Root exudates play a central role in rhizosphere processes, many of which support plant growth. While increased exudation under abiotic stresses has been frequently linked to enhanced plant resilience, crop- and genotype- and soil-specific exudation patterns under non-stress conditions remain poorly understood. This study aimed to assess how soil type and genotype influence root exudation in major and emerging European crops and to explore how root morphology and plant growth are related to exudation. Four genotypes each of barley (Hordeum vulgare), faba bean (Vicia faba), potato (Solanum tuberosum), and sweet potato (Ipomoea batatas (L.) Lam.) were grown in three distinct European soils under non-stress conditions. Exudates were collected using a soil-hydroponic-hybrid approach and analysed for dissolved organic carbon and nitrogen, as well as total carbohydrates, amino acids, and phenolic compounds. Biomass and root morphology were assessed to examine correlations with exudation patterns. Results showed that soil type and genotype affected exudation patterns, but their influence varied by crop. Plant growth was negatively correlated with exudation rates across most crops, likely reflecting a trade-off in carbon and nitrogen allocation between biomass accumulation and rhizodeposition. Root morphological traits partly correlated with root exudation rates, but no universal relationships were detected across crops. Our results provide novel insights into belowground resource partitioning and broaden the understanding of exudation patterns to previously underexplored crops, highlighting resource allocation trade-offs shaped by genotype and soil as important drivers of exudation dynamics.

Nitrification drives nitrogen loss in agricultural systems, resulting in leached nitrate and increased emissions of the greenhouse gas nitrous oxide, thereby reducing nitrogen use efficiency (NUE). Biological nitrification inhibition (BNI) provides a promising nature-based solution to low-NUE by suppressing nitrifying microorganisms via plant-exuded bioactive metabolites. Although BNI is well documented in several major cereal grasses, evidence of BNI in barley (Hordeum vulgare) is lacking. This study demonstrates barley BNI activity through suppression of rhizosphere ammonia-oxidizer abundance, without a corresponding inhibition of the total prokaryotic community. Several barley lines exhibited strong inhibition of rhizosphere ammonia oxidizers consistent with high-BNI efficiency. The impact of BNI on the rhizosphere microbial community revealed clear differential effects across multiple phylogenetic clades of ammonia oxidizers, revealing that nitrifier clades differ in sensitivity to BNI in the rhizosphere. This led to a decrease in ammonia-oxidizer community richness correlating with BNI activity. The selective inhibition of rhizosphere ammonia oxidizers suggests that further research across diverse soils is needed. This study clearly demonstrates barley BNI activity in soil through suppression of rhizosphere ammonia oxidizers, identifying promising high-BNI lines, and providing a foundation for developing high-BNI barley cultivars to enhance NUE and increase agricultural sustainability.

CONTEXT Salt-affected soils are increasingly widespread in agricultural landscapes, but their responses to management practices in terms of greenhouse gas (GHG) emissions remain poorly constrained. Understanding how agricultural management influences GHG emissions in these soils is therefore essential for developing sustainable strategies that alleviate salinity stress, sustain crop productivity, and minimize environmental impacts. OBJECTIVE This study aims to quantitatively assess the impacts of different fertilization and irrigation practices on CO2 and N2O emissions in salt-affected soils. METHODS A meta-analysis of 68 peer-reviewed studies was conducted to address this objective. RESULTS AND CONCLUSIONS The results showed that, from a mitigation perspective, a single biochar application was the most effective option, reducing carbon dioxide (CO2) emissions by 10.8% (p = 0.2) and nitrous oxide (N2O) emissions by 25.5% (p = 0.1) compared to conditions without fertilizer application. However, when agronomic performance was also considered, the organic fertilizer combined with nitrogen (N) application emerged as the most balanced fertilization strategy, reducing GHG emissions while sustaining crop productivity. Similarly, Irrigation regimes below 60% of field capacity (FC) substantially reduced CO2 (−41.3%, p < 0.01) and N2O (−87.5%, p < 0.01) emissions compared with full irrigation (100% FC). However, irrigation at 60–80% FC represented an optimal compromise between emission reduction and crop productivity. Across fertilization strategies, soil moisture and salinity were the primary environmental drivers of GHG emissions, whereas under irrigation regimes, soil moisture exerted the dominant control on CO2 emissions. SIGNIFICANCE These findings indicate that GHG emissions in salt-affected agroecosystems can be mitigated without compromising crop yield through appropriate fertilization and irrigation management, providing a robust scientific basis for optimizing soil management practices.

Nutrient enrichment alters the functioning of grassland ecosystems, but the community structure and functions of microbes associated with the hyphosphere of arbuscular mycorrhizal (AM) fungi under nitrogen (N) and phosphorus (P) amendments remain poorly understood. Using a compartmented microcosm system and 16S rRNA gene and metagenomic sequencing, we studied the effects of AM fungal hyphae on soil microbial community composition, carbohydrate metabolism, and P cycling in four soils subjected to long-term N and/or P amendments. In long-term N-amended soils, AM fungal hyphae markedly altered the composition of the microbial community, improved P uptake and transport, and enriched genes associated with amino acid and secondary metabolite metabolism. Conversely, in long-term P-amended soils, the hyphae significantly reduced the concentration of available P in the soil and decreased the relative abundance of glucosyl transferases. Under combined NP amendments, the hyphae also induced significant changes in the composition of the microbial community and decreased the concentration of available P in the soil. In addition, AM fungal hyphae selectively modulated the abundance of specific genes involved in carbohydrate metabolism and P cycling, with variable effects depending on the soil. These results show that long-term nutrient amendments reshape AM fungal regulation of hyphosphere microbial communities and functions.

Although cover crops can potentially improve on-farm soil and water management to reduce erosion, their ability to bind soil and whether multi-species cover crops offer additional benefits has attracted little attention. This study aimed to assess the impact of cover crop diversity (Secale cereale, Brassica juncea, Vicia faba as monocultures and mixtures) on soil loss through changes in root-soil binding using rhizosheath mass an indicator in a silt loam field near Dundee, Scotland. Using a randomized block design, overland flow simulations (8 L min−1) tested soil loss across treatments, and soil cores were collected for rhizosheath and root measurements. Shoots were removed from half of the plots prior to measurements to isolate root diversity effects. Individual species identity, rather than species diversity, determined root and rhizosheath mass, with treatments containing V. faba having 64 % more root mass than the other species, and treatments containing S. cereale having 50 % more rhizosheath mass per unit of root dry mass than others. Shoot presence delayed runoff, but neither rhizosheath mass nor species diversity affected soil loss. Between-block variation in sediment concentration, total sediment and total runoff suggested that soil loss was influenced more by intra-field variability in soil structural and hydraulic properties. This work highlights how intra-field variability in soil structural and hydraulic properties can critically influence the success of erosion control measures, offering valuable guidance for future research and practical application of site-specific strategies for conserving soil function.

Arbuscular mycorrhizal (AM) fungi connect plant roots and soil bacteria, forming a cross-kingdom holobiont driven by plant-derived carbon flux and soil-derived nutrient flux. This holobiont encompasses not only roots and rhizosphere but also interfaces expanded by slender AM fungal hyphae. Our understanding of the microbiomes across these interconnected interfaces remains limited and fragmented. We used a split-root microcosm to inoculate the same maize root system with three AM fungal species, establishing a simplified holobiont. Amplicon sequencing, Biolog-ECO plates, and 13CO₂ labelling revealed the bacterial diversity and community-level physiological profiles (CLPPs). Bacterial communities colonizing non-mycorrhizal roots, mycorrhizal roots, and hyphae exhibited distinct structures and CLPPs. AM fungal species significantly influenced these bacterial communities, particularly in the mycorrhizosphere and hyphosphere, where notable changes occurred in key nutrient-cycling groups, such as phosphate solubilizers and nitrogen fixers. The diversity of the hyphosphere microbiome was closely aligned with fungal phylogeny. Additionally, a stable core microbiome persisted across all interfaces within the plant-AM fungi-bacterial holobiont, with key taxa such as Pseudomonas and Bacillus harboring the P-mobilizing genes encoding quinoprotein glucose dehydrogenase (gcd) and β-propeller phytase (bpp), highlighting their functional importance in nutrient cycling. Our study provides a comprehensive and precise hyphal-scale characterization of microbial communities across key interfaces, offering detailed insights into plant-microbial dynamics driving nutrient cycling and ecosystem functioning.

A nutritious and healthy diet relies on consuming cereals with sufficient micronutrient content, making the production of nutrient-rich crops a crucial agricultural goal. Identifying key strategies for plant micronutrient acquisition is essential, and this is especially critical for regions where calcareous or nutrient-deficient soils limit micronutrient bioavailability.Plants can enhance nutrient uptake by increasing exploration of the soil volume through root growth or by releasing root exudates that facilitate nutrient mining. Barley, along with other gramineous plants, employs an efficient strategy to mobilize micronutrients which is based on chelating agents called phytosiderophores (PS). While the role of these compounds in iron acquisition is well known, their function in zinc (Zn) nutrition is unclear. Furthermore, root-associated microorganisms are also known to interplay on the plant's micronutrient status either by enhancing the general plant health or directly making micronutrients bioavailable.This study aimed to identify key root traits for an efficient Zn acquisition in barley. Sixteen barley genotypes with diverse genetic backgrounds were grown in a Zn-deficient soil. Total carbon and nitrogen exudation were measured, and PS quantification as well as characterization was performed. To investigate the root-associated microbiome, amplicon sequencing of the 16S rRNA gene and the ITS2 region was conducted. PS exudation showed a positive correlation with barley Zn shoot concentration highlighting its potential role in plant Zn nutrition. While root-associated microorganisms were influenced by the plant’s micronutrient status, we didn´t see clear evidence of their role in plant Zn nutrition. These findings provide valuable insights about plant-soil-microbe interaction for nutrient-efficient crop production.

Pot size is a critical factor in plant growth experiments, influencing root architecture, nutrient uptake, and overall plant development as well as sensing of stress. In controlled environments, variation in pot size can impact phenotypic and molecular outcomes and may bias experimental results. Here, we investigated how pot size affects the root system architecture and molecular responses of two barley genotypes, the landrace BERE and the modern elite CONCERTO, through assessment of shoot and root traits and by using X-ray computed tomography complemented by transcriptomic and metabolomic analyses. The two genotypes showed distinctly different adaptations to changes in pot size. The landrace showed greater stability and adaptability with consistent root traits and enhanced accumulation of osmoprotectant metabolites across different pot sizes with respect to CONCERTO. Conversely, the elite line was more sensitive to pot size variations, particularly showing altered root architecture and transcriptomic responses. Overall, this study highlights the importance of selecting an appropriate pot size for plant growth experiments, particularly when focused on root traits, and highlights the importance of considering the physiological and molecular changes due to growth environment choice in experimental design in barley.

Arbuscular mycorrhizal (AM) fungi acquire photosynthetically fixed carbon (C) from host plants and transport some of it to hyphosphere bacteria via an extensive extraradical hyphal network. The hyphosphere microbiome, fostered by hyphal exudates, is crucial for AM fungi to access soil organic phosphorus (Po) and enhance plant growth, but the impact of plant-AM fungal combinations is still not well-elucidated. To answer this question, we selected two plant species with differing photosynthetic efficiency, medic (a C3 plant) and maize (a C4 plant), along with 4 AM fungal species, and successfully established various plant-AM fungal combinations. We examined the growth of plants and AM fungi, the mineralization process of soil Po, and the absolute quantity, community composition, and metabolic preferences of the hyphosphere microbiome. Maize-AM fungi combinations exhibited greater abilities to increase soil phosphatase activity and promote Po mineralization compared to medic-AM fungi combinations. This was related to substantial disparities in the hyphosphere core microbiome between maize and medic. Massilia, a pivotal member of the core microbiome and a keystone taxon within the hyphosphere network, showed a notably greater relative abundance in maize-AM fungal systems than in the medic treatment. Thirteen core bacterial strains isolated from the hyphosphere showed a universal ability to secrete phosphatase, with Massilia being the most proficient. Additionally, community level physiological profiles showed that the maize-associated hyphosphere microbiomes had a heightened capacity for metabolizing fructose and glucose, key components of hyphal exudates. Our study demonstrates that different combinations of plants and AM fungal species modulate the relative abundance of the core taxon through hyphal exudates, thus influencing the functionality of hyphosphere microbiomes for Po mineralization in the phytate-enriched soil. This provides novel insights into AM symbiosis for nutrient cycling and underscores the potential of tailored plant-fungal pairings in improving agricultural nutrient management and soil health.

To efficiently obtain P from soil, most terrestrial plants form symbiosis with arbuscular mycorrhizal(AM) fungi and thus have two P uptake pathways, i.e.,the direct pathway(DP) via roots, particularly root hairs, and the mycorrhizal pathway(MP) via AM fungal hyphae. AM fungi form an extraradical hyphal network to expand their contact area with soil and release carbon-rich compounds, which provide a high-energy habitat for soil bacteria. The bacteria affected by AM fungi support P nutrition of AM fungi by secreting extracellular phosphatases. During the P acquisition process, both DP and MP function and require C fixed by plant photosynthesis to maintain P transport. Plants make trade-offs between DP and MP based on C inputs and P benefits. This review first systematically explores the potential trade-offs between plant C inputs and P gains of DP and MP as well as the factors that influence such trade-offs.Then the response of AM fungi to soil nutrient heterogeneity and the mechanisms by which AM fungi select bacteria to mineralize organic P and increase the P contribution of MP were analyzed. Future studies need to apply emerging methods and technologies to accurately quantify the contribution of DP and MP to plant P absorption under different conditions and provide the theoretical basis for optimizing sustainable agricultural production systems.

Agricultural intensification has simplified landscapes thereby reducing biodiversity, depleting natural resources, and threatening ecosystem services. Resilience to abiotic stress is therefore decreasing, creating uncertainty about effects of climate change on agricultural production and environmental degradation. While much research has focused on the direct benefits of increased plant diversity for crop productivity, there is limited evidence on how diversity and species selection affect soil stabilisation. How cover crops bind soil (rhizosheath development) has attracted little attention even though they can decrease soil erodibility. A field trial investigated the impact of cover crop diversity on rhizosheath development and soil erodibility by conducting overland flow simulations. Species (Secale cereale, Brassica juncea, Vicia faba) were chosen for their suitability to UK environmental conditions. Results established that root biomass increased with cover crop diversity and was determined by the presence of Vicia faba. Rhizosheath formation was not affected by crop diversity and was greater in treatments containing Secale cereale. Overland flow simulations showed neither rhizosheath mass nor species diversity had an impact on soil erodibility, and the field variability of soil structural and hydraulic properties had a greater influence. By providing evidence for increased plant diversity effects on agroecosystem function, this work will inform land managers about cropping practices to conserve soil function and aid in delivering environmental policy targets.

Soil suspension assays were used to demonstrate synergistic interaction between citrate and phytase for mobilization and in situ mineralization of organic P. This synergy was evident in both unfertilized and fertilized soil where P mobilization by citrate was increased by 3.7 to 7.0-fold across both inorganic and organic pools. In the presence of citrate, phytase from different fungal sources further increased the proportion of P mineralization by an average of 47% from the total extracted P. Specific analysis by 31P NMR of the monoester-P extracted from the fertilized soil showed that the P released was associated with both direct hydrolysis of identifiable biomolecules of inositol hexakisphosphate (IHP, identified as the myo and scyllo isomers) and via a significant reduction of the broad-peak of monoester P. Functionality of endogenous soil phosphatase and phytase activities were also evident in the mineralization assays. The specific hydrolysis of IHP was further enhanced when phytase was added, where the total concentration of the extracted IHP was reduced by 92%. The addition of phytase in the absence of citrate (i.e., water suspensions only) by contrast had no measurable effect on the mineralization of soil organic P. Our results further our understanding of the biochemical nature and speciation of organic P in soils and the potential contribution that mineralization of organic P makes to the soil P cycle. This is particularly relevant to the rhizosphere where functional interaction of citrate and phytase and utilization of specific organic P substrates may offer opportunity for improved P-use efficiency.

Agricultural intensification coupled with changing climate are causing soils to become increasingly vulnerable to stresses such as drought, soil erosion, and compaction. The mechanisms by which roots detect and respond to soil stresses remain poorly understood. Recent breakthroughs show that roots release volatile and soluble hormone signals into the surrounding soil, then monitor their levels to sense soil stresses. Our review discusses how hormones can act 'outside the plant' as 'rhizocrine' signals that function to improve plant resilience to different soil stresses. We also propose a novel signalling paradigm which we term 'root RADAR' where 'rhizocrine' levels change in soil in response to environmental stresses, feeding back to roots and triggering adaptive responses.

Plants strategically allocate their limited carbon resources between root hairs and arbuscular mycorrhizal (AM) fungi, balancing the two key phosphorus (P) uptake pathways. This enables the exploitation of alternative P sources, including organic P and inorganic P, depending on their bioavailability in the soil. These pathways closely interact and influence rhizosphere microbial dynamics. However, the mechanisms underlying trade-offs under varying qualitative and quantitative P source conditions and their relationship with the rhizosphere microbiome remain poorly understood. Here, a three-factorial experiment was conducted with barley (Hordeum vulgare) rhizotype (wild type/bold root barley root hairless mutant), AM fungal inoculation (+/-), and inorganic P addition (+/-), using soil amended with phytin as a model organic P compound. We combined 13C-DNA stable isotope probing with 16S rRNA metabarcoding and root exudation analysis to explore the intricate interactions among root hairs, the AM symbiosis, and the bacterial rhizosphere microbiome in shaping plants' P source exploitation. We found that barley employed a strategic trade-off between root hairs and the AM symbiosis, favoring the AM symbiosis under high organic P and root hairs under high inorganic P conditions. This trade-off is driven by the functional divergence of the AM symbiosis and root hairs in P acquisition: the AM symbiosis triggered bacterial organic P mineralization and raised alkaline phosphatase activity, whereas root hairs depleted the inorganic P pool. Both the AM symbiosis and root hairs shaped the bacterial microbiome by exudation of carboxylates, such as citrate. Notably, the functional specialization of the AM symbiosis to organic P-dominated soil was associated with a bacterial microbiome driving organic P mineralization. These findings advance our understanding of plant-AM fungal-soil microbiome interactions and highlight the importance of plant microbiome selection in P acquisition.

While much research has focused on the benefits of cover crop diversity for crop productivity, there is limited evidence on how root diversity and species selection stabilise soil. Although cover crops can potentially improve on-farm soil and water management, how they bind soil (through rhizosheath development) and whether multi-species cover crops offer additional benefits has attracted little attention. This study aimed to assess rhizosheath persistence in field-grown cover crops and their mixtures to understand the impact of species diversity on soil binding capacity. Brassica juncea, Secale cereale and Vicia faba were sown as monocultures and mixtures in a winter cover crop field trial near Dundee, Scotland. Soil cores were collected three times during January-March 2023. Measurements included rhizosheath mass, root length, and root hair length and density. While overall rhizosheath mass decreased by 27

In 2016, a group of experts convened to set priorities for organic phosphorus (P) research, addressing global issues, methodological strengths and weaknesses, and the benefits of understanding the organic P cycle. Seven years later, scientists and students with an interest in organic P reconvened to discuss progress and new insights, and this review highlights recent major research updates. Interest in organic P research has increased since 2016, and new priorities have emerged, including the impact of climate change on organic P, the influence of geopolitical crises on P supplies, and the adoption of sustainable practices like regenerative agriculture. Climate change was a central theme in the 2023 discussions, with an increased emphasis on integrating P and especially organic P into climate change research, which has traditionally focused more on carbon (C) and nitrogen (N). The discussions highlighted disparities in accessing analytical equipment globally, and its consequent impact on research quality and scope. To address these issues, coordinated efforts involving the research community, government policies, and international cooperation are needed, much the same as we see with the climate and biodiversity crises. Promoting sustainable agricultural practices, investing in soil health, and enhancing education and extension services are crucial. Future research should focus on standardizing analytical methods, integrating nutrient balance into models, and exploring soil-microbiome-plant interactions. Regular and intedisciplinary workshops, social media engagement, and the establishment of research networks are recommended to maintain momentum in organic P research. Raising public and stakeholder awareness about the importance of organic P is essential for advancing knowledge in this area.

Plant-derived metabolites play a crucial role in mediating plant–microbe interactions affecting plant development, health and ability to withstand biotic and abiotic stresses. However, how the key plant metabolites, e.g., flavonoids and fatty acids secreted by roots, regulate soil microbial communities to promote plant phosphorus (P) nutrition, growth and development remains unclear. We determined whether the addition of different concentrations (0, 50 or 500 μmol kg−1) of myristic acid (fatty acid), quercetin, naringenin or luteolin (flavonoids) to the soil to improved soil organic P utilization efficiency and enhanced plant growth by changing microbial community. Flavonoids could directly regulate rhizosphere bacterial community structure, with a significant increase in the relative abundance of Micrococcaceae and Nocardioidaceae by the addition of 50 μmol kg−1 of naringenin, luteolin, 500 μmol kg−1 of quercetin, naringenin or luteolin. The addition of myristic acid had weaker impact on bacterial community structure. The altered bacterial community structure lead to the increased alkaline phosphatase activity in the rhizosphere to promote the mineralization of organic P, which could facilitate plant growth and P uptake to different extents. Our results indicate that the addition of flavonoids enhanced organic P mineralization by selecting individuals which secreted more phosphatases. These findings can provide guidance for effective manipulation of composition of plant-microbial communities to increase plant P nutrition and/or efficiency of use of P fertilizers.

Efficient micronutrient acquisition is a critical factor in selecting micronutrient dense crops for human consumption. Enhanced exudation and re-uptake of metal chelators, so-called phytosiderophores, by roots of graminaceous plants has been implicated in efficient micronutrient acquisition. We compared PS biosynthesis and exudation as a response mechanism to either Fe, Zn or Cu starvation. Two barley (Hordeum vulgare L.) lines with contrasting micronutrient grain yields were grown hydroponically and PS exudation (LC-MS) and root gene expression (RNAseq) were determined after either Fe, Zn, or Cu starvation. The response strength of the PS pathway was micronutrient dependent and decreased in the order Fe > Zn > Cu deficiency. We observed a stronger expression of PS pathway genes and greater PS exudation in the barley line with large micronutrient grain yield suggesting that a highly expressed PS pathway might be an important trait involved in high micronutrient accumulation. In addition to several metal specific transporters, we also found that the expression of IRO2 and bHLH156 transcription factors was not only induced under Fe but also under Zn and Cu deficiency. Our study delivers important insights into the role of the PS pathway in the acquisition of different micronutrients.