Effects of Freeze-thaw Cycles on Soil Aggregates Turnover in Mollisols Using Rare Earth Oxides as Tracers

1.Guilin University of Technology;2.Institute of Soil Science, Chinese Academy of Sciences

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he National Key Research and Development Program (No. 2021YFD1500801), National Natural Science Foundation of China (No. 42207360), Jiangsu Funding Program for Excellent Postdoctoral Talent (No. 2022ZB466), and China Postdoctoral Science Foundation (No. 2022M723238).

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    【Objective】In order to elucidate the effects of freeze-thaw cycles and initial water content on soil aggregates structure, rare earth oxides (REOs) were used as tracers to separate soil aggregates formation and breakdown processes. 【Method】REOs-labelled soil was reformed and investigated herein. Two initial water contents (50 % field water holding capacity (T50) vs. 100 % field water holding capacity (T100)) and five freeze-thaw cycles (0, 3, 6, 12 and 20 cycles) were involved in the simulation experiments. Soil aggregates distribution, mean weight diameter (MWD), the aggregate turnover process were measured accordingly. 【Result】The results showed that freeze-thaw cycles significantly reduced MWD, the contents of > 0.25 mm aggregates and <0.053 mm aggregates but increased the contents of 0.25~0.053 mm aggregates under the same initial water content. After 6 freeze-thaw cycles, MWD was significantly higher under T50 compared with that under T100(P < 0.05), there was no significant difference between the aggregate content of 5~2 mm and <0.25 mm. Except for 5~2 mm aggregates, the intensive transformations between neighboring size aggregates were observed during the whole simulation experiments. For the same freeze-thaw cycles, the fragmentation amount of 5~2 mm aggregate to 0.25~0.053 mm aggregate was significantly higher at T100 compared with T50 treatment(P < 0.05).The freeze-thaw cycles promoted the breakdown of >0.25 mm aggregates and the formation of 0.25~0.053 mm aggregates both under T50 and T100 treatments. MWD was significantly positively correlated with the relative formation of soil aggregates and negatively related with the relative breakdown of soil aggregates(P < 0.05). The turnover time of soil aggregate significantly increased with freeze-thaw cycles(P < 0.05). The aggregate turnover time of > 0.25 mm aggregates was higher than that for <0.25 mm aggregates. The aggregate turnover time was significantly higher under T100 than that under T50 with the same freeze-thaw cycle(P < 0.05). 【Conclusion】In conclusion, the number of freeze-thaw cycles and the initial water content of the soil significantly affect the aggregate turnover, which changes the stability of the soil structure by affecting the aggregate formation and fragmentation process. The results can provide a theoretical basis for further exploration of the structural changes of black soil under the freeze-thaw cycle.

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  • Received:December 06,2022
  • Revised:May 22,2023
  • Adopted:July 27,2023
  • Online: August 14,2023
  • Published: