Response of Soil Nematode Community Structure and Function to Monocultures of Pumpkin and Melon

It is well known that crop monoculture can induce negative effects on soil ecosystems and crop productivity. However, little is known about how vegetable monoculture affects the soil nematode community structure and its relationship with vegetable yields. In this study, the composition, abundance, metabolic footprint, and ecological indices of soil nematodes are investigated in monocultures of pumpkin and melon. The relationships between nematode community structure and yields of pumpkin and melon were analyzed by linear regression. Both monoculture soils of pumpkin and melon suppressed the relative abundance of bacterivores but increased the relative abundance of plant parasites. Pumpkin monoculture soils decreased soil nematode diversity but increased the maturity index of plant parasites. Monoculture soils of pumpkin and melon decreased the metabolic footprint of lower- and higher-level trophic groups of the soil food web, respectively. Pumpkin and melon monoculture soils increased the food web indices channel index (CI) but decreased the enrichment index (EI) and the structure index (SI). The monoculture soils of pumpkin and melon led to a more fungal-dominated decomposition pathway and degraded soil food web conditions. The abundance of bacterivores and food web indices EI and SI were positively correlated with soil nutrients and pH, while the abundance of plant parasites and CI were negatively correlated with soil nutrients and pH. Paratylenchus was negatively correlated with pumpkin and melon yields and could be the potential plant parasites threatening pumpkin and melon productions. Redundancy analysis showed that monocultures of pumpkin and melon altered the soil nematode community via soil properties; total N, total P, alkeline-N, and pH were the main driving factors.

Animal soil food web complexity triggers shifts in microbial communities, including PAH degraders, but without clear effects on phenanthrene phytoremediation

The aim of this study was to determine whether the complexity of the animal soil food web (SFWC) is a significant factor influencing the soil microbial communities, the productivity of the willow, and the degradation rates of 100 mg kg-1 phenanthrene contamination. The SFWC treatment had eight levels: just the microbial community (BF), or the BF with nematodes (N), springtails (C), earthworms (E), CE, CN, EN, CEN. After eight weeks of growth, the height and biomass of willows were significantly affected by the SFWC, whereas the amount of phenanthrene degraded was not affected, reaching over 95% in all pots. SFWC affected the structure and the composition of the bacterial, archaeal and fungal communities, with significant effects of SFWC on the relative abundance of fungal genera such as Sphaerosporella, a known willow symbiont during phytoremediation, and bacterial phyla such as Actinobacteriota, containing many PAH degraders. These SFWC effects on microbial communities were not clearly reflected in the community structure and abundance of PAH degraders, even though some degraders related to the Actinobacteriota and the diversity of Gram-negative degraders were affected by the SFWC treatments. Overall, our results suggest that, under our experimental conditions, SFWC does not affect significantly willow phytoremediation outcomes.

Nature Restoration Shifts the Abundance and Structure of Soil Nematode Communities in Subtropical China

Aims Soil nematode community is an important component of the soil food web, which has been widely recognized as a key bio-indicator for assessing the influence of nature restoration on ecological functions. However, the dynamics of the abundance, diversity and function of soil nematode community remain unclear under different forest succession phases. Methods The soil nematode community of natural secondary forests was investigated using a chronosequence approach. Nature restoration for five succession stages were sampled in this study to represent a wide range of stand age groups.Results Soil nematode abundance gradually increased with forest stand age, which reached a peak value (574 individuals 100 g-1 dry soil) in the older age classes. In contrast, soil nematode diversity was not affected by forest stand age. Soil available nitrogen and phosphorus were key factors influencing soil nematode abundance and diversity during forest secondary succession. The plant parasite index decreased with forest stand age, which indicated that ecosystem function and health would be improved as nature restoration progresses. In addition, the structure of soil nematode community was more sensitive to forest secondary succession compared to plant community and soil microbial community. The bottom-up effects of the plant and microbial communities on soil nematode community were important drivers of nematode community structure in subtropical forests. Conclusions Overall, this study demonstrates the active responses of soil nematode community to nature restoration, and highlights the importance of the above-ground and below-ground interactions to the soil food web.

Multifunctionality of belowground food webs: resource, size and spatial energy channels

The belowground compartment of terrestrial ecosystems drives nutrient cycling, the decomposition and stabilisation of organic matter, and supports aboveground life. Belowground consumers create complex food webs that regulate functioning, ensure stability and support biodiversity both below and above ground. However, existing soil food-web reconstructions do not match recently accumulated empirical evidence and there is no comprehensive reproducible approach that accounts for the complex resource, size and spatial structure of food webs in soil. Here I build on generic food-web organization principles and use multifunctional classification of soil protists, invertebrates and vertebrates, to reconstruct "multichannel" food-web across size classes of soil-associated consumers. This reconstruction is based on overlying feeding preference, prey protection, size spectrum and spatial distribution matrices combined with biomasses of trophic guilds to infer weighted trophic interactions. I then use food-web reconstruction, together with assimilation efficiencies, to calculate energy fluxes assuming a steady-state energetic system. Based on energy fluxes, I describe a number of indicators, related to stability, biodiversity and multiple ecosystem-level functions such as herbivory, top-down control, translocation and transformation of organic matter. I illustrate the approach with an empirical example, comparing it with traditional resource-focused soil food-web reconstruction. The multichannel reconstruction can be used to assess trophic multifunctionality (analogous to ecosystem multifunctionality), i.e. simultaneous support of multiple trophic functions by the food-web, and compare it across communities and ecosystems spanning beyond the soil. With further validation and parametrization, my multichannel reconstruction approach provides an effective tool for understanding and analysing soil food webs. I believe that having this tool will inspire more people to comprehensively describe soil communities and belowground-aboveground interactions. Such studies will provide informative indicators for including consumers as active agents in biogeochemical models, not only locally but also on regional and global scales.

Using Nematode Community to Evaluate Banana Soil Food Web in Mekargalih, Cianjur, West Java

Soil biota is very diverse and contributes widely to ecosystem services that are important in the sustainable function of natural and managed ecosystems. Knowing the condition of the soil food web through the communities that inhabit it is necessary to assess the productivity of the soil. Nematode communities in the soil food web can be used as indicators because of their high abundance, and they inhabit various trophic levels, and participate in several important processes in the soil. The soil food web condition from three locations (Agr1, Agr2, Agr3) through the nematode functional index was evaluated using the maturity index (MI), the maturity index 2-5 (MI-25), the plant-parasitic index (PPI), the channel index (CI), the enrichment index (EI), the structure index (SI), and the basal index (BI). Nematode diversity was evaluated using Simpson’s index of diversity, dominance, and evenness. The MI and MI2-5 scores indicated that Agr3 (3.81) had an undisturbed food web, while Agr2 (2.88 and 3.0) and Agr1 (2.5 and 2.51) were in a moderate condition with minor disturbances. Fauna profile analysis using SI and EI shows that Agr3 and Agr1 had an undisturbed soil food web, and Agr2 was in enriched conditions. CI results found that Agr1 and Agr3 had a fungal decomposition pathway while Agr2 had a bacterial decomposition pathway. We concluded from this research, that prospect of the nematode community to serve as a collection of biological indicator data in assessing soil or ecosystem health can be considered in further research.