Organic amendment combined with mineral fertilizer is known as an effective management practice to improve soil carbon (C) sequestration in cropland. We evaluated the effects of three organic amendments combined with mineral fertilizer on soil organic carbon (SOC), labile SOC fractions, amino sugars, C mineralization, and C-cycle enzyme activities in a coastal saline-alkali soil. The three amendments, including straw (C/N of 75.5:1), straw biochar (C/N of 43:1), and soybean cake (C/N of 7.4:1), were continuously added into the soil at an equal C amount of 2250 kg C ha for four years. Compared to mineral fertilizer alone, the contents of SOC in plots receiving straw, straw biochar, and soybean cake were increased by 7.6%, 17.3%, and 12.7%, respectively. The amendment of straw biochar mainly increased easily oxidizable carbon (EOC), particulate organic carbon (POC), and fungal-derived glucosamine, whereas straw and soybean cake mainly increased dissolved organic carbon (DOC), microbial biomass carbon (MBC), and bacteria-derived muramic acid. Meanwhile, the activities of C-cycle enzymes and C mineralization were higher in straw and soybean cake treatments than in straw biochar treatment. EOC and POC, but not DOC and MBC, were strongly positively correlated with fungal-derived glucosamine and SOC, suggesting that EOC or POC could be used as appropriate indicators to predict SOC sequestration potential. In addition, the C/N ratio of organic material did not affect SOC and its components. In conclusion, straw biochar promotes the maximum accumulation of SOC through increasing EOC, POC, and fungal necromass.

中文翻译：

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沿海盐碱土壤中 SOC、不稳定 SOC 分数和氨基糖对不同有机改良剂的响应

有机改良剂与矿物肥料相结合被认为是改善农田土壤碳（C）固存的有效管理实践。我们评估了三种有机改良剂与矿物肥料的结合对沿海盐碱土壤中土壤有机碳 (SOC)、不稳定 SOC 分数、氨基糖、C 矿化和 C 循环酶活性的影响。将秸秆（C/N 75.5:1）、秸秆生物炭（C/N 43:1）、豆饼（C/N 7.4:1）三种改良剂等量连续添加到土壤中。四年碳用量为 2250 公斤碳公顷。与单独施用矿肥相比，施用秸秆、秸秆生物炭和豆饼的地块SOC含量分别提高了7.6%、17.3%和12.7%。秸秆生物炭的改良主要增加易氧化碳（EOC）、颗粒有机碳（POC）和真菌源葡萄糖胺，而秸秆和豆饼主要增加溶解性有机碳（DOC）、微生物生物质碳（MBC）和细菌-衍生的胞壁酸。同时，秸秆和豆饼处理的碳循环酶活性和碳矿化程度均高于秸秆生物炭处理。EOC 和 POC（而非 DOC 和 MBC）与真菌来源的葡萄糖胺和 SOC 呈强正相关，表明 EOC 或 POC 可以作为预测 SOC 封存潜力的适当指标。此外，有机材料的C/N比不影响SOC及其组分。总之，秸秆生物炭通过增加EOC、POC和真菌坏死物来促进SOC的最大积累。