Rhizosphere Soil pH Research Articles

Maize-Straw Biochar Enhances Soil Properties and Grain Yield of Foxtail Millet in a Newly Reclaimed Land

Large-scale land reclamation has become common in northwestern China; however, low soil fertility and poor soil water-holding capacity limit agricultural production on these reclaimed lands, requiring increased fertilizer and irrigation inputs. Biochar, produced from agricultural waste, has shown potential in improving soil quality and water-holding capacity. In this two-year field study (2021 and 2022), we investigated the effects of biochar produced from maize straw on soil properties and grain yield of foxtail millet grown on newly reclaimed land. Three biochar treatments (3000, 4500, and 6000 kg ha−1) were compared to a control (CK) with no biochar application. Biochar application resulted in increased soil organic matter, total phosphorus, total nitrogen, soil enzyme activity, and soil organic acid content. It also significantly decreased soil pH and bulk density. Compared with the CK, biochar increased available nitrogen from 29.7% to 108% in 2021 and 37.0% to 88.4% in 2022. Similarly, biochar increased available phosphorus from 64.7% to 143% in 2021 and 41.9% to 96.5% in 2022. Grain yields ranged from 3092 to 4753 kg ha−1. Biochar treatments increased grain yield compared to the CK, ranging from 12.2% to 24.6% in 2021 and 27.1% to 53.7% in 2022. Correlation analysis revealed that soil pH was negatively related to soil oxalic acid content, phosphorus content, and sucrase activity. Available nitrogen and phosphorus contents were negatively related to soil bulk density and positively related to catalase activity. Soil water content was negatively correlated with soil bulk density and positively correlated with organic matter. In conclusion, biochar improved the rhizosphere soil pH and the effectiveness of soil fertility in the newly reclaimed soil, resulting in an enhanced grain yield of foxtail millet.

Rhizophagus intraradices symbiosis with Amaranthus hypochondriacus improves rhizosphere soil pH and nutrient status in sodic soil

As a forage crop belonging to the Amaranthaceae family (often considered as non-mycorrhizal plants), Amaranthus hypochondriacus can grow in sodic soil. It is worth exploring whether arbuscular mycorrhizal fungi (AMF) can successfully form a symbiotic relationship with A. hypochondriacus to alleviate the environmental stress it experiences and improve rhizosphere soil quality. This study aims to evaluate the potential for AMF to form a symbiotic relationship with salt-tolerant Amaranthaceae plants. By measuring the colonization rate, biomass, and rhizosphere soil chemical properties of the plants, we assessed the response of A. hypochondriacus to AMF under different concentrations of saline-alkali stress. The results showed that Rhizophagus intraradices could form a good symbiotic relationship with A. hypochondriacus and reduce the rhizosphere soil pH and increase the effective nutrient content.

Nitrification inhibitor effect on manganese and phosphorus shoot concentrations in maize under different textured soils from northern Germany

High soil pH can result in Mn2+ and P deficiency, leading to crop yield losses. Therefore, supplying soil with NH4+-N fertilizer in stabilized or unstabilized form can increase soil Mn2+ availability and shoot concentration. Nitrification inhibitors (NIs) have been proposed to lower rhizosphere soil pH, thus improving plant P uptake and preventing P deficiency in soils with high pH. Thus, this study investigated whether NI-stabilized or unstabilized NH4+-N could increase Mn2+ availability in three differently-textured soils (sand, loamy sand, and silt loam) and promote Mn2+ and P shoot concentration in maize. Two greenhouse experiments were conducted to investigate the effects of applying NH4+-N fertilizer with or without the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) combined with different nitrogen (N) sources (calcium nitrate (CN), ammonium nitrate (AN), and ammonium sulphate (AS)). The measured variables were bulk and rhizosphere soil pH and Mn2+ availability, maize biomass, as well as Mn2+ and P shoot concentrations. The results indicated that DMPP-stabilized AS significantly decreased rhizosphere pH by 7.2 % in loamy sand soil texture compared with unstabilized AS. Similarly, only in the loamy sand texture, DMPP-stabilized AS increased Mn2+ availability and shoot concentration by 86 % and 47 %, respectively, relative to unstabilized AS. Furthermore, DMPP-treated AS and AN promoted P shoot concentration by 30 % and 21 % in the loamy sand and silt loam soil textures, respectively, relative to the corresponding N sources without DMPP. Conversely, DMPP did not impact the investigated variables in the sand texture for all N sources. Moreover, AN and AS increased biomass yield, Mn2+ availability, and shoot concentration by 72 %, 30 %, and 46 %, respectively, in relation to the CN fertilizer in the sand soil texture. In conclusion, this study confirmed the effectiveness of DMPP-induced rhizosphere acidification in enhancing Mn2+ and P shoot concentration in loamy sand soil textures, as well as P shoot concentration in fine-textured soil.

The Combination of Biochar and Phosphorus-Containing Materials Can Effectively Enhance the Remediation Capacity of Amaranth on Cadmium-Contaminated Soil and Improve the Structure of Microbial Communities

Cadmium (Cd) pollution in soil has become a huge problem for agricultural production in China and even the world. Passivation and phytoremediation are two important remediation technologies for Cd pollution. In this study, the cadmium-contaminated and phosphorus-poor farmland soil around a mining area in Huainan was taken as the research object, and the remediation effect of biochar and phosphorus-containing materials on soil cadmium pollution was discussed. The results showed that the combined application of biochar and phosphorus-containing materials significantly reduced the pH of non-rhizosphere soil and rhizosphere soil, and increased the content of soil dissolved organic carbon (DOC). The combined application of biochar and phosphorus-containing materials significantly reduced soil pore water Cd and soil available Cd. In addition, both a single application of biochar and synergistic application of biochar and phosphorus-containing materials significantly increased the biomass of aboveground and underground parts of amaranth and soil urease and catalase activities. Phosphorus application reduced the bioavailability of Cd in soil. With the increase in phosphorus application, the content of available Cd in soil decreased significantly, and there was a certain negative correlation between Cd content and phosphorus content in plants. The abundance of beneficial microorganisms such as Ochrobactrum, Anaerolinea, Achromobacter, and Cellvibrio in soil was significantly increased after the synergistic application of biochar and phosphorus-containing materials.

Host genotype and age shape the microbial community in the rhizosphere soils of Camellia forests.

Microbiota living in the rhizosphere influences plant growth and fitness, from the opposite perspective; whether host genotypes control its root microbiota is of great interest to forest breeders and microbiologists. To improve low-yield plantations and promote sustainable management of Camellia oleifera, high-throughput sequencing was used to study the chemical properties and microbiome in rhizosphere soil of Camellia forests under three genotypes (common C. oleifera, local C. gauchowensis, and C. chekiangoleosa) and three growth stages (sapling stage at 4-year-old, primary fruit stage at 7-year-old, and full fruiting stage at 11-year-old). The results showed that the rhizosphere soil organic matter (OM), nutrient concentrations, diversity, and community composition of the microbiome were significantly varied among different Camellia genotypes. The relative abundance of symbiotic and pathotrophic fungi in the rhizosphere soil of C. chekiangoleosa was significantly higher than that of C. gauchowensis. Concentrations of OM, available phosphorus (AP), and bacterial alpha diversity increased with tree age. Fungi of Saitozyma, Mortierella, and Glomeromycota and bacteria of Burkholderia-Caballeronia-Paraburkholderia and Vicinamibacterales had potential for fertilizer development for Camellia plantation. Camellia genotypes and growth stages were significantly correlated with the rhizosphere soil pH, OM, and available potassium (AK). Soil pH and OM were key factors that affected the microbiome in the Camellia rhizosphere soils. In conclusion, tree genotypes and growth stages shaped microbial communities in Camellia rhizosphere soils, and some plant growth-promoting rhizobacteria were identified as preliminary candidates for improving Camellia plantation growth.

Cover crop alters rhizosphere sediments to recruit plant growth-promoting microorganisms, enhancing peanut production

Peanuts are typically grown in continuous monoculture in China, leading to continuous cropping obstacles and reduced yields. Cover cropping is emerging as a pivotal strategy for enhancing soil quality and promoting sustainable agriculture. However, the effects of cover crops on the rhizosphere environment, and how they benefit subsequent crops, are not well understood. We hypothesize that planting cover crop ryegrass during the winter fallow period could alter peanut rhizosphere sediments, recruit plant growth-promoting microorganisms, and ultimately enhance peanut production. This study aims to fill this gap by investigating the impact of ryegrass cover cropping on rhizosphere sediments and peanut yield. Rhizosphere soil organic carbon, total nitrogen, pH, and soil enzymes, including sucrase, urease, N-acetyl-β-D-glucosaminidase, and β-glucosidase, were analyzed, along with metabolomics, 16S rRNA, and fungal ITS sequence analyses, under traditional planting management (TP) and long-term cover crop (CC) treatments. The results showed that CC treatment significantly increased rhizosphere pH, enhanced soil organic carbon and total nitrogen levels, and elevated soil enzyme activities compared to TP treatment. Metabolomic analysis revealed that CC treatment upregulated compounds such as D-pinitol, palmitoleic acid, fructose, sorbitol, and sucrose, while downregulated compounds including benzoic acid, dodecanoic acid, and carbamic acid. This alteration in metabolite composition influenced the recruitment and function of the microbial community. Specifically, CC treatment markedly enhanced the abundance of growth-promoting microbes such as Bacillus, Paenibacillus, Pseudomonas, Lysobacter, Bradyrhizobium, and Mortierell etc., which are involved in important functions such as chemoheterotrophy, nitrate reduction, and plant saprotroph. Simultaneously, there was a decrease in pathogenic microorganisms, such as Aspergillus flavus and Fusarium oxysporum. Moreover, CC treatment positively influenced peanut root growth, resulting in longer roots and ultimately increase pod yield by 21.15 % compared to traditional winter fallow practices. These findings underscore the potential of cover cropping with ryegrass to improve rhizosphere microecosystem components, and ultimately enhance peanut productivity, providing valuable insights for sustainable agricultural practices.

The potential of durum wheat-chickpea intercropping to improve the soil available phosphorus status and biomass production in a subtropical climate.

The intercropping system is a promising approach to augmenting the soil nutrient status and promoting sustainable crop production. However, it is not known whether intercropping improves the soil phosphorus (P) status in alluvial soils with low P under subtropical climates. Over two growing seasons--2019-2020 and 2020-2021--two experimental fields were employed to explore the effect of durum wheat (Dw) and chickpea (Cp) cropping systems on the soil available P. A randomized complete block design was used in this experiment, with three blocks each divided into three plots. Each plot was used for one of the following three treatments with three replications: Dw monocrop (Dw-MC), Cp monocrop (Cp-MC), and Dw + Cp intercrop (CpDw-InC), with bulk soil (BS) used as a control. A reduction in the rhizosphere soil pH (-0.44 and -0.11 unit) was observed in the (Cp-MC) and (CpDw-InC) treatments over BS, occurring concomitantly with a significant increase in available P in the rhizosphere soil of around 28.45% for CpDw-InC and 24.9% for Cp-MC over BS. Conversely, the rhizosphere soil pH was significantly higher (+0.12 units) in the Dw-MC treatments. In addition, intercropping enhanced the soil microbial biomass P, with strong positive correlations observed between the biomass P and available P in the Cp-MC treatment, whereas this correlation was negative in the CpDw-InC and Dw-MC treatments. These findings suggested that Cp intercropped with Dw could be a viable approach in enhancing the available P through improved pH variation and biomass P when cultivated on alluvial soil under a subtropical climate.

Disease-induced changes in bacterial and fungal communities from plant below- and aboveground compartments

The plant microbes are an integral part of the host and play fundamental roles in plant growth and health. There is evidence indicating that plants have the ability to attract beneficial microorganisms through their roots in order to defend against pathogens. However, the mechanisms of plant microbial community assembly from below- to aboveground compartments under pathogen infection remain unclear. In this study, we investigated the bacterial and fungal communities in bulk soil, rhizosphere soil, root, stem, and leaf of both healthy and infected (Potato virus Y disease, PVY) plants. The results indicated that bacterial and fungal communities showed different recruitment strategies in plant organs. The number and abundance of shared bacterial ASVs between bulk and rhizosphere soils decreased with ascending migration from below- to aboveground compartments, while the number and abundance of fungal ASVs showed no obvious changes. Field type, plant compartments, and PVY infection all affected the diversity and structures of microbial community, with stronger effects observed in the bacterial community than the fungal community. Furthermore, PVY infection, rhizosphere soil pH, and water content (WC) contributed more to the assembly of the bacterial community than the fungal community. The analysis of microbial networks revealed that the bacterial communities were more sensitive to PVY infection than the fungal communities, as evidenced by the lower network stability of the bacterial community, which was characterized by a higher proportion of positive edges. PVY infection further increased the bacterial network stability and decreased the fungal network stability. These findings advance our understanding of how microbes respond to pathogen infections and provide a rationale and theoretical basis for biocontrol technology in promoting sustainable agriculture.Key points• Different recruitment strategies between plant bacterial and fungal communities.• Bacterial community was more sensitive to PVY infection than fungal community.• pH and WC drove the microbial community assembly under PVY infection.

Manganese and phosphorus maize shoot concentrations are differently affected by nitrification inhibitor‐driven rhizosphere acidification

AbstractHigh soil pH can lead to Mn2+ and P deficiency and yield losses. In addition, it is unclear which process, nitrification‐induced acidification of bulk soil or nitrification inhibitor‐driven rhizosphere acidification, is more effective in increasing Mn2+ availability and shoot concentration. Thus, this topic was investigated in this study. Moreover, we also evaluated if applying NIs can avoid P deficiency in soil with high pH and high buffering capacity. Two greenhouse experiments were carried out to investigate the impact of applying 3,4‐Dimethylpyrazole phosphate (DMPP) in sandy soil subjected to the application of different lime rates, simulating several soil pH and buffering capacity conditions. The utilized lime rates were 0, 0.5, 1, 2 and 4 g CaCO3 kg−1. The measured variables were bulk and rhizosphere soil pH, Mn2+ and P availability, maize biomass production, as well as Mn and P shoot concentrations. DMPP significantly reduced shoot biomass by 10% in unlimed soil; however, it promoted the overall shoot biomass by 30% in limed soil in both experiments. In addition, DMPP decreased the overall Mn shoot concentration by 24 and 21% in experiments I and II, respectively. In contrast, DMPP increased the overall P shoot concentration due to rhizosphere acidification by 24 and 17% in experiments I and II, respectively. The DMPP application did not avoid P deficiency under the highest lime rate (4 g CaCO3 kg−1) despite alleviating it. In conclusion, the application of NIs is not beneficial for increasing Mn2+ shoot concentration and, when performed to increase P availability in high pH soils, should consider the likelihood of causing Mn deficiency.

Bio-organic fertilizer facilitated phytoremediation of heavy metal(loid)s-contaminated saline soil by mediating the plant-soil-rhizomicrobiota interactions

Bio-organic fertilizer (BOF) was effective to promote the phytoremediation efficiency of heavy metal(loid)s-contaminated saline soil (HCSS) by improving rhizosphere soil properties, especially microbiome. However, there existed unclear impacts of BOF on plant metabolome and plant-driven manipulation on rhizosphere soil microbiota in HCSS, which were pivotal contributors to stress defense of plants trapped in adverse conditions. Here, a pot experiment was conducted to explore the mechanisms of BOF in improving alfalfa (Medicago sativa)-performing phytoremediation of HCSS. BOF application significantly increased the biomass (150.87–401.58 %) to support the augments of accumulation regarding heavy metal(loid)s (87.50 %–410.54 %) and salts (38.27 %–271.04 %) in alfalfa. BOF promoted nutrients and aggregates stability but declined pH of rhizosphere soil, accompanied by the boosts of rhizomicrobiota including increased activity, reshaped community structure, enriched plant growth promoting rhizobacteria (Blastococcus, Modestobacter, Actinophytocola, Bacillus, and Streptomyces), strengthened mycorrhizal symbiosis (Leohumicola, Funneliformis, and unclassified_f_Ceratobasidiaceae), optimized co-occurrence networks, and beneficial shift of keystones. The conjoint analysis of plant metabolome and physiological indices confirmed that BOF reprogrammed the metabolic processes (synthesis, catabolism, and long-distance transport of amino acid, lipid, carbohydrate, phytohormone, stress-resistant secondary metabolites, etc) and physiological functions (energy supply, photosynthesis, plant immunity, nutrients assimilation, etc) that are associated intimately. The consortium of root metabolome, soil metabolome, and soil microbiome revealed that BOF facilitated the exudation of metabolites correlated with rhizomicrobiota (structure, biomarker, and keystone) and rhizosphere oxidative status, e.g., fatty acyls, phenols, coumarins, phenylpropanoids, highlighting the plant-driven regulation on rhizosphere soil microbes and environment. By compiling various results and omics data, it was concluded that BOF favored the adaptation and phytoremediation efficiency of alfalfa by mediating the plant-soil-rhizomicrobiota interactions. The results would deepen understanding of the mechanisms by which BOF improved phytoremediation of HCSS, and provide theoretical guidance to soil amelioration and BOF application.

Effects of Ozone Stress on Rhizosphere Soil of Poplar Seedlings

Near-surface O3 has negative effects on plant productivity; however there were few studies on the effects of O3 pollution on the belowground part of the ecosystem. The effect of O3 stress on the belowground parts of poplar is unclear. We investigated the effects of O3 pollution on poplar rhizosphere soil in open-top chambers (OTC). Two kinds of plants with different O3 sensitivity were selected, i.e., high-sensitive poplar clone 546 and low-sensitive poplar clone 107. The control group and high-concentration O3 group were set up: charcoal-filtered air, CF; unfiltered air + 60 ppb O3, NF. Poplar rhizosphere soil was taken after 96 days (15 June to 17 September 2020) of cultivation in OTCs. O3 stress decreased the amplicon sequence variations (ASVs) of microorganisms in poplar 107 and poplar 546 rhizosphere soil, with no significant interspecific difference. The effect of O3 fumigation on the fungal community was greater than that on the bacterial community. The correlation between the bacterial community and rhizosphere soil physicochemical indices was closer than that of the fungal community. Some fungi, such as Clitopilus hobsonii, Mortierella sp., and Minimedusa, might help poplar resist the O3 stress. O3 stress had direct impacts on the pH, nutrients, and enzyme activities of rhizosphere soil, while it had indirect negative impacts on microbial community composition by nutrients. There was no difference in sensitivity between rhizosphere soil response to O3 stress of poplar clone 107 and clone 546, which might take a longer accumulation time to show the effect. This study provides a certain basis for accurately evaluating the ecological effects of O3 pollution.

Sasa argenteostriata – A potential plant for phytostabilization remediation of lead-zinc tailing-contaminated soil

Phytoremediation is an effective way to remediate metal-contaminated soils. During phytoremediation, plants immobilize heavy metals through the roots to reduce the mobility, toxicity and dispersal of the metals, and the changes in the activity of the roots are often accompanied by changes in the rhizosphere ecosystems, in which rhizobacteria are essential components and interact with roots to maintain the stability of the rhizosphere ecosystem and improve soil health. In this study, the phytoremediation potential of Sasa argenteostriata (Regel) E.G. Camu and the response of rhizobacteria were revealed with different levels of lead-zinc tailing contamination (Pb, Zn, and Cd concentrations of 1197.53, 3243.40, and 185.44 mg/kg for M1 and 2301.71, 6087.95, and 364.00 mg/kg for M2, respectively). The BCF of Sasa argenteostriata increased with increasing soil pollution, and the BCFPb, BCFZn, and BCFCd were 0.19, 0.27, and 0.08, respectively, under the M2 treatment; in contrast, the TF decreased with increasing soil pollution, and the TFPb, TFZn, and TFCd were 0.39, 0.85, and 0.07, respectively, under the M1 treatment. The mobility of Pb in the rhizosphere was higher than that of Zn and Cd, and the percentage of residual (Res) Zn and Cd in the rhizosphere increased, while the acid-soluble (Aci) Pb was significantly higher, leading to obvious uptake of Pb by the roots. Correlation analysis showed that Sasa argenteostriata affected the rhizobacterial community by changing the rhizosphere soil pH, the contents of organic matter and NRFM, and bacteria such as Proteobacteria and MND1, which are highly resistant to heavy metals (HMs), became the dominant species in the community. Further PICRUSt2 analysis showed that reducing metal transport across the membranes and increasing the efficiency of cellular reproduction were the main metabolic mechanisms of bacterial tolerance to HMs. Overall, the roots of Sasa argenteostriata were able to immobilize more heavy metals in PbZn tailing-contaminated soil, reducing the toxicity of HMs in the soil, and then influencing the rhizobacteria to change the community structure and metabolism mechanism to adapt to the HM-contaminated environment, and the soil fertility was increased, which together promoted the health and stability of the soil. This study is the first to illustrate the phytoremediation potential and response of the rhizobacterial community of Sasa argenteostriata under multimetal contamination of PbZn tailings. The results of the study provide some guidance for the practice of lead-zinc tailing-phytoremediation and soil health.

Using Biochar and Iron-calcium Material to Remediate Paddy Soil Contaminated by Cadmium and Arsenic

In this study, iron-calcium material (FC) and hickory-cattail biochar (BC) were applied to prepare composite material (BF), which was used to repair the combined pollution of cadmium and arsenic in paddy soil to reduce the content of cadmium (Cd) and arsenic (As) in rice grain. Soil pore water, rhizosphere soil, bulk soil, rice plants, and root iron plaque samples were collected during the growth period of rice in a pot experiment to explore the effects and mechanism of FC, BC, and BF on the bioavailability of Cd and As in paddy soil and their contents in plants. The results showed that biochar could significantly (P < 0.05) increase the pH value of bulk soil (0.55-0.66 units) and rhizosphere soil (0.28-0.36 units) and elevate the soil dissolved organic carbon (DOC) content. FC material could significantly (P < 0.05) reduce the pH of bulk soil (0.14-0.27 units) and rhizosphere soil (0.38-0.41 units), as well as the soil DOC content. Iron-calcium materials and composite could simultaneously reduce the contents of available Cd and As in soil pore water, rhizosphere soil, and bulk soil, whereas biochar could reduce the content of Cd but increase the content of As. Among them, a 1% addition of composite had the best effect. The available Cd and As in soil decreased by 41.8%-48.2% and 6.1%-10.1%, respectively. Biochar, iron-calcium materials, and composites improved plant biomass (dry weight of root, stem, leaf, and grain). For example, the dry weights of rice grains under these treatments were higher (48.5%-184.0%) than that of CK, as was the root iron plaque content (7.5%-13.6%). Compared with that in the CK, biochar could effectively reduce the Cd content in rice grain by 21.0%-26.1%. Iron-calcium material and composite could simultaneously reduce the Cd and As contents in rice grain. Among them, the BF treatment had the best effect on the reduction of Cd and As in rice grain, with a decrease of 36.9%-42.0% and 40.4%-44.4%, respectively. The Cd and As contents in rice grain were lower than the national standard values (GB 2762-2017).

Characteristics of anion and cation in rhizosphere soil of saline grassland in North China under different nitrogen addition levels

We investigated the effects and mechanisms of nitrogen additions (0, 1, 2, 4, 8, 16, 24, 32 g N·m-2·a-1) on contents of anion and cation in rhizosphere soil, bulk soil, and mixed rhizosphere and bulk soil in the heavily salinized grassland in the agro-pastoral ecotone of North China. The results showed that pH of rhizosphere, mixed and bulk soils decreased significantly with the increases of nitrogen addition levels. Moreover, pH of three soil types under the 32 g N·m-2·a-1 treatment decreased by 1.2, 0.9, and 0.6, respectively, while pH of rhizosphere soil decreased by 0.44 compared with the bulk soil. Na+ content of rhizosphere, mixed and bulk soils significantly decreased, while the NO3- content significantly increased. The proportion of Na+ content in total soluble salt content in rhizosphere soil decreased by 14% and that in bulk soil decreased by 12% after the 32 g N·m-2·a-1 addition. NO3- content increased by 29% in rhizosphere soil and by 26% in bulk soil. There was significant negative correlation between pH and NO3- content, and significant positive correlation between pH and Na+ content. The total soluble salt content of rhizosphere soil under the 32 g N·m-2·a-1 treatment was significantly reduced by 31.5%. Collectedly, nitrogen deposition could reduce soil pH and total soluble salt content of rhizosphere soil and alleviate saline-alkali stress.

The response of nutrient cycle, microbial community abundance and metabolic function to nitrogen fertilizer in rhizosphere soil of Phellodendron chinense Schneid seedlings.

Nitrogen (N) as an essential macronutrient affects the soil nutrient cycle, microbial community abundance, and metabolic function. However, the specific responses of microorganisms and metabolic functions in rhizosphere soil of Phellodendron chinense Schneid seedlings to N addition remain unclear. In this study, four treatments (CK, N5, N10 and N15) were conducted, and the soil physicochemical properties, enzyme activities, microbial community abundances and diversities, metabolism, and gene expressions were investigated in rhizosphere soil of P. chinense Schneid. The results showed that N addition significantly decreased rhizosphere soil pH, among which the effect of N10 treatment was better. N10 treatment significantly increased the contents of available phosphorus (AP), available potassium (AK), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N) and sucrase (SU) activity, as well as fungal diversity and the relative expression abundances of amoA and phoD genes in rhizosphere soil, but observably decreased the total phosphorus (TP) content, urease (UR) activity and bacterial diversity, among which the pH, soil organic matter (SOM), AP, NH4+-N and NO3--N were the main environmental factors for affecting rhizosphere soil microbial community structure based on RDA and correlation analyses. Meanwhile, N10 treatment notably enhanced the absolute abundances of the uracil, guanine, indole, prostaglandin F2α and γ-glutamylalanine, while reduced the contents of D-phenylalanine and phenylacetylglycine in rhizosphere soil of P. chinense Schneid seedlings. Furthermore, the soil available nutrients represented a significant correlation with soil metabolites and dominant microorganisms, suggesting that N10 addition effectively regulated microbial community abundance and metabolic functions by enhancing nutrient cycle in the rhizosphere soil of P. chinense Schneid seedlings.

Shoot and root responses to low phosphorus and their genotypic variability in selected cultivars of Japanese core collections of maize and soybean

ABSTRACT Low phosphorus (P) stress in agricultural soils is a global problem in crop production. A greater understanding of the genotype-specific responses under low P stress is imperative for producing P-efficient genotypes. This study first evaluated Japanese core collections of maize (86 landraces) and soybean (94 landraces) to low P under hydroponic conditions. Ten cultivars of each species were further evaluated in a pot experiment with two P supply rates: low P (10 mg P kg−1) and high P (50 mg P kg−1). Root morphology, acid phosphatase (ACP) activity, and rhizosphere soil pH were characterized 30 days after planting. A sufficient genotypic variation was found in both species under both P conditions. A significant decrease in biomass, except in maize cultivar JMC 76 and soybean cultivar GmJMC033, and increased phosphorus use efficiency (PUE) under low P conditions were observed. The maize cultivars: JMC 76, JMC 57, JMC 58, and JMC 8 and soybean cultivars: GmJMC033, GmJMC040, and GmJMC085 showed distinctive root modifications characterized by the high root-to-shoot ratio (RRS), total root length (TRL) and specific root length (SRL) under low P stress indicating their low P tolerance. Maize had more significant ACP activity compared to soybean under low P stress. The maize cultivars, which showed low P tolerance, were highly dependent on root morphological traits rather than physiological traits (ACP activity, rhizosphere acidification, and PUE), whereas soybean cultivars were dependent on both traits. In conclusion, the plasticity of the root system is crucial in both maize and soybean to tolerate P deficiency. These genotype-specific adaptations could be combined with agronomic strategies to enhance the overall P-use efficiency in cropping systems.

Critical transition of soil microbial diversity and composition triggered by plant rhizosphere effects.

Over the years, microbial community composition in the rhizosphere has been extensively studied as the most fascinating topic in microbial ecology. In general, plants affect soil microbiota through rhizodeposits and changes in abiotic conditions. However, a consensus on the response of microbiota traits to the rhizosphere and bulk soils in various ecosystems worldwide regarding community diversity and structure has not been reached yet. Here, we conducted a meta-analysis of 101 studies to investigate the microbial community changes between the rhizosphere and bulk soils across various plant species (maize, rice, vegetables, other crops, herbaceous, and woody plants). Our results showed that across all plant species, plant rhizosphere effects tended to reduce the rhizosphere soil pH, especially in neutral or slightly alkaline soils. Beta-diversity of bacterial community was significantly separated between into rhizosphere and bulk soils. Moreover, r-strategists and copiotrophs (e.g. Proteobacteria and Bacteroidetes) enriched by 24-27% in the rhizosphere across all plant species, while K-strategists and oligotrophic (e.g. Acidobacteria, Gemmatimonadete, Nitrospirae, and Planctomycetes) decreased by 15-42% in the rhizosphere. Actinobacteria, Firmicutes, and Chloroflexi are also depleted by in the plant rhizosphere compared with the bulk soil by 7-14%. The Actinobacteria exhibited consistently negative effect sizes across all plant species, except for maize and vegetables. In Firmicutes, both herbaceous and woody plants showed negative responses to rhizosphere effects, but those in maize and rice were contrarily enriched in the rhizosphere. With regards to Chloroflexi, apart from herbaceous plants showing a positive effect size, the plant rhizosphere effects were consistently negative across all other plant types. Verrucomicrobia exhibited a significantly positive effect size in maize, whereas herbaceous plants displayed a negative effect size in the rhizosphere. Overall, our meta-analysis exhibited significant changes in microbial community structure and diversity responding to the plant rhizosphere effects depending on plant species, further suggesting the importance of plant rhizosphere to environmental changes influencing plants and subsequently their controls over the rhizosphere microbiota related to nutrient cycling and soil health.

The joint action of biochar and plant roots on U-stressed soil remediation: Insights from bacteriomics and metabolomics

Although biological remediation of U-stressed soil has been studied for a long time, the combined effects of biochar and plant roots are rarely discussed and its influence on rhizosphere microecology are still unknown. Based on pot experiments, we explored the combined efforts of biochar addition and plant roots on U-stressed rhizosphere soil in several ways, including soil physicochemical properties, soil enzyme activities, uranium chemical speciation, bacterial community structure and metabolic pathways. Our results indicates that the content of DTPA-extractable U decreased by 49.31% after biochar and plant roots application, whereas plant roots only treatment just decreased by 25.46%. Further research has found that the pH, CEC, enzyme activities and nutritional level of rhizosphere soil were more significantly improved after biochar and plant roots application. Meanwhile, the abundance and diversity of bacterial community was also upregulated, which was also suggested by the stronger metabolisms of lipids, carbohydrate, nucleotides as well as amino acids. Correlation analyses also certified the positive associations between soil properties, bacterial communities and metabolism. We speculated that the uranium immobilization was mainly attributed to the direct fixation of biochar for its alkalinity, CEC, DOC, etc. and the joint action of biochar and plant roots for their stimulating effects on bacteria. Our findings suggested that combination of biochar and plant roots could limit bioaccessibility of U in a larger extend than plant roots only, which may be a better strategy for rapid remediation of U-streesed soil.

Adding nitrification inhibitors to N fertilisers induces rhizosphere acidification and enhances P acquisition: A meta-analysis

Ammonium (NH4+) absorption by crops enhances inorganic phosphate (Pi) acquisition efficiency mediated by rhizosphere acidification. The application of nitrification inhibitors (NIs) prolong NH4+ retention in soil by inhibiting ammonia oxidation and facilitating ammonium uptake by crops which may promote crop P utilisation. However, the efficacy of NIs on enhanced P-utilisation efficiency has not been comprehensively evaluated, and the mechanism underlying these effects remains unclear. Here, a meta-analysis of 92 peer-reviewed articles (1217 paired observations) was conducted to investigate soil pH and crop P absorption changes under NIs amendment, and boosted regression tree model was adopted to identify the primary factor regulating enhanced P-efficiency. The results showed that the addition of NIs reduced the rhizosphere soil pH by 12.37% and increased bulk soil pH by 2.38%, increased plant N and P uptake by 16.09% and 8.49%, respectively, and shoot N and P concentrations by 4.38% and 6.73%, respectively. NIs significantly decreased the crop N/P ratio and alleviated P limitation for crop production. Fertiliser (N and P) application method, NI product type, and soil properties (soil organic carbon, available P, total N content and soil texture) are major factors affecting crop P uptake. Using dicyandiamide (DCD) or 3,4-dimethylpyrazole phosphate (DMPP) as NIs combined with the application of ammonium-based fertiliser, adoption of subsurface or one-time N application, or application of these fertilisers to coarse-textured soils could significantly decrease rhizosphere soil pH while increasing crop P uptake. This study quantitatively demonstrated the positive impact of NIs on crop P acquisition using a meta-analysis approach, enhanced the knowledge on the incidental efficacy of N stabilisers and provide a strategy for the sustainable management of N and P in agriculture.

Polyamine-producing bacteria inhibit the absorption of Cd by spinach and alter the bacterial community composition of rhizosphere soil

Polyamines (PAs) are small aliphatic nitrogenous bases with strong biological activity that participate in plant stress response signaling and the alleviation of damage from stress. Herein, the effects of the PA-producing bacterium Bacillus megaterium N3 and PAs on the immobilization of Cd and inhibition of Cd absorption by spinach and the underlying mechanisms were studied. A solution test showed that strain N3 secreted spermine and spermidine in the presence of Cd. Both strain N3 and the PAs (spermine+spermidine) immobilized Cd and increased the pH of the solution. Untargeted metabolomics results showed that strain N3 secreted PAs, N1-acetylspermidine, 3-indolepropionic acid, indole-3-acetaldehyde, cysteinyl-gamma-glutamate, and choline, which correlated with plant growth promotion and Cd immobilization. A pot experiment showed that rhizosphere soil inoculation with strain N3 and PAs improved spinach dry weight and reduced spinach Cd absorption compared with the control. These positive effects were likely due to the increase in rhizosphere soil pH and NH4+-N and PA contents, which can be attributed primarily to Cd immobilization. Moreover, inoculation with strain N3 more effectively inhibited the absorption of Cd by spinach than spraying PAs, mainly because strain N3 enabled a better relative abundance of bacteria (Microvirga, Pedobacter, Bacillus, Brevundimonas, Pseudomonas, Serratia, Devosid, and Aminobacter), that have been reported to have the ability to resist heavy metals and produce PAs. Strain N3 regulated the structure of rhizosphere functional bacterial communities and inhibited Cd uptake by spinach. These results provide a theoretical basis for the prevention of heavy metal absorption by vegetables using PA-producing bacteria.