Search

Natural vegetation succession is a process of interactions between plants and various environmental factors. The dynamics of soil microbes during successional stages have been intensively explored in the past two decades. The effect of rhizosphere interactions of interspecies on microbial properties, however, has received less attention. During the early stage of succession on a Loess Plateau soil from China, we investigated microbial properties in the rhizospheres of three dominant grass species: Artemisia capillaris , Artemisia sacrorum and Stipa bungeana . Experiments with monocultured and polycultured potted plants were designed to determine the effects of rhizosphere interactions on plant growth and soil microbial properties. The results showed that root biomass, shoot biomass, plant height, microbial biomass carbon (C), microbial biomass nitrogen (N), invertase and urease activities, Gram-negative and Gram-positive bacteria were significantly higher for A. capillaris than for A. sacrorum and S. bungeana in both monocultures and polycultures. Lower root biomass, shoot biomass, plant height, microbial biomass C, microbial biomass N, invertase and alkaline phosphatase activities, and levels of microbial phospholipid-derived fatty acids in polycultures relative to the monocultures indicated that rhizosphere interactions led to lower plant growth and soil microbial activities. Our study suggests that rhizosphere interactions had a significant effect on the microbial properties of plant rhizospheres. The advantage of A. capillaris over A. sacrorum and S. bungeana in growth characteristics and rhizosphere microbial conditions is likely responsible for the dominance of A. capillaris in the early stage of succession in abandoned cropland on the Loess Plateau. [ABSTRACT FROM AUTHOR]

This study examined the structure and function of rhizospheric microbial communities of two successionally dominant species ( Artemisia capillaries and Artemisia sacrorum ) during the natural recovery of abandoned cropland on the Loess Plateau in China. Soil samples were collected from the roots of A. capillaries from cropland abandoned for 1, 3, 5, 10, and 13 years and from the roots of A. sacrorum from cropland abandoned for 13, 15, 20, and 30 years. The levels of phospholipid fatty acids (PLFA) were determined to characterize microbial community structure, and community-level physiological profiles for identifying the patterns of use of carbon (C) substrates were determined to describe the functional diversity of the microbial communities. The rhizospheric microbial biomass (total PLFA), Gram-negative bacterial PLFA, fungal PLFA, and the carbon use (carbohydrates, amino acids, carboxylic acids, and polymers) of the pioneering successional species, A. capillaries , tended to decrease during the first 10 years and thereafter increased. The middle-late successional species, A. sacrorum , exhibited increasing Gram-negative bacterial, Gram-positive bacterial, bacterial, total PLFA, and use of carbohydrates, amino acids, carboxylic acids, phenolic acids, and polymers as the abandonment time increased. The higher microbial biomass, Gram-negative bacterial and bacterial PLFAs was found in the rhizospheric soil than that in the bulk soil for A. capillaries . Redundancy and correlation analyses indicated that the rhizospheric microbial PLFAs and C use for A. capillaries were more closely correlated with its coverage and aboveground biomass than with soil organic C and total nitrogen (N), while those for A. sacrorum were correlated more with organic C and total N contents than with coverage and aboveground biomass. Our study demonstrated that the structure and function of the rhizospheric microbial communities of different successional species generally changed differentially over time. Rhizospheric microbial communities were initially determined primarily by the host plant, but the soil C and N supplies selected for specific microfloras during the middle-late stage. [ABSTRACT FROM AUTHOR]

Abstract: Rhizosphere is a microbiosphere with chemical, physical, and biological properties different from those of bulk soils. Knowledge of the changes in the microbial properties of plant rhizospheres is important in understanding the interactions between soil and plant communities. The present study aims to investigate the effect of bulk and rhizosphere soils on the microbial properties of eight croplands abandoned for 1, 3, 5, 10, 13, 15, 20, and 30 years and to evaluate the change in the rhizosphere soil microbial properties with time in the Loess Plateau, China. The results show that during the succession on the abandoned croplands, the pioneer species, Artemisia capillaries Thunb, was an important species in the 1- to 13-year sites, whereas the late species, Artemisia sacrorum Ledeb, emerged into the community after 13 years and became the dominant community species in 30 years. The species richness of the community exhibited an increasing trend during the first 15 years, and rapidly decreased thereafter. The organic carbon, total nitrogen, microbial biomass carbon, and microbial biomass nitrogen contents in the rhizosphere soil increased compared with those in bulk soil. Basal respiration and saccharase, alkaline phosphatase, catalase, and peroxidase activities were also enhanced, and the pH value decreased. Compared with the companion species, the dominant species showed higher organic carbon, total nitrogen, microbial biomass carbon, and microbial biomass nitrogen contents as well as enhanced respiration, but no significant difference in urease, catalase, alkaline phosphatase, and peroxidase activities was observed. As the succession proceeded, both A. capillaries and A. sacrorum showed increased microbial biomass carbon and microbial biomass nitrogen, and a decreased metabolic quotient. The soil enzymes of these two species behaved differently. Coverage and aboveground biomass of A. capillaries and A. sacrorum exhibited different relationships with microbial biomass and enzymes. In conclusion, the soil microbial activity in the rhizosphere is affected by plants, the soil condition, and the successional stage. Plant root exudates play an important role in the change in rhizosphere microbial properties. [Copyright &y& Elsevier]

Abstract: Severe soil and water loss has led to widespread land degradation of the Loess Plateau, China. During the past two decades, significant efforts have been made to revegetate degraded soil in the region. However, a better understanding of the ability of plants to promote soil microbial processes is important for successful revegetation. The current study was conducted at the Dunshan watershed on the Loess Plateau, with the aim of evaluating the effect of different vegetation types on the microbial properties of rhizosphere soil. Six vegetation types were evaluated: two natural grassland (Artemisia capillaries and Heteropappus altaicus), two artificial (i.e. planted by humans) grassland (Astragalus adsurgens and Panicum virgatum) and two artificial shrubland (Caragana korshinskii and Hippophae rhamnoides) species; an area without vegetation cover was used as a control. The results indicated that the highest values of soil organic C, total nitrogen (TN), microbial biomass carbon (MBC), MBN, saccharase, urease, catalase and peroxidase were recorded for H. altaicus and A. capillaries; of basal respiration (BR), the MBN: TN ratio, alkaline phosphatase and polyphenol oxidase for A. adsurgens; and of the BR: MBC ratio for P. virgatum. A rhizosphere soil microbial index (RSMI) was obtained using principal component analysis, and metabolic quotient (BR/MBC), BR, urease, water-soluble C and cellulase were found to be most important for assessing rhizosphere soil quality. All revegetated soil showed higher RSMI compared with control soil, with soil under natural grassland species (H. altaicus and A. capillaries) recording the highest value. It was concluded that plant species under arid climatic conditions have different effects on the microbial properties of rhizosphere soil owing to their different root exudates and plant debris. In addition, natural grasslands are most effective for revegetation of the Loess Plateau. [Copyright &y& Elsevier]

• C:N:P stoichiometry in plants, soils, and enzymes varied with succession time. • Plant species showed a relatively strong homeostasis during secondary succession. • Rhizosphere stoichiometry differed among plant species and succession stages. • Enzyme is crucial than soil nutrients in determining plant tissue stoichiometries. Ecological stoichiometry is the study of the interaction and balance of multiple chemical elements in ecological processes. However, how ecological stoichiometric interactions among plants, soils, and enzymes in the rhizosphere affect secondary plant succession is largely unknown. In this study, we collected the dominant and main companion species Artemisia capillaris , A. sacrorum , and Stipa bungeana , along a secondary succession chronosequence (7, 12, 17, 22, and 32-year) following a cropland abandonment in the Loess Plateau, China. We measured the carbon (C), nitrogen (N) and phosphorus (P) concentrations of plant shoots and roots, as well as the concentrations of C, N, P, available N (aN), available P (aP), and the activity of one C-acquiring enzyme (β-glucosidase (BG)), two N-acquiring enzymes (N-acetylglucosaminidase (NAG), leucineaminopeptidase (LAP)), and one P-acquiring enzyme (alkaline phosphatase (AP)) found in the rhizospheric soil to explore the C:N:P stoichiometry that drives secondary plant succession. The C:P and N:P ratios in the shoots of dominant plant species significantly decreased to a minimum value at the 22-year site and then increased with plant secondary succession. Compared with the 7-year site, the rhizosphere soil C:P and N:P ratios, and enzyme N:P ratios (ln(NAG + LAP):ln(AP)) increased 103.6%, 72.0%, and 221.3%, respectively, but enzyme C:N ratios (ln(BG):ln(NAG + LAP)) decreased 48.2% in the dominant plant species at the 32-year site. Principal component analysis indicated that the stoichiometry characteristics of the plant-soil-enzyme continuum differed for each plant species and succession stage. Stoichiometric homeostasis indices for the plant species indicated a relatively strong homeostasis, while redundancy analysis revealed that the variations in soil BG, NAG, and AP activity and enzyme C:N ratio had significant effects on the stoichiometries and nutrient concentrations of the plant tissues. The results indicated that rhizosphere stoichiometry is a powerful tool for evaluating plant-soil interactions in terrestrial ecosystems and that the variation in rhizospheric soil enzyme activity driving the secondary succession of plants. [ABSTRACT FROM AUTHOR]

Forests are composed of various plant species, and rhizosphere soil microbes are driven by root exudates. However, the interplay between root exudates, microbial communities in the rhizosphere soil of canopy trees, understory shrubs, grasses, and their responses to nitrogen (N) deposition remains unclear. Pinus tabulaeformis, Rosa xanthina, and Carex lancifolia were used to investigate root exudates, rhizosphere soil microbial communities, and their responses to N application in forest ecosystem. Root exudate abundances of P. tabulaeformis were significantly higher than that of R. xanthina and C. lancifolia, with carbohydrates dominating P. tabulaeformis and R. xanthina root exudates, fatty acids prevailing in C. lancifolia root exudates. Following N application, root exudate abundances of P. tabulaeformis and R. xanthina initially increased before decreasing, whereas those of C. lancifolia decreased. Microbial number of rhizosphere soil of C. lancifolia was higher than that of P. tabulaeformis and R. xanthina, but there was insignificant variation of rhizosphere soil microbial diversity among plant species. N application exerted promotional and inhibitory impacts on bacterial and fungal numbers, respectively, while bacterial and fungal diversities were increased by N application. Overall, N application had negative effects on root exudates of P. tabulaeformis, inhibiting rhizosphere soil microbial populations. N application suppressed rhizosphere soil microbial populations by increasing root exudates of R. xanthina. Conversely, N application elevated nutrient content in the rhizosphere soil of C. lancifolia, reducing root exudates and minimally promoting microbial populations. This study highlights the importance of understory vegetation in shaping soil microbial communities within forests under N deposition. [ABSTRACT FROM AUTHOR]

Elevated CO 2 and drought are key consequences of climate change and affect soil processes and plant growth. This study investigated the effects of elevated CO 2 and drought on the microbial biomass and enzymatic activities in the rhizospheres of Bothriochloa ischaemum and Medicago sativa in loess soil. Drought exerted significant species-specific negative effects on root and shoot biomass and microbial properties except for the soil basal respiration in the rhizospheres of B. ischaemum and M. sativa . Increased CO 2 exerted weak effects on plant biomass and enzymatic activities but demonstrated significant effects on the amounts of carbon and nitrogen in soil microbial biomass, basal respiration, substrate-induced respiration, and the metabolic quotients in the rhizospheres of M. sativa and B. ischaemum . The rhizosphere soil microbial index was a good aggregative indicator of the general state of the microbial properties of the rhizospheres. The interactive effects of elevated CO 2 and drought on plant growth and microbial properties significantly differed, indicating that elevated CO 2 significantly alleviated the effects of drought stress on the microbial properties of the rhizosphere. In addition, the effects of elevated CO 2 and drought on microbial biomass and enzymatic activities considerably varied between the two selected species. M. sativa generally experienced a better ameliorative effect than B. ischaemum . [ABSTRACT FROM AUTHOR]

Plant–plant interactions are dynamic and complicated processes that strongly influence soil nutrient cycling in ecosystems. Climate warming-induced drought stress and the duration of plant interactions may reshape or complicate this ecological process. However, little is known about how plant–plant interaction time (co-growth duration) combined with drought stress affect soil chemical properties and enzyme activities. In this study, Stipa bungeana and Bothriochloa ischaemum , which were the main plant species during the later stages of secondary succession in an abandoned cropland on the Loess Plateau of China, were planted as a single plant or in combination, in a plastic pot with two water regimes (ample water, 80 % of field capacity (FC); drought stress, 60 % of FC) for two consecutive years. The rhizosphere soil was collected each year to determine the nutrient contents and enzyme activities, and the microbial metabolic limitations were calculated. We found that plant–plant interactions, drought stress, and sampling year had a significant influence on most rhizosphere soil nutrient contents and enzyme activities. Redundancy analysis showed that soil pH, available phosphorus (aP), and total phosphorus had significant effects on soil enzyme activities in the first year, and soil total nitrogen and aP had significant effects on soil enzyme activities in the second year. Vector analysis indicated that drought stress increased microbial carbon (C) and phosphorus (P) limitation under each planting pattern, and these metabolic limitations showed a decreasing trend in the second year. An structural equation model demonstrated that plant–plant interactions on microbial C and P limitation were larger than drought stress in the first year. Conversely, in the second year, the plant–plant interactions on microbial C and P limitation were lower than that of drought stress. Our findings highlighted that the duration of plant–plant interactions had a significant influence on C flows and nutrient cycling in plant–soil systems, and improved the understanding of plant–plant interactions and drought stress on soil nutrient cycling and microbial metabolic limitations in vegetation restoration ecosystems. • Plant interaction and drought influence rhizosphere nutrient and enzyme activities. • Soil pH, nitrogen, and phosphorus had significant effects on enzyme activities. • Drought stress significantly increased microbial C and P limitation. • Plant interaction duration regulates soil microbial metabolic limitation. [ABSTRACT FROM AUTHOR]

The application of fractal geometry to describe soil structure is an increasingly useful tool for better understanding the performance of soil systems. Only a few studies, however, have focused on the structure of rhizospheric zones, where energy flow and nutrient recycling most frequently occur. We used fractal dimensions to investigate the characteristics of particle-size distribution (PSD) in the rhizospheres and bulk soils of six croplands abandoned for 1, 5, 10, 15, 20, and 30 years on the Loess Plateau of China and evaluated the changes over successional time. The PSDs of the rhizospheres and the fractal dimensions between rhizosphere soil and bulk soils during the natural succession differed significantly due to the influence of plant roots. The rhizospheres had higher sand (0.05–1.00 mm) contents, lower silt (<0.002 mm) contents, and lower fractal dimensions than the bulk soils during the early and intermediate successional stages (1–15 years). The fractal dimensions of the rhizosphere soil and bulk soil ranged from 2.102 to 2.441 and from 2.214 to 2.459, respectively, during the 30-year restoration. Rhizospheric clay and silt contents and fractal dimension tended to be higher and sand content tended to be lower as abandonment age increased, but the bulk soils had the opposite trend. Linear regression analysis indicated that the fractal dimensions of both the rhizospheres and bulk soils were significantly linearly correlated with clay, sand, organic-carbon, and total-nitrogen contents, with R2 ranging from 0.526 to 0.752 (P<0.001). In conclusion, PSD differed significantly between the rhizosphere soil and bulk soil. The fractal dimension was a sensitive and useful index for quantifying changes in the properties of the different soil zones. This study will greatly aid the application of the fractal method for describing soil structure and nutrient status and the understanding of the performance of rhizospheric zones during ecological restoration. [ABSTRACT FROM AUTHOR]

Aims: Extensive studies have demonstrated a significant impact of nitrogen (N) addition on microbial community diversity, composition, and functions in various soils. However, microbial co-occurrence patterns and assembly processes under enhanced N levels is less known, especially with respect to the rhizosphere where microbes are closely linked with plant growth. Methods: In this study, we performed a pot experiment using N addition gradient (0, 2.5, 5, 7.5, 10, and 15 g N·m−2·year−1) and amplicon sequencing and metabolomics to investigate the effect of short-term N addition (2 years) on the co-occurrence patterns and assembly process of bacterial communities as well as their potential drivers in the rhizosphere. Results: Short-term N addition significantly altered bacterial community diversity and composition in the rhizosphere soil but not in the bulk soil; i.e., the rhizosphere bacterial diversity increased with N addition but decreased under high N input (>5 g N·m−2·year−1). The rhizosphere co-occurrence networks showed a more complex topology than the bulk soil, and this complexity could be strengthened by the quantity of N added. The N-induced establishment of the bacterial community in the rhizosphere was mainly dominated by deterministic processes with an increase in the variable selection in response to the increase in the N-addition rate, while the bacterial community in the bulk soil exhibited a transition from stochastic to deterministic processes. N addition stimulated the release of amino acids and short-chain organic acids into the rhizosphere, and these changes in root exudates and the soil NH4+-N level were mainly responsible for the changes in the structure of the rhizosphere bacterial community and co-occurrence networks of keystone species. Conclusions: Our results demonstrated the differences in the co-occurrence patterns and assembly processes of bacterial communities between rhizosphere and bulk soils under N addition, which were closely associated with root exudates. These findings improve our understanding of plant–microbial interactions. [ABSTRACT FROM AUTHOR]

Global nitrogen (N) deposition has a significant impact on the structure and function of above-ground plant communities; however, the impact of N enrichment on below-ground microbial communities remains insufficiently elucidated, especially regarding the functional gene structure. An 18-month pot experiment was conducted to examine the effects of N addition rate (0, 5, 10, and 15 g N m−2 yr−1) on the functional gene composition of rhizosphere microorganisms of Bothriochloa ischaemum , a native grass species of the semiarid area, and to evaluate the soil and plant variables connected with the observed variation. Using microarray GeoChip analysis, 2676, 744, 308, and 515 gene probes involved in carbon (C), N, phosphorus (P) and sulfur (S) cycling, respectively, were detected. Compared with the weak response of genes in the bulk soil, N addition significantly increased the abundance of genes involved in C fixation (tkta , rubisco , TIM), C degradation (amyA , ara , chitinase), methanogenesis (mcra), N 2 -fixation (nifH), denitrification (narG , nirK/S , nosZ), polyphosphate degradation (ppx), and sulfite reduction (dsrA , dsrB , cysJ) in the rhizosphere. The abundance of genes responsible for C-, N-, P-, and S-cycling increased with the N addition rate and was mainly regulated by variations in plant biomass and root exudates. The quantity of soil dissolved organic C played a crucial role in determining the abundance of genes related to the cycling of C, N, P, and S. Plant biomass indirectly affected gene abundance by increasing organic acids in root exudates and dissolved organic C. These findings facilitate our understanding of microbial function to elevated N levels and highlight the key role of root exudates and plant biomass in regulating microbial functions under future N-enrichment scenarios. [Display omitted] • The C, N, P, and S cycling gene abundance increases with the N addition rate. • Increased N deposition would accelerate biogeocycling in semi-arid grassland. • The functional gene abundance was mainly regulated by plant biomass and root exudates. • Soil dissolved organic C plays a crucial role in determining gene abundance. [ABSTRACT FROM AUTHOR]

Forest ecosystem is a complex community, and its soil microbes play a vital role in global matter cycling. However, the patterns of rhizosphere soil microbial characteristics among tree-shrub-grass and their responses to nitrogen (N) deposition are still unclear. This study evaluated the microbial biomasses, processes (gas fluxes), and enzyme activities in the rhizosphere soils of tree (Pinus tabuliformis), shrub (Rosa xanthina), and grass (Carex lanceolata) and their responses to N addition (0, 3, 6, 9 g N m−2 y−1 corresponding to N0, N3, N6, N9) in a P. tabuliformis plantation. (1) Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) contents, as well as CO 2 , CH 4 flux rates in the rhizosphere soil of C. lanceolata were significantly higher than those in the rhizosphere soils of P. tabuliformis and R. xanthina (P < 0.05). The activities of alkaline phosphatase (ALT), leucine aminopeptidase (LAP), β-glucosidase (BG), D -cellulosidase (CBH), N-acetyl-glucosaminidase (NAG), and xylosidase (XYL) in the rhizosphere soils of C. lanceolata and R. xanthina were significantly higher than those in the rhizosphere soil of P. tabuliformis. (2) Soil MBC content, N 2 O, and CH 4 flux rates increased after N addition, while the CO 2 flux rate decreased. MBP content initially increased and then reduced with N additions, and the maximum values observed in N3 or N9 treatments. (3) In the rhizosphere soil of P. tabuliformis , N addition enhanced the NAG, BG, CBH, and XYL activities. While low N increased and high N decreased these enzyme activities in the rhizosphere soils of C. lanceolata and R. xanthina , with the maximum values obtained in N3 treatment. (4) N addition directly reduced the CO 2 flux rate and indirectly enhanced the gas flux rate by increasing soil MBC and MBP contents. Species change indirectly affected the microbial biomass and enzyme activity by altering soil chemical properties, which eventually affected gas flux rates. Our study emphasizes the effects of tree-shrub-grass on soil microbial characteristics, which can improve the evaluation of soil ecological processes and responses to N deposition in forest ecosystems. • Rhizosphere soil of understory vegetations had higher microbial biomass, enzyme activity, and gas flow than that of canopy tree. • Nitrogen addition increased soil microbial biomass carbon content, N 2 O and CH 4 flux rates, but decreased CO 2 flux rate. • Enzyme activities in rhizosphere soils of different plant species exhibited varied responses to nitrogen addition in forest plantation. [ABSTRACT FROM AUTHOR]