Soil microbial interconnections along ecological restoration gradients of lowland forests after slash-and-burn agriculture

Interconnected versus unconnected microorganisms: Does it matter in anaerobic digestion functioning

Microorganisms in anaerobic digestion (AD) are essential for wastes/pollutants treatment and energy recovery. Due to microbial enormous diversity, developing effective perspectives to understand microbial roles therein is urgent. This study conducted AD of swine manure, used an ensemble-based network analysis to distinguish interconnected, unconnected, copresence (positively interconnected) and mutual-exclusion (negatively interconnected) microorganisms within microbial communities, and explored their importance towards AD performances, using amplicon sequencing of 16S rRNA and 16S rRNA gene. Our analyses revealed greater importance of interconnected than unconnected microorganisms towards CH₄ production and AD multifunctionality, which was attributed to higher niche breadth, deterministic community assembly, community stability and phylogenetic conservatism. The diversity was higher in unconnected than interconnected microorganisms, but was not linked to AD performances. Compared to copresence microorganisms, mutual-exclusion microorganisms showed greater and equal importance towards CH₄ production and AD multifunctionality, which was attributed to their roles in stabilizing microbial communities. The increased feedstock biodegradability, by replacing part of manure with fructose or apple waste, hardly affected the relative importance of interconnected versus unconnected microorganisms towards CH₄ production or AD multifunctionality. Our findings develop a new framework to understand microbial roles, and have important implications in targeted manipulation of critical microorganisms in waste-treatment systems.

Microbial features of mature and abandoned soils in refractory clay deposits

Processes of soil restoration in anthropogenically disturbed soils is an urgent topic in modern ecology and nature management. Being mediator between mineral soil composition and plant vegetation, soil microbial community is important factor of soil restoration processes. Analysis of main soil nutrition components followed by 16S amplicon sequencing are sufficient methods for primary analysis of novel locations. Here is the primary analysis in a novel location in Northwest Europe (Russia). Main nutrition parameters (pH, P, Na and NH₄⁺) and 16S rDNA Illumina amplicons were explored in abandoned soils from sandy pit quarry (2 sites) and refractory clay mining dumps (4 sites).Microbial communities of mature soils and dumps are variable and different in terms both nutritional and microbial components. pH, N and TOC are strong predictors for microbial composition. Dumps of refractory clays pQ_2 are non-developed soils, highly acidic and form specific microbial community. Differences between dumps and mature soils in both pre-quaternary and quaternary soils are connected with specific bacterial taxa. Those taxa are connected more with plant composition, not the soil properties themselves. The exact changes in microbial community are unique for different soils and areas.

Secondary Succession Altered the Diversity and Co-Occurrence Networks of the Soil Bacterial Communities in Tropical Lowland Rainforests

The characteristics of plant and soil bacterial communities in forest ecosystems have been reported, but our understanding of the relationship between plant communities and soil bacteria in different stages of secondary tropical rainforest succession is still poor. In June 2018, three different natural successional stages of tropical lowland rainforests, early (33 years), early-mid (60 years), and mid successional stage (73 years), in Hainan Island, China, were selected for this study. By conducting field investigation and 16S rRNA gene high-throughput sequencing, the composition and diversity of tree communities, the niche overlap of tree species with legumes among tree species, and the diversity and composition of soil bacterial communities and co-occurrence networks within communities across the successional stages were investigated. The results showed that plant richness and species diversity increased significantly during the secondary succession of tropical lowland rainforests. The order of positive correlations between nitrogen-fixing legumes and other species in plant communities was early-mid > mid > early successional stage. Soil nutrient content and soil bacterial richness were highest in the early-mid stages of succession, followed by mid and early stages of succession. Organic matter (OM), total nitrogen (TN), alkali nitrogen (AN), and available phosphorus (AP) had a stronger positive impact on soil bacterial communities. Co-occurrence network analysis showed that with the advancement of rainforests succession, the negative correlation between soil bacterial species decreased, and the community stability increased. Overall, as a result of tropical lowland rainforest secondary natural succession, the richness and diversity of plant communities increased, which altered the living conditions of nitrogen-fixing legumes and the soil properties, and the network complexity of soil bacterial communities increased with the rising of rainforest soil nutrient content.