Microbial necromass carbon (MNC) is an important contributor to soil organic carbon (SOC). Soil carbon storage has increased significantly since the return of farmland to forestland (grassland) on the Loess Plateau. However, the contribution of MNC to SOC accumulation in different vegetation types and the influence factors remain unclear. Herein, we used the biomarker (amino sugar) technique to determine the MNC content and analyzed the influencing factors in 0-5 cm and 5-20 cm soil layers of natural grassland, shrubland (Caragana microphylla), and forestland (Quercus liaodongensis) in the Loess Plateau. The results showed that: 1) the soil pH decreased significantly from grassland to shrubland and then to forestland within the same soil layer. However, the SOC, total nitrogen (TN), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) contents showed a reverse trend, with forestland displaying the highest values followed by shrubland and then grassland. The 0-5 cm had significantly higher values than the 5-20 cm depth. 2) The MNC contents varied 0.69-16.41 g·kg-1 in the two soil horizons of the three vegetation types. There were significant increases in the contents of bacterial necromass carbon (BNC), fungal necromass carbon (FNC), and MNC in the 0-5 cm soil from grassland, shrubland to forestland. The contents of MBC were 1.9 times higher in forestland than in shrubland, and 3.2 times higher in shrubland than in grassland. In the 5-20 cm soil layer, the contents of FNC and MBC were significantly higher in the forestland than in the shrubland and grassland. The FNC content was significantly higher than that of the BNC, ranging from 1.16 to 9.83 times greater than the BNC. 3) The contribution of MNC to SOC was 0.6 and 0.7 times higher in shrubland and forestland than in grassland, respectively, with FNC accounting for 15.2%-42.7%, and BNC accounting for 1.4%-7.4%. 4) pH, TN, MBC, and MBN were important factors that influenced MNC accumulation. In summary, the variation in vegetation type altered soil nutrients, microbial activity, and soil pH, resulting in forestland and shrubland being more beneficial to the formation and accumulation of MNC, which was dominated by fungi, compared to grassland.
微生物残体碳是土壤有机碳的重要来源。黄土高原自退耕还林(还草)以来土壤碳储量显著增加,但不同植被类型土壤微生物残体碳对有机碳积累的贡献及其影响因素尚不明晰。本研究利用生物标志物(氨基糖)技术,测定黄土高原天然草地、柠条灌丛、辽东栎林地0～5和5～20 cm土层土壤中的微生物残体碳含量,并分析其与土壤理化指标的关系,探究不同植被类型土壤中微生物残体碳对有机碳的贡献及其影响因素。结果表明: 1)同一土层,土壤pH值由草地、灌丛至林地依次显著降低,而有机碳、全氮、微生物生物量碳、微生物生物量氮表现为林地>灌丛>草地,差异显著,且0～5 cm土层显著高于5～20 cm土层。2)土壤微生物残体碳含量在3种植被类型的两个土层中的变化范围为0.69～16.41 g·kg-1,其中,在0～5 cm土层,细菌、真菌和微生物残体碳含量均由草地、灌丛至林地依次显著增加,林地微生物残体碳含量是灌丛的2.9倍,灌丛是草地的4.2倍;在5～20 cm土层,林地真菌和微生物残体碳含量显著高于灌丛和草地。真菌残体碳含量高于细菌残体碳含量,是细菌残体碳的2.16～10.83倍。3)微生物残体碳对有机碳的贡献在灌丛和林地分别是草地的1.6和1.7倍,其中,真菌残体碳的贡献占15.2%～42.7%。细菌占1.4%～7.4%。4)pH、全氮、微生物生物量碳和微生物生物量氮是微生物残体碳积累的重要影响因素。综上,植被类型的变化改变了土壤养分、微生物活性和土壤pH值,从而使林地和灌丛较草地更有利于由真菌主导的微生物残体碳的形成和积累。.
Keywords: influencing factor; microbial necromass; soil organic carbon; vegetation type.