Coarse Roots Research Articles

Segmentation uncertainty of vegetated porous media propagates during X-ray CT image-based analysis

Abstract Background and Aims Phase segmentation is a crucial step in X-ray computed tomography (CT) for image-based analysis (CT-IBA) to derive soil and root information. How segmentation uncertainty (SU) affects CT-IBA of vegetated soil has never been explored. Methods We proposed a new framework enabled by machine learning to measure SU and its propagation from the first to the second-order parameters derived from CT-IBA. Vegetated glass beads of varying moisture contents and plant species were CT scanned. Segmented images were used to determine volumetric fractions and morphological properties of each phase for determining the absolute permeability (K). Results Although the root phase is susceptible to SU, its influence on CT-IBA is minimal when the root content is low. However, its SU was magnified when the water phase is present. The grain phase has a lower SU susceptibility, but due to its large volumetric content, the IBA can be affected significantly. Fine roots were found to exhibit higher SU than coarse roots, indicating that root architecture has an effect on the segmentation of the root phase, and thus higher-order properties like K. Conclusion Segmentation of the grain phase is sensitive to SU. A small SU will lead to a remarkably erroneous estimation of pore morphological properties and K. To reduce SU, we suggest reducing the water content to a discontinuous state of a cohesionless vegetated porous media specimen before sending it for CT scanning and IBA. However, caution should be taken when fine roots were dried and experienced excessive shrinkage.

Native Gramineae outperform Leguminosae in enhancing ecosystem multifunctionality during semiarid desert steppe restoration

The effects of reseeded native Gramineae and Leguminosae species on the multifunctionality of desert steppe have remained unclear. Therefore, we examined a semiarid desert steppe that was reseeded 5 years earlier with a dominant native Gramineae species, Agropyron mongolicum; a dominant native Leguminosae species, Lespedeza potaninii; and a 1:1 reseeded mixture of A. mongolicum × L. potaninii. We evaluated the changes in plant communities and soil properties and then quantified aboveground ecosystem multifunctionality (AEMF), belowground ecosystem multifunctionality (BEMF), and overall ecosystem multifunctionality (EMF) using an averaging approach. Compared with the native steppe without reseeding, both reseeded A. mongolicum and A. mongolicum × L. potaninii increased fine root volume, plant height, plant cover, aboveground biomass (AGB), belowground biomass (BGB), soil water storage (SWS), soil organic carbon, light fraction organic carbon, labile organic carbon, total nitrogen (TN), nitrate nitrogen, and total phosphorus (P), but decreased soil bulk density. However, reseeded L. potaninii increased coarse root volume, plant height, plant cover, AGB, BGB, and SWS but decreased plant richness, plant diversity, TN, and total P. In addition, reseeded A. mongolicum and A. mongolicum × L. potaninii increased AEMF, BEMF, and overall EMF, but reseeded L. potaninii only increased AEMF. Further analysis indicated that the fine roots played a crucial role in improving individual ecosystem functions and eventually in determining EMF. Therefore, the reseeding of a desert steppe with Gramineae species has greater potential than with Leguminosae species for improving EMF, since Gramineae species have greater fine roots volume than Leguminosae species.

Woody Encroachment Modifies Subsurface Structure and Hydrological Function

ABSTRACTWoody encroachment—the expansion of woody shrubs into grasslands—is a widely documented phenomenon with global significance for the water cycle. However, its effects on watershed hydrology, including streamflow and groundwater recharge, remain poorly understood. A key challenge is the limited understanding of how changes to root abundance, size and distribution across soil depths influence infiltration and preferential flow. We hypothesised that woody shrubs would increase and deepen coarse‐root abundance and effective soil porosity, thus promoting deeper soil water infiltration and increasing soil water flow velocities. To test this hypothesis, we conducted a study at the Konza Prairie Biological Station in Kansas, where roughleaf dogwood (Cornus drummondii) is the predominant woody shrub encroaching into native tallgrass prairie. We quantified the distribution of coarse and fine roots and leveraged soil moisture time series and electrical resistivity imaging to analyse soil water flow beneath shrubs and grasses. We observed a greater fraction of coarse roots beneath shrubs compared to grasses, which was concurrent with greater saturated hydraulic conductivity and effective porosity. Half‐hourly rainfall and soil moisture data show that the average soil water flow through macropores was 135% greater beneath shrubs than grasses at the deepest B horizon, consistent with greater saturated hydraulic conductivity. Soil‐moisture time series and electrical resistivity imaging also indicated that large rainfall events and greater antecedent wetness promoted more flow in the deeper layers beneath shrubs than beneath grasses. These findings suggest that woody encroachment alters soil hydrologic processes with cascading consequences for ecohydrological processes, including increased vertical connectivity and potential groundwater recharge.

Nutrient Stoichiometry and Tree Development: Insights from a 5-Year Study on Catalpa bungei Fertilization

Short-term fertilization may provide limited improvements in tree growth and demonstrate suboptimal fertilizer efficiency; however, its benefits often fall short of expectations. Unfortunately, research addressing the sustained impacts of prolonged fertilization (e.g., beyond five years) on trees’ developmental dynamics and productivity remains relatively scarce. This study focused on a 7-year-old Catalpa bungei plantation located in Jinan City, Shandong Province, China. The study employed two fertilization techniques: hole fertilization (HF) and integrated water and fertilizer application (WF), with a no-fertilization treatment serving as the control (CK). The findings revealed that the WF significantly enhanced stand productivity. When comparing the different treatments, the productivity of WF stands demonstrated a remarkable increase of 39.7% compared to HF stands and 55.1% compared to CK stands. After five years of fertilization, the stands treated with WF exhibited a significant increase in volume accumulation, reaching 112.36 m3·hm−2. Additionally, the productivity of these WF-fertilized stands achieved an impressive 41.75 m3·hm−2·a−1. Fertilization notably enhanced the nitrogen content in the leaves and fine roots of C. bungei, as well as the potassium content in the coarse roots. These nutrients were found to be more concentrated in the corresponding organs within the WF stands. Over the entire growth cycle, there was a substantial consumption of key nutrients, with leaf nitrogen, phosphorus, and potassium contents decreasing by 30.5%, 18.8%, and 47.3%, respectively. Similarly, the coarse root potassium and fine root phosphorus content decreased by 24.7% and 24.4%, respectively. The enhancement in leaf nitrogen content following fertilization significantly contributed to increases in tree height, breast height diameter (DBH), and individual tree volume. Similarly, the enrichment of potassium in the branches and coarse roots was associated with improvements in DBH and tree volume. To maximize forest stand productivity, the WF fertilization method demonstrated superior results compared to HF. Therefore, WF should be prioritized in future fertilization experiments for C. bungei.

A Mechanistic Prediction Model of Resistance to Uprooting of Coniferous Trees in Heilongjiang Province, China.

Coarse roots and the root plate play an important role in tree resistance to uprooting. In this study, a qualitative mechanistic model was developed to analyze coniferous tree resistance to uprooting in relation to tree morphological characteristics. The sizes of the crown, stem, and root plate of twenty sample spruces and twenty sample Korean pines were individually measured for this purpose. Using Ground Penetrating Radar (GPR), the coarse root distribution and root plate size were detected. In the qualitative mechanistic model, a larger crown area increased the overturning moment, while higher DBH and root plate mass increased the resistance moment. The resistance coefficient (Rm) was calculated by comparing resistive and overturning moments, classifying samples into three uprooting hazard levels. Trees with smaller crown areas, larger stems, and root plates tend to have higher resistance to uprooting, as indicated by higher Rm values. This qualitative mechanistic model provides a useful tool for assessing coniferous standing tree uprooting resistance.

Nutritional convergence in plants growing on gypsum soils in two distinct climatic regions.

Soil endemics have long fascinated botanists due to the insights they can provide about plant ecology and evolution. Often, these species have unique foliar nutrient composition patterns that reflect potential physiological adaptations to these harsh soil types. However, understanding global nutritional patterns to unique soil types can be complicated by the influence of recent and ancient evolutionary events. Our goal was to understand whether plant specialization to unique soils is a stronger determinant of plant nutrient composition than climate or evolutionary constraints. We worked on gypsum soils. We analyzed whole-plant nutrient composition (leaves, stems, coarse roots and fine roots) of 36 native species of gypsophilous lineages from the Chihuahuan Desert (North America) and the Iberian Peninsula (Europe) regions, including widely distributed gypsum endemics, as specialists, and narrowly distributed endemics and non-endemics, as non-specialists. We evaluated the impact of evolutionary events and soil composition on the whole-plant composition, comparing the three categories of gypsum plants. Our findings reveal nutritional convergence of widely distributed gypsum endemics. These taxa displayed higher foliar Sulfur and higher whole-plant Magnesium than their non-endemic relatives, irrespective of geographic location or phylogenetic history. Sulfur and Magnesium concentrations were mainly explained by non-phylogenetic variation among species related to gypsum specialization. Other nutrient concentrations were determined by more ancient evolutionary events. For example, Caryophyllales usually displayed high foliar Calcium, whereas Poaceae did not. In contrast, plant concentrations of Phosphorus was mainly explained by species-specific physiology not related to gypsum specialization or evolutionary constraints. Plant specialization to a unique soil may strongly influence plant nutritional strategies, as we described for gypsophilous lineages. Taking a whole-plant perspective (all organs) within a phylogenetic framework has enabled us to gain a better understanding of plant adaptation to unique soils when studying taxa from distinct regions.

Terrestrial laser scanning and low magnetic field digitization yield similar architectural coarse root traits for 32-year-old Pinus ponderosa trees

BackgroundUnderstanding how trees develop their root systems is crucial for the comprehension of how wildland and urban forest ecosystems plastically respond to disturbances such as harvest, fire, and climate change. The interplay between the endogenously determined root traits and the response to environmental stimuli results in tree adaptations to biotic and abiotic factors, influencing stability, carbon allocation, and nutrient uptake. Combining the three-dimensional structure of the root system, with root morphological trait information promotes a robust understanding of root function and adaptation plasticity. Low Magnetic Field Digitization coupled with AMAPmod (botAnique et Modelisation de l’Architecture des Plantes) software has been the best-performing method for describing root system architecture and providing reliable measurements of coarse root traits, but the pace and scale of data collection remain difficult. Instrumentation and applications related to Terrestrial Laser Scanning (TLS) have advanced appreciably, and when coupled with Quantitative Structure Models (QSM), have shown some potential toward robust measurements of tree root systems. Here we compare, we believe for the first time, these two methodologies by analyzing the root system of 32-year-old Pinus ponderosa trees.ResultsIn general, at the total root system level and by root-order class, both methods yielded comparable values for the root traits volume, length, and number. QSM for each root trait was highly sensitive to the root size (i.e., input parameter PatchDiam) and models were optimized when discrete PatchDiam ranges were specified for each trait. When examining roots in the four cardinal direction sectors, we observed differences between methodologies for length and number depending on root order but not volume.ConclusionsWe believe that TLS and QSM could facilitate rapid data collection, perhaps in situ, while providing quantitative accuracy, especially at the total root system level. If more detailed measures of root system architecture are desired, a TLS method would benefit from additional scans at differing perspectives, avoiding gravitational displacement to the extent possible, while subsampling roots by hand to calibrate and validate QSM models. Despite some unresolved logistical challenges, our results suggest that future use of TLS may hold promise for quantifying tree root system architecture in a rapid, replicable manner.

Allometric equations for estimation of above- and below-ground biomass of Acacia mearnsii in northwestern Ethiopia

Correct estimation of tree biomass is important when calculating uptake or emission of CO2 in relation to land-use and land-use change. The objectives of this study were (1) to estimate the root/shoot ratio for the estimation of root biomass based on the above-ground biomass (AGB) of Acacia mearnsii, and (2) to develop allometric equations for the estimation of the above-and below-ground biomass (BGB) of Acacia mearnsii. To estimate the AGB and BGB, twenty-four trees of varying ages (3, 4, 5, and 6 years) were harvested, with six trees per age group. We measured the dry biomass for different tree parts and developed allometric models using tree height (H) and diameter at breast height (DBH) as independent variables. The results showed that the biomass of the stem accounted for 69% of the total biomass, followed by branches (14%), roots (8.1%), and leaves (7.3%). The recorded mean root/shoot ratio was 0.11. The biomass of the stem and coarse roots increased with increasing tree age, while a contrary trend was observed for the other tree components. Each component has its unique allometric model.

Nutrient Accumulation in Silver Birch (Betula pendula Roth) Biomass in a Lignite Mining Area

The influence of lignite mining on vegetation constitutes a key issue due to the role of plants in restoring and maintaining the ecological balance of ecosystems. In this context, the identification of its impact on the functioning of silver birch (Betula pendula Roth) as a species often colonizing disturbed habitats takes on particular importance. Therefore, we aimed to determine the changes in nutrient content in silver birch overgrowing a spoil heap and in the vicinity of a fly ash settling pond and power plant. For this purpose, plant tissues (fine and coarse roots, stemwood, bark, coarse and fine branches, leaves) and soil samples (0–10, 10–20, 20–40, 20–40 cm deep) were examined. The basic soil characteristics were determined, along with the N, P, K, Ca, Mg, S, Fe, Mn, Cu, and Zn contents of the soil and plant samples. The soils varied in terms of soil pH and were poor in total organic carbon and other elements. The plant nutrient content varied strongly across the analyzed tissues, with the leaves usually containing the most and the stemwood the least nutrients. Statistical analysis indicated significant differences between the control vs spoil heap (particularly in Mn, S, and Mg) and the stand close to the settling pond (particularly in Ca, Mn, P, K, and S). We found that the chemical properties of the spoil heap and fly ash originating from the lignite mining operations are likely factors influencing nutrient accumulation in silver birch trees.

Distinct variations of soil infiltrability of contrasting root types in a temperate mosaic-pattern grassland in northern China

Soil infiltration capacity is an important factor affecting soil moisture, and is of great significance to plant growth and groundwater recharge in arid and semiarid areas. Patchiness of grasslands widely exist and have a crucial effect on hydrological processes in water-limited regions. This study investigated soil infiltrability under natural grasslands with patchy mosaic patterns based on a series of in-situ tests. Two dominated natural restoration vegetation communities (Bothriochloa ischaemum (B. ischaemum) with fibrous root systems and Artemisia gmelinii (A. gmelinii) with tap root systems) and abandoned land (as control) were selected in the loess hilly and gully region of the Loess Plateau, China. The results showed that natural restoration grasslands significantly improved soil infiltrability in both plant and bare patches, and the emergence of patchy mosaic patterns can result in infiltration heterogeneity to redistribute water on a hillslope scale. Compared to B. ischaemum, A. gmelinii are more likely to facilitate the formation of preferential flow, contributing to the increased soil infiltration rates. The initial, steady and average infiltration rates (IIR, SIR, and AIR, respectively) and soil infiltration capacity index (SIC) were all negatively correlated with both root length density (RLD) and root surface area density (RSAD) of fine roots (diameter < 2 mm) but positively correlated with those of coarse roots (diameter ≥ 2 mm). The main factors influencing the infiltration capacity were the mean weight diameter in the 10−20 cm layer and the RSAD of the fine roots in the 0−20 cm layer, which can explain 98.6 %, 81.7 %, 63.9 %, and 91.3 % of the total variance of IIR, SIR, AIR, and SIC, respectively. This work highlights the important roles of patchy mosaic patterns in affecting soil water redistribution and the stabilization of ecological systems, providing a scientific basis for vegetation selection in the process of vegetation restoration in water-limited regions.

Linking Post-fire Tree Density to Carbon Storage in High-Latitude Cajander Larch (Larix cajanderi) Forests of Far Northeastern Siberia

AbstractWith climate warming and drying, fire activity is increasing in Cajander larch (Larix cajanderi Mayr.) forests underlain by continuous permafrost in northeastern Siberia, and initial post-fire tree demographic processes could unfold to determine long-term forest carbon (C) dynamics through impacts on tree density. Here, we evaluated above- and belowground C pools across 25 even-aged larch stands of varying tree densities that established following a wildfire in ~ 1940 near Cherskiy, Russia. Total C pools increased with increased larch tree density, from ~ 9,000 g C m−2 in low-density stands to ~ 11,000 g C m−2 in high and very high-density stands, with increases most pronounced at tree densities &lt; 1 stem m−2 and driven by increased above- and belowground (that is, coarse roots) and live and dead (that is, woody debris and snags) larch biomass. Total understory vegetation and non-larch coarse root C pools declined with increased tree density due to decreased shrub C pools, but these pools were relatively small compared to larch biomass. Fine root, soil organic matter (OM), and near surface (0–30 cm) mineral soil (MS) C pools varied little with tree density, although soil C pools held most (18–28% in OM and 44–51% in MS) C stored in these stands. Thus, if changing fire regimes promote denser stands, C storage will likely increase, but whether this increase offsets C lost during fires remains unknown. Our findings highlight how post-fire tree demographic processes impact C pool distribution and stability in larch forests of Siberian permafrost regions.

Variation in Root Biomass and Distribution Based on the Topography, Soil Properties, and Tree Influence Index: The Case of Mt. Duryun in Republic of Korea.

Root biomass and distribution are influenced by abiotic factors, such as topography and soil physicochemical properties, determining belowground productivity. Hence, we investigated the variation in root biomass and vertical root distribution based on the topography, soil physicochemical properties, and tree influence index, and their relationships, across soil depths (0-10 cm, 10-20 cm, and 20-30 cm) and topographical gradients in a warm-temperate forest in Mt. Duryun, Republic of Korea. Two contrasting research sites were established: a lower slope oriented at ≤3° and an upper slope with a slope of 30°. Each site comprised eleven 400 m2 sampling plots from which root samples from various diameter classes (<2 mm, 2-5 mm, 5-10 mm, and >10 mm) were collected. While the bulk density increased with soil depth in the lower slope, the organic matter, available phosphorus, Ca2+, and Mg2+ showed a reversed pattern. Linear mixed-effects models generally revealed significant negative correlations between root biomass and soil pH, total nitrogen, and cation exchange capacity, particularly in small roots (βstd = -1.03 to -1.51) and coarse roots (βstd = -6.30). Root biomass exhibited a 10-15% increase in the upper slope compared to the lower slope, particularly in fine (median = 52.0 g m2-65.64 g m2) and medium roots (median = 56.04 g m2-69.52 g m2) at a 0-20 cm soil depth. While no significant correlation between root biomass and the tree influence index was found on the lower slope, a different pattern was found on the upper slope. Our results indicate that the variation in root biomass and distribution can also be explained by the differences in the soil environment and topographical positions.

Influence of reforestation tree species on decomposition of larch stumps and coarse roots: role of wood microbial communities and soil properties

Abstract Stumps and coarse roots are the most important coarse woody debris component in managed forests. However, their decomposition is still poorly understood, especially the influence of the characteristics of the microbial communities on wood decomposition. In this study, we investigated decaying larch (Larix olgensis Henry) stumps and coarse roots in reforestations of birch (Betula pendula Roth.), ash (Fraxinus mandshurica Rupr.), pine (Pinus sylvestris var. Mongolica), and larch in the northeast of China. We measured wood density loss, cellulose, and lignin concentrations, analyzed microbial community composition, and assessed the physical and chemical properties of woodland soils. Our findings reveal that larch stumps and coarse roots experienced the most rapid decomposition within birch reforestation areas, exhibiting significant density loss in stumps (33.84%) and coarse roots (43.68%). Bacterial diversity on larch stumps and coarse roots was highest in birch reforestation, with dominant phyla including Proteobacteria, Actinobacteriota, and Bacteroidota. Fungal diversity was also highest in birch reforestation, with Ascomycota as the dominant phylum in larch stumps and coarse roots. Furthermore, a mantel test analysis indicated that soil pH and temperature were significant factors in wood decomposition which affected microbial communities. This suggests that the choice of the reforestation tree species affects the decomposition of stumps and coarse roots by affecting soil properties and wood microbial communities. Understanding this process is vital for refining carbon balance evaluations, and enhancing ecosystem-level carbon modeling.

Non-structural carbohydrate dynamics of Pinus yunnanensis seedlings under drought stress and re-watering

Non-structural carbohydrates (NSC) are an important “buffer” for maintaining plant physiological functions under drought conditions; however, our understanding of the dynamics of NSC at the organ level during sustained drought of varying intensities and re-watering remains poor. In this study, two-year-old Pinus yunnanensis seedlings were subjected to drought and re-watering trials. Plants were subjected to three drought intensities (light drought, moderate drought, and severe drought) as well as control conditions (suitable moisture) for 51 days, including 30 days of drought followed by 21 days of re-watering for drought-treated seedlings, to study the dynamics of NSC in the leaves, stems, coarse roots, and fine roots. Changes in the distribution of NSC concentrations in the organ of P. yunnanensis seedlings under drought stress varied; in the early drought stages, the drought resistance of P. yunnanensis seedlings was enhanced by increasing soluble sugar concentrations; in later stages of drought, the stored starch in organs, stems, and coarse roots was consumed. Drought inhibited the growth of P. yunnanensis seedlings, but the maximum limit of drought tolerance was not reached under the different drought treatments after 30 days. P. yunnanensis seedlings in all treatment groups resumed growth after re-watering, and the growth of seedlings was actually promoted during re-watering in the moderate drought treatment group, indicating that drought induced the compensatory growth of seedlings. The growth of P. yunnanensis seedlings during re-watering was inhibited in the severe drought treatment group, and NSC continued to be regulated in seedlings in this group. Given that P. yunnanensis seedlings maintain growth through the consumption of coarse root starch in the late stages of drought, seedlings with a larger root-to-shoot ratio should be selected for cultivation in actual production. Based on our findings, exposure to moderate drought stress can enhance the drought tolerance of P. yunnanensis seedlings and promote the compensatory growth of seedlings.

The Response of Endogenous ABA and Soluble Sugars of Platycladus orientalis to Drought and Post-Drought Rehydration.

To uncover the internal mechanisms of various drought stress intensities affecting the soluble sugar content in organs and its regulation by endogenous abscisic acid (ABA), we selected the saplings of Platycladus orientalis, a typical tree species in the Beijing area, as our research subject. We investigated the correlation between tree soluble sugars and endogenous ABA in the organs (comprised of leaf, branch, stem, coarse root, and fine root) under two water treatments. One water treatment was defined as T1, which stopped watering until the potted soil volumetric water content (SWC) reached the wilting coefficient and then rewatered the sapling. The other water treatment, named T2, replenished 95% of the total water loss of one potted sapling every day and irrigated the above-mentioned sapling after its SWC reached the wilt coefficients. The results revealed that (1) the photosynthetic physiological parameters of P. orientalis were significantly reduced (p < 0.05) under fast and slow drought processes. The photosynthetic physiological parameters of P. orientalis in the fast drought-rehydration treatment group recovered faster relative to the slow drought-rehydration treatment group. (2) The fast and slow drought treatments significantly (p < 0.05) increased the ABA and soluble sugar contents in all organs. The roots of the P. orientalis exhibited higher sensitivity in ABA and soluble sugar content to changes in soil moisture dynamics compared to other organs. (3) ABA and soluble sugar content of P. orientalis showed a significant positive correlation (p < 0.05) under fast and slow drought conditions. During the rehydration stage, the two were significantly correlated in the T2 treatment (p < 0.05). In summary, soil drought rhythms significantly affected the photosynthetic parameters, organ ABA, and soluble sugar content of P. orientalis. This study elucidates the adaptive mechanisms of P. orientalis plants to drought and rehydration under the above-mentioned two water drought treatments, offering theoretical insights for selecting and cultivating drought-tolerant tree species.

Soil fertility as a mediator of interactions between an introduced specialist beetle and a native generalist nematode on an exotic invasive plant and its native congener

Abstract Invasive plants are often attacked by both introduced specialist and native generalist natural enemies in new ranges. Soil fertility can potentially alter the interactions of these natural enemies with native versus invasive plants in ways that have largely unexplored implications for biological invasions and biological control. A common garden experiment was conducted to compare the performance of an introduced specialist flea beetle, Agasicles hygrophila, and/or a native generalist nematode, Meloidogyne incognita, on invasive alligator weed, Alternanthera philoxeroides, and its native congener sessile joyweed, Alternanthera sessilis, under different levels of soil nitrogen (N) and phosphorus (P). At a relatively low or moderate N and P levels, the flea beetle and the nematodes were not significantly affected by each other. Under these conditions, alligator weed responded plastically by producing more branches and biomass, as well as longer stolons, in response to attack by the flea beetle and/or the nematode, compared to sessile joyweed responses to similar levels of damage. However, under a relatively high N and P levels, nematode infestations significantly reduced flea beetle damage on alligator weed, resulting in significantly greater above‐ and below‐ground biomass and longer stolons than plants without herbivory. In contrast, beetle herbivory significantly increased the level of nematode infestations on sessile joyweed, resulting in significantly fewer fine and coarse roots, and lower above‐ and below‐ground biomass compared to plants without herbivory. Synthesis and applications. Our findings illustrate the importance of soil fertility in mediating interactions between specialist biocontrol agents and native generalists on native versus invasive plants. High phenotypic plasticity seems to be an important attribute that contributes to the success of invasive plants like alligator weed in relatively nutrient‐poor environments. However, nutrient‐rich environments could potentially confer greater growth benefits on invasive plants than on native ones by changing herbivore–herbivore interactions on plants differently. There is a great need to fully investigate the direct and indirect interactions between biocontrol agents and generalists across food webs following classical biocontrol releases. Nutrient measurements of both soil and water bodies should also be incorporated into all stages of biocontrol programmes.

Searching for mechanisms driving root pressure in Zea mays—a transcriptomic approach

While there are many theories and a variety of innovative datasets contributing to our understanding of the mechanism generating root pressure in vascular plants, we are still unable to produce a specific cellular mechanism for any species. To discover these mechanisms, we used RNA-Seq to explore differentially expressed genes in three different tissues between individual Zea mays plants expressing root pressure and those producing none. Working from the perspective that roots cells are utililizing a combination of osmotic exudation and hydraulic pressure mechanisms to generate positively-pressured flow of water into the xylem from the soil, we hypothesized that differential expression analysis would yield candidate genes coding for membrane transporters, ion channels, ATPases, and hormones with clear relevance to root pressure generation. In basal stem and coarse root tissue, we observed these classes of differentially expressed genes and more, including a strong cytoskeletal remodeling response. Fine roots displayed remarkably little differential expression relevant to root pressure, leading us to conclude that they either do not contribute to root pressure generation or are constitutively expressing root pressure mechanisms regardless of soil water content.

A systematic review of studies on fine and coarse root traits measurement: towards the enhancement of urban forests monitoring and management

The analysis of fine and coarse roots’ functional traits has the potential to reveal the performance of the root system, which is pivotal in tree growth, development, and failure in both natural and urban forest ecosystems. Furthermore, root traits may be a powerful indicator of tree resilience mechanisms. However, due to the inherent difficulties in measuring ‘the hidden half,’ and despite the recent advancements, the relationships among root functional traits and biotic and abiotic drivers still suffer from a lack of information. Thus, our study aimed to evidence knowledge milestones and gaps and to categorize, discuss, and suggest future directions for effective experimental designs in fine and coarse root studies. To this end, we conducted a systematic literature review supported by backward manual referencing based on 55 root functional traits and 136 plant species potentially suitable for afforestation and reforestation of natural and urban forest ecosystems. The majority of the 168 papers on fine and coarse root studies selected in our review focused predominantly on European natural contexts for a few plant species, such as Fagus sylvatica, Picea abies, Pinus sylvestris, and Pinus cembra, and root functional traits such as standing biomass, phenology production, turnover rate, and non-structural carbohydrates (NSC). Additionally, the analyzed studies frequently lack information and uniformity in experimental designs, measurements, and statistical analysis, highlighting the difficult integration and comparison of outcomes derived from different experiments and sites. Moreover, no information has been detected in selected literature about urban forest ecosystems, while most of the studies focus on natural forests. These biases observed during our literature analysis led us to give key indications for future experiment designs with fine and coarse roots involved, which may contribute to the building up of common protocols to boost the monitoring, managing, and planning of afforestation and reforestation projects.

Belowground morphology as a clue for plant response to disturbance and productivity in a temperate flora.

Plants possess a large variety of nonacquisitive belowground organs, such as rhizomes, tubers, bulbs, and coarse roots. These organs determine a whole set of functions that are decisive in coping with climate, productivity, disturbance, and biotic interactions, and have been hypothesized to affect plant distribution along environmental gradients. We assembled data on belowground organ morphology for 1712 species from Central Europe and tested these hypotheses by quantifying relationships between belowground morphologies and species optima along ecological gradients related to productivity and disturbance. Furthermore, we linked these data with species co-occurrence in 30 115 vegetation plots from the Czech Republic to determine relationships between belowground organ diversity and these gradients. The strongest gradients determining belowground organ distribution were disturbance severity and frequency, light, and moisture. Nonclonal perennials and annuals occupy much smaller parts of the total environmental space than major types of clonal plants. Forest habitats had the highest diversity of co-occurring belowground morphologies; in other habitats, the diversity of belowground morphologies was generally lower than the random expectation. Our work shows that nonacquisitive belowground organs may be partly responsible for plant environmental niches. This adds a new dimension to the plant trait spectrum, currently based on acquisitive traits (leaves and fine roots) only.

Estimates of N accumulated below-ground by grain legumes derived using leaf or stem 15N-feeding: in search of a practical method for potential use at remote field locations

Background and aimsBelow-ground (BG) N of N2 fixing grain legumes is an important N input to farming systems, likely underestimated as N solely in coarse roots. 15N methodology can improve measures of BG N accumulation. Our objective was to identify a 15N method for potential use at remote field sites. We hypothesised that method and frequency of 15N feeding may result in different estimates of BG N.MethodsGlasshouse-grown grain legumes, leaf or stem fed 15N once or twice, were sampled three weeks after feed and at physiological maturity. Three BG fractions were isolated using 2 mm sieving; recovered cleaned roots>2 mm, unrecovered roots >2 mm remaining on sieve with adhering soil, and bulk soil that passed through sieve along with fine roots <2 mm. Fractions were measured for N/15N to estimate BGN. Inorganic, total soluble organic and microbial N/15N were also assessed for bulk soil.ResultsEstimates of BG N were not influenced by method or frequency of 15N feeding. Recovered root N was 33–55% of estimated plant BG N at physiological maturity. Low amounts of fed 15N detected as inorganic or soluble organic N (0.1–0.7%) and microbial biomass N (0.2–2.5%) were attributed to rhizodeposition. A large proportion of fed 15N in bulk soil (51–67%) was present as ‘insoluble’ N attributed to fine roots.ConclusionsA single 15N stem-feeding at remote field sites should suffice to provide a measure of BG N larger than that N measured in recovered roots on a 2 mm sieve. Little evidence for direct leakage into soil labile N pools of highly labelled 15N post-feed.