Unit Weight Of Root Research Articles

Humic acids affect root characteristics of fodder radish (Raphanus sativus L. var. oleiformis Pers.) in metal-polluted wastes

In a series of pot trials, fodder radish (Raphanus sativus L. var. oleiformis Pers.) was cultivated in pyrite cinders heavily polluted by various heavy metals (HM). The effects of application of humic acids (HA) to the cultures were evaluated at various concentrations (0.1 and 1 g kg−1 of cinders) and for different methods of application (mixed with cinders before sowing; applied on the top of substrate after sowing; foliar spraying), in comparison with untreated controls. HA increased the bioavailability of various HM, especially when applied at high concentrations. Low concentrations of HA, either mixed with cinders or applied on foliage, slightly enhanced shoot growth. High levels of HA were generally phytotoxic, probably because of the ensuing higher heavy metal concentrations in the shoots. Foliar spraying was partially able to attenuate the phytotoxicity of high dosages of HA, as revealed by the increased rate of leaf expansion. A negative correlation was found between shoot biomass and concentration of HM, and higher removals were generally associated with smaller doses of HA and foliar application. Within the range of concentrations tested, humic substances led to a reduction in root diameter and an increase in specific root length (SRL, length per unit weight of roots), significant only at the highest dosage, together with a tendency towards enhancement of translocation of HM to the shoot – both positive traits for phytoremediation purposes.

Phosphorus uptake and growth of barley as affected by soil temperature and mycorrhizal infection

Abstract A glasshouse study was conducted to investigate the effects of soil temperatures of 20, 15 and 10°C on growth and phosphorus (P) uptake of barley (Hordeum vulgare L. cv. Galleon) inoculated with Glomus intraradices Schenck & Smith. Vesicular‐arbuscular (VA) mycorrhiza formation was significantly reduced as the soil temperature decreased. Plant growth depression due to temperature stress was more pronounced in mycorrhizal plants than in non‐mycorrhizal plants. The lower the soil temperature, the higher was the root‐shoot ratio. The ratio was also higher in non‐mycorrhizal plants than in mycorrhizal plants. Concentration of P in roots was influenced by mycorrhiza. Significant interaction between mycorrhiza and soil temperature was observed for root dry matter and specific P uptake (P uptake per unit weight of root). Compared to non‐mycorrhizal plants, specific P uptake in mycorrhizal plants was higher.

Preliminary evaluation of experimental techniques for studying the absorption of rubidium by grape roots

Abstract The experimental material consisted of root segments excised from grape cuttings maintained in nutrient culture. In every experiment reported here washed roots absorbed Rb at substantially higher rates than unwashed root segments. The absorption of Rb per unit weight of root was generally in the same low range for unwashed roots with little regard to diameter, age, browning, or the presence of an intact root apex. On the other hand, after washing, uptake was much higher in large diameter roots than smaller ones, higher in white roots than in brown ones, and higher in younger tissues than older ones, The response to washing is markedly reduced by the presence of an intact attached root apex.

Influence of the Form of Nitrogen Supply on Root Uptake and Translocation of Cations in the Xylem Exudate of Maize (Zea maysL)

Concentrations of inorganic cations are often lower in plants supplied with NH4+ as compared with NO3−. To examine whether this is attributable to impaired root uptake of cations or lower internal demand, the rates of uptake and translocation of K, Mg, and Ca were compared in maize plants (Zea mays L.) with different growth-related nutrient demands. Plants were grown in nutrient solution with either 1·0 mol m−3 NO3− or NH4+ and the shoot growth rate per unit weight of roots was modified by varying the temperature of the shoot base (SBT) including the apical shoot meristem. The shoot growth rate per unit weight of roots, which was taken as the parameter for the nutrient demand imposed on the root system, was markedly lower at 12°C than at 24°C SBT. As a consequence of the lower nutrient demand at 12°C SBT, uptake rates of NO3− and NH4+ declined by more than 50% Compared with NO3− supply, NH4+ nutrition depressed the concentrations of K and particularly of Ca in the shoot, both in plants with high and with low nutrient demand. This indicates a control of cation concentration by internal demand rather than by uptake capacity of the roots. Translocation rates of K, Mg and Ca in the xylem exudate were lower in NH4+- than in NO3−-fed plants. Net accumulation rates of Ca in the shoot were also decreased, whereas net accumulation rates of K in the shoot were even higher in NH4+-fed plants. It is concluded that reduced cation concentrations in the xylem sap of plants supplied with NH4+ are due to the lower demand of cations for charge balance. The lower K translocation to the shoot is compensated by reduced retranslocation to the roots. For Ca, in contrast, decreased translocation rates in NH4+-fed plants result in lower shoot concentration.

Short‐ and long‐term effects of a change in the spatial distribution of nitrate in the root zone on N uptake, growth and root development of young lettuce plants

Abstract. The effects of a change in the distribution of nitrate within the root zone on N uptake and growth were studied using young lettuce plants after reducing the proportion of their root systems supplied with nitrate from 100 to ca 10% in split‐root experiments in the glasshouse. The main effects of the localized nitrate supply were concentrated in a 2‐week period immediately after the treatment was imposed, when a temporary reduction in nitrate uptake caused the gradual development of N deficiency and a decline in plant growth rate. The plants adapted to the change in nitrate distribution, initially by increasing unit absorption rates (uptake rates per unit weight of root) and more gradually by increasing production of new roots in the high‐nitrate zone. As a result, relative N uptake rates and relative growth rates were restored to the same levels as for control plants (given a spatially uniform N supply throughout) after ca 12d, even though only ca 12–15% of their roots were exposed to nitrate at this time. Thereafter, the plants continued to adapt by concentrating new root growth in the nitrate‐containing zone, ultimately allowing unit absorption rates to return to normal. There was no evidence of any significant N deficiency in the plants after the initial adaptive response was complete, even though the total‐N concentrations of the plants given the localized supply were consistently less than those given the uniform N treatment, and nitrate concentrations in the petiole sap were generally lower in leaves on one side of the plant (because of limited lateral movement of nitrate between xylem vessels during its transport to the shoot).The delay in the initiation of an adaptive response caused a significant check in growth, and the resulting relative weight differences were maintained throughout the subsequent life of the plant. Plants in all treatments matured on the same date, so yields for those grown with the localized supply were less than those of the control, and could not be recovered by delaying final harvest without unacceptable loss of quality. The pattern of the changes in N uptake and plant growth, and the effect on final yield, were similar to those exhibited by young lettuce plants subjected to a temporary interruption in nitrate supply, suggesting that the reduction in final yield for plants grown with the localized supply was largely the effect of the check in growth which occurred whilst the Plants were adapting to the change in nitrate distribution during the early part of the experiment. This implies that the rate of dry matter production of young lettuce plants can be altered by N treatment without affecting their rate of physiological development.

The influence of some soil and plant factors on the concentration of copper in perennial ryegrass

The absorption and transport of Cu were studied in perennial ryegrass grwon on 21 soils under controlled environment conditions. Neither the concentration, nor the total amount, of Cu in the shoots was related to available Cu in the soils as assessed by extraction with 0.05M EDTA, 0.005M DTPA, or 1.95 per cent HNO3. The concentration in the roots and, more especially, absorption per unit weight of root (i.e. μg Cu g dry wt−1) were, however, highly correlated with available soil Cu. This suggests that, unless the extent of exploitation of the soil by roots is taken into account, measurements of available Cu will not be effective in predicting uptake by plants. On average, 63 per cent of the Cu absorbed by the roots was retained in the roots, and variation in the proportion retained was related to the transport of nitrogen from roots to shoots. On some soils the concentrations of N and Cu in the shoots were significantly correlated, and variation in N concentration accounted for a considerable proportion of the variance in the Cu concentration at later harvests. The relative importance of the measured soil (pH, organic matter) and plant (dry weight, N content) factors changed markedly over 6 successive harvests.

Phosphorus Uptake and Utilization by Tree Seedlings

Seedlings of five native forest species and of Pinus radiata D. Don were grown in pots in a forest soil at a range of levels of added phosphate for up to 20 weeks. At intervals of 3 weeks, roots were examined for root hairs and mycorrhizas and the weights of plant parts and their phosphorus contents were measured. Components of growth and response were calculated from three-dimensional surfaces which had level of phosphate and time as the independent variables. Except for Banksia grandis Willd., the species responded to phosphate but the time at which the response appeared was affected by seed reserves of phosphorus. Thus response appeared much earlier for the small-seeded Eucalyptus divevsicolor F. Muell. and Acacia pulchella R. Br. than for the large-seeded Eucalyptus calophylla R. Br. and Eucalyptus marginata Donn. ex Sm. The absence of a response by the banksia seemed to arise because of a large seed reserve of phosphorus, a low relative growth rate and a very low concentration of phosphorus in the leaves for maximum photosynthesis. The rates of uptake of phosphorus per unit weight of roots were generally low but increased at a time coincident with the development of mycorrhizas. Relative growth rates and the net assimilation rates were also low and reached maximum values at low concentrations of phosphorus in the leaf. The outcome was that the level of applied phosphate needed for good early growth did not differ greatly from that of Trifolium subterraneum L.