Variation of the Linkage of Root Function with Root Branch Order

Mounting evidence has shown strong linkage of root function with root branch order. However, it is not known whether this linkage is consistent in different species. Here, root anatomic traits of the first five branch order were examined in five species differing in plant phylogeny and growth form in tropical and subtropical forests of south China. In Paramichelia baillonii, one tree species in Magnoliaceae, the intact cortex as well as mycorrhizal colonization existed even in the fifth-order root suggesting the preservation of absorption function in the higher-order roots. In contrast, dramatic decreases of cortex thickness and mycorrhizal colonization were observed from lower- to higher-order roots in three other tree species, Cunninghamia lanceolata, Acacia auriculiformis and Gordonia axillaries, which indicate the loss of absorption function. In a fern, Dicranopteris dichotoma, there were several cortex layers with prominently thickened cell wall and no mycorrhizal colonization in the third- and fourth-order roots, also demonstrating the loss of absorptive function in higher-order roots. Cluster analysis using these anatomic traits showed a different classification of root branch order in P. baillonii from other four species. As for the conduit diameter-density relationship in higher-order roots, the mechanism underpinning this relationship in P. baillonii was different from that in other species. In lower-order roots, different patterns of coefficient of variance for conduit diameter and density provided further evidence for the two types of linkage of root function with root branch order. These linkages corresponding to two types of ephemeral root modules have important implication in the prediction of terrestrial carbon cycling, although we caution that this study was pseudo-replicated. Future studies by sampling more species can test the generality of these two types of linkage.     

海南岛4个热带阔叶树种前5级细根的形态、解剖结构和组织碳氮含量

细根具有复杂的分支系统, 以根序(root order)为取样单元的细根生理生态学研究正在成为根系生态学研究领域的重要内容。该研究以海南岛尖峰岭4个热带阔叶树种海南蕈树(Altingia obovata)、厚壳桂(Cryptocarya chinensis)、山杜英(Elaeocarpus sylvestris)和黄桐(Endospermum chinense)为研究对象, 测定了1-5级细根的形态、解剖结构和组织碳(C)、氮(N)含量, 旨在探讨这些根系特征之间的联系。研究表明: 4个树种的细根形态差异较大, 但在树种水平上直径、根长和组织密度均随着根序的升高而增加, 比根长则随着根序的升高而降低; 低级根(前2级根或前3级根)具有皮层组织, 是典型的吸收根, 而高级根皮层组织消失, 是典型的运输和储藏根; 影响直径大小最重要的因子是皮层厚度, 它可以解释细根直径变异的97%, 而维管束直径仅能解释细根直径变异的70%; 根组织N和C浓度受维管束-根直径比(维根比)的影响, 随着维根比增加, 组织N浓度显著降低, 组织C浓度显著升高。4个树种细根的C/N比的变异受组织N浓度的影响程度为76%, 而受C浓度的影响程度不足10%。上述结果表明, 细根的形态特征、解剖结构和组织化学含量之间存在着紧密联系, 这为我们理解根系结构与功能变异提供了重要依据。     

落叶松和水曲柳不同根序细根形态结构、组织氮浓度与根呼吸的关系

根系具有高度的形态和生理功能异质性, 在森林生态系统碳和养分循环中起重要作用。根系分枝的顺序构成根序,是根系最基本的构型特征, 根序代表根系不同的发育阶段。然而, 目前直接测定不同根序细根生理功能的研究很少。以落叶松(Larix gmelinii)和水曲柳(Fraxinus mandshurica)的细根为研究对象, 使用气相氧电极测定不同根序细根的呼吸速率, 探讨根系呼吸速率与其形态、结构和组织氮浓度的关系。结果表明: 落叶松和水曲柳细根的直径、根长和维管束直径均随着根序的增加(1–5级)而增加, 而比根长、组织氮浓度和呼吸速率随着根序的增加而降低, 各根序之间差异显著(P < 0.05); 1级根比根长最大、皮层组织发达、组织氮浓度最高且呼吸速率也最高, 其呼吸速率分别为17.57 nmolO₂·g^–1·s^–1(落叶松)和18.80 nmolO₂·g^–1·s^–1(水曲柳), 比5级根分别高148%(落叶松)和124%(水曲柳); 并且, 落叶松根的呼吸速率几乎有96%与根系组织氮浓度相关, 而水曲柳根的呼吸速率则有89%与根系组织氮浓度相关。上述结果说明, 细根的形态和生理功能异质性是紧密相连的, 低级根的形态、结构决定其功能是吸收养分和水, 而高级根的形态、结构决定其功能是运输和贮存养分。     

Relationship between mycorrhizal fungi and functional traits in absorption roots: research progress and synthesis

吸收根(absorption root)一般是指根枝系统末端少数几级具有初生结构、负责物质吸收的根。吸收根功能性状被广泛用于评价和预测植物个体到生态系统水平上的一系列功能和过程。菌根真菌侵染是吸收根的一个关键性状, 它可以深刻影响吸收根的形态、结构, 以及功能性状之间的关系。该文针对与吸收功能密切相关的菌根真菌与根毛和根直径之间的关系进行了研究综述, 提出了真菌侵染、根毛和化学防御之间关系的一个假说; 探讨了温带和热带不同类型的吸收根如何通过菌根真菌影响根的功能性状, 从而适应不同的水热条件、养分状况和能量消耗; 提出一些需要关注的议题和研究方向, 以期为菌根真菌与吸收根功能性状之间关系的研究提供借鉴。     

华北山地6个外生菌根树种的根属性及其与菌根侵染率的关系

该研究以共存于同一暖温带森林的6个外生菌根(ECM)树种为研究对象,测定分析不同根序(1～5级)和功能根系(吸收细根和运输细根)的主要形态和构型属性及ECM侵染率,探究不同外生菌根树种的根属性变异模式及其与菌根真菌侵染程度的关系。结果表明:(1)随着根序的增加,不同树种根直径和单根长度均增加,而比根长和根分支强度均降低;根属性在同一根序下均存在显著的种间差异,尤其是2个裸子植物(落叶松和油松)的根直径较其他4个被子植物大。(2)同一树种的所有根属性在吸收细根和运输细根之间均有显著差异;吸收细根和运输细根的根直径、比根长和根组织密度在树种间均存在显著差异,而其单根长度和根分支强度在树种间无显著差异。(3)ECM侵染率以落叶松最高,千金榆和白桦最低,且与根尖直径呈显著正相关关系,与根尖比根长呈显著负相关关系。研究发现,基于根序或者功能根系,根属性在种间的变异模式不完全一致,单根长度和根分支强度在两个功能根系中均没有表现出显著的种间差异;吸收细根的比根长和根分支强度的变异系数较大,对环境变化有较敏感的响应;古老树种的根直径相对较粗,对菌根真菌的依赖性更高。     

亚热带典型树种根毛特征及其与共生真菌的关系

根毛和共生真菌增加了吸收面积,提高了植物获取磷等土壤资源的能力。由于野外原位观测根表微观结构较为困难,吸收细根、根毛、共生真菌如何相互作用并适应土壤资源供应,缺乏相应的数据和理论。该研究以受磷限制的亚热带森林为对象,选取了21种典型树种,定量了根毛存在情况、属性变异,分析了根毛形态特征与共生真菌侵染率、吸收细根功能属性之间的关系,探讨了根表结构对低磷土壤的响应和适应格局。结果表明:1)在亚热带森林根毛不是普遍存在的, 21个树种中仅发现7个树种存有根毛, 4个为丛枝菌根(AM)树种, 3个为外生菌根(ECM)树种。其中,马尾松(Pinus massoniana)根毛出现率最高,为86%;2)菌根类型是理解根-根毛-共生真菌关系的关键,AM树种根毛密度与共生真菌侵染率正相关,但ECM树种根毛直径与共生真菌侵染率负相关; 3) AM树种根毛长度和根毛直径、ECM树种根毛出现率与土壤有效磷含量呈负相关关系。该研究揭示了不同菌根类型树种根毛-共生真菌-根属性的格局及相互作用,为精细理解养分获取策略奠定了基础。     

树木不同着生位置1级根的形态、解剖结构和氮含量

树木根系中1级根在养分和水分吸收方面发挥着重要作用。研究1级根的形态结构与功能的联系,对了解1级根的生理功能和寿命,以及森林生态系统碳和养分的循环具有重要的理论意义。但是,1级根在根系统中,因着生的位置不同,可能表现出不同的生理生态功能。该研究以胡桃楸(Juglans mandshurica)、黄波罗(Phellodendron amurense)和水曲柳(Fraxinus mandshurica)人工林根系的1级根为研究对象,研究了不同着生位置的1级根的形态、解剖结构和组织化学特征。将1级根按着生位置的不同分成3类:Ar类根为2级根上的1级根;Br类根为2级–4级根的根尖;Cr类根为3级–5级根上的1级根。结果表明:不同着生位置的1级根,形态、解剖结构和组织化学方面都具有高度的异质性。3类1级根中,Ar类根数量多、根长较短、直径细,N含量高,皮层比例高、维根比低,主要由二原型原生木质部的根组成;Br类和Cr类根数量较少、单根较长、直径粗,N含量低,皮层比例低、维根比高,主要由多原型原生木质部的根组成。研究结果对了解不同着生位置的1级根的吸收功能和寿命具有重要的理论意义。     

常绿阔叶林外生和丛枝菌根树种细根形态和构型性状对氮添加的可塑性响应

以中亚热带常绿阔叶林外生菌根树种罗浮栲和丛枝菌根树种木荷为研究对象,采用根袋法进行野外原位氮添加试验,研究了细根形态性状(比根长、比表面积、组织密度、平均根直径)和构型性状(分枝数、分枝比、根长增长速率、根尖密度、分枝密度),分析不同菌根树种细根形态和构型性状对氮沉降的响应.结果表明:随序级增加,外生和丛枝菌根树种细根...     

Root anatomy, morphology, and longevity among root orders in Vaccinium corymbosum (Ericaceae)

Understanding root processes at the whole-plant or ecosystem scales requires an accounting of the range of functions within a root system. Studying root traits based on their branching order can be a powerful approach to understanding this complex system. The current study examined the highly branched root system of the ericoid plant, Vaccinium corymbosum L. (highbush blueberry) by classifying its root orders with a modified version of the morphometric approach similar to that used in hydrology for stream classification. Root anatomy provided valuable insight into variation in root function across orders. The more permanent portion of the root system occurred in 4th- and higher-order roots. Roots in these orders had radial growth; the lowest specific root length, N:C ratios, and mycorrhizal colonization; the highest tissue density and vessel number; and the coarsest root diameter. The ephemeral portion of the root system was mainly in the first three root orders. First- and 2nd-order roots were nearly anatomically identical, with similar mycorrhizal colonization and diameter, and also, despite being extremely fine, median lifespans were not very short (115-120 d; estimated with minirhizotrons). Our research underscores the value of examining root traits by root order and its implications to understanding belowground processes.     

Predicting fine root lifespan from plant functional traits in temperate trees

? Although linkages of leaf and whole-plant traits to leaf lifespan have been rigorously investigated, there is a limited understanding of similar linkages of whole-plant and fine root traits to root lifespan. In comparisons across species, do suites of traits found in leaves also exist for roots, and can these traits be used to predict root lifespan? ? We observed the fine root lifespan of 12 temperate tree species using minirhizotrons in a common garden and compared their median lifespans with fine-root and whole-plant traits. We then determined which set of combined traits would be most useful in predicting patterns of root lifespan. ? Median root lifespan ranged widely among species (95-336?d). Root diameter, calcium content, and tree wood density were positively related to root lifespan, whereas specific root length, nitrogen (N)?:?carbon (C) ratio, and plant growth rate were negatively related to root lifespan. Root diameter and plant growth rate, together (R(2) =?0.62) or in combination with root N?:?C ratio (R(2) =?0.76), were useful predictors of root lifespan across the 12 species. ? Our results highlight linkages between fine root lifespan in temperate trees and plant functional traits that may reduce uncertainty in predictions of root lifespan or turnover across species at broader spatial scales.     

Anatomical patterns of condensed tannin in fine roots of tree species from a cool-temperate forest

Background and AimsCondensed tannin (CT) is an important compound in plant biological structural defence and for tolerance of herbivory and environmental stress. However, little is known of the role and location of CT within the fine roots of woody plants. To understand the role of CT in fine roots across diverse species of woody dicot, we evaluated the localization of CT that accumulated in root tissue, and examined its relationships with the stele and cortex tissue in cross-sections of roots in 20 tree species forming different microbial symbiotic groups (ectomycorrhiza and arbuscular mycorrhiza).MethodsIn a cool-temperate forest in Japan, cross-sections of sampled roots in different branching order classes, namely, first order, second to third order, fourth order, and higher than fourth order (higher order), were measured in terms of the length-based ratios of stele diameter and cortex thickness to root diameter. All root samples were then stained with ρ-dimethylaminocinnamaldehyde solution and we determined the ratio of localized CT accumulation area to the root cross-section area (CT ratio).Key ResultsStele ratio tended to increase with increasing root order, whereas cortex ratio either remained unchanged or decreased with increasing order in all species. The CT ratio was significantly positively correlated to the stele ratio and negatively correlated to the cortex ratio in second- to fourth-order roots across species during the shift from primary to secondary root growth. Ectomycorrhiza-associated species mostly had a higher stele ratio and lower cortex ratio than arbuscular mycorrhiza-associated species across root orders. Compared with arbuscular mycorrhiza species, there was greater accumulation of CT in response to changes in the root order of ectomycorrhiza species.ConclusionsDifferent development patterns of the stele, cortex and CT accumulation along the transition from root tip to secondary roots could be distinguished between different mycorrhizal associations. The CT in tissues in different mycorrhizal associations could help with root protection in specific branching orders during shifts in stele and cortex development before and during cork layer formation.     

中国温带、亚热带和热带森林45个常见树种细根直径变异

 细根在发挥植物功能以及生态系统碳和养分循环过程中起着重要作用。为了解我国不同森林生态系统细根直径变化规律, 提供建立根系模型的基础, 该文研究了我国温带、亚热带和热带45个常见树种1～5级根直径的变异以及直径与根序的关系。结果表明: 1)在所有树种中, 1级根直径最细, 5级根直径最粗, 直径随根序的增加而增加。此外, 同一根序的直径在不同树种间变异较大, 在不同生态系统中, 各树种1级根的总体平均直径呈现温带<亚热带<热带的格局。2)不同生态系统树种同一根序平均直径变异程度不同, 各个根序都是温带最小, 亚热带次之, 热带最大。3)细根内部各个根序的平均直径变异的52%由根序解释, 33%由树种解释, 生态系统类型和生活型分别解释7%和2%。不同系统不同树种直径的变异说明无法用统一的直径级来研究根的功能, 也无法用统一的根序和直径间的关系来建立根系形态模型。今后的研究需要进一步认识根序和直径在不同树种中如何与根的功能相联系。     

Fine-root trait plasticity of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>) and spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) forests on two contrasting soils

Aim

The fine roots of trees may show plastic responses to their resource environment. Several, contrasting hypotheses exist on this plasticity, but empirical evidence for these hypotheses is scattered. This study aims to enhance our understanding of tree root plasticity by examining intra-specific variation in fine-root mass and morphology, fine-root growth and decomposition, and associated mycorrhizal interactions in beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.) forests on soils that differ in resource availability.

Methods

We measured the mass and morphological traits of fine roots (i.e. ≤ 2 mm diameter) sampled to 50 cm depth. Fine-root growth was measured with ingrowth cores, and fine-root decomposition with litter bags. Mycorrhizal fungal biomass was determined using ingrowth mesh bags.

Results

Both tree species showed more than three times higher fine-root mass, and a ten-fold higher fine-root growth rate on sand than on clay, but no or marginal differences in overall fine-root morphology. Within the fine-root category however, beech stands had relatively more root length of their finest roots on clay than on sand. In the spruce stands, ectomycorrhizal mycelium biomass was larger on sand than on clay.

Conclusions

In temperate beech and spruce forests, fine-root mass and mycorrhizal fungal biomass, rather than fine-root morphology, are changed to ensure uptake under different soil resource conditions. Yet enhancing our mechanistic understanding of fine-root trait plasticity and how it affects tree growth requires more attention to fine-root dynamics, the functional diversity within the fine-roots, and mycorrhizal symbiosis as an important belowground uptake strategy.

     

Embracing fine-root system complexity in terrestrial ecosystem modeling

Projecting the dynamics and functioning of the biosphere requires a holistic consideration of whole-ecosystem processes. However, biases toward leaf, canopy, and soil modeling since the 1970s have constantly left fine-root systems being rudimentarily treated. As accelerated empirical advances in the last two decades establish clearly functional differentiation conferred by the hierarchical structure of fine-root orders and associations with mycorrhizal fungi, a need emerges to embrace this complexity to bridge the data-model gap in still extremely uncertain models. Here, we propose a three-pool structure comprising transport and absorptive fine roots with mycorrhizal fungi (TAM) to model vertically resolved fine-root systems across organizational and spatial–temporal scales. Emerging from a conceptual shift away from arbitrary homogenization, TAM builds upon theoretical and empirical foundations as an effective and efficient approximation that balances realism and simplicity. A proof-of-concept demonstration of TAM in a big-leaf model both conservatively and radically shows robust impacts of differentiation within fine-root systems on simulating carbon cycling in temperate forests. Theoretical and quantitative support warrants exploiting its rich potentials across ecosystems and models to confront uncertainties and challenges for a predictive understanding of the biosphere. Echoing a broad trend of embracing ecological complexity in integrative ecosystem modeling, TAM may offer a consistent framework where modelers and empiricists can work together toward this grand goal.     

黄河三角洲滨海盐碱地11个造林树种细根解剖性状对土壤条件的响应

细根作为植物与土壤连接的重要部位,能够反映植物对生存环境的适应性。以黄河三角洲滨海盐碱地不同立地条件下11个造林树种为对象,基于细根分支等级划分1-4级根序并进行解剖特征测定,分析细根解剖性状对滨海盐碱地不同土壤条件的响应规律。结果表明：（1）不同根序的细根直径存在显著差异,细根直径随根序升高呈增大趋势,而同根序的细根直径在不同树种间表现出显著的种间差异（P < 0.05）。1-2级细根皮层厚度、3-4级细根导管密度在树种间的差异均达显著水平（P < 0.05）。（2）在较为严重盐渍化土壤条件下（立地1）,细根皮层厚度较其他立地显著增大,但细根导管密度较小;在轻度盐碱立地条件下（立地3）,细根导管密度较大;较为严重的盐碱立地具有更为发达的细根直径及维管柱直径。（3）树种1-2级细根解剖结构与土壤环境关系最为密切,其中1级根直径与土壤pH值显著正相关（P < 0.05）,与土壤硝态氮含量呈显著负相关（P < 0.05）。对土壤理化性质与细根解剖性状的冗余分析表明,前两个轴的特征值达0.640和0.196,土壤速效养分含量与轴一（RDA1）呈正相关,低级根解剖性状则与轴二（RDA2）呈显著负相关。低级根解剖结构以及土壤的pH值能解释较多树种的差异性,其中低级根直径与皮层厚度对盐碱环境表现出较强的响应。     

Nitrogen dynamics differed among the first six root branch orders of Fraxinus mandshurica and Larix gmelinii during short-term decomposition

Fine root (<2 mm) decomposition provides a substantial amount of available nitrogen (N) that sustains plant growth. The N release pattern during litter decomposition is generally controlled by initial N concentrations or C/N. Because root branch order and mycorrhizal colonization (related with branch order) are both highly related with different initial chemistry, a hypothesis was proposed that N dynamics during root decomposition varied among different branch orders. Using the litterbag method, decomposition of the first six order roots for Fraxinus mandshurica (an arbuscular mycorrhizal species) and Larix gmelinii (an ectomycorrhizal species) was studied in Northeast China during a 513-day period. Results showed a similar pattern for the two species with contrasting mycorrhizal type: lower-order roots (the lateral root tips), which had an initial C/N of 17–21, continuously released N without any immobilization and maintained a consistently low C/N (<20), whereas higher-order roots, which had an initial C/N of 28–48, periodically immobilized N, leading to a declining C/N over time. In addition, the magnitude of N dynamics is different between species for lower-order roots, but no different for higher-order roots. These results suggest that fine root N dynamics are heterogeneous among branch orders and that species-specific differences depend on the behavior of lower-order roots.     

Ephemeral root modules in Fraxinus mandshurica

Historically, ephemeral roots have been equated with 'fine roots' (i.e. all roots of less than an arbitrary diameter, such as 2 mm), but evidence shows that 'fine roots' in woody species are complex branching systems with both rapid-cycling and slow-cycling components. A precise definition of ephemeral roots is therefore needed. Using a branch-order classification, a rhizotron method and sequential sampling of a root cohort, we tested the hypothesis that ephemeral root modules exist within the branching Fraxinus mandshurica (Manchurian ash) root system as distal nonwoody lateral branches, which show anatomical, nutritional and physiological patterns distinct from their woody mother roots. Our results showed that in F. mandshurica, distal nonwoody root branch orders die rapidly as intact lateral branches (or modules). These nonwoody branch orders exhibited highly synchronous changes in tissue nitrogen concentrations and respiration, dominated root turnover, nutrient flux and root respiration, and never underwent secondary development. The ephemeral root modules proposed here may provide a functional basis for differentiating and sampling short-lived absorptive roots in woody plants, and represent a conceptual leap over the traditional coarse-fine root dichotomies based on arbitrary size classes.     

Can hypodermal passage cell distribution limit root penetration by mycorrhizal fungi?

* The basis for significant interspecific variability in colonization by arbuscular mycorrhizal fungi is poorly understood. Limited evidence suggests that, for species with a dimorphic hypodermis, colonization of the root cortex occurs only through hypodermal passage cells. Therefore, the hypothesis that interspecific variability in mycorrhizal colonization is accounted for by interspecific variation in passage cell distribution was tested. * The arbuscular mycorrhizal colonization and distribution of fungal penetration points and hypodermal passage cells in the root systems of eight species (seven plant families) possessing a dimorphic hypodermis were characterized. * Mycorrhizal fungal penetration of the hypodermis occurred exclusively through passage cells. Moreover, the proportion of root length with passage cells explained nearly 99% of the variability among the eight plant species in the proportion of root length with penetration points. * In dimorphic hypodermal species, passage cells appear to be key determinants of mycorrhizal colonization because they are the cells through which fungal penetration of the hypodermis occurs. Variation among such species in mycorrhizal colonization may be at least partly determined by variation in the proportion of root length with passage cells.     

Fine-root system development and susceptibility to pathogen colonization

Root development may exert control on plant–pathogen interactions with soil-borne pathogens by shaping the spatial and temporal availability of susceptible tissues and in turn the impact of pathogen colonization on root function. To evaluate the relationship between root development and resistance to apple replant disease (ARD) pathogens, pathogen abundance was compared across root branching orders in a bioassay with two rootstock genotypes, M.26 (highly susceptible) and CG.210 (less susceptible). Root growth, anatomical development and secondary metabolite production were evaluated as tissue resistance mechanisms. ARD pathogens primarily colonized first and second order roots, which corresponded with cortical tissue senescence and loss in second and third order roots. Defense compounds were differentially allocated across root branching orders, while defense induction or stress response was only detected in first order and pioneer roots. Our results suggest disease development is based largely on fine-root tip attrition. In accordance, the less susceptible rootstock supported lower ARD pathogen abundance and altered defense compound production in first order and pioneer roots and maintained higher rates of root growth in both the ARD soil and pasteurized control compared to the more susceptible. Thus, this rootstock’s ability to maintain shoot growth in replant soil may be attributable to relative replant pathogen resistance in distal root branches as well as tolerance of infection based on rates of root growth.     

Root cortical anatomy is associated with differential pathogenic and symbiotic fungal colonization in maize

Root anatomical phenotypes vary among maize (Zea mays) cultivars and may have adaptive value by modifying the metabolic cost of soil exploration. However, the microbial trade‐offs of these phenotypes are unknown. We hypothesized that nodal roots of maize with contrasting cortical anatomy have different patterns of mutualistic and pathogenic fungal colonization. Arbuscular mycorrhizal colonization in the field and mesocosms, root rots in the field, and Fusarium verticillioides colonization in mesocosms were evaluated in maize genotypes with contrasting root cortical anatomy. Increased aerenchyma and decreased living cortical area were associated with decreased mycorrhizal colonization in mesocosm and field experiments with inbred genotypes. In contrast, mycorrhizal colonization of hybrids increased with larger aerenchyma lacunae; this increase coincided with larger root diameters of hybrid roots. F. verticillioides colonization was inversely correlated with living cortical area in mesocosm‐grown inbreds, and no relation was found between root rots and living cortical area or aerenchyma in field‐grown hybrids. Root rots were positively correlated with cortical cell file number and inversely correlated with cortical cell size. Mycorrhizae and root rots were inversely correlated in field‐grown hybrids. We conclude that root anatomy is associated with differential effects on pathogens and mycorrhizal colonization of nodal roots in maize.