Annals of botany最新文献

Background and aims: Root water uptake (RWU) is influenced by rhizosphere conductance and soil-root contact, which vary with soil texture and root structure, including root hairs. Current simplified models often fail to capture the spatial complexity of these interactions in drying soils. The aim of this study was to examine how rhizosphere conductance, soil-root contact and root hairs affect RWU.

Methods: We used an explicit three-dimensional functional-structural model to investigate how root and rhizosphere hydraulics influence the transpiration rate-leaf water potential relationship of two maize (Zea mays) genotypes (with and without root hairs) grown in two contrasting soil textures (loam and sand) during soil drying. The model incorporated rhizosphere resistance in series with radial root resistance, with the latter being influenced by maturation (development of apoplastic barriers with age). It considered two critical processes: (1) the decrease in soil water potential between bulk soil and the soil-root interface; and (2) the extent of soil-root contact.

Key results: The simulations revealed that RWU was highly soil texture specific. In loam, the non-linearity in the transpiration rate-leaf water potential relationship was attributable primarily to localized uptake fluxes and high rhizosphere resistance as soil dried. In sand, however, where soil-root contact was less effective, rhizosphere conductance became a significant limiting factor for RWU, even at relatively higher soil water potential in comparison to loam. Root hairs did not make a significant contribution to rhizosphere conductance, probably owing to the dominant effect of soil-root interaction. Additionally, variations in root hydraulic conductance and its change with root tissue age impacted the accuracy of the model.

Conclusions: The explicit three-dimensional model provides a more precise representation of RWU dynamics by pinpointing exact uptake locations and primary limiting factors and by quantifying the proportion of root surface actively engaged in RWU. This approach offers notable improvements over conventional models for understanding the spatial dynamics of water uptake in different soil environments.

Background and aims: Root axes with greater penetration ability are often considered to be beneficial in hard soils. We hypothesized that maize root phenotypes with greater plasticity (meaning reduced elongation in response to mechanical impedance, i.e. a 'stop signal') have fitness advantages over phenotypes with reduced plasticity (i.e. unimpeded root elongation) in native (virgin, uncultivated) soils, by reallocating root foraging to softer, presumably wetter, soil domains, and that the value of the stop signal reduced with soil cultivation and crop domestication.

Methods: We used OpenSimRoot to simulate native and cultivated soils and evaluated maize root phenotypes with varying axial and lateral root penetration ability in water, nitrogen (N) and impedance regimes associated with Neolithic agriculture.

Key results: The stop signal was advantageous in native soils but was less beneficial in cultivated, irrigated soils. Reduced root foraging in hard, dry topsoil enabled root growth in deeper domains where water is available, resulting in an improved balance of resource expenditure and acquisition. The value of the stop signal declined during crop domestication with the advent of irrigation, which increased water availability in the topsoil. Soil cultivation reduced N availability, while irrigation increased N leaching, resulting in a shift in the fitness landscape, with greater lateral root length (i.e. reduced plasticity) being advantageous by colocalizing root foraging with N availability. The importance of the stop signal is evident in modern high-input systems in which drought is a limiting factor.

Conclusions: Our results support the hypotheses that the reduction of lateral root growth by mechanical impedance is adaptive in native soil, but became less adaptive with soil cultivation and irrigation associated with Neolithic agriculture.

Background and aims: We have abundant knowledge on drought responses of plants or soil microorganisms individually. However, there is a severe lack of knowledge regarding interactions in the plant-soil-microbiome continuum, and specifically root-soil interface traits including the role of root hairs. Here we investigated how water limitation propagates in a plant-soil-microbiome system upon stopping irrigation. We used two Zea mays genotypes [rth3 and its isogenic wild type (WT), B73], differing in root hair formation, to elucidate the effect of rhizosphere extension under water limitation.

Methods: For 22 d, WT and rth3 plants were grown in a climate chamber, with irrigation stopped for drought treatment during the last 7 d. Daily measurements included soil water status, plant evapotranspiration and gas exchange. At harvest, root exudates, shoot relative water content, osmolality and nutrients, root morphological traits and transcriptomics, and soil microbial β-diversity and enzyme activity were determined.

Key results: In line with a larger plant size, drought stress developed more rapidly and the number of differentially expressed genes was higher in the WT compared with rth3. Under water limitation, root exudation rates increased and soil enzyme activities decreased more strongly in the WT rhizosphere. In both genotypes, water level significantly altered microbial β-diversity in the bulk soil, particularly affecting fungi more than bacteria/archaea. The genotype affected only bacteria/archaea and was more pronounced in rhizosphere than in bulk soil.

Conclusions: This interdisciplinary study assessed how a short drought stress manifested in a plant-soil-microbiome system. Water limitation altered microbial (fungal) diversity in distance from the root surface. Genotype-specific stress-induced increases in exudation rates modified microbial activity in root proximity, possibly pointing to root hair functions under water limitation. Less intense drought responses of rth3 were confirmed at all levels of investigation and may be due at least in part to its smaller plant size.

Background and aims: Phosphorus (P)-impoverished soils shape plant adaptation in biodiverse ecosystems worldwide, from Australian heathlands to Amazonian rainforests to southern China's karst regions. While non-mycorrhizal lineages like Proteaceae and Cyperaceae use carboxylate exudation that mobilise P, and are celebrated for such strategies, the mechanisms allowing mycorrhizal Myrtaceae-especially eucalypts-to thrive in these soils without fungal assistance remain unclear. Given Myrtaceae's dominance in P-impoverished Australian ecosystems, a key question arises: How do mycorrhizal plants succeed in P-impoverished environments without relying on fungal symbiosis? We challenge the paradigm that carboxylate-driven P acquisition is exclusive to non-mycorrhizal species.

Methods: Using leaf manganese concentrations ([Mn]) as a proxy for carboxylate exudation, we assessed trait diversification across Myrtaceae genera. We collected leaf and soil samples from 34 species of eucalypt (Angophora, Blakella, Corymbia, Eucalyptus) and other Myrtaceae from 18 sites in south-eastern Australia.

Key results: Our findings reveal consistently high leaf [Mn] in many Myrtaceae, comparable to that in known carboxylate-releasing species, indicating intensive P mining. This suggests convergent evolution of carboxylate exudation in mycorrhizal Myrtaceae, fundamentally reshaping our understanding of nutrient acquisition in symbiotic plants. Significant interspecific variation was observed, with Angophora showing markedly higher [Mn] than Eucalyptus, suggesting divergent P-acquisition strategies within Myrtaceae. Weak phylogenetic signals for leaf [Mn] and [P] in eucalypts imply repeated evolutionary change in these traits, similar to what is known in other Australian species adapted to P scarcity.

Conclusions: By demonstrating carboxylate-driven P mining in mycorrhizal Myrtaceae, we redefine the mechanisms behind their dominance in low-P environments. Trait diversity-linked to variation in carboxylate-mediated P acquisition and plant-soil feedbacks-likely drives niche differentiation and genus-level distribution across south-eastern Australia. Connecting leaf [Mn] to carboxylate-driven P mining advances our understanding of trait evolution in Myrtaceae and provides a framework for predicting plant-soil interactions in P-impoverished ecosystems globally.

Background and aims: Absorptive root traits play important roles in acquisition of water and nutrients from soil by plants. Despite numerous reports on the changes in species dominance under long-term drought in grassland communities, few studies have specifically investigated absorptive root traits of these dominant species in grasslands, especially in alpine grasslands.

Methods: Here, two grass species (Leymus secalinus and Stipa purpurea) differing in their responses to drought were selected from an alpine steppe. A series of absorptive root traits were examined under drought in a 3-year glasshouse experiment.

Key results: We found that drought had no effects on root morphological and architectural traits, whereas root physiological traits and rooting depth differed in their responses to drought. Specifically, drought significantly reduced root respiration and enhanced organ carbon (C) exudation rate, carboxylate exudation rate, acid phosphatase activity and rooting depth of L. secalinus. In particular, L. secalinus released more citrate into the rhizosphere under drought than S. purpurea. In contrast, these root traits of S. purpurea remained relatively unchanged in response to the drought. These differential responses would render L. secalinus more competitive in acquisition of nutrients and water, thus contributing to its dominance in the community under drought. Moreover, root respiration was negatively correlated with organic C exudation rate, carboxylate exudation rate and acid phosphatase activity, indicating a trade-off between root respiration and root exudates to acquire nutrients and water by optimizing C allocation under drought. Additionally, all root traits exhibited two independent dimensions in root economic space for both species under drought.

Conclusions: These results indicate that the plant species with great capacity to acquire water and nutrients in soil by optimizing C allocation under drought will be dominant in the community of the alpine grasslands. These findings provide an important insight into species re-ordering under drought on the Tibetan Plateau.

Background and aims: Wheat (Triticum aestivum L.) is widely grown in regions prone to both drought and flooding conditions. Although root responses to drought and flooding have been extensively studied separately, studies comparing key anatomical root traits in wheat in both conditions side-by-side are rare. We tested the hypothesis that wheat roots respond in a similar manner to both drought and flooding, despite these being contrasting water regimes.

Methods: Two wheat cultivars ('Jackson' and 'Frument') were grown hydroponically in control conditions, drought and flooding, and the responses in plant growth, root morphology, root anatomy, development of apoplastic barriers and their capacity to reduce radial water loss were measured.

Key results: Xylem-to-stele ratio decreased by 33% under water stress compared with control conditions, whereas aerenchyma-to-cortex ratio increased 2.1-fold during both drought and flooding compared with control conditions. Compared with control conditions, lateral root growth was more reduced than adventitious root growth, 86% and 67%, respectively, under both types of water stress. There was comparably stunted root and shoot growth under water stress, and adventitious roots grew slower likewise and to one-third of length compared with control conditions. Our findings did not indicate differences in soil flooding tolerances between the two cultivars.

Conclusions: We conclude that different underlying physical processes during contrasting water regimes, e.g., water limitation during drought and oxygen deficiency during flooding, result in similar root responses, e.g., increased relative aerenchyma area, lignin and suberin deposition in the endodermis, and decreased lateral-to-adventitious root length. Future research should provide a more comprehensive understanding of cross-stress effects on root morphology, anatomy and physiology.

Background and aims: Phosphorus (P) is a crucial macronutrient for plant growth that, despite its abundance in soils, is often a limiting factor in agricultural productivity, particularly for cereals such as wheat. In this study, the response of different wheat genotypes to two different levels of P was evaluated in a large trial encompassing 26 genotypes using two distinct root phenotyping platforms, ALSIA and 4PMI.

Methods: Rhizotubes allowed non-invasive root phenotyping, revealing significant genotypic effects on biomass production and root system traits. Phosphorus acquisition and use efficiency of the wheat genotypes were estimated by using five different metrics.

Key results: A synthetic indicator for agronomic relevance integrating the efficiency metrics was established. Under optimal conditions, after 96 d, P acquisition efficiency (PAE) was inversely correlated with P utilization efficiency (PUE), suggesting an acquisition-use trade-off. Conversely, under low P conditions, both after 27 and 96 days PAE and PUE showed moderate positive correlations, indicating adaptive coordination to improve P utilization under scarcity.

Conclusions: Overall, our findings highlighted the importance of root-target strategies in P efficiency in wheat, providing insights for breeders to enhance P deficiency tolerance in wheat.

Background and aims: Increasing soil salinity is an emerging and potent threat to agricultural crop production. Plant root tissues are the most important place for salt sensing. Thus, root traits associated with salt tolerance are very important. Identification of new root traits might help us to optimize the overall performance of plants under stress.

Methods: An experiment was conducted with eight rice genotypes, and root aerenchymatous gas space, Na+ and K+ concentrations of roots and leaves were measured. Another experiment was performed with four selected rice genotypes based on morphological, physiological, biochemical and molecular traits.

Key results: We identified that root tissue porosity and root aerenchymatous gas space were increased under salt stress, and the induction of these traits was greater in salt-tolerant genotypes (FL478, AC39416A and Rashpanjor) compared with a salt-susceptible genotype (Naveen). Most interestingly, root porosity and aerenchymatous gas space showed a strong correlation with leaf Na+ ion concentration and with leaf and root K+ ion retention. Thereby, it seems that more porous roots can play an important role in Na+ transport and K+ retention in salt-tolerant rice plants. Additionally, we observed relatively higher expression of reactive oxygen species-induced NADPH oxidase (OsNOX5 and OsNOX9) genes, whose function is associated with programmed cell death and formation of lysigenous aerenchyma in rice, in FL478, AC39416A and Rashpanjor compared with Naveen.

Conclusions: Overall, the findings suggest that tolerant and moderately tolerant rice genotypes followed programmed cell death in root cortical tissues that help to restrict upward movement of Na+ and retention of K+ in rice in saline conditions.

Background and aims: Roots and rhizomes are crucial for the adaptation of clonal plants to soil water gradients. Oryza longistaminata, a rhizomatous wild rice, is of particular interest for perennial rice breeding owing to its resilience in abiotic stress conditions. Although root responses to soil flooding are well studied, rhizome responses to water gradients remain underexplored. We hypothesize that physiological integration of Oryza longistaminata mitigates heterogeneous water-deficit stress through interconnected rhizomes, and both roots and rhizomes respond to contrasting water conditions.

Methods: We investigated the physiological integration between mother plants and ramets, measuring key photosynthetic parameters (photosynthetic and transpiration rates and stomatal conductance) using an infrared gas analyser. Moreover, root and rhizome responses to three water regimes (flooding, well watered and water deficit) were examined by measuring radial water loss and apparent permeance to O2, along with histochemical and anatomical characterization.

Key results: Our experiment highlights the role of physiological integration via interconnected rhizomes in mitigating water-deficit stress. Severing rhizome connections from mother plants or ramets exposed to water-deficit conditions led to significant decreases in key photosynthetic parameters, underscoring the importance of rhizome connections in bidirectional stress mitigation. Additionally, O. longistaminata rhizomes exhibited constitutive suberized and lignified apoplastic barriers, and such barriers were induced in roots in water stress. Anatomically, both rhizomes and roots respond in a similar manner to water gradients, showing smaller diameters in water-deficit conditions and larger diameters in flooding conditions.

Conclusion: Our findings indicate that physiological integration through interconnected rhizomes helps to alleviate water-deficit stress when either the mother plant or the ramet is experiencing water deficit, while the counterpart is in control conditions. Moreover, O. longistaminata can adapt to various soil water regimes by regulating anatomical and physiological traits of roots and rhizomes.

Background: The CLV3/EMBRYO-SURROUNDING REGION (CLE) peptides control plant development and response to the environment. Key conserved roles include the regulation of shoot apical meristems and the long-distance control of root colonization by nutrient-acquiring microbes, including the widespread symbioses with arbuscular mycorrhizal fungi and nodulation with nitrogen-fixing bacteria in legumes. At least some signalling elements appear to operate across both processes but clear gaps in our understanding remain. In legumes, although CLE peptide signalling has been examined in detail in symbioses, the role of this pathway in shoot apical meristem (SAM) development is poorly understood.

Scope: In this Research in Context, we review the literature to clarify the conserved and divergent elements of the CLAVATA-CLE peptide signalling pathways that control SAM development, mycorrhizal colonization and nodulation. We used novel pea mutants to determine the role of CLE signalling in regulating SAM development of a model legume, including interactions with temperature.

Conclusions: We found that in pea, both genetic and environmental buffering of the CLE pathway influence SAM development. In pea, the CLAVATA2 (CLV2) CLE receptor-like protein and the unknown gene product encoded by the K301 gene are required to limit SAM size and floral organ production under cool conditions. In contrast, the CLAVATA1 receptor-like kinase promotes SAM proliferation and appears to do so via a CLV2-independent pathway. In contrast, we found no role for the RDN1 enzyme, capable of arabinosylating CLE peptides, in SAM development. Future studies in other legumes are required to examine the role of other CLE peptide signalling elements in SAM control. Studies in non-vascular mycorrhizal hosts could explore if the control of symbioses is also an ancestral role for this signalling pathway.