Geographical, climatic, and soil factors control the altitudinal pattern of rhizosphere microbial diversity and its driving effect on root zone soil multifunctionality in mountain ecosystems.

Shifts in rhizosphere soil microorganisms of dominant plants' response to climate change profoundly impact mountain soil ecosystem multifunctionality; relatively little is known about the relationship between them and how they depend on long-term environmental drivers. Here, we conducted analyses of rhizosphere microbial altitudinal pattern, community assembly, and co-occurrence network of 6 dominant plants in six typical vegetation zones ranging from 1350 to 2900 m (a.s.l.) in Helan Mountains by absolute quantitative sequencing technology, and finally related the microbiomes to root zone soil multifunctionality ('soil multifunctionality' hereafter), the environmental dependence of the relationship was explored. It was found that the altitudinal pattern of rhizosphere soil bacterial and fungal diversities differed significantly. Higher co-occurrence and more potential interactions of Stipa breviflora and Carex coninux were found at the lowest and highest altitudes. Bacterial α diversity, the identity of some dominant bacterial and fungal taxa, had significant positive or negative effects on soil multifunctionality. The effect sizes of positive effects of microbial diversity on soil multifunctionality were greater than those of negative effects. These results indicated that the balance of positive and negative effects of microbes determines the impact of microbial diversity on soil multifunctionality. As the number of microbes at the phylum level increases, there will be a net gain in soil multifunctionality. Our study reveals that geographical and climatic factors can directly or modulate the effects of soil properties on rhizosphere microbial diversity, thereby affecting the driving effect of microbial diversity on soil multifunctionality, and points to the rhizosphere bacterial diversity rather than the fungi being strongly associated with soil multifunctionality. This work has important ecological implications for predicting how multiple environment-plant-soil-microorganisms interactions in mountain ecosystems will respond to future climate change.

High-Throughput Absolute Quantification Sequencing Reveals that a Combination of Leguminous Shrubs Is Effective in Driving Soil Bacterial Diversity During the Process of Desertification Reversal.

Desertification leads to the extreme fragility of ecosystems and seriously threatens ecosystem functioning in desert areas. The planting of xerophytes, especially leguminous shrubs, is an effective and common means to reverse desertification. Soil microorganisms play a crucial role in nutrient cycling and energy flow in ecosystems. However, the effects of introducing leguminous shrubs on soil microbial diversity and the relevant mechanisms are not clear. Here, we employed the high-throughput absolute quantification 16S rRNA sequencing method to analyze the diversity of soil bacteria in sand-fixing areas of mixed shrublands with three combinations of shrubs, i.e., C. korshinskii × Corethrodendron scoparium (CaKCoS), C. korshinskii × Calligonum mongolicum (CaKCaM), and C. scoparium × C. mongolicum (CoSCaM), in the south of the Mu Us Sandy Land, China. This area suffered from moving dunes 20 years ago, but after introducing these shrubs to fix the dunes, the ecosystem was restored. Additionally, the effects of soil physicochemical properties on soil bacterial composition and diversity were analyzed with redundancy analysis (RDA) and structural equation modeling (SEM). It was found that the Shannon index of soil bacteria in CaKCoS was significantly higher than that in CaKCaM and CoSCaM, and the abundance of the dominant phyla, including Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, Planctomycetes, Thaumarchaeota, Armatimonadetes, candidate_division_WPS-1, and Nitrospirae, increased significantly in CaKCoS and CaKCaM compared to that in CoSCaM. RDA showed that the majority of soil properties, such as total nitrogen (TN), available potassium (AK), N:P ratio, soil moisture (SM), and available phosphorus (AP), were important soil environmental factors affecting the abundance of the dominant phyla, and RDA1 and RDA2 accounted for 56.66% and 2.35% of the total variation, respectively. SEM showed that the soil bacterial α-diversity was positively affected by the soil organic carbon (SOC), N:P ratio, and total phosphorus (TP). Moreover, CaKCoS had higher SM, total carbon (TC), total potassium (TK), and AP than CaKCaM and CoSCaM. Collectively, these results highlight a conceptual framework in which the combination of leguminous shrubs can effectively drive soil bacterial diversity by improving soil physicochemical properties and maintaining ecosystem functioning during desertification reversal.

Years of sand fixation with Caragana korshinskii drive the enrichment of its rhizosphere functional microbes by accumulating soil N.

C. korshinskii is one of the most widely-planted sand-fixing legumes in northwest China and exploring its rhizosphere microbiome is of great ecological importance. However, the effect of long-term sand fixation on the composition, diversity, and underlying functions of microbes in the C. korshinskii rhizosphere in dryland ecosystems remain unclear. Here, we performed high-throughput sequencing using a 16S rRNA (absolute quantification) and bacterial functional annotation of prokaryotic taxa (FAPROTAX) analysis and an ITS (relative quantification) and fungal functional guild (FUNGuild) analysis to investigate the C. korshinskii rhizosphere microbiome and metabolic functional groups at different sand-fixing ages (six years, CK6; twelve years, CK12; and eighteen years, CK18) and determined the physicochemical properties of the rhizosphere soil. Results showed that the key bacterial taxa of the rhizosphere were significantly more abundant in CK18 than in CK12 and CK6 at the phylum-class-genus level, and that fungal Glomeromycota was also significantly more abundant in the CK18 rhizosphere compared to CK12 and CK6. Among these bacterial taxa, the enrichment effect of key, functional, genus-level species of bacteria was the most obvious, including Rhizobium, Ensifer, Neorhizobium, Mesorhizobium, Streptomyces, Sphingomonas, and Flavobacterium, which are N-fixing and/or phosphate-solubilizing groups. The significant improvement seen in the physicochemical properties of the CK18 rhizosphere soil, including the higher total nitrogen (TN), available nitrogen (AN), pH, electrical conductivity (EC), higher N:P ratio, and lower C:N ratio, all demonstrated the relationship between the rhizosphere microbes and soil carbon (C) and nitrogen (N) cycling. A redundancy analysis (RDA) of different taxonomic levels indicated a close positive relationship between rhizosphere microbes and AN. In addition, the functional groups of the C. korshinskii rhizosphere bacteria were closely related to soil AN and were mainly composed of chemoheterotrophy and aerobic chemoheterotrophy. A Spearman correlation analysis revealed that these functional groups were mainly identified from bacterial Actinobacteria, Proteobacteria, Verrucomicrobia, Bacteroidetes, and fungal Glomeromycota. Our study provides evidence that the rhizosphere microbes of C. korshinskii are closely related to the accumulation of N in the restoration of desert ecosystems, and that the ecological functional processes they are involved in mainly involve C and N cycles, which play an important role in desertification reversal.

Knockdown of ubiquitin-like modifier-activating enzyme 2 promotes apoptosis of clear cell renal cell carcinoma cells.

Small ubiquitin-related modifier (SUMO) proteins are involved in the development of tumors. Ubiquitin-like modifier-activating enzyme 2 (UBA2) is an important member of the SUMO modification system; however, its role in clear cell renal cell carcinoma (ccRCC) is unclear. Therefore, we investigated the expression and function of UBA2 in ccRCC. Both mRNA and protein expression levels of UBA2 were found to be higher in ccRCC than in normal renal tissues and significantly related to the tumor size, Fuhrman grade, and tumor stage. UBA2 knockdown inhibited ccRCC cell growth, promoted apoptosis in vitro and in vivo, and decreased the abundance of a p53 mutant, c-Myc, and key enzymes of the SUMO modification system. Meanwhile, overexpression of UBA2 had the opposite effects. Overexpression of the p53 mutant or c-Myc alleviated the effects of UBA2 knockdown on ccRCC cell proliferation and apoptosis. In conclusion, targeting UBA2 may have a therapeutic potential against ccRCC.

The complete chloroplast genome sequence of Pennisetum flaccidum (Poaceae).

Pennisetum flaccidum Grisebach is a typical high-quality forage and adrought-tolerant grass. In this study, we firstly reported the complete chloroplast (cp) genome of P. flaccidum, which was 138,336 bp in length, including a pair of inverted repeats (IR: 22,293 bp), a large single copy (LSC: 81,329 bp), and a small single copy (SSC: 12,421 bp) region. A total of 131 genes were annotated, containing seven rRNA genes, 38 tRNA genes, and 86 protein-coding genes. The GC content of the cp genome was 38.63%. The maximum-likelihood (ML) phylogenetic tree indicated that P. flaccidum was closely related to P. cetaceum in Poaceae.

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Exploring the distribution patterns of soil nutrients in aggregates of forests along different altitudes in arid and semi-arid areas can provide a theoretical basis for understanding nutrient cycling in vulnerable mountain ecosystems. In this study, we analyzed the distribution and stability of aggregates in the 0-20 cm soil layer along different altitudes (1380-2438 m) of Helan Mountains and measured the storage and stoichiometric characteristics of organic carbon, total nitrogen, and total phosphorus in soil aggregates. Results showed that the main soil aggregates of Helan Mountains changed from micro-aggregates (0.25-0.053 mm) to macro-aggregates (>0.25 mm) with increa-sing elevation. The mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates in high altitude (2139-2248 m) were significantly higher than those in low altitude (1380-1650 m). The content and storage of organic carbon and total nitrogen in soil aggregates of different size fractions were positively correlated with altitude, while the content of total phosphorus fluctuated with the increase in elevation and distributed uniformly in aggregates. Macro-aggregates and micro-aggregates had more contribution to soil nutrient storage than the silt and clay fractions, indicating that the proportion of aggregates with different size fractions was the key factor affecting soil nutrient storage and that macro-aggregates and micro-aggregates were the main carriers of soil nutrients. Moreover, the C:N ratio in aggregates of different size fractions did not change across different altitudes, whereas the C:P and N:P ratio were higher at mid and high elevations than those at low elevations. Our results indicated that the mid and high elevations of Helan Mountains had higher nutrient storage in the surface soil layer, and that higher content of macro-aggregates and micro-aggregates would help to retain organic carbon and nutrients in the soil. Soil nitrogen limitation was strong at low altitude in our study, suggesting that the appropriate amount of nitrogen addition in low altitudes could improve total nitrogen status during forest cultivation.

Reduction of traffic-related particulate matter by roadside plants: effect of traffic pressure and sampling height.

Atmospheric particulate matters (PM) caused by urban traffic system put residents' health at serious risk. As a method of phytoremediation to mitigate this risk, roadside plants show significant potential to remove PM from the air. However, the relationship between traffic pressure, height, and leaves' capturing capacity is rarely reported. In this study, two common effective roadside plants (Hedera helix, Taxus baccata) with typical leaf shapes (broad and needle-leaved) were selected to explore the foliage capacity under high, middle and low traffic burden. A green wall covered by H. helix was tested to find out the relationship between heights and the amount of accumulated PM. Although the PM capturing capacity varied between different traffic pressures, needle-leaved species generally accumulated more PM than broad-leaved species. For PM10 capturing, needle-leaved species showed higher capacity under all traffic pressures except under the low traffic pressure. For PM2.5 capturing, needle-leaved species accumulated more PM only under the high traffic pressure. Needle-leaved plants were more sensitive to the change of traffic pressures, its PM capturing capacity changed notably between different traffic pressures because its leaf wax is more susceptible to be corroded. Leaf surface contact angle was slightly affected by the change of traffic pressure for broad-leaved species, but for needle-leaved species, it changed greatly. Leaf surface was the main zone for large PM capturing because the large PM was more likely to be stuck in grooves on the leaf surface, while leaf wax was mainly for fine PM absorption because PM with small sizes could adhere to the surface of the wax crystal. By comparing the amount of captured PM by leaf surface of urban roadside plants under different traffic pressures and height ranges, this study optimizes the benefits of roadside plants as traffic-related PM filter under different traffic conditions.

Reduction of urban traffic-related particulate matter-leaf trait matters.

Particulate matter in European cities, especially in urban areas, is mainly from urban road traffic and constitutes a great threat to the health of inhabitants. Therefore, understanding of the role of common urban roadside plant plays for particulate matter (PM) reduction would have important meaning for the mitigation of urban air pollution. The leaf surface PM capturing capacity of 12 representative urban plants (five shrubs and seven trees) alongside one main street in Hanover Germany was explored in this study. Significant differences for the amount of captured PM (both PM10 and PM2.5) on the leaf surface were found between plant species. Leaves of Taxus baccata, Berberis thunbergii, Pinus nigra, and Quercus robur showed the highest capturing capacity, while leaves of Prunus laurocerasus and Carpinus betulus showed the lowest value. Leaf shape is an important factor which affects the capturing capacity of the tested plant species. Needle-leaved pants were relatively more effective than broad-leaved species. Besides, species with small leaf surface area (0-10 cm2) showed a notably higher capacity than species with large leaf surface area (over 100 cm2). Additionally, by the observation of leaf surface characteristics, plant species with rough and hairy leaf surface tended to be more effective than species with smooth leaf surface. More PM was found distributed on the upper leaf surface close to the midrib rather than on the surface area away from it. At last, no significant correlation was found between the leaf surface contact angle and its PM capturing capacity for the 12 tested plant species in September. In summary, leaf traits including leaf form, leaf shape, leaf surface area, leaf surface hydrophilicity and leaf surface characteristics all have notable effects on the PM capturing capacity of the roadside plant species. This study provides a scientific basis for roadside plants as an eco-friendly solution for the reduction of urban traffic-related PM and stresses the importance of leaf traits as criteria for the plant selection.

Deep soil C and N pools in long-term fenced and overgrazed temperate grasslands in northwest China.

Fencing for grazing exclusion has been widely found to have an impact on grassland soil organic carbon (SOC) and total nitrogen (TN), but little is known about the impact of fenced grassland on the changes in deep soil carbon (C) and nitrogen (N) stocks in temperate grasslands. We studied the influence of 30 years fencing on vegetation and deep soil characteristics (0-500 cm) in the semi-arid grasslands of northern China. The results showed that fencing significantly increased the aboveground biomass (AGB), litter biomass (LB), total biomass, vegetation coverage and height, and soil water content and the SOC and TN in the deep soil. The belowground biomass (BGB) did not significantly differ between the fenced and grazed grassland. However, fencing significantly decreased the root/shoot ratio, forbs biomass, pH, and soil bulk density. Meanwhile, fencing has significantly increased the C and N stocks in the AGB and LB but not in the BGB. After 30 years of fencing, the C and N stocks significantly increased in the 0-500 cm soil layer. The accumulation of SOC mainly occurred in the deep layers (30-180 cm), and the accumulation of TN occurred in the soil layers of 0 to 60 cm and 160 to 500 cm. Our results indicate that fencing is an effective way to improve deep soil C and N stocks in temperate grassland of northwest China. There were large C and N stocks in the soil layers of 100 to 500 cm in the fenced grasslands, and their dynamics should not be ignored.

Comparison of microbial community structures in soils with woody organic amendments and soils with traditional local organic amendments in Ningxia of Northern China.

BACKGROUND: Addition of organic amendments has been commonly adopted as a means to restore degraded soils globally. More recently, the use of woody organic amendments has been recognized as a viable method of capturing and retaining water and restoring degraded and desertified soil, especially in semi-arid regions. However, the impacts of woody amendments on soil microbial community structure, versus other traditional organic supplements is less understood. METHODS: Three locally available natural organic materials of different qualities, i.e., cow manure (CM), corn straw (CS), and chipped poplar branches (PB) were selected as treatments in Ningxia, Northern China and compared with control soils. Four microcosms served as replicates for each treatment. All treatments contained desertified soil; treatments with amendments were mixed with 3% (w/w) of one of the above organic materials. After 7 and 15 months from the start of the experiment, soil samples were analyzed for chemical and physical properties, along with biological properties, which included microbial α-diversity, community structure, and relative abundance of microbial phyla. RESULTS: Both bacterial and fungal α-diversity indices were weakly affected by amendments throughout the experimental period. All amendments yielded different microbial community compositions than the Control soils. The microbial community composition in the CS and PB treatments also were different from the CM treatment. After 15 months of the experiment, CS and PB exhibited similar microbial community composition, which was consistent with their similar soil physical and chemical properties. Moreover, CS and PB also appeared to exert similar effects on the abundance of some microbial taxa, and both of these treatments yield different abundances of microbial taxa than the CM treatment. CONCLUSION: New local organic amendment with PB tended to affect the microbial community in a similar way to the traditional local organic amendment with CS, but different from the most traditional local organic amendment with CM in Ningxia, Northern China. Moreover, the high C/N-sensitive, and lignin and cellulose decompose-related microbial phyla increased in CS and PB have benefits in decomposing those incorporated organic materials and improving soil properties. Therefore, we recommend that PB should also be considered as a viable soil organic amendment for future not in Ningxia, but also in other places.

Ecosystem functions including soil organic carbon, total nitrogen and available potassium are crucial for vegetation recovery.

The effects of biodiversity on ecosystem functions have been extensively studied, but little is known about the effects of ecosystem functions on biodiversity. This knowledge is important for understanding biodiversity-ecosystem functioning relationships. Desertification reversal is a significant global challenge, but the factors that play key roles in this process remain unclear. Here, using data sampled from areas undergoing desertification reversal, we identify the dominant soil factors that play a role in vegetation recovery with ordinary least squares and structural equation modelling. We found that ecosystem functions related to the cycling of soil carbon (organic C, SOC), nitrogen (total N, TN), and potassium (available K, AK) had the most substantial effects on vegetation recovery. The effects of these ecosystem functions were simultaneously influenced by the soil clay, silt and coarse sand fractions and the soil water content. Our findings suggest that K plays a critical role in ecosystem functioning and is a limiting factor in desertification reversal. Our results provide a scientific basis for desertification reversal. Specifically, we found that plant biodiversity may be regulated by N, phosphorus (P) and K cycling. Collectively, biodiversity may respond to ecosystem functions, the conservation and enhancement of which can promote the recovery of vegetation.