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Transformation of selenium fractions driven by freeze-thaw cycles in two soils: Soil aggregate reconstruction and
Mengqin Ren1, Jiacheng Wu1, Yumeng Liu1
1College of Ecology and Environment, Xinjiang University, Urumqi, 830046, China.
Abstract:
Climate change has increased the frequency of freeze-thaw (FT) cycles, but the impact of this change on soil selenium (Se) behavior remains unclear. This study investigated Se fraction transformation across different aggregate sizes fractions in irrigation-silted and gray desert soils, as well as its relationships with soil properties and microbial communities. The results indicated that FT cycles promoted the transformation of large macroaggregates (>2 mm, LMA) into medium macroaggregates (0.25-2 mm, MMA) and small macroaggregates (<0.25 mm, SMA). FT cycles increased pH in LMA, decreased redox potential and electrical conductivity across all aggregates, and significantly increased ferrous iron in the LMA of irrigation-silted soil (25.88%, p < 0.05). FT cycles converted stable Se fractions into available fractions, increasing soluble Se (SO-Se) by 28.4%-36.7% in irrigation-silted soil and by 14.5%-81.3% in gray desert soil. In irrigation-silted soil, bacterial diversity increased in LMA but decreased in SMA, whereas in gray desert soil, it declined across all aggregate fractions. Fungal diversity and evenness increased in all aggregates of both soils. Partial least squares path modeling indicated that Se mobilization was driven by bacteria communities and iron oxide reduction in irrigation-silted soil, whereas fungal communities played a dominant role in the gray desert soil. Overall, frequent FT cycles increase the availability and migration risk of soil Se.
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