Bacterial rather than fungal diversity and community assembly drive soil multifunctionality in a subtropical forest ecosystem

Microbial diversities are key drivers of soil multifunctionality in terrestrial ecosystems and are important for stability and productivity of ecosystems. However, the relationships among microbial diversity, community assembly and soil multifunctionality in forest ecosystems remained unclear. Here, soil samples were collected from a subtropical forest ecosystem, Lushan Mountain, China. High-throughput sequencing was employed to reveal the bacterial/fungal community assembly and biodiversity, as well as 10 enzyme activities were measured to assess soil multifunctionality. We found that soil multifunctionality was negatively regulated by bacterial and fungal alpha diversity, implying a higher potential functional redundancy in this forest soil. The null model indicated that deterministic processes (variable selection) and stochastic processes (dispersal limitation) govern bacterial and fungal phylogenetic turnover, respectively. Correlation analysis revealed that bacterial rather than fungal community assembly processes have a significant linkage to soil multifunctionality. These observations projected that soil variables could regulate multifunctionality by shaping the phylogenetic and taxonomic turnover of bacteria rather than fungi. In summary, our study highlighted that soil multifunctionality is mainly driven by bacterial diversity and community assembly processes while not fungal, presenting different views and knowledge of microbial diversity and community assembly processes in ecosystem functioning.

The limited effects of carbonaceous material amendments on nitrite-oxidizing bacteria in an Alfisol

Carbonaceous materials are soil conditioners that affect nitrogen cycles. However, how carbonaceous materials influence nitrite-oxidizing bacteria (NOB) is yet unclear. In this study, we investigated the NOB community and its potential activities under different treatments (control, biochar, straw, limestone, biochar + limestone, and straw + limestone) in an Alfisol, a type of arable soil depleted in calcium carbonate but enriched in aluminum- and iron-bearing minerals. Treatments with limestone increased soil pH, and straw inputs caused an increment of available potassium (AK). Ammonia (NH₄⁺) was inversely changed under the straw and biochar + limestone amendments. None of the treatments significantly impacted the abundance of Nitrobacter (nxrA) or the potential nitrite oxidation activity (PNO). The abundance of Nitrospira (nxrB) increased in the biochar + limestone-treated samples and was significantly correlated with PNO, pH, and AK. High-throughput sequencing results showed that the α-diversity of NOB did not change in response to the treatments. The dominant Nitrobacter OTUs were affiliated within the Clusters 3, 4, 8, and 9 (a new cluster named in this study), while those of Nitrospira were in the lineage II and Namibian soil cluster 2. The limited compositional variation for Nitrobacter was explained by pH, and that for Nitrospira by pH, TN, and NH₄⁺. Among all available data in this study, the richness of Nitrospira was the most important predictor (73%) for PNO. Therefore, we assumed that the community of nitrite oxidizers (Nitrospira) could be relatively redundant in function, supported by the observation that the carbonaceous inputs did not impact either the potential activity or the α-diversity but did affect the abundance and community composition.