The Distribution and Turnover of Bacterial Communities in the Root Zone of Seven Stipa Species Across an Arid and Semi-arid Steppe

Predicted changes in distribution and grazing value of Stipa-based plant communities across the Eurasian steppe

The Eurasian steppe is one of the world's largest continuous areas of grassland and has an important role in supporting livestock grazing, the most ubiquitous land use on Earth. However, the Eurasian steppe is under threat, from irrational grazing utilization, climate change, and resource exploitation. We used an ensemble modeling approach to predict the current and future distribution of Stipa-dominated plant communities in three important steppe subregions; the Tibetan Alpine, Central Asian, and Black Sea-Kazakhstan subregions. We combined this with an assessment of the grazing value of 22 Stipa species, the dominant grassland species in the area, to predict how grazing value might change under future climate change predictions. We found that the effects of changing climates on grazing values differed across the three subregions. Grazing values increased in the Tibetan alpine steppe and to a lesser extent in Central Asia, but there were few changes in the Black Sea-Kazakhstan subregion. The response of different species to changing climates varied with environmental variables. Finally, our trait-based assessment of Stipa species revealed variations in grazing value, and this had major effects on the overall grazing value of the region. Our results reinforce the importance of trait-based characteristics of steppe plant species, how these traits affect grazing value, and how grazing values will change across different areas of the Eurasian steppe. Our work provides valuable insights into how different species will respond to changing climates and grazing, with important implications for sustainable management of different areas of the vast Eurasian steppe ecosystem.

Spatial variations of fungal community assembly and soil enzyme activity in rhizosphere of zonal Stipa species in inner Mongolia grassland

Rhizosphere soil fungal and enzyme activities affect the nutrient cycling of terrestrial ecosystems, and rhizosphere fungi are also important participants in the ecological process of vegetation succession, responding to changes in plant communities. Stipa is an excellent forage grass with important ecological and economic value, and has the spatial distribution pattern of floristic geographical substitution. In order to systematically investigate the synergistic response strategies of fungal communities and enzyme activities in the rhizosphere under the vegetation succession. Here we explored the turnover and assembly mechanisms of Stipa rhizosphere fungal communities and the spatial variation of metabolic activity under the succession of seven Stipa communities in northern China grassland under large scale gradients. The results indicated that the composition, abundance and diversity of fungal communities and microbial enzyme activities in rhizosphere soil differed among different Stipa species and were strikingly varied along the Stipa community changes over the geographic gradient. As the geographical distribution of Stipa community changed from east to west in grassland transect, Mortierellomycetes tended to be gradually replaced by Dothideomycetes. The null models showed that the rhizosphere fungal communities were governed primarily by the dispersal limitation of stochastic assembly processes, which showed decreased relative importance from S. grandis to S. gobica. Moreover, the MAT and MAP were the most important factors influencing the changes in the fungal community (richness, β-diversity and composition) and fungal community assembly, while SC and NP also mediated fungal community assembly processes. These findings deepen our understanding of the responses of the microbial functions and fungal community assembly processes in the rhizosphere to vegetation succession.

Changes of root AMF community structure and colonization levels under distribution pattern of geographical substitute for four Stipa species in arid steppe

The establishment of symbiotic relationship between arbuscular mycorrhizal fungi (AMF) and roots is a mutually beneficial process and plays an important role in plant succession in ecosystems. However, there is less understanding of information about the AMF community in roots under vegetation succession on a large regional scale, especially the spatial variation in the AMF community and its potential ecological functions. Here, we elucidated the spatial variations in root AMF community structure and root colonization along a distribution pattern of four zonal Stipa species in arid and semiarid grassland systems and explored key factors regulating AMF structure and mycorrhizal symbiotic interactions. Four Stipa species established a symbiosis with AMF, and annual mean temperature (MAT) and soil fertility were the main positive and negative driving factors of AM colonization, respectively. The Chao richness and Shannon diversity of AMF community in the root system of Stipa species tended to increase firstly from S. baicalensis to S. grandis and then decreased from S. grandis to S. breviflora. While evenness of root AMF and root colonization showed a trend of increasing from S. baicalensis to S. breviflora, and biodiversity was principally affected by soil total phosphorus (TP), organic phosphorus (Po) and MAT. It is emphasized that Stipa species have certain dependence on AMF, especially in a warming environment, and the root AMF community structure among the four Stipa taxa was different. Additionally, the composition and spatial distribution of root AMF in host plants varied with MAT, annual mean precipitation (MAP), TP and host plant species. These results will broaden our understanding of the relationship between plant and AMF communities and their ecological role, and provide basic information for the application of AMF in the conservation and rehabilitation of forage plants in degraded semiarid grasslands.

Changes of Arbuscular Mycorrhizal Fungal Community and Glomalin in the Rhizosphere along the Distribution Gradient of Zonal Stipa Populations across the Arid and Semiarid Steppe

Arbuscular mycorrhizal fungi (AMF) have been reported to have a wide distribution in terrestrial ecosystems and to play a vital role in ecosystem functioning and symbiosis with Stipa grasses. However, exactly how AMF communities in the rhizosphere change and are distributed along different Stipa population with substituted distribution and their relationships remain unclear. Here, the changes and distribution of the rhizosphere AMF communities and their associations between hosts and the dynamic differences in the glomalin-related soil protein (GRSP) in the rhizosphere soil of seven Stipa species with spatial substitution distribution characteristics in arid and semiarid grasslands were investigated. Along with the substituted distribution of the Stipa populations, the community structures, taxa, species numbers, and alpha diversity index values of AMF in the rhizosphere changed. Some AMF taxa appeared only in certain Stipa species, but there was no obvious AMF taxon turnover. When the Stipa baicalensis population was replaced by the Stipa gobica population, the GRSP tended to decline, whereas the carbon contribution of the GRSP tended to increase. Stipa grandis and Stipa krylovii had a great degree of network modularity of the rhizosphere AMF community and exhibited a simple and unstable network structure, while the networks of Stipa breviflora were complex, compact, and highly stable. Furthermore, with the succession of zonal populations, the plant species, vegetation coverage, and climate gradient facilitated the differentiation of AMF community structures and quantities in the rhizospheres of different Stipa species. These findings present novel insights into ecosystem functioning and dynamics correlated with changing environments. IMPORTANCE This study fills a gap in our understanding of the soil arbuscular mycorrhizal fungal community distribution, community composition changes, and diversity of Stipa species along different Stipa population substitution distributions and of their adaptive relationships; furthermore, the differences in the glomalin-related soil protein (GRSP) contents in the rhizospheres of different Stipa species and GRSP's contribution to the grassland organic carbon pool were investigated. These findings provide a theoretical basis for the protection and utilization of regional biodiversity resources and sustainable ecosystem development.

Biochar-Based Compost Affects Bacterial Community Structure and Induces a Priming Effect on Soil Organic Carbon Mineralization

Urban forests are key to mitigating the Urban Heat Island Effect, which contributes to temperature increases in urban areas. However, the trees in these forests are usually under stress because urban soil is typically degraded. Biochar/compost amendments help with soil management by improving the physiochemical properties and bacterial communities of soil. Here, we compared the physiochemical properties and bacterial communities before and after (1) biochar-only and (2) biochar-based compost amendments. Our results suggested that biochar-only application did not improve soil properties after 1 year of treatment, whereas in the biochar-based compost treatment, the soil properties and bacterial communities changed after just four months. The increase in potassium and decrease in organic material, calcium, and available phosphorus in the soil of the former treatment indicated that the nutrient uptake of its trees had improved. Although there was no significant variation in the soil’s total nitrogen, the higher abundance of potential nitrogen-fixing bacteria in the biochar-based treatment suggested that the soil contained a supplement to nitrogen. Our results show that biochar-based compost amendment improves soil quality and associated bacterial communities in urban forest management.