Grazing practices affect soil microbial networks but not diversity and composition in alpine meadows of northeastern Qinghai-Tibetan plateau

Biodiversity in mountain soils above the treeline

Biological diversity in mountain ecosystems has been increasingly studied over the last decade. This is also the case for mountain soils, but no study to date has provided an overall synthesis of the current state of knowledge. Here we fill this gap with a first global analysis of published research on cryptogams, microorganisms, and fauna in mountain soils above the treeline, and a structured synthesis of current knowledge. Based on a corpus of almost 1400 publications and the expertise of 37 mountain soil scientists worldwide, we summarise what is known about the diversity and distribution patterns of each of these organismal groups, specifically along elevation, and provide an overview of available knowledge on the drivers explaining these patterns and their changes. In particular, we document an elevation-dependent decrease in faunal diversity above the treeline, while for cryptogams there is an initial increase above the treeline, followed by a decrease towards the nival belt. Thus, our data confirm the key role that elevation plays in shaping the biodiversity and distribution of these organisms in mountain soils. The response of prokaryote diversity to elevation, in turn, was more diverse, whereas fungal diversity appeared to be substantially influenced by plants. As far as available, we describe key characteristics, adaptations, and functions of mountain soil species, and despite a lack of ecological information about the uncultivated majority of prokaryotes, fungi, and protists, we illustrate the remarkable and unique diversity of life forms and life histories encountered in alpine mountain soils. By applying rule- as well as pattern-based literature-mining approaches and semi-quantitative analyses, we identified hotspots of mountain soil research in the European Alps and Central Asia and revealed significant gaps in taxonomic coverage, particularly among biocrusts, soil protists, and soil fauna. We further report thematic priorities for research on mountain soil biodiversity above the treeline and identify unanswered research questions. Building upon the outcomes of this synthesis, we conclude with a set of research opportunities for mountain soil biodiversity research worldwide. Soils in mountain ecosystems above the treeline fulfil critical functions and make essential contributions to life on land. Accordingly, seizing these opportunities and closing knowledge gaps appears crucial to enable science-based decision making in mountain regions and formulating laws and guidelines in support of mountain soil biodiversity conservation targets.

Long-term grazing reduces soil fungal network complexity but enhances plant-soil microbe network connectivity in a semi-arid grassland

Grazing plays a significant role in shaping both aboveground vegetation and belowground microbial communities in arid and semi-arid grasslands, which in turn affects ecosystem functions and sustainability. Therefore, it was essential to implement effective grazing management practices to preserve ecological balance and support sustainable development in these delicate environments. To optimize the traditional continuous grazing policy, we conducted a 10-year seasonal grazing experiment with five treatments in a typical grassland in northern China: no grazing (NG), continuous summer grazing (CG), and three seasonal grazing treatments (G57 in May and July, G68 in June and August, and G79 in July and September). Our study found that although grazing reduced plant community biomass, G68 treatment maintained high plant height and community diversity (P < 0.05). Grazing did not affect soil bacterial and archaeal alpha diversity, but CG treatment reduced soil fungal diversity (P < 0.05). CG reduced the archaeal network's vertices (which represent microbial taxa, OTUs) and connections (ecological interactions between taxa), but seasonal grazing increased its complexity. Furthermore, grazing did not change bacterial networks but enhanced cross-domain interactions (relationships between different biological groups) of plant-soil fungi and plant-soil archaea. Overall, we used the Mantel test to find that soil microbial diversity was positively correlated with soil physicochemical properties rather than plant community characteristics after grazing. These findings are beneficial for the optimization of sustainable grassland management policies and the protection of plant and soil biodiversity.

Compositional and functional analysis of the bacterial community of Mediterranean Leptosols under livestock grazing

The composition and functioning of soil bacterial communities, as well as their responses to multiple perturbations, are not well understood in the terrestrial ecosystems. Our study focuses on the bacterial community of erosive and poorly developed soils (Haplic Leptosols) in Mediterranean rangelands of Extremadura (W Spain) with different grazing intensities. Leptosols from similar natural conditions were selected and sampled at two depths to determine the soil properties as well as the structure and activity of bacterial communities. As grazing intensified, the soil C and N content increased, as did the number and diversity of bacteria, mainly of fast-growing lineages. Aridibacter, Acidobacteria Gp6 and Gp10, Gemmatimonas, and Segetibacter increased their abundance along the grazing-intensity gradient. Firmicutes such as Romboutsia and Turicibacter from livestock microbiome also increased. In functional terms, the KEGG pathways enriched in the soils with moderate and high grazing intensity were ABC transporters, DNA repair and recombination proteins, the two-component system, and the degradation of xenobiotics. All of these proved to be related to stronger cell division and response mechanisms to environmental stressors such as drought, warming, toxic substances, and nutrient deprivation. Consequently, the bacterial community was affected by grazing, but appeared to adapt and counteract the effects of a high grazing intensity. Therefore, a clearly detrimental effect of grazing was not detected in the bacterial community of the soils studied.

Enhancing the component intra- and interrelationship of Elymus nutans mono- and mixed sowing communities via adjusting sowing patterns in the Qinghai Tibetan Plateau

Spatial arrangement is a key factor in maintaining community yield and stability via regulating component intra-/interspecific competition in an alpine climate environment. A 2-yr field trial was conducted on the Qinghai Tibetan Plateau, including cross row (S_C), double row (S_D), single row (S_R), broadcast (M_B), dependent row (M_D) and independent row (M_I). Our results showed that S_C could avoid intraspecific competition by reasonable spatial arrangement, which favored the dominant component growth (1st year: leaf; 2nd year: stem and reproductive organ). For mixed communities, RII (relative interaction intensity) implied that interspecific competition also embodied on dominant component, and higher Elymus nutans component advantages seriously limited Onobrychis viciifolia's components growth in the 2nd year. More details displayed that E. nutans in M_B or M_D produced the maximum system yield via increasing leaf investment at the initial stages and stem investment after July 2019. Besides, M_I possessed lower component numbers than M_B and M_D in the unit area. PCA analysis revealed that component numbers or biomasses changed synchronously, besides the E. nutans of S_C, M_B, and M_D presented significant discrepancies compared to other treatments in September 2019, which verified the effect of sowing patterns on component growth (P < 0.05), but O. viciifolia in different sowing patterns was similar in the 2nd year. Considering the adaptability and production for the environment of the Qinghai Tibetan Plateau, S_C is recommended for the promoted effect on component biomasses. M_B and M_D, with the merit of spacing utilization as well as higher resistance to variation in seasonal growth conditions via optimizing interspecific relationships for mixed communities, are adapted for increasing yield via component harvesting. Our results unveiled the potential of optimizing spatial usage efficiency via controlling component growth characteristics and stressed the importance of dynamic change of dominant components to enhance forage system production in alpine regions.