The beneficial element silicon (Si) may affect radial oxygen loss (ROL) of rice roots depending on suberization of the exodermis and lignification of sclerenchyma. Thus, the effect of Si nutrition on the oxidation power of rice roots, suberization and lignification was examined. In addition, Si-induced alterations of the transcript levels of 265 genes related to suberin and lignin synthesis were studied by custom-made microarray and quantitative Real Time-PCR. Without Si supply, the oxidation zone of 12 cm long adventitious roots extended along the entire root length but with Si supply the oxidation zone was restricted to 5 cm behind the root tip. This pattern coincided with enhanced suberization of the exodermis and lignification of sclerenchyma by Si supply. Suberization of the exodermis started, with and without Si supply, at 4–5 cm and 8–9 cm distance from the root tip (drt), respectively. Si significantly increased transcript abundance of 12 genes, while two genes had a reduced transcript level. A gene coding for a leucine-rich repeat protein exhibited a 25-fold higher transcript level with Si nutrition. Physiological, histochemical, and molecular-biological data showing that Si has an active impact on rice root anatomy and gene transcription is presented here.

Paddy rice is a global staple food which in some circumstances can contain high levels of the toxic element arsenic (As). In order to elucidate factors influencing As dissolution in the soil solution during paddy rice cultivation, rice (Oryza sativa L. "Selenio") was cultivated to maturity in six paddy soils in the greenhouse in 2005 and 2006. Concentrations of Mn, Fe, As, P, and silicic acid in soil solution and As concentrations in rice straw and polished rice grain were determined. There was a close relationship between Fe and As concentrations in the soil solution, suggesting that the major part of dissolved As originated from reduced iron-(hydr)oxide. However, in addition to the factors causing As dissolution in the soil, other factors influenced the uptake of As by rice. The inhibitory effect of indigenous silicic acid in the soil solution on As uptake was clearly shown. This implied that soils with high plant available Si contents resulted in low plant As contents and that Si application to soils may decrease the As content of rice.

Plant utilization of P applied to soils is usually low. Utilization may be increased by having more roots present or by improving P uptake characteristics of the roots. The objective of this research was to determine the effect of varying corn (Zea mays L.) root characteristics, by using different genotypes, on P uptake and to determine if the Claassen‐Barber simulation model predicted these differences accurately. Five corn genotypes were grown in the growth chamber in soil at two levels of P and harvested a three ages. Increasing P level increased shoot yield of all genotypes, but had little effect on the amount of roots. The root surface area per unit of shoot weight varied between genotypes at low soil P but not at high soil P. Wih high soil P here was a linear correlation with r = 0.98 and a slope of 0.97 between P uptake predicted by the simulation model and observed P uptake. At low soil P observed P uptake was double the predicted uptake, however, the correlation was r = 0.90. Root hair effects, not included in the simulation model, were probably the reason for the greater observed P uptake at low soil P. Differences between genotype in morphological and physiological root characteristics in. fluenced the amount of P absorbed by corn plants. It appears that genotypes could be developed that would be more efficient in absorbing P from soil.

Phosphate uptake by plants growing in soil is influenced by the P uptake properties of the root and the P supply characteristics of the soil. This system may be described by mathematical simulation models. The objective of this research was to determine if a model used successfully for describing K uptake by corn (Zea mays L.) could be used for describing P uptake. A growth chamber experiment with corn grain on six soils varying widely in physical and chemical characteristics was conducted. Three harvests were made and root morphology and P uptake were measured. The significance of the differences in root morphology and in soil P‐supply parameters of initial P concentration in soil solution, buffer power, and effective diffusion coefficient for P were determined by using them in the Claassen‐Barber simulation model which considers these soil factors, root morphology, and root physiology to predict P uptake by plants. The calculated P uptake, y was correlated (r = 0.93) with observed P uptake, x. The regression equation, y = 1.09x + 27.3 indicated a 9% overprediction of P uptake which was probably because the model did not consider root to root competition for P. The parameters used in this objective simulation model appear to be the important ones determining P absorption by plants from soil. In this study, root morphology varied with soil and was highly correlated with P uptake (r = 0.88). This simulation model should be a useful tool in P fertilization research.

No abstract