Clarifying the accumulation pattern of soil microbial residue carbon and its contribution to soil organic carbon (SOC) across stand age is helpful to understand the mechanism underlying soil carbon cycling. In this study, we analyzed the differences of amino sugar content, physicochemical properties and microbial composition in surface soil (0-10 cm) in young (6 a), middle-aged (13 a), near-mature (29 a), mature (38 a) and over-mature (57 a) Pinus massoniana plantations of subtropical China, quantified the microbial residue carbon content and its contribution to SOC, and discussed the mechanism. The results showed that SOC, total nitrogen, amorphous iron oxide and leucine aminopeptidase contents in the middle-aged plantation were significantly lower than those in the mature plantation. Soil pH and fungal/bacteria in young plantation were significantly higher than those in other age groups. Across the stand age gradient, the ranges of microbial, fungal and bacterial residue carbon were 7.52-14.63, 4.03-8.00 and 3.48-6.63 g·kg-1, respectively. The contents of all the residue carbon were significantly higher in the mature plantation than that of the middle-aged plantation, which were positively affected by soil total nitrogen content. The contribution of microbial, fungal, and bacterial residue carbon to SOC was 59.7%-72.3%, 33.4%-45.6%, and 24.3%-30.8%, respectively. The contribution of fungal residue carbon to SOC in young plantation was significantly higher than that in other age groups, and the contribution of bacterial residue carbon to SOC in middle-aged plantation was significantly higher than that in young and near-mature plantations, both of which were affected by soil inorganic nitrogen. Fungal residue carbon content was 1.2-1.7 times as that of bacterial residue carbon content, and dominated for the accumulation of microbial residue carbon. Results of the partial least squares model showed that stand age, soil environmental factors (such as leucine aminopeptidase, amorphous iron oxide, pH, and total nitrogen), bacterial residue carbon, fungal residue carbon and the contribution of bacterial residue carbon to SOC had total effects on the contribution of fungal residue carbon to SOC (-0.37, -1.16, 0.90, 1.09, and 0.83, respectively). In conclusion, stand age promoted the accumulation of microbial residue carbon but did not increase its contribution to SOC.
明晰人工林林分发育过程中土壤微生物残体碳的积累模式及其对土壤有机碳(SOC)的贡献有助于理解土壤碳循环和固碳机制。本研究以亚热带马尾松人工林为对象,分析了幼龄林(6 a)、中龄林(13 a)、近熟林(29 a)、成熟林(38 a)和过熟林(57 a)表层(0～10 cm)土壤氨基糖含量、理化性质和微生物组成等的差异,量化微生物残体碳含量及其对SOC的贡献,并探讨其影响机制。结果表明: 中龄林SOC、全氮、非晶形铁氧化物含量和亮氨酸氨基肽酶活性显著低于成熟林,幼龄林土壤pH和真菌/细菌显著高于其他龄组。在林分发育过程中,微生物、真菌和细菌残体碳的变化范围分别为7.52～14.63、4.03～8.00和3.48～6.63 g·kg-1,且成熟林显著高于中龄林,受土壤全氮含量的正影响。微生物、真菌和细菌残体碳对SOC的贡献分别为59.7%～72.3%、33.4%～45.6%和24.3%～30.8%。真菌残体碳对SOC的贡献在幼龄林显著高于其他龄组,细菌残体碳对SOC的贡献在中龄林显著高于幼龄林和近熟林,两者受土壤无机氮的影响。真菌残体碳是细菌残体碳的1.2～1.7倍,主导了微生物残体碳的积累。偏最小二乘模型分析表明,真菌残体碳对SOC的贡献受林龄、土壤环境因子(如亮氨酸氨基肽酶、非晶形铁氧化物、pH和全氮)、细菌残体碳、真菌残体碳和细菌残体碳对SOC贡献影响的总效应分别为-0.37、-1.16、0.90、1.09和0.83。综上,林龄促进微生物残体碳的积累,但并未增加其对SOC的贡献。.
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