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Abstract. Climate change is particularly strong in northern Eurasia and substantial ecological changes are expected in this extensive region. The reshaping and migration northwards of bioclimatic zones may offer opportunities for agricultural development in western and central Siberia. However, the bioclimatic vegetation models currently employed for projections still do not consider soil fertility, in spite of this being highly critical for plant growth. In the present study, we surveyed the phosphorus (P) status in the south-west of Siberia where soils have developed on loess parent material. We selected six sites differing in pedoclimatic conditions and the soil was sampled at different depths down to 1 m in aspen (Populus tremula L.) forest as well as in grassland areas. The P status was assessed by conventional methods and by isotope dilution kinetics. We found that P concentrations and stocks, as well as their distribution through the soil profile, were fairly homogeneous on the regional scale studied, although there were some differences between sites (particularly in organic P). The young age of the soils, together with slow kinetics of soil formation processes have probably not yet resulted in a sufficiently wide range of soil physico-chemical conditions to observe a more diverging P status. The comparison of our data set with similar vegetation contexts on the global scale revealed that the soils of south-western Siberia, and more generally of northern Eurasia, often have (very) high levels of total, organic and inorganic P. The amount of plant-available P in topsoils, estimated by the isotopically exchangeable phosphate ions, was not particularly high but was intermediate on the global scale. However, large stocks of plant-available P are stored in subsurface layers which currently have low fine-root exploration intensities. These results suggest that the P resource is unlikely to constrain vegetation growth and agricultural development under the present conditions or in the near future.

Southwest Siberia encompasses the forest-steppe and sub-taiga climatic zones and has historically been utilized for agriculture. Coinciding with predicted changes in climate for the region is the pressure of agricultural development; however, a characterization of the soil water and carbon dynamics is lacking. We assessed current soil water properties and soil organic carbon turnover in forests and grasslands for two sites that span the forest steppe and sub-taiga bioclimatic zones. Soil evaporation was 0.62 ± 0.17 mm d−1 (mean ± standard error) in grasslands and 0.45 ± 0.08 mm d−1 in the forests of the forest-steppe site. Evaporation at the sub-taiga site was 1.80 ± 1.70 mm d−1 in grasslands and 0.96 ± 0.05 mm d−1 in forest plots. Evaporation was significantly greater at the sub-taiga site than the forest-steppe site. The density of fine roots explained the soil water isotopic patterns between vegetation types and sites. We found soil organic matter turnover to be three times faster in the sub-taiga site than in the forest-steppe site. Our results show that while climate factors, in particular snow levels, between the two sites are drivers for water and carbon cycles, site level hydrology, soil characteristics, and vegetation directly interact to influence the water and carbon dynamics.

To cite this version:Pascale Henner, Félix Bredoire, Antoine Tailliez, Frederic Coppin, Sylvie Pierrisnard, et al.. Influence of root exudation of white lupine (Lupinus albus L.) on uranium phytoavailability in a naturally uranium-rich soil . Journal of Environmental Radioactivity, Elsevier, 2018Elsevier, , 190-191, pp.39-50. 10.1016Elsevier, /j.jenvrad.2018 Influence of root exudation of white lupine (Lupinus albus L.) on uranium 1 phytoavailability in a naturally uranium-rich soil 2 Mechanisms of uranium (U) transfer from soil to plants remain poorly understood. The 35 kinetics of supply of U to the soil solution from solid phases could be a key point to 36 understand its phytoavailability and implications for environmental risk assessment. Root 37 activity, particularly the continuous release of organic acids in the rhizosphere, could have an 38 effect on this supply. We tested the impact of citrate exudation by roots of Lupinus albus, 39 either P-sufficient (P+) or P-deficient (P-), on the phytoavailability of U from a naturally 40 contaminated soil (total content of 413 mg U kg -1 ) using a rhizotest design. Combined effects 41 of P (P-/P+ used to modulate plant physiology) and citrate (model exudate) on the 42 solubilization of U contained in the soils were tested in closed reactors (batch). The batch 43 experiment showed the existence of a low U available pool (0.4% total U) and high 44