Mapping the Rhizosheath Research Landscape: A Bibliometric and Thematic Analysis of Root–Soil Interactions, Stress Adaptation, and Crop Resilience

1. Introduction

The rhizosheath, a layer of soil that remains physically attached to roots through the combined action of root hairs, mucilage, root exudates, and microbial adhesives, is increasingly recognized as a functional component of the rhizosphere rather than a passive by-product of root growth [1,2,3,4]. It is important to distinguish the rhizosheath from a broader rhizosphere. The rhizosphere encompasses the entire soil volume influenced by root activity, including chemical gradients, microbial communities, and nutrient depletion zones. In contrast, the rhizosheath refers specifically to the physically bound layer of soil particles that remains attached to the roots upon excavation [4,5]. This distinction is critical because the rhizosheath mass, the most used metric, captures a defined structural trait, whereas rhizosphere processes extend across a broader, more diffuse spatial domain. More importantly, the rhizosheath mass represents the amount of adhering soil and should not be interpreted as a direct measure of the hydraulic, nutritional, or microbial functions operating at the root–soil interface.

Over the past decade, the rhizosheath has emerged as a measurable root-associated trait that links rhizosphere structure to plant–water relations and nutrient acquisition under environmental stress [1,6,7,8]. Studies on cereals, legumes, and drought-adapted species have shown that rhizosheath development enhances root–soil contact, modifies water retention and rewetting, and improves access to poorly mobile nutrients, particularly phosphorus, under drying or nutrient-limited conditions [9,10,11,12]. These functions position the rhizosheath as part of an extended root phenotype, in which plant traits actively modify soil physical and biological processes to improve resource acquisition and plant performance [3]. Therefore, the rhizosheath is better understood as an emergent plant–soil phenotype than as an isolated morphological property of the root [13].

Mechanistically, rhizosheath formation results from tightly integrated interactions between root structural traits, rhizodeposition chemistry, soil physical properties, and the rhizosphere microbiota. Root hairs provide a structural framework that anchors the soil particles. In contrast, mucilage and root exudates act as physicochemical agents that promote soil aggregation, regulate moisture retention, and influence nutrient diffusion at the root–soil interface [2,14,15]. Mucilage and other rhizodeposits can also modify soil wettability, viscosity, pore connectivity, and the dynamics of drying and rewetting around the roots [16,17,18]. However, the magnitude and direction of these effects depend on soil texture, water content, root development, and physicochemical properties of the released compounds.

These processes are further reinforced by rhizosheath-associated microbial communities, whose extracellular polymeric substances enhance soil adhesion, stabilize aggregates, and contribute to nutrient cycling [7,10,19]. Rhizosheath-associated bacteria and fungi may also transform nutrients, modify plant hormonal signaling, and interact with root hairs and exudates. Studies in crops such as rice, barley, sorghum, pearl millet, and switchgrass indicate that soil drying and plant genotype can restructure rhizosheath microbial communities, while selected bacterial taxa can enhance rhizosheath formation through auxin- or ethylene-related pathways. Accordingly, rhizosheath development results from dynamic plant–soil–microbe interactions shaped by plant genotype, soil texture, and moisture regime, rather than being a purely structural property of the root [20].

These integrated processes are directly relevant to drought tolerance and nutrient acquisition, particularly under water-limited and low-soil-fertility conditions. Maintaining hydraulic continuity at the root–soil interface reduces air gaps and sustains water flow to the roots, thereby buffering plants against transient drought stress [1,12,21]. The chemically active microenvironment within the rhizosphere also promotes phosphorus mobilization through rhizodeposition and microbial activity, which is critical in soils with limited nutrients [11,22,23]. Moreover, evidence of genetic variation in rhizosheath traits across crops, such as wheat, barley, sorghum, and legumes, highlights their potential as targets for phenotyping and breeding aimed at improving resource-use efficiency under climate stress [20,24,25,26]. However, the functional and agronomic relevance of rhizosheath variation remains uncertain because rhizosheath mass is influenced by plant development, soil conditions, sampling procedures, and genotype × environment interactions. Consequently, a larger rhizosheath does not necessarily improve water or nutrient acquisition, stress tolerance, or productivity. Therefore, distinguishing structural expression from physiological function and breeding value is essential before rhizosheath traits can be reliably incorporated into phenotyping and climate-resilient crop improvement. Despite these advances, the conceptual understanding of rhizosheath biology remains fragmented across disciplines such as plant physiology, soil physics, and microbial ecology. In addition, commonly used metrics, such as rhizosheath mass, do not fully capture the structural and functional complexity of rhizosphere processes, particularly under heterogeneous soil conditions or when measured in disturbed systems [9]. This fragmentation limits the integration of rhizosheath traits into predictive frameworks and breeding strategies.

Bibliometric analysis provides a systematic approach to address this limitation by quantitatively mapping the development, structure, and thematic evolution of research fields. By combining performance indicators (e.g., publication output, citation impact, and collaboration networks) with science-mapping techniques (e.g., co-citation, bibliographic coupling, and keyword co-occurrence), these approaches reveal how knowledge domains are organized and how research priorities have evolved [27,28]. Such analyses enhance conventional reviews by pinpointing dominant research clusters, emerging topics, and underexplored areas that narrative syntheses alone may not easily detect. However, bibliometric networks alone cannot explain the biological significance of the relationships they reveal. Combining bibliometric mapping with thematic synthesis addresses this limitation by identifying influential publications, research communities, and emerging topics while clarifying their underlying mechanisms, applications, and knowledge gaps through a critical examination of the literature.

In this context, the present study conducted a bibliometric and thematic synthesis of rhizosheath research published between 2015 and 2026. It examined the development of the field through publication output, citation influence, source distribution, author contributions, and international collaboration. This study further mapped the intellectual and conceptual structure by identifying influential publications, dominant research clusters, and the evolution of themes related to root traits, soil physical processes, microbiome interactions, drought responses, nutrient acquisition, genetics, and breeding. Particular attention was given to the conceptual and methodological gaps that limit the translation of rhizosheath formation into measurable physiological functions, field-relevant phenotypes, and agricultural applications. By integrating performance analysis, science mapping, and content-based interpretation, this study provides a reproducible overview of the field. This review outlines the research priorities for incorporating rhizosheath-related traits into climate-resilient crop phenotyping and breeding.

2. Materials and Methods

2.1. Research Questions

This bibliometric study examined the development and structure of rhizosheath research, with an emphasis on rhizosheath–microbiome interactions and plant stress adaptation. A combined bibliometric and thematic synthesis design was employed. Performance analysis characterized research productivity and influence; science-mapping techniques examined the social, intellectual, and conceptual organization of the literature; and qualitative examination of titles, abstracts, and keywords interpreted the biological meaning of the resulting clusters.

Four questions guided this analysis:

(a) How did publication output, citation influence, source distribution, geographical contributions, and international collaboration evolve during the study period?

(b) Which authors, publications, journals, and collaboration networks shaped the intellectual and social structure of rhizosheath research?

(c) Which thematic clusters and conceptual structures characterized the field, and how did themes related to root traits, soil physical processes, microbial interactions, plant stress responses, nutrient acquisition, genetics, and breeding evolve?

(d) Which conceptual and methodological gaps constrain the translation of rhizosheath formation into functional phenotyping, field application, and climate-resilient crop improvement?

2.2. Data Source, Search Strategy, and Eligibility Criteria

The analysis was based on the Web of Science Core Collection (WoSCC; https://www.webofscience.com/). The search was conducted on March 10, 2026, using the following query: TS=(rhizosheath) AND TS=(microbiome OR microbiota OR bacteria OR fungi OR drought OR breeding OR genetics OR “root hair”). In WoSCC, the TS field searches the title, abstract, author keywords, and Keywords Plus fields. The search period extended from January 1, 2015, to March 10, 2026; consequently, the publication output for 2026 represented only a partial year and was interpreted accordingly. Citation counts were also recorded as they appeared in WoSCC on March 10, 2026, because citation indicators are dynamic and may change after the search date.

This strategy combined the core concept of rhizosheath with key biological, ecological, and stress-related terms to capture studies on root–soil–microbiome interactions and plant adaptive processes. The Boolean structure intentionally restricted the dataset to publications that contained “rhizosheath” together with at least one of the selected microbiological, stress-related, genetic, or root-trait terms. Therefore, it represents a focused subset of the broader rhizosheath literature rather than an exhaustive inventory of every publication mentioning rhizosheath.

We acknowledge that this keyword-based approach may have excluded relevant studies using alternative terminology such as mucilage, soil aggregation, root hydraulics, rhizodeposition, root–soil contact, water retention, or phosphorus dynamics. Conversely, records in which a search term appeared only in Keywords Plus could have been retrieved despite limited relevance to the study objectives. These limitations were addressed through title and abstract relevance screening and were considered when interpreting the resulting networks and research trends.

The search was limited to English-language publications from 2015 to 2026 and included original articles, reviews, and conference proceedings; other document types were excluded to ensure consistency. Records were eligible if their title, abstract, or keywords addressed at least one aspect of rhizosheath formation, function, measurement, microbial association, environmental response, genetic variation, or agricultural application. Records were excluded when the rhizosheath was mentioned only incidentally or when the study did not provide information relevant to the research questions.

The query retrieved 136 documents: 118 research articles, 17 review articles, and one conference proceeding. Records were exported in the BibTeX format with full metadata (authors, titles, abstracts, keywords, affiliations, cited references, publication year, source titles, and document types) in accordance with established bibliometric guidelines [25].

2.3. Data Processing and Bibliometric Analysis

Analyses were performed in RStudio (version 2026.01.1-403; RStudio Team, Posit, USA) using the Bibliometrix R package, a widely adopted open-source framework for bibliometric and scientometric analyses [29]. The BibTeX file was imported and converted into a structured data frame using the convert2df() function [30]. Preprocessing included verification of metadata completeness, harmonization of author names and keywords, and removal of duplicate or incomplete records. The outputs were tabulated and visualized using Microsoft Excel (Microsoft Corporation, Redmond, WA, USA).

Two complementary approaches were applied: performance analysis summarized annual publication output, leading journals, authors, and country contributions; science mapping explored the intellectual and conceptual structure through citation, co-authorship, and keyword co-occurrence networks [27,28]. Networks were built using co-occurrence and co-citation matrices, with frequency thresholds applied to reduce noise and improve interpretability. Normalization (association strength) and clustering (Louvain algorithm) followed the standard Bibliometrix procedures, enabling the identification of major thematic and intellectual structures.

2.4. Screening and Data Extraction

Retrieved records were screened against predefined inclusion criteria (publication year, language, and document type) following established guidelines for bibliometric and systematic analyses [1,2]. Duplicates, incomplete entries, and records lacking essential bibliographic information were removed prior to the analysis. Key metadata, including authorship, publication year, source, author keywords, institutional affiliations, document type, and citation counts, were extracted to compute descriptive indicators (productivity, citation impact) and to construct science-mapping networks (co-authorship, keyword co-occurrence) [3]. The original BibTeX dataset and analysis outputs were retained throughout the pipeline to ensure transparency and reproducibility [4].

3. Results

3.1. Dataset Overview and Growth Dynamics

The bibliometric dataset comprised 136 publications on rhizosheath research published between 2015 and 2026 across 60 sources, with 6,366 citations and 723 authors (Table 1). The annual publication growth rate during the study period was −3.62%, the mean document age was 4.29 years, and the average citation impact was 31.71 citations per document. Content analysis identified 501 Keywords Plus and 470 author keywords. Multi-author collaborations dominated, with only one document being single-authored, an average of 8.25 co-authors per document, and 54.41% of the international co-authorship.

The temporal distribution of rhizosheath publications followed a logistic growth pattern (Figure 1a), with a fitted carrying capacity (K) of 159.64 publications, an inflection point at 2022.54, and a life cycle duration (Δt) of 9.15 years. The estimated peak annual output (~19 documents) occurred around 2022–2023, with 10% and 99% cumulative development thresholds reached in 2017.96 and 2032.11, respectively. Cumulative output rose from 3 documents in 2015 to 136 by 2026, with model projections approaching the saturation level near 160 publications by 2029 (Figure 1b; R² = 0.587, RMSE = 4.86). Annual production began with one article in 2015, stabilized at eight publications per year between 2017 and 2019, increased to 14–15 in 2020–2021, peaked at 24 in 2022, and subsequently declined to 10 per year in 2023–2025 (Figure 1c).

Among the most productive authors, W. Xu and J. Zhang sustained continuous activity from 2019 to 2025, while J. Pang and M.H. Ryan published consistently from 2017 onward (Figure 1d). More recent contributors included A. Carminati (2023–2026) and I.C. Dodd (2021–2025), reflecting the field’s continued expansion.

3.2. Core Knowledge Sources and Leading Authors

Plant and Soil clearly dominated the field with 27 articles, followed by New Phytologist (7) and Journal of Experimental Botany (6). The second tier, Annals of Botany, Frontiers in Plant Science, Plant, Cell & Environment, Rhizosphere, and Scientific Reports, each contributed five articles (Figure 2a). Bradford’s Law analysis identified Plant and Soil, New Phytologist, Journal of Experimental Botany, and Annals of Botany as the core zone (Zone 1), beyond which the number of articles per journal progressively decreased (Figure 2b).

H. Lambers and W. Xu were the most productive authors, each contributing 15 publications (fractionalized 1.74 and 1.77, respectively), followed by J. Zhang (14; 1.34), J. Pang (12, 1.36), and M.H. Ryan (10; 1.28) (Table 2). I.C. Dodd showed the highest fractional contribution among mid-productivity authors (1.33 from 7 publications), indicating leading authorship roles.

3.3. Global Scientific Production and Collaboration

China led the field with 48 corresponding-author articles (35.29%; 30 SCP and 18 MCP), followed by Australia (23; 14 SCP and 9 MCP), the United Kingdom (11; 5 SCP and 6 MCP), and Germany (10; all MCP) (Figure 3a; Table 2). African and Latin American contributions were present but limited, with Ghana, Senegal, Brazil, and Nigeria each producing 1–3 articles, predominantly via international collaborations.

Citation impact, however, did not track productivity. Pakistan recorded the highest average citations per article (110.3), followed by Saudi Arabia (72.8) and the United Kingdom (57.4). Despite its leading output, China averaged 25.7 citations per article (Table 2). This pattern suggests that a small number of widely cited international collaborations have shaped the field’s intellectual core.

The collaboration network was centered on Europe, with Germany and Switzerland acting as hubs (Figure 3b). Germany’s strongest bilateral links were with Switzerland (8 collaborations), the Netherlands (5), and the United Kingdom and USA (3 each). The United Kingdom anchored cross-regional links to India, Pakistan, Japan, Kenya, Tunisia, and Saudi Arabia, whereas collaborations involving Africa, the Middle East, and Latin America remained sparser.

3.4. Intellectual Structure: Document Coupling

Document coupling resolved the literature into nine clusters (Table 3). The largest, Cluster 8 (n = 51; 1,358 citations), captured soil–root interface processes, aggregation dynamics, and ecosystem-level functioning, anchored by Pang et al. (2017), Brown et al. (2017), Marin et al. (2021), and Delhaize et al. (2015). Cluster 5 (n = 18, 895 citations) grouped studies on plant–microbe interactions and the functional rhizosphere (Naseem et al. 2018; Koebérnick et al. 2017).

Mechanistic dimensions of rhizosheath formation were distributed across three clusters: Cluster 1 (n = 6; 652 citations) focused on root trait regulation and rhizosheath formation (Wen et al. 2019, 2020; Pang et al. 2018); Cluster 4 (n = 8; 200 citations) addressed rhizosphere processes and root–soil interactions; and Cluster 2 (n = 2; 108 citations) covered rhizosphere microbiome interactions. The remaining clusters captured emerging or applied domains, including crop physiology and yield (Cluster 6), functional genomics (Cluster 7), soil management (Cluster 3), and agronomic applications (Cluster 9).

3.5. Global Collaboration: A Converging Network of Rhizosheath Science

High-frequency terms in rhizosheath research clustered around three conceptual domains (Figure 4a). Core terms, rhizosheath (60), soil (52), rhizosphere (49), and growth (46), dominated the dataset and occupied the largest treemap blocks. The second tier reflected crop and trait dimensions (wheat 22; tolerance 20; plant, root hairs, and traits each 19; phosphorus acquisition 18), while stress, nutrient, and microbial terms (water stress 16; responses 15; root 15; root hair length 14; phosphorus 13; drought 13; bacteria 12) formed a third tier. Lower-frequency terms (≤9) included mucilage, exudation, carboxylates, microbiome, microbial community, and soil aggregation, indicating finer-grained subtopics.

The keyword co-occurrence network resolved three clusters with distinct centrality patterns (Figure 4b). Cluster 1, the largest and most central, was dominated by rhizosheath (betweenness = 261.55; PageRank = 0.0903), tightly linked to soil (150.98; 0.0738) and rhizosphere (147.22; 0.0702), and included microbial and process-oriented terms (mucilage, exudation, microbiome, and arbuscular mycorrhizal fungi). Cluster 2 was centered on growth (115.72; 0.0687) and connected crop- and trait-related terms (wheat, tolerance, root hairs, phosphorus acquisition, and efficiency). Cluster 3 grouped stress- and morphology-related terms (water stress, root hair length, morphology, and rhizosheath formation), with water stress (betweenness = 10.63) and root hair length (PageRank = 0.0254) showing the highest connectivity within the cluster.

3.6. Intellectual Structure of Literature

Temporal analysis of the trend topics revealed a clear evolution in research priorities (Table 4). Early keywords (2016–2018) focused on phosphorus uptake, root hairs, and rhizosphere carboxylates. From 2019 onward, tolerance, acquisition, and soil gained prominence, while core terms (rhizosheath, rhizosphere, and soil) reached their median occurrence around 2022 and remained active through 2024. The most recent keywords concentrated on stress and water-related processes, responses (median 2023), drought (2023), mucilage (2023), water (2024), and stress (2024), signaling a shift toward the functional and hydraulic dimensions of rhizosheath research.

The thematic map organized the literature into seven keyword clusters spanning four quadrants (Figure 5; Table 4). The basic-theme quadrant was dominated by soil (centrality = 30.08; 381 keyword occurrences) and rhizosheath (20.68; 332), both of which anchored the conceptual core of the field. The motor-theme quadrant was led by water stress (centrality = 21.98; density = 89.85; 250 occurrences), confirming drought- and hydraulic-related processes as key drivers of recent research. Niche themes with high density but low centrality included root (density = 116.00), drought tolerance (100.92), and strategies (96.70), reflecting specialized but well-developed subdomains. Traits (centrality = 10.44; density = 90.94) occupied an intermediate position between the basic and motor themes. At the keyword level, the strongest network hubs were growth (betweenness = 1,353.90), responses (1,190.84), rhizosheath (1,187.44), rhizosphere (1,121.36), and soil (980.72).

4. Thematic Architecture and Way Ahead: A Synthesis of Rhizosheath Research

4.1. Conceptual Backbone: A Connected Rhizosheath–Soil–Rhizosphere System

The bibliometric synthesis of 136 publications and 6,366 citations (Table 1) revealed a highly interconnected research field anchored by a clear conceptual backbone. The dominance of rhizosheath, soil, rhizosphere, and growth in the treemap (Figure 4a) and their central positions in the keyword co-occurrence network (Figure 4b; rhizosheath betweenness = 261.55; soil = 150.98; rhizosphere = 147.22) demonstrate that the field now operates around a tightly coupled rhizosheath–soil–rhizosphere continuum rather than treating these elements as separate entities.

This interpretation was supported by document coupling: the two largest clusters, soil–root interface processes (Cluster 8; n = 51; 1,358 citations) and plant–microbe interactions (Cluster 5; n = 18; 895 citations), together represented more than half of the analyzed publications. Their prominence demonstrates that soil physical processes and biological interactions constitute the principal knowledge domains linking the literature.

Foundational contributions identified by these clusters [5,20,50] reframed the rhizosheath as a root-driven soil-engineering system rather than a passive adherent layer. Subsequent work confirmed that this interface emerges from the coordinated action of root hairs, mucilage, exudates, soil texture, moisture regime, and microbial communities [4,46,55,56]. However, recent evidence cautions that rhizosheath mass alone does not always capture broader rhizosphere structure or function across intact and disturbed soils [57]. Therefore, the conceptual backbone identified here should be interpreted as dynamic and environmentally contingent.

4.2. Functional Modules: Stress Adaptation, Resource Acquisition, and Microbial Interfaces

Building on this conceptual backbone, three interrelated functional modules emerged from bibliometric and thematic analyses.

First, stress adaptation was represented by the motor-theme position of the water stress cluster and the recent occurrence of responses, drought, water, and stress (centrality = 21.98; density = 89.85; Figure 5; Table 4), and was reinforced by the temporal rise of responses (median 2023), drought (2023), water (2024), and stress (2024) in trend topics (Table 4). Across cereals and legumes, water deficit promotes rhizosheath development through coordinated ABA–auxin regulation of root hair growth, mucilage production, and exudation [1,41,58,59,60], positioning the rhizosheath as a dynamic adaptive interface rather than a static structural response [55].

Second, root traits and resource acquisition formed a second module anchored in document coupling Cluster 1 (root trait regulation and rhizosheath formation; 652 citations; Table 3) and represented in the keyword network by phosphorus acquisition (PageRank = 0.067), root hairs, and efficiency (Figure 4b). Root hair architecture and carboxylate exudation jointly drive rhizosheath development and phosphorus mobilization, often enhanced by microbial activity [5,35,52,61]. The persistence of carboxylates as a trending topic from 2018 to 2023 (Table 4) reflects the durability of this research line.

Third, biochemical and microbial interfaces constitute a third module, captured by document coupling Cluster 2 (rhizosphere microbiome interactions; Table 3) and the recent emergence of mucilage (median 2023) as a trending topic. Polysaccharide-rich mucilage and exudates simultaneously structure the rhizosheath and selectively recruit microbial communities, including AMF and rhizobacteria, whose extracellular polymeric substances further stabilize aggregates and mobilize nutrients [10,23,46,62]. These reciprocal interactions identify the rhizosheath as a biologically active interface, rather than demonstrating that every rhizosheath necessarily functions as an equivalent microbial hotspot.

4.3. Integration Towards a System-Level Perspective

Although historically partitioned across root genetics, microbiome ecology, and soil physics, this field is converging toward an integrated, multi-scale perspective. This convergence is visible in the network structure (Figure 4b), where all three keyword clusters, rhizosheath/soil/microbiome, growth/traits/crop, and water stress/morphology, are linked through high-betweenness hub terms (growth = 1,353.90; responses = 1,190.84; rhizosheath = 1,187.44; Section 3.6). The thematic map (Figure 5) further illustrates that no single domain functions in isolation; traits occupy an intermediate position between basic (soil and rhizosheath) and motor (water stress) themes, indicating that crop trait research is actively bridging structural and stress adaptation perspectives.

At the process level, root-derived compounds alter microbial assembly and soil aggregation, and microbial products further influence aggregate stability and nutrient turnover, and the resulting root–soil structure affects water and nutrient transport [12,14,22]. Imaging and modeling approaches are beginning to connect these microscale interactions with whole-root hydraulics and plant performance [63,64]. Nevertheless, robust system-level predictions will require the explicit separation of rhizosheath structure, physiological function, and agronomic value.

4.4. Way Forward: Four Strategic Directions

The intellectual and thematic structures of the dataset identified four priorities.

4.4.1. From Structural Description to Mechanistic Understanding

The rhizosheath mass remains the most widely used descriptor; however, it does not distinguish among the contributions of root hairs, mucilage, rhizodeposition, microorganisms, and soil properties. The recent prominence of mucilage and the high density of root clusters indicate growing mechanistic interest. Future research should quantify the relative and interactive contributions of root hair genetics, mucilage properties, exudate composition, microbial activity, and soil structure [15,65,66].

4.4.2. From Isolated Traits to Integrated Root–Soil–Microbiome Systems

The strong connectivity among rhizosheath, soil, and rhizosphere themes supports an integrated framework in which structural and biological components act through coupled feedback [14,18,63]. Cross-scale imaging, chemical characterization, microbial profiling, and mechanistic modeling are required to establish how local processes influence whole-root water and nutrient acquisition.

4.4.3. From Controlled Experiments to Field Validation

Geographical and collaboration analyses revealed that research activity was concentrated in a limited number of countries and institutional networks. This concentration may restrict the range of soils, climates, crops, and management systems reported in the literature. Therefore, multi-location experiments and standardized field phenotyping are needed to quantify genotype × soil × microbiome interactions and test whether the responses observed under controlled conditions remain consistent in agricultural environments [67,68,69].

4.4.4. From Biological Understanding to Breeding and Agronomic Application

The relatively small document-coupling clusters associated with functional genomics and agronomic applications indicate an emerging but not yet mature translational frontier. Genetic variation in rhizosheath mass, root hairs, and associated traits provides opportunities for breeding under drought and phosphorus limitations [13,26,65,70]. However, the rhizosheath mass should be treated as a structural proxy, and its relationship with water uptake, nutrient acquisition, and yield must be validated rather than assumed.

Combining rhizosheath measurements with root hair traits, physiological indicators, microbial profiles, and soil properties may improve selection accuracy. Multi-environment validation is essential because soil texture, moisture, and management can modify both trait expression and its relationship with crop performance [56,71]. Integrating genetic selection with microbiome and soil management interventions could ultimately support the development of crop ideotypes adapted to defined target environments [1,68].

5. Conclusions

This bibliometric and thematic synthesis mapped the development of 136 publications and 6,366 citations. The analyses identified the rhizosheath–soil–rhizosphere interface as the field’s principal conceptual foundation, with water stress as a prominent and internally developed research theme. Temporal and network patterns further indicated increasing attention to drought responses, water relations, mucilage, and microbial interactions. The literature was structured around three interrelated themes: stress adaptation, root-mediated resource acquisition, and biochemical–microbial interactions.

Despite this progress, the synthesis revealed a persistent gap between structural measurements and functional interpretation. Although rhizosheath mass remains a dominant structural phenotype, it does not directly quantify water uptake, nutrient acquisition, microbial activity, stress tolerance, or crop productivity. It is considered a consistent indicator of physiological and agronomic performance. Genotype, root system size, soil properties, moisture regime, microbiome composition, plant developmental stage, and sampling procedures influence its expression and functional significance. Consequently, a larger rhizosheath should not be automatically interpreted as evidence of improved physiological performance or greater breeding value. Establishing these relationships will require standardized measurements that integrate rhizosheath structure with physiological, hydraulic, nutritional, microbial, and agronomic parameters.

These findings should be interpreted within the scope of this study. The analysis was restricted to English-language records indexed in the Web of Science Core Collection and retrieved using a focused keyword strategy; therefore, relevant studies employing alternative terminology may have been omitted. Citation indicators are database- and time-dependent, and the 2026 records represent only a partial publication year.

Despite these limitations, this study provides a reproducible map of the field and identifies priorities for further development. Multi-environment field experiments, standardized phenotyping, and the integration of genetics, plant physiology, soil physics, microbial ecology, and crop management are required to determine when and under which environmental conditions rhizosheath-related traits can reliably contribute to drought resilience, nutrient-use efficiency, and crop improvement.