A Case Study of Nematode Communities’ Dynamics along Successional Paths in the Reclaimed Landfill

Abstract

<jats:p>We assessed the abundance and composition of nematode communities in soil under herbaceous vegetation in reclaimed landfill sites at different ages after closure (3, 10 and 14 years) compared to those in neighboring semi-natural grazed grasslands (reference sites). We further applied network analysis based on the co-occurrence patterns of nematodes. Nematode abundance decreased between 3 and10 years of regeneration, but significantly increased from 10 to 14 years of regeneration. The number and identity of genera were comparable along the succession; however, there were dissimilarities in community composition during early- and mid-succession. The diversity, community composition and abundance at the sites after 14 years of regeneration converged with those at the reference sites. Moreover, changes during succession were not accompanied by the maturation of the soil food web, as demonstrated by Enrichment and Channel indices. In all the networks, centrality and modularity metrics differed significantly from those for random networks, whereas cohesion metrics showed no difference. All the networks exhibited Small-worldness indices higher than one, demonstrating that the networks of the interactions among genera at all the sites shared features that matched both random and non-random networks. The succession trajectory in reclaimed landfills was represented by a sequence of changes that differed in relation to the variable under consideration; network parameters tended to converge with those of a relatively resistant reference community, while the Enrichment and Channel indices did not. Additionally, the succession trajectory was not linear or steady; only the Channel index and Worldness index showed linear responses to succession time. However, across all the successional stages, the resource status remained basal or degraded while the nematode communities had an enhanced ability to cope with sudden changes.</jats:p>

Recurring heavy rainfall resulting in degraded-upgraded phases in soil microbial networks that are reflected in soil functioning

“…A non-modular network is mainly deterministically regulated while a modular one is regulated by stochastic processes (Zhou et al, 2014). According to those authors, dispersal limitation favors deterministic processes while the easy dispersal of organisms promotes stochastic processes that induce homogeneous architectures, enabling the easy spread of the consequences of environmental constraints throughout the network (Stamou et al, 2020). However, despite the above-mentioned statement, the networks in most hydrated mesocosms supporting easy dispersal exhibited modular architecture.…”

“…A merit of network analysis is that it reveals global and local aspects of the interactions' configuration simultaneously (Glo-cal analysis; Stamou and Papatheodorou, 2016). This Glo-cal approach was applied successfully to assess ecosystem connectivity in perturbated soil mesocosms (Stamou et al, 2019), to describe the associative patterns of soil nematode communities in reclaimed landfills (Stamou et al, 2020), and to depict changes in microbial co-occurrence patterns in cultivated areas inoculated with Plant Growth Rhizobacteria (Papatheodorou et al, 2021). Further, such an approach helped us to analyze the interplay between the deterministic and stochastic processes that are thought to modulate the structure of a community and control its resistance and resilience (Stamou et al, 2020).…”

“…This Glo-cal approach was applied successfully to assess ecosystem connectivity in perturbated soil mesocosms (Stamou et al, 2019), to describe the associative patterns of soil nematode communities in reclaimed landfills (Stamou et al, 2020), and to depict changes in microbial co-occurrence patterns in cultivated areas inoculated with Plant Growth Rhizobacteria (Papatheodorou et al, 2021). Further, such an approach helped us to analyze the interplay between the deterministic and stochastic processes that are thought to modulate the structure of a community and control its resistance and resilience (Stamou et al, 2020). However, the use of network analysis to examine the stochasticity-deter-minism balance in the regulation of communities' structure and how this is related to their ability to overcome disturbances, is a new field of research.…”

“…In contrast, the theory of neutrality against organisms' identity postulates that the structure of a community is driven by the intrinsic stochasticity of demographic traits (ecological drift), speciation, extinction, disturbance outbreaks and lack of dispersal limitation (Vellend et al, 2014;Zhou and Ning, 2017). Recently, it has been accepted that deterministic and stochastic processes operate simultaneously, but the contribution of each of them varies over time (Vellend et al, 2014;Maignien et al, 2014), along a deterministic-stochastic continuum (Stamou et al, 2020). The prevalence of stochastic processes is related to modular architecture (Zhou et al, 2014).…”

Fire and Rhizosphere Effects on Bacterial Co-Occurrence Patterns

“…Net deterministic and net stochastic perspectives occupy the two endpoints of a determinism-stochasticity continuum reflecting competitive and stochastic exclusion, respectively [ 38 ]. In the real world, the relative influence of determinism and stochasticity can vary in both time and space between the two endpoints of the continuum [ 36 , 39 ]. Discussion of the forces governing the composition and structure of ecological communities could also be informed by differences in the competitive ability and/or species’ niches.…”