Organic Acids Secreted from Plant Roots under Soil Stress and Their Effects on Ecological Adaptability of Plants

[Objective] In this study,the secretion of organic acids from plant roots under soil nutrient and water stress and the effects of organic acids on ecological adaptability of plants were investigated,which provided theoretical basis for improving the adaptability of plants to a variety of stress conditions.The results showed that,under nutrient and water stress,the content of organic acids secreted from plant roots increased significantly as a common active adaptive response.Organic acids could improve the activities of a variety of antioxidant enzymes,contents of osmotic regulatory substances,contents of chlorophyll and photosynthesis levels,promote nutrient absorption and transportation in plants,and ultimately contribute to plant growth and biomass accumulation,reduce the toxicity of stress conditions to plants and improve the stress resistance and adaptability of plants.

Effects of loading rate on root pullout performance of two plants in the eastern Loess Plateau,China

Root pullout performance of plants is an important mechanical basis for soil reinforcement by plant roots in the semi-arid areas.Studies have shown that it is affected by plant factors(species,ages,root geometry,etc.)and soil factors(soil types,soil moisture,soil bulk densities,etc.).However,the effects of loading rates on root pullout performance are not well studied.To explore the mechanical interactions under different loading rates,we conducted pullout tests on Medicago sativa L.and Hippophae rhamnoides L.roots under five loading rates,i.e.,5,50,100,150,and 200 mm/min.In addition,tensile tests were conducted on the roots in diameters of 0.5-2.0 mm to compare the relationship between root tensile properties and root pullout properties.Results showed that two root failure modes,slippage and breakage,were observed during root pullout tests.All M.sativa roots were pulled out,while 72.2%of H.rhamnoides roots were broken.The maximum fracture diameter and fracture root length of H.rhamnoides were 1.22 mm and 7.44 cm under 100 mm/min loading rate,respectively.Root displacement values were 4.63%(±0.43%)and 8.91%(±0.52%)of the total root length for M.sativa and H.rhamnoides,respectively.The values of maximum pullout force were 14.6(±0.7)and 17.7(±1.8)N under 100 mm/min for M.sativa and H.rhamnoides,respectively.Values of the maximum pullout strength for M.sativa and H.rhamnoides were 38.38(±5.48)MPa under 150 mm/min and 12.47(±1.43)MPa under 100 mm/min,respectively.Root-soil friction coefficient under 100 mm/min was significantly larger than those under other loading rates for both the two species.Values of the maximum root pullout energy for M.sativa and H.rhamnoides were 87.83(±21.55)mm•N under 100 mm/min and 173.53(±38.53)mm•N under 200 mm/min,respectively.Root pullout force was significantly related to root diameter(P<0.01).Peak root pullout force was significantly affected by loading rates when the effect of root diameter was included(P<0.01),and vice versa.Except for the failure mode and peak pullout force,other pullout parameters,including root pullout strength,root displacement,root-soil friction coefficient,and root pullout energy were not significantly affected by loading rates(P>0.05).Root pullout strength was greater than root tensile strength for the two species.The results suggested that there was no need to deliberately control loading rate in root pullout tests in the semi-arid soil,and root pullout force and pullout strength could be better parameters for root reinforcement model compared with root tensile strength as root pullout force and pullout strength could more realistically reflect the working state of roots in the semi-arid soil.

Influence of environment and substrate quality on the decomposition of wetland plant root in the Sanjiang Plain,Northeast China

The litterbag method was used to study the decomposition of wetland plant root in three wetlands along a water level gradient in the Sanjiang Plain,Northeast China.These wetlands are Calamagrostis angustifolia(C.aa),Carex meyeriana(C.ma)and Carex lasiocarpa (C.la).The objective of our study is to evaluate the influence of environment and substrate quality on decomposition rates in the three wetlands.Calico material was used as a standard substrate to evaluate environmental influences.Roots native to each we...

Effect of Plant Roots on Penetrability and Anti-Scouri-bility of Red Soil Derived from Granite

Distribution of plant roots in a red soil derived from granite was investigated to study the effect of plantroots on intensifying soil penetrability and anti-scouribility by the double-cutting-ring and the undisturbedsoil-flume methods, respectively. The plant roots system consisting mostly of fibrils, < 1 mm in diameter,was mainly distributed in the upper surface soil 30 cm in depth. It can remarhably increase the penetrabilityand anti-scouribility of the red soil derived from granite. When the root density was > 0.35 root cm-2, theintensifying effect of roots on both the penetrability and the anti-scouribility could be described by exponentequations, △ Ks = 0.0021RD1.4826 (R2 = 0.9313) and △ As = 0.0003RD1.8478 (R2 = O.9619), where △ Ks isthe value of intensified soil penetrability, a As the value of intensified soil anti-scouribility and RD the rootdensity, especially in the top soils within 30 cm in depth where plant roots were conceotrated.

Evaluation of Cytogenetic Effects of Isoproturon on the Root Meristem Cells of Allium sativum

Objective\ To validate the use of Allium sativum as a reliable test model for genotoxicity, isoproturon, a substituted phenylalkylurea herbicide, was evaluated on the root meristem cells by this plant system. Method\ Test concentrations were selected by determining EC50 and root tips were exposed to various concentrations for 6 or 24 hr. EC50 concentration was calculated to be 70.8 ppm for the root growth. In addition to root growth retardation exposure to isoproturon induced morpholoogical changes like discolouration and stiffness of roots. Results\ Exposure to various experimental concentrations of isoproturon (35-280 ppm), including EC50, significantly and dose-dependently inhibited the mitotic index and induced chromosome breaks/mitotic aberrations at 6 or 24 hr. Conclusion\ The frequency of aberrations was found to be decreased in a dose dependant manner at 24 or 48 hr post exposure, however in comparison of control cells the frequency of aberrations was considerably high which indicates genotoxicity potentials of isoproturon. Further, present study also suggests that Allium sativum is a sensitive, efficient, and reliable test system for measuring the genotoxicity potential of environmental chemicals.

Digital biofabrication to realize the potentials of plant roots for product design

Technological and economic opportunities,alongside the apparent ecological benefits,point to biodesign as a new industrial paradigm for the fabrication of products in the twenty-first century.The presented work studies plant roots as a biodesign material in the fabrication of self-supported 3D structures,where the biologically and digitally designed materials provide each other with structural stability.Taking a material-driven design approach,we present our systematic tinkering activities with plant roots to better understand and anticipate their responsive behaviour.These helped us to identify the key design parameters and advance the unique potential of plant roots to bind discrete porous structures.We illustrate this binding potential of plant roots with a hybrid 3D object,for which plant roots connect 600 computationally designed,optimized,and fabricated bioplastic beads into a low stool.

Testing allometric scaling relationships in plant roots

Background:Metabolic scaling theory predicts that plant productivity and biomass are both size-dependent.However,this theory has not yet been tested in plant roots.Methods:In this study,we tested how metabolic scaling occurs in plants using a comprehensive plant root dataset made up of 1016 observations from natural habitats.We generated metabolic scaling exponents by logtransformation of root productivity versus biomass.Results:Results showed that the metabolic scaling exponents of fine root(<2mm in diameter)productivity versus biomass were close to 1.0 for all ecosystem types and functional groups.Scaling exponents decreased in coarse roots(>2mm in diameter).Conclusions:We found isometric metabolic scaling in fine roots,a metabolically active organ similar to seedlings or saplings.Our findings also indicate a shift in metabolic scaling during plant development.Overall,our study supports the absence of any unified single constant scaling exponent for metabolism-biomass relationships in terrestrial plants,especially for forests with woody species.

Positive Effects of Biochar on the Degraded Forest Soil and Tree Growth in China:A Systematic Review

Soil degradation threatens the forest sustainable productivity,particularly in afforestation system.Biochar derived from agroforestry waste or biomass can potentially improve the degraded forest soil and promote the tree growth.To expand the application of biochar for forestry productivity improvement,we here reviewed the effects and the underlying mechanisms of biochar on the degraded forest soil and tree growth.Totally 96 studies that conducted from pot to field investigations in China were summarized.The result suggested that biochar generally exerted positive effects on restoration of degraded forest soil such as that with compaction,acidification or soil erosion,which are mainly manifested by improving soil porosity,increasing pH,enhancing erosion resistance and mitigating greenhouse gas emissions.Furthermore,biochar incorporation promoted the growth of tested trees in most cases,which effect was mainly attributing to directly supplying nutrients,improving soil physio-chemical properties,enhancing the root’s nutrient absorption capacity,and enlarging the living space.In summary,current studies demonstrate that biochar has a unique potential for improving degraded forest soils and promoting tree growth.However,investigations on the underlying mechanisms and the long-term effects should be strengthened.

Fast and abundant in vitro spontaneous haustorium formation in root hemiparasitic plant Pedicularis kansuensis Maxim. (Orobanchaceae)

Haustorium formation is the characteristic feature of all parasitic plants and a vital process for successful parasitism.Previous investigations on haustorium initiation and development are constricted to induced processes by host-derived signals or synthetic analogs.Spontaneous haustorium formation in the absence of host signals,a process representing an early stage in the evolution of parasitic plants,remains largely unexplored.Lack of fast and frequent formation of spontaneous haustoria greatly hinders full understanding of haustorium formation in root hemiparasites.In this study,seedlings of Pedicularis kansuensis Maxim.,a facultative root hemiparasitic species in Orobanchaceae observed to produce many spontaneous haustoria,were grown in autoclaved water agar in the absence of any known haustoriuminducing stimulants.We aimed to test the temporal and developmental pattern of spontaneous haustorium formation.Also,effects of sucrose supply and root contact on spontaneous haustorium formation were tested.Spontaneous haustoria were observed starting from six days after germination,much earlier than previously reported root hemiparasites.A majority of the spontaneous haustoria formed on lateral roots.Percentage of seedlings with spontaneous haustoria was 28.8% when grown on water agar plates,with a mean of four haustoria per seedling two weeks after germination.Haustorium formation by seedlings grown in water agar amended with 2% sucrose was more than twice of those without sucrose amendment.Singly grown seedlings were able to develop spontaneous haustoria at similar levels as those grown with another conspecific seedling.In view of the fast and abundant formation of spontaneous haustoria,P.kansuensis may be developed as an excellent experimental system in future investigations for unraveling endogenous regulation of haustorium initiation and development in root hemiparasitic plants.

Analysis for Soil Characteristics of Degraded Grassland on Alpine Meadow

[Objective]The aim of this study is to explore the effects of grassland degradation on soil physical and chemical properties.[Method]The ratio of plant root to soil and soil texture on Alpine Meadow were investigated in this study,and soil available N,P,K,Cu,Zn,organic matter and pH value were also analyzed by routine analysis of soil nutrients in different degraded grasslands.[Result]With the intensification of degraded gradient and the soil depth,the ratio of plant root to soil was decreased gradually.The highest ratio of plant root to soil was in 0-10 cm depth of soil in grassland with different degraded gradients,while its ratio of plant root to soil changed from 0.001 to 0.040 with soil type of loam.Soil chemical characteristic changed in different degraded gradients.The content of available N,P,K reduced significantly with the soil depth and the intensification of degraded gradients.The content of Cu and Zn was relatively lack in degraded grassland.[Conclusion]There is no significant correlation between nutrition content or pH value and the succession degree of degraded grassland.

Soil substrate as a cascade of capillary barriers for conserving water in a desert environment:lessons learned from arid nature

Interaction between soil pedogenesis, subsurface water dynamics, climate, vegetation and human ingenuity in a desert environment has been found to result in a unique ecohydrological system with an essentially three dimensional sedimentation structure in the bed of a recharge dam in Oman. A 3-D array of silt blocks sand- wiched by dry sand-filled horizontal and vertical fractures was studied in pot experiments as a model of a natural prototype. Pots are filled with a homogenous sand-silt mixture （control） or artificially structured （smart design, SD） soil substrates. Rhodes grass and ivy （Ipomea, Convolvulaceae） were grown in the pots during the hottest season in Oman. Soil moisture content （SMC） was measured at different depths over a period of 20 days without irrigation. SD preserved the SMC of the root zone for both ivy and grass （SMC of around 25%-30% compared to 〈10% for control, 3 days after the last irrigation）. Even after 20 days, SMC was around 18% in the SD and 7% in the control. This, similar to the case of a natural prototype, is attributed to the higher upward capillary movement of water in control pots and intensive evaporation. The capillary barrier of sand sheaths causes discontinuity in moisture mi- gration from the micro-pores in the silt blocks to sand pores. The blocks serve as capillarity-locked water buffers, which are depleted at a slow rate by transpiration rather than evaporation from the soil surface. This creates a unique ecosystem with a dramatic difference in vegetation between SD-pots and control pots. Consequently, the Noy-Meir edaphic factor, conceptualizing the ecological impact of 1-D vertical heterogeneity of desert soils, should be generalized to incorporate 3-D soil heterogeneity patterns. This agro-engineering control of the soil substrate and soil moisture distribution and dynamics （SMDaD） can be widely used by desert farmers as a cheap technique, with significant savings of irrigation water.

TAA family contributes to auxin production during de novo regeneration of adventitious roots from Arabidopsis leaf explants

Many differentiated plant organs have the ability to regenerate into a new plant after detachment via de novo organogenesis. During de novo root organogenesis from Arabidopsis thaliana leaf explants, wounding first induces endogenous auxin production in mesophyll cells. Auxin is then polar transported to, and accumulates in, regenerationcompetent cells near the wound to trigger the cell-fate transition. The TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS(TAA) family proteins and the YUCCA(YUC) family proteins catalyze two successive biochemical steps in auxin biogenesis, and YUCs have been shown to be involved in auxin production in mesophyll cells during de novo root organogenesis. In thisstudy, we show that the TAA family is also required for adventitious rooting. Inhibition of TAA blocked adventitious root formation from leaf explants. Intriguingly,whereas YUC1 and YUC4 have been shown to be highly induced by wounding, TAA genes retained consistent expression levels before and after leaf detachment.Therefore, we suggest that TAAs and YUCs are both required for auxin biogenesis in leaf explants, but they play different roles in regeneration. While YUC1 and YUC4 function in response to wounding to catalyze the ratelimiting step in auxin biosynthesis, TAAs probably serve as abiding and basal enzymes during de novo root organogenesis from leaf explants.

Computational investigation of small RNAs in the establishment of root nodules and arbuscular mycorrhiza in leguminous plants

Many small RNAs have been confirmed to play important roles in the development of root nodules and arbuscular mycorrhiza. In this study, we carried out the identification of certain small RNAs in leguminous plants(Medicago truncatula, soybean, peanut and common bean), such as miRNAs, tRFs and srRNAs, as well as the computational investigation of their regulations. Thirty miRNAs were predicted to be involved in establishing root nodules and mycorrhiza, and 12 of them were novel in common bean and peanut. The generation of tRFs in M. truncatula was not associated with tRNA gene frequencies and codon usage. Six tRFs exhibited different expressions in mycorrhiza and root nodules. Moreover, srRNA^(5.8S) in M. truncatula was generated from the regions with relatively low conservation at the rRNA 3′ terminal. The protein-protein interactions between the proteins encoded by the target genes of miRNAs, tRFs and srRNAs were computed. The regulation of these three types of sRNAs in the symbiosis between leguminous plants and microorganisms is not a single regulation of certain signaling or metabolic pathways but a global regulation for the plants to own growth or specific events in symbiosis.

A Bioinspired Robot Growing like Plant Roots

Plants are usually considered static organisms,but they can perform a wide range of movements that can be a source of inspiration for robots.The roots’growing motion is the most noteworthy since they are excellent diggers that can move in unstructured environments and navigate past barriers.Furthermore,root growth has a high energy efficiency since it penetrates the soil at its tip,adding new material without displacing the already grown portion,minimizing the energy dissipation due to friction and lowering the inertia.A robot inspired by the growth of roots could be used in search and rescue or environmental monitoring.The design of a soft robot inspired by root growth is presented in this article.The robot body consists of a cylindrical plastic membrane folded inside itself.The robot body is inflated,and its tip is everted,expanding its length as air is blown from the base.Velcro straps are placed on the membrane’s exterior surface to keep it folded.The head is positioned inside the tip,which houses the mechanism that controls the growth direction.It consists of housing for two balloons that are selectively inflated,and their expansion applies pressure on the exterior surface,opening the Velcro straps and determining the growth direction.The robot was constructed,and a kinematic model of its motion in the plane was created and compared with experimental data.The error in predicting the turning angle is only 5%,and the resulting predicted position differs on average by 55 mm on a total length of 850 mm.

Characteristics of Dried Soil Layers Under Apple Orchards of Different Ages and Their Applications in Soil Water Managements on the Loess Plateau of China

Negative soil water balance （i.e., water input 〈 water output） can lead to soil desiccation and subsequently the occurrence of a dried soil layer （DSL）. The DSLs are generally studied at a specific sampling depth （e.g., 500 cm）, and the actual extent of DSLs remains unknown due to the challenge of collecting deep soil samples. To investigate the characteristics of actual DSLs under different ages of apple orchards and ascertain the optimal age of apple orchards for avoiding/controlling the formation of DSLs, soil samples were collected to a depth of 1800 cm under apple orchards of different ages in Changwu on the Loess Plateau of China. As the ages increased, soil water content （SWC） and mean SWC in DSLs showed an overall decreasing trend, whereas while DSL thickness and the quantity of water deficit （QWD） in DSLs demonstrated an increasing trend. The DSL was the thickest （1 600 cm） under the 17-yeax-old orchard, the forming velocity of DSL thickness was the highest at the apple tree growth stage of 9-17 years （168 cm year-l）, and the highest increasing velocity of QWD （-181 mm year-1） was also observed at this stage. The thickness of DSL was significantly correlated with growth age and root depth of apple trees （r 〉 0.88）, whereas the QWD and mean SWC in DSLs were found to have no correlation with them. The optimal age of apple orchards for avoiding/controlling the formation of DSLs was about 9 years. This information provided pertinent references for the management of deep water resources by controlling the growth age of plants. Key Words： deep soil, growth age, plant roots, soil desiccation, soil water content, soil-plant water relation.

Confirming Stereochemical Structures of Strigolactones Produced by Rice and Tobacco

Major strigolactones （SLs） produced by rice （Oryza sativa L. cv. Nipponbare） and tobacco （Nicotiana tabacum L. cv. Michinoku No. 1） were purified and their stereochemical structures were determined by comparing with optically pure synthetic standards for their NMR and CD data and retention times and mass fragmentations in ESI-LC/MS and GC-MS. SLs purified from root exudates of rice plants were orobanchol, orobanchyl acetate, and ent-2＂-epi-5-deoxystr- igol. In addition to these SLs, 7-oxoorobanchyl acetate and the putative three methoxy-5~deoxystrigol isomers were detected by LC-MS/MS. The production of 7-oxoorobanchyl acetate seemed to occur in the early growth stage, as it was detected only in the root exudates collected during the first week of incubation. The root exudates of tobacco contained at least 11 SLs, including solanacol, solanacyl acetate, orobanchol, ent-2＂-epi-orobanchol, orobanchyl acetate, ent-2＇- epi-orobanchyl acetate, 5-deoxystrigol, ent-2＂-epi-5-deoxystrigol, and three isomers of putative didehydro-orobanchol whose structures remain to be clarified. Furthermore, two sorgolactone isomers but not sorgolactone were detected as minor SLs by LC-MS/MS analysis. It is intriguing to note that rice plants produced only orobanchol-type SLs, derived from ent-2＂-epi-5-deoxystrigol, but both orobanchol-type and strigol-type SLs, derived from 5-deoxystrigol were detected in tobacco plants.

Effect of rhizosphere on soil microbial community and in-situ pyrene biodegradation

To access the influence of a vegetation on soil microorganisms toward organic pollutant biogegration,this study examined the rhizospheric effects of four plant species(sudan grass,white clover,alfalfa,and fescue)on the soil microbial community and in-situ pyrene(PYR)biodegradation.The results indicated that the spiked PYR levels in soils decreased substantially compared to the control soil without planting.With equal planted densities,the efficiencies of PYR degradation in rhizosphere with sudan grass,white clover,alfalfa and fescue were 34.0%,28.4%,27.7%,and 9.9%,respectively.However,on the basis of equal root biomass the efficiencies were in order of white clover..alfalfa.sudan.fescue.The increased PYR biodegradation was attributed to the enhanced bacterial population and activity induced by plant roots in the rhizosphere.Soil microbial species and biomasses were elucidated in terms of microbial phospholipid ester-linked fatty acid(PLFA)biomarkers.The principal component analysis(PCA)revealed significant changes in PLFA pattern in planted and non-planted soils spiked with PYR.Total PLFAs in planted soils were all higher than those in non-planted soils.PLFA assemblages indicated that bacteria were the primary PYR degrading microorganisms,and that Gram-positive bacteria exhibited higher tolerance to PYR than Gram-negative bacteria did.

New Strigolactone Analogs as Plant Hormones with Low Activities in the Rhizosphere

Strigolactones （SLs） are known not only as plant hormones, but also as rhizosphere signals for establishing symbiotic and parasitic interactions. The design of new specific SL analogs is a challenging goal in understanding the basic plant biology and is also useful to control plant architectures without favoring the development of parasitic plants. Two different molecules （23 （3＇-methyI-GR24）, 31 （thia-3＇-methyl-debranone-like molecule）） already described, and a new one （AR36）, for which the synthesis is presented, are biologically compared with the well-known GR24 and the recently identified CISA-1. These different structures emphasize the wide range of parts attached to the D-ring for the bioactivity as a plant hormone. These new compounds possess a common dimethylbutenolide motif but their structure varies in the ABC part of the molecules： 23 has the same ABC part as GR24, while 31 and AR36 carry, respectively, an aromatic ring and an acyclic carbon chain. Detailed information is given for the bioactivity of such derivatives in strigolactone synthesis or in perception mutant plants （pea rmsl and rms4, Arabidopsis max2 and, max4） for different hormonal functions along with their action in the rhizosphere on arbuscular mycorrhizal hyphal growth and parasitic weed germination.

SIMPLIFIED ORDER CONDITIONS OF SOME CANONICAL DIFFERENCE SCHEMES

The main purpose of this paper is to develop and simplify the general conditions for an s-stage explicit canonical difference scheme of q-th order, while the simplified order conditions for canonical RKN methods which are applied to a special kind of second order ordinary differential equations are also obtained here.

Effect of Asiasari radix on osteoblastic differentiation of stem cells derived from gingiva

OBJECTIVE: To examine the dose-dependent impact of Asiasari Radix(A. radix) on the cell viability,differentiation and mineralization of stem cells derived from gingiva.METHODS: Stem cells that were derived from gingiva were grown in the presence of A. radix at final concentrations that ranged from 0.001 to 10 μg/m L. The morphology of the cells was viewed under an inverted microscope and the analysis of cell proliferation was performed by using Cell Counting Kit-8(CCK-8) on day 1. The alkaline phosphatase activity test was used to assess differentiation and Alizarin red S staining was used to assess mineralization of treated cells.RESULTS: The control group showed spindleshaped, fibroblast-like morphology and the shapesof the cells in 0.001, 0.01, 0.1, 1 and 10 μg/mL of A.radix were similar to that of the control group at day 1. The cultures growing in the presence of0.001 μg/m L of A. radix at day 1 showed an increase in the CCK-8 value(P < 0.05). Cultures growing in the presence of 0.001 μg/m L of A. radix presented the highest value for alkaline phosphatase activity(P > 0.05). Mineralized extracellular deposits were observed after Alizarin Red S staining and the cultures grown in the presence of 0.001 μg/m L of A. radix showed the highest value for quantitative results for bound dye(P < 0.05).CONCLUSION: Within the limits of this study, A. radix influenced the proliferation of stem cells derived from the gingiva and low concentrations of A.radix might enhance osteogenic differentiation of the stem cells.