Root Growth of the Annual Tillering Grass Panicum miliaceum in Heterogeneous Nutrient Environments

To study growth responses of the roots of Panicum miliaceum L. to heterogeneous supply of nutrients. The authors analyzed the effects of the nutrient levels in both original patches (O) and destination patches (D) on the root growth of P. miliaceum when its roots were allowed to extend from original patch into destination patch. When the nutrient levels in the original patches were low, coarse root biomass ratio (coarse root biomass in the D/total coarse root biomass), coarse root length ratio (coarse root length in the D/total coarse root length), coarse root surface area ratio (coarse root surface area in the D/total coarse root surface area) and fine root length ratio (fine root length in the D/total fine root length) were greater in the destination patches with lower nutrient levels than in the destination patches with higher nutrient levels, while fine root length, fine root length density, fine root surface index, and fine root surface area density were smaller in the former than in the latter. When the nutrient levels in the original patches were high, fine root length, fine root length density, fine root surface area index and fine root surface density were greater in the destination patches with lower nutrient levels than in the destination patches with higher nutrient levels, coarse roots did not respond to the nutrient levels in the destination patches significantly. When the roots extended from the original patches with the same nutrient level into the destination patches with contrasting nutrient levels, fine root biomass and its percentage allocation did not respond to the nutrient levels in the destination patches significantly, whereas both root length and root surface area did. This indicates that the fine roots of P. miliaceum responded to difference in nutrient supply by plasticity in their length and surface area, rather than in their root biomass.

Root Physiological and Morphological Characteristics of Two Rice Cultivars with Different Nitrogen-Use Efficiency

The variation in nitrogen （N） uptake by rice has been widely studied but differences in rice root morphology that may contribute to this variation are not completely understood. Field and greenhouse experiments were carried out to study N accumulation, root dry weights, total root lengths, root surface areas, and root bleeding rates of two rice cultivars, Elio with low N-use efficiency and Nanguang with high N-use efficiency. Low （1 mmol N L^-1） and high （5 mmol N L^-1） N applications were established in the greenhouse experiment, and the N rates were 0, 120, and 240 kg ha^-1 in the field experiments at Jiangning and Jiangpu farms, Nanjing, China. The results showed that the N accumulation, root dry weight, total root length, and root surface area increased with an increase in N application. At the heading stage, N accumulation in the shoots and roots of Nanguang was greater than that of Elio in the field experiments and that of Elio at 5 mmol N L^-1 in the greenhouse experiment. After the heading stage, N accumulation was higher for Nanguang at both 1 and 5 mmol N L^-1 in the greenhouse experiment. The total root length and root surface area were significantly different between the two cultivars. Over the range of the fertilizer application rates, the root lengths of Nanguang at Jiangning Farm were 49%-6170 greater at booting and 26%-39% greater at heading than those of Elio, and at Jiangpu Farm they were 22%-42% and 26%-38% greater, respectively. Nanguang had a greater root bleeding rate than Elio. It was concluded that the N-use efficiency of the two rice cultivars studied depended to a great extent on the root morphological parameters and root physiological characteristics at different growth stages.

Differential response of root morphology to potassium deficient stress among rice genotypes varying in potassium efficiency

Disparity in the root morphology of six rice(Oryza sativa L.) genotypes varying in potassium(K) efficiency was studied with three K levels:5 mg/L(low),10 mg/L(moderate) and 40 mg/L(adequate) in hydroponic culture. Morphological parameters included root length,surface area,volume and count of lateral roots,as well as fine(diameter<0.2 mm) and thick(diameter>0.2 mm) roots. The results indicate that the root growth of all genotypes was reduced under low K,but moderate K deficiency increased the root length of the efficient genotypes. At deficient and moderate K levels,all the efficient rice genotypes developed more fine roots(diameter<0.2 mm) than the inefficient ones. Both fine root count and root surface area were found to be the best parameters to portray K stress in rice. In accordance with the root morphology,higher K concentrations were noted in shoots of the efficient genotypes when grown at moderate and deficient K levels,indicating that root morphology parameters are involved in root uptake for K and in the translocation of K up to shoots. K deficiency affected not only the root morphology,but also the root ultra-structure. The roots of high-efficient genotypes had stronger tolerance to K deficient stress for root membrane damage,and could maintain the developed root architecture to adapt to the low K growth medium.

Soil nutrients in relation to vertical roots distribution in the riparian zone of Three Gorges Reservoir,China

Since the impoundment of the Three Gorges Reservoir(TGR), the riparian zone has been subjected to numerous environmental changes. This study was conducted to recognize the distribution of grass roots and its impacts on soil nutrients in the water level fluctuation zone of TGR. Roots of four predominant herbaceous plants in the study area, specifically, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, and their corresponding relation with soil nutrient contents were investigated. Root surface area density was determined with Win RHIZO, and the relationships of root distribution with soil depths and soil nutrient contents were studied. The results indicates that most roots are distributed in the top soil layer of 0-10 cm. Estimated root surface area density for the selected grass species ranges from 0.16 to 13.44 cm^2/cm^3, and decreases exponentially with an increase in soil depth. Soil organic matter and total nitrogen contents are significantly lower on bare control area than the corresponding values on the grasslands. Total nutrient contents on grasslands of C. dactylon and H. compressa are higher than those of other grass areas. Root length density and root surface area density are significantly correlated with soil organic matter and total nitrogen content for the four grasslands. The present results suggests that plant roots have significant effects on the distribution of soil nutrients in soil profiles in the riparian zone along the TGR. Nevertheless, additional investigations are needed to reveal the specific interactions between plant roots distribution, soil nutrients and water level fluctuations.

Combined toxicity of copper and cadmium to six rice genotypes (Oryza sativa L.)

Accumulations of copper （Cu） and cadmium （Cd） in six rice cultivars （94D-22, 94D-54, 94D-64, Gui630, YY-1, and KY1360） were evaluated through exposure to heavy metal contamination （100 mg/kg Cu, 1.0 mg/kg Cd, and 100 mg/kg Cu ＋ 1.0 mg/kg Cd） in a greenhouse. The dry weights of shoot and root, concentrations of Cu and Cd in plant tissues and the Cu, Cd, P, Fe concentrations in the root surface iron plaques were analyzed eight weeks later after treatment. The results indicated that the plant biomass was mainly determined by rice genotypes, not Cu and Cd content in soil. Separated treatment with Cu/Cd increased each metal level in shoot, root and iron plaques. Soil Cu enhanced Cd accumulation in tissues. In contrast, Cu concentrations in shoot and root was unaffected by soil Cd. Compared to single metal contamination, combined treatment increased Cd content by 110.6%, 77.0%, and 45.2% in shoot, and by 112.7%, 51.2% and 18.4% in root for Gui630, YY-1, and KY1360, respectively. The content level of Cu or Cd in root surface iron plaques was not affected by their soil content. Cu promoted Fe accumulation in iron plaques, while Cd has no effect on P and Fe accumulation in it. The translocation of Cu and Cd from iron plaques to root and shoot was also discussed. These results might be beneficial in selecting cultivars with low heavy metal accumulation and designing strategies for soil bioremediation.

Mechanistic Model for Predicting NO_3-N Uptake by Plants and Its Verification

Some mechanistic models have been proposed to predict the No3- concentrations in the soil solution at root surface and the NO3-N uptake by plants, but all these relatively effective non-steady state models have not yet been verified by any soil culture experiment. In the present study, a mathematical model based on the nutrient transport to the roots, root length and root uptake kinetics as well as taking account of the inter-root competition was used for calculation, and soil culture experiments with rice, wheat and rape plants grown on alkali, neutral and acid soils in rhizoboxes with nylon screen as a isolator were carried out to evaluate the prediction ability of the model through comparing the measured NO3-concentrations at root surface and N uptake with the calculated values. Whether the inter-root competition for nutrients was accounted for in the model was of less importance to the calculated N uptake but could induce significant changes in the relative concentrations of NO3- at root surface. For the three soils and crops, the measured NO3-N uptake agreed well with the calculated one, and the calculated relative concentrations at root surface were approximate to the measured values. But an appropriate rectification for some conditions is necessary when the plant uptake parameter obtained in solution culture experiment is applied to soil culture. In contrast with the present non-steady state model, the predicted relative concentrations, which show an accumulation, by the Phillips' steady-state model were distinct from the measured values which show a depletion, indicating that the present model has a better prediction ability than the steady-state model.

Pathogen of root surface caries in the elderly

Abstract:Objective To study the pathogen of root surface caries in the elderly. Methods Plaque samples from the experimental group and the control group were collected. After culturing in selective and non-selective media, the different bacteria were isolated. The counts and the positive rates of total bacteria, porphyromonas group, pervotella group, streptococcus mutants group, actinomyces group and lactobacillus group were compared.Results The counts of total bacteria, streptococcus mutants, actinomyces and lactobacillus of the experimental group were higher than those of the control group. The positive rates of actinomyces and lactobacillus of the experimental group were significantly higher than those of the control group. Conclusion Actinomyces and lactobacillus are the main related pathogens of root surface caries in the elderly.

Soil Anti-Scouribility Enhanced by Plant Roots

: The magnitude of soil anti-scouribility depends on the physical condition of the soil. Plant roots can greatly enhance soil stability and anti-erodibility. A scouring experiment of undisturbed soil was conducted to investigate the effects of roots on soil anti-scouribility and its distribution in the soil profile. At the end of each erosion test, plant roots were collected from soil samples and root surface area was calculated by means of a computer image analysis system (CIAS). Root surface area density (RSAD), the surface area of the roots per unit of soil volume, was related to soil anti-scouribility. More than 83% of root surface area was concentrated in the 0 - 30 cm soil layer. Soil anti-scouribility increased with an increase in RSAD and the value of intensified soil anti-scouribility (ΔAS) can be expressed by exponential equations, depending on the plant species. These equations were ΔAS =9.578 6 RSAD0.8321 (R2= 0.951) for afforested Pinus tabulaeformis Carr, ΔAS = 7.808 7 RSAD0.7894 (R2= 0.974) for afforested Robinia pseudoacacia L., and ΔAS= 9.256 6RSAD0.8707 (R2= 0.899) for Bothriochloa ischemum L.

Intercropping of Sonchus asper and Vicia faba affects plant cadmium accumulation and root responses

The cadmium(Cd)pollution of farmland soil is serious in the world.The present study investigated the effects of intercropping Vicia faba and the hyperaccumulator Sonchus asper on the Cd accumulation and root responses(morphology and secreted organic acids)of plants grown on soil from a mining area in Yunnan Province,China,under different Cd stress levels(0,50,100,and 200 mg kg-1).Intercropping increased the biomass of both S.asper and V.faba,as well as the Cd accumulation and Cd transfer coefficient from roots to shoots of S.asper,but decreased those of V.faba in the 200 mg kg-1Cd treatment.The Cd concentrations in roots,shoots,and grains from intercropped V.faba plants were positively correlated(P<0.05)with the N,N-diethyl phenylacetamide-extractable Cd content in soil.In the 50 mg kg-1Cd treatment,intercropping decreased citric and malic acids in root secretions of S.asper.Intercropped V.faba secreted more citric,oxalic,acetic,and malic acid compared with S.asper.Intercropping also increased root length and root surface area of both S.asper and V.faba.At 50 mg kg-1Cd,root length for S.asper was higher than that at 0 mg kg-1Cd,whereas V.faba roots had significantly decreased length and mean diameter.Intercropping of S.asper and V.faba is suggested as an in situ phytoremediation strategy of Cd-contaminated soils and may improve the food quality of V.faba.

Quantifying the adsorption and uptake of CuO nanoparticles by wheat root based on chemical extractions

Extensive application of metal nanoparticles is attracting more attention because of their potential environmental risks.Many studies have focused on the uptake of metal nanoparticles （NPs） by plant,but the adsorption of nanoparticles on root surface is often mistakenly regarded as their uptake.This study optimized the methods to distinguish the adsorption and uptake of CuO-NPs on the wheat root by applying different metal competing ions （Na ＋,Mg 2＋,and La 3＋ ）,surfactant （i.e.,sodium dodecyl benzene sulfonate,SDBS）,or complexing agents like NaOAc and Na 4 EDTA,as well as ultrasonic technique.The results indicated that some CuO-NPs is strongly adsorbed on the plant root surface,and part of them by mechanical adhesion.Competing ions could not desorb the CuO-NPs from the root surface,while NaOAc and Na 4 EDTA well dissolved the adsorbed CuO-NPs.In addition,the uptake and adsorption of CuO-NPs increased with increasing exposure concentrations of CuO-NPs in the range of 5–200 mg/L.The amount of CuO-NPs adsorption is always lower than that of their uptake.

Decoupled drought responses of fine-root versus leaf acquisitive traits among six Prunus hybrids

Aims Predicting drought consequences on forests and fruit crop plantings requires improved understanding of drought responses of both leaf and fine-root resource acquisitive traits(specific leaf area—SLA,specific root surface area—SRA and specific root length—SRL).We hypothesize their responses are coordinated towards integrated plant resource conservation under severe drought.Methods We tested the hypothesis with a greenhouse-based drought experiment on saplings of six Prunus hybrids with a priori known contrasting drought sensitivity.Saplings were subjected to either control(100%field capacity)or severe drought stress treatment(33%evapotranspiration of hybrid-specific control plants).Sample collections were carried out at 30 and at 60 days after the start of treatments,for both control and stressed saplings.Important Findings No hybrid showed concurrent significant decrease of SLA and SRA(or SRL)under severe drought.The fine-root traits of the six hybrids showed two major drought-response scenarios,in particular:(i)increased root tissue density(RTD)and decreased average root diameter without significant change of SRL and(ii)increased RTD and decreased SRL without significant change of average root diameter.Drought responses of leaf gas exchange,SRA,SRL and RTD were closely correlated along a gradient towards resource conservation from control to drought-stressed plants in all hybrids,which was orthogonal to another gradient characterized by a hybrid-dependent decrease of SLA.These findings highlight(i)the multi-dimensionality of root-trait drought responses,(ii)the decoupling between leaf economics and leaf hydraulics and(iii)the covariation of leaf and root hydraulics in terms of trait drought responses.The study contributes to identifying the origin of the multi-dimensionality of root-trait drought response at intraspecific scale,and highlights differential drought–response combinations of leaf and fine-root traits among hybrids to survive under severe soil drought stress.

Effects of Optimized Root Water Uptake Parameterization Schemes on Water and Heat Flux Simulation in a Maize Agroecosystem

As root water uptake（RWU）is an important link in the water and heat exchange between plants and ambient air,improving its parameterization is key to enhancing the performance of land surface model simulations.Although different types of RWU functions have been adopted in land surface models,there is no evidence as to which scheme most applicable to maize farmland ecosystems.Based on the 2007–09 data collected at the farmland ecosystem field station in Jinzhou,the RWU function in the Common Land Model（Co LM）was optimized with scheme options in light of factors determining whether roots absorb water from a certain soil layer（W_x）and whether the baseline cumulative root efficiency required for maximum plant transpiration（W_c）is reached.The sensibility of the parameters of the optimization scheme was investigated,and then the effects of the optimized RWU function on water and heat flux simulation were evaluated.The results indicate that the model simulation was not sensitive to W_x but was significantly impacted by W_c.With the original model,soil humidity was somewhat underestimated for precipitation-free days;soil temperature was simulated with obvious interannual and seasonal differences and remarkable underestimations for the maize late-growth stage;and sensible and latent heat fluxes were overestimated and underestimated,respectively,for years with relatively less precipitation,and both were simulated with high accuracy for years with relatively more precipitation.The optimized RWU process resulted in a significant improvement of Co LM’s performance in simulating soil humidity,temperature,sensible heat,and latent heat,for dry years.In conclusion,the optimized RWU scheme available for the Co LM model is applicable to the simulation of water and heat flux for maize farmland ecosystems in arid areas.

Effect of Silicon on Arsenic Concentration and Speciation in Different Rice Tissues

Rice is a major source of inorganic arsenic(As) exposure for billions of people worldwide. Therefore, strategies to reduce As accumulation in rice should be adopted. Silicon(Si) application can effectively mitigate As accumulation in rice. In this study, a pot experiment was performed to investigate the effect of Si on As speciation and distribution in different rice tissues. The results showed that Si addition significantly increased As and Si concentrations in soil solution and Si concentration in iron plaque formed around rice root surface, whereas As in the iron plaque was significantly decreased. Total As concentrations in the stem, leaf, husk, and brown rice were remarkably decreased by 51.9%, 31.9%, 33.8%, and 24.1%, respectively, after Si addition, and inorganic As concentrations were reduced by 52.3%, 35.5%, 50.1%, and 20.1%, respectively. Moreover, both dimethylarsinic acid concentration and percentage in rice grain were significantly elevated by Si application. Therefore, Si application is promising as a way to mitigate inorganic As accumulation in rice and to reduce consumer health risk.

Modelling sulphate-enhanced cadmium uptake by Zea mays from nutrient solution under conditions of constant free Cd^(2+) ion activity

A controlled hydroponic experiment was undertaken to investigate Cd uptake in relation to the activity of Cd species in solution other than the free ion （Cd^2＋） by maintaining a constant Cd^2＋ activity under variable SO4^2- and Cl^- concentrations exposed to maize （Zea mays vat. Cameron） plants. The objectives of these experiments were： （1） to distinguish and quantify the different uptake rates of free and inorganic-complexed Cd from nutrient solution, and （2） to model the uptake of Cd by maize with a Biotic Ligand Model （BLM） in a system which facilitates the close examination of root characteristics. Results of the current experiments suggest that, in addition to the free ion, CdSO4^0 complexes are important factors in determining Cd uptake in nutrient solution by maize plants. Higher nominal SO4^2- concentrations in solution generally resulted in a greater Cd accumulation by maize plants than predicted by the Cd^2＋ activity. A better integration of the complete dataset for the 3 harvest times （6, 9 and 11 days after treatment） was achieved by including consideration of both the duration of Cd exposure and especially the root surface area to express Cd uptake. Similarly, the fit of the BLM was also improved when taking into account exposure time and expressing uptake in terms of root morphological parameters.