Plasticity Of Root Traits Research Articles

Changes in the degree of lateral root trait plasticity and trade-offs of maize under long-term no tillage.

While no tillage (NT) can significantly influence soil structure stratification compared to conventional tillage (CT), a comprehensive understanding of the degree of root trait plasticity and trade-offs of lateral roots of crops at various growth stages along a deep soil profile in response to NT remains elusive. This knowledge gap is important for understanding soil resource acquisition strategies and yield of crops. We systematically investigated the traits of lateral roots at jointing and flowering stages in a long-term (12 years) experiment in Northeast China where maize (Zea mays) has been continuously planted under CT and NT with or without maize residue mulch on soil surface. We also measured soil penetration resistance and bulk density. Soil penetration resistance was reduced at the jointing stage, and was increased at the flowering stage under NT especially at a depth of 10 - 40 cm. Root length density decreased under NT across the two growth stages by on average 22%. In contrast, specific root length and diameter showed greater plasticity, ranging from -14% to 20% and from -11% to 8%, respectively, relative to those under CT. These responses could be attributed to changes in root length proportions with different diameters associated with differences in soil penetration resistance between tillage practices. The negative relationships between root traits were stronger under CT than NT, and became weaker from the jointing stage to the flowering stage. To the best of our knowledge, for the first time, our study provides empirical evidence for pivotal root trait plasticity and trade-offs across growth stages as key indicators of changes in soil structure and resources in response to NT. These insights contribute to a better understanding of soil resource acquisition strategies of crops under NT.

Intraspecific competition hinders drought recovery in a resident but not in its range-expanding congener plant independent of mycorrhizal symbiosis

Background and aimsUnderstanding biotic interactions within plant populations and with their symbiotic partners is crucial for elucidating plant responses to drought. While many studies have highlighted the importance of intraspecific plant or mutualistic fungal interactions in predicting drought responses, we know little about the combined effects of these two interactions on the recovery of plants after drought.MethodsWe conducted an experiment to study the recovery after an extreme drought event of a native European plant species (Centaurea jacea) and its range-expanding congener (Centaurea stoebe), across a gradient of plant density and in association with an AM fungal species (Rhizophagus irregularis).ResultsOur results showed strong intraspecific competition in C. jacea, which constrained their post-drought recovery. We further found that AM fungi constrained root biomass recovery of C. jacea after drought under high intraspecific competition. The post-drought recovery in C. stoebe was high potentially due to its greater plasticity in the root diameter under drought conditions.ConclusionStrong intraspecific competition can constrain recovery in plants like C. jacea with lesser root trait plasticity after drought, independent of mycorrhizal symbiosis.

Response of yield, root traits and plasticity of nitrogen-efficient cultivars of drip-irrigated rice to a nitrogen environment

The response of drip-irrigated rice physiological traits to water and fertilisers has been widely studied. However, the responses of yield, root traits and their plasticity to the nitrogen environment in different nitrogen-efficient cultivars are not fully understood. An experiment was conducted from 2020-2022 with high nitrogen efficient (high-NUE) cultivars (T-43) and low-NUE cultivars (LX-3), and four nitrogen levels (0, 150, 300, and 450 kg ha-1) under drip irrigation in large fields were used. The aim was to study the relationship between root morphology, conformation, biomass, and endogenous hormone content and yield and nitrogen use efficiency. The results showed the following: 1) Under the same N application rate, compared with LX-3, T-43’s yield, N partial factor productivity (PFP), fine root length density (FRLD), shoot dry weight (SDW), root indole-3-acetic acid (IAA), and root zeatin and zeatin riboside (Z+ZR) were significantly increased by 11.4-18.9%, 11.3-13.5%, 11.6-15.7%, 9.9-31.1%, 6.1-48.1%, and 22.8-73.6%, respectively, while the root-shoot ratio (RSR) and root abscisic acid (ABA) were significantly decreased (P<0.05). 2) Nitrogen significantly increased rice root morphological indexes and endogenous hormone contents (P<0.05). Compared to N0, yield, root length density (RLD), surface area density (SAD), Root volume density (RVD), and root endogenous hormones (IAA, Z+ZR) were significantly increased in the 2 cultivars under N2 by 61.6-71.6%, 64.2-74.0%, 69.9-105.6%, 6.67-9.91%, 54.0-67.8%, and 51.4-58.9%, respectively. Compared with N3, the PFP and N agronomic efficiency (NAE) of nitrogen fertiliser under N2 increased by 52.3-62.4% and 39.2-63.0%, respectively. 3) The response of root trait plasticity to the N environment significantly differed (P<0.05). Compared with LX-3, T-43 showed a longer root length and larger specific surface area, which is a strategy for adapting to changes in the nutrient environment. For rice cultivars with high-NUE, the root-shoot ratio was optimised by increasing the FRLD, root distribution in upper soil layers, and root endogenous hormones (IAA, Z+ZR) under suitable nitrogen conditions (N2). An efficient nutrient acquisition strategy can occur through root plasticity, leading to increased yield and NUE.

Changes in crop trait plasticity with domestication history: Management practices matter.

Crop domestication has led to the development of distinct trait syndromes, a series of constrained plant trait trade-offs to maximize yield in high-input agricultural environments, and potentially constrained trait plasticity. Yet, with the ongoing transition to organic and diversified agroecosystems, which create more heterogeneous nutrient availability, this constrained plasticity, especially in root functional traits, may be undesirable for nutrient acquisition. Such agricultural systems require a nuanced understanding of the soil-crop continuum under organic amendments and with intercropping, and the role crop genetic resources play in governing nutrient management and design. In this study, we use a functional traits lens to determine if crops with a range of domestication histories express different functional trait plasticity and how this expression changes with soil amendments and intercropping. We utilize a common garden experiment including five wheat (Triticum aestivum) varietals with a range of domestication histories planted in a factorial combination with amendment type (organic and inorganic) and cropping design (monoculture or intercropped with soybean). We use bivariate, multivariate and trait space analyses to quantify trait variation and plasticity in five leaf and five root functional traits. Almost all leaf and root traits varied among varieties. Yet, amendment type was nearly inconsequential for explaining trait expression across varieties. However, intercropping was linked to significant differences in root acquisitive strategies, regardless of the varietals' distinct history. Our findings show substantial leaf and root trait plasticity, with roots expressing greater trait space occupation with domestication, but also the strong role of management in crop trait expression. We underscore the utility of a functional trait-based approach to understand plant-soil dynamics with organic amendments, as well as the role of crop genetic histories in the successful transition to low-input and diversified agroecosystems.

Root plasticity benefits a global invasive species in eutrophic coastal wetlands

Abstract Invasive species usually benefit more than native species from increases in nutrient availability. Phenotypic plasticity in above‐ground traits has often been used to explain the superiority of invasive species in response to increased nutrient availability. However, it remains largely unclear whether and how root trait plasticity predicts the ascendancy of invasive plants following nutrient enrichment. Using a 3‐year field nitrogen (N) enrichment experiment, we evaluated the effect of N enrichment on the root traits and growth performance of a globally invasive cordgrass, Spartina alterniflora, and a co‐occurring native plant, Phragmites australis. We found that S. alterniflora exhibited high plasticity in root traits in response to N enrichment, whereas the root traits of P. australis largely remained unresponsive to fertilization. Specifically, in response to N enrichment, S. alterniflora decreased soil exploitation with a lower length ratio of lateral to adventitious roots. However, the root traits of S. alterniflora shifted to be more acquisitive under N enrichment with higher root N concentrations and lower root tissue density. Moreover, there were a series of anatomical adjustments in the adventitious roots of S. alterniflora in response to N enrichment, such as a thicker diameter, lower living cortex‐to‐stele ratio and higher xylem‐to‐root area ratio. These plastic adjustments in root traits jointly resulted in fast nutrient uptake and transportation in S. alterniflora, boosting its above‐ground productivity under fertile N conditions. Our study demonstrated that greater plasticity in root traits enables a globally successful invasive species to take advantages of increased nutrient availability, potentially increasing its invasiveness. We suggest that consideration of root traits can improve our understanding of below‐ground mechanisms underlying invasion under global nutrient enrichment. Read the free Plain Language Summary for this article on the Journal blog.

Phenotypic plasticity and genetic diversity shed light on endemism of rare Boechera perstellata and its potential vulnerability to climate warming.

The rapid pace of contemporary environmental change puts many species at risk, especially rare species constrained by limited capacity to adapt or migrate due to low genetic diversity and/or fitness. But the ability to acclimate can provide another way to persist through change. We compared the capacity of rare Boechera perstellata (Braun's rockcress) and widespread B. laevigata to acclimate to change. We investigated the phenotypic plasticity of growth, biomass allocation, and leaf morphology of individuals of B. perstellata and B. laevigata propagated from seed collected from several populations throughout their ranges in a growth chamber experiment to assess their capacity to acclimate. Concurrently, we assessed the genetic diversity of sampled populations using 17 microsatellite loci to assess evolutionary potential. Plasticity was limited in both rare B. perstellata and widespread B. laevigata, but differences in the plasticity of root traits between species suggest that B. perstellata may have less capacity to acclimate to change. In contrast to its widespread congener, B. perstellata exhibited no plasticity in response to temperature and weaker plastic responses to water availability. As expected, B. perstellata also had lower levels of observed heterozygosity than B. laevigata at the species level, but population-level trends in diversity measures were inconsistent due to high heterogeneity among B. laevigata populations. Overall, the ability of phenotypic plasticity to broadly explain the rarity of B. perstellata versus commonness of B. laevigata is limited. However, some contextual aspects of our plasticity findings compared with its relatively low genetic variability may shed light on the narrow range and habitat associations of B. perstellata and suggest its vulnerability to climate warming due to acclimatory and evolutionary constraints.

Contrasting patterns of community-weighted mean traits and functional diversity in driving grassland productivity changes under N and P addition.

Fertilization could influence ecosystem structure and functioning through species turnover (ST) and intraspecific trait variation (ITV), especially in nutrient limited ecosystems. To quantify the relative importance of ITV and ST in driving community functional structure and productivity changes under nitrogen (N) and phosphorous (P) addition in semiarid grasslands. In this regard, we conducted a four-year fertilizer addition experiment in a semiarid grassland on the Loess Plateau, China. We examined how fertilization affects species-level leaf and root trait plasticity to evaluate the ability of plants to manifest different levels of traits in response to different N and P addition. Also, we assessed how ITV or ST dominated community-weighted mean (CWM) traits and functional diversity variations and evaluated their effects on grassland productivity. The results showed that the patterns of plasticity varied greatly among different plant species, and leaf and root traits showed coordinated variations following fertilization. Increasing the level of N and P increased CWM_specific leaf area (CWM_SLA), CWM_leaf N concentration (CWM_LN) and CWM_maximum plant height (CWM_Hmax) and ITV predominate these CWM traits variations. As a results, increased CWM_Hmax, CWM_LN and CWM_SLA positively influenced grassland productivity. In contrast, functional divergence decreased with increasing N and P and showed negative relationships with grassland productivity. Our results emphasized that CWM traits and functional diversity contrastingly drive changes in grassland productivity under N and P addition.

A novel proxy to examine interspecific phosphorus facilitation between plant species.

Resource complementarity can contribute to enhanced ecosystem functioning in diverse plant communities, but the role of facilitation in the enhanced complementarity is poorly understood. Here, we use leaf manganese concentration ([Mn]) as a proxy for rhizosheath carboxylate concentration to explore novel mechanisms of complementarity mediated by phosphorus (P) facilitation. In pot experiments, we showed that mixtures involving Carex korshinskyi, an efficient P-mobilizing species, exhibited greater biomass and relative complementarity effect than combinations without C. korshinskyi on P-deficient soils. Compared with monocultures, leaf [Mn] and [P] of species that are inefficient at P mobilization increased by 27% and 21% when grown with C. korshinskyi (i.e. interspecific P facilitation via carboxylates) rather than next to another inefficient P-mobilizing species. This experimental result was supported by a meta-analysis including a range of efficient P-mobilizing species. Phosphorus facilitation enhanced the relative complementarity effect in low-P environments, related to a greater change in several facilitated species of their root morphological traits relative to those in monoculture. Using leaf [Mn] as a proxy, we highlight a vital mechanism of interspecific P facilitation via belowground processes and provide evidence for the pivotal role of P facilitation mediated by the plasticity of root traits in biodiversity research.

Drought Eliminates the Difference in Root Trait Plasticity and Mycorrhizal Responsiveness of Two Semiarid Grassland Species with Contrasting Root System.

Root traits and arbuscular mycorrhizal (AM) fungi are important in determining the access of plants to soil resources. However, whether plants with different root systems (i.e., taproot vs. fibrous-root) exhibit different root trait plasticity and mycorrhizal responsiveness under drought remains largely unexplored. Tap-rooted Lespedeza davurica and fibrous-rooted Stipa bungeana were grown in monocultures in sterilized and live soils, followed by a drought treatment. Biomass, root traits, root colonization by AM fungi, and nutrient availability were evaluated. Drought decreased biomass and root diameter but increased the root:shoot ratio (RSR), specific root length (SRL), soil NO3--N, and available P for the two species. Under control and drought conditions, soil sterilization significantly increased the RSR, SRL, and soil NO3--N for L. davurica, but this only occurs under drought condition for S. bungeana. Soil sterilization significantly reduced AM fungal root colonization of both species, but drought significantly increased it in live soil. In water-abundant conditions, tap-rooted L. davurica may depend more on AM fungi than fibrous-rooted S. bungeana; however, under drought conditions, AM fungi are of equal importance in favoring both plant species to forage soil resources. These findings provide new insights for understanding the resource utilization strategies under climate change.

Belowground carbon allocation, root trait plasticity, and productivity during drought and warming in a pasture grass.

Sustaining grassland production in a changing climate requires an understanding of plant adaptation strategies, including trait plasticity under warmer and drier conditions. However, our knowledge to date disproportionately relies on aboveground responses, despite the importance of belowground traits in maintaining aboveground growth, especially in grazed systems. We subjected a perennial pasture grass, Festuca arundinacea, to year-round warming (+3 °C) and cool-season drought (60% rainfall reduction) in a factorial field experiment to test the hypotheses that: (i) drought and warming increase carbon allocation belowground and shift root traits towards greater resource acquisition and (ii) increased belowground carbon reserves support post-drought aboveground recovery. Drought and warming reduced plant production and biomass allocation belowground. Drought increased specific root length and reduced root diameter in warmed plots but increased root starch concentrations under ambient temperature. Higher diameter and soluble sugar concentrations of roots and starch storage in crowns explained aboveground production under climate extremes. However, the lack of association between post-drought aboveground biomass and belowground carbon and nitrogen reserves contrasted with our predictions. These findings demonstrate that root trait plasticity and belowground carbon reserves play a key role in aboveground production during climate stress, helping predict pasture responses and inform management decisions under future climates.

Precipitation predictability affects intra- and trans-generational plasticity and causes differential selection on root traits of Papaver rhoeas.

Climate forecasts show that in many regions the temporal distribution of precipitation events will become less predictable. Root traits may play key roles in dealing with changes in precipitation predictability, but their functional plastic responses, including transgenerational processes, are scarcely known. We investigated root trait plasticity of Papaver rhoeas with respect to higher versus lower intra-seasonal and inter-seasonal precipitation predictability (i.e., the degree of temporal autocorrelation among precipitation events) during a four-year outdoor multi-generation experiment. We first tested how the simulated predictability regimes affected intra-generational plasticity of root traits and allocation strategies of the ancestors, and investigated the selective forces acting on them. Second, we exposed three descendant generations to the same predictability regime experienced by their mothers or to a different one. We then investigated whether high inter-generational predictability causes root trait differentiation, whether transgenerational root plasticity existed and whether it was affected by the different predictability treatments. We found that the number of secondary roots, root biomass and root allocation strategies of ancestors were affected by changes in precipitation predictability, in line with intra-generational plasticity. Lower predictability induced a root response, possibly reflecting a fast-acquisitive strategy that increases water absorbance from shallow soil layers. Ancestors' root traits were generally under selection, and the predictability treatments did neither affect the strength nor the direction of selection. Transgenerational effects were detected in root biomass and root weight ratio (RWR). In presence of lower predictability, descendants significantly reduced RWR compared to ancestors, leading to an increase in performance. This points to a change in root allocation in order to maintain or increase the descendants' fitness. Moreover, transgenerational plasticity existed in maximum rooting depth and root biomass, and the less predictable treatment promoted the lowest coefficient of variation among descendants' treatments in five out of six root traits. This shows that the level of maternal predictability determines the variation in the descendants' responses, and suggests that lower phenotypic plasticity evolves in less predictable environments. Overall, our findings show that roots are functional plastic traits that rapidly respond to differences in precipitation predictability, and that the plasticity and adaptation of root traits may crucially determine how climate change will affect plants.

Scions impact biomass allocation and root enzymatic activity of rootstocks in grafted melon and watermelon plants.

Vegetable grafting is increasingly recognized as an effective and sustainable plant production alternative. Grafted plants usually show increased uptake of water and minerals compared with self-rooted plants, mostly thought a consequence of the vigorous rootstocks selected. However, while studies frequently addressed the effects of rootstocks on the performance of scions, knowledge on the influences of scions on biomass allocation, morphology, and metabolic activity of roots is rare. In particular, the plasticity of root traits affecting resource acquisition and its efficiency remains poorly understood. Two different rootstock species, Cucurbita maxima × Cucurbita moschata and Lagenaria siceraria, were grafted in combination with melon (Cucumis melo) and watermelon (Citrullus lanatus). Self-grafted rootstocks were used as control. Plant biomass and root traits were determined after destructive harvesting 30 and/or 60 days after grafting. Traits included biomass allocation, leaf and root morphology, potential activities of four extracellular enzymes on root tips and basal root segments, and root respiration. Successfully grafted scions increase the ratio of root to whole plant dry matter (RMF), and increased ratios of root length to whole plant dry matter (RLR) and to plant leaf area (RL : LA). In contrast, morphological root traits such as diameter, tissue density, and specific root length remain surprisingly stable, and thus scion-induced changes of those traits may only play a minor role for the beneficial effects of grafting in Cucurbitaceae. Incompatibility in melon/L. siceraria grafts, however, was likely responsible for the reduced root growth in combination with clear changes in root morphological traits. Reduced root respiration rates seem to be the effects of a non-compatible rootstock–scion combination rather than an active, C-efficiency increasing acclimation. In contrast, heterografts with melon and watermelon frequently resulted in root-stock-specific, often enhanced potential enzymatic activities of acid phosphatase, β-glucosidase, leucine-amino-peptidase, and N-acetyl-glucosaminidase both at root tips and basal parts of lateral roots—presenting a potential and complementary mechanism of grafted plants to enhance nutrient foraging. The studied melon and watermelon scions may thus increase the nutrient foraging capacity of grafted plants by fostering the relative allocation of C to the root system, and enhancing the extracellular enzymatic activities governed by roots or their rhizobiome.

Many paths to one goal: Identifying integrated rice root phenotypes for diverse drought environments.

Drought is a major source of yield loss in the production of rice (Oryza sativa L.), and cultivars that maintain yield under drought across environments and drought stress scenarios are urgently needed. Root phenotypes directly affect water interception and uptake, so plants with root systems optimized for water uptake under drought would likely exhibit reduced yield loss. Deeper nodal roots that have a low metabolic cost per length (i.e., cheaper roots) via smaller root diameter and/or more aerenchyma and that transport water efficiently through smaller diameter metaxylem vessels may be beneficial during drought. Subsets of the Rice Diversity Panel 1 and Azucena × IR64 recombinant inbred lines were grown in two greenhouse and two rainout shelter experiments under drought stress to assess their shoot, root anatomical, and root architectural phenotypes. Root traits and root trait plasticity in response to drought varied with genotype and environment. The best-performing groups in the rainout shelter experiments had less plasticity of living tissue area in nodal roots than the worst performing groups. Root traits under drought were partitioned into similar groups or clusters via the partitioning-around-medoids algorithm, and this revealed two favorable integrated root phenotypes common within and across environments. One favorable integrated phenotype exhibited many, deep nodal roots with larger root cross-sectional area and more aerenchyma, while the other favorable phenotype exhibited many, deep nodal roots with small root cross-sectional area and small metaxylem vessels. Deeper roots with high theoretical axial hydraulic conductance combined with reduced root metabolic cost contributed to greater shoot biomass under drought. These results reflect how some root anatomical and architectural phenes work in concert as integrated phenotypes to influence the performance of plant under drought stress. Multiple integrated root phenotypes are therefore recommended to be selected in breeding programs for improving rice yield across diverse environments and drought scenarios.

Plasticity of root traits in a seedling apple intercropping system driven by drought stress on the Loess Plateau of China

Plasticity of root traits in a seedling apple intercropping system driven by drought stress on the Loess Plateau of China

Root trait shifts towards an avoidance strategy promote productivity and recovery in C3 and C4 pasture grasses under drought

Abstract Plant species show a broad spectrum of plasticity in their covarying root traits in response to soil water limitation ranging from no change to shifts towards traits that enhance water and nutrient acquisition. Knowledge of root trait correlations and associated trait plasticity under drought is crucial to sustaining grassland production, including rangelands and pastures, under future, drier climates. Here, we investigated below‐ground responses to drought in four C3 and three C4 grasses and whether these explain above‐ground responses during extreme cool‐season drought and post‐drought recovery in a well‐replicated field experiment. We hypothesised that (a) C3 and C4 functional groups differ in their below‐ground trait responses to drought: C3 species shift their traits in line with a drought avoidance strategy and C4 species shift towards drought tolerance strategies; (b) post‐drought recovery is associated with below‐ground carbon reserves in both functional groups. Root traits in the C3 functional group differed from C4 by having higher values for specific root length, nitrogen and soluble sugar concentrations, while C4 root traits were associated with higher mean diameter, tissue density and starch concentrations. Drought‐induced plasticity in root traits in both functional groups was evidenced by increased values for specific root length, soluble sugars and nitrogen concentrations, and reduced values for tissue density, which we interpret as a drought avoidance strategy. Increasing root soluble sugars in C3 and C4 grasses and lower root tissue density in C4 species under drought were associated with greater above‐ground productivity. Above‐ground biomass recovery post‐drought was predicted by root and crown soluble sugar concentrations and root longevity across both plant functional groups. These findings highlight the importance of understanding links between root trait plasticity and plant productivity during and following drought for predicting plant species' responses to changes in a future climate. Read the free Plain Language Summary for this article on the Journal blog.

Root hairs matter at field scale for maize shoot growth and nutrient uptake, but root trait plasticity is primarily triggered by texture and drought

AimsRoot hairs are important for uptake, especially for nutrients with low mobility in soils with high sorption capacity. Mutants with defective root hairs are expected to have lower nutrient uptake, unless they compensate with more root growth. Since root hairs can also contribute to the plant's water uptake their importance could change over the course of a growing season. It was our objective to investigate the role of root hairs under field conditions.MethodsThe root hair mutant rth3 of Zea mays and the corresponding wild-type were grown for two years under field conditions on sand and loam.ResultsShoot growth and P and K uptake of the plants were promoted by the presence of hairs at all growth stages. Differences between genotypes were greater on loam than on sand until tassel emergence, presumably as additional exploitation by hairs is more relevant in loam. Compensation for the absence of root hairs by increased root growth was not observed in absolute terms. The root to shoot ratio was higher for rth3 than for wild-type. Root traits showed high plasticity in response to texture, the most salient being a greater mean root diameter in sand, irrespective of genotype. The mechanism causing the increase in mean root diameter is still unknown. Root length density was higher in sand, which can be explained by a greater need for exploration than exploitation in this substrate.ConclusionThe role of hairs for nutrient uptake could be confirmed under field conditions. The large impact of texture on root growth and consequences for carbon balance require further investigations.

Drought Impacts on Tree Root Traits Are Linked to Their Decomposability and Net Carbon Release

Root trait plasticity can facilitate plant adjustment to water shortages, but the impact of altered traits on belowground carbon (C) cycling is mostly unknown. While drought and nutrient availability can alter root morphological and chemical traits that may affect root decomposition, direct assessments of drought mediated changes on decomposability are not available. We exposed four tree species contrasting in drought stress tolerance and root traits to three dry-down and recovery periods (over 5 months after 11 months of growth in well-watered conditions) under high and low nutrient conditions. We then assessed early stage root decomposability in relation to their morphology and chemistry as well as implications for CO2 release when accounting for effects on root biomass. While each species showed a unique set of responses, drought generally reduced root diameter and increased nitrogen concentration. We found limited evidence that morphological responses to drought were counteracted by high nutrient supply. Results indicated that the degree of association between morphological and nutrient root trait responses to drought and decomposability varied with different species. However, across these contrasting woody species, drought-induced increases in nitrogen and phosphorus concentrations were associated with drought-induced increases in early stage root decomposability. When accounting for changes in root biomass, estimated overall C loss through root decomposition increased with drought stress. Our experimental results demonstrate that changes in tree root traits with drought can enhance C loss via root decomposition, and with other factors being equal, drought may potentially contribute to a positive feedback to climate change. Our findings contribute empirical evidence to help disentangle the multiple factors involved in root contribution to C balances at the ecosystem level.

Belowground facilitation and trait matching: two or three to tango?

High biodiversity increases ecosystem functions; however, belowground facilitation remains poorly understood in this context. Here, we explore mechanisms that operate via 'giving-receiving feedbacks' for belowground facilitation. These include direct effects via root exudates, signals, and root trait plasticity, and indirect biotic facilitation via the effects of root exudates on soil biota and feedback from biota to plants. We then highlight that these two- or three-way mechanisms must affect biodiversity-ecosystem function relationships via specific combinations of matching traits. To tango requires a powerful affinity and harmony between well-matched partners, and such matches link belowground facilitation to the effect of biodiversity on function. Such matching underpins applications in intercropping, forestry, and pasture systems, in which diversity contributes to greater productivity and sustainability.

Wheat root trait plasticity, nutrient acquisition and growth responses are dependent on specific arbuscular mycorrhizal fungus and plant genotype interactions

This study aimed to examine how interactions at both plant genotype and arbuscular mycorrhizal fungus species levels affected the expression of root traits and the subsequent effect on plant nutrition and growth. We used two wheat cultivars with contrasting phosphorus (P) acquisition efficiencies (Tukan and Crac) and two arbuscular mycorrhizal (AM) fungi (Rhizophagus intraradices and Claroideoglomus claroideum). Plant growth, as well as morphological and architectural root traits, were highly dependent on the myco-symbiotic partner in the case of the less P-acquisition efficient cultivar Tukan, with mycorrhizal responses ranging from -45 to 54 % with respect to non-mycorrhizal plants. Meanwhile, these responses were between only -7 and 5 % in the P-acquisition efficient cultivar Crac. The AM fungal species produced contrasting mechanisms in the improvement of plant nutrition and root trait responses. Colonization by R. intraradices increased Ca accumulation, regardless of the cultivar, but reduced root growth on Tukan plants. On the other hand, C. claroideum increased P content in both cultivars, with a concomitant increase in root growth and diffusion-based nutrient acquisition by Tukan. Moreover, plants in symbiosis with R. intraradices showed greater organic acid concentration in their rhizosphere compared to C. claroideum-colonized plants, especially Tukan (24 and 35 % more citrate and oxalate, respectively). Our results suggest that the responses in plant-AM fungal interactions related to nutrient dynamics are highly influenced at the fungus level and also by intra-specific variations in root traits at the genotype level, while growth responses related to improved nutrition depend on plant intrinsic acquisition efficiency.

Plant Nutritional Status Explains the Modifying Effect of Provenance on the Response of Beech Sapling Root Traits to Differences in Soil Nutrient Supply

Forests dominated by beech (Fagus sylvatica L.) cover large parts of Europe where they occupy a broad ecological niche in terms of soil fertility. This indicates a large potential to adapt to different soil conditions over long time periods. Recent changes in tree mineral nutrition across Europe raise the question to what degree beech can acclimate to changing soil conditions in the short term. In this study, we aimed at assessing the plasticity of root traits and rhizosphere properties of young beech trees from populations, that are adapted to either high or low nutrient supply, when growing in soils differing in their fertility. We sampled beech saplings from two forest sites of contrasting nutrient supply, most distinctly in terms of phosphorus. We grew them for two years in rhizoboxes in mineral soil either from their own site or from the other site. We assessed the influence of the factors „plant origin“ and „current soil“ on root traits and rhizosphere properties. Fine root traits related to growth (biomass, length), architecture (branching) and morphology (diameter) responded strongly to the factor “current soil”. Provenance (factor “plant origin”) modified the response. The modifying effect was consistent with an influence of the plant status in those nutrients, which were not in sufficient supply in the soil. An additional genotypic difference in the sensitivity of the beech saplings to different soil nutrient supply could not be excluded. Fine root parameters normalized for length, mass or volume (root tip density and frequency, specific root length and area, root tissue density) did not differ among the treatments. Differences in percentage of mycorrhizal root tips and rhizosphere parameters related to phosphorus mobilization potential (pH, abundance of organic acid anions, phosphatase activity) were small and mainly determined by the “current soil”. Provenance had only a minor modifying effect, possibly due to differences in the ability of the plants to transfer carbon compounds from the shoot to the root and the fungal partner. Our results indicate a high plasticity of young beech trees to adapt their root system to different soil nutrient supply, thereby also taking into account internal nutrient reserves.