Ferris Howard, Bongers Tom
Department of Nematology, University of California, Davis, CA 95616 Laboratory of Nematology, Wageningen University, PO Box 8123, 6700 ES, Wageningen, the Netherlands.
J Nematol. 2006 Mar;38(1):3-12.
The organisms of the soil food web, dependent on resources from plants or on amendment from other sources, respond characteristically to enrichment of their environment by organic matter. Primary consumers of the incoming substrate, including bacteria, fungi, plant-feeding nematodes, annelids, and some microarthropods, are entry-level indicators of enrichment. However, the quantification of abundance and biomass of this diverse group, as an indicator of resource status, requires a plethora of extraction and assessment techniques. Soluble organic compounds are absorbed by bacteria and fungi, while fungi also degrade more recalcitrant sources. These organisms are potential indicators of the nature of incoming substrate, but current methods of biomass determination do not reliably indicate their community composition. Guilds of nematodes that feed on bacteria (e.g., Rhabditidae, Panagrolaimidae) and fungi (e.g., Aphelenchidae, Aphelenchoididae) are responsive to changes in abundance of their food. Through direct herbivory, plant-feeding nematodes (e.g., many species of Tylenchina) also contribute to food web resources. Thus, analysis of the nematode community of a single sample provides indication of carbon flow through an important herbivore channel and through channels mediated by bacteria and fungi. Some nematode guilds are more responsive than others to resource enrichment. Generally, those bacterivores with short lifecycles and high reproductive potential (e.g., Rhabditidae) most closely mirror the bloom of bacteria or respond most rapidly to active plant growth. The feeding habits of some groups remain unclear. For example, nematodes of the Tylenchidae may constitute 30% or more of the individuals in a soil sample; further study is necessary to determine which resource channels they portray and the appropriate level of taxonomic resolution for this group. A graphic representation of the relative biomass of bacterivorous, fungivorous, and herbivorous nematodes provides a useful tool for assessing the importance of the bacterial, fungal, and plant resource channels in an extant food web.
土壤食物网中的生物依赖于植物资源或其他来源的改良，它们对环境中有机物的富集具有典型反应。进入底物的初级消费者，包括细菌、真菌、植食性线虫、环节动物和一些小型节肢动物，是富集的入门级指标。然而，作为资源状况的指标，对这一多样群体的丰度和生物量进行量化需要大量的提取和评估技术。可溶性有机化合物被细菌和真菌吸收，而真菌也会降解更难分解的来源。这些生物是进入底物性质的潜在指标，但目前的生物量测定方法并不能可靠地表明它们的群落组成。以细菌为食的线虫类群（如小杆线虫科、全齿蚓科）和以真菌为食的线虫类群（如滑刃线虫科、细滑刃线虫科）对其食物丰度的变化有反应。通过直接食草，植食性线虫（如许多垫刃线虫属物种）也为食物网资源做出贡献。因此，对单个样本的线虫群落进行分析，可以表明碳通过一个重要的食草动物通道以及通过细菌和真菌介导的通道的流动情况。一些线虫类对比其他类对资源富集更敏感。一般来说，那些生命周期短、繁殖潜力高的食细菌者（如小杆线虫科）最能反映细菌的大量繁殖，或对植物的活跃生长反应最快。一些类群的摄食习性仍不清楚。例如，垫刃线虫科的线虫可能占土壤样本中个体的30%或更多；需要进一步研究来确定它们描绘的是哪些资源通道以及该类群合适的分类分辨率水平。以食细菌、食真菌和食草线虫的相对生物量为基础的图表，为评估现存食物网中细菌、真菌和植物资源通道的重要性提供了一个有用的工具。
