宁夏不同草地类型土壤微生物残体碳积累特征及其影响因素

Accumulation and influencing factors of soil microbial necromass carbon in different grassland types of Ningxia,China

为探究不同草地类型土壤微生物残体碳积累特征,明确微生物残体碳对土壤有机碳(SOC)的贡献及影响因素。研究利用生物标记物的方法,测定宁夏草甸草原(MS)、典型草原(TS)、荒漠草原(DS)、草原化荒漠(SD)和荒漠(D)5种草地类型0—20 cm土壤的理化性质、微生物群落组成及氨基糖含量,进一步分析微生物残体碳含量与土壤理化性质和微生物群落的关系。结果表明:MS和TS土壤有机碳、全氮、铵态氮、硝态氮、微生物量碳、微生物量氮、真菌、细菌、放线菌和原生动物含量显著高于其他草地类型(P<0.05)。土壤氨基葡萄糖(GluN)、氨基甘露糖(ManN)、氨基半乳糖(GalN)和胞壁酸(MurA)含量均表现为MS最大,D最小(P<0.05);不同草地类型土壤氨基葡萄糖含量((0.62±0.18)μg/mg)最高,胞壁酸含量((0.04±0.01)μg/mg)最低。不同草地类型土壤细菌残体碳(BNC)、真菌残体碳(FNC)和总残体碳(TNC)变化范围为0.12—5.74μg/mg、0.22—15.31μg/mg和0.34—21.05μg/mg;BNC、FNC和TNC对SOC贡献分别为9.0%—17.8%、22.0%—48.2%和33.5%—66.0%;FNC对SOC的贡献是BNC的1.8—3.8倍。相关性分析显示,微生物残体碳含量与海拔、年降雨量、干旱指数、地上生物量、地下生物量以及土壤有机碳、全氮、铵态氮、硝态氮、全磷、微生物生物量(微生物量碳、微生物量氮、微生物量磷、真菌、细菌、放线菌和原生动物)显著正相关(P<0.05),与年均温及土壤容重、pH显著负相关(P<0.05)。细菌残体碳和真菌残体碳含量分别随细菌和真菌含量的增大而增大(P<0.001),微生物残体碳含量随真菌/细菌值的增大而增大(P<0.05),随革兰氏阳性/革兰氏阴性细菌(GP/GN)值的增大而减小(P<0.01)。随机森林模型预测显示,土壤全氮和pH是土壤微生物残体碳的主要影响因子。研究分析了宁夏不同草地类型微生物来源有机碳的积累特征及影响因素,可为进一步探讨干旱半干旱草地生态系统土壤有机碳固存的微生物学机制提供数据支撑。

In order to explore the accumulation of soil microbial necromass carbon(MNC)in different grassland types,and determine the contribution of MNC to soil organic carbon(SOC)and its influencing factors.In this study,we measured soil physicochemical properties,microbial community and soil amino sugars contents through the biomarker method in 0—20 cm soil layers of Meadow steppe(MS),Typical steppe(TS),Desert steppe(DS),Steppe desert(SD)and Desert(D)in Ningxia,and further analyzed the relationship between MNC and soil physicochemical properties and microbial community.Our results indicated that:the contents of soil organic carbon(SOC),total nitrogen(TN),ammonium nitrogen(NH+4-N),nitrate nitrogen(NO-3-N),microbial biomass carbon(MBC),microbial biomass nitrogen(MBN),fungi,bacteria,actinomycetes and protozoa in MS and TS had significantly higher other grassland types(P<0.05).The contents of glucosamine(GluN),mannosamine(ManN),galactosamine(GalN),muramic acid(MurA)were the highest in MS,and the lowest in D(P<0.05).The content of GluN((0.62±0.18)μg/mg)in different grassland types was the highest,and the content of MurA((0.04±0.01)μg/mg)was the lowest.The contents of bacterial necromass carbon(BNC),fungal necromass carbon(FNC)and total necromass carbon(TNC)in different grassland types varied 0.12—5.74μg/mg,0.22—15.31μg/mg and 0.34—21.05μg/mg,respectively.The contribution of BNC,FNC and TNC to SOC in different grassland types varied 9.0%—17.8%,22.0%—48.2%and 33.5%—66.0%,respectively.We found that the contribution of MNC to SOC was 1.3—3.8 times higher in FNC than in BNC.The correlation analysis showed that MNC was significantly positively correlated with elevation,MAP,AI,AGB,BGB,SOC,TN,NH+4-N,NO-3-N,TP and microbial biomass(MBC,MBN,MBP,fungi,bacteria,actinomycetes and protozoa),and significantly negatively correlated with MAT,BD and pH.The content of BNC and FNC increased with the increase of bacteria and fungi,respectively(P<0.001).The content of TNC increased with the increase of fungi/bacteria ratios(P<0.05),and decreased with the increase of GP/GN ratios(P<0.01).The random forest analysis showed that the different importance of climate,plant and soil factors on the MNC.In conclusion,the variation in grassland types altered soil physicochemical properties and microbial community,resulting in more beneficial to the formation and accumulation of FNC,and TN and pH were the main influencing factors of MNC.Thus,this study can provide data support for further research on the microbiological mechanism of SOC sequestration in arid and semi-arid grassland ecosystems.