The network of interactions among soil quality variables and nematodes: short-term responses to disturbances induced by chemical and organic disinfection

Anthropogenic pressures that involve different kinds of inflows (chemical vs organic) to soils are likely to induce different responses of individual soil components as well as to affect the web of interactions between them. The aim of this paper was to explore whether chemical or organic disinfection constitute two different types of disturbance, regarding both their severity on individual soil components and the structural changes they induce on the network of interactions among soil biochemical variables and nematode functional guilds. Network analysis, a novel approach in the context of soil ecology, was used to explore these interactions.Different plots within a field cultivated conventionally with Phaseolus vulgaris for many years were disinfected either with metham sodium or with a mixture of plant-based alternatives (neem and essential oils). Control plots receiving no disinfectants were also included in our study. One month after the treatments were applied, we estimated microbial C and N, activities of asparaginase, glutaminase, urease and phosphatase, organic C and N, inorganic N and P as well as the functional diversity of nematodes.Chemical disinfection had a direct lethal effect on all nematodes, while the effect on the microbial community was less obvious, implying that at the time of sampling, microbial populations, especially bacterial ones had started to recover from disturbance. Urease and phosphatase activities were inhibited, which may partly be responsible for the reduced amounts of inorganic N and P. Organic disinfectants reduced microbial populations, mainly the fungal ones, but they did not inhibit enzyme activities. The availability of N and P increased and nematode abundance was not affected significantly.The results demonstrate the usefulness of network analysis in providing insight into the structure and robustness of the soil network and its response to disturbance. Despite the pronounced reduction in nematode numbers due to chemical disinfection, the importance of nematode guilds within the interaction network was amplified and a more compact network was formed. On the other hand, interactions within organic plots were found to be primarily dictated by soil biochemistry. Finally, the analysis showed that both types of disinfection increased the vulnerability of the interaction network and this was more pronounced in chemically treated plots.