Non-rhizosphere Soil Research Articles

English

The objective of this study was to improve rice and maize yields using native Azospirillum-based biofertilizer. To reach this objective, samples of rhizosphere soil, non-rhizosphere soil and roots of maize plants were collected from the particular locations of Samanko and Bamako of the south Mali. Thirty-three different colonies of bacteria were isolated from the different samples. Based on their better growth in nitrogen free semi-solid medium, their morphological, biochemical and plant growth promotion characteristic, ten bacterial isolates were identified as Azospirillum isolates following the Bergey’s Manual of Determinative Bacteriology. Ten isolates were selected: Az1, Az2, Az3, Az4, Az5, Az6, Az7, Az8, Az9 and Az10. Strain Az6 showed great potential on both rice and maize production. Therefore, this strain is suggested for large scale rice and maize fields’ application. While the Azospirillum sp. Az5, Az6 and Az10 strains are suggested for large scale application in maize field, which may reduce production cost. Top dressing with 25% of the recommended nitrogen-fertilizer was found to decrease maize grain yield.   Key words: Azospirillum, Nitrogen-fixing bacteria, plant growth-promoting rhizobacteria (PGPR), biopesticide, maize, rice, Mali.

N-acyl-homoserine lactones (AHLs) in intertidal marsh: diversity and potential role in nitrogen cycling

N-acyl-L-homoserine lactones (AHLs) based quorum sensing (QS) phenomenon is recognized as an effective agent for regulating bacterial growth and metabolism. However, diversity and biological role of AHLs in natural environments remain largely unknown. This study focuses on compositions of AHLs and their potential role in nitrogen transformation in intertidal marshes. We investigated the levels of AHLs in rhizosphere (Phragmites australis, Spartina alterniflora and Scirpus mariqueter) and non-rhizosphere soils from Chongming eastern intertidal wetland of the Yangtze Estuary using gas chromatography-mass spectrometry (GC/MS). Molecular techniques were employed to investigate the compositions and structure of bacterial community. Soil-slurry experiments in combination with nitrogen isotope tracing technique were conducted to examine the effects of AHLs on nitrogen transformation processes. AHLs were higher in rhizosphere than non-rhizosphere soils, and correlated significantly with soil organic carbon and pH. C6-, C8-, C10- and C12-HSLs were identified as the probably universal QS signal molecules in intertidal marsh soils. The bacterial biodiversity might be regulated by AHLs, and 12 of the 50 most abundant microorganisms in intertidal marsh soils were related significantly with AHL concentrations. Furthermore, C6-, C8- and C12-HSLs might play an important role in mediating nitrogen transformation processes including nitrification, denitrification and anaerobic ammonium oxidation (anammox). AHLs are favored to accumulate in rhizospheric environments and thus further mediate the bacterial diversity and soil nitrogen cycling. This study highlights the associations of QS signal molecules with the dynamics and activity of nitrogen cycling bacteria in intertidal marshes.

Mo-Inefficient Wheat Response Toward Molybdenum Supply in Terms of Soil Phosphorus Availability

Phosphorus (P) deficiency is a major constraint to crop growth due to strong soil P fixation. The effects of molybdenum (Mo) on leaf anatomy and dynamics of rhizosphere P in Mo-inefficient crops have still not been investigated. A field study was conducted to investigate the effects of long-term fertilization on dynamics of rhizosphere P transformations and leaf anatomy in Mo-inefficient wheat consisting of Mo (+Mo) and without Mo applied (−Mo) treatments. The results revealed that Mo supply increased plant biomass, grain yield, uptake of P and Mo by 34.9%, 14.8%, 98.1% and 654.1% respectively and preserved the leaf cuticle, stomata, chloroplast, and mesophyll tissue cell configuration. Molybdenum application significantly increased the concentration of radially available P fractions [NaHCO3-Pi (115.5 to 129.8 mg kg−1 and 67.4 to 80.7 mg kg−1) and H2O-Pi (14.4–21.9 mg kg−1 and 4.63–6.40 mg kg−1)] in rhizosphere and non-rhizosphere soils, respectively. The acid phosphatase (ACP) activity (19.5 μmol day−1 g−1) was highest during March as compared to alkaline (ALP) and phytase (PHY) enzymes in the rhizosphere soil of +Mo treatment. The highest expression of gene lppC (6.11) was observed in rhizosphere soil as compared to non-rhizosphere soil which indicated that higher gene expressions induced the higher P enzymatic activities. Our findings suggest that Mo fertilizer application increases P availability through induced alteration in dynamics of rhizosphere soil P fractions, higher P and Mo assimilation and phosphatases enzymes activities along with preserving the leaf anatomy and ultrastructure of Mo-inefficient wheat.

Influence of Bio Fertilizer on Growth and Yield Parameters of Tomato Plants

Tomato is a major food that has many benefits to human health. The risk of getting disorders such as heart disease, cancer, and diabetes can be reduced by consuming tomato. The aim of this study is to measure the nutritional properties of tomato plants using various cultivation methods. On the other hand, this is also comparing which type of fertilizer, either chemical fertilizer or natural fertilizer, is producing better results in planting tomato. Phosphorus solubilizing bacteria (PSB) is isolated from the rhizosphere soil using the Pikovskaya medium and Modified Aleksandrow medium. Instead of chemical fertilizer, the efficiency of phosphate solubilize will be evaluated in the presence of eggshells and bones. This study starts with the collection of rhizosphere and non-rhizosphere soil for tomato planting. The land of cultivation for planting well estimated for the growth of tomato. For further investigation, the leaves and fruits obtained from the tomato plants will be dried and ground into powder form. The leaf is used for the estimation of chlorophyll. In contrast, the fruit powder is used for the analysis of antioxidant activity. The result showed that the growth and yield parameters of the plant increases with natural fertilizer compare to chemical fertilizer. This can be concluded that natural fertilizers are more preferable in the agriculture industry as they are environmentally friendly, which does not produce side effects in either the soils or the crops.

Effects of tourmaline catalyzed Fenton-like combined with bioremediation on the migration of PBDEs in soil-plant systems: Soil properties and physiological response of lettuce and selective uptake of PBDEs

A series of pollutants can be removed from soil using a Fenton-like oxidation and biological treatment. As a natural mineral, tourmaline has been used for as a material of Fenton-like reaction. In the present study, the risks of remediation technology tourmaline catalyzed Fenton-like reaction (TCFR) combined with Phanerochaete chrysosporium (TCFR + P) were assessed through measuring soil properties, physiological response of plant, and PBDEs migration from soil to plant. Batch pot experiments showed that the silicon contents, specific surface area and soil pore size of soil in TCFR and 5%TCFR + P groups increased obviously. TCFR and TCFR + P treatments promoted the lettuce growth compared to control. Moreover, chlorophyll content of lettuce in 2%TCFR + P and 5%TCFR + P group increased by 46.74% and 44.57% than that in the CK, respectively. The treatment of 2%TCFR decreased the total concentration of PBDEs in rhizosphere soil and non-rhizosphere soil by 52.0.2% and 64.17%, respectively, after 60 days compared to the soil of CK, and did not prompt the uptake of lower-brominated PBDEs by lettuce. TCFR and TCFR + P can alter the migration of BDE isomers from soil to plant, the ratio of BDE99/BDE100 in lettuce shoots decreased slightly. BDE-99/BDE-100 ratios in the shoots were lower than those in the roots, while BDE153/BDE154 ratios were higher than 1.0 and ratios in shoots were higher than those in roots. Therefore, our findings illustrated that the TCFR could be applied to remediate the agricultural soil, considering the appropriate doses of tourmaline.

Soil bacterial diversity, structure, and function of Suaeda salsa in rhizosphere and non-rhizosphere soils in various habitats in the Yellow River Delta, China

Soil microorganisms play a key role in regulating the biogeochemical cycles of ecosystems. However, studies that quantitatively examine bacterial metabolic groups to predict the environmental and biological impacts are limited. In this research, we employed 16S rRNA gene sequencing on an Illumina MiSeq platform to analyze bacterial diversity, structure, function, and driving factors of Suaeda salsa in rhizosphere and non-rhizosphere soils in intertidal and supratidal habitats in the Yellow River Delta, China. Results showed that bacterial richness and Shannon diversity index of the rhizosphere soil were greater in the intertidal than in the supratidal habitat. Although the bacteria of the two habitats changed extremely in community structure, the bacterial groups related to carbohydrate metabolism (CM) and amino acid metabolism (AAM) had higher abundance than the other groups in both habitats. Furthermore, they were higher in the supratidal than the intertidal habitats, and bacterial groups associated with energy metabolism (EM) are opposite. Furthermore, bacterial diversity showed no significant difference between the rhizosphere and non-rhizosphere soils. In the intertidal habitat, the rhizosphere soil had higher EM but lower AAM and CM than the non-rhizosphere soil, which indicated that bacterial structure and function were obviously influenced by the root exudates of S. salsa under flooding and salt stresses. Redundancy analysis showed that the dominant phyla were significantly affected by available phosphorus (51.0%), total potassium (32.2%), moisture content (28.1%), available potassium (25.3%), electrical conductivity (24.2%), total nitrogen (22.8%), total carbon (21.9%), and soil organic matter (21.0%). Overall, the findings provide important insights into the roles of bacterial groups in coastal wetland under climate changes.

Screening and Application of Bacillus Strains Isolated from Nonrhizospheric Rice Soil for the Biocontrol of Rice Blast.

Rice blast, caused by Magnaporthe oryzae, is one of the most destructive rice diseases worldwide. The aim of this study was to screen bacterial isolates to efficiently prevent the occurrence of rice blast. A total of 232 bacterial isolates were extracted from nonrhizospheric rice soil and were screened for antifungal activity against M. oryzae using a leaf segment assay. Strains S170 and S9 showed significant antagonistic activity against M. oryzae in vitro and in leaf disk assays, and controlled M. oryzae infection under greenhouse conditions. The results showed that strains S170 and S9 could effectively control rice leaf blast and panicle neck blast after five spray treatments in field. This suggested that the bacterial strains S170 and S9 were valuable and promising for the biocontrol of rice disease caused by M. oryzae. Based on 16S rDNA, and gyrA and gyrB gene sequence analyses, S170 and S9 were identified as Bacillus amyloliquefaciens and B. pumilus, respectively. The research also demonstrated that B. amyloliquefaciens S170 and B. pumilus S9 could colonize rice plants to prevent pathogenic infection and evidently suppressed plant disease caused by 11 other plant pathogenic fungi. This is the first study to demonstrate that B. amyloliquefaciens and B. pumilus isolated from nonrhizospheric rice soil are capable of recolonizing internal rice stem tissues.

Rhizosphere engineering through exogenous growth-regulating small molecules improves the colonizing efficiency of a plant growth-promoting rhizobacterium in rice.

Enhancing the rhizosphere colonization and persistence of plant growth-promoting rhizobacteria (PGPR) is necessary for maximizing PGPR-mediated benefits for crop growth and fitness in environmentally friendly agriculture. In the present investigation, we attempted manipulation of the rice rhizosphere by spraying of low molecular weight plant-regulating metabolites on the foliage of rice plants to in turn enhance the colonizing efficiency of soil-inoculated PGPR strain. The green fluorescent protein gene-tagged rhizobacterial strain, Pseudomonas chlororaphis ZSB15-M2, was inoculated in sterile plant growth medium (vermiculite coco peat mixture) and non-autoclaved agricultural soil. We sprayed different plant growth-regulating small molecules on the foliage of rice seedlings and monitored the colonizing efficiency of ZSB15-M2 in the rice rhizosphere. Among the chemicals assessed, salicylic acid (SA) at 1mM or Corynebacterium glutamicum cell extract (CGCE, 0.2% w/v) or Saccharomyces cerevisiae cell extract (SCCE, 0.2% w/v) showed a tenfold increase in rhizosphere colony-forming units of ZSB15-M2 compared to control with a significant decline in non-rhizosphere bulk soil population. Foliar spray of CGCE enhanced soil organic carbon, microbial biomass carbon and soil protein by 21.86%, 9.68% and 11.57% respectively in the rice rhizosphere as compared to mock control. Additionally, CGCE spray enhanced the key soil enzymes, viz., dehydrogenase and acid- and alkaline phosphatase in the rhizosphere ranging 15-36%. The cumulative effect of this engineered rhizosphere resulted in the elevation of nitrogen, phosphorus, potassium and zinc availability by 21.83%, 28.83%, 23.95% and 61.94%, respectively, in rice rhizosphere as compared to control. On the other hand, SCCE and SA spray had an equal influence on the rhizosphere's biological attributes, which is lower than that of GCGE and higher than that of mock control. From the study, we propose that the aboveground management of rice with microbial-based small molecules will modulate the rice rhizosphere to attract more beneficial PGPR-based inoculants, thus improving the crop and soil health.

The Effects of Tetracycline Residues on the Microbial Community Structure of Tobacco Soil in Pot Experiment

To evaluate the micro-ecological effects of tetracycline residues on tobacco soil, high-throughput sequencing technology was used to study the effects of the addition of different concentrations (0, 5, 50, and 500 mg·kg−1) of tetracycline on the abundance, diversity, and structure of bacterial and fungal communities in the rhizosphere and non-rhizosphere soil of flue-cured tobacco in China. Results showed that the presence of tetracycline had an important but varying effect on soil bacterial and fungal community richness, diversity, and structure. Changes in the diversity indices (Chao index and Shannon index) of soil bacterial and fungal communities showed a similar pattern after the addition of tetracycline; however, a few differences were found in the effects of tetracycline in the rhizosphere and non-rhizosphere soil, suggesting an evident rhizosphere-specific effect. The bacterial community at the phylum level in the rhizosphere closely clustered into one group, which might be the result of tobacco root secretions and rhizodeposition. Tetracycline showed a concentration-dependent effect on the soil bacterial community structure. The soil bacterial community structures observed after treatments with higher concentrations of tetracycline (50 and 500 mg·kg−1) were found to be closely related. Moreover, the effects of the treatments with higher concentrations of tetracycline, on the soil bacterial community at the phylum level, were different from those with lower concentrations of tetracycline (5 mg·kg−1), and CK treatments. This might have resulted from the induction of increasing selective pressure with increasing antibiotic concentration. Tetracycline continued to affect the soil bacterial community throughout the experiment. Tetracycline was found to have a varying impact on the community structure of soil fungi compared to that of soil bacteria, and the addition of an intermediate concentration of tetracycline (50 mg·kg−1) significantly increased the soil fungal diversity in the non-rhizosphere soil. The biological effects of tetracycline on the soil fungal community and the fungal-bacterial interactions, therefore, require further elucidation, warranting further research.

Effect of dibutyl phthalate on microbial function diversity and enzyme activity in wheat rhizosphere and non-rhizosphere soils

The pollution of farm soils by the plasticizer dibutyl phthalate (DBP) should be researched owing to the extensive use of plastic film. We investigated the influence of DBP on microbial communities and enzyme activities in rhizosphere and non-rhizosphere soil during the different growth stages of wheat and determined the response through simulations. The results indicated that protease, polyphenol oxidase, and β-glucosidase activity in soil decreased with increasing DBP dosage, while dehydrogenase, urease, and acid phosphatase activities increased. Moreover, the effects of DBP on soil enzyme activity gradually weakened with DBP degradation. Dibutyl phthalate has a certain inhibitory effect on the activity, diversity, and heterogeneity of microorganisms in soil. In addition, DBP can increase the utilization of amines and carboxylic acids and decrease the utilization of carbohydrates and amino acids by soil microorganisms. According to the Gaussian and molecular docking analysis, we considered that monobutyl phthalate and DBP could affect the utilization of amino acids by Proteobacteria. The enzyme activity, microbial activity, and heterogeneity of rhizosphere soil were higher than those of non-rhizosphere soil. Microbial carbon source utilization in rhizosphere and non-rhizosphere soils depends on wheat growth, soil type, and DBP dosage. Owing to the widespread presence of DBP in agriculture, negative effects of phthalic acid esters should be considered in relation to soil quality and food safety in future.

Molybdenum-induced effects on leaf ultra-structure and rhizosphere phosphorus transformation in Triticum aestivum L

Soil phosphorus (P) occurs in pools of lower availability due to soil P fixation and therefore, it is a key constrain to crop production. Long term molybdenum-induced effects in wheat and rhizosphere/non-rhizosphere soil P dynamics have not yet been investigated. Here, a long term field experiment was conducted to explore these effects in wheat consisting of two treatments i.e. with molybdenum (+Mo) and without molybdenum (-Mo). The results revealed that molybdenum (Mo) supply increased plant biomass, grain yield, P uptake, preserved the configuration of chloroplast, stomata, and mesophyll tissue cells, suggesting the complementary effects of Mo on wheat yield and P accumulation. During the periods of vegetative growth, soil organic carbon, organic matter, and microbial biomass P were higher and tended to decrease in rhizosphere soil at maturity stage. In +Mo treatment, the most available P fractions [H2O-Pi (16.2–22.9 mg/kg and 4.24–7.57 mg/kg) and NaHCO3-Pi (130–149 mg/kg and 77.2–88 mg/kg)] were significantly increased in rhizosphere and non-rhizosphere soils, respectively. In addition, the +Mo treatment significantly increased the acid phosphatase activity and the expression of phoN/phoC, aphA, olpA/lppC gene transcripts in rhizosphere soil compared to -Mo. Our research findings suggested that Mo application has increased P availability not only through biochemical and chemical changes in rhizosphere but also through P assimilation and induced effects in the leaf ultra-structures. So, it might be a strategy of long term Mo fertilizer supply to overcome the P scarcity in plants and rhizosphere soil.

Caracterización molecular de bacterias rizosféricas asociadas a Echinocactus platyacanthus en invernadero y silvestres

La biznaga dulce (Echinocactus platyacanthus) es una cactácea endémica de México caracterizada por su lento crecimiento y baja tasa de reproducción, lo que aunado a una alta presión de recolecta, coloca a las poblaciones silvestres en una situación de riesgo. Actualmente, el estudio de las comunidades bacterianas asociadas a cactáceas es escaso y se desconoce qué bacterias cultivables están presentes en la rizósfera de las biznagas dulces que crecen en la naturaleza y en las que se cultivan en viveros. Para este estudio se recolectó material rizosférico de biznagas silvestres y cultivadas, además de suelo no rizosférico. Se aislaron en total de 268 morfotipos y se agruparon en 41 ribotipos diferentes por RFLP. Representantes de cada ribotipo se identificaron mediante la secuenciación del gen 16S rRNA. La fracción cultivable de la comunidad bacteriana asociada con E. platyacanthus está compuesta principalmente por miembros de los géneros Bacillus (21 cepas), Pseudomonas (seis cepas), Stenotrophomonas (cuatro cepas), Paenibacillus (dos cepas), Brevibacterium, Staphylococcus y Cutibacterium (una cepa, cada una), siendo Bacillus el género predominante. Los géneros Bacillus y Pseudomonas han sido reportados previamente por llevar a cabo actividades beneficiosas para las plantas a las que están asociados.

Characteristics of the soil microbial community in the forestland of Camellia oleifera.

Characterizing soil microbial community is important for forest ecosystem management and microbial utilization. The microbial community in the soil beneath Camellia oleifera, an important woody edible oil tree in China, has not been reported before. Here, we used Illumina sequencing of 16S and ITS rRNA genes to study the species diversity of microorganisms in C. oleifera forest land in South China. The results showed that the rhizosphere soil had higher physicochemical properties, enzyme activities and microbial biomass than did the non-rhizosphere soil. The rhizosphere soil microorganisms had a higher carbon source utilization capacity than the non-rhizosphere soil microorganisms, and attained the highest utilization capacity in summer. The soil microbial community of C. oleifera was characterized by rich ester and amino acid carbon sources that played major roles in the principal functional components of the community. In summer, soil microbes were abundant in species richness and very active in community function. Rhizosphere microorganisms were more diverse than non-root systems in species diversity, which was associated with soil pH, Available phosphorous (AP) and Urease (URE). These results indicated that microbial resources were rich in rhizosphere soil. A priority should be given to the rhizosphere microorganisms in the growing season in developing and utilizing soil microorganisms in C. oleifera plantation. It is possible to promote the growth of C. oleifera by changing soil microbial community, including carbon source species, pH, AP, and URE. Our findings provide valuable information to guide microbial isolation and culturing to manage C. oleifera land.

Dissimilatory nitrate/nitrite reduction to ammonium (DNRA) pathway dominates nitrate reduction processes in rhizosphere and non-rhizosphere of four fertilized farmland soil

Nitrate (NO3−) reduction partitioning between denitrification, anaerobic ammonium oxidation (anammox), denitrifying anaerobic methane oxidation (DAMO), and dissimilatory nitrate reduction to ammonium (DNRA), can influence the nitrogen (N) use efficiency and crop production in arid farmland. The microbial structure, function and potential rates of denitrification, anammox, DAMO and DNRA, and their respective contributions to total NO3− reduction were investigated in rhizosphere and non-rhizosphere soil of four typical crops in north China by functional gene amplification, high-throughput sequencing, network analysis and isotopic tracing technique. The measured denitrification and DNRA rate varied from 0.0294 to 20.769 nmol N g−1 h−1and 2.4125–58.682 nmol N g−1 h−1, respectively, based on which DNRA pathway contributed to 84.44 ± 14.40% of dissimilatory NO3− reduction, hence dominated NO3− reduction processes compared to denitrification. Anammox and DAMO were not detected. High-throughput sequencing analysis on DNRA nrfA gene, and denitrification nirS and nirK genes demonstrated that these two processes did not correlate to corresponding gene abundance or dominant genus. RDA and Pearson's correlation analysis illustrated that DNRA rate was significantly correlated with the abundance of Chthiniobacter, as well as total organic matter (TOM); denitrification rate was significantly correlated with the abundance of Lautropia, so did TOM. Network analysis showed that the genus performed DNRA was the key connector in the microbial community of dissimilatory nitrate reducers. This study simultaneously investigated the dissimilatory nitrate reduction processes in rhizosphere and non-rhizosphere soils in arid farmland, highlighting that DNRA dominated NO3− reduction processes against denitrification. As denitrification results in N loss, whereas DNRA contributes to N retention, the relative contributions of DNRA versus denitrification activities should be considered appropriately when assessing N transformation processes and N fertilizer management in arid farmland fields.

Insights on comparative bacterial diversity between different arid zones of Cholistan Desert, Pakistan.

The present study was conducted to analyze bacterial diversity profile of Cholistan desert located in Pakistan. The study investigates the influence of physicochemical parameters of soil on distribution of different bacteria at all taxonomic levels and also study the distribution pattern between different desert environments, particularly rhizospheric and bulk desert sands. Species richness showed phyla Proteobacteria and Chloroflexi as the dominant OTUs in all the samples. Besides the two phyla, the rhizospheric soils with root remnants were dominated by Firmicutes, Deinococcus-Thermus, Actinobacteria and Acidobacteri, while phylum Thermotogae was present in significant quantity in rhizosheaths devoid of roots. In non-rhizospheric desert soils, a considerable number of OTUs belonged to phyla Proteobacteria, Chloroflexi, Bacteroidetes and Acidobacteria. An important finding from this study is that a bulk portion of the OTUs were assigned to unclassified taxa, indicating a large repertoire of unexplored taxa in the desert ecology of Pakistan. Distribution of taxonomic groups among various regions of the desert was collaborating well with the physicochemical parameters of the sites. The findings of this study establish the fundamental relationships between desert ecosystem, specific native plant and the total bacterial flora. This is the first study of microbial community analysis of any desert in Pakistan and thus, will serve as a future platform to explore further on desert ecosystem functioning by employing the ever-changing biotechnological tools.

The effect of tillage systems on phosphorus distribution and forms in rhizosphere and non-rhizosphere soil under maize (Zea mays L.) in Northeast China

An appropriate tillage method must be implemented by maize growers to improve phosphorus dynamics in the soil in order to increase phosphorus uptake by plant. The objective of this study was to investigate the effects of tillage systems on phosphorus and its fractions in rhizosphere and non-rhizosphere soils under maize. An experimental field was established, with phosphate fertilizers applied to four treatment plots: continuous rotary tillage (CR), continuous no-tillage (CN), plowing-rotary tillage (PR), and plowing-no tillage (PN). Under the different tillage methods, the available P was increased in the non-rhizosphere region. However, the concentration of available P was reduced in the rhizosphere soil region. The soil available P decreased with the age of the crop until the maize reached physiological maturity. The non-rhizosphere region had 132.9%, 82.5%, 259.8%, and 148.4% more available P than the rhizosphere region under the CR, PR, CN, and PN treatments, respectively. The continuous no-tillage method (CN) improved the uptake of soil phosphate by maize. The concentrations of Ca2-P, Ca8-P, Fe-P, Al-P and O-P at the maturity stage were significantly lower than other seedling stages. However, there was no significant relationship between total P and the P fractions. Therefore, a continuous no-tillage method (CN) can be used by farmers to improve phosphorus availability for spring maize. Soil management practices minimizing soil disturbance can be used to impove phosphorus availability for maize roots, increase alkaline phosphatase activity in the rhizosphere soil and increase the abundance of different phosphorus fractions.

Microbial carbon source utilization in rice rhizosphere and nonrhizosphere soils with short-term manure N input rate in paddy field

Carbon (C) plays a vital role in regulating soil nutrient cycling and increasing soil microbial community, but there is still limited information on how C source utilization characteristics responds to soil physical and chemical properties changes under double-cropping rice (Oryza sativa L.) paddy field in southern China. Therefore, the effects of different short-term manure nitrogen (N) input rate managements on C source utilization characteristics in rice rhizosphere and non-rhizosphere soils under double-cropping rice field in southern China were studied by using 18O-H2O method. Therefore, a field experiment were established in Ningxiang city of Hunan Province, and five different fertilizer treatments were applied: (1) 100% N of chemical fertilizer (M0), (2) 30% N of organic manure and 70% N of chemical fertilizer (M30), (3) 50% N of organic manure and 50% N of chemical fertilizer (M50), (4) 100% N of organic manure (M100), and (5) without N fertilizer input as control (CK). The results showed that soil microbial biomass C content, soil microbial growth rate, and soil microbial basal respiration with application of organic manure treatments (M30, M50, M100) were significantly higher (p < 0.05) than that of CK treatment. And the soil C utilization efficiency with M0 treatment were significantly higher (p < 0.05) than that of M100 treatment. Compared with CK and M0 treatments, the metabolic capacity of soil microorganisms to exogenous C sources with M30, M50 and M100 treatments were increased. The largest types of exogenous C source was carboxylic acids, followed by amino acid and carbohydrate, and complex compounds was the smallest. The RDA analysis results indicated that fertilizer treatments significantly changed the utilization characteristics of soil microorganisms to exogenous C sources. As a result, this study found that characteristics of soil C source utilization were significantly affected by different short-term manure N input rate managements.

Comammox bacterial abundance, activity, and contribution in agricultural rhizosphere soils

The newly identified complete ammonia oxidation (comammox), which is capable of oxidizing ammonia directly to nitrate, has complemented our knowledge of nitrification in the global nitrogen (N) cycle. However, understanding the contribution and ecological roles of comammox in complex soil environments is still in its infancy. Here, the community structure and function of comammox and the interactions with other ammonia oxidation processes in rhizosphere and non-rhizosphere soils of four different crop fields (maize, cotton, soybean, and millet) were investigated in summer and winter. The only identified comammox species Candidatus Nitrospira nitrificans was widely distributed in all sampled soils. Comammox bacterial abundance was lower than that of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). The measured comammox potential rate ranged from 0.01 ± 0.002 to 0.40 ± 0.02 mg N kg−1 d−1, contributing <19.2 and 22.1% to ammonia oxidation in summer and winter, the remainder being due to AOA and AOB. The potential rate and community composition of comammox bacteria were significantly different on a temporal scale, while crop species and soil types (rhizosphere and non-rhizosphere) showed no obvious influences. In terms of oxidation rates, AOA (1.2 ± 0.7 mg N kg−1 d−1) dominated the ammonia oxidation in agricultural soils over AOB (0.31 ± 0.1 mg N kg−1 d−1) and comammox (0.2 ± 0.1 mg N kg−1 d−1). Both anammox bacterial abundance and activity were below the detection limits, indicating a negligible contribution of anammox in agricultural rhizosphere soils. The identification of comammox bacterial abundance and activity in situ enriches our knowledge of nitrification in agricultural systems.

Influence of slope aspect on the macro- and micronutrients in Artemisia sacrorum on the Loess Plateau in China.

Slope aspect is an important topographic factor for a micro-ecosystem environment that may affect macro- and micronutrients in plants and soil. The south-, northwest-, and north-facing slopes were selected to investigate the influence of slope aspect on the concentrations, storage, and allocation of macro- and micronutrients in Artemisia sacrorum on the Loess Plateau in China. The concentrations of available manganese (Mn) in both rhizosphere and non-rhizosphere soils reached their maximum on the north-facing slope. The concentrations of available iron (Fe) in rhizosphere soil and available copper (Cu) in non-rhizosphere soil reached their maximum on the south-facing slope. Slope aspect significantly affected the total concentrations of potassium (K), calcium (Ca), magnesium (Mg), Cu, and Mn in rhizosphere and non-rhizosphere soils, and all of these elements reached their maximum on the northwest-facing slope. Slope aspect significantly influenced the concentrations of aboveground K, Ca, and Mg, sodium (Na), Mn, and belowground K in A. sacrorum, and the concentrations of aboveground K, Ca, Mg, and Na and belowground Mn, Na, Fe, Ca, and Mg in weed. Most elements in A. sacrorum and the weeds reached their maximum on the south-facing slope. Slope aspect significantly changed the aboveground-to-belowground concentration ratios of K, Ca, and Na in A. sacrorum and weed. Slope aspect significantly affected the storage of macro- and micronutrients in A. sacrorum and weed but not the storage in the plants of the entire plot. Slope aspect predominantly affected the storage allocation of macro- and micronutrients in A. sacrorum but not those in weed. Slope aspect is an important topographic factor that affects the macro- and micronutrients in plants and soil in micro-ecosystem environments.

Short-term effects of biochar and Bacillus pumilus TUAT-1 on the growth of forage rice and its associated soil microbial community and soil properties

The synergistic effects of biochar (BC) and plant growth-promoting bacteria inoculant on crop growth and microbial communities’ composition in the rhizosphere and endorhizosphere (roots) of forage rice were examined under a short-term greenhouse condition. We performed in-pot experiments to evaluate the effects of BC and Bacillus pumilus strain TUAT-1 inoculant (Bio), both alone and in combination (BB), on the growth and microbial community of rhizosphere and roots in forage rice at 2 and 5 weeks after transplantation. At both growth stages, rice growth was improved by either BC or Bio alone. TUAT-1 was readily detected in rhizosphere with greater abundance following BB treatment than after Bio treatment alone. The bacterial communities of the rhizosphere, non-rhizosphere soil (un-planted bulk), and endorhizosphere of roots were determined using next-generation sequencing. Compared with the microbial community and diversity in the rhizosphere and endorhizosphere of roots, BC had greater effects on rhizosphere than on endorhizosphere, whereas Bio more effectively altered the microbial communities of the endorhizosphere layer of roots. Soil properties (pH and total N, exchangeable NH4-N, and K levels) were improved by either BC or Bio alone, suggesting that the changes of soil microbial communities might occur directly or indirectly as an effect of the alteration of soil physico-chemical properties. Overall, the result from this study suggests that biochar amendment and TUAT-1 inoculant have the potential to enhance growth and nutrient uptake in forage rice, and they depend on soil physico-chemical properties and the alteration of native microbial communities’ composition.