not-yet-known not-yet-known not-yet-known unknown Salinization severely impacts soil health. The seasonal freeze-thaw period is a crucial time for the restoration of soil fertility, and soil microorganisms play an important role in the cycling of soil ecosystems. Therefore, it is essential to determine the changes in microbial abundance under the influence of soil salinity gradients during the seasonal freeze-thaw period and to understand their relationships with soil environmental factors.This study designed 19 different gradients of chloride and sulfate salts. Soil samples were collected after the seasonal freeze-thaw period to examine the abundance of soil microorganisms and soil environmental factors, followed by correlation analysis. We found that with increasing salinity, the abundance of soil bacteria and fungi significantly decreased, but chloride and sulfate concentrations at 3 g/kg promoted fungal proliferation.We also observed that during the seasonal freeze-thaw period under the chloride gradient: in the 0-5 cm soil layer, soil bacteria and fungi exhibited a symbiotic relationship, with the abundance of soil bacteria primarily influenced by soil pH, Na +, Ca 2+, Cl -, organic matter, and nitrate nitrogen; the abundance of soil fungi was mainly affected by soil pH. In the 5-20 cm soil layer, the abundance of soil bacteria was mainly influenced by soil salinity, soil pH, Ca 2+, Cl -, and nitrate nitrogen, while the abundance of soil fungi was affected by soil salinity, soil pH, Na +, Ca 2+, Cl -, and nitrate nitrogen.We also found that under the sulfate gradient during the seasonal freeze-thaw period: in the 0-5 cm soil layer, the abundance of soil bacteria was not significantly correlated with various soil indicators, and the abundance of soil fungi was mainly influenced by Na +, Ca 2+, Cl -, and SO 4 2-; in the 5-20 cm soil layer, the abundance of soil bacteria was influenced by soil pH, Na +, Ca 2+, Cl -, and SO 4 2-, while the abundance of soil fungi was affected by nitrate nitrogen. The thresholds for chloride and sulfate concentrations were 5.5 g/kg and 6.5 g/kg, respectively.

Soil salinisation is vital factor limited crop yield in dryland oasis cropland. A film-mulched drip irrigation and subsurface pipe drainage (MDI-SPD) system has been proved its high efficiency all over the world. However, soil salt balance and simulation in time and spatial dimension are unclear in this system. Based on four-year observation data, we use HYDRUS-2D model to simulate the soil salt balance in a MDI-SPD system in western China. We conducted a set of MDI-SPD experiments three times in a field in Manas River Basin, western China: The laying depth of the subsurface pipe was 1 m, and drain spacing was 15 m. Three treatments were set at 0, 5, and 7.5 m horizontal from the subsurface pipe. Results after four years indicated that the total salt output in the irrigated area was 260.16 t, with 103.4 t salt drained by the subsurface pipe (39.74% of the total salt output in the irrigation area). Soil salt balance indicated desalination state. Soil EC response ranged from 8.33 to 11.21 dS m-1. The mineralization of subsurface pipe drainage was positively correlated with drainage flow and salt discharge, and negatively correlated with drainage discharges and time (P<0.05). If salinity leaching stops, 0−200 cm depth soil salt balance will achieve critical value in 8 years. Thus, we recommend salinity leaching once every three years. An increase in shaft drainage would also reduce the deep seepage of salt.