Bacterivore nematodes stimulate soil gross N transformation rates depending on their species
2018
Zhu, Tongbin | Yang, Cheng | Wang, Jun | Zeng, Siman | Liu, Manqiang | Yang, Jinling | Bai, Bing | Cao, Jianhua | Chen, Xiaoyun | Müller, Christoph
We conducted a microcosm experiment with soil being sterilized, reinoculated with native microbial community and subsequently manipulated the bacterivorous nematodes, including three treatments: without (CK) or with introducing one species of the two bacterivores characterized with different body size but similar c-p (colonizer-persister) value (Rhabditis intermedia and Protorhabditis oxyuroides, accounted for 6 and 59% of bacterivores in initially undisturbed soil, respectively). We monitored the N₂O and CO₂ emissions, soil properties, and especially quantified gross N transformation rates using ¹⁵N tracing technique after the 50 days incubation. No significant differences were observed on soil NH₄⁺ and NO₃⁻ concentrations between the CK and two bacterivores, but this was not the case for gross N transformation rates. In comparison to CK, R. intermedia did not affect soil N transformation rates, while P. oxyuroides significantly increased the rates of mineralization of organic N to NH₄⁺, oxidation of NH₄⁺ to NO₃⁻, immobilization of NO₃⁻ to organic N and dissimilatory NO₃⁻ reduction to NH₄⁺. Furthermore, the mean residence time of NH₄⁺ and NO₃⁻ pool was greatly lowered by P. oxyuroides, suggesting it stimulated soil N turnover. Such stimulatory effect was unrelated to the changes in abundance of bacteria and ammonia-oxidizing bacteria (AOB). In contrast to CK, only P. oxyuroides significantly promoted soil N₂O and CO₂ emissions. Noticeably, bacterivores increased the mineralization of recalcitrant organic N but decreased soil δ¹³C₋TOC and δ¹⁵N₋TN values, in particular for P. oxyuroides. Combining trait-based approach and isotope-based analysis showed high potential in moving forward to a mechanistic understanding of bacterivore-mediated N cycling.
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