Effects of drought and water pulses on microbial functionality and the role of Cyanoprokaryota in the rhizospheres of gypsophytes

Seasonal variations of soil bacterial and fungal communities in a subtropical Eucalyptus plantation and their responses to throughfall reduction

Climatic change causes obvious seasonal meteorological drought in southern China, yet there is a lack of comprehensive in situ studies on the effects of drought in Eucalyptus plantations. Here, a 50% throughfall reduction (TR) experiment was conducted to investigate the seasonal variations of soil bacterial and fungal communities and functions in a subtropical Eucalyptus plantation and their responses to TR treatment. Soil samples were collected from control (CK) and TR plots in the dry and rainy seasons and were subjected to high-throughput sequencing analysis. Results showed that TR treatment significantly reduced soil water content (SWC) in the rainy season. In CK and TR treatments, fungal alpha-diversity decreased in the rainy season while bacterial alpha-diversity did not change significantly between dry and rainy seasons. Moreover, bacterial networks were more affected by seasonal variations compared with fungal networks. Redundancy analysis showed that alkali hydrolyzed nitrogen and SWC contributed the most to the bacterial and fungal communities, respectively. Functional prediction indicated that the expression of soil bacterial metabolic functions and symbiotic fungi decreased in the rainy season. In conclusion, seasonal variations have a stronger effect on soil microbial community composition, diversity, and function compared with TR treatment. These findings could be used to develop management practices for subtropical Eucalyptus plantations and help maintain soil microbial diversity to sustain long-term ecosystem function and services in response to future changes in precipitation patterns.

The coupling interaction of soil organic carbon stock and water storage after vegetation restoration on the Loess Plateau, China

Vegetation restoration may increase the soil organic carbon stock (SOCS) but decrease the soil water storage (SWS) of terrestrial ecosystems in arid and semiarid regions. To guarantee the sustainability of restoration, it is critical to evaluate the coupling interaction of SOCS and SWS. Here, we examined the spatial distributions of SOCS and SWS across a 0-200 cm soil profile in a grassland, forestland and shrubland on the Loess Plateau and determined the driving factors that affected their variations. Our results showed that SOCS and SWS varied across the 0-200 cm soil profile and considerably accumulated in the deep soil layers (100-200 cm). In comparison to SOCS, SWS generally had higher relative benefits in most studied plant communities, which ensured sustainable restoration. In addition, land use played a less important role than local environmental conditions in determining the variations in SOCS and SWS. Specifically, the interaction between SOCS and SWS was mainly strong in the surface soil layers (0-20 cm). Topography was a predominant factor that affected SOCS and SWS in the deep soil layers (100-200 cm), while soil texture was a stable driving factor influencing their variations across the whole soil profile (0-200 cm). Given the low moisture consumption of grasslands and the lowest root mean square deviation (RMSD) of Hippophae rhamnoides, we proposed an advanced scenario for ecological restoration on the Loess Plateau: establishing reasonably large Hippophae rhamnoides patches with fewer edges in a contiguous grassland matrix. Furthermore, this scenario should be tailored to local environmental conditions, such as soil water, texture and topography, followed by natural vegetation succession.

Soil Bacterial and Fungal Community Responses to Throughfall Reduction in a Eucalyptus Plantation in Southern China

In subtropical plantations in southern China, how soil microbial communities respond to climate change-induced drought is poorly understood. A field experiment was conducted in a subtropical Eucalyptus plantation to determine the impacts of 50% of throughfall reduction (TR) on soil microbial community composition, function, and soil physicochemical properties. Results showed that TR reduced soil water content (SWC) and soil available phosphorus (AP) content. TR significantly altered 196 bacterial operational taxonomic units (OTUs), most of them belonging to Acidobacteria, Actinobacteria, and Proteobacteria, while there were fewer changes in fungal OTUs. At the phylum level, TR increased the relative abundance of Acidobacteria at 0–20 cm soil depth by 37.18%, but failed to influence the relative abundance of the fungal phylum. Notably, TR did not alter the alpha diversity of the bacterial and fungal communities. The redundancy analysis showed that the bacterial communities were significantly correlated with SWC, and fungal communities were significantly correlated with AP content. According to predictions of bacterial and fungal community functions using PICRUSt2 and FUNGuild platforms, TR had different effects on both bacterial and fungal communities. Overall, SWC and AP decreased during TR, resulting in greater changes in soil bacterial community structure, but did not dramatically change soil fungal community structure.

Soil desiccation cracking and its characterization in vegetated soil: A perspective review

The formation and propagation of surface desiccation cracks in vegetated infrastructures involve coupled factors including unsaturated soil mechanics, atmospheric conditions and vegetation parameters. Vegetation induces a "Love-hate" relationship in the development of desiccation cracks due to plant induced suction as well as root reinforcement. The objective of the paper is to provide a state-of-the-art that comprehensively reviews the desiccation process in context of the soil-water-plant interaction together. At first, basic theories of crack initiation and propagation in literature are discussed in the context of unsaturated soil mechanics. Thereafter, influence of vegetation on soil cracking is discussed systematically based on transpiration induced suction, root reinforcement, plantation strategy, root exudate and basic plant traits. Intrusive and non-intrusive measurement approaches of desiccation cracks including lab and field studies are put forward. Various schools of desiccation models have been briefly touched upon. More than 150 studies on desiccation cracks have been tabulated in this review, considering soil types, vegetation cover, drying-wetting cycles, approaches of characterizing cracks, sample size, crack pattern, hydraulic conductivity and water retention. Future scopes involving measurement considerations, usage of geotechnical centrifuge modelling, bio-amendments and plant effects on desiccation cracking have been put forward.