Although various measurements (including organic amendments) have been used to ameliorate saline–alkaline soils, soil organic matter (SOM) remains low in most salt-affected agriculture soils. It was hypothesized that lower SOM level was partly attributable to weaker SOM stability (thus greater desorption) in the salt-affected soils. To test this hypothesis, we conducted a 16-week incubation experiment using low- and high-salinity soils to evaluate the effects of soil ameliorants (gypsum, CaCO3, rice straw and biochar) on SOM labile fractions, i.e., water extractable organic carbon (WEOC) and nitrogen (WEON), together with microbial biomass carbon (MBC) and nitrogen (MBN). Our results showed an increase in MBC and MBN under all amendments in both low- and high-salinity soils, reflecting improvements in soil properties. Gypsum amendment led to a decrease in both WEOC (by 15–21%) and WEON (by 14–31%). CaCO3 amendment only caused a decrease in WEON (by 14–27%), with a greater decrease found in the high-salinity soil. There was an increase in WEOC (by 13–66%) but a decrease in WEON (7.6–46%) under biochar and straw amendments in both low- and high-salinity soils. WEOC:SOC ratio (an indicator for SOC desorption) showed a decrease under gypsum and biochar amendments but an increase with CaCO3 and straw treatments. There was a decrease in WEON:TN ratio (an indicator for ON desorption) under all amendments, with the greatest decrease under biochar treatment. Our analyses demonstrated an enhancement in SOC or ON adsorption under all amendments, indicating that SOM stability might be enhanced in association with soil amelioration. Our study also highlights that there is strong decoupling between carbon and nitrogen cycles and further studies are needed to examine the impacts of such decoupling on SOM stability.

中文翻译：

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改良剂对黄河三角洲农业土壤碳氮组分的影响

尽管已使用各种措施（包括有机改良剂）来改良盐碱地，但在大多数受盐害影响的农业土壤中，土壤有机质 (SOM) 仍然很低。据推测，较低的 SOM 水平部分归因于受盐影响的土壤中较弱的 SOM 稳定性（因此更大的解吸）。为了验证这一假设，我们使用低盐度和高盐度土壤进行了为期 16 周的孵化实验，以评估土壤改良剂（石膏、碳酸钙、稻草和生物炭）对 SOM 不稳定组分（即水可提取有机碳）的影响（ WEOC) 和氮 (WEON)，以及微生物生物量碳 (MBC) 和氮 (MBN)。我们的结果表明，在低盐度和高盐度土壤中的所有改良剂下，MBC 和 MBN 均有所增加，反映了土壤特性的改善。石膏修正导致 WEOC（降低 15-21%）和 WEON（降低 14-31%）。CaCO3 修正仅导致 WEON 降低（降低 14-27%），在高盐度土壤中降低幅度更大。在低盐度和高盐度土壤中，在生物炭和秸秆改良剂的作用下，WEOC 增加（增加 13-66%）但 WEON 减少（7.6-46%）。WEOC:SOC 比率（SOC 解吸的一个指标）显示在石膏和生物炭改良剂下降低，但在 CaCO3 和秸秆处理下增加。在所有修正案中，WEON:TN 比率（ON 解吸的指标）均有所降低，其中生物炭处理的降幅最大。我们的分析表明，在所有修正案下，SOC 或 ON 吸附均有所增强，表明 SOM 稳定性可能与土壤改良有关。