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Outline
To investigate the impacts of different freeze-thaw cycles on the pore structure, pore water redistribution and compositional shifts in saline soil, and further reveal the responses of soil microbial carbon emissions, a moderately saline soil from the Hetao Irrigation District in Inner Mongolia, China, was subjected it to 0, 1, 3, 5, 7, and 9simulated freeze-thaw cycles (hereafter termed as CK, FT1, FT3, FT5, FT7, FT9). The CO2 emission rate was monitored every day (12h freezing + 12h thawing), and the pore water content and major ion concentrations across eight suction levels were determined through high-speed centrifugation. The results showed that: 1) The water-holding capacity of the small pores (size of 0.3~3.5 μm) was significantly higher than that of the large and medium pores (size of 3.5~34μm). After disturbed by freeze-thaw, the soil water-holding capacity decreased significantly, and the water content at the lower suction levels (0~1053cm) of the FT5 group dropped to 18.9%, which was 5.4% lower than the CK group. The total dissolved solids (TDS) content in the small pores reached 75673mg/L for the FT3 group, whilst that in the large and medium pores was only 46955mg/L for the FT5 group. Furthermore, multiple freeze-thaw cycles significantly promoted the soil CO2 emission rates. 2)The average pore water content varied between 19.97% and 18.9% at the lower suction levels, but ranged only from 6.992% to 5.402% at the higher suction levels. 3) Limited numbers of freeze-thaw cycles (FT1-FT3) significantly increased the ion concentration in pore water, and the Na+ concentration reached a peak of 7353.8mg/L in the FT3 group, which was 64.2% higher than that in the CK group (initial value). However, after five freeze-thaw cycles, the Na+ concentration abruptly dropped to 3881.5mg/L in the FT5 group, and then rebounded to 92.1% of the initial value in the FT7-FT9 groups. 4) The soil CO2 emission rates increased with the freeze-thaw cycles, where the FT9 group released 2.94 times the amount of CO2 compared to the FT1 group. Post the freeze-thaw disturbances, the soil CO2 emission rate gradually declined to the levels comparable with the non-freeze-thaw group.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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