Broader environmental adaptation of rare rather than abundant bacteria in reforestation succession soil.

Revealing the responses of rare and abundant bacteria to environmental change is crucial for understanding microbial community assembly and ecosystem function. However, both the environmental adaptability and the ecological assembly processes exhibited by rare and abundant soil bacteria remain poorly understood. Here we investigated the assembly processes of rare and abundant bacteria along a chronosequence of a 35-year reforestation succession (8, 17, and 35 years), particularly with regard to their environmental adaptations. Compared to the abundant taxa, the phylogenetic clustering of rare taxa was tighter but their environmental breadth wider. Homogeneous selection (65.8%) belonging to deterministic processes dominated the rare bacterial assembly, whereas homogenizing dispersal and undominated process (57.9%) belonging to stochastic processes governed the abundant taxa. Neutral processes had a significant impact on shaping the rare taxa compared to the abundant taxa. Rare taxa were environmentally less constrained than abundant taxa. Soil EC was the major determinant factor for the assembly processes of both rare and abundant taxa. Ecological assembly processes showed a significant negative correlation with rare bacterial functional redundancies, while they had a significant positive correlation with the abundant taxa. Microbial network modularity further demonstrated that rare taxa developed stronger environmental adaptation strategies than their abundant counterparts. Our study significantly advances the knowledge of the environmental adaptability of rare and abundant bacteria and emphasizes their key role in reforestation ecological succession soils.

Genome-Resolved Metagenomics Reveals Distinct Phosphorus Acquisition Strategies between Soil Microbiomes.

Enhancing soil phosphate solubilization is a promising strategy for agricultural sustainability, while little is known about the mechanisms of how microorganisms cope with differing phosphorus availability. Using a combination of genome-resolved metagenomics and amplicon sequencing, we investigated the microbial mechanisms involved in phosphorus cycling under three agricultural treatments in a wheat-maize rotation system and two natural reforestation treatments. Available soil phosphorus was the key factor shaping bacterial and fungal community composition and function across our agricultural and reforestation sites. Membrane-bound quinoprotein glucose dehydrogenase (PQQGDH) and exopolyphosphatases (PPX) governed microbial phosphate solubilization in agroecosystems. In contrast, genes encoding glycerol-3-phosphate transporters (ugpB, ugpC, and ugpQ) displayed a significantly greater abundance in the reforestation soils. The gcd gene encoding PQQGDH was found to be the best determinant for bioavailable soil phosphorus. Metagenome-assembled genomes (MAGs) affiliated with Cyclobacteriaceae and Vicinamibacterales were obtained from agricultural soils. Their MAGs harbored not only gcd but also the pit gene encoding low-affinity phosphate transporters. MAGs obtained from reforestation soils were affiliated with Microtrichales and Burkholderiales. These contain ugp genes but no gcd, and thereby are indicative of a phosphate transporter strategy. Our study demonstrates that knowledge of distinct microbial phosphorus acquisition strategies between agricultural and reforestation soils could help in linking microbial processes with phosphorus cycling. IMPORTANCE The soil microbiome is the key player regulating phosphorus cycling processes. Identifying phosphate-solubilizing bacteria and utilizing them for release of recalcitrant phosphate that is bound to rocks or minerals have implications for improving crop nutrient acquisition and crop productivity. In this study, we combined functional metagenomics and amplicon sequencing to analyze microbial phosphorus cycling processes in natural reforestation and agricultural soils. We found that the phosphorus acquisition strategies significantly differed between these two ecosystems. A microbial phosphorus solubilization strategy dominated in the agricultural soils, while a microbial phosphate transporter strategy was observed in the reforestation soils. We further identified microbial taxa that contributed to enhanced phosphate solubilization in the agroecosystem. These microbes are predicted to be beneficial for the increase in phosphate bioavailability through agricultural practices.