First-order Roots Research Articles

Elevational variation in anatomical traits of the first-order roots and their adaptation mechanisms

Root anatomical traits play an important role in understanding the link between root physiological function and ecological process. To determine how plants change root anatomical traits to adapt to distinct environments, we measured four key root anatomical traits---stele diameter (SD), cortex thickness (CT), root diameter (RD), and the stele to root diameter ratio (SDRD)---of first-order roots of 82 species were collected from different vegetation zones along a 2000 m altitudinal gradient on the northern slope of Taibai Mountain. Compared with other altitudes, plants located in temperate birch and fir forests had thinner SD, CT, RD, and SDRD. We found that elevational variation in root anatomical traits could largely be explained by phylogenetic taxonomy (clade). In addition, changes in SD were driven by soil bulk density, whereas variations in CT and RD were influenced by soil available nitrogen. When phylogenetic factors were removed from our analysis, allometric relationships between RD and root anatomical traits (SD and CT) were observed across different altitudes. Our study reveals the influence of phylogeny and environment on the elevational variation in root anatomical traits and further supports the allometric relationship between root anatomical traits (SD and CT) and RD. These findings enhance our understanding of the evolutionary and adaptive mechanisms of root anatomical structures, providing a basis for predicting how root anatomical traits respond to global changes.

Nutrient uptake strategy selection by first-order roots of Juglans mandshurica under shading and phosphorus limitation

We investigated root growth of 1-year-old Juglans mandshurica seedlings under different light environments and varying doses of phosphorus fertilizer, to understand the relationship between root resource acquisition strategies and the variations of light and phosphorus availability. There were four shading intensities (full light, 65% full light, 35% full light, and 20% full light) along with three doses of phosphate fertilizer (0 (CK), 200% soil background available phosphorus, and 500% soil background available phosphorus). We measured in root morphology characteristics, architectural characteristics, and mycorrhizal colonization rates of first-order roots. The results showed that average diameter, average root length, and mycorrhizal colonization rates of first-order roots gradually decreased, and the specific root length, specific surface area, branching ratio and branching intensity showed a trend of first increasing and then decreasing with the increases of shading degree. As the phosphorus content decreased, the first-order root diameter gradually became thinner, and the mycorrhizal infection rate gradually increased. Root morphology and architecture of J. mandshurica would undergo adaptive changes under shade, adapting to the shading environment by expanding specific root length, specific surface area, branching ratio and branching intensity. Under phosphorus limitation, root system of J. mandshurica would increase phosphorus absorption through symbiosis with mycorrhizal fungi. When J. mandshurica was artificially regenerate in forest land with a light transmittance of 35%, root morphology and architecture would adapt to the shading environment. The symbiosis between J. mandshurica and mycorrhizal fungi would be enhanced under phosphorus limitation, which could improve phosphorus absorption of roots.

Low-order fine roots of Picea asperata have different physiological mechanisms in response to seasonal freeze and freeze-thaw of soil.

Seasonal soil freezing (F) and freeze-thaw cycles (FTCs) are common natural phenomena in high latitude or altitude areas of the world, and seriously affect plant physiological processes. However, studies on the effect of soil F and FTCs on fine roots are less common, especially in subalpine coniferous forests of western Sichuan, China. We set up a controlled experiment in growth chambers to explore the effects of F and FTCs on low-order fine roots of Picea asperata and differential responses of first-order roots and the first three root orders (1st, 2nd and 3rd order roots combined as a unit). Soil F and FTCs resulted in serious damage to cell membranes and root vitality of low-order fine roots, accompanied by increased MDA content and O2 ·- production. FTCs had a stronger effect than F treatment. In turn, low-order fine roots are the unit that responds to cold stress. These roots had increased unsaturated fatty acid contents, antioxidant enzyme activities, osmolytes and plant hormones contents when acclimation to cold stress. The first-order roots were more sensitive to cold stress than the combined first three root orders for several processes (e.g. antioxidant enzymes, osmolytes and hormones) because of their specific structure and physiological activity. This study explains physiological differences in responses of fine roots of different root orders to seasonal soil freezing, which will improve the understanding of fine root heterogeneity and support agriculture and forest management.

The Age of Absorptive Roots Impacts Root-Adjacent Microbial Composition in Grapevines

In grapevine, metabolic activity of absorptive roots changes rapidly as roots age but it is unclear whether nearby microbial assemblages shift as well. Here, we investigated whether first-order root age affects bacterial and fungal variation adjacent to the root surface, and whether root age should be integrated into future studies on root functional traits and associated microbes. We hypothesized that microbial diversity and composition would differ between young (≤11 days old) and old (11.5 to 40 days old) first-order roots due to expected differences in metabolism over the root lifespan (i.e., higher metabolism in young roots). Overall, we found that microbial composition was distinct between young and old absorptive roots, with stronger evidence at the phylum and amplicon sequence variant (ASV) taxonomic levels for fungi ( P = 0.003 and P = 0.038, respectively) than bacteria ( P = 0.082 and P = 0.129, respectively). Furthermore, we identified differentially abundant fungal and bacterial ASVs in young and old roots that related to expected differences in root function, including instances of microbes previously described as copiotrophs more abundant adjacent to young roots and microbes described as oligotrophs and saprotrophs more abundant adjacent to old roots. In contrast to the distinct shifts in microbial composition, there was little evidence of shifts in α diversity (i.e., observed ASVs and Shannon diversity) between young and old roots. Our study suggests that future work on the impacts of root functional traits on localized microbial composition may improve results interpretation and reduce some variation by accounting for root age at sampling.

Shifting of the first-order root foraging strategies of Chinese fir (Cunninghamia lanceolata) under varied environmental conditions

Shifting of the first-order root foraging strategies of Chinese fir (Cunninghamia lanceolata) under varied environmental conditions

Корневая система тополя бальзамического (Populus balsamifera L.)

The research aims at studying the features of the balsam poplar root system in the conditions of Arkhangelsk. The relevance of the topic is determined by the poplar multifunctionality in urban conditions. The effectiveness of sanitation functions, phytoremediation, carbon sequestration, and sustainability of poplars is determined by their root system condition. Understanding the specifics of its structure will enable the selection and creation of conditions necessary for the successful growth of trees of this species. Studies of the root system structure, recording the number, diameter, and branching of roots of different orders were carried out on uprooted trees growing isolated as well as in groups. In public gardens, the length of poplar skeletal roots with their subsequent surface excavation was assessed using the Arbotom device with the Arboradix module. A strong foundation in the central part of the root system, formed of the overgrown core, buttress roots of the first order and fibrous roots, provides resistance of poplars to windthrow. The bending of first-order roots early in tree development creates a holding platform for the branch cuttings. The close group growth of poplars leads to “storeying” and deepening of the root system. Poplars growing in groups form a greater number of proximal roots with a smaller diameter compared to isolated growth. Thus, the average diameter of the base of the first-order roots in group growth is 11.5 cm; in single growth – 24.5 cm. The length of poplar skeletal roots in public gardens ranges from 2 to 9 m. Reducing the share of poplars in the plantation by 2.3 times together with a decrease in stand density by 2 times or track area by 2 times leads to an increase in the length of skeletal roots by 1.5–2 times and the formation of a more uniform root system. The results can be used in the design of urban green spaces. For citation: Tyukavina O.N., Popova L.F. Root System of Balsam Poplar (Populus balsamifera L.). Lesnoy Zhurnal = Russian Forestry Journal, 2022, no. 6, pp. 71–81. (In Russ.). https://doi.org/10.37482/0536-1036-2022-6-71-81

Влияние кверцетина на регенерацию микрорастений картофеля в условиях in vitro

Potato biotechnology in vitro has found wide application in the primary seed production of this crop - in the technologies of rehabilitation, micropropagation, depositing varietal collections in vitro, obtaining microtuber planting material. The article considers the effect of quercetin on the growth and development of potato micro plants under in vitro conditions. The objectives of the study included the morphological assessment of potato regenerants on nutrient media of various mineral compositions, as well as the study of the response of potato mericlons to the presence of quercetin in the nutrient medium. Potato varieties "Rivera" were used as objects. Murashige-Skoog (MS) Hamburg (½B5) culture media were chosen for the study. Quercetin (100 mg/l) was used as a growth stimulant. The use of a phenolic compound showed a different reaction of plants depending on the mineral composition of the nutrient medium. The presence of bioflavonoid in the MS nutrient medium contributed to a decrease in plant height, as well as the length of roots in experimental plants. Propagation of explants on nutrient medium B5 with the introduction of quercin made it possible to achieve a powerful root system. The number of first-order roots and their length increased relative to the control by 12 and 5%. The use of querticin led to a decrease in the height of the shoot due to the shortening of the internodes. Keywords: POTATOES, MICROCLONAL REPRODUCTION, BIOFLAVANOID, QUERCETIN

Fine root litter traits of Chamaecyparis obtusa

The purpose of this study was to clarify the process of Chamaecyparis obtusa (Sieb. & Zucc.) Endl. fine root shedding and the morphological traits of the resulting root litter. We developed a method for direct monthly sampling of root litter from the fine root system in the field. We proposed a field incubation method using centrifuge tubes with glass beads as the medium and throughfall as the nutrient solution, in which an undamaged sample of the fine root system still connected to the tree is inserted. Using this method, we collected root litter from C. obtusa for 12 months after the installation. The monthly amounts of the root litter of from the incubated fine root systems differed significantly among the sampling months. On the other hand, the morphological traits such as the root litter length and diameter of each branch order did not differ significantly among months. The first-order root litter was shorter than the incubated living first-order roots. The first-order roots were shed both at the branching positions and in the middle of first-order roots. We concluded that fine root litter with similar morphology is shed every month. Assessment of the fine root litter traits by using the new direct sampling method and the new soil ecological indicator “initial tissue C inputs” from fine roots into forest soil will improve our understanding of forest belowground carbon cycling and its indexation.

Temporal dynamics of fine root production, mortality and turnover deviate across branch orders in a larch stand.

Fine roots play a key role in carbon, nutrient, and water biogeochemical cycles in forest ecosystems. However, inter-annual dynamics of fine root production, mortality, and turnover on the basis of long-term measurement have been less studied. Here, field scanning rhizotrons were employed for tracking fine root by branch order over a 6years period in a larch plantation. For total fine roots, from the first- to the fifth-order roots, annual root length production, length mortality, standing crops, and turnover rate varied up to 3.4, 2.3, 1.5, and 2.3-folds during the study period, respectively. The inter-annual variability of those roots indices in the first-order and the second-order roots were greater than that of the higher order (third- to fifth-order) roots. The turnover rate was markedly larger for the first-order roots than for the higher order roots, showing the greatest variability up to 20times. Seasonal dynamics of root length production followed a general concentrated pattern with peak typically occurring in June or July, whereas root length mortality followed a general bimodal mortality pattern with the dominant peak in May and the secondary peak in August or October. Furthermore, the seasonal patterns of root length production and mortality were similar across years, especially for the first-order and the second-order roots. These results from long-term observation were beneficial for reducing uncertainty of characterizing fine root demography in consideration of large variation among years. Our findings highlight it is important for better understanding of fine root dynamics and determining root demography through distinguishing observation years and root branch orders.

Enriched CO2 and Root-Associated Fungi (Mycorrhizae) Yield Inverse Effects on Plant Mass and Root Morphology in Six Asclepias Species.

While milkweeds (Asclepias spp.) are important for sustaining biodiversity in marginal ecosystems, CO2 flux may afflict Asclepias species and cause detriment to native communities. Negative CO2-induced effects may be mitigated through mycorrhizal associations. In this study, we sought to determine how mycorrhizae interacts with CO2 to influence Asclepias biomass and root morphology. A broad range of Asclepias species (n = 6) were chosen for this study, including four tap-root species (A. sullivantii, A. syriaca, A. tuberosa, and A. viridis) and two fibrous root species (A. incarnata and A. verticillata). Collectively, the six Asclepias species were manipulated under a 2 × 2 full-factorial design that featured two mycorrhizal levels (−/+ mycorrhizae) and two CO2 levels (ambient and enriched (i.e., 3.5× ambient)). After a duration of 10 months, Asclepias responses were assessed as whole dry weight (i.e., biomass) and relative transportive root. Relative transportive root is the percent difference in the diameter of highest order root (transportive root) versus that of first-order absorptive roots. Results revealed an asymmetrical response, as mycorrhizae increased Asclepias biomass by ~12-fold, while enriched CO2 decreased biomass by about 25%. CO2 did not impact relative transportive roots, but mycorrhizae increased root organ’s response by more than 20%. Interactions with CO2 and mycorrhizae were observed for both biomass and root morphology (i.e., relative transportive root). A gene associated with CO2 fixation (rbcL) revealed that the two fibrous root species formed a phylogenetic clade that was distant from the four tap-root species. The effect of mycorrhizae was most profound in tap-root systems, as mycorrhizae modified the highest order root into tuber-like structures. A strong positive correlation was observed with biomass and relative transportive root. This study elucidates the interplay with roots, mycorrhizae, and CO2, while providing a potential pathway for mycorrhizae to ameliorate CO2 induced effects.

Relationship between root traits and arbuscular mycorrhizal fungi in three species of weeds with different synanthropy index


 Background: Nutrient foraging strategies between thin and thick roots, including mycorrhizal symbionts are resource-costly, and therefore a trade-off could exist. These strategies can vary with the synanthropy index (degree to which a species associates with anthropogenic habitats), thus maximizing the benefits for the acquisition of soil resources.
 Objectives: To quantify the arbuscular mycorrhizal colonization of Melampodium species with different synanthropy index, and to determine the correlations between arbuscular mycorrhizal colonization and the architectural and morphological root traits.
 Methods: Roots of Melampodium divaricatum, M. perfoliatum and M. tepicense, with highest to lowest synanthropy index, respectively were collected. The root branching rate (RBR), total root length (TRL), diameter of first-order root, (FOR), root tissue density (RTD), specific root length (SRL), and arbuscular mycorrhizal colonization were quantified. Additionally, soil chemistry analyses were done.
 Results and conclusion: Melampodium tepicense had lowest FOR, highest SRL and lowest arbuscular mycorrhizal colonization, whereas M. divaricatum and M. perfoliatum had the opposite values. Additionally, M. divaricatum and M. perfoliatum had higher TRL, RTD, and RBR, suggesting that both strategies, arbuscular mycorrhiza and fine roots, are used for acquisition of nutrients, independently of their phylogenetic relationship and soil nutrients.

Plastic responses of fine root morphology and architecture traits to nitrogen addition in ectomycorrhizal and arbuscular mycorrhizal tree species in an evergreen broadleaved forest.

We measured the morphology traits (specific root length, specific root surface area, root tissue density, average root diameter) and architecture traits (root fork, root fork ratio, increase rate of root length, root tip density, root fork density) of fine roots in two mycorrhiza tree species, Castanopsis faberi (ectomycorrhizal) and Schima superba (arbuscular mycorrhizal), in an evergreen broadleaved forest in the middle subtropical zone. Root bags method was used in an in situ nitrogen deposition experiment. The aim of this study was to reveal the differences in the plastic responses of fine root morphology and architecture traits to nitrogen deposition between the different mycorrhizal trees. The plastic responses of specific root length, specific root surface area and root fork to nitrogen addition decreased from the first-order root to the fourth-order root, while root tissue density showed an opposite pattern. Such a result indicated a trade-off between nutrient acquisition and resource maintenance of different fine root orders. Different mycorrhizal tree species adopted diffe-rent adaptation strategies to the variations of soil nitrogen availability. C. faberi adopted an opportuni-stic strategy, which relied on fine root to improve nutrient absorption efficiency, enhanced the capacity of space expansion and in-situ nutrient absorption to focus on rapid nutrient absorption strategy. S. superba did not change fine root morphological traits through the trade-off between nutrient absorption efficiency and root construction cost, but relied more on the complementarity between mycorrhizal fungi and fine root architecture traits for nutrient acquisition. The differences in the cost of maintaining and constructing fine root C between different mycorrhizal trees led to fine root adopting the most suitable nutrient capture strategy.

Mini-cutting of Plathymenia reticulata benth. with ministumps conducted in suspended seedbed and tubes

ABSTRACT Background: Despite the importance of Plathymenia reticulata for forestry and ecological purposes, a protocol for the vegetative propagation of the species remains unclear mainly due to the low adventitious rooting of the propagules of the species. In this sense, this work aimed to evaluate the rooting of mini-cuttings of juvenile materials of P. reticulata and our hypothesis: (1) maintaining propagules under mist chamber for different periods affects the rooting process; (2) the mini-stump management system due to the restriction of the root system affects the production of mini-cuttings and the quality of clonal seedlings. Results: It was not necessary for more than 30 days in a mist chamber to induce rooting. The highest percentage of rooting was obtained 50 days after staking. Mini-gardens set up in suspended seed bed and tubes (280 cm3) had the average mini-cuttings productivity of 4.32 and 2.06, respectively, over 270 days of exploration (monthly collections). At 120 days after staking, there was no difference in the survival and in the final quality of clonal seedlings produced. However, clonal seedlings from mini-garden in tubes had higher height, leaf area, and number of first-order roots. Regardless of the mini-garden management, the clonal seedling production index was 50%. Conclusion: We can conclude that P. reticulata seedling production via mini-cutting technique is possible.

The influence of treatment methods on agrophysical soil properties and old Eastern galega stand root development

All mechanical effects are primarily aimed at improving soil conditions and the root system. Different treatment methods with different types of working organs affect the fractional composition of particles, agrophysical soil properties, and the ability to restore the root system of old-age, degraded stands of perennial grasses with a root-shoot root system. The article presents data on the results of three field experiments (2017–2019). An analysis of the fractional composition of soil with various cultivation methods was carried out, and the relationship between the number of first-order roots of the eastern goat grass stand and agrophysical soil properties was identified. The maximum soil fraction was 7 and 10 mm when treating with a BDT aggregate in one track, the minimum percentage was observed when treating with a Leader aggregate in two tracks to a depth of 10–12 and 16–18 cm. The greatest “clumpiness” of fractions was revealed with a smaller number of treatments. The optimal soil conditions for the growth and development of the root system of old-age goat grass stands in the 0–20 cm layer were established during flat cutting. By the end of the growing season, the number of first-order roots increased from 15,000 to 22,000 thousand units/ha.

On characterizing root function in perennial horticultural crops.

While root-order approaches to fine-root classification have shown wide utility among wild plants, they have seen limited use for perennial crop plants. Moreover, inadequate characterization of fine roots across species of domesticated perennial crops has led to a knowledge gap in the understanding of evolutionary and functional patterns associated with different fine-root orders. We examined fine-root traits of common horticultural fruit and nut crops: Malus ×domestica, Prunus persica, Vitus vinifera, Prunus dulcis, and Citrus ×clementina. Additional roots were sampled from 33 common perennial horticultural crops, native to tropical, subtropical, and temperate regions, to examine variation in 1st- and 2nd-order absorptive roots. First-order roots of grape and 1st- and 2nd-order roots of apple and peach were consistently thin, nonwoody, mycorrhizal, and had high N:C ratios. In contrast, 4th- and 5th-order roots of grape and 5th-order roots of apple and peach were woody, nonmycorrhizal, had low N:C ratios, and were thicker than lower-order roots. Among the 33 horticultural species, diameter of 1st- and 2nd-order roots varied about 15-fold, ranging from 0.04 to 0.60 mm and 0.05 to 0.89 mm respectively. This variation generally was phylogenetically conserved across plant lineages. Collectively, our research shows that root-order characterization has considerably more utility than an arbitrary diameter cutoff for identifying roots of different functions in perennial horticultural crops. In addition, much of the variation in root diameter among species can be predicted by evolutionary relationships.

The role of different root orders in nutrient uptake

The root system is essential for plant water and nutrient uptake, however, the functions and roles of different root orders are unclear. We investigated the anatomical and physiological differences among different root orders. Tomato plants were grown in either polyethylene bags or a hydroponic system. Mineral uptake, protein profiles, respiration rates, and anatomical profiles of the different root orders were measured. First-order roots absorbed significantly more nutrients than the other root orders. The concentrations of elements surrounding the third-order roots remained constant throughout the experiment. Respiration rates were found to be higher in the first- and second-order roots than in the third-order roots. Analysis of anatomical cross-sections demonstrated different structures in the different root orders. Protein profile analysis presented differences in different root orders, these proteins included element transporters and those related to protein translocation in the cell. Moreover, specific proteins related to mineral absorption were found at higher levels in the first- and second-order roots than in the third-order roots. Our results demonstrate, that different root orders vary in their nutrient uptake and translocation and that distal root orders play a key role in the uptake and translocation of minerals.

Variation in the morphology of fine roots in Cryptomeria japonica determined by branch order-based classification

This study assessed intraspecific variation in morphological traits of the fine root branch orders of Cryptomeria japonica, and identified variation in the diameter of the first three-order roots among species types with mycorrhiza, and the diameter of first-order roots at the family level. Diameter, length, and specific root length of branch order roots (up to the fourth-order) were measured in intact fine root systems collected in four C. japonica stands. Relationships between soil chemical properties and morphological traits of the first- to fourth-order roots were investigated. The diameter of roots of 52 tree species reported in previous studies was compared at species types with mycorrhiza and at family level. The diameter of first-order roots in C. japonica varied by 1.2 times among stands. Negative correlations between soil NH4+ content and specific root length of the second- and third-order roots were observed in C. japonica. The diameter of first- and second-order roots forming arbuscular mycorrhiza in coniferous trees were significantly higher than those of roots forming ectomycorrhiza in coniferous and broadleaf trees. The diameter of first-order roots in Cupressaceae were significantly larger than those of Pinaceae, Sapindaceae, Betulaceae, and Fagaceae. Clarifying intraspecific variation in morphological traits of C. japonica lower-order roots may contribute to understanding their responses to different site conditions such as soil inorganic nitrogen contents.

Tradeoffs among root morphology, exudation and mycorrhizal symbioses for phosphorus-acquisition strategies of 16 crop species.

Plant roots exhibit diverse root functional traits to enable soil phosphorus (P) acquisition, including changes in root morphology, root exudation and mycorrhizal symbioses. Yet, whether these traits are differently coordinated among crop species to enhance P acquisition is unclear. Here, eight root functional traits for P acquisition were characterized in 16 major herbaceous crop species grown in a glasshouse under limiting and adequate soil P availability. We found substantial interspecific variation in root functional traits among species. Those with thinner roots showed more root branching and less first-order root length, and had consistently lower colonization by arbuscular mycorrhizal fungi (AMF), fewer rhizosheath carboxylates and reduced acid phosphatase activity. In response to limiting soil P, species with thinner roots showed a stronger response in root branching, first-order root length and specific root length of the whole root system, Conversely, species with thicker roots exhibited higher colonization by AMF and/or more P-mobilizing exudates in the rhizosheath. We conclude that, at the species level, tradeoffs occur among the three groups of root functional traits we examined. Root diameter is a good predictor of the relative expression of these traits and how they change when P is limiting.

Variation in the functional traits of fine roots is linked to phylogenetics in the common tree species of Chinese subtropical forests

The phylogenetic variations of fine root traits, which are related to plant growth and development as well as to physiological and ecological processes, are not fully understood. This study aimed to: (1) examine how tree species and sampling methodology affect the anatomical, morphological and nutrient traits of fine roots; and (2) determine whether phylogenetic signals affect fine root trait relationships and influence comparison of root traits between the branch order-based and diameter-based cut-off sampling categories. Fine root samples of 16 subtropical forest tree species were obtained and their anatomical, morphological and nutrient traits were studied. The phylogenetic signals of trait variations were calculated to determine trait relationships. Tree species and sampling methodology significantly affected fine root traits (p < 0.05). Mean root diameters, root tissue density (RTD) and carbon-to-nitrogen ratio were the lowest in the first-order category and highest in the ≤2 mm category. The reverse pattern was found for specific root length, specific root area and nitrogen concentration. Morphological traits showed significant phylogenetic signals; however, nutrient traits did not reflect phylogenetic conservatism. Phylogenetic factors influenced correlations between traits for the first-order root economics spectrum. Root traits were multidimensional and RTD was loaded on a novel phylogenetic principal component analysis. Functional traits of fine roots are multidimensional for subtropical tree species and closely linked to phylogeny. Morphological traits of first order roots showed a much stronger phylogenetic signal than those of roots ≤2 mm (traditionally defined fine roots). The findings improve understanding of root trait strategies in response to environmental changes.

Variations in the first-order root diameter in 89 woody species in a subtropical evergreen broadleaved forest

Variations in the first-order root diameter in 89 woody species in a subtropical evergreen broadleaved forest