模拟氮沉降增加条件下土壤团聚体对酶活性的影响

氮沉降增加改变了森林土壤生态系统物质输入,影响土壤生物及酶活性,而土壤团聚体内相对稳定的微域生境可能减弱或延缓土壤生物和酶对氮沉降增加的响应强度。以广东省东莞大岭山森林公园荷木人工林为研究对象,用模拟N沉降方法,分析了2011年12月到2012年11月一年内氮沉降增加条件下表层混合土壤和土壤团聚体内脲酶、蔗糖酶和酸性磷酸酶活性的变化及影响因素,旨在理解氮沉降增加条件下土壤团聚体对酶活性的影响。结果表明:氮沉降增加对表层混合土壤中脲酶和蔗糖酶的抑制作用不显著,而酸性磷酸酶受氮沉降显著影响,表现为低氮(50 kg N hm-2a-1)促进,高氮(300 kg N hm-2a-1)抑制的规律。表层土壤团聚体内脲酶活性随氮沉降增加而降低,N300处理显著低于对照;蔗糖酶和酸性磷酸酶活性随氮沉降增加先降低后增加,N100处理最低,分别比其他处理降低了6.46%—25.53%和42.33%—68.25%。试验区内各粒径土壤团聚体内酶活性高于混合土壤,且随团聚体粒径增加酶活性均为先增加后降低。不同粒径土壤团聚体的3种酶活性均以2—5 mm最高,但脲酶、酸性磷酸酶在各团聚体粒径间差异不显著,蔗糖酶活性2—5 mm显著高于5—8 mm。土壤酶相对活性指数和相对活性综合指数结果显示,超过85%的团聚体粒径内的相对酶活性指数大于1,而土壤酶相对活性综合指数均大于1。以上结果表明,氮沉降增加条件下土壤团聚体对其团聚体内的土壤酶活性有隔离保护作用,但其隔离保护效果与酶的种类和土壤团聚体粒径有关。

Early effect of soil aggregates on enzyme activities in a forest soil with simulated N deposition elevation

Soil biota and enzyme activities would be impacted under elevated nitrogen deposition condition. However, the relative stability of micro habitat within soil aggregates could also decrease or delay the response intensity of soil enzyme activities. This study was conducted in a Schima superba plantation, which located in Dalingshan forest park, Dongguan city, Guangdong, China in 2011.12-2012.11 by simulated nitrogen deposition treatments. Soil urease, invertase and acid phosphatase activities in surface homogenized soil (0-5 cm), as well as in soil aggregates (0.25-1 mm, 1-2 mm, 2-5 mm, and 5-8 mm) were analyzed to study the impacts of soil aggregates on soil enzyme activities under elevated N deposition. It showed that no significant effects of N deposition on soil urease and invertase activities were observed in the surface homogenized soil, while the soil acid phosphatase activities were dramatically impacted by N deposition with promotion in the low N deposition treatment (50 kg N hm^-2 a^-1) and inhibition in the high N deposition treatment (300 kg N hm^-2 a^-1). The urease activities in surface soil aggregates decreased with the increase of N deposition addition, and there were significant differences of urease activity in surface soil aggregates between N300 treatment and N0 treatment. With the increase amount of N deposition, the invertase and acid phosphatase activities in soil aggregates decreased at first and then increased. There were the lowest invertase and acid phosphatase activities in N100 treatment, 6.46%-25.53% and 42.33%-68.25% lower than that in other N deposition treatments, respectively. Almost all enzyme activities in soil aggregates were higher than that in homogenized soils, and the activities increased at first and then decreased with the soil aggregate size increase. In this study, the highest soil enzyme activities were found in the 2-5 mm size aggregates. No significant differences of urease and acid phosphatase activities were observed among different soil aggregate sizes, while the invertase activities in 2-5 mm aggregates were significantly higher than that in 5-8 mm aggregates. The relative enzyme activity indexes in more than 85% soil aggregates were higher than 1, and the relative enzyme activity composite index were all higher than 1. The results suggested that stimulated N deposition changed the soil enzyme activities both in homogenized soils and aggregated soils; soil aggregates could protect the internal soil enzyme activities under N deposition addition to a certain extent, which were related to the kinds of soil enzymes and soil aggregate sizes.