BIODIVERSITAS ISSN: 1412-033X Volume 21, Number 10, October 2020 E-ISSN: 2085-4722 Pages: 4813-4820 DOI: 10.13057/biodiv/d211047 Bacterial (9A2H) enhancement alters the nematode community structure and decomposition pathway of amended nutrient-limited soil DEMA R. LUCKYANA, I G. A. AYU RATNA PUSPITASARI, ARDHINI R. MAHARNING ♥ Faculty of Biology, Universitas Jenderal Soedirman, Jl. dr. Suparno 63, Purwokerto Utara, Banyumas 53122, Central Java, Indonesia, Tel./fax.: +62-281-625865,  email: ardhini.maharning@unsoed.ac.id Manuscript received: 4 July 2020. Revision accepted: 25 September 2020. Abstract. Luckyana DR, Puspitasari IGAAR, Maharning AR. 2020. Bacterial (9A2H) enhancement alters the nematode community structure and decomposition pathway of amended nutrient-limited soil. Biodiversitas 21: 4813-4820. This study examined the influence of paddy litter amendment and bacterial enhancement of nutrient-limited soil on the nematode community structure and investigated the decomposition rate of the litter due to the treatment. We applied a microcosm-based approach using sand as the medium, including the following treatments: no-bacteria, 9A-autotrophic-bacteria, 2H-heterotrophic-bacteria, and 9A-2H-mix-bacteria, with five replicates. The litter bag experiment and exponential decay model estimated the litter decomposition rate in the microcosm. The soil samples and litter bags were retrieved after days 21, 42, and 63. The structure, enrichment, channel index (CI), and canonical correspondence analysis were employed to investigate the nematode community response. Bacterial enhancement shifted the nematode community and the soil food web toward the dominant bacterial pathway by day 63 (CI: 0), with a slightly less structured food web that was supported by bacterivorous nematodes mostly related to available nutrients. These changes coincided with soil organic carbon and nitrogen increases over time. Our experiments showed that paddy litter amendment and the 9A, 2H, and 9A-2H-mix bacterial enhancements improved nutrient-limited soil, according to the analysis of the nematode community, its composition, and the food web conditions determining nutrient mobility and availability. However, these factors have no impact on the litter decay rate. Keywords: Baerman funnel method, forest soil resource, nematode feeding group, paddy litter decomposition, soil food web index INTRODUCTION Nematodes are the most abundant and dominant metazoans in soil and interact with one another through a food web (Van Den Hoogen et al. 2019; Wilschut et al. 2019). The trophic structure links omnivorous, carnivorous, bacterivorous, and fungivorous nematodes within the soil microfood web responsible for decomposing organic matter and nutrient cycling. In the web, bacteria and fungi are the primary decomposers that enzymatically degrade complex organic substances and function as nutrient sources for nematodes. These primary decomposers regulate the bacterivorous and fungivorous nematode populations, most likely by means of bottom-up control (Ferris 2010; Scharroba et al. 2016; Zhang et al. 2016). The close linkages between these trophic levels give rise to the fundamental concept that changes in nutrient sources, such as bacterial abundance and composition, might lead to changes in the higher trophic levels of the soil food web, such as the nematode community. Microfood web development is partly determined by available organic matter, as the basal resource in the soil environment (Morriien 2016; Sauvadet et al. 2016). Organic matter is the carbon source used by soil bacteria and fungi. Bacteria use labile substances, and fungi utilize both labile and recalcitrant substances in organic matter. They promote the growth of bacterivorous or fungivorous nematodes via changes in bacterial and fungal communities, therefore altering the nematode composition, which might progress toward the bacterial or fungal decomposition pathway. The classical food web view indicates that soil organic matter containing labile substances is related to bacterial energy channels and that resistant substances in organic matter stimulate fungal energy channels (De Vries and Caruso 2016). The linkages between trophic levels in the soil food web, the control exerted by microorganisms on their feeder populations, and the influence of soil organic matter on the nematode community suggest a food web concept that is applicable for improving nutrient-limited soil. The food web system is expected to mobilize nutrients through trophic linkages, to mineralize soil organic matter by feeding and enzymatic activities, and to improve soil structure by forming soil aggregates, thereby creating heterogeneity and a suitable microclimate for soil organisms (Kardol et al. 2016). Trophic linkage complexity might indicate functional improvement of nutrient-limited soil because the soil food web is most likely to include more trophic linkages as the habitat progresses toward the natural stage (Hannula et al. 2017). As nutrient resources for soil nematodes, bacteria have the potential to be enhancing agents supporting and determining nematode community development in nutrient- limited soil, leading to the further mobilization of nutrients via the web and promotion of organic matter mineralization (Sauvadet et al. 2016). The bacteria require soil organic matter as their growth medium and nutrient sources to play their role during the enhancement process in less fertile