模拟氮沉降对湿性常绿阔叶次生林土壤碳氮组分和酶活性的影响

为了研究氮沉降对次生林土壤碳氮组分和酶活性的影响,以华西雨屏区湿性常绿阔叶次生林为对象,从2014年1月起进行野外定位模拟氮沉降试验,分别设置对照(CK,+0 g/(m^2·a))、低氮(LN,+5 g/(m^2·a))和高氮(HN,+15 g/(m^2·a))3个氮添加水平。在氮沉降进行27个月后,按照腐殖质层和淋溶层表层进行取样,测定不同土层土壤总有机碳(TOC)、可浸提溶解性有机碳(EDOC)、易氧化碳(ROC)、全氮(TN)、硝态氮(NO_3^-—N)和铵态氮(NH_4^+—N)含量以及蔗糖酶、脲酶、酸性磷酸酶和多酚氧化酶活性。结果表明:模拟氮沉降显著增加该次生林腐殖质层土壤的TOC和NH_4^+—N含量,显著增加腐殖质层和淋溶层表层土壤的NO_3^-—N含量,腐殖质层土壤C/N显著升高。淋溶层表层土壤TOC、NH_4^+—N、C/N以及2层土壤的EDOC、ROC、TN和NH_4^+—N/NO_3^-—N均无显著影响。2层土壤的多酚氧化酶活性均随着氮添加量的升高而降低,其中淋溶层表层达到显著差异。模拟氮沉降对蔗糖酶、脲酶和酸性磷酸酶活性均无显著影响。腐殖质层中,NH_4^+—N和NO_3^-—N含量与TOC含量存在极显著正相关关系。2层土壤的多酚氧化酶活性均与NO_3^-—N含量呈极显著负相关。结果说明,模拟氮沉降使该次生林中原本较高的腐殖质层土壤TOC含量进一步显著增加,并且促进土壤无机氮的积累,而模拟氮沉降对多酚氧化酶的抑制作用更加有利于土壤有机质的积累。

Effects of Simulated Nitrogen Deposition on Soil Carbon and Nitrogen Fractions and Enzyme Activity in Moist Evergreen Broad-leaved Secondary Forest

In order to study the effects of nitrogen deposition on soil carbon and nitrogen fractions and enzyme activity in secondary forests, we took the moist evergreen secondary forests in rainy area of west China as the object. A simulated nitrogen deposition experiment in the field was conducted from January 2014. The addition levels of nitrogen included control (CK, +0 g/(m²·a)), low nitrogen (LN,+5 g/(m²·a)) and high nitrogen (HN,+15 g/(m²·a)). After 27 months of nitrogen deposition, soil samples of the humus layer and the surface of the leaching layer were collected to measure the contents of soil total organic carbon (TOC), extractable dissolved organic carbon (EDOC), readily oxidizable carbon(ROC), total nitrogen (TN), NO₃^--N, NH₄⁺-N as well as enzyme activities of sucrase, urease, acid phosphatase and polyphenol oxidase. The results showed that simulated nitrogen deposition significantly increased contents of TOC and NH₄⁺-N in the humus layer, and the contents of NO₃^--N in the humus layer and the surface of the leaching layer, and increased significantly the value of C/N in the humus layer of the secondary forest. The contents of TOC, NH₄⁺-N and C/N in the surface of the leaching layer and the contents of EDOC, ROC, TN and ammonium nitrate ratios in the two kinds of soil layers were not influenced by simulated nitrogen deposition. The polyphenol oxidase activity of the two soil layers decreased with the increasing of nitrogen addition, and the difference in surface of the leaching layer was significant. Simulated nitrogen deposition had no significant effect on the activities of invertase, urease and acid phosphatase. In the humus layer, there was a very significant positive correlation between the contents of NH₄⁺-N and NO₃^--N and the TOC. The polyphenol oxidase activities were significantly negatively correlated with the NO₃^--N content in the two soil layers. The results showed that the simulated nitrogen deposition further increased the TOC content in the humus layer of the secondary forest, and promoted the accumulation of soil inorganic nitrogen. The inhibition of simulated nitrogen deposition on polyphenol oxidase was more conducive to the accumulation of soil organic matter.