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.

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.

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.

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.