Ionomics is the study of elemental accumulation in living organisms using high-throughput elemental profiling. In the present study, we examined the ionomic responses to nutrient deficiency in maize grown in the field in long-term fertilizer trials. Furthermore, the available elements in the field soils were analyzed to investigate their changes under long-term fertilizer treatment and the ionomic relationships between plant and soil. Maize was cultivated in a field with the following five long-term fertilizer treatments: complete fertilization, fertilization without nitrogen, without phosphorus, without potassium, and no fertilization. Concentrations of 22 elements in leaves at an early flowering stage and in soils after harvest were determined. The fertilizer treatments changed the availabilities of many elements in soils. For example, available cesium was decreased by 39 % and increased by 126 % by fertilizations without nitrogen and potassium, respectively. Effects of treatments on the ionome in leaves were evaluated using the translocation ratio (the concentration in leaves relative to the available concentration in soils) for each element. Nitrogen deficiency specifically increased the uptake ability of molybdenum, which might induce the enhancement of nitrogen assimilation and/or endophytic nitrogen fixation in plant. Potassium deficiency drastically enhanced the uptake ability of various cationic elements. These elements might act as alternatives to K in osmoregulation and counterion of organic/inorganic anions. Two major groups of elements were detected by multivariate analyses of plant ionome. Elements in the same group may be linked more or less in uptake and/or translocation systems. No significant correlation between plant and soil was found in concentrations of many elements, even though various soil extraction methods were applied, implying that the interactions between the target and other elements in soil must be considered when analyzing mineral dynamics between plant and soil.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-015-1562-x) contains supplementary material, which is available to authorized users.

Soil contains various essential and nonessential elements, all of which can be absorbed by plants. Plant ionomics is the study of the accumulation of these elements (the ionome) in plants. The ionomic profile of a plant is affected by various factors, including species, variety, organ, and environment. In this study, we cultivated various vegetable crop species and cultivars under the same field conditions and analyzed the level of accumulation of each element in the edible and nonedible parts using ionomic techniques. The concentration of each element in the edible parts differed between species, which could be partly explained by differences in the types of edible organs (root, leaf, seed, and fruit). For example, the calcium concentration was lower in seeds and fruit than in other organs because of the higher dependency of calcium accumulation on xylem transfer. The concentration of several essential microelements and nonessential elements in the edible parts also varied greatly between cultivars of the same species, knowledge of which will help in the breeding of vegetables that are biofortified or contain lower concentrations of toxic elements. Comparison of the ionomes of the fruit and leaves of tomato (Solanum lycopersicum) and eggplant (S. melongena) indicated that cadmium and boron had higher levels of accumulation in eggplant fruit, likely because of their effective transport in the phloem. We also found that homologous elements that have been reported to share the same uptake/transport system often showed significant correlation only in a few families and that the slopes of these relationships differed between families. Therefore, these differences in the characteristics of mineral accumulation are likely to affect the ionomic profiles of different families.

It is well known that lupin forms cluster roots, which help in dissolving insoluble P in soils. In nonleguminous species, cluster roots also appear to contribute to the utilization of organic N in soils. In white lupin ( Lupinus albus L.), however, the characteristics of its organic N utilization have not been studied. Therefore, we examined whether white lupin can utilize organic N in soils. Soybean ( Glycine max (L.) Merr.), which does not form cluster roots, was used as a control plant. Seedlings of lupin and soybean were cultivated in soils with different N sources (non-N, ammonium sulphate, ammonium sulphate plus cattle farmyard manure, or cattle farmyard manure). The rate of glycine uptake by excised roots was determined in a hydroponic experiment to investigate the ability of lupin and soybean to directly utilize amino acids. Nitrogen accumulation in soybean corresponded to the decrease in inorganic N in the soils. In contrast, N accumulation in lupin was higher than the decrease in inorganic N in the soil, especially with the cattle farmyard manure treatment, indicating that lupin derived more N from an organic N source. Wheat ( Triticum aestivum L.) cultivated with lupin in a pot accessed more available N than wheat with soybean or wheat in monoculture, suggesting that lupin roots themselves or the lupin rhizosphere microorganisms were able to decompose organic N in soils. Excised roots of lupin, especially cluster roots, exhibited higher rates of glycine uptake than roots of soybean. In conclusion, lupin decomposed organic N in the rhizosphere and was able to absorb amino acids from decomposition in addition to any inorganic N produced by further microbial decomposition.

By using good varieties (lines) and by applying coating urea which releases nitrogen slowly, extremely high yields were obtained in several crops. Based on the high yields and appropriate fertilizer application, it was difficult to consider in this experiment that deficiency or excess of nutrient elements (minerals) occurred in plant, so that the mineral status of crops could be adopted as criterion for high yield. The results obtained were as follows.1) Amount of minerals absorbed was calculated by the following equation: Ym=Ym/YbxYb=MRI• where Yb is the biological yield, Ym is the mineral yield (amount of minerals absorbed), MRI is the mineral requirement index. The MRI did not show any significant difference between the "high yield" and "standard yield" treatments in each crop with a few exceptions, indicating that the Yb is the main factor which determines the Ym in each crop.2) The MRI differed clearly among crops in the "high yield" treatment. MRI(N) was higher in soybean and winter wheat than in rice, maize, and potato. The MRI(P) was high in soybean, low in winter wheat and maize. The MRI(K) values were almost identical among the crops except for the "standard yield" treatment in winter wheat and maize. The MRI(Ca) and the MRI(Mg) were high in only soybean.3) For the "high yield" treatment, the Ym(N), the Ym(Ca), and the Ym(Mg) were high in winter wheat, and soybean, the Ym(P) was high in soybean, the Ym(K) was high in winter wheat, maize, and potato.4) The HI(DM) was 46% in soybean, 92% in potato, and 47-59% in gramineous plants, but the HI(N), the HI(P), and the HI(K) were higher in soybean and potato than in gramineous plants. Thus, harvesting organs required carbohydrate, N, P, and K intensively in potato, but only N, P, and K intensively in soybean.Key Words: harvest index of mineral, high yield, mineral requirement index.Abbreviations: Yb, biological yield (dry weight of whole plant without roots); Ye, economic yield (dry weight of harvesting organs, e.g. grains or tubers); Ym, amount of mineral absorbed (mineral yield), Ym(N), Ym(P), Ym(K), Ym(Ca), and Ym(Mg), Ym of N, P, K, Ca, and Mg, respectively; MRI, mineral requirement index; MRI(N), MRI(P), MRI(K), MRI(Ca), and MRI(Mg), MRI of N, P, K, Ca, and Mg, respectively; HI, harvest index; HI(DM), HI(N), HI(P), HI(K), HI(Ca), and HI(Mg), HI of dry matter, N, P, K, Ca, and Mg, respectively. 446M. OSAKI et al.As the productivity (Tanaka and Osaki 1983) and content of nutrient elements (minerals) in each organ (Tanaka 1985) depend on the kind of crops and the conditions of cultivation, the accumulation of minerals, distribution to each organ, and balance among each mineral also vary with each crop and methods of cultivation.In a previous paper (Osaki et al. 1991), the productivity of the "high yield" crops, which gave yields about 1.5 to 2 times higher than those of the "standard yield" crops, was reported. Namely, "high yield" crops were cultivated by the application of slow release coating urea and a slightly high planting density using high-yielding ...