强冻融作用下土壤微生物残体碳的累积特征及其对玉米秸秆输入的响应

Soil microbial residual carbon accumulation as affected by freeze-thaw intensity and maize straw incorporation

【目的】微生物残体碳是土壤稳定碳库的主要组成部分。探究不同冻融强度下东北黑土区土壤真菌和细菌残体碳的变化和积累特征,以及玉米秸秆对这一过程的影响,以加深对东北黑土土壤有机碳循环过程和微生物调控机理的认知,为东北黑土区土壤肥力提升提供理论支撑。【方法】研究采用室内模拟培养试验,供试材料为玉米秸秆和黑土。设置3个冻融强度处理:弱冻融(融冻温度/冻结温度为5℃/-4℃)、强冻融(融冻温度/冻结温度为5℃/-9℃)和5℃常温对照,每个冻融处理分别设置添加和不添加玉米秸秆处理。一个冻融循环为土壤样品在5℃培养24 h,逐渐降低温度至冻结温度,保持48 h,然后升温至5℃,直到总时间96 h(4天),然后进入下一个循环。冻融试验共进行了16次循环,总培养周期为65天。在第0、3、8、12和16次冻融后采集土壤样品,测定土壤氨基葡萄糖(真菌残体标识物)和胞壁酸(细菌残体标识物)含量,分析微生物残体碳的累积特征及其对土壤有机碳的贡献。【结果】不添加玉米秸秆条件下,强冻融处理在前期较恒温对照显著增加了真菌和细菌残体碳含量及其对土壤有机碳的贡献,降低了土壤真菌细菌残体碳比值(F/B),而弱冻融处理相关指标较恒温处理则变化不明显;在第16次循环,强冻融显著降低了微生物残体碳含量及其对土壤有机碳的贡献,增加了F/B值。在恒温和弱冻融处理中,添加秸秆在前期促进了真菌和细菌残体碳的累积,但在第16次循环,降低了真菌和细菌残体碳含量;而在强冻融处理中,添加秸秆则在试验结束时显著增加了细菌残体碳含量,降低了F/B值。试验结束时,添加秸秆后不同冻融强度对微生物残体碳贡献率影响不大。【结论】反复多次强冻融会降低土壤中微生物残体碳的累积,尤以细菌残体碳损失比例更大。添加玉米秸秆对真菌残体碳积累无显著影响,但能够显著增加细菌残体碳的积累,增加细菌残体碳的比例和其对土壤有机碳的贡献,在一定程度上抵消强冻融对微生物残体碳累积的不利影响。因此,添加秸秆可提高反复强冻融土壤中微生物源碳的稳定性。

【Objectives】Microbial residual carbon is an important composition for the stability of soil carbon pool.Study on the effects of freeze-thaw intensity on the accumulation of fungal and bacterial residual C and their contributions to soil organic carbon(SOC),as well as the impact of corn straw incorporation on these processes,will deepen the knowledge on the microbial regulatory mechanism of SOC sequestration,and provide a theoretical support for the improvement of soil fertility in Northeast China.【Methods】Indoor incubation method was used in the research,with maize straw and black soil as experimental materials.Freeze-thaw intensity treatments of weak(melting temperature/freezing temperature was 5℃/-4℃)and strong(melting temperature/freezing temperature was 5℃/-9℃)were setup,whereas constant 5℃ room temperature served as control.Each freezethaw intensity treatment was conducted under straw and non-straw conditions.The soil samples were incubated at 5℃ for 24 h,then decreased to the treated freezing temperature for 48 h,and then rose to 5℃ for 24 h to complete a freeze-thaw cycle.The experiment included 16 times freeze-thaw cycle and lasted 65 days.After the 0,3,8,12,and 16 times freeze-thaw cycle,soil samples were collected to determine the glucosamine(fungal residue biomarker)and muramic acid(bacterial residue biomarker)contents,and the accumulation of microbial residue C and its contribution to SOC were analyzed.【Results】In the non-straw control,the strong freeze-thaw treatment significantly increased the fungal and bacterial residue C contents and their contributions to SOC,and decreased the fungal/bacterial residue C(F/B)compared with the constant temperature treatment in the early stage,while the relevant indicators in the weak freeze-thaw treatment did not change significantly compared with the constant temperature treatment.After 16 times cycle,strong freeze-thaw treatment significantly reduced the soil microbial residue C and its contribution to SOC,and increased the F/B value.At constant temperature and weak freezethaw treatments,straw addition promoted the accumulation of fungal and bacterial residue C at the early stage,but after the 16th cycle,the contents of fungal and bacterial residue C were reduced.For the strong freeze-thaw treatment,straw addition significantly increased the content of bacterial residue C and decreased the F/B value at the end of the experiment.At the end of the experiment,the freeze-thaw intensity had little effect on the contribution of microbial residue C to SOC after straw incorporation.【Conclusions】Repetitive and intensive freeze-thaw reduces the microbial residue C,especially bacterial residue C accumulation.When maize straw was added into soil,the fungal residue C was not influenced,but the accumulation of bacterial residual C was increased significantly,which led to higher ratio of fungi to bacterial C and higher contribution of microbial C to the whole soil organic carbon storage.So,straw addition could help the stability of soil organic carbon pool to a certain extent.