【目的】长期高氮(N)沉降对具有磷(P)限制的亚热带森林土壤有机碳(SOC)及其储量具有影响,探究长期N添加下活性SOC、土壤有机氮(SON)组分对有机碳储量的影响,为亚热带森林土壤的碳(C)固存能力以及亚热带森林生态系统的可持续经营提供依据。【方法】在安徽省祁门县查湾自然保护区的常绿阔叶林内,选取中坡和坡顶两个区位,各设置3种不同的N、P添加处理,即对照(CK,每年N、P添加量为0 kg/hm²)、N添加(N,每年N添加量为100 kg/hm²)、N+P添加(N+P,每年N添加量为100 kg/hm²、P添加量为50 kg/hm²),各处理设置3个重复样地,大小为30 m×15 m,共18块样地。自2011年5月开始,进行为期10年的N及N+P添加野外模拟试验。于2020年10月,采集不同处理样地内[0,40)cm土层的土壤样品,测定SOC含量及储量、活性SOC组分、SON组分以及其他土壤基本理化性质。将采集的土样平均分成两份,一部分土样自然风干压碎后过孔径0.25 mm筛,用于测定土壤SOC及TN含量。另一部分鲜土样经不同处理后,用于测定SOC、SON组分及其他理化性质。【结果】与对照相比,连续10年N及N+P添加并未显著改变SOC储量,但显著降低土壤微生物生物量碳、氮。相关性分析结果表明,土壤有机碳储量与大多数土壤理化性质密切相关,除溶解性有机碳外,与其余有机碳氮组分均极显著正相关。另外,有机碳储量与pH、土壤容重呈显著负相关。线性回归分析结果显示,颗粒有机碳、氮对有机碳储量的解释率分别为75.4%、71.7%,微生物生物量碳、氮对有机碳储量的解释率分别为26.0%、49.3%;而土壤可溶性有机碳与有机碳储量无显著相关关系,可溶性氮对有机碳储量的解释率仅为11.4%。【结论】长期添加N及N+P后,土壤微生物生物量碳氮含量显著下降,并可能不利于土壤有机碳存量,而颗粒有机碳氮是对土壤有机碳储量影响最大的组分。

【Objective】The aim of the present study is to simulate the effects of long-term nitrogen (N) deposition on soil organic carbon (SOC) and organic carbon storage in subtropical forests with phosphorus (P) limitation to investigate the effects of active SOC and soil organic nitrogen (SON) components on organic carbon storage under long-term N addition, as well as to provide the basis for soil carbon (C) sequestration capacity and sustainable management of subtropical forest ecosystems.【Method】In an evergreen broad-leaved forest of Zhawan Nature Reserve, Qimen County, Anhui Province, two sites were selected, the middle slope and flat ridge, for the present study. Three different N and P addition treatments were designed at each site as follows: control (CK, N and P addition of 0 kg/hm² per year), N addition (N, N addition of 100 kg/hm² per year), and N+P addition (N+P, N addition of 100 kg/hm² and P addition of 50 kg/hm² per year). There were three replicate plots of 30 m × 15 m for each treatment, with a total of 18 sampling plots. In October 2020, soil samples were collected from the 0-40 cm layer in each plot to determine SOC content, SOC storage, active SOC fraction, SON fraction, and other basic physicochemical properties. The collected soil samples were divided into two parts. One part of the soil sample was naturally air-dried, crushed, and passed through a 0.25 mm sieve for the determination of soil SOC and total nitrogen (TN) content. The other part of the soil sample was treated differently to determine soil SOC, SON fraction, and other physicochemical properties to investigate the effect of long-term simulated N deposition on the organic carbon storage capacity of subtropical forest soils, as well as the effects of SOC and SON fractions on organic carbon storage. 【Result】Compared to the CK treatment, N and P additions did not significantly change the SOC content and storage, but it significantly reduced the soil microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents. Correlation analysis showed that SOC storage was significantly and positively correlated with most soil physical and chemical properties but significantly and negatively correlated with pH and bulk density. Linear regression analysis demonstrated that particulate organic carbon (POC) and particulate organic nitrogen (PON) explained 75.4% and 71.7% of the effects on SOC storage, respectively, while MBC and MBN explained 26.0% and 49.3% of the effects on SOC storage, respectively. There was no significant relationship between dissolved organic carbon (DOC) and SOC storage, and DOC explained 11.4% of the effects on SOC storage.【Conclusion】Long-term N and N+P additions significantly reduce the C and N contents of soil microbial biomass and may be detrimental to SOC stocks, with POC and PON having the greatest impact on SOC storage.