中亚热带3种典型森林土壤碳氮含量和酶活性的关系

Relationships between carbon and nitrogen contents and enzyme activities in soil of three typical subtropical forests in China

森林类型更替是影响生态系统有机质循环的重要因素,它对森林生态系统的生产力、碳吸存和养分保持功能有影响。然而关于中亚热带不同森林类型对土壤碳氮含量和酶活性的影响及土壤碳氮含量和酶活性之间的关系鲜有报道。该文研究了福建省三明市3种典型亚热带森林——米槠(Castanopsis carlesii)天然次生林(SF)、米槠人工促进天然更新林(AR)、马尾松(Pinus massoniana)人工林(PM)的淋溶层(A层)土壤碳氮含量和土壤微生物酶活性的关系。结果表明:在3种森林类型表层土壤中,可溶性有机质中可溶性有机碳、可溶性有机氮(DON)、荧光发射光谱腐殖化指数的趋势均为SF>AR>PM,芳香化指数大小为PM>AR>SF;SF和AR的NH^4^+-N显著高于PM,NO_3~–-N在3种林分中的含量低且差异不明显,造成这种差异的原因是树种差异和人为干扰程度不同。PM的β-葡萄糖苷酶活性显著低于SF和AR;纤维素水解酶活性大小为AR>SF>PM;PM多酚氧化酶显著高于SF和AR,3种林分过氧化物酶无显著差异。AR的β-N-乙酰氨基葡萄糖苷酶(NAG)显著高于其他两种林分。冗余分析显示土壤总氮和DON是驱动淋溶层土壤酶活性的主要环境因子。总之,土壤总氮含量与NAG活性呈正相关关系,并且可溶性有机氮可能是氮循环中的重要一环;土壤微生物优先利用易分解碳;且碳氮养分循环之间存在一定的耦合关系。氮提高了与土壤碳相关的水解酶活性,从而可促进碳周转。

Aims Forest conversion is an important factor affecting the ecosystem organic matter cycle,and has an impact on the productivity of forest ecosystems,carbon sequestration and nutrient conservation.This study aims to provide more scientific evidence for better understanding the mechanism of different forest types regulating forest soil carbon and nitrogen cycling in the context of forest conversion.Methods The study site is located in Sanming City,Fujian Province,in subtropical China.Soil samples in the A horizon from an artificial-assisted natural regeneration forest of Castanopsis carlesii（AR）,a natural secondary forest of C.carlesii（SF）and a plantation of Pinus massoniana（PM）sites were collected in November,2016.We investigated the contents of soil organic carbon,soil organic nitrogen,soil dissolved organic matter（DOM）,NH^4＋-N and NO3^–-N The spectroscopic characteristics of soil DOM were also measured by means of ultraviolet absorbance and fluorescence emission spectroscopic techniques.The activity of five kinds of enzymes related to carbon and nitrogen cycle were determined to decipher their relationships with soil properties.Important findings The results showed that,due to different tree species and man-made disturbance,the contents of dissolved organic carbon（DOC）,DON,humification index of fluorescence emission spectrum were all in the order SF〉AR〉PM,whereas the aromatization index was in the order PM〉AR〉SF.NH4^＋-N were significantly richer for SF and AR than for PM,while NO3^–-N content was low and similar across the three stands.Theβ-glucosidase activity of PM was significantly lower than that of SF and AR.The activities of cellulolytic enzyme were in sequence of AR〉SF〉PM.The activities of polyphenol oxidase enzyme in PM was significantly higher than in SF and AR.There was no significant difference in the type of forest peroxidase.The activity ofβ-N-acetylglucosaminidase of AR was significantly higher than those of the other two kinds of stands.The redundancy analysis indicates that total nitrogen（TN）and DON are the major environmental factors driving soil enzyme activity.Soil total nitrogen content and NAG activity were positively correlated,and DON may be an important component of the N cycle.Soil microorganisms prefer to use readily decomposable carbon;and there is a certain coupling relationship between carbon and nitrogen cycles.Higher soil N contents would increase the C-related hydrolytic enzyme activity,thereby promoting carbon turnover.