High long-term soil moisture may either stimulate or inhibit soil organic carbon (SOC) losses through changes to mineral and chemical composition, and resultant organo-mineral interactions. Yet, the trade-off between mineralization and accrual of SOC under long-term variation in unsaturated soil moisture remains uncertain. We tested the underexplored relationships between long-term soil moisture and organo-mineral chemical composition and its implications for SOC persistence in an experimental field in New York, USA, with differences in long-term mean soil volumetric water content (0 - 0.15 m depth) ranging from 0.4 - 0.63 (v/v) during the growing season. Long-term soil moisture across 20 subplots on four fallow plots were positively correlated with SOC (R² = 0.228; P = 0.019, n = 20), mineral-associated organic matter (MAOM) content (g fraction/g soil) (R² = 0.442; P = 0.001; n = 20) and occluded particulate organic matter (oPOM) content (R² = 0.178; P = 0.033; n = 20). Higher long-term soil moisture was associated with a decrease in the relative content of sodium pyrophosphate extractable Fe (R² = 0.33; P < 0.005; n = 20), an increase in sodium dithionite extractable Fe (R² = 0.443; P < 0.001; n = 20), and an increase in SOC retention by non-crystalline Al pools (R² = 0.513; P = 0.0002 for sodium pyrophosphate extracts, R² = 0.411; P = 0.0014 for hydroxylamine hydrochloride extracts; n = 20 for both). Increasing long-term soil moisture was associated with a four-fold increase in microbial biomass C (per unit SOC) and lower metabolic quotient (R² = 0.557, P < 0.001). MAOM fractions of high-moisture soils had lower C:N (from C:N 9.5 to 9, R² = 0.267, P = 0.011, n = 20). Consistent with decreasing C:N, increasing decomposition with increasing moisture was reflected by a 15% and 10% greater proportion of oxidized carboxylic-C to aromatic-C and O-alkyl C, respectively, as measured with ¹³C-NMR, and a more pronounced FTIR signature of N-containing proteinaceous compounds in high-moisture MAOM fractions, indicative of microbial metabolites and transformation products. A partial least squares regression showed that SOC content increased with greater long-term moisture (P = 0.019), pyrophosphate-extractable Al (P = 0.0001), and exchangeable Ca (P = 0.013). Taken together, our results show that higher long-term soil moisture resulted in SOC accrual by enhancing conversion of plant inputs into microbial biomass that interacts with reactive minerals.

长期高土壤水分可能会通过改变矿物和化学成分以及由此产生的有机-矿物相互作用来刺激或抑制土壤有机碳 (SOC) 损失。然而，在非饱和土壤水分的长期变化下，矿化和 SOC 积累之间的权衡仍然不确定。我们在美国纽约的一个试验田测试了长期土壤水分和有机矿物化学成分之间未充分探索的关系及其对 SOC 持久性的影响，长期平均土壤体积含水量（0 - 0.15 m 深度）存在差异) 在生长季节的范围为 0.4 - 0.63 (v/v)。四个休耕地的 20 个子地的长期土壤水分与 SOC 呈正相关（R ² = 0.228；P = 0.019，n= 20)、矿物相关有机物 (MAOM) 含量 (g 分数/g 土壤) (R ² = 0.442; P = 0.001; n = 20) 和截留颗粒有机物 (oPOM) 含量 (R ² = 0.178; P = 0.033；n = 20)。较高的长期土壤湿度与焦磷酸钠可提取铁的相对含量降低有关（R ² = 0.33；P < 0.005；n = 20），连二亚硫酸钠可提取铁的增加（R ² = 0.443；P < 0.001；n = 20），以及非结晶铝池的 SOC 保留增加（R ² = 0.513；焦磷酸钠提取物的 P = 0.0002，R ²= 0.411; 对于盐酸羟胺提取物，P = 0.0014；n = 20 两者）。增加长期土壤水分与微生物生物量 C（每单位 SOC）增加四倍和代谢商降低（R ² = 0.557，P < 0.001）有关。高水分土壤的 MAOM 组分具有较低的 C:N（从 C:N 9.5 到 9，R ² = 0.267，P = 0.011，n = 20）。与 C:N 的降低一致，随着水分的增加分解增加，这反映在氧化的羧基-C 与芳族-C 和 O-烷基 C 的比例分别增加 15% 和 10%，用^13测量C-NMR，以及高水分 MAOM 馏分中含氮蛋白质化合物的更明显 FTIR 特征，表明微生物代谢物和转化产物。偏最小二乘回归表明 SOC 含量随着长期水分 (P = 0.019)、焦磷酸盐可萃取铝 (P = 0.0001) 和可交换钙 (P = 0.013) 的增加而增加。总之，我们的研究结果表明，较高的长期土壤水分通过增强植物投入物转化为与活性矿物质相互作用的微生物生物量来增加 SOC。