Deterministic processes dominate nematode community structure in the Fynbos Mediterranean heathland of South Africa

Soil nematode community assembly in a primary tropical lowland rainforest

More than half of the world's tropical lowland rainforests have been lost due to conversion to agricultural land (such as rubber plantations). Thus, ecological restoration in degraded tropical lowland rainforests is crucial. The first step to restoration is restoring soil functioning (i.e., soil fertility, carbon, and nitrogen cycling) to levels similar to those in the primary tropical lowland rainforest. This requires understanding soil nematode community assembly in primary tropical lowland rainforest, which has never been explored in this habitat. In this study, we measured species compositions of plant and soil nematode communities and soil characteristics (pH, total and available nitrogen, phosphorus, and soil water content) in a primary tropical lowland rainforest, which is located on Hainan Island, China. We performed two tests (the null-model test and distance-based Moran's eigenvector maps (MEM) and redundancy analysis-based variance partitioning) to quantify the relative contribution of the deterministic (abiotic filtering and biotic interactions) and stochastic processes (random processes and dispersal limitation) to the soil nematode community. We found that a deterministic process (habitat filtering) determined nematode community assembly in our tropical lowland rainforest. Moreover, soil properties, but not plant diversity, were the key determinants of nematode community assembly. We have, for the first time, managed to identify factors that contribute to the nematode community assembly in the tropical lowland rainforest. This quantified community assembly mechanism can guide future soil functioning recovery of the tropical lowland rainforest.

Plant Compartments and Developmental Stages Modulate the Balance between Niche-Based and Neutral Processes in Soybean Microbiome

Understanding the dynamics of plant-associated microbial communities within agriculture is well documented. However, the ecological processes that assemble the plant microbiome are not well understood. This study elucidates the relative dominance of assembly processes across plant compartments (root, stem, and leaves) and developmental stages (emergence, growth, flowering, and maturation). Bacterial community composition and assembly processes were assessed using 16S rRNA gene amplicon sequencing. Null models that couple phylogenetic community composition and species distribution models were used to evaluate ecological assembly processes of bacterial communities. All models highlighted that the balance between the assembly process was modulated by compartments and developmental stages. Dispersal limitation dominated amongst the epiphytic communities and at the maturation stage. Homogeneous selection dominated assembly across plant compartments and development stages. Overall, both sets of models were mostly in agreement in predicting the prevailing assembly processes. Our results show, for the first time, that even though niche-based processes dominate in the plant environment, the relative influence of dispersal limitation in community assembly is important.

Functional Diversity of Soil Nematodes in Relation to the Impact of Agriculture—A Review

The analysis of the functional diversity of soil nematodes requires detailed knowledge on theoretical aspects of the biodiversity–ecosystem functioning relationship in natural and managed terrestrial ecosystems. Basic approaches applied are reviewed, focusing on the impact and value of soil nematode diversity in crop production and on the most consistent external drivers affecting their stability. The role of nematode trophic guilds in two intensively cultivated crops are examined in more detail, as representative of agriculture from tropical/subtropical (banana) and temperate (apple) climates. The multiple facets of nematode network analysis, for management of multitrophic interactions and restoration purposes, represent complex tasks that require the integration of different interdisciplinary expertise. Understanding the evolutionary basis of nematode diversity at the field level, and its response to current changes, will help to explain the observed community shifts. Integrating approaches based on evolutionary biology, population genetics and ecology can quantify the contribution of nematode fauna to fundamental soil functions. These include carbon transformation, nutrient cycling, pest control and disease transmission. In conclusion, different facets of nematode diversity such as trophic groups, life history traits, variability in body size and/or taxa identities in combination with DNA-based techniques are needed in order to disclose nematode–soil–ecosystem functioning relationships. Further experimental studies are required to define locally adapted and sustainable management practices, through ecosystem-based approaches and nature-based solutions.