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Splash is an essential process in interrill erosion because it detaches soil fragments from their substrate and transports them. However, splash measurements are difficult to interpret and relatively little is known about the influence of particle characteristics on the spatial distribution of splash. The objective of this work is to study the splash distribution of different size fractions for aggregated soils. We used a recently proposed theory for spatial distribution by splash to interpret experimental data on the radial distribution of soil fragments splashed by simulated rainfall. A laboratory device with five concentric rings was used to determine average splash lengths for 16 fragment size fractions (0.05 to > 2000 [micro]m) of four soils. Sieved soil (3- to 5-mm size fraction) was exposed to simulated rainfall at 29 mm [h.sup.-1] and with a time-specific kinetic energy of 252 J [m.sup.-2] [h.sup.-1]. We interpreted the measured masses of fragments splashed into the different rings using an approximate solution of the exponential splash distribution theory applied to the experimental design. We demonstrated that the theory is valid for bulk aggregated soil as well as for individual fragment size fractions. The derived average splash lengths ranged from 4 to 23 cm, depending on the fragment size and soil. Splash lengths were greatest for soil fragments of 100 to 200 [micro]m, and decreased for finer and coarser size fractions. Comparison of these findings with physically-based theory suggests that the coarser fragments, 50 to 2000 [micro]m, are transported as single airborne particles, whereas the smaller ones,

Various interactions, particularly those existing between the rainfall intensity, the slope gradient, the slope length, and the tillage supposedly can affect the runoff features for interrill erosion. Despite numerous studies, their effect on runoff production and pathways and the resulting soil losses have seldom been analyzed. This is especially true under field and tillage conditions. This study investigated the effect of rainfall intensity, slope length, and gradient on runoff amount and pathways for interrill erosion in tilled fields. Runoff features and soil losses were evaluated on bounded plots of 1- and 5-m length located on 4 to 8% slope gradients, and under natural and simulated rainfalls with intensities ranging from 1.5 to 30 mm [h.sup.-1]. Runoff coefficients (R) ranged from 34 to 98% whereas sediment concentrations (SC) varied from 2.9 to 49 g [l.sup.-1]. The runoff coefficient was affected by all three factors: rainfall intensity (r = 0.48; P < 0.0001), slope gradient (r = 0.51; P < 0.0001) and slope length (r = 0.29; P = 0.02); whereas SC was correlated with only rainfall intensity (r = 0.48; P < 0.0001) and slope length (r = 0.44; P = 0.0004). The runoff coefficient and SC ratios between 1- and 5-m long plots were systematically greater for the intermediate rainfall intensity. Runoff features mainly affected by tillage implements may explain higher interrill erosion at longer and steeper slopes. Lower differences between 1- and 5-m plots at high rainfall intensity may reflect greater ponded runoff absorbing raindrop kinetic energy and lowering detachment and transport processes. Finally, the effects of rainfall intensity, slope length, and gradient and tillage are discussed in respect of possible erosion processes operating in the experiments.

Soil surface crusts and seals reduce soil infiltration rate, increase soil strength, and may increase erosion by increasing runoff. Among the most important factors determining amounts of erosion are the soil chemical and physical properties that determine soil sealing and erodibility. Soil splash and wash erosion, runoff, and splash volume were measured for 17 soils, which ranged in clay content from 80 to 360 g kg to the -1, exchangeable sodium percentage (ESP) from

The structural stability of soil is a physical characteristic that affects soil degradation processes. Calcium‐based amendments, such as calcium carbonate, calcium sulfate, and calcium oxide/hydroxide, have been shown to improve the stability of soil aggregates. This study seeks to determine which calcium‐based soil amendments, and at what concentration, are the most efficient in improving aggregate stability of sandy topsoils derived from granitic and metamorphic parent materials, and to analyze the mechanisms involved. In the pot experiment, soils amended with CaCO3, CaCl2, and CaSO4 did not present significant differences in aggregate stability compared to the control or among each other. In contrast, Ca(OH)2 soil amendment brought the greatest stability to the soil aggregates. A dose of 1% Ca(OH)2 significantly increased the stability of soil aggregates. This effect is due to the reaction of Ca(OH)2 with atmospheric CO2 which leads to the formation of CaCO3, a delayed reaction not showed by the other soil amendments tested. Likewise, the greater solubility of Ca(OH)2 compared to CaCO3 exerts a greater aggregation effect on soil. Thus, the mechanism of action of Ca(OH)2 is related to cementation, rather than flocculation. Future studies should be carried out to demonstrate the effectiveness of Ca(OH)2 under field conditions. [ABSTRACT FROM AUTHOR]

Abstract: Using concepts of connectivity in challenges regarding land and water management (flooding, erosion, nutrient leaching, landslides) can only be fully harnessed if knowledge is communicated well between scientists and stakeholders. Proper communication requires prior understanding of end‐users' perception of connectivity as a useful framework. Therefore, we analysed (a) perceptions of ‘connectivity’ for stakeholders involved in water and land management across Europe, (b) potential for stakeholders to apply connectivity‐related measures in their management decisions, (c) stakeholders' biggest challenges in water and land management, and (d) stakeholders' expectations for future connectivity research agendas. We studied 85 questionnaires from 19 countries using a grounded theory approach. One third of stakeholders understood connectivity in its scientific context, whereas 39% perceived connectivity indirectly through their personal experiences (e.g., water and sediment fluxes and erosion). Half of stakeholders' perceived links and challenges were related to availability of data and methods, communication, and institutions or policy, whereas others believed they were related to water quality and quantity, soil erosion and quality, and climate change. Half of the stakeholders considered connectivity management important, and one third showed high interest in managing connectivity. Adopting connectivity into management is hindered by institutional‐ and policy‐based management limitations, insufficient data and methods, and ineffective knowledge transfer. Explicitly considering heterogeneity of stakeholder perceptions is required for projects regarding management of connectivity at European, national, and local scales. [ABSTRACT FROM AUTHOR]

Abstract: Soil resources are important for the socioeconomic development of the Mediterranean area. Their durability may be threatened because of intense erosion processes that result in severe degradation in the field (on‐site effects) and downstream degradation (off‐site effects). Based on the literature and results obtained during several research projects, this paper presents the main lessons and challenges dealing with Mediterranean soil resources under global change. After a review of the main drivers of Mediterranean soil erosion and the main impacts of water erosion processes, the paper highlights that the nature and intensity of active erosion processes are as diverse as the mosaic of the Mediterranean landscape. It then discusses the expected evolution of Mediterranean soil resources under global change and illustrates the prevalent influences of land use (partly depending on climatic constraints) on the evolution of erosion risk and soil vulnerability. Finally, it details some main challenges for the future of Mediterranean soil resources dealing with a better knowledge of factors and processes involved in soil erosion, a better evaluation of soil vulnerability through a combined quantitative and qualitative soil erosion approach, and the need for a site‐specific conservation strategy for Mediterranean soil resources. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Shrink-swell soils, such as those in a Mediterranean climate regime, can cause changes in terms of hydrological and erosive responses because of the changing soil water storage conditions. Only a limited number of long-term studies have focused on the impacts on both hydrological and erosive responses and their interactions in an agricultural environment. In this context, this study aims to document the dynamics of cracks, runoff and soil erosion within a small Mediterranean cultivated catchment and to quantify the influence of crack processes on the water and sediment supplied to a reservoir located at the catchment outlet using water and sediment measurements at a cultivated field outlet as baseline. Detailed monitoring of the presence of topsoil cracks was conducted within the Kamech catchment (ORE OMERE, Tunisia), and runoff and suspended sediment loads were continuously measured over a long period of time (2005-2012) at the outlets of a field (1.32 ha) and a catchment (263 ha). Analysis of the data showed that topsoil cracks were open approximately half of the year and that the rainfall regime and water table level conditions locally control the seasonal cracking dynamics. Topsoil cracks appeared to seriously affect the generation of runoff and sediment concentrations and, consequently, sediment yields, with similar dynamics observed at the field and catchment outlets. A similar time lag in the seasonality between water and sediment delivery was observed at these two scales: although the runoff rates were globally low during the presence of topsoil cracks, most sediment transport occurred during this period associated with very high sediment concentrations. This study underlines the importance of a good prediction of runoff during the presence of cracks for reservoir siltation considerations. In this context, the prediction of cracking effects on runoff and soil erosion is a key factor for the development of effective soil and water management strategies and downstream reservoir preservation. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Reservoir siltation because of water erosion is an important environmental issue in Mediterranean countries where storage of clear surface water is crucial for their economic and agricultural development. The high density of gully systems observed in Mediterranean regions raises the question of their contribution to reservoir siltation. In this context, this study quantified the absolute and relative contributions of rill/interrill and gully/channel erosion in sediment accumulation at the outlet of small Tunisian catchments (0·1-10 km2) during the last 15 years (1995-2010). To this end, a fingerprinting method based on measurements of caesium-137 and total organic carbon combined with long-term field monitoring of catchment sediment yield was applied to five catchments in order to cover the diversity of environmental conditions found along the Tunisian Ridge and in the Cape Bon region. Results showed the very large variability of erosion processes among the selected catchments, with rill/interrill erosion contributions to sediment accumulated in outlet reservoirs ranging from 20 to 80%. Overall, rill/interrill erosion was the dominant process controlling reservoir siltation in three catchments whereas gully/channel erosion dominated in the other two catchments. We identified the presence of marly gypsum substrates and the proportion of catchment surface covered by soil management/conservation measures as the main drivers of erosion process variability at the catchment scale. These results provided a sound basis to propose guidelines for erosion mitigation in these Mediterranean environments and suggested to apply models simulating both rill/interrill and gully/channel erosion in catchments of the region. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The spatial distribution of land management practices (LMPs), such as the use of vegetated filters, may have a strong impact on their efficiency in trapping sediments and pollutants. Distributed water erosion models help managers, planners, and policymakers optimize the efficiency of these LMPs regarding their location relative to water and sediment pathways. In this work, the authors analyzed the impact of the spatial distribution of LMPs using an existing distributed model and sensitivity analysis procedures. The distributed model that was used is a distributed single-event physically based water erosion model developed to calculate erosion rates and sediment flow for small (less than 10 km²) agricultural catchments. To measure the impact of the spatial distribution of LMPs, the authors developed a stochastic model that generates LMP locations over the entire catchment. The stochastic model has three input parameters: the density of LMPs, their downslope/ upslope location probability, and the probability density function shape controller. Because of its ability to account for the cross effects between parameters, the variance-based Sobol method was used to calculate the sensitivity of the soil loss ratio of a typical Mediterranean agricultural catchment (Roujan, southern France) to the LMP locationmodel parameters. Threemeasurement points (two subcatchment outlets and themain outlet) were used to examine the spatially distributed effects of the LMP locations. The simulation results indicated that 70% of the variation of the net erosion is explained by variations in LMP density for the main outlet catchment, making LMP density the most sensitive parameter. However, the total Sobol sensitivity indices indicate a strong interaction among the three parameters when the density values are low (few LMPs are applied). Thus, although the density of the LMPs is themost sensitive parameter, their locationmay influence their global trapping efficiency in (real) cases where few LMPs are applied. [ABSTRACT FROM AUTHOR]

Aggregate stability is a key property affecting the movement and storage of water, seedling emergence, and soil sensitivity to erosion. Many studies have shown that aggregate stability changes through time. Field monitoring studies performed with a relatively large (monthly) time step showed the seasonal trend of aggregate stability. However, shorter time step monitoring is required to explore dynamics of aggregate stability at short term. For now, biological activity was recognized to be the main factor of aggregate stability dynamics, but previous studies were currently based on the external stimulation of aggregate stability. The objectives of this study were to assess variations in aggregate stability at short time steps in the field and to identify the factors controlling these variations of stability. A 6-mo field monitoring was performed at short time step (2-5 d) on a bare field of Luvisol without organic amendment. Aggregate stability was measured for both on surface and subsurface materials by the ISO 10930 (2012) method. Rain amount and intensity, air temperature and humidity, soil temperature, water content and hydric history, and soil water repellency were measured as explanatory factors. The results showed that aggregate stability varied greatly (up to 40%) over a few days for both surface and subsurface. Short term dynamics of aggregate stability were already shown by laboratory experiments, but such dynamics was never observed in the field for a bare soil without external stimulation of biological activity. For the surface, short time step variations of surface aggregate stability were primarily controlled by soil water content (WC0 and WC1/2), hydric history (ΔWC4 and API), and rain intensity. While large changes in aggregate stability were found for the subsurface, explanatory factors remain to be found. [ABSTRACT FROM AUTHOR]

Because soil surface structure has a considerable influence on infiltration rate, the sealing process is postulated to have a significant effect on herbicide loss through runoff. We evaluated the effect of degraded soil surface structures on herbicide loss in runoff, and used the experimental data to test the uniform mixing zone concept and two‐site sorption kinetics for modeling herbicide transfer to runoff. The experiments were done with simulated rainfall on 10‐m2 plots in the field and 0.25‐m2 plots in the laboratory after a surface application of 1.5 kg ha−1 of isoproturon [3‐(4‐isopropylphenyl)‐1,1‐dimethylurea] and 0.187 kg ha−1 of diflufenican [2′,4′‐difluoro‐2‐(α,α,α‐trifluoro‐m‐tolyloxy) nicotinanilide]. Isoproturon (IPU) and diflufenican (DFF) concentrations were very high in the first runoff (up to 60 mg L−1 for IPU and 2 mg L−1 for DFF) when simulated rainfall was applied 24 h after the treatment. The concentrations decreased very rapidly with total rainfall depth. Degradation of the structural state of the soil surface increased the ratio of pesticide loss to application rate from 0.3 to 10% for IPU and from 0.7 to 7.8% for DFF for a runoff depth of less than 1 mm. The structural state of the soil surface influences the rapidity at which runoff begins after the onset of rain, and the runoff coefficient at steady state. Furthermore, the development of a surface seal seems to limit the depth of soil–runoff interaction and thus influences the dynamics of herbicide mobilization. Concentrations of IPU in the runoff were satisfactorily described with a model incorporating a uniform mixing zone and two‐site sorption–desorption. [ABSTRACT FROM AUTHOR]

Wildfire is known to create the pre-conditions leading to accelerated soil erosion. Unfortunately, its occurrence is expected to increase with climate change. The objective of this study was to assess the impacts of fire on runoff and soil erosion in a context of global change, and to evaluate the effectiveness of mulching as a post-fire erosion mitigation measure. For this, the long-term soil erosion model LandSoil was calibrated for a Mediterranean catchment in north-central Portugal that burnt in 2011. LandSoil was then applied for a 20-year period to quantify the separate and combined hydrological and erosion impacts of fire frequency and of post-fire mulching using four plausible site-specific land use and management scenarios (S1. business-as-usual, S2. market-oriented, S3. environmental protection and S4. sustainable trade-off) and an intermediate climate change scenario Representative Concentration Pathway (RCP) 4.5 by 2050. The obtained results showed that: (i) fire had a reduced impact on runoff generation in the studied catchment (<5%) but a marked impact on sediment yield (SY) by about 30%; (ii) eucalypt intensification combined with climate change and fires can increase SY by threefold and (iii) post-fire mulching, combined with riparian vegetation maintenance/restoration and reduced tillage at the landscape level, was highly effective to mitigate soil erosion under global change and associated, increased fire frequency (up to 50% reduction). This study shows how field monitoring data can be combined with numerical erosion modeling to segregate the prominent processes occurring in post forest fire conditions and find the best management pathways to meet international goals on achieving land degradation neutrality (LDN). [ABSTRACT FROM AUTHOR]

The objective of this study was to address the role of gully erosion on sediment delivery at the catchment scale by assessing the contribution of gullies to the total sediment yield at the outlet of the Kamech (Cape Bon, Tunisia), which is a small cultivated catchment in the Mediterranean environment. The methodology was based on the long-term analysis of the evolution of gully volume, and the total volume of sediment that reached the catchment outlet. The evolution of gully volume was assessed by field surveys and image analysis. The total volume of sediment was calculated using intensive field monitoring of the runoff and erosion in the reservoir at the catchment outlet. The contribution of gullies to the total flux of sediment that reached the catchment outlet was estimated to be less than 30%. This means that siltation of the reservoir was mainly due to erosion processes other than gully erosion, i.e., topsoil erosion processes such as rill and interrill erosion in cropland areas. This result was consistent with a previous independent estimation of the apportionment of gully and topsoil erosion sources conducted at the same site using the fingerprinting approach. Therefore, the study confirms that, even in a heavily eroded agricultural catchment area with a dense network of gullies, gully erosion nevertheless accounted for less than 30% of the total erosion balance. The results also showed that the cumulated gully length has decreased in the last fifty years, thus revealing the declining role of gullies. However, the decrease in gully activity could not be linked to an isolated factor. Complementary observations, such as the appearance of vegetation in the permanent gullies and the decrease in the percentage of active gullies, showed that the degree of hydro-sedimentary connectivity in the Kamech catchment has probably entered a decreasing phase. We also analysed the potential use of historical aerial images for studying gully erosion. We found that these images were useful for calculating accurate ortho-photography but failed to provide a DEM with the precision required to measure the historical volume of gullies. [ABSTRACT FROM AUTHOR]

Abstract: Aggregate stability often exhibits a large inter-annual and seasonal variability which occurs regardless of residue treatments and is often larger than the differences between soils or cropping systems. Variations in soil moisture and seasonal stimulation of microbial activity are frequently cited as the major causes. The goal of this paper was to evaluate the effects of drying–rewetting cycles on aggregate stability and on its main microbially mediated agents from a mechanistic point of view. The 3–5mm aggregates of a silty soil were incubated at 20°C for 63 days with the following treatments and their combinations: (i) with or without straw input and (ii) with or without exposure to four dry–wet cycles. Microbial activity was followed by measuring the soil respiration. We estimated the microbial agents of aggregate stability measuring hot-water extractable carbohydrate-C, microbial biomass carbon and ergosterol content. We measured the water drop penetration time to estimate the hydrophobicity and aggregate stability according to Le Bissonnais [1996. Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology. European Journal of Soil Science 47, 425–437] to distinguish three breakdown mechanisms: slaking, mechanical breakdown and microcracking. The addition of straw stimulated microbial activity and increased the resistance to the three tests of aggregate stability, enhancing the internal cohesion and hydrophobicity of aggregates. All the estimated microbial agents of aggregate stability responded positively to the addition of organic matter and were highly correlated with aggregate stability. Fungal biomass correlated better with aggregate stability than total microbial biomass did, showing the prominent role of fungi by its triple contribution: physical entanglement, production of extracellular polysaccharides and of hydrophobic substances. Dry–wet cycles had less impact on aggregate stability than the addition of straw, but their effects were more pronounced when microbial activity was stimulated demonstrating a positive interaction. [Copyright &y& Elsevier]

Soil aggregate stability is a key factor in soil resistance to water erosion, which is a threat to soils in a large part of northern Tunisia. The analysis of the spatial variability of soil aggregate stability provides both agronomic and environmentally useful information. However, extensive measurements of soil aggregate stability remain tedious and expensive. This study explores two different approaches as alternative to measurements of soil aggregate stability. One approach estimated aggregate stability via laboratory measurements of soil elementary properties using multiple linear regressions known as pedotransfer functions. The second approach, which is methodologically innovating, was based on the geological pattern as a proxy for aggregate stability using regression-kriging analysis. A set of 113 soil samples from an 800 km 2 agricultural region that included the Lebna watershed (Cap Bon, Tunisia) were collected from the soil surface layer (0–10 cm depth). Samples were analyzed for elementary properties (i.e., soil texture, total carbon and nitrogen, iron, CaCO 3 , salinity, CEC and pH) and for soil aggregate stability according to the normalized method (ISO/DIS 10930, 2012), which considers three indexes (MWD) calculated for three contrasted wetting conditions and disruptive energies. Most soils in the study area were non-salted with an alkaline pH and relatively low organic carbon content. Of the soils, 35% were clay soils, and 55% had a balanced soil texture. The average of the three soil aggregate stability indexes (MWD mean ) ranged from 0.38 to 2.80 mm, and this property showed large variability from instable soils to very stable ones. Analysis of pedotransfer functions determined that the best predictor variables for soil aggregate stability were silt, organic matter and iron. Geostatistical analyses at the regional scale showed spatially structured soil aggregate stability (variograms with sills reaching a 5 km distance). Using geological information as ancillary data, the prediction of soil aggregate stability with regression-kriging was similar to that of pedotransfer functions. A regression-kriged map of soil aggregate stability associated with a map of prediction uncertainties was developed. The resulting maps and methods of this study can be useful in the development of management options that minimize water erosion risks in the studied area. [ABSTRACT FROM AUTHOR]

Soil aggregates are organomineral associations with a fundamental importance for soil structure and function. Litter from vegetation alters aggregate formation and stability, and polyphenols such as tannins found in leaves, roots and wood play an important role in soil biogeochemical and biological processes. However, the effect of tannins on soil physical properties remains largely unexplored. We hypothesized that tannins influence aggregate stability through their ability to (i) complex proteins in the soil and (ii) perturb the gelling property of root mucilage. Therefore, Mediterranean soil aggregates were incubated with condensed tannins, either as a pure substrate or in combination with a standard protein (bovine serum albumin, BSA) and with a model root mucilage polysaccharide (polygalacturonic acid, PGA) able to form gel-like structures with divalent cations (notably Ca 2+ ) widely present in Mediterranean calcareous soils. The changes in aggregate stability were monitored under controlled conditions, immediately after the addition of tannins, after 2 weeks, 3 and 6 months of incubation. Tannins added alone did not yield a significant effect on aggregate stability. However, modulatory effects were found when combinations of treatments occurred. Tannins positively modulated the stabilizing effect of the BSA, giving credit to our hypothesis on the stabilizing role of the tannin-protein complex forming macromolecules, thus enforcing soil particle cohesion within aggregates. However, tannins negatively altered the stabilizing effect of PGA, suggesting that the expected perturbation of the PGA gelation occurred, with detrimental consequences for aggregate stability. Over time, tannins maintained the effect of BSA, suggesting a protective effect of tannins, possibly linked to their ability to slow down the degradation of nitrogen compounds through protein binding. Overall, we showed that tannins reacted with other organic compounds resulting in specific effects on physical soil properties, thus demonstrating that tannins in soils play a role beyond their effects on biogeochemical aspects. [ABSTRACT FROM AUTHOR]

Abstract: Inappropriate agricultural land management practices cause irreversible soil losses in many parts of Europe. Soil degradation is predicted to increase in the next future as an effect of climate and cropping system changes. The most concerned areas are expected to be those already severely affected by erosion, as is the whole of the Mediterranean. Medium-term soil erosion models could be useful tools to analyse, understand and simulate complex interactions between geomorphic processes and human pressures for better assessment of medium-term soil redistributions associated with land use and landscape design change. The aim of this study was to compare the effects of various agricultural land uses and landscape design strategies on water and tillage erosion. The first step was to develop land use and landscape design scenarios of an agricultural Mediterranean landscape. Then, all of the scenarios were compared in terms of the soil redistribution using the LandSoil model. The results indicate that potential soil conservation associated with the adoption of sustainable land uses surpasses the potential conservation associated with certain landscape design. A detailed analysis of within-landscape soil redistributions suggests that land use is a major factor controlling sediment production, whereas landscape design is a major factor controlling hillslope connectivity. [Copyright &y& Elsevier]

Abstract: The modeling of soil erosion by water supposes an accurate and thorough understanding of the hydrology. Thus, it is critical to have a good delineation of the surface flow path. The flow network data are critical for important uses such as flood forecasting and watershed management. Geographic Information System (GIS) functions are able to compute a flow network directly from the digital elevation models. Because the flow directions are only based on the topography, the other factors controlling the flow directions are overlooked. In the agricultural areas, work such as tillage can have a large impact on the flow direction. We propose a 5-step procedure to account for such man-made features. The use of this procedure clearly improves the quality of the computed flow network. This procedure has been successfully implemented in a GIS and improves the prediction of surface flow and therefore improves water erosion modeling at the watershed scale. [Copyright &y& Elsevier]

Soil aggregates are critical to soil functionality, but there remain many uncertainties with respect to the role of biotic factors in forming aggregates. Understanding the interacting effects of soil, land use type, vegetation and microbial communities is a major challenge that needs assessment in both field and controlled laboratory conditions, as well as in bulk and rhizosphere soils. To address these effects and their feedbacks, we first examined the influence of soil, root and litter characteristics along a land use gradient (ancient woodland, secondary woodland, grassland, pasture and arable land) on microbial community structure (in both bulk and rhizosphere soil), as well as on aggregate stability. Then, we performed an inoculation experiment where we extracted soil columns from the arable and secondary woodland and used a third unstructured loamy soil as a control. We sterilized these three soils to remove microbial communities, and then inoculated the tops of sterilized soil columns with soil from the secondary woodland or the arable field sites. Control columns of all soil types were not inoculated. In a fully-crossed design, we planted two species possessing distinct root system morphologies: Brachypodium sylvaticum (fibrous system with many thin and fine roots) and Urtica dioica (taproot system with few fine roots). After four months, microbial communities (in bulk and rhizospheric soil) and aggregate stability were measured, along with root traits. In both the field and laboratory experiments, bacterial (16S) and fungal (ITS) diversity was determined using high throughput sequencing. In the field study we found that: i) there were strong relationships between aggregate stability and microbial community composition that were driven by land use, ii) the relationship between aggregate stability along the land use gradient and the trophic nature of bacterial communities was not significant, but certain soil, root and litter parameters shaped bacterial phyla, with oligotrophic bacteria conditioned by the rhizosphere niche, and copiotrophic phyla more dependent on bulk soil conditions, iii) land use gradient (from woodland to arable), reduced the relative abundance of saprotrophic and ectomycorrhizal fungi with an increase in the relative abundance of Ascomycota and a reduction in the relative abundance of Basidiomycota. In the laboratory experiment we found that: i) the inoculation of sterilized soils with soils from the field significantly increased aggregate stability in control soil that was initially poorly structured, ii) the effects of inoculation on aggregate stability were similar when either secondary woodland or arable soils were used as inoculums and iii) these effects were impacted significantly by root length density. Our results show that microbial communities influence soil structure and that bacterial communities are intimately associated to rhizospheric conditions and root traits (of which root length density was the most pertinent). • Complex relationships between soil, land use and plant traits shape microbial communities. • Strong relationships exist between microbial communities and soil aggregate stability. • Bacterial trophic modes were related to bulk soil and rhizosphere niche differentiation. • Microbial inoculation with communities from intact soils affected aggregate stability. • The effect of microbial inoculation was modulated by root length density. [ABSTRACT FROM AUTHOR]

Erosion and mass wasting processes on mountain slopes can benefit from or be adversely affected by the presence of biopores formed by plant root systems or soil fauna. The relationship between biopores and subsurface flow during rainstorms is poorly understood. Here, we examined the link between subsurface flow and biopores formed through different processes, including soil faunal activity and abundance of fine and coarse roots. As the distribution of biopores is influenced by the type of vegetation present, we investigated the effect of plant diversity (forest with or without understorey vegetation) on the pattern of water infiltration throughout the soil. We hypothesized that increased species diversity would enhance the extension of subsurface flow because biopores would be distributed throughout the soil profile and that more coarse roots would create large biopores, increasing subsurface flow. In situ experiments were conducted on hillslopes with plantations of rubber trees (Hevea brasiliensis) growing on terraces, or with secondary mixed forests, in the tropical zone of Yunnan province, China. Three sites with Ferralsol soils and different vegetation types were examined: (1) plantation with no understorey; (2) clear-cut plantation with understorey; and (3) secondary mixed forest with understorey. Irrigation experiments with Brilliant Blue FCF dyed water were performed upslope of trees at each site and staining patterns resulting from infiltrated dyed water were examined at two different scales. After dye irrigation, soil was removed in 1.0 × 0.8 m slices starting 1 m downslope and soil profiles were photographed for subsequent mapping of dyed areas in the profile (macroscale). Each profile was then divided into a 0.1 × 0.1 m grid (microscale) and burrows formed by macrofauna and fine and coarse root densities were measured. At the macroscale, the greatest lateral extension in subsurface flow occurred in the natural forest and the least in the rubber tree plantation with no understorey vegetation. At the microscale, and in all types of vegetation, fine roots significantly increased the incidence of subsurface flow compared to coarse roots and macrofauna activity. We conclude that in tropical Ferralsols, fine roots, and hence understorey vegetation, play a positive role in promoting subsurface flow and therefore reducing water erosion and mass wasting processes. Thus, planting mixtures that include a diversity of species and strata could significantly improve soil conservation. • Hydrological processes in soil are affected by biopores. • Irrigation tests in forests show that fine roots increase preferential flow. • Coarse roots and macrofaunal activity had little effect on preferential flow. • Preferential flow was highest in mixed forest compared to rubber tree plantations. • Diversifying planting mixtures would reduce runoff and improve soil conservation. [ABSTRACT FROM AUTHOR]