Tiunov Alexei V, Scheu Stefan
Laboratory of Soil Zoology, Institute of Ecology and Evolution, Leninsky Prospect 33, 119071 Moscow, Russia.
Oecologia. 2004 Jan;138(1):83-90. doi: 10.1007/s00442-003-1391-4. Epub 2003 Oct 3.
Activity of soil decomposer microorganisms is generally limited by carbon availability, but factors controlling saprophagous soil animals remain largely unknown. In contrast to microorganisms, animals are unable to exploit mineral nutrient pools. Therefore, it has been suggested that soil animals, and earthworms in particular, are limited by the availability of nitrogen. In contrast to this view, a strong increase in density and biomass of endogeic earthworms in response to labile organic carbon addition has been documented in field experiments. The hypothesis that the growth of endogeic earthworms is primarily limited by carbon availability was tested in a laboratory experiment lasting for 10 weeks. In addition, it was investigated whether the effects of earthworms on microbial activity and nutrient mineralization depend on the availability of carbon resources. We manipulated food availability to the endogeic earthworm species Octolasion tyrtaeum by using two soils with different organic matter content, providing access to different amounts of soil, and adding labile organic carbon (glucose) enriched in (13)C. Glucose addition strongly increased the growth of O. tyrtaeum. From 8 to 17% of the total C in earthworm tissue was assimilated from the glucose added. Soil microbial biomass was not strongly affected by the addition of glucose, though basal respiration was significantly increased and up to 50% of the carbon added as glucose was incorporated into soil organic matter. The impact of earthworms on the mineralization and leaching of nitrogen depended on C availability. As expected, in C-limited soil, the presence of earthworms strongly increased nitrogen leaching. However, when C availability was increased by the addition of glucose, this pattern was reversed, i.e. the presence of O. tyrtaeum decreased nitrogen leaching and its availability to soil microflora. We conclude that irrespective of the total carbon content of soils, O. tyrtaeum was primarily limited by carbon, and that increased carbon availability allowed earthworms to be more effective in mobilizing N. The presence of earthworms increases C limitation of soil microorganisms, due to increased availability of N and P in earthworm casts or a direct depletion of easily available carbon resources by earthworms.
土壤分解微生物的活性通常受碳有效性的限制，但控制食腐性土壤动物的因素在很大程度上仍不为人知。与微生物不同，动物无法利用矿质养分库。因此，有人提出土壤动物，尤其是蚯蚓，受氮有效性的限制。与这种观点相反，在田间试验中已记录到，随着易分解有机碳的添加，内生蚯蚓的密度和生物量大幅增加。在一项为期10周的实验室实验中，对内生蚯蚓的生长主要受碳有效性限制这一假设进行了检验。此外，还研究了蚯蚓对微生物活性和养分矿化的影响是否取决于碳资源的有效性。我们通过使用两种不同有机质含量的土壤、提供不同量的土壤以及添加富含¹³C的易分解有机碳（葡萄糖），来控制内生蚯蚓八毛枝蚓（Octolasion tyrtaeum）的食物可利用性。添加葡萄糖极大地促进了八毛枝蚓的生长。蚯蚓组织中总碳的8%至17%是从添加的葡萄糖中同化而来的。添加葡萄糖对土壤微生物生物量的影响不大，不过基础呼吸显著增加，添加的葡萄糖中高达50%的碳被纳入土壤有机质中。蚯蚓对氮矿化和淋溶的影响取决于碳的有效性。正如预期的那样，在碳受限的土壤中，蚯蚓的存在显著增加了氮的淋溶。然而，当通过添加葡萄糖提高碳有效性时，这种模式发生了逆转，即八毛枝蚓的存在减少了氮的淋溶及其对土壤微生物群落的可利用性。我们得出结论，无论土壤的总碳含量如何，八毛枝蚓主要受碳的限制，碳有效性的提高使蚯蚓在调动氮方面更有效。蚯蚓的存在增加了土壤微生物的碳限制，这是由于蚯蚓粪中氮和磷的有效性增加，或者蚯蚓直接消耗了易利用的碳资源。
