N沉降增加对森林生态系统地表土壤动物群落的影响

Responses of Aboveground Soil Fauna Community to Simulated N Deposition Addition in Forest Ecosystems

在3种南亚热地带代表性森林(季风常绿阔叶林、针阔混交林和马尾松林)中,历经16个月,通过5次取样,对模拟氮沉降增加条件下地表土壤动物群落的响应特征进行了比较研究。试验采用模拟的方法,人为构建了一个氮沉降增加梯度系列,即对照、低氮处理(50kg·hm-2·a-1)、中氮处理(100kg·hm-2·a-1)和高氮处理(150kg·hm-2·a-1)。结果表明,N处理水平整体上并未造成土壤动物群落的显著差异。但是,N沉降增加的处理效应在时间尺度上的动态变化中,也即,其在与不同植被演替类型、同一植被内不同取样期的交互作用中可以清楚地表现出来。在演替尺度上,季风林和针叶林对N处理的反应都很灵敏,前者负效应明显,后者则正效应明显,并因此最终改变了土壤动物群落在不同林分内的分布格局;同时,不同林分对各N处理水平的反应也不同。季风林内,只有低N处理显示了利好效应;混交林内,N处理的利好作用有一个从较高浓度的中N处理向较低浓度低N处理转移的过程;针叶林内,中N处理自始至终都表现了正向作用。N处理效应的表现也有一个年变化的动态过程。在持续的施N处理过程中,各林分中表现良好的处理效应最后都有减弱的趋势,甚至发展到负向效应或转移至更低的N处理水平中。N处理效应的年动态变化过程表明N沉降的累积效应是存在的。与区内的人工苗圃地试验结果进行了比较,并对产生以上响应的内在机制进行了初步探讨。

The responses of aboveground soil fauna in three native typical forests, monsoon evergreen leaf_broad, pine and leaf_broad mixed and pine forests (MEBF, MF and PF) in subtropical China to simulated N deposition addition in more than one year were studied in this paper. Treatments including control (No addition), low N deposition (50 kg.hm^(2).a^(-1)), middle N deposition (100 kg.hm^(2).a^(-1)), high N deposition (150 kg.hm^(2).a^(-1))by spreading water or NH_4NO_3. It suggested that there were not significant effects of N deposition addition on soil fauna when the values averaged across all of the samplings. But when the variances of time dimension were added to, it was clear of the influences of N treatments. In other words, there were significant interactions between N treatment and forest succession and the interactions between N treatment and sampling time in a certain forest. For the succession responses, mature MEBF and primary PF were all sensitive to N deposition addition. On the whole, the treatments produced negative effects in MEBF, and positive effects in PF, and the distribution pattern of soil fauna in the three forests were changed drastically. At the same time, the influences of a certain N treatment level on soil fauna varied with forest types:it was advantaged of low N treatment in MEBF; in MF, medium N firstly and then low N was favorable; medium N treatment consistently advantaged in PF. The effects of N deposition were also varied with sampling times. Because of the consistently N inputs, the advantage effects of a certain treatment in a certain forest would decrease at last, or even shift to negative effects and a lower treatment would be favorable at the same time. It indicated that deposited N would be accumulated in a long time treatment. Comparison between the study and the results from man_made seeding plots were conducted and the mechanism in the responses of soil fauna to N deposition addition were also discussed preliminaoily.