Activity In Rhizosphere Research Articles

Effects of continuous cropping of Pinellia ternata (Thunb.) Breit. on soil physicochemical properties, enzyme activities, microbial communities and functional genes

BackgroundPinellia ternata (Thunb.) Breit. is a commonly used herb in traditional Chinese medicine, and the main raw material of various Chinese patent medicines. Continuous cropping obstacle (CCO) is the main factor leading to the decline of crop yields and quality.MethodsMetagenomics sequencing technology was used to analyze the microbial community and functional genes of continuous cropping (CC) and control (CK) soils of P. ternata. In addition, differences in physicochemical properties, enzyme activities, microbial community composition and the abundance of functional genes in CC and CK were evaluated, as well as the relationship between these factors and CCO.ResultsResults indicated that CC of P. ternata led to the decline of rhizosphere soil pH, nutrient imbalance and enzyme activity reduction. Metagenomic analysis indicted that CC also changed the composition of the microbial community, causing an increase in the relative abundance of pathogenic microorganisms such as Fusarium, Klebsiella oxytoca and Pectobacterium carotovorum in the P. ternata rhizosphere. The relative abundance of potentially beneficial Burkholderia and Bradyrhizobium was recorded to decrease. Results also showed that there were considerable differences in CC and CK about the abundances of functional genes related to soil enzymes and the degradation of P. ternata allelochemicals, as well as the microbial groups which they belong. These results clarified the effects of CC on the microbial community structure and functional genes of soil. In addition, Burkholderia and Bradyrhizobium might play important roles in enhancing soil fertility and reducing the toxicity of phenolic acids in rhizosphere soil.ConclusionsCC of P. ternata changed the physicochemical properties, microbial community and functional genes of rhizosphere soil. Burkholderia and Bradyrhizobium for enhancing soil fertility and reducing the toxicity of phenolic acids might be potentially beneficial. These results provide theoretical guidance for bioremediation of CCO soil of P. ternata and other staple crops.Graphic abstract

Influence of microbial preparations on biomorphological indicators of tulip (<i>Tulipa</i> L.) ‘Anna Krasavitsa’ and soil fertility under steppe Crimea conditions

The data on the study of the effect of treatment of tulip bulbs of the Anna Krasavitsa cultivar before planting with microbial preparations (MP) Aurill and the Complex of microbial preparations (CMP) on the growth, state, ability for vegetative propagation of tulips, as well as the fertility and biological activity of the tulip rhizosphere in Crimea have been presented in the article. The studies were carried out in 2017-2019 in a small-plot field experiment on the tulip collection site of the NBG-NSC (v. Novy Sad, Simferopol district of the Republic of the Crimea) on the southern carbonate chernozem. Tulip bulbs were treated with MP working suspensions before planting with a dose of the preparation equal to 2 % of the bulb mass. The control - treatment with tap water. The study, collection and processing of the obtained data on the state of plants, fertility and biological activity of the soil was carried out by generally accepted methods. As a result of the studies was found that MPs increased the coefficient of vegetative propagation of bulbs, the mass of the nest and replacement bulb by 6-23 %, at the same time, a positive effect of CMP on an increase in the mass of large bulbs was revealed in the axils of the storage scales. The features of the influence of the treatment of tulip bulbs ‘Anna Krasavitsa’ with Aurill and CMP preparations on the morphometric characteristics of the plant have been revealed: the height and size of the flower and the lower leaf were increased. A positive effect of the preparations on soil fertility under tulips was shown: CMP promoted an increase in the organic matter content in the soil by 0.19 %, Aurill - the accumulation of nitrate nitrogen and exchangeable potassium in the rhizosphere of a tulip, and increasing its biological activity. The use of MP increased the number of ammonifying and amylolytic bacterial groups in the rhizosphere of the tulip; to a greater extent, Aurill, CMP increased the number of phosphate-mobilizing (by 58 %), as well as oligotrophic and cellulolytic bacteria by 8 and 78 % respectively. Aurill suppressed the number of micromycetes by 48 %.

Microorganisms number in sorghum (Sorghum bicolor (L.) Moench) rhizosphere after herbicide, plant growth regulator, and a biopreparation use

In the modern agricultural production, the use of herbicides and other biologically active substances is an important part of the cultivation technologies of most cereals, including the grain sorghum. It is known that most preparations, including the chemical ones, can directly or indirectly influence the development of microorganisms in the rhizosphere of plants, but the nature of their effect on the microbiota of grain sorghum rhizosphere has not been studied enough, which reasoned the relevance of this research. Microbiological activity of the grain sorghum rhizosphere (hybrid Milo W) was studied during 2019–2020 under the treatment by the herbicide Citadel 25 OD (0.6; 0.8 and 1.0 l/ha), plant growth regulator Endophit L1 (30 ml/ha) and biological preparation Bioarsenal (800 g/ 100 kg). The analysis of the obtained experimental data showed that use of the studied preparations both separately and in different compositions had a stimulating effect on the number of grain sorghum rhizosphere microbiota, which was observed in its increase, especially in variants with the combined use of the herbicide Citadel 25 OD, plant growth regulator Endophit L1 and the biopreparation Bioarsenal (compared to the control the number of rhizosphere microbiota increased by 29.4–80.6% in average by groups).

Enthralling the impact of engineered nanoparticles on soil microbiome: A concentric approach towards environmental risks and cogitation

Nanotechnology is an avant-garde field of scientific research that revolutionizes technological advancements in the present world. It is a cutting-edge scientific approach that has undoubtedly a plethora of functions in controlling environmental pollutants for the welfare of the ecosystem. However, their unprecedented utilization and hysterical release led to a huge threat to the soil microbiome. Nanoparticles(NPs) hamper physicochemical properties of soil along with microbial metabolic activities within rhizospheric soils.Here in this review shed light on concentric aspects of NP-biosynthesis, types, toxicity mechanisms, accumulation within the ecosystem. However, the accrual of tiny NPs into the soil system has dramatically influenced rhizospheric activities in terms of soil properties and biogeochemical cycles. We have focussed on mechanistic pathways engrossed by microbes to deal with NPs.Also, we have elaborated the fate and behavior of NPs within soils. Besides, a piece of very scarce information on NPs-toxicity towards environment and rhizosphere communities is available. Therefore, the present review highlights ecological perspectives of nanotechnology and solutions to such implications. We have comprehend certain strategies such as avant-garde engineering methods, sustainable procedures for NP synthesis along with vatious regulatory actions to manage NP within environment. Moreover, we have devised risk management sustainable and novel strategies to utilize it in a rationalized and integrated manner. With this background, we can develop a comprehensive plan about NPs with novel insights to understand the resistance and toxicity mechanisms of NPs towards microbes. Henceforth, the orientation towards these issues would enhance the understanding of researchers for proper recommendation and promotion of nanotechnology in an optimized and sustainable manner.

Stimulated saprotrophic fungi in arable soil extend their activity to the rhizosphere and root microbiomes of crop seedlings.

SummarySaprotrophic fungi play an important role in ecosystem functioning and plant performance, but their abundance in intensively managed arable soils is low. Saprotrophic fungal biomass in arable soils can be enhanced with amendments of cellulose‐rich materials. Here, we examined if sawdust‐stimulated saprotrophic fungi extend their activity to the rhizosphere of crop seedlings and influence the composition and activity of other rhizosphere and root inhabitants. After growing carrot seedlings in sawdust‐amended arable soil, we determined fungal and bacterial biomass and community structure in roots, rhizosphere and soil. Utilization of root exudates was assessed by stable isotope probing (SIP) following 13CO2‐pulse‐labelling of seedlings. This was combined with analysis of lipid fatty acids (PLFA/NLFA‐SIP) and nucleic acids (DNA‐SIP). Sawdust‐stimulated Sordariomycetes colonized the seedling's rhizosphere and roots and actively consumed root exudates. This did not reduce the abundance and activity of bacteria, yet higher proportions of α‐Proteobacteria and Bacteroidia were seen. Biomass and activity of mycorrhizal fungi increased with sawdust amendments, whereas exudate consumption and root colonization by functional groups containing plant pathogens did not change. Sawdust amendment of arable soil enhanced abundance and exudate‐consuming activity of saprotrophic fungi in the rhizosphere of crop seedlings and promoted potential beneficial microbial groups in root‐associated microbiomes.

The adaptive metabolomic profile and functional activity of tomato rhizosphere are revealed upon PGPB inoculation under saline stress

Salinization of agricultural lands is of increasing concern at global scale due to its negative impacts on several physiological and developmental processes of most crops, that in turn can lead to threatening food security. Salt-tolerant plant growth-promoting bacteria (PGPB) represent an emerging strategy to protect plants and enhance the productivity of agroecosystems suffering from salinization. This study aimed at investigating the individual effect of two PGPB in alleviating salt-stressed tomato plants, as well as the rhizosphere functioning and metabolomic profiles under soil salinity and PGPB inoculation treatments. The Biolog Eco-Plate functional analysis and untargeted metabolomics approaches were used to this aim. Under saline conditions, plants inoculated with Pseudomonas 16S showed higher biomass (p < 0.05) than both uninoculated and Enterobacter 15S-inoculated plants, indicating that the former strain was efficient in alleviate the saline stress. Moreover, independently from PGPB inoculation, the microbial metabolism in tomato’s rhizosphere was significantly increased by salinity, especially related to the catabolism of amines, carbohydrates, and polymers. The UHPLC/QTOF-MS approach allowed the identification of signature metabolomic patterns for the rhizosphere of tomato, with inflected accumulation of compounds imposed by either Pseudomonas 16S, Enterobacter 15S or saline stress. Crucial compounds from primary and secondary metabolism related to salinity stress or PGPB inoculation were detected, including low molecular weight osmolytes (e.g., amino acids), as well as anthocyanins, hydroxycinnamic acids, coumarins and saponins. An increase in the content of ROS-scavenging and antioxidant compounds in addition to the facilitation of Fe acquisition induced by Pseudomonas 16S, are suggested as mechanisms responsible for the higher biomass accumulation by tomato plants grown under saline stress.

Effect of Plant Growth Regulators on Protease Activity in Forest Floor of Norway Spruce Stand

Soil proteases are involved in organic matter transformation processes and, thus, influence ecosystem nutrient turnovers. Phytohormones, similarly to proteases, are synthesized and secreted into soil by fungi and microorganisms, and regulate plant rhizosphere activity. The aim of this study was to determine the effect of auxins, cytokinins, ethephon, and chlorocholine chloride on spruce forest floor protease activity. It was concluded that the presence of auxins stimulated native proteolytic activity, specifically synthetic auxin 2-naphthoxyacetic acid (16% increase at added quantity of 5 μg) and naturally occurring indole-3-acetic acid (18%, 5 μg). On the contrary, cytokinins, ethephon and chlorocholine chloride inhibited native soil protease activity, where ethephon (36% decrease at 50 μg) and chlorocholine chloride (34%, 100 μg) showed the highest inhibitory effects. It was concluded that negative phytohormonal effects on native proteolytic activity may slow down organic matter decomposition rates and hence complicate plant nutrition. The study enhances the understanding of rhizosphere exudate effects on soil microbial activity and soil nitrogen cycle.

Cellulolytic activity of Trichoderma reesei and Bacillus subtilis against the plant pathogen Pythium debaryanum

This work focused on the degradability of Pythium debaryanum cell wall by cellulase enzymes produced by Bacillus subtilis MK537378 and Trichoderma reesei MK934489. B. subtilis showed higher Exo-1,4-β-D glucanase and Endo-1,4-β D-glucanase activities than T. reesei while the highest β-glucosidase activities were recorded for T. reesei. Antagonistic activities against P. debaryanum were investigated by the tested B. subtilis and T. reesei. Moreover, the cellulolytic activity of both B. subtilis and T. reesei against P. debaryanum was confirmed by using Congo red staining technique. Microscopic observations showed clear hyphal lysis and degradation of the fungal cell wall in a dual plate assay. Results of the greenhouse experiment emphasized that the inoculated tomato seeds with B. subtilis or T. reesei in the presence of P. debaryanum showed 73.5% and 76% reduction in disease incidence, respectively as compared to the seed treated with pathogen alone (85%). Dehydrogenase activity (DHA) of soil rhizosphere was significantly increased in all inoculated soil with B. subtilis and/or T. reesei compared with uninoculated ones. The inoculation of tomato with B. subtilis and T. reesei in presence of P. debaryanum induced high activities of peroxidase, polyphenoloxidase, and chitinase by increasing 49.3, 55.2, and 56.9%, respectively, over the control. The growth parameters and yield of the tomato plants significantly increased in response to the inoculation of B. subtilis MK537378 and T. reesei MK934489 compared to individual inoculation.

Phosphatase activity and acidification in lupine and maize rhizosphere depend on phosphorus availability and root properties: Coupling zymography with planar optodes

Increase of phosphatase activity and rhizosphere acidification are two main physiological mechanisms of phosphorus mobilization by plants. To understand plant P-acquisition strategies, the spatial distribution of phosphatase activity and pH in the rhizosphere in response to P availability between legumes and cereals and along individual roots were investigated. Zymography of acid and alkaline phosphatase activities visualizing P hydrolysis potential was combined with planar optodes to localize pH changes in maize and lupine rhizosphere. Lupine was more adapted to P-deficiency than maize by increasing phosphatase activity (up to 30%), decreasing pH for 0.8 units in the rhizosphere and having larger hotspot areas compared to P addition. The P deficiency-induced increases of phosphatase activities and acidification were position-specific along taproot of lupine: acid phosphatase was highest while alkaline phosphatase was least at apical parts; pH was 1.7 units lower at the apical than at the basal part. The phosphatase activities and pH along lateral roots of lupine were independent on P availability but had specific distribution patterns: acid phosphatase activity declined from the root tips toward basal part, while the alkaline phosphatase activity was slightly increased from root tips; the pH was highest at the root tips (first 5 mm) and declined thereafter until stabilized after 20 mm. We conclude that 1) lupine is better adapted to P deficiency than maize by a stronger increase of phosphatase activities and facilitation of rhizosphere acidification; 2) The organic P mobilization by phosphatases and mineral P solubilization by acidification along individual roots were dependent on the root zone.

Zincated Nanoclay Polymer Composite (ZNCPC): Effect on DTPA-Zn, Olsen-P and Soil Enzymatic Activities in Rice Rhizosphere

ABSTRACT Zinc (Zn) is the most deficient micronutrient globally resulting in malnutrition and requires improved mode of delivery for increased nutrient use efficiency. An innovative fertilizer formulation, Zincated nanoclay polymer composite (ZNCPC), containing a total 6.59% Zn was evaluated in a pot experiment in comparison with ZnSO4 using rice (Oryza Sativa L.) (PRH 10 variety) as a test crop. The ZNCPC was applied in two doses [5.0 mg Zn kg−1 (T1) and 2.5 mg Zn kg−1 (T2)] whereas ZnSO4. 7 H2O was applied at single dose (5.0 mg Zn kg−1) (T3) in Zn deficient soil along with a control (without application of Zn) (T4). Effects of two modes of Zn application were evaluated under maximum tillering (MT) (55 days after transplanting) and panicle initiation stage (PI) (70 days after transplanting) on DTPA Zn, Zn uptake, Olsen-P, P uptake and soil enzymatic activities in rhizosphere and non-rhizosphere soil. Treatment T1 increased DTPA-extractable Zn content in rhizosphere soil to 157% in PI stage in comparison with T3. Stimulation of soil enzymes activity namely, dehydrogenase, acid and alkaline phosphatase was recorded in rhizosphere soil. Our study demonstrates that ZNCPC could potentially to be novel and innovative fertilizer formulation to increase Zn uptake in rice.

Soil enzymes activity: Effect of climate smart agriculture on rhizosphere and bulk soil under cereal based systems of north-west India

In agriculture production system, soil enzymes are important indicators of soil quality. Measurements of soil quality parameter changes are essential for assessing the impact of soil and crop management practices. Keeping this in view, an experiment was conducted to evaluate the enzyme activities namely dehydrogenase (DHA), β-glucosidase, acid and alkaline phosphatase (AcP &AlP), fluorescein diacetate hydrolases (FDH), cellulase, urease and aryl sulphatase in rhizosphere and bulk soil after 8 years of different management regimes. Soil organic carbon (SOC), moisture content and few enzyme indices such as enzymatic pH indicator (AcP/AlP), alteration index three (Al3) and geometric mean (GMea) were also measured. The treatments were conventional rice-wheat system (termed as scenario (Sc1), CT system), partial conservation agriculture (CA)-based rice-wheat-mungbean system (Sc2, PCA-RW), partial climate smart agriculture (CSA)-based rice-wheat-mungbean system (Sc3), partial CSA-based maize-wheat-mungbean system (Sc4), full CSA-based rice-wheat-mungbean system (Sc5), and full CSA-based maize-wheat-mungbean system (Sc6). Soil samples were collected from rhizosphere and away from roots (bulk soil) at 0–15 cm soil depth before sowing (from rhizosphere of previous crops), at maximum tillering, flowering, and after harvesting of wheat crop. Results showed that DHA activity was higher before sowing (59.8%), at maximum tillering (48.4%), flowering (8.6%) and after harvesting (19.1%) in rice based CSA systems (mean of Sc3 and Sc5) over maize based CSA systems (mean of Sc4 and Sc6) in rhizospheric soil. On average, β-glucosidase activity was significantly higher in rhizospheric soils of rice based system over maize based CSA system. Before sowing of wheat, significantly higher (21.4%) acid phosphatase activity was observed in rhizosphere over bulk soils of maize based CSA system. Significantly higher alkaline phosphatase activity was observed before sowing of wheat in bulk soils of rice (25.3%) and maize (38.5%) based CSA systems over rhizospheric soils. Rice based CSA systems showed 27% higher FDH activity than maize based systems. Significant interaction effect was observed between the managements and enzymes. SOC played an important role in regulating the enzymes activity both in rhizosphere and bulk soil. Significant variation in AcP/AlP, Al3 and GMea was observed among the managements. Therefore, CSA managements are beneficial in improving enzyme activities not only in rhizosphere but also in bulk soil where residues are retained thereby may help in improving nutrient cycling.

Differences in microbial community response to nitrogen fertilization result in unique enzyme shifts between arbuscular and ectomycorrhizal-dominated soils.

While the effect of nitrogen (N) deposition on belowground carbon (C) cycling varies, emerging evidence shows that forest soils dominated by trees that associate with ectomycorrhizal fungi (ECM) store more C than soils dominated by trees that associate with arbuscular mycorrhizae (AM) with increasing N deposition. We hypothesized that this is due to unique nutrient cycling responses to N between AM and ECM-dominated soils. ECM trees primarily obtain N through fungal mining of soil organic matter subsidized by root-C. As such, we expected the largest N-induced responses of C and N cycling to occur in ECM rhizospheres and be driven by fungi. Conversely, as AM trees rely on bacterial scavengers in bulk soils to cycle N, we predicted the largest AM responses to be driven by shifts in bacteria and occur in bulk soils. To test this hypothesis, we measured microbial community composition, metatranscriptome profiles, and extracellular enzyme activity in bulk, rhizosphere, and organic horizon (OH) soils in AM and ECM-dominated soils at Bear Brook Watershed in Maine, USA. After 27years of N fertilization, fungal community composition shifted across ECM soils, but bacterial communities shifted across AM soils. These shifts were mirrored by enhanced C relative to N mining enzyme activities in both mycorrhizal types, but this occurred in different soil fractions. In ECM stands these shifts occurred in rhizosphere soils, but in AM stands they occurred in bulk soils. Additionally, ECM OH soils exhibited the opposite response with declines in C relative to N mining. As rhizosphere soils account for only a small portion of total soil volume relative to bulk soils, coupled with declines in C to N enzyme activity in ECM OH soils, we posit that this may partly explain why ECM soils store more C than AM soils as N inputs increase.

Effect of Rice Planting on Nitrous Oxide (N2O) Emission under Different Levels of Nitrogen Fertilization

Nitrogen (N) fertilization is one of the most effective practices to increase productivity, and has therefore had a fast global increase. Consequently, the effects of the application of N fertilizer on emissions of N2O have been widely studied, but the effect of rice planting on N2O emission was not adequately quantified. To evaluate the effect of rice cultivation on N2O emissions, different levels of N were applied in a typical temperate rice field, and the N2O fluxes were compared in rice-planted and non-planted soils. Seasonal N2O fluxes responded differently with respect to N fertilization in the two different soil conditions. In non-planted soils, seasonal N2O fluxes ranged within 0.31–0.34 kg N2O ha−1 under 0 kg N ha−1 fertilization, and significantly increased by increasing N fertilization rates, with an average rate of 0.0024 kg N2O kg−1 N for 3 years. In rice-planted soils, seasonal N2O fluxes were also increased by N fertilization but showed large negative N2O fluxes, irrespective of the N fertilization level. This study confirms that the rice reacted as a reducer of N2O emissions, not an emission source, in paddy fields, suggesting that N2O fluxes should be estimated by the static chamber planted with rice to obtain a more precise field environment. The differences of N2O fluxes between the rice-planted and non-planted soils might have been caused by the rice plant’s rhizospheric activities, which may have influenced the N2O consumption potential in the rice plants’ rhizosphere. The N2O consumption potential was significantly increased with increasing N fertilization rates and was highly correlated with rice biomass yields. Therefore, the decrease in N2O fluxes by N fertilization in rice-planted soils might have been caused by a decreasing denitrification potential in paddy soils.

Soil Enzyme Activity and Microbial Metabolic Function Diversity in Soda Saline–Alkali Rice Paddy Fields of Northeast China

Western Jilin province has the most serious area of soda salinization in Northeast China, which affects and restricts the sustainable development of agriculture. The effects of physico-chemical properties of rhizosphere and non-rhizosphere soil on soil microbial diversity and enzyme activities (polyphenol oxidase, catalase, invertase, amylase) were evaluated in typical soda saline-alkali paddy field. Community-level physiological profile (CLPP) based on Biolog-ECO plates was used to assess the functional diversity of soil microorganisms. Exchangeable sodium percentage (ESP) and pH were negative correlated with the microbial activity (AWCD), soil enzyme activities (amylase, sucrose, and catalase, except for polyphenol oxidase) in rice rhizosphere and non-rhizosphere soil (P &lt; 0.05). The indexes of microbial diversity in rice rhizosphere soil were significantly higher than that of non-rhizosphere soil. The utilization of amino acids by rice rhizosphere microorganisms was relatively high, while non-rhizosphere soil had relatively high utilization of carboxylic acid, phenolic acid, and amine. Among the selected physico-chemical properties, soil organic carbon (SOC) and soil water content (SWC) had the greatest influence on the variation of microbial diversity indexes and enzyme activities in rhizosphere soil. ESP and pH showed a significant positive correlation with carbon source utilization, especially for amine (AM) and phenolic acid (PA) carbon source utilization (P &lt; 0.05) by means of RDA, and the utilization rate of AM and PA carbon sources by rice rhizosphere and non-root soil microorganisms was P1 &lt; P2 &lt; P3.

Carbon Dioxide Production in Bedrock Beneath Soils Substantially Contributes to Forest Carbon Cycling

AbstractSoils are widely considered the primary terrestrial organic matter pool mediating carbon transactions with the atmosphere and groundwater. Because soils are both a host and a product of rhizosphere activity, they are thought to mark the location where photosynthetic fixation of carbon dioxide (CO2) is balanced by the oxidation of organic matter. However, in many terrestrial environments, the rhizosphere extends below soils and into fractured bedrock, and it is unknown if the resulting biological and hydrologic dynamics in bedrock have a significant impact on carbon cycling. Here we show substantial production of CO2 in weathered bedrock at 4–8 m below the thin soils (&lt;0.5 m thick) of a Northern California forest using innovative monitoring technology for sampling gases and water in fractured rock. The deep CO2 production supports a persistent upward flux of CO2(g) year‐round from bedrock to soil, constituting between 2% and 29% of the average daily CO2 efflux from the land surface. When water is rapidly transported across the fractured bedrock vadose zone, nearly 50% of the CO2 produced in the bedrock dissolves into water, promoting water‐rock interaction and export of dissolved inorganic carbon (DIC) from the unsaturated zone to groundwater, constituting as much as 80% of the DIC exiting the hillslope. Such CO2 production in weathered bedrock is subject to unique moisture, temperature, biological, and mineralogical conditions which are currently missing from terrestrial carbon models.

Subsurface drip irrigation reduces cadmium accumulation of pepper (Capsicum annuum L.) plants in upland soil

Given that Cd pollution in dry land has aroused wide public concern, numerous remediation technologies has been utilized, yet there are limited cost-effective techniques that do not affect the original planting patterns. Fortunately, irrigation management can meet these requirements, while the effects of irrigation practices on Cd uptake by crops in slightly Cd-polluted upland soil remain elusive. Here, we aimed to investigate how the irrigation methods altered the Cd availability in soil, Cd accumulation in plants, microorganism population in soil, root morphology, and enzyme activities in soil and plants. We examined three irrigation treatments - surface drip irrigation (DI), subsurface drip irrigation (SDI), alternate-rows irrigation (ARI), and the control conventional furrow irrigation (CFI). The results showed that SDI remarkably reduced Cd content in roots, shoots and fruits, increased yield, and improved root growth and activity in soil of 20–40 cm compared to other treatments, though the Cd concentration in rhizosphere was not decreased significantly. The microbial population and enzyme activities in rhizosphere and enzyme activities in leaves and roots in SDI and ARI were basically higher than DI and CFI. Therefore, SDI has the prominent potential to reduce Cd uptake by crops in upland soil polluted with low Cd.

Major phosphorus in soils is unavailable, yet critical for plant development

Phosphorus (p) is a chemical component that has a concentration in the world’s land mass of around one gram for each kilogram. 85% to 95% of cellular phosphorus is available in the vacuole, 31p-nmr examinations uncovers the inadequacy of inorganic phosphorus (pi) efflux from the vacuole to make-up for a fast reduction of the cytosolic pi focus during phosphorus starvation. Activities of phosphorus use involve biogeochemical mechanisms of phosphorus in soil, the phosphorus cycle, chelation of iron (Fe), manganese (Mn) and aluminium (Al) and their subsequent removal from forming insoluble phosphorus compounds, transformation of phosphorus in the soil, and fixation of phosphorus in the soil. Phosphorus utilisation occur through solubilization by microbes which could be bacteria, fungi or bio-fertilizers that produce phytohormone, siderophores and antibiotics. However, factors affecting phosphorus solubilization are pH and temperature which are key predominant players for phosphorus adsorption dynamics from the soil and rhizosphere by plants, soil phosphorus transformation, spatial availability and acquisition of soil phosphorus, root architecture, bioavailability and acquisition of soil phosphorus, phosphorus cycling and bioavailability in soil-plant systems, its chemistry as well as its final uptake and utilization by plants. Overall, the phosphorus nutrition of plants is majorly monitored by phosphorus dynamics in the soil/rhizosphere-plant continuum. Given the usefulness of phosphorus to plants and its importance as a strategic resource, a better understanding of phosphorus dynamics in the soil/rhizosphere-plant continuum is necessary to lead the establishment of integrated phosphorus-management strategies involving manipulation of soil and rhizosphere activities, development of phosphorus-efficient crops, and improving phosphorus-recycling efficiency in the future.

Rhizosphere activity in an old-growth forest reacts rapidly to changes in soil moisture and shapes whole-tree carbon allocation

Drought alters carbon (C) allocation within trees, thereby impairing tree growth. Recovery of root and leaf functioning and prioritized C supply to sink tissues after drought may compensate for drought-induced reduction of assimilation and growth. It remains unclear if C allocation to sink tissues during and following drought is controlled by altered sink metabolic activities or by the availability of new assimilates. Understanding such mechanisms is required to predict forests' resilience to a changing climate. We investigated the impact of drought and drought release on C allocation in a 100-y-old Scots pine forest. We applied 13CO2 pulse labeling to naturally dry control and long-term irrigated trees and tracked the fate of the label in above- and belowground C pools and fluxes. Allocation of new assimilates belowground was ca. 53% lower under nonirrigated conditions. A short rainfall event, which led to a temporary increase in the soil water content (SWC) in the topsoil, strongly increased the amounts of C transported belowground in the nonirrigated plots to values comparable to those in the irrigated plots. This switch in allocation patterns was congruent with a tipping point at around 15% SWC in the response of the respiratory activity of soil microbes. These results indicate that the metabolic sink activity in the rhizosphere and its modulation by soil moisture can drive C allocation within adult trees and ecosystems. Even a subtle increase in soil moisture can lead to a rapid recovery of belowground functions that in turn affects the direction of C transport in trees.

Impact of transgenic sugarcane overexpressing SoSPS1 gene on bacterial diversity, enzyme activity and minerals content in soil rhizosphere

The transgenic sugarcane overexpressing SoSPS1 gene increased sugar content which may alter the root exudation that interact with soil rhizosphere microorganism. The microbial plays an important role in biochemical cycling and nutrient transformation in the soil. Therefore, it is important to investigate the potential risk of the transgenic sugarcane on soil ecosystem. This study is designed to evaluate the impact of overexpressing gene for sucrose-phosphate synthesis (SoSPS1) on the bacterial diversity, enzyme activity and nutrient contents. The transgenic sugarcane showed no significant difference in the population of culturable bacteria in the soil rhizosphere compared to non-transgenic counterpart. The populations of total, nitrogen-fixing and phosphate-solubilizing bacteria were similar in transgenic and non-transgenic sugarcane, although the bacterial population tends to increase at later sugarcane growth stage may due to the rise in nutrition from the root exudation. The PCR analysis showed no detection of horizontal gene flow in the bacteria. However, urease activity was significantly decreased in the transgenic sugarcane concomitant with lower nitrogen content in the soil rhizosphere at a later growth stage might due to the transgenic sugarcane lines increased nitrogen absorption for higher growth rate. Furthermore, the nutrient contents, such as organic carbon, phosphorus, potassium, magnesium and calcium, slightly varied in the soil rhizosphere but did not affected by the transgenic sugarcane. The results suggested that the transgenic sugarcane overexpressing SoSPS1 gene may not affect the bacterial diversity, nutrient contents and soil ecosystem.

Water management impact on denitrifier community and denitrification activity in a paddy soil at different growth stages of rice

Rice is one of the largest water-consuming crops. Alternate wetting and drying (AWD) is now an effective water-saving practice for rice cultivation that has been widely applied across the world. AWD may increase denitrification loss. However, the underlying mechanism remains unclear. This study investigated denitrifier activity, abundance and community structure in the rice rhizosphere and bulk soil in response to water management at the internode elongation (IE) and flowering (F) stages. The results revealed that at the IE stage, AWD significantly increased denitrification capacity (DC) in the rhizosphere compared with continuously flooded practice (CF). DC was significantly and positively related to electrical conductivity (EC) and the abundance of nirS-harboring denitrifiers. AWD led to higher EC in the 0–20 cm soil layer than CF. Although AWD lowered nirS abundance by 15 % compared with CF, the activity of nirS-harboring denitrifiers was enhanced by 1.89-folds of CF. At the F stage, AWD significantly decreased DC relative to CF. AWD had lower dissolved organic carbon (DOC) than CF, and DOC was significantly correlated with DC. Compared with CF, AWD also markedly changed the structure and network stability of nirS and nirK communities, resulting in sharp decreases in the total number of links in nirK and nirS networks of rhizosphere. The soil pH and EC were the key factors shaping the structure of nirS and nirK communities. Overall, the increase in denitrification losses due to AWD occurred primarily at the IE rather than F stage, and this increase was attributed to a rise in EC and changes in the activity and structure of nirS community. These findings provide a new insight into the mechanism of impact of the water-saving practice on denitrification loss for rice cultivation.