华北低丘陵山区人工林土壤微生物生物量碳氮变化及其影响因素

Microbial Biomass Carbon and Nitrogen at Man-made Forests in Northern China Hilly Areas

【目的】土壤微生物是土壤中重要的存在,土壤中的微生物量碳和微生物量氮能直接或间接参与土壤理化过程,是维持土壤质量的重要指标,可综合反映土壤肥力特性和生物活性。【方法】在河南省济源市黄河小浪底生态系统定位站内选择3种人工纯林,包括刺槐(Robinia pseudoacacia)林、栓皮栎(Quercus variabilis)林和侧柏(Platyclodus orientalis)林,采集未分解枯落物层(L层)、半分解/腐殖化枯落物层(F/H层)以及矿质土层(0~10、10~20 cm)的土壤样品,测定微生物生物量碳(Microbial biomass carbon,MBC)、微生物生物量氮(Microbial biomass nitrogen,MBN)、MBC/MBN以及枯落物层和土壤层总碳(Total carbon,TC)、总氮(Total nitrogen,TN)、可溶性有机碳(Dissolved organic carbon,DOC)和可溶性有机氮(Dissolved organic nitrogen,DON),研究探讨土壤微生物生物量(Soil microbial biomass,SMB)与树种、土深的关系及其机理。【结果】(1)在枯落物层,3种林型的TC最高值均出现在F/H层,而TN的最高值则均出现在L层;3种林型TC和TN均表现为F/H层>L层>0~10 cm、10~20 cm土层,差异显著(P<0.05)。3种林型的DOC表现为枯落物层高于矿质土壤层,DON为矿质土壤层高于枯落物层。枯落物层3种林分之间的DOC含量均表现为栓皮栎林显著高于刺槐林,二者与侧柏林之间差异不显著(P>0.05)。(2)在枯落物层,3种林型的MBC均表现为F/H层高于L层,表现为刺槐林>栓皮栎林>侧柏林。在矿质土层中,3种林型的MBC均为0~10 cm高于10~20 cm土层,表现为栓皮栎林>刺槐林>侧柏林,同一土层的刺槐林和栓皮栎林之间差异不显著(P>0.05)。枯落物层及矿质土层的MBN均表现为栓皮栎林>刺槐林>侧柏林。栓皮栎林在各个土层中均是MBN最高的树种,且与侧柏林之间差异显著(P<0.05)。(3)L和F/H层的MBC/MBN比值相差不大,而在矿质土层中,随土深增加MBC/MBN呈上升趋势。在矿质土层,3种林型MBC/MBN均表现为10~20 cm显著高于0~10 cm;在0~10 cm,3种林型之间差异不显著(P>0.05),在10~20 cm,刺槐林显著高于侧柏林(P>0.05),而与栓皮栎林之间差异不显著(P<0.05)。(4)相关性分析表明,3种林型的MBC均与总碳、总氮呈极显著正相关(P<0.01),其中栓皮栎林MBC与总碳的相关系数最大,为0.959。刺槐林和栓皮栎林的C/N与总碳、总氮呈负相关,而侧柏林的C/N则与总碳、总氮呈正相关,相关系数分别为0.512和0.524。【结论】在华北低丘陵山区种植栓皮栎对土壤的生态恢复效果较好,更有利于生态系统的碳氮循环。

【Objective】Microbial biomass carbon and nitrogen(MBC and MBN)in soil at the man-made forests on northern China hilly lands were studied.【Method】Three man-made forests that contained solely Robinia pseudoacacia,Quercus variabilis or Platyclodus orientalis trees at the Xiaolangdi Ecosystem Positioning Station of the Yellow River in Jiyuan,Henan were selected for the study.Soil samples in the layers of undecomposed litter(L),semi-decomposed/humic litter(F/H),and litter-free 0-10 cm and 10-20 cm depths were collected to determine the MBC,MBN,MBC/MBN ratio,and physiochemical properties.Correlations of the soil microbial biomass(SMB)with different tree species and soils were analyzed.【Result】(1)The highest total carbon(TC)in the soil that contained plant litter at the 3 forests was found in the F/H layer,and the greatest total nitrogen(TN)in the L layer.The TC and TN of the forests ranked in the order of F/H layer>L layer>0-10 cm and 10-20 cm soils with no fallen wastes(P<0.05).DOC was higher in the layers with litter than without,but opposite on DON.The DOC in the littered soil was significantly higher at the Q.variabilis forest than the R.pseudoacacia forest,and no significant difference between the two and the P.orientalis forest(P>0.05).(2)In the soil layers with tree litter,MBC was higher in the F/H than in the L layer with a ranking of R.pseudoacacia>Q.variabilis>P.orientalis among the 3 forests.In the two layers of litter-free mineral soil,MBC was higher in the depth of 0-10 cm than in the deeper layer.It ranked among the different forests as Q.variabilis>R.pseudoacacia>P.orientalis with no significant difference between the Q.variabilis and R.pseudoacacia forests(P>0.05).The MBNs of both the littered and litter-free soil at the forests were Q.variabilis>R.pseudoacacia>P.orientalis,while Q.variabilis generated the highest MBN that was significantly different from P.orientalis(P<0.05).(3)The MBC/MBN ratios of the L and F/H layers did not differ significantly,whereas those of the mineral soils tended to increase with the depth.The 0-10 cm litter-free soil did not differ significantly on the ratio among the forests(P>0.05).However,that of the 10-20 cm soil at the R.pseudoacacia forests were significantly higher than that at the P.orientalis forest(P>0.05),but no significant difference between them and that at the Q.variabilis forest(P<0.05).(4)Significant correlations existed between the MBC and the TC and TN at the 3 forests.The correlation coefficient of 0.959 between MBC and TC of Q.variabilis was the highest among all.The C/N ratios of R.pseudoacacia and Q.variabilis negatively,while the C/N of P.orientalis positively,correlated with TC and TN,with correlation coefficients of 0.512 and 0.524,respectively.【Conclusion】Conducive to environmental carbon and nitrogen cycling,Q.variabilis appeared to be a prudent choice of plant for the ecological restoration in the low mountainous areas in northern China.