Distribution of Burkholderia pseudomallei within a 300-cm deep soil profile: implications for environmental sampling.

The environmental distribution of Burkholderia pseudomallei, the causative agent of melioidosis, remains poorly understood. B. pseudomallei is known to have the ability to occupy a variety of environmental niches, particularly in soil. This paper provides novel information about a putative association of soil biogeochemical heterogeneity and the vertical distribution of B. pseudomallei. We investigated (1) the distribution of B. pseudomallei along a 300-cm deep soil profile together with the variation of a range of soil physico-chemical properties; (2) whether correlations between the distribution of B. pseudomallei and soil physico-chemical properties exist and (3) when they exist, what such correlations indicate with regards to the environmental conditions conducive to the occurrence of B. pseudomallei in soils. Unexpectedly, the highest concentrations of B. pseudomallei were observed between 100 and 200 cm below the soil surface. Our results indicate that unravelling the environmental conditions favorable to B. pseudomallei entails considering many aspects of the actual complexity of soil. Important recommendations regarding environmental sampling for B. pseudomallei can be drawn from this work, in particular that collecting samples down to the water table is of foremost importance, as groundwater persistence appears to be a controlling factor of the occurrence of B. pseudomallei in soil

Can Organic Amendments Improve Soil Physical Characteristics and Increase Maize Performances in Contrasting Soil Water Regimes?

International audienceOrganic amendments are believed to help increase the soil carbon storage and therefore improve soil quality, which may be important in the context of climate change. However, the added value of organic amendments for farmers must be clearly demonstrated in order to convince them of the utility of their use. The aims of this study were: (i) to investigate the impact on maize of compost and vermicompost combined with two levels (negligible and significant) of plant water stress; and (ii) to determine how the organic amendments affected the soil’s physical properties and maize productivity. Water stress levels were imposed by controlling the matric potential of soil columns in which cultivated soil characteristics was mimicked (10 cm topsoil with organic amendments, above a 50 cm subsoil without any inputs containing the majority of the roots). Plant and soil characteristics were monitored daily for 70 days. Our results show that the use of organic amendments is profitable for farmers as: (i) maize performances were increased in both moisture regimes; and (ii) the improvement was particularly striking in terms of yield. No additional benefits were measured when using vermicompost instead of compost. The data suggest that the improvement in plant characteristics did not result from increased water storage in the soils with organic amendments, but rather from better access to the water, resulting in faster root development in the macroporosity of the amended soils

Distribution of Burkholderia pseudomallei and soil properties within a 300-cm deep profile

This dataset has been collected thanks to the long-term partnership with Department of Agricultural Land Management (DALaM), Lao PDR, which granted the permission for field access, and to the financial, scientific, technical, and/or logistical support of the Multiscale TROPIcal CatchmentS (SNO M-TROPICS; https://mtropics.obs-mip.fr/) critical zone observatory (previously MSEC). This .csv dataset includes Burkholderia pseudomallei concentrations (CFU g-1) within a 300-cm soil profile, along with physico-chemical parameters: soil texture, i.e. clay < 2 μm, silt 2–50 μm, sand 50–2000 μm (%); pH (-); organic matter content (%); bulk density (1000 kg m-3); total porosity (100(1-BD/2.65)) considering a real density value of 2.65 (%); groundwater persistence rate (%); saturated hydraulic conductivity (mm h-1); soil water content (m3 m-3); exchangeable cations (Ca2+, Mg2+, K+, and Na+; meq 100 g-1); and soil elemental concentrations (Fe, Mn, Mg, Ca, K, Na, Al, Si, Ti, and S; ppm). The authors acknowledge financial support from French national grant CNRS/INSU EC2CO-Biohefect/Ecodyn//Dril/MicrobiEen(BurLuMic) and the IRD International Joint Laboratory LUSES. Essential support with microbiological analyses was provided by the Lao-Oxford-Mahosot-Wellcome Trust-Research Unit (LOMWRU), Vientiane, Lao PDR, funded by the Wellcome Trust [Grant number 106698/Z/14/Z]. The Department of Agricultural Land Management (DALaM) of the Ministry of Agriculture and Forestry of Lao PDR facilitated access to the field and provided invaluable support with soil analyses. IRD staff in Laos would like to sincerely thank Mr Outhong Sengouthai, owner of the paddy field as well as village authorities to have permitted us to make field measurements in Ban Nabone. KP would like to acknowledge financial support for her PhD from Campus France (BGF) and expresses her gratitude to IRD GET and iEES-Paris staff in France and Lao PDR for assistance and guidance with her work

Escherichia coli concentration, multiscale monitoring over the decade 2011-2021 in the Mekong River basin, Lao PDR

International audienceBacterial pathogens in surface waters may threaten human health, especially in developing countries, where untreated surface water is often used for domestic needs. The objective of the long-term multiscale monitoring of Escherichia coli ([E. coli]) concentration in stream water, and that of associated variables (temperature (T), electrical conductance (EC), dissolved oxygen concentration ([DO]) and saturation (DO%), pH (pH), oxidation-reduction potential (ORP), turbidity (Turb), and total suspended sediment concentration ([TSS])), was to identify the drivers of bacterial dissemination across tropical catchments. This data description paper presents three datasets (see "Data availability" section) collected at 31 sampling stations located within the Mekong River and its tributaries in Lao PDR (0.6-25 946 km2) from 2011 to 2021. The 1602 records have been used to describe the hydrological processes driving in-stream E. coli concentration during flood events, to understand the land-use impact on bacterial dissemination on small and large catchment scales, to relate stream water quality and diarrhea outbreaks, and to build numerical models. The database may be further used, e.g., to interpret new variables measured in the monitored catchments, or to map the health risk posed by fecal pathogens

The Multiscale TROPIcal CatchmentS critical zone observatory M‐TROPICS dataset II: land use, hydrology and sediment production monitoring in Houay Pano, northern Lao PDR

International audienceMountain regions of the humid tropics are characterized by steep slopes and heavy rains. These regions are thus prone to both high surface runoff and soil erosion. In Southeast Asia, uplands are also subject to rapid land-use change, predominantly as a result of increased population pressure and market forces. Since 1998, the Houay Pano site, located in northern Lao PDR (19.85°N 102.17°E) within the Mekong basin, aims at assessing the long-term impact of the conversion of traditional slash-and-burn cultivation systems to commercial perennial monocultures such as teak tree plantations, on the catchment hydrological response and sediment yield. The instrumented site monitors hydro-meteorological and soil loss parameters at both microplot (1 m2) and small catchment (0.6 km2) scales. The monitored catchment is part of the network of critical zone observatories named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Houay Pano are (1) rainfall, (2) air temperature, air relative humidity, wind speed, and global radiation, (3) catchment land use, (4) stream water level, suspended particulate matter, bed particulate matter and stones, (5) soil surface features, and (6) soil surface runoff and soil detachment. The dataset has already been used to interpret suspended particulate matter and bed particulate matter sources and dynamics, to assess the impact of land-use change on catchment hydrology, soil erosion, and sediment yields, to understand bacteria fate and weed seed transport across the catchment, and to build catchment-scale models focused on hydrology and water quality issues. The dataset may be further used to e.g. assess the role of headwater catchments in large tropical river basin hydrology, support the interpretation of new variables measured in the catchment (e.g. contaminants other than fecal bacteria), and assess the relative impacts of both climate and land-use change on the catchment