Glavatska Olena, Müller Karolin, Butenschoen Olaf, Schmalwasser Andreas, Kandeler Ellen, Scheu Stefan, Totsche Kai Uwe, Ruess Liliane
Institute of Biology, Ecology Group, Humboldt-Universität zu Berlin, Berlin, Germany.
Institute of Soil Science and Land Evaluation, Soil Biology Department, University of Hohenheim, Stuttgart, Germany.
PLoS One. 2017 Jul 13;12(7):e0180264. doi: 10.1371/journal.pone.0180264. eCollection 2017.
Soil food web structure and function is primarily determined by the major basal resources, which are living plant tissue, root exudates and dead organic matter. A field experiment was performed to disentangle the interlinkage of the root-and detritus-based soil food chains. An arable site was cropped either with maize, amended with maize shoot litter or remained bare soil, representing food webs depending on roots, aboveground litter and soil organic matter as predominant resource, respectively. The soil micro-food web, i.e. microorganisms and nematodes, was investigated in two successive years along a depth transect. The community composition of nematodes was used as model to determine the changes in the rhizosphere, detritusphere and bulk soil food web. In the first growing season the impact of treatments on the soil micro-food web was minor. In the second year plant-feeding nematodes increased under maize, whereas after harvest the Channel Index assigned promotion of the detritivore food chain, reflecting decomposition of root residues. The amendment with litter did not foster microorganisms, instead biomass of Gram-positive and Gram-negative bacteria as well as that of fungi declined in the rooted zone. Likely higher grazing pressure by nematodes reduced microbial standing crop as bacterial and fungal feeders increased. However, populations at higher trophic levels were not promoted, indicating limited flux of litter resources along the food chain. After two years of bare soil microbial biomass and nematode density remained stable, pointing to soil organic matter-based resources that allow bridging periods with deprivation. Nematode communities were dominated by opportunistic taxa that are competitive at moderate resource supply. In sum, removal of plants from the system had less severe effects than expected, suggesting considerable food web resilience to the disruption of both the root and detrital carbon channel, pointing to a legacy of organic matter resources in arable soils.
土壤食物网的结构和功能主要由主要的基础资源决定，这些资源包括活的植物组织、根系分泌物和死亡的有机物质。进行了一项田间试验，以理清基于根系和碎屑的土壤食物链之间的联系。一块耕地分别种植玉米、添加玉米秸秆凋落物或保持裸土状态，分别代表以根系、地上凋落物和土壤有机质为主要资源的食物网。连续两年沿着深度剖面研究了土壤微食物网，即微生物和线虫。以线虫的群落组成为模型，来确定根际、碎屑圈和土体土壤食物网的变化。在第一个生长季节，处理对土壤微食物网的影响较小。在第二年，玉米下取食植物的线虫数量增加，而收获后通道指数显示碎屑食性食物链得到促进，这反映了根系残留物的分解。添加凋落物并没有促进微生物生长，相反，在有根系的区域，革兰氏阳性菌和革兰氏阴性菌以及真菌的生物量都下降了。可能是由于线虫的更高放牧压力降低了微生物现存量，因为食细菌和食真菌的线虫数量增加了。然而，较高营养级的种群并没有得到促进，这表明沿着食物链的凋落物资源通量有限。经过两年的裸土状态后，微生物生物量和线虫密度保持稳定，这表明基于土壤有机质的资源能够在缺乏资源的时期起到桥梁作用。线虫群落以机会主义类群为主，这些类群在中等资源供应条件下具有竞争力。总之，从系统中去除植物的影响比预期的要小，这表明食物网对根系和碎屑碳通道的破坏具有相当的恢复力，这表明耕地土壤中存在有机质资源遗留效应。
