Severe Prolonged Drought Favours Stress-Tolerant Microbes in Australian Drylands

Drylands comprise one-third of Earth's terrestrial surface area and support over two billion people. Most drylands are projected to experience altered rainfall regimes, including changes in total amounts and fewer but larger rainfall events interspersed by longer periods without rain. This transition will have ecosystem-wide impacts but the long-term effects on microbial communities remain poorly quantified. We assessed belowground effects of altered rainfall regimes (+ 65% and -65% relative to ambient) at six sites in arid and semi-arid Australia over a period of three years (2016-2019) coinciding with a significant natural drought event (2017-2019). Microbial communities differed significantly among semi-arid and arid sites and across years associated with variation in abiotic factors, such as pH and carbon content, along with rainfall. Rainfall treatments induced shifts in microbial community composition only at a subset of the sites (Milparinka and Quilpie). However, differential abundance analyses revealed that several taxa, including Acidobacteria, TM7, Gemmatimonadates and Chytridiomycota, were more abundant in the wettest year (2016) and that their relative abundance decreased in drier years. By contrast, the relative abundance of oligotrophic taxa such as Actinobacteria, Alpha-proteobacteria, Planctomycetes, and Ascomycota and Basidiomycota, increased during the prolonged drought. Interestingly, fungi were shown to be more sensitive to the prolonged drought and to rainfall treatment than bacteria with Basidiomycota mostly dominant in the reduced rainfall treatment. Moreover, correlation network analyses showed more positive associations among stress-tolerant dominant taxa following the drought (i.e., 2019 compared with 2016). Our result indicates that such stress-tolerant taxa play an important role in how whole communities respond to changes in aridity. Such knowledge provides a better understanding of microbial responses to predicted increases in rainfall variability and the impact on the functioning of semi-arid and arid ecosystems.

Alternation of soil bacterial and fungal communities by tomato-rice rotation in Hainan Island in Southeast of China

Tomato-rice rotation is prevalent in subtropical and tropical regions in China. This practice enhances crop productivity and the disease suppression property of soils against soil-borne plant pathogens. To explore the variations and dynamics of bacterial and fungal communities, bulk soil samples were collected during two consecutive years under a rotation system between tomato and rice originated from the year of 2010 in Hainan Island, and 16S rDNA and ITS amplicons were sequenced by Illumina MiSeq. The results demonstrated that potentially beneficial bacterial phyla Acidobacteria, Chloroflexi and genus Paenibacillus, as well as the fungal genus Mortierella were significantly enriched, while the potentially pathogenic fungal genus Fusarium was significantly decreased during the crop rotation. Measurements of soil physicochemical properties indicated that the soil acidification was improved. Redundancy analysis (RDA) revealed the correlation of the microbial community with soil pH and identified soil total phosphorus (TP) level as the highest determinant factor for both bacterial and fungal communities. This work provides a preliminary description of changes of the bacterial and fungal communities related to tomato-rice rotation in China and offered experimental evidences for exploring the effects of this agricultural practice on soil ecology.

Yucatán in black and red: Linking edaphic analysis and pyrosequencing-based assessment of bacterial and fungal community structures in the two main kinds of soil of Yucatán State

Yucatán State is dominated by two kinds of soil, named "Black Leptosol" and "Red Leptosol", which are interwoven across the State. In this work, we analyzed the relation between the edaphic characteristics and the bacterial and fungal community structures in these two kinds of Leptosol. The results revealed that Black Leptosol (BlaS) had a higher content of calcium carbonates, organic matter, nitrogen, and phosphorus than Red Leptosol (RedS). The most outstanding difference in the bacterial community structure between BlaS and RedS was that while in BlaS Actinobacteria was the most abundant phylum (43.7%), followed by Acidobacteria (26.9%) and Proteobacteria (23.6%), in RedS the bacterial community was strongly dominated by Acidobacteria (83%). Two fungal phyla were identified in both kinds of soil; Ascomycota, with 77% in BlaS and 56% in RedS, and Basidiomycota, with 22% in RedS and only 0.67% in BlaS. The most relevant difference between the two fungal communities was that excepting for Fusarium sp., all the species they had were different. Thus, in contrast with bacterial communities, where most of the major OTUs were present in both kinds of soil, fungal communities appeared to be unique to each kind of Leptosol.