coarse roots. Additional shear strength (at the yield point) provide by roots decreased 85.9% twelve months after stem cutting. Our findings demonstrate a higher rate of root reinforcement deterioration after stem cutting than previously reported in literatures. Our results suggest that the underlying mechanism of deterioration of root reinforcement is more likely caused by a shift of root failure from tensile breakage to slide-out failure, and a decline in root Young’s modulus.

Quantifying effects of root systems of planted and natural vegetation on rill detachment and erodibility of a loessial soil

The objectives of this study were to evaluate different root parameters for estimating rill detachment, and to compare and quantify the effectiveness of planted and natural vegetation on soil physical characteristics and in reducing rill detachment and erodibility. Laboratory-concentrated-flow flume tests were performed under a flow discharge of 3 L min−1 and a slope of 15° with intact soil samples. A silt loam soil (Calcic Cambisol, in Loess Plateau in China) was sampled in 2015 from laboratory with planted ryegrass (Lolium perenne L.) and in 2014 from natural vegetation fields under 12 to 36-a restoration. The results indicated that root length density was the best parameter for estimating the effects of roots on rill detachment and erodibility for both planted ryegrass and natural vegetation, with exponential reduction equations. The exponents were more negative for natural vegetation (−0.411) than for planted species (−0.217) because of the existence of more complex root networks under more diverse natural vegetation. Rill erodibility of soil samples with roots decreased exponentially from the baseline erodibility of the root-free soil as RLD increased. Root systems of the restored natural vegetation ameliorated soil characteristics (bulk density, aggregate stability and organic matter content) more profoundly than those of the laboratory tests due to stronger bonding and binding effects, resulting in a lower absolute soil detachment rate for a given root density. There existed a vertical decay distribution pattern of root densities with soil depth for natural vegetation and planted ryegrass, and this distribution of root systems reached a steady state after 12 years natural vegetation restoration. More vegetation types under more different hydraulic conditions should be evaluated in future studies to provide better scientific bases for modelling their impacts on rill detachment and erodibility.

Grassland Management Influences the Response of Soil Respiration to Drought

Increasing soil carbon stocks in agricultural grasslands has a strong potential to mitigate climate change. However, large uncertainties around the drivers of soil respiration hinder our ability to identify management practices that enhance soil carbon sequestration. In a context where more intense and prolonged droughts are predicted in many regions, it is critical to understand how different management practices will temper drought-induced carbon losses through soil respiration. In this study, we compared the impact of changing soil volumetric water content during a drought on soil respiration in permanent grasslands managed either as grazed by dairy cows or as a mowing regime. Across treatments, root biomass explained 43% of the variability in soil respiration (p &lt; 0.0001). Moreover, analysis of the isotopic composition of CO2 emitted from the soil, roots, and root-free soil suggested that the autotrophic component largely dominated soil respiration. Soil respiration was positively correlated with soil water content (p = 0.03) only for the grazed treatment. Our results suggest that the effect of soil water content on soil respiration was attributable mainly to an effect on root and rhizosphere activity in the grazed treatment. We conclude that farm management practices can alter the relationship between soil respiration and soil water content.