Annals of botany最新文献

Background and aims: Plant dehydration and rehydration cycles are universal phenomena in natural environments, especially in arid environments. Once a moderate water stress is relieved, the plant hydraulic system can recover, but the recovery process across roots, stems and leaves remains unknown. We examined the recovery dynamics of plant hydraulics and photosynthetic activity following moderate water stress in one herbaceous plant (Glycine max) and one woody shrub (Caragana korshinskii).

Methods: The research was conducted on pot-grown plants in a glasshouse and the recovery dynamics of the predawn leaf water potential (ψleaf), hydraulic conductance of the leaf (Kleaf), stem (Kstem) and root (Kroot), stomatal conductance (gs), leaf photosynthetic rate (An) and non-structural carbohydrates (NSCs) were monitored after the plants were released from a moderate water stress.

Key results: Under moderate water stress with decreasing predawn ψleaf, Kleaf and Kroot in both species were more sensitive to water deficit than was Kstem, and the decrease in gs was faster than that in An, resulting in an increase in intrinsic water use efficiency (WUEi); NSCs decreased in leaves and stems but accumulated in roots. After rehydration, both species showed a faster recovery in Kroot and Kstem than in Kleaf, and a slower recovery in gs than in An, resulting in an increase in WUEi.

Conclusions: The rapid recovery in Kroot contributes to plant recovery from water stress, and slow recovery in Kleaf limits stomatal reopening, thus reducing transpiration and maintaining high WUEi. These traits enable species to tolerate drought.

Background and aims: Increasing C storage in cultivated soils requires a better understanding of C dynamics, particularly at depth, where root litter decomposition dynamics is expected to be slower than in ploughed layers.

Methods: We assessed the effect of barley root diameter on root decomposition in situ using a non-invasive method at different depths. Temporal decreases in root diameter and length were measured using images acquired by optical scanners buried at depths of 20, 50 and 90 cm from seeding and for 1.5 years. A parallel root litterbag experiment was performed to measure root mass loss.

Results: Root decomposition was observed on the scanned images before the flowering stage, with up to 85 % of the maximum root volume achieved being lost at harvest. Thinner roots (<0.3 mm) decomposed more slowly than thicker roots. Root length decreased faster at 20 cm than at 50 cm, but soil depth had no significant impact on the dynamics of root-diameter decrease.

Conclusions: Optical scanner-based image analysis complements litterbags by enabling individual root tracking and in situ decomposition assessment without root manipulation. This method offers the opportunity to measure root decomposition at various soil depths over long periods, and could improve the estimation of root-derived soil C inputs.

Background and aims: Natural rainfed conditions present drought episodes interspersed with periods of moderate to high soil moisture levels. This study investigates the genetic variation in root-to-shoot growth in response to a wet-drought-wet cycle and aims to identify rice (Oryza sativa) lines differing in drought recovery, focusing on detailed root trait investigations.

Methods: In total, 100 different rice accessions were screened under fluctuating moisture across three field seasons for GWAS (genome-wide association study) analysis. In a subset of 20 genotypes, crown root number and leaf length were recorded regularly to calculate a water recovery index (WRI). Two lines contrasting in WRI were grown in a glasshouse experiment to resolve detailed root phenotypes in simulated field drought and re-watering.

Key results: GWAS co-locations indicated drought recovery-associated loci that included candidate genes previously reported for several abiotic stressors. In the subset of 20 genotypes, crown root growth was impacted most by the transition from drought to re-watering. The calculated WRI distinguishes different responses to drought and re-watering. A glasshouse study reproduced the contrasting growth of two selected lines, with 'ADT 12' shoot and root growth being strongly impaired by drought, while 'ARC 18202' growth was not suppressed. Drought caused a significant decrease in S-type lateral root production in both lines, while a significant increase in L-type lateral root proportion was only found for 'ADT 12'. These phenotypes were reversed 7 d after re-watering to values of the well-watered control plants.

Conclusions: Overall, in-depth root phenotyping confirmed the drought-resistance and recovery ability of 'ARC 18202' in the field and highlighted the importance of S-type and L-type lateral root formation already under well-watered conditions prior to drought. 'ARC 18202' had a higher amount of thick lateral roots before drought and, therefore, less change in lateral root formation under drought and re-watering conditions.

Background and aim: Root anatomy, determining the composition and organization of root tissues, has implications for water uptake and transport, and potential for enhancing crop resilience amid changing environmental conditions and erratic water supply. While our understanding of the functional relationship between root anatomical traits and soil resource acquisition continues to improve, anatomical traits are commonly investigated on adventitious roots emerging from a single node or averaged across nodes. We test the hypothesis that drought adaptations of anatomical and hydraulic phenes are specific to the nodal origin of the root.

Methods: We grew four maize (Zea mays L.) genotypes in the field under control and drought conditions, imposed by rainout shelters. Subsequently, we investigated the effect of soil drought on crown root anatomical phenes between consecutive shoot nodes. Based on these phenotypes, we inferred root cross-sectional hydraulic properties by integrating simulations of root anatomical networks via the GRANAR model and translating the outputs into hydraulic properties using the MECHA model.L.

Key results: At the individual node level, drought-induced changes in root anatomical and hydraulic phenes were neither consistently significant nor unidirectional across nodes or genotypes. Notably, only second node crown roots consistently exhibited significant changes in response to drought. However, we observed distinct treatment differences in the development of phenes between consecutive shoot nodes. Most root anatomical and hydraulic phenes showed a (hyper)allometric relationship with increasing root cross-sectional area from older to younger roots. However, under drought, those allometric trajectories shifted. Specifically, root cross-sectional area and the areas of stele, cortex, metaxylem and aerenchyma, as well as cortical cell size and the axial hydraulic conductance increased more strongly from older to younger roots under drought. In contrast, metaxylem number increased more strongly under controlled conditions.

Conclusion: Our findings suggest that examining the drought response of root anatomical phenes at a single node may not provide a comprehensive understanding of root system responses to the environment.

Background and aims: Plant volatile organic compounds (VOCs) induced by herbivory boost defences in neighbouring plants. These effects have been shown primarily for direct plant defences and are often stronger when emitter and receiver plants are genetically related. However, we know much less about how plant indirect defence is affected by VOC signalling. To address this, we conducted field experiments controlling for plant relatedness, testing the effects of VOC signalling on extrafloral nectar (EFN) production, a key indirect defence, and its impact on ant recruitment and attacks on herbivores of wild cotton (Gossypium hirsutum) plants.

Methods: Experiments consisted of plant triplets, where one individual acted as an emitter of VOCs and two as receivers. One receiver shared the same mother plant as the emitter, and the other was descended from a different mother. Half of the emitter plants were induced using the specialist caterpillar Alabama argillacea, and VOCs were collected. We then induced receivers and measured their EFN production as well as ant abundance and attack on sentinel caterpillars. Immediately after, we excluded ants from half of the receivers to test for ant-mediated effects on natural herbivory occurring over the following weeks.

Key results: Receivers exposed to VOCs of damaged emitters produced a greater volume and concentration of EFN in response to herbivory relative to those exposed to undamaged emitters, and, accordingly, showed higher rates of ant attack on sentinel caterpillars but there were no differences in ant abundance. These effects were not contingent on emitter-receiver relatedness. In addition, we found no effect of ant exclusion on natural herbivory levels on receiver plants, though damage was overall very low.

Conclusions: These findings provide insight into inter-plant VOC signalling effects on multitrophic interactions by revealing indirect defence induction that leads to herbivore reduction by ants independently of the emitter-receiver relatedness.

Background and aims: While we know a lot about variation of root traits across large set of species, knowledge on differences in root traits among species with different ecological optima, simultaneously considering species lifespan and phylogeny, is limited. We also do not know if inter-specific differences in root traits measured in one environment apply in another environment. Such knowledge is crucial to predict species responses to future environments.

Methods: Using 65 species cultivated under uniform conditions, we studied the effects of species habitat preference, describing under which conditions the species naturally occur, on root morphological and chemical traits and allocation to roots while also considering species lifespan, phenology at harvest and phylogeny. In a subset of species, we explored if species rankings in values of different traits depend on the specific substrate of growth.

Key results: Inter-specific trait differences were strongly linked to species habitat preferences. The best predictor was an indicator value for soil disturbance with roots of species preferring disturbed habitats having higher specific root length and lower diameter, suggesting low collaboration with mutualists. While lifespan and phylogeny also determined trait values, their inclusion into models did not change the effects of habitat preferences. The patterns are thus not a result of species niche conservatism, but contemporary species adaptations. Species ranking in different substrates was more consistent for root morphology than for root chemistry and root/shoot ratio.

Conclusions: Root trait variation is driven by species habitat preferences, indicating that inter-specific root trait variation is a result of species adaptations to different environments. Interestingly, the disturbance indicator value was a better predictor of root trait variation than other, more commonly considered, habitat characteristics. Inter-specific differentiation in root morphology is consistent among substrates and can thus be compared across studies, but root chemistry and allocation data have to be used with caution.

Background and aims: A vigorous root system is crucial for maize seedling establishment. Its formation and subsequent plant performance are hindered by nutrient and water deficiency. Upon germination, maize seedlings develop primary, then seminal roots, covered with pubescent root hairs. The functions of root hairs at this developmental stage remain largely unknown. This study examined their role during phosphorus (P) and water limitations during early seedling development at the physiological, elemental and molecular level, comparing a roothairless maize mutant (rth3) and its isogenic wildtype (WT).

Methods: Shoot and root system architecture phenotyping and elemental analysis were performed on 5-d-old rth3 and WT plants experiencing various P- and water-deficient conditions in different growth substrates. Microscopy of root hairs and specific reverse transcription quantitative PCR of various P-nutrition regulators and aquaporins in roots were performed.

Key results: WT seedlings responded with a morphologically typical root hair elongation solely to water-reduced but not P-deficient conditions. In contrast, at the molecular level, WT and rth3 responsively upregulated P transporters in roots upon P deficiency, while water channel transcript abundances did not change upon water limitation. Surprisingly, under these adverse seedbed conditions no differences in shoot biomass, shoot nutrient concentrations or shoot water content were detected between the WT and the roothairless mutant which additionally formed a generally shorter total root length compared to the WT. P deficiency caused the development of thicker primary roots in rth3 and a significant increase in expression of P transporters compared to the WT.

Conclusions: Germinating rth3 seedlings showed neither disadvantages in terms of shoot vigour, nor with respect to shoot water and nutrient levels in suboptimal seedbed conditions compared to the WT, despite possessing shorter roots and no root hairs. An increase in root diameter and P-transporter expression particularly in rth3 seminal roots may have been sufficient to physiologically compensate for the missing root hairs.

Background: A major challenge in agriculture is the low nitrogen (N) uptake efficiency of crops, which poses environmental and economic costs. Root adaptive architectural and anatomical phenotypes in synergy with root microbes could be a promising approach to improve plant N uptake. However, little is known about such synergies. Here, we aimed to characterize the spatial distribution of the root prokaryotes of maize (Zea mays) under low N in 30-L mesocosms, where root architecture and anatomy are freely expressed, searching for correlations between prokaryotic genus abundance and ten phenotypes.

Methods: We studied the root prokaryotic community of 4-week-old plants growing in 30-L mesocosms under low N using two sandy soil mixtures. We collected root, rhizosphere and bulk soil samples at various locations, including depths (0-20, 20-70, 70-150 cm), root classes (lateral and axial) and root types (seminal and crown). We measured plant growth response to low N availability and performed 16S rRNA gene metabarcoding on extracted DNA.

Key results: Sampling location was the third most important factor after soil mixture and compartment, explaining ∼5 % of the variance in root prokaryotic diversity. Seminal roots (0-20 cm depth), shallow crown roots (0-20 cm) and deep crown roots (20-150 cm) showed well-separated root microbial communities. Lateral root branching density (LRBD) explained 10 % of this variance in the rhizosphere and the root tissue. We identified prokaryotic genera specific to depth, soil-root compartment, root class and type under LN. Moreover, architectural phenotypes LRBD and lateral root length significantly correlated with the abundance of 37 genera.

Conclusions: We highlight the importance of sampling location and architectural traits that may be associated with the microbial cycling of soil N. The exploration of synergies between root traits and microbes that participate in the N cycle has the potential to increase sustainability in agriculture.

Background and aims: The mechanical properties of plant roots are crucial for soil stabilization and vegetation restoration. To effectively employ bioengineering methods, understanding the tensile properties of plant roots is essential. In most studies, root diameter is used as a predictor of tensile strength but this fails to accurately describe root mechanical behaviour. The stele and cortex are two anatomical parts of the root whose actual mechanical behaviour and specific contributions to root biomechanisms remain unclear.

Methods: Tensile tests and scanning electron micrography were performed on roots of four typical species (Robinia pseudoacacia, Pinus tabuliformis, Vitex negundo and Syzygium aromaticum) in the Loess Plateau of China to investigate the roles of the stele and cortex in explaining the root's tensile strength. Then, based on the 'same strain' principle, a tensile strength prediction model was developed and validated using experimental data from plant root.

Key results: The stele and cortex of roots exhibited distinct mechanical behaviours: elastic plasticity and linear elasticity, respectively. Tensile strength was negatively correlated with diameter and stelar diameter and cortical thickness were positively correlated with diameter. The cortex had lower tensile strength, strain at maximum stress and thickness compared with the stele. The observed increase in scatter of tensile strength with decreasing root diameter was attributed to the higher coefficient of variation in cortical tensile strength compared with the stele. Notably, predicted results of intact root tensile strength fell within the 95 % prediction interval of the measured intact root tensile strength and could be enhanced 30-80 % by strengthening dataset quality.

Conclusions: Our results demonstrated the actual mechanical behaviour characteristics of cortex and stele, and provide a new perspective for addressing the mechanical properties of roots using composite materials mechanics. The findings of this study will provide a theoretical foundation for implementing plant-based ecological restoration and disaster prevention measures.

Background and aims: The trait plasticity may be critical to the successful invasion of invasive plants (IPS). Furthermore, multiple IPS can coexist in a given habitat. Nevertheless, it remains unclear which functional trait's plasticity contributes most to the competitive advantage of IPS under the co-invasion scenarios. This study aims to evaluate the differences in the trait plasticity, and to assess the contribution of the trait plasticity of multiple IPS on their competitive advantage under the co-invasion scenarios mediated by three IPS, namely Erigeron canadensis L., E. sumatrensis Retz. and Solidago canadensis L., in comparison to native plants, in Jiangsu, China.

Methods: This study was conducted by cross-comparing plant communities under different invasion scenarios mediated by different species number of IPS, including plant communities invaded by one, two and three IPS listed above and plant communities without any invasion.

Key results: These three IPS displayed a significantly lower trait plasticity, particularly with regard to plant height, leaf size and green leaf area, in comparison to coexisting native plants, regardless of the invasion scenario. The competitive advantage of these three IPS was greatest when they invaded independently.

Conclusions: The competitive advantage of these three IPS was largely contributed by the plasticity of green leaf area and leaf nitrogen content.