土壤有机碳(SOC)与森林地力维持和碳汇功能密切相关，土壤SOC的微小波动就能引起大气二氧化碳浓度的显著变化。凋落物管理作为人工林主要经营措施，如何影响SOC化学结构和稳定性及其机制尚不清楚。本研究以杉木(Cunninghamia lanceolata)林为对象，采用完全随机区组设置凋落物添加、凋落物移除和对照3种处理的野外控制试验。处理6年后，0～10、10～20和20～40cm三层采集土壤样品，采用透射傅里叶红外光谱法(T-FTIR)测定SOC化学结构，热重法(TG)和差示扫描量热法(DSC)分析SOC热稳定性，并测定土壤其他理化性质。结果表明:(1)凋落物移除显著降低0～10、20～40 cm 土层铵态氮(NH4+-N)和10～20 cm 土层硝态氮(NO3--N)含量;(2)凋落物添加显著降低SOC的醇酚相对占比，提高芳香族的相对占比;(3)凋落物添加显著降低热稳定系数(H)，凋落物移除处理下SOC燃烧过程中质量损失50％所对应的温度显著提高(Tg-T50);(4)NH4+-N、NO3--N与Tg-T50呈显著负相关;醇酚和芳香族分别与H呈显著正相关和负相关。综上所述，凋落物移除通过降低氮有效性提高SOC热稳定性;凋落物添加通过降低SOC化学分子结构中易分解碳，增加难分解碳的形成从而提高SOC热稳定性。研究结果可为亚热带人工林通过凋落物管理措施提升土壤碳汇功能来实现"碳中和"提供科学依据。
Effects of litter management on chemical structure and thermal stability of soil organic carbon in a Chinese fir forest
Soil organic carbon(SOC)is closely related to forest land maintenance and carbon sink function.Small fluctuations in soil SOC can cause significant changes in atmospheric CO2 concentrations.As a main management measure of plantation,how and why litter management affects the chemical structure and stability of SOC remains unclear.In this study,a field control experiment was conducted in a Chinese fir(Cunninghamia lanceolata)forest with three treatments,namely,litter addition,litter removal and control,following a completely randomized block design.After 6 years of treatment,soil samples from three layers(0-10 cm,10-20 cm,and 20-40 cm)were col-lected,and the chemical structure of SOC was determined by transmission Fourier-transform infrared spectroscopy(T-FTIR).The thermal stability of SOC was analyzed by thermogravimetry(TG)and differential scanning calorim-etry(DSC),and the soil physicochemical properties were determined.The results showed that(1)Litter removal significantly decreased NH4+-N concentration in the 0-10 and 20-40 cm layers and NO3--N concentration in the 10-20 cm layer;(2)Litter addition significantly decreased the relative proportion of alcohols and phenols in SOC and increased the relative proportion of aromatics;(3)Litter addition significantly decreased the thermal stability coefficient(H),and litter removal treatment significantly increased the temperature corresponding to 50％mass loss during SOC combustion(Tg-T50);(4)The NH4+-N and NO3--N concentrations were significantly negatively correlated with Tg-T50.Alcohol phenols and aromatic groups were positively and negatively correlated with H,re-spectively.In summary,litter removal improved the thermal stability of SOC by decreasing N effectiveness,while litter addition improved thermal stability of SOC by decreasing the readily decomposable carbon and increasing the formation of refractory carbon in the chemical molecular structure of SOC.Our results can provide a scientific basis for subtropical plantation to achieve"carbon neutrality"by improving soil carbon sink function through litter man-agement.
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