Length Density Research Articles

Bidispersity Improves the Toughness and Impact Resistance of Star-Polymer Thin Films.

Branched polymer architectures are used to tune the mechanical properties of impact-resistant thin films through parameters, such as chain length and grafting density. While chain dispersity affects molecular properties, such as interpenetration and entanglements, structure-property relationships accounting for dispersity are challenging to obtain experimentally and are often neglected in computational models. We employ molecular dynamics simulations to model the high-rate tensile elongation and nanoballistic impact of thin films composed of bidisperse star polymers with varying arm lengths. We find that, at fixed molecular weight, high dispersity can significantly enhance the toughness and impact resistance of the films without decreasing their elastic modulus. Bidisperse stars with fewer longer arms are less entangled, but stretch and interpenetrate for longer times during crazing, leading to increased toughness. These findings highlight controlled dispersity as a design strategy to improve the mechanical properties of polymer composites across Pareto fronts.

Correlating structure and activity of pepsin enzyme in H2O and D2O for the study of gastric digestion

D2O, an isotope of H2O, is commonly used as a solvent in neutron scattering; the large difference in scattering length density between H and D can provide better contrast between the sample and the solvent. However, this is of concern for studies using enzymes as the use of D2O can influence protein interactions (due to differences in hydrogen bonding) and is therefore expected to affect the function, activity and solubility of enzymes. Neutron-based in vitro digestion assays on proteins, including those found in food or as oral protein and peptide drugs, often involve different solvents or pH conditions where the activity of the digestive enzyme may not be optimal. Herein, we investigate the structure and activity of the main gastric protease, porcine pepsin, in both H2O and D2O at pH values in the range 1 – 8. We showed that the activity of pepsin was lower in D2O, although the relative change in activity with pH was similar for both solvents. We demonstrated using a combination of SAXS and CD that this relative change in activity was not related to any structural change within the protein but was, rather, linked to relative changes in solubility of the protein.

Characterization of soil pores in strip-tilled and conventionally-tilled soil using X-ray computed tomography

Changes in soil pore size distribution and connectivity can affect contaminant transport. Climate, soil type, and agricultural management practices can influence these characteristics. Conservation tillage practices, such as strip tillage, have been promoted as agricultural management practices that can help reduce soil erosion and nutrient loss in runoff. However, limited information exists in the literature on the effect of strip tillage on soil pore characteristics. Thus, the objective of this research study was to assess the effects of different tillage practices i.e., conventional tillage (CT) vs. strip tillage (ST), on soil pore properties and quantify change in soil pore characteristics as a function of season. Undisturbed cylindrical soil columns (150 mm diameter and 640 mm length) were collected from a field in Alabama, USA planted with cotton (Gossypium hirsutum L.) under ST and CT treatments during two seasons i.e., fall 2021 and spring 2022. Soil cores were collected from CT and ST portions of the field, in the fall, following cotton harvest and before planting a cover crop (season 1), and in the spring, after the cover crop had matured (season 2). X-ray computed tomography was used to scan the soil cores and quantify soil pore characteristics. Results show that the ST treatment had significantly (p < 0.05) greater macroporosity values, network density, macropore length density, and interconnectivity compared to the CT in season 1. This was attributed to ST being a minimally disturbed treatment: thereby, it has a better chance of preserving cracks and biological activity as compared to CT, which is more prone to destruction of large macropores. The pore properties also showed a drastic decrease in values during season 2, especially for the top 200 mm of the soil profile in response to rainfall induced soil reconsolidation in both the tillage systems. Overall, this study showed that pore morphology can be affected by tillage and seasonal aspects associated with them.

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.

Microvascular Network Remodeling in the Ischemic Mouse Brain Defined by Light Sheet Microscopy.

Until now, the analysis of microvascular networks in the reperfused ischemic brain has been limited due to tissue transparency challenges. Using light sheet microscopy, we assessed microvascular network remodeling in the striatum from 3 hours to 56 days post-ischemia in 2 mouse models of transient middle cerebral artery occlusion lasting 20 or 40 minutes, resulting in mild ischemic brain injury or brain infarction, respectively. We also examined the effect of a clinically applicable S1P (sphingosine-1-phosphate) analog, FTY720 (fingolimod), on microvascular network remodeling. Over 56 days, we observed progressive microvascular degeneration in the reperfused striatum, that is, the lesion core, which was followed by robust angiogenesis after mild ischemic injury induced by 20-minute middle cerebral artery occlusion. However, more severe ischemic injury elicited by 40-minute middle cerebral artery occlusion resulted in incomplete microvascular remodeling. In both cases, microvascular networks did not return to their preischemic state but displayed a chronically altered pattern characterized by higher branching point density, shorter branches, higher unconnected branch density, and lower tortuosity, indicating enhanced network connectivity. FTY720 effectively increased microvascular length density, branching point density, and volume density in both models, indicating an angiogenic effect of this drug. Utilizing light sheet microscopy together with automated image analysis, we characterized microvascular remodeling in the ischemic lesion core in unprecedented detail. This technology will significantly advance our understanding of microvascular restorative processes and pave the way for novel treatment developments in the stroke field.

Tree mycorrhizal type mediates the responses of foliar stoichiometry and tree growth to functionally dissimilar neighbours in a subtropical forest experiment

Abstract Plant nutrient stoichiometry is of critical importance to productivity and nutrient cycling in terrestrial ecosystems. The impacts of tree species diversity on productivity have been well studied at the stand level. However, it is unclear how neighbourhood interactions impact the foliar nutrient stoichiometry of trees at the neighbourhood scale and how plant mycorrhizal associations can mediate such effects. We randomly selected eight tree species from a large‐scale biodiversity experiment with mixtures up to 32 tree species in subtropical China to assess the effects of species richness, phylogenetic and trait dissimilarities and competition on the foliar nutrient stoichiometry of focal trees associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. We further investigated whether neighbourhood diversity can alter focal tree growth by regulating C:N:P stoichiometry. Neighbourhood species richness had no significant impact on the foliar C:N, N:P or C:P for both AM and EM trees. Increased neighbourhood phylogenetic dissimilarity significantly decreased the foliar N:P and C:P of AM trees but did not affect those of EM tree species. Foliar C:N, N:P and C:P of AM trees decreased with increasing neighbour trait (specific leaf area, root diameter, wood density dissimilarity, total trait) dissimilarities, while those of EM trees increased or remained unchanged. The increase of the neighbourhood competition index resulted in an increase in the foliar C:N of AM tree species but not EM tree species. The structural equation model analysis revealed that the increase of neighbourhood phylogenetic dissimilarity and functional trait dissimilarity indirectly enhanced tree growth of AM trees by decreasing foliar C:N. Conversely, the increase of neighbourhood‐specific root length and wood density dissimilarity indirectly reduced the growth of EM trees by increasing foliar N:P. Synthesis. Our results indicate that neighbourhood trait dissimilarity regulated tree foliar stoichiometry and growth performance, but the effects depended on the mycorrhizal type of trees. Our findings highlight the importance of tree mycorrhizal associations for better understanding the relationship between plant diversity and ecosystem functions. Read the free Plain Language Summary for this article on the Journal blog.

Effects of binders and die geometry on quality of densified rice bran using a screw-type laboratory scale pelleting machine

Cellulosic biomass could solve environmental challenges posed by utilization of fossil fuels. Biomass needs to be processed through densification to ease handling, transport and storage. This study considered the densification of rice bran into pellets using a screw-type pelleting machine. Investigations determined the effect of the starch binder quantity, compression ratio and die configuration on the properties of the pellets. The bulk density, pellet length, pellet density, compressive strength, durability and higher heating value of the rice bran pellets ranged between 254 and 367 kg/m3, 16.85 to 39.90 mm, 283.42 and 793.87 kg/m3, 1.68 and 8.31 N/mm2, 89.06 and 98.32 %; and 16.54 to 17.30 MJ/kg. The binder quantity significantly determined the length of the rice bran pellets. The bulk density was significantly influenced by binder quantity, die type and compression ratio. The higher heating value of the rice bran pellets was significantly influenced by the compression ratio and binder quantity. The study established that interactions of the variables considered had influence on the pellet length and bulk density of pellets.

Small-angle neutron scattering from cellulose solutions in phosphoric acid at different water content

Cellulose from biomass is an abundant and renewable alternative source for chemicals and fuels, yet its utilization by chemical or biological process requires pre-treatment in order to release the macromolecules from their tightly packed crystal structure. Phosphoric acid (PA) has been known for many years to be an efficient solvent for crystalline cellulose. It is also established that a certain quantity of water content in PA is required for efficient pretreatment. This study uses small-angle neutron scattering (SANS) measurements to evaluate cellulose dissolution in deuterated phosphoric acid (dPA), at different wt% dPA between 78 and 97 % (different D2O content). The SANS method is useful for this purpose due to the availability of deuterated dPA, its contrast in scattering length density towards cellulose, and its low incoherent scattering cross-section. The results indicate that most of the cellulose in 2 wt% solution is dissolved in PA as individual chains, at acid content of 81–94 wt% PA. Structural differences of the dissolved cellulose in PA of the various water compositions in this range are insignificant. At 78 % dPA the cellulose crystal still seem to be disrupted, yet the structure can be modeled as mass-surface fractals of small fibrils with irregular surface, possibly due to dissolved chain segments, which are aggregated as mass fractals of rods. At 97 % dPA evidence for a small content of undissolved fibrils is noted.

Belowground Response of a Bahiagrass Pasture to Long-Term Elevated [CO2] and Soil Fertility Management.

Effects of rising atmospheric CO2 concentration [CO2] on pastures and grazing lands are beginning to be researched, but these important systems remain understudied compared to other agronomic and forest ecosystems. Therefore, we conducted a long-term (2005-2015) study of bahiagrass (Paspalum notatum Flüggé) response to elevated [CO2] and fertility management. The study was conducted at the USDA-ARS, National Soil Dynamics Laboratory open-top field chamber facility, Auburn, AL. A newly established bahiagrass pasture was exposed to either ambient or elevated (ambient + 200 µmol mol-1) [CO2]. Following one year of pasture establishment, half the plots received a fertilizer treatment [N at 90 kg ha-1 three times yearly plus P, K, and lime as recommended by soil testing]; the remaining plots received no fertilization. These treatments were implemented to represent managed (M) and unmanaged (U) pastures; both are common in the southeastern US. Root cores (0-60 cm depth) were collected annually in October and processed using standard procedures. Fertility additions consistently increased both root length density (53.8%) and root dry weight density (68.2%) compared to unmanaged plots, but these root variables were generally unaffected by either [CO2] or its interaction with management. The results suggest that southern bahiagrass pastures could benefit greatly from fertilizer additions. However, bahiagrass pasture root growth is unlikely to be greatly affected by rising atmospheric [CO2], at least by those levels expected during this century.

Soil CO2 and CH4 Dynamics and Their Relationships with Soil Nutrients, Enzyme Activity, and Root Biomass during Winter Wheat Growth under Shallow Groundwater

Soil CO2 and CH4 concentrations are crucial determinants of crop physiology and the soil environment. However, the intricate relationships among soil respiration, soil nutrients, enzyme activities, and winter wheat growth in the presence of shallow groundwater remain enigmatic. This study aimed to investigate the dynamics of soil CO2 and CH4 concentrations and their correlations with soil nutrient content, enzymatic activities, and wheat root biomass to better understand the influence of shallow groundwater on soil environmental conditions. Lysimeter experiments were conducted at five groundwater depths (20, 40, 50, 60, and 80 cm) and three fertilizer application rates (low, 75%; normal, 100%; high, 125%). Soil CO2 (soil layer &gt; 10 cm) and CH4 concentrations significantly decreased with increasing groundwater depth. The maximum values of root parameters and shoot biomass were mainly concentrated at 50–60 cm at the high fertilization level (except root length density, which was higher at the normal fertilization level), and were 0.36–77.4% higher than other treatments. Soil CO2 concentration showed positive correlations with organic matter and total N content, enzyme activities, and root biomass. Soil CH4 concentration had significant correlations with soil organic matter, total N, and available K. Compared to the fertilization level, groundwater depth emerged as a crucial factor as it affected soil physicochemical properties, soil enzymatic activities, root respiration, and winter wheat growth in shallow groundwater.

Charge-Patterned Disordered Peptides Tune Intracellular Phase Separation in Bacteria.

Subcellular phase-separated compartments, known as biomolecular condensates, play an important role in the spatiotemporal organization of cells. To understand the sequence-determinants of phase separation in bacteria, we engineered protein-based condensates in Escherichia coli using electrostatic interactions as the main driving force. Minimal cationic disordered peptides were used to supercharge negative, neutral, and positive globular model proteins, enabling their phase separation with anionic biomacromolecules in the cell. The phase behavior was governed by the interaction strength between the cationic proteins and anionic biopolymers, in addition to the protein concentration. The interaction strength primarily depended on the overall net charge of the protein, but the distribution of charge between the globular and disordered domains also had an impact. Notably, the protein charge distribution between domains could tune mesoscale attributes such as the size, number, and subcellular localization of condensates within E. coli cells. The length and charge density of the disordered peptides had significant effects on protein expression levels, ultimately influencing the formation of condensates. Taken together, charge-patterned disordered peptides provide a platform for understanding the molecular grammar underlying phase separation in bacteria.

Trade‐offs in rooting strategy dimensions along an edaphic gradient in a grassland ecosystem

Abstract Roots are essential to the diversity and functioning of plant communities, but trade‐offs in rooting strategies are still poorly understood. We evaluated existing frameworks of rooting strategy trade‐offs and tested their underlying assumptions, guided by the hypothesis that community‐level rooting strategies are best described by a combination of variation in organ‐level traits, plant‐level root:shoot allocation and symbiosis‐level mycorrhizal dependency. We tested this hypothesis using data on plant community structure, above‐ and below‐ground biomass, eight root traits including mycorrhizal colonisation and soil properties from an edaphic gradient driven by elevation and water availability in sandhills prairie, Nebraska, USA. We found multidimensional trade‐offs in rooting strategies represented by a two‐way productivity‐durability trade‐off axis (captured by root length density and root dry matter content) and a three‐way resource acquisition trade‐off between specific root length, root:shoot mass ratio and mycorrhizal dependence. Variation in rooting strategies was driven to similar extents by interspecific differences and intraspecific responses to soil properties. Organ‐level traits alone were insufficient to capture community‐level trade‐offs in rooting strategies across the edaphic gradient. Instead, trait variation encompassing organ, plant and symbiosis levels revealed that consideration of whole‐plant phenotypic integration is essential to defining multidimensional trade‐offs shaping the functional variation of root systems. Read the free Plain Language Summary for this article on the Journal blog.

Experimental Model Exposed to Bisphenol and Submitted to a High-Fat Diet and Related Morphologic Testicular Parameters Alterations Analysis.

To evaluate the morphological and stereological parameters of the testicles in mice exposed to bisphenol S and/or high-fat diet-induced obesity. Forty adult male C57BL/6 mice were fed a standard diet (SC) or high-fat diet (HF) for a total of 12 weeks. The sample was randomly divided into 4 experimental groups with 10 mices as follows: a) SC - animals fed a standard diet; b) SC-B - animals fed a standard diet and administration of BPS (25 μg/kg of body mass/day) in drinking water; c) HF: animals fed a high-fat diet; d) HF-B - animals fed a high-fat diet and administration of BPS (25 μg/Kg of body mass/day) in drinking water. BPS administration lasted 12 weeks, following exposure to the SC and HF diets. BPS was diluted in absolute ethanol (0.1%) and added to drinking water (concentration of 25 μg/kg body weight/day). The animals were euthanized, and the testes were processed and stained with hematoxylin and eosin (H&E) for morphometric and stereological parameters, including density of seminiferous tubules per area, length density and total length of seminiferous tubules, height of the tunica albuginea and the diameter of the seminiferous tubules. The images were captured with an Olympus BX51 microscope and Olympus DP70 camera. The stereological analysis was done with the Image Pro and Image J programs. Means were statistically compared using ANOVA and the Holm-Sidak post-test (p<0.05). The seminiferous tubule density per area reduced in all groups when compared with SC samples (p<0.001): HF (40%), SC-B 3(2%), and HF-B (36%). Length density was reduced significantly (p<0.001) in all groups when compared with SC group: HF (40%), SC-B (32%), and HF-B (36%). The seminiferous tubule total length was reduced (p<0.001) when compared to f HF (28%) and SC-B (26%) groups. The tubule diameter increased significantly (p<0.001) only when we compared the SC group with SC (54%) an SC-B (25%) groups and the tunica thickness increased significantly only in HF group (117%) when compared with SC-B (20%) and HF-B 31%. Animals exposed to bisphenol S and/or high-fat diet-induced obesity presented important structural alterations in testicular morphology.

Male, female, and mixed-sex poplar plantations support divergent soil microbial communities.

Males and females of dioecious plants have sex-specific adaptations to diverse habitats. The effects of inter- and intrasexual interactions in poplar plantations on composition, structure, and function of soil microbiota have not been explored in degraded areas. We conducted a series of greenhouse and field experiments to investigate how belowground competition, soil microbial communities, and seasonal variation nitrogen content differ among female, male, and mixed-sex Populus cathayana plantations. In the greenhouse experiment, female neighbors suppressed the growth of males under optimal nitrogen conditions. However, male neighbors enhanced stable isotope ratio of nitrogen (δ15 N) of females under intersexual competition. In the field, the root length density, root area density, and biomass of fine roots were lower in female plantations than in male or mixed-sex plantations. Bacterial networks of female, male, and mixed-sex plantations were characterized by different composition of hub nodes, including connectors, modules, and network hubs. The sex composition of plantations altered bacterial and fungal community structures according to Bray-Curtis distances, with 44% and 65% of variance explained by the root biomass, respectively. The total soil nitrogen content of mixed-sex plantation was higher than that in female plantation in spring and summer. The mixed-sex plantation also had a higher β-1,4-N-acetyl-glucosaminidase activity in summer and a higher nitrification rate in autumn than the other two plantations. The seasonal soil N content, nitrification rate, and root distribution traits demonstrated spatiotemporal niche separation in the mixed-sex plantation. We argue that a strong female-female competition and limited nitrogen content could strongly impede plant growth and reduce the resistance of monosex plantations to climate change and the mixed-sex plantations constitutes a promising way to restore degraded land.

Choriocapillaris and Retinal Vascular Alterations in Presymptomatic Alzheimer's Disease.

To compare optical coherence tomography angiography (OCTA) retina metrics between cognitively healthy subjects with pathological versus normal cerebrospinal fluid (CSF) Aβ42/tau ratios. Swept-source OCTA scans were collected using the Zeiss PLEX Elite 9000 and analyzed on 23 cognitively healthy (CH) subjects who had previously undergone CSF analysis. Thirteen subjects had a pathological Aβ42/tau (PAT) ratio of <2.7132, indicative of presymptomatic Alzheimer's disease (AD), and 10 had a normal Aβ42/tau (NAT) ratio of ≥2.7132. OCTA en face images of the superficial vascular complex (SVC) and deep vascular complex were binarized and skeletonized to quantify the perfusion density (PD), vessel length density (VLD), and fractal dimension (FrD). The foveal avascular zone (FAZ) area was calculated using the SVC slab. Choriocapillaris flow deficits (CCFDs) were computed from the en face OCTA slab of the CC. The above parameters were compared between CH-PATs and CH-NATs. Compared to CH-NATs, CH-PATs showed significantly decreased PD, VLD, and FrD in the SVC, with a significantly increased FAZ area and CCFDs. Swept-source OCTA analysis of the SVC and CC suggests a significant vascular loss at the CH stage of pre-AD that might be an indicator of a neurodegenerative process initiated by the impaired clearance of Aβ42 in the blood vessel wall and by phosphorylated tau accumulation in the perivascular spaces, a process that most likely mirrors that in the brain. If confirmed in larger longitudinal studies, OCTA retinal and inner choroidal metrics may be important biomarkers for assessing presymptomatic AD.

Relationship between visual acuity and OCT angiography parameters in diabetic retinopathy eyes after treatment.

To assess the relationship between visual acuity and OCT angiography parameters in diabetic retinopathy eyes after treatment, and to analyze the relative factors in PDR eyes. A total of 89 eyes, including 42 eyes with non-PDR (NPDR), and 47 eyes after vitrectomy with PDR were included and underwent OCTA. All images were processed by Python or FIJI. Multivariable linear regression models were used to analyze the associations between postoperative BCVA and OCTA parameters in PDR patients. Postoperative OCTA parameters including deep capillary plexus (DCP) parafoveal and perifoveal vessel density (VD), DCP parafoveal and perifoveal vessel length density (VLD), DCP fractal dimension (FD), choriocapillaris plexus (CCP) VD, CCP VLD, were significantly lower in the PDR group than in the NPDR group. In the superficial capillary plexus (SCP), we found a negative correlation between the postoperative BCVA and VD (parafovea: β coefficient = -0.351, p = 0.023; perifovea: β coefficient = -0.338, p = 0.036). Perifoveal VLD (β coefficient = -0.343, p = 0.031) and FD (β coefficient = -0.375, p = 0.016) of the SCP were also negatively correlated with postoperative BCVA. Regarding the DCP, perifoveal VD (β coefficient = -0.396, p = 0.008), perifoveal VLD (β coefficient = -0.334, p = 0.025), vessel tortuosity (VT) (β coefficient = -0.369, p = 0.015) were negatively correlated with postoperative BCVA. In CCP, VLD (β coefficient = -0.373, p = 0.023) and number of flow voids (β coefficient = -0.334, p = 0.036) exhibited a negative association with postoperative BCVA. Postoperative BCVA of PDR patients was related to OCTA parameters of the SCP (parafoveal and perifoveal VD, perifoveal VLD and FD), DCP (perifoveal VD, VLD, and VT) and CCP (VLD and number of flow voids).

The Osteoblast Transcriptome in Developing Zebrafish Reveals Key Roles for Extracellular Matrix Proteins Col10a1a and Fbln1 in Skeletal Development and Homeostasis.

Zebrafish are now widely used to study skeletal development and bone-related diseases. To that end, understanding osteoblast differentiation and function, the expression of essential transcription factors, signaling molecules, and extracellular matrix proteins is crucial. We isolated Sp7-expressing osteoblasts from 4-day-old larvae using a fluorescent reporter. We identified two distinct subpopulations and characterized their specific transcriptome as well as their structural, regulatory, and signaling profile. Based on their differential expression in these subpopulations, we generated mutants for the extracellular matrix protein genes col10a1a and fbln1 to study their functions. The col10a1a-/- mutant larvae display reduced chondrocranium size and decreased bone mineralization, while in adults a reduced vertebral thickness and tissue mineral density, and fusion of the caudal fin vertebrae were observed. In contrast, fbln1-/- mutants showed an increased mineralization of cranial elements and a reduced ceratohyal angle in larvae, while in adults a significantly increased vertebral centra thickness, length, volume, surface area, and tissue mineral density was observed. In addition, absence of the opercle specifically on the right side was observed. Transcriptomic analysis reveals up-regulation of genes involved in collagen biosynthesis and down-regulation of Fgf8 signaling in fbln1-/- mutants. Taken together, our results highlight the importance of bone extracellular matrix protein genes col10a1a and fbln1 in skeletal development and homeostasis.

Wave-like oscillations of clamped microtubules driven by collective dynein transport

Microtubules (MTs) are observed to move and buckle driven by ATP-dependent molecular motors in both mitotic and interphasic eukaryotic cells as well as in specialized structures such as flagella and cilia with a stereotypical geometry. In previous work, clamped MTs driven by a few kinesin motors were seen to buckle and occasionally flap in what was referred to as flagella-like motion. Theoretical models of active-filament dynamics and a following force have predicted that, with sufficient force and binding-unbinding, such clamped filaments should spontaneously undergo periodic buckling oscillations. However, a systematic experimental test of the theory and reconciliation to a model was lacking. Here, we have engineered a minimal system of MTs clamped at their plus ends and transported by a sheet of dynein motors that demonstrate the emergence of spontaneous traveling-wave oscillations along single filaments. The frequencies of tip oscillations are in the millihertz range and are statistically indistinguishable in the onset and recovery phases. We develop a 2D computational model of clamped MTs binding and unbinding stochastically to motors in a “gliding-assay” geometry. The simulated MTs oscillate with a frequency comparable to experiment. The model predicts the effect of MT length and motor density on qualitative transitions between distinct phases of flapping, regular oscillations, and looping. We develop an effective “order parameter” based on the relative deflection along the filament and orthogonal to it. The transitions predicted in simulations are validated by experimental data. These results demonstrate a role for geometry, MT buckling, and collective molecular motor activity in the emergence of oscillatory dynamics.

Straw return influences the structure and functioning of arbuscular mycorrhizal fungal community in a rice-wheat rotation system

Straw incorporation is a sustainable soil fertility-building practice, which can affect soil microbial communities. However, how straw incorporation affects arbuscular mycorrhizal fungi (AMF) is not well explored. Here, we studied the impacts of different straw management practices over eight years on the structure and function of AMF communities in a rice-wheat rotation system. The straw managements included no tillage with no straw (NTNS), rotary tillage straw return (RTSR) and ditch-buried straw return (DBSR). The community structure of AMF was characterized using high-throughput sequencing and the mycorrhizal functioning was quantified using an in situ mycorrhizal-suppression treatment. Different straw management practices formed unique AMF community structure, which was closely related to changes in soil total organic carbon, available phosphorus, total nitrogen, ammonium and nitrate. RTSR significantly increased Shannon diversity in 0-10 cm soils while DBSR increased it in 10–20 cm soils when compared with NTNS. DBSR significantly increased hyphal length density in the whole (0–20 cm) ploughing layer, but RTSR only increased it in the subsoil layer (10–20 cm). The mycorrhizal responses of shoot biomass and nutrient (N and P) uptake were positive under both straw incorporation treatments (RTSR and DBSR), but negative under NTNS. AMF community composition was significantly correlated to hyphal length density, and the latter was further a positive predictor for the mycorrhizal responses of plant growth and nutrient uptake. These findings suggest that straw return can affect AMF community structure and functioning, and farmers should manage mycorrhizas to strengthen their beneficial effects on crop production.

Root spatial distribution and belowground competition in an apple/ryegrass agroforestry system

CONTEXTForestry and fruit industry is a unique and advantageous industry in Xinjiang, China, and it is an important channel for farmers to increase income. With limited land resources and a shortage of forage in southern Xinjiang, farmers began to establish a fruit-grass interplanting model to improve the comprehensive economic benefits of orchards. OBJECTIVEThe objective of this study was to explore the effects of apple/ryegrass intercropping system on root spatial distribution and competition, and to evaluate the performance of field microclimate, soil physical properties and productivity under intercropping. METHODSIn the study, three different planting patterns were designed: sole-cropped apple (The spacing of the rows of apple trees was 4.0 m, and the plant spacing was 1.0 m), sole-cropped ryegrass (Strip sowing, row spacing was 0.25 m), and apple/ryegrass intercropping (The distance from apple row to ryegrass row was 1.0 m). Two-year field experiments were conducted to measure the root length density (RLD), specific root length (SRL), interspecific competitiveness index, soil moisture content, organic matter content, air temperature, relative humidity, wind speed, yield, land equivalent ratio (LER) and aggressivity. RESULTS AND CONCLUSIONCompared with sole cropping, intercropping reduced the RLD of apple and ryegrass and increased the SRL of ryegrass. The competition space between apple and ryegrass was concentrated in the soil area of 100 cm horizontally and 0–20 cm vertically, and apple was more competitive than ryegrass. Intercropping increased the content of soil moisture and organic matter and improved the microclimate of farmland, decreased the air temperature, increased the relative humidity of an orchard, and decreased wind speed. Although intercropping reduced ryegrass and apple yield, land equivalent ratio (LER) was 1.27–1.30, indicating that intercropping improved land use efficiency. Root competition led to an uneven distribution of root length density (RLD) and specific root length (SRL). The plasticity of root morphology and root spatial distribution was key to adapting to competition and maximizing the absorption of water and nutrients in apple/ryegrass agroforestry systems. SIGNIFICANCEApple/ryegrass intercropping system maximizes resource utilization and reduces interspecies resource competition. It improved land use efficiency, improved the comprehensive benefits of fruit and grass production.