Fine Root System Research Articles

Total Polyphenol Content and Antioxidant Activity of Leaves and Fine Roots as Indicators of Drought Resistance in the Native Quercus robur and Alien Quercus rubra

Research Highlights: Environmental abiotic stressors generate secondary stresses in plants, such as osmotic and oxidative stresses, which negatively influence their normal growth, development, and metabolism. Research about other non-enzymatic components with antioxidant capacity has recently focused on polyphenols. However, their role as indicators of drought and shade tolerance in woody species leaves and roots has been poorly explored or was limited to leaves only. Background and Objectives: Under a scenario of increasing drought, understanding the seedling responses in terms of total polyphenols and their antioxidant activity, in particular at the fine root system level, may help to elucidate the native–alien species interaction. Materials and Methods: At the beginning of July, 5-month-old native Quercus robur and alien Quercus rubra seedlings were transferred indoors to the growth chamber and subjected to progressive soil drying for 21 days. Results: The decrease in soil water content was more pronounced for Q. robur (9%) than for Q. rubra (34% of field capacity). Leaf water potential significantly decreased over time in Q. robur but did not differ from the control in Q. rubra. The total polyphenol concentration in Q. robur was markedly lower in the leaves and significantly higher in the fine roots than in Q. rubra. For the leaves, both species showed markedly higher values if well-watered, and the values significantly decreased in response to drought only in Q. rubra. In contrast, the fine root values for both species were markedly higher if droughted and decreased significantly in time only in Q. robur. Differently from the polyphenol concentration, the antioxidant capacity of Q. rubra was always higher in both the leaves and fine roots. Conclusions: The higher antioxidant activity of the alien species Q. rubra revealed by this work, combined with its isohydric behaviour, could further shed some light on our understanding of its competitive performance at the seedling stage against the native Q. robur.

Vertical movement of microplastics by roots of wheat plant (Triticum aestivum) and the plant response in sandy soil

Microplastics persist as a challenging pollutant in agroecosystems, posing potential risks to soil health and crop productivity. Root growth, elongation and expansion may significantly influence the vertical transport and infiltration of microplastics into the soil profile. Wheat plants (Triticum aestivum) grown in 70 cm deep rhizotrons were investigated for their influence on the vertical movement of two prevalent microplastic shapes, polyester fibres and polyvinyl chloride (PVC) fragments. Wheat was chosen for its dense and extensive fibrous and fine root system, which is a robust model for studying root-soil-microplastic interactions. Microplastics at a 0.24% w/w dry soil weight concentration were homogeneously distributed in the topsoil (0–20 cm). Infiltration of polyester fibres up to 50 cm into the soil profile was discerned as strong adherence to plant roots. PVC fragments exhibited greater mobility, reaching depths of 70 cm in the presence and absence of wheat plants. Plant growth response on exposure to microplastics appeared in the form of increased root branching and decreased shoot biomass, indicating a stress response in wheat plants. The results prove the vertical movement of microplastics, while the infiltration depth was influenced by microplastic shape. Movement was detected as either strong adherence of polyester fibres to plant roots or infiltration of PVC fragments. PVC fragments may have infiltrated through preferential flow paths in soil pores and the fissures created by root elongation and water movement.

Quantitative phenotyping of crop roots with spectral electrical impedance tomography: a rhizotron study with optimized measurement design

BackgroundRoot systems are key contributors to plant health, resilience, and, ultimately, yield of agricultural crops. To optimize plant performance, phenotyping trials are conducted to breed plants with diverse root traits. However, traditional analysis methods are often labour-intensive and invasive to the root system, therefore limiting high-throughput phenotyping. Spectral electrical impedance tomography (sEIT) could help as a non-invasive and cost-efficient alternative to optical root analysis, potentially providing 2D or 3D spatio-temporal information on root development and activity. Although impedance measurements have been shown to be sensitive to root biomass, nutrient status, and diurnal activity, only few attempts have been made to employ tomographic algorithms to recover spatially resolved information on root systems. In this study, we aim to establish relationships between tomographic electrical polarization signatures and root traits of different fine root systems (maize, pinto bean, black bean, and soy bean) under hydroponic conditions.ResultsOur results show that, with the use of an optimized data acquisition scheme, sEIT is capable of providing spatially resolved information on root biomass and root surface area for all investigated root systems. We found strong correlations between the total polarization strength and the root biomass (R2=0.82\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R^2 = 0.82$$\\end{document}) and root surface area (R2=0.8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R^2 = 0.8$$\\end{document}). Our findings suggest that the captured polarization signature is dominated by cell-scale polarization processes. Additionally, we demonstrate that the resolution characteristics of the measurement scheme can have a significant impact on the tomographic reconstruction of root traits.ConclusionOur findings showcase that sEIT is a promising tool for the tomographic reconstruction of root traits in high-throughput root phenotyping trials and should be evaluated as a substitute for traditional, often time-consuming, root characterization methods.

An assessment of nutrient removal by harvesting constructed floating wetlands in two coastal lagoons in the SE Baltic Sea

AbstractIn the last decades, so‐called internal or sea‐based mitigation measures have been suggested as nature‐based solutions to remove nutrients and improve water quality in semi‐enclosed coastal waters. However, these have rarely been tested in the field, especially in colder climates where winter ice cover is common. The aim of this experimental research was to investigate plant growth conditions in such an environment, as well to estimate nutrient removal capacity by harvesting constructed floating wetlands (CFWs). We tested small (24–28 m2) CFWs (Biomatrix®, Scotland, UK) at two demonstration sites: the Curonian lagoon (CL, Lithuania) and Szczecin lagoon (SL, Poland). In the CL, CFWs were planted predominantly with Carex acutiformes (Ehrh.), while the SL CFW was planted mainly with the reed Phragmites australis (Cav.) Trin. ex Steud. We aimed to test the amount of nutrient removal by plant harvesting over three subsequent years (2019–2021). We investigated carbon storage capacity and plant nutrient stoichiometry as indicators of potential nutrient limitation in the brackish coastal waters. Plant biomass increased annually, stabilising at 2.5–3.7 kg wet weight m−2. The total nutrient uptake per installed island area varied with the plant species composition. In the successive years, the harvested plants from the CL CFW dominated by Carex accumulated 10.4–13.1 g N m−2, 0.6–0.8 g P m−2 and 318–431 g C m−2 per year. The harvest from the SL CFW dominated by Phragmites contained a two‐times higher amount of nutrients, the respective figures being 21.2 g N m−2, 1.6 g P m−2 and 704 g C m−2. The nutrient stoichiometry in the vegetation did not suggest the presence of sub‐optimal growth conditions due to nitrogen limitation. However, the CL's dissolved nutrient supply was very low during the summer cyanobacteria bloom and indicated a severe nitrogen deficiency (as reflected in the dissolved inorganic nitrogen:dissolved inorganic phosphorus [DIN:DIP] molar ratio of 6). We suggest that to maximise nutrient removal capacity, tall plants with high biomass should be selected and/or plants with fine root systems to efficiently uptake the limiting nutrient from the water.

Root Distribution and Water Uptake Applied by Hydrogen and Oxygen Stable Isotopes for Lianas in Northwest China

The root distribution and water uptake of irrigated vines (Vitis vinifera L.) in arid oasis areas remain poorly understood, particularly in terms of the variations in water uptake resulting from plant type and growing period. In this study, excavation and soil coring were employed to investigate the root distribution of vines. Meanwhile, the water uptake dynamics of irrigated vines in an arid oasis area were developed using stable isotopes of hydrogen and oxygen in water bodies (δD and δ18O) and in crops and soil water, coupled with a direct inference approach and a linear mixed model (IsoSource). The soil layers were divided into nine layers via hierarchical cluster analysis. The results indicated that the vertical distributions of the total and fine roots of grapevines were mainly in the range of 40–160 cm, accounting for 93.1% (91.2%) and 92.5% (90.0%) of the total root (200 cm) distribution during May and October, respectively. In the horizontal direction, both the total root and fine root systems were mainly distributed within 0–100 cm from the trunk and contributed 81.2% and 79.8% of the total root distribution, respectively. Meanwhile, both the total root weight (length) density and fine root weight (length) density decreased gradually with increasing radial distance from the trunk in the 0–80 cm range. The main water uptake of vines was at 0–40 cm in June, 20–80 cm in July, and 40–100 cm in August. These findings suggest that the main depth of root water uptake increases during the whole growth stage for grapevines in arid oasis ecosystems. This information will help growers to improve irrigation efficiency and provide a data analysis of water conservation in an arid oasis area during water stress.

Fine-Root Distribution and Soil Physicochemical Property Variations in Four Contrasting Urban Land-Use Types in South Korea.

Urbanization and associated forest conversions have given rise to a continuum of native (forest fragments) and modified (artificial grasslands and perennial ecosystems) land-use types. However, little is known about how these shifts affect soil and fine-root compartments that are critical to a functioning carbon and nutrient circulation system. In this study, soil physicochemical properties, fine-root mass, and vertical distribution patterns were investigated in four representative urban land-use types: grassland (ZJ), perennial agroecosystem (MP), broadleaf deciduous forest patch (QA), and coniferous evergreen forest patch (PD). We quantified the fine-root mass in the upper 30 cm vertical profile (0-30 cm) and at every 5 cm depth across three diameter classes (<2 mm, 2-5 mm, and <5 mm). Soil physicochemical properties, except for phosphorus, nitrogen, ammonium nitrogen, and sodium cations, varied significantly across land-use types. The total root biomass (<5 mm) decreased in the order of QA (700.3 g m-2) > PD (487.2 g m-2) > ZJ (440.1 g m-2) > MP (98.3 g m-2). The fine-root mass of ZJ and MP was correlated with soil nutrients, which was attributed to intensive management operations, while the fine-root mass of QA and PD had a significant relationship with soil organic matter due to the high inputs from forest litter. Very fine roots (<2 mm) presented a distinct decremental pattern with depth for all land-use types, except for MP. Very fine roots populated the topmost 5 cm layer in ZJ, QA, and PD at 52.1%, 49.4%, and 39.4%, respectively. Maintaining a woody fine-root system benefits urban landscapes by promoting soil stabilization, improving ground infiltration rates, and increasing carbon sequestration capacity. Our findings underscore the importance of profiling fine-root mass when assessing urban expansion effects on terrestrial ecosystems.

Fine-root morphology of woody and herbaceous plants responds differently to altered precipitation: A meta-analysis

The growth of plant roots and their acquisition of resources are significantly impacted by changes in precipitation patterns. Although numerous studies have examined the impact of precipitation on fine root systems, the rooting strategies of woody and herbaceous plants under different precipitation patterns remain to be comparatively evaluated. Accordingly, in the current study, we conducted a meta-analysis of 64 peer-reviewed articles to explore the response of 17 biomass and fine-root traits of woody and herbaceous plants to precipitation changes. Our findings demonstrate that woody and herbaceous plants have developed different root strategies to cope with altered precipitation. Specifically, when precipitation increased, the fine roots of woody plants had a larger surface area and significantly increased shallow root growth. In contrast, the fine-root morphological traits of herbaceous plants showed a stronger response to increased precipitation, in which fine-root length, volume, and tissue density increased. This may result in more effective use of available water by herbaceous than woody plants. When precipitation decreased, woody plants displayed more active fine-root morphological alterations, presenting a conservative fine-root phenotype of resource acquisition, with lower specific root length and higher fine-root tissue density. Moreover, woody plants transfer absorptive fine-root structures to deep soil layers, whereas herbaceous plants are less drought-tolerant. Furthermore, woody plants may allocate biomass more optimally than herbaceous plants in precipitation-reduction scenarios. Increased precipitation may boost soil carbon sequestration and stability in woody plant-dominated forest ecosystems under future climate change scenarios, while drought may considerably reduce soil carbon storage in grassland ecosystems. In more arid environments, where woody and herbaceous plants coexist, drought may lead to the expansion of woody plants and subsequent predominance of woody plants vegetation change. our findings will fill knowledge gaps in the literature regarding the effects of precipitation changes on the fine-root dynamics of various functional plants and will improve predictions of the vegetation dynamics of forests, grasslands, and other ecosystems vegetation dynamics under changing precipitation patterns.

Drought legacy effects on fine-root-associated fungal communities are modulated by root interactions between tree species

With climate change, the frequency of severe droughts is predicted to increase globally, resulting in increased forest dieback. Although fine-root systems and their associated fungi are considered crucial for tree nutrient exchange after a drought period and consequently for tree recovery, post-drought dynamics remain poorly understood. We rewatered mature European beech and Norway spruce after a 5-year experimental summer drought to shed light on belowground recovery processes. Therefore, we tracked the fine-root parameters growth, vitality, and mycorrhization in monospecific rooting zones with intraspecific root contact and mixed rooting zones with interspecific root contact of both tree species during the first 3 months of recovery, and we analyzed compositions of their root-associated fungal communities by DNA- and RNA-ITS2 sequencing. During recovery, the fine-root parameters differed between both tree species, with only minor effects of the tree rooting zone. Root-associated fungal communities showed no significant response to irrigation within 3 months after drought release. The rooting zone was the dominating factor affecting the root-associated fungal diversity, the abundance of trophic modes, and the response of individual saprotrophic and ectomycorrhizal (ECM) species. Furthermore, an analysis of the most abundant fungal species revealed that for ECM fungi, drought tolerance was common and for saprotrophs, a facultative, root-associated lifestyle. These results suggest that tree species-specific fungal communities are stable despite previous long-term drought and are closely associated with tree species-specific response patterns related to root survival and recovery. Moreover, an association between saprotrophic fungi and roots might be a strategy to support fungal drought survival.

Effects of land-use change and disturbance on the fine root biomass, dynamics, morphology, and related C and N fluxes to the soil of forest ecosystems at different elevations at Mt. Kilimanjaro (Tanzania)

Tropical forests are threatened by anthropogenic activities such as conversion into agricultural land, logging and fires. Land-use change and disturbance affect ecosystems not only aboveground, but also belowground including the ecosystems' carbon and nitrogen cycle. We studied the impact of different types of land-use change (intensive and traditional agroforestry, logging) and disturbance by fire on fine root biomass, dynamics, morphology, and related C and N fluxes to the soil via fine root litter across different ecosystems at different elevational zones at Mt. Kilimanjaro (Tanzania). We found a decrease in fine root biomass (80–90%), production (50%), and C and N fluxes to the soil via fine root litter (60–80%) at all elevation zones. The traditional agroforestry 'Chagga homegardens' (lower montane zone) showed enhanced fine root turnover rates, higher values of acquisitive root morphological traits, but similar stand fine root production, C and N fluxes compared to the natural forest. The decrease of C and N fluxes with forest disturbance was particularly strong at the upper montane zone (60 and 80% decrease, respectively), where several patches of Podocarpus forest had been disturbed by fire in the previous years. We conclude that changes on species composition, stand structure and land management practices resulting from land-use change and disturbance have a strong impact on the fine root system, modifying fine root biomass, production and the C and N supply to the soil from fine root litter, which strongly affects the ecosystems' C and N cycle in those East African tropical forest ecosystems.

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.

Effects of Soil Water Shortage on Seedling Shoot and Root Growth of Saragolle Lucana Tetraploid Wheat (Triticum durum Desf.) Landrace.

Ancient wheats may be a source of traits that are useful for the tolerance of climate change foreseen conditions of raising temperatures and low water availability. Previous research has shown a fine root system and a high mass of rhizosheath per unit root mass in the italian durum wheat (Triticum durum Desf) landrace Saragolle Lucana, and this may be relevant for successfully facing adverse conditions during seedling establishment. We investigated the effect of soil water shortage in Saragolle seedlings on root architecture, rhizosheath formation and biomass allocation. Pot experiments were conducted by comparing two levels of soil available water content (AWC): WW (100% of AWC) and DS (50% of AWC). Phenology was delayed by eight days in DS and above and belowground traits were measured at Zadoks 1.3 for each treatment. Biometric data collected at the same phenological stage show that DS plants did not reach the levels of biomass, surface area and space occupation of WW even after attaining the same developmental stage. Namely, plant dimensions were lower at low soil water availability, with the exception of rhizosheath production: DS yielded a 50% increase in rhizosheath mass and 32% increase in rhizosheath mass per unit root mass. The proportion of plant mass reduction in DS was 29.7% for aboveground parts and 34.7% for roots, while reductions in leaf and root surface areas exceeded 43%. The root/shoot mass and area ratios were not significantly different between treatments, and a higher impact on aboveground than on belowground traits at reduced available water was shown only by a lower ratio of shoot height to root depth in DS than in WW. Increases in rhizosheath in absolute and relative terms, which were observed in our experiment in spite of smaller root systems in the ancient durum wheat variety Saragolle lucana at DS, may provide an interesting trait for plant performance in conditions of low soil water availability both for water-related issue and for other effects on plant nutrition and relations with the rhizosphere.

Can Lunar and Martian Soils Support Food Plant Production? Effects of Horse/Swine Monogastric Manure Fertilisation on Regolith Simulants Enzymatic Activity, Nutrient Bioavailability, and Lettuce Growth

To make feasible the crewed missions to the Moon or Mars, space research is focusing on the development of bioregenerative life support systems (BLSS) designed to produce food crops based on in situ resource utilisation (ISRU), allowing to reduce terrestrial input and to recycle organic wastes. In this regard, a major question concerns the suitability of native regoliths for plant growth and how their agronomic performance is affected by additions of organic matter from crew waste. We tested plant growth substrates consisting of MMS-1 (Mars) or LHS-1 (Lunar) simulants mixed with a commercial horse/swine monogastric manure (i.e., an analogue of crew excreta and crop residues) at varying rates (100:0, 90:10, 70:30, 50:50, w/w). Specifically, we measured: (i) lettuce (Lactuca sativa L. cultivar 'Grand Rapids') growth (at 30 days in open gas exchange climate chamber with no fertilisation), plant physiology, and nutrient uptake; as well as (ii) microbial biomass C and N, enzymatic activity, and nutrient bioavailability in the simulant/manure mixtures after plant growth. We discussed mechanisms of different plant yield, architecture, and physiology as a function of chemical, physico-hydraulic, and biological properties of different substrates. A better agronomic performance, in terms of plant growth and optically measured chlorophyll content, nutrient availability, and enzymatic activity, was provided by substrates containing MMS-1, in comparison to LHS-1-based ones, despite a lower volume of readily available water (likely due to the high-frequency low-volume irrigation strategy applied in our experiment and foreseen in space settings). Other physical and chemical properties, along with a different bioavailability of essential nutrients for plants and rhizosphere biota, alkalinity, and release of promptly bioavailable Na from substrates, were identified as the factors leading to the better ranking of MMS-1 in plant above and below-ground mass and physiology. Pure Mars (MMS-1) and Lunar (LHS-1) simulants were able to sustain plant growth even in absence of fertilisation, but the amendment with the monogastric manure significantly improved above- and below-ground plant biomass; moreover, the maximum lettuce leaf production, across combinations of simulants and amendment rates, was obtained in treatments resulting in a finer root system. Increasing rates of monogastric manure stimulated the growth of microbial biomass and enzymatic activities, such as dehydrogenase and alkaline phosphomonoesterase, which, in turn, fostered nutrient bioavailability. Consequently, nutrient uptake and translocation into lettuce leaves were enhanced with manure supply, with positive outcomes in the nutritional value of edible biomass for space crews. The best crop growth response was achieved with the 70:30 simulant/manure mixture due to good availability of nutrients and water compared to low amendment rates, and better-saturated hydraulic conductivity compared to high organic matter application. A 70:30 simulant/manure mixture is also a more sustainable option than a 50:50 mixture for a BLSS developed on ISRU strategy. Matching crop growth performance and (bio)chemical, mineralogical, and physico-hydraulic characteristics of possible plant growth media for space farming allows a better understanding of the processes and dynamics occurring in the experimental substrate/plant system, potentially suitable for an extra-terrestrial BLSS.

Effects of the Root System Architecture of Pinus taeda and Phyllostachys edulis on the Index of Hydrological Connectivity in Subtropical Forest Ecosystems

The hydrological connectivity below the soil surface can influence the forest structure and function, especially soil and plant productivity. However, few studies have determined the changes in the hydrological connectivity below the soil surface with increasing soil depth and have quantified the effects of root systems on the hydrological connectivity in forest ecosystems. In this study, we evaluated the index of the hydrological connectivity (IHC) below the soil surface using a field dye tracing method and compared the difference in the index of hydrological connectivity in two subtropical forest stands (i.e., pine trees [SS] and bamboo [ZL]). We analyzed the interactions between the parameters of root system architecture and the index of hydrological connectivity. Back propagation (BP) neural networks were used to quantify which parameter can contribute the most relative importance to the changes of the IHC. The results revealed that the maximum value of the index of hydrological connectivity occurs at the soil surface, and it exhibits a non-linear decreasing trend with increasing soil depth. The parameters of root system architecture (root length, root projected area, root surface area, root volume, and root biomass) were rich in the top soil layers (0–20 cm) in the two sites. Those parameters were positively correlated with the IHC and the root length had the largest positive influence on the hydrological connectivity. Furthermore, we found that root system architecture with different root diameters had different degrees of influence on the index of hydrological connectivity. The very fine root systems (0 &lt; D &lt; 1 mm) had the greatest effect on the hydrological connectivity (p &lt; 0.01). The results of this study provide more information for the assessment of the hydrological connectivity below the soil surface and a better understanding of the effects of root systems in soil hydrology within the rhizosphere.

Tree root distribution modelling in different environmental conditions

The ability to predict the spatial distribution of tree root system variables (e.g., the Root system Area (RA), the maximum root diameter, the number of roots in diameter classes, the density of fine roots, etc.) under different environmental conditions is relevant to several scientific disciplines and to engineering practice. In this work, three well known analytical models from the literature are assembled into a unique framework called the Root Distribution Model (RDM). RDM models the expected vertical and horizontal distribution of coarse and fine root system variables for mature plants growing in different environmental conditions ranging from moderately humid to arid climates. All soil and moisture dynamic parameters are physically based, which make the model straightforward to calibrate via a single tuning parameter. At this investigative stage, it is shown that the model has the flexibility to represent a broad range of situations where soil moisture may result from precipitation inputs or from water level fluctuations due to either the presence of a water coarse or of deep aquifers or both. Accordingly, the distribution of the sectional RA may be either positively or negatively skewed, as well as show a peculiar bi-modal structure. The model can be used to study the impact of changing scenarios affecting precipitation, aquifer and channel hydrology.

Dynamics of initial carbon allocation after drought release in mature Norway spruce-Increased belowground allocation of current photoassimilates covers only half of the carbon used for fine-root growth.

After drought events, tree recovery depends on sufficient carbon (C) allocation to the sink organs. The present study aimed to elucidate dynamics of tree-level C sink activity and allocation of recent photoassimilates (Cnew ) and stored C in c. 70-year-old Norway spruce (Picea abies) trees during a 4-week period after drought release. We conducted a continuous, whole-tree 13 C labeling in parallel with controlled watering after 5 years of experimental summer drought. The fate of Cnew to growth and CO2 efflux was tracked along branches, stems, coarse- and fine roots, ectomycorrhizae and root exudates to soil CO2 efflux after drought release. Compared with control trees, drought recovering trees showed an overall 6% lower C sink activity and 19% less allocation of Cnew to aboveground sinks, indicating a low priority for aboveground sinks during recovery. In contrast, fine-root growth in recovering trees was seven times greater than that of controls. However, only half of the C used for new fine-root growth was comprised of Cnew while the other half was supplied by stored C. For drought recovery of mature spruce trees, in addition to Cnew , stored C appears to be critical for the regeneration of the fine-root system and the associated water uptake capacity.

Archaeal community structures associated with fine root systems of Cryptomeria japonica (Cupressaceae) in central Japan

ABSTRACT Archaea live in extreme environments and have been found in non-extreme environments in recent years. Although most studies have focused on the nitrification function of archaea in forest soils, few studies have focused on how archaea in rhizospheres are involved in nutrient absorption. To elucidate the archaeal community pattern inhabiting the fine roots of trees, we examined the taxonomic identity and community structure of archaea in Japanese cedars (Cryptomeria japonica). Root samples were collected from six C. japonica plantations in central Japan. DNA was separately extracted from the first- and third-order roots, and archaeal taxa were determined by the cloning method focusing on 16S rDNA. As a result, 90% of the sequences were classified as in the phylum Thaumarchaeota, with 1.1b and 1.1c groups in the phylum accounting for 65% and 25%, respectively. Archaeal community structures were significantly correlated with soil pH, but neither the root orders nor the plantation sites showed significant clustering. These results suggest that Thaumarchaeota is the dominant archaeal group in the fine roots of C. japonica, and community structures are affected by a proximate chemical factor of soil acidity.

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.

Consequences of tropical rainforest conversion to tree plantations on fine root dynamics and functional traits

Despite the crucial role of fine roots for water and nutrient uptake, soil biological activity and ecosystem carbon cycling, the response of root dynamics to rapidly advancing land‐use change in the tropics is still poorly understood. To address this uncertainty, we investigated the consequences of tropical forest conversion to intensively managed tree plantations for a suite of functional fine root traits. We analysed fine root morphology (diameter, specific root length (SRL), tissue density) and chemistry, as well as root lifespans in four prevalent land‐use systems in the lowlands of Sumatra (Indonesia), namely natural forest, jungle rubber, rubber and oil palm monocultures. Fine root production was estimated using three independent approaches (sequential coring, ingrowth cores, mini‐rhizotrons). Contradicting the expected trend from more conservative to more acquisitive fine root traits with increasing land‐use intensity, we found that SRL and tissue density were significantly higher in forest trees, while fine root diameter was largest in rubber trees and root N content lowest in the oil palm system. Median fine root longevity in the top soil was 11% higher in rubber plantations (238 days) than in jungle rubber (211 days), and more than 50% greater than in the forest (140 days) and oil palm plantations (125 days). Fine root production was higher in the forest and oil palm plantations (ranging between 2 and 9 Mg ha−1 year−1) than the rubber stands, but annual totals varied depending on the methodological approach. Conversion of tropical lowland forest to agricultural systems significantly altered community‐level fine root morphology, dynamics and longevity, with likely consequences for soil carbon cycling and soil biological activity. However, land‐use intensification did not consistently lead to more acquisitive fine root systems; rather, differences in root morphology and dynamics were driven by species‐specific root trait syndromes especially of rubber and oil palm.

Relationship between the vertical distribution of fine roots and residual soil nitrogen along a gradient of hardwood mixture in a conifer plantation

In forest ecosystems, understanding the relationship between the vertical distribution of fine roots and residual soil nitrogen is essential for clarifying the diversity-productivity-water purification relationship. Vertical distributions of fine-root biomass (FRB) and concentrations of nitrate-nitrogen (NO3 -N) in soil water were investigated in a conifer plantation with three thinning intensities (Control, Weak and Intensive), in which hardwood abundance and diversity were low, moderate and high, respectively. Intensive thinning led to the lowest NO3 -N concentration in soil water at all depths (0-100 cm) and highest FRB at shallow depths (0-50 cm). The NO3 -N concentration at a given depth was negatively correlated with total FRB from the surface to the depth at which NO3 -N concentration was measured, especially at shallow depths, indicating that more abundant fine roots led to lower levels of downward NO3 -N leaching. FRB contributed positively to nitrogen content of hardwood leaves. These findings demonstrate that a hardwood mixture in conifer plantations resulted in sufficient uptake of NO3 -N from soil by well developed fine-root systems, and translocation to canopy foliage. This study suggests that productivity and water purification can be achieved through a hardwood mixture in conifer plantations.

Holm oak decline is determined by shifts in fine root phenotypic plasticity in response to belowground stress.

Summary Climate change and pathogen outbreaks are the two major causes of decline in Mediterranean holm oak trees (Quercus ilex L. subsp. ballota (Desf.) Samp.). Crown‐level changes in response to these stressful conditions have been widely documented but the responses of the root systems remain unexplored. The effects of environmental stress over roots and its potential role during the declining process need to be evaluated.We aimed to study how key morphological and architectural root parameters and nonstructural carbohydrates of roots are affected along a holm oak health gradient (i.e. within healthy, susceptible and declining trees).Holm oaks with different health statuses had different soil resource‐uptake strategies. While healthy and susceptible trees showed a conservative resource‐uptake strategy independently of soil nutrient availability, declining trees optimized soil resource acquisition by increasing the phenotypic plasticity of their fine root system.This increase in fine root phenotypic plasticity in declining holm oaks represents an energy‐consuming strategy promoted to cope with the stress and at the expense of foliage maintenance. Our study describes a potential feedback loop resulting from strong unprecedented belowground stress that ultimately may lead to poor adaptation and tree death in the Spanish dehesa.