Ekelund F, Rønn R
Department of Population Biology, University of Copenhagen, Denmark.
FEMS Microbiol Rev. 1994 Dec;15(4):321-53. doi: 10.1111/j.1574-6976.1994.tb00144.x.
Heterotrophic flagellates and naked amoebae are usually very numerous in agricultural soils; with numbers in the magnitude of 10,000 to 100,000 (active+encysted) cells per gram of soil. In 'hotspots' influenced by living roots or by dead organic material, the number may occasionally be as high as several millions per gram of soil. An exact enumeration of these organisms is virtually impossible. As they most often adhere closely to the soil particles, direct counting will underestimate numbers since the organisms will be masked. The method usually applied for enumeration of these organisms, the 'most probable number (MPN) method', is based on the ability of the organisms to grow on particular culture media. This method will in many cases underestimate the total protozoan number (active+encysted). It is uncertain how many of the heterotrophic flagellates and naked amoebae are actively moving and how many are encysted at a particular time; the 'HCl-method' which has usually been used to discriminate between active and encysted has proven to be highly unreliable. Despite the methodological difficulties many investigations of these organisms indicate that they play an important role in agricultural soils as bacterial consumers, and to a minor extent as consumers of fungi. Because of their small size and their flexible body they are able to graze bacteria in small pores in the soil in which larger organisms are precluded from coming. Key factors restricting the number and activity of heterotrophic flagellates and naked amoebae in soils seem to be water potential and soil structure and texture. In micro-cosm experiments, small heterotrophic flagellates and naked amoebae regulate the size and composition of the bacterial community. Bacterial activity seems to be stimulated by these organisms in most cases as well as the mineralization of carbon and nitrogen and possibly other mineral nutrients. In the rhizosphere of living plants the activity of protozoa has proven to stimulate uptake of nitrogen in pot experiments, and it has been hypothesized that organic matter liberated by plants in the root zone will stimulate bacterial and protozoan activity, leading to mineralization of organic soil nitrogen which is subsequently taken up by the plants.
异养鞭毛虫和裸变形虫在农业土壤中通常数量众多；每克土壤中的数量可达10000至100000个（活动态+包囊态）细胞。在受活根或死亡有机物质影响的“热点”区域，每克土壤中的数量偶尔可能高达数百万个。对这些生物进行精确计数几乎是不可能的。由于它们大多紧密附着在土壤颗粒上，直接计数会低估数量，因为这些生物会被掩盖。通常用于计数这些生物的方法，即“最大可能数（MPN）法”，是基于这些生物在特定培养基上生长的能力。在许多情况下，这种方法会低估原生动物的总数（活动态+包囊态）。不确定在特定时间有多少异养鞭毛虫和裸变形虫处于活动状态，有多少处于包囊状态；通常用于区分活动态和包囊态的“盐酸法”已被证明极不可靠。尽管存在方法上的困难，但对这些生物的许多研究表明，它们作为细菌消费者在农业土壤中发挥着重要作用，在较小程度上也作为真菌消费者。由于它们体型小且身体灵活，它们能够在土壤中的小孔中捕食细菌，而较大的生物无法进入这些小孔。限制土壤中异养鞭毛虫和裸变形虫数量及活动的关键因素似乎是水势以及土壤结构和质地。在微观实验中，小型异养鞭毛虫和裸变形虫会调节细菌群落的大小和组成。在大多数情况下，这些生物似乎会刺激细菌活动以及碳、氮和可能其他矿质养分的矿化。在活植物的根际，盆栽实验已证明原生动物的活动会刺激氮的吸收，并且有人推测植物在根区释放的有机物质会刺激细菌和原生动物的活动，导致有机土壤氮矿化，随后被植物吸收。
