Masako Takebe

Variable response of growth and arbuscular mycorrhizal colonization of maize plants to preceding crops in various types of soils

Abstract. The effects of the preceding crops, sunflower (mycorrhizal host) and mustard (nonhost), on arbuscular mycorrhizal (AM) colonization and growth of succeeding maize were examined in 17 soils in an attempt to clarify the influence of soil characteristics on the effects of preceding crops. Shoot weight and P uptake of maize planted after sunflower were much higher than those after mustard in 14 soils, although the preceding crop had little effect on soil-P availability. AM colonization of maize after sunflower was much higher than that after mustard. The effect of the preceding crop was eliminated by soil sterilization. These results suggested that the differences in maize growth were caused by differences in the AM colonization. Correlation analysis of the effect of the preceding crop and soil properties showed that the difference in the effects on maize growth could not be explained by soil chemical properties, but only by the AM colonization of the preceding sunflower crop. In one of the 17 soils, however, the effect was not evident despite the higher AM colonization of sunflower. This soil was sterilized, and the effect of inoculation by AM fungi (AMF) on maize was examined. However, it was found that the inoculation increased AM colonization but did not improve maize growth at any P level, suggesting that the effect of AMF was unusually inhibited in this soil by unknown soil physicochemical properties. In most soils, however, the preceding mycorrhizal host crop, sunflower, improved the growth and AM colonization of maize depending on the AM colonization of sunflower.

Temporal or spatial arrangements of cover crops to promote arbuscular mycorrhizal colonization and P uptake of upland crops grown after nonmycorrhizal crops

AimsA field experiment was conducted where maintenance of indigenous arbuscular mycorrhizal (AM) fungal populations was attempted using AM host cover crops arranged temporally or spatially during growth of nonmycorrhizal crops.MethodsTo arrange AM hosts temporally, sunflower or oat was grown as a cover crop after non-host cropping (cabbage) or fallowing. In order to arrange AM hosts spatially, red clover, white clover or vetch was intercropped during growth of non-host cabbage.ResultsThe AM colonization and growth of maize with previously introduced sunflower or oat were much greater than those without introduction of cover crops or those with introduction of non-host cover crops. The AM colonization and yield of winter wheat grown after cabbage with AM host intercropping were greater than those after cabbage only cropping, suggesting that arrangement of AM hosts between cabbage rows is effective for maintaining the AM fungal population in soil during non-host cropping.ConclusionsMycorrhizal hosts cropped after or during non-host cropping is an effective means to increase indigenous AM fungal populations. The results show that AM colonization, P uptake and productivity of crops after cultivation of nonmycorrhizal crops can be improved by arranging AM hosts temporally or spatially as cover crops.

Comparison of Whole System of Carbon and Nitrogen Accumulation Between Two Maize Hybrids Differing in Leaf Senescence

A field experiment was conducted to investigate the carbon (C) and nitrogen (N) balance in relation to grain formation and leaf senescence in two different senescent types of maize (Zea mays L.), one stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55). In comparison with Hokkou 55, P3845 had a higher N concentration (Nc) in the leaves and a higher specific N absorption rate by roots (SARN), which indicated that a large amount of N was supplied to the leaves from the roots during maturation. This resulted in a higher photosynthetic rate, which supports saccharide distribution to roots. Thus, stay-green plants maintained a more balanced C and N metabolism between shoots and roots. Moreover, the coefficients of the relationship between the relative growth rate (RGR) and Nc, and between the photon-saturated photo-synthetic rate (Psat) and Nc were lower in P3845. The Psat per unit Nc in leaves was lower in the stay-green cultivars, which indicated that high yield was attained by longer green area duration and not by a high Psat per unit Nc in the leaf. Consequently, a high Psat caused a high leaf senescence rate because C and N compounds will translocate actively from the leaves.

Nitrous oxide evolved from soil covered with plastic mulch film in horticultural field

Soil solarization practice, in which soil is covered with plastic mulch film and exposed to high temperature prior to crop cultivation, is expected to be an effective method for reducing weeds and pathogenic microorganisms without using agricultural chemicals. Although the production of nitrous oxide (N2O), a major greenhouse gas, is enhanced in fertilized soil covered with plastic mulch films, its transport route to the atmosphere has not been sufficiently elucidated to date. In this study, we investigated the N2O evolution from plastic-mulch-film-covered agricultural soil. In a horticultural field where ridge soil was covered with a plastic mulch film after fertilization, we observed significant N2O flux from the soil surface of the unfertilized furrow between the ridges, indicating the horizontal diffusion of N2O from the ridge soil covered with the mulch film to the adjacent furrow soil surface. On the other hand, the measurement of the permeance (permeation coefficient) of the plastic mulch film for gaseous N2O by laboratory experiment revealed that N2O gradually permeated the mulch film; the permeance increased exponentially with an increase in ambient temperature, indicating possible N2O emission by permeation through the mulch film under field conditions. In winter, the amount of N2O emission by permeation through the mulch film was estimated to be lower than that emitted from the furrow soil surface, and it was lower than that in summer. On the other hand, it was estimated to be much higher in summer owing to the higher permeance of the film at high temperatures.

Changes of Photosynthetic Characteristics in Relation to Leaf Senescence in Two Maize Hybrids with Different Senescent Appearance

A field experiment was conducted to investigate the changes in chlorophyll (Chl) and nitrogen (N) contents, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase (PEPC) contents and PEPC activity, and the photon-saturated net photosynthetic rate (PNsat), and their relationships with leaf senescence in two maize hybrids with different senescent appearance. One stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55) hybrid were used in this study, and we found that Chl and N contents and the PNsat in individual leaves of P3845 were greater than those in corresponding leaves of Hokkou 55 at the successive growth stages. In addition, larger contents of RuBPCO and PEPC, and a greater activity of PEPC were observed in P3845. Due to the lower rates of decrease of Chl, RuBPCO, and PEPC amounts per unit of N, and the lower net C translocation rate per unit of N in the stay-green hybrid, leaf senescence was delayed in comparison to the earlier senescent hybrid.

Maintenance of soybean yield with reduced phosphorus application by previous cropping with mycorrhizal plants

Abstract Previous cultivation of arbuscular mycorrhizal (AM)-host plants promotes AM colonization, phosphorus (P) uptake and the growth of succeeding AM-host plants. Three field experiments were conducted to investigate whether reduced application rates of P fertilizer could maintain soybean (Glycine max (L.) Merr. cv. Tsurumusume) yields when fields were previously cropped with AM-host plants. In the experiments, soybean was cropped after growing both AM-host (wheat, sunflower, vetch, maize and azuki bean) and non-AM-host plants (radish, white mustard, sugar beet and buckwheat) or fallow with different rates of P fertilizer (0–200 kg P2O5 ha−1). The results showed that previous cropping with AM-host plants increased AM colonization of soybean roots, soybean growth, shoot P content and yield compared with either previous cropping with a non-AM host or fallow treatment. Soybean yields following AM-host plants did not decrease with reductions in the P application rate from 150 to 50 kg P2O5 ha−1, although soybean yields decreased in some cases after non-AM-host plants or fallow treatment. A general linear model analysis revealed that soybean yield following AM-host plants was less affected by a reduction in P application rate than plants following non-AM-host plants. As a result, P application rates can be reduced from 150 kg P2O5 ha−1 (the rate recommended by the Hokkaido Government) to 50 kg P2O5 ha−1 for soybean cultivation in soils after AM-host plants.

Metabolite profiling of spinach (Spinacia oleracea L.) leaves by altering the ratio of NH+ 4/NO− 3 in the culture solution

Abstract To observe the effect of different forms of N, we have applied metabolic profiling using gas chromatography mass spectrometry to evaluate the metabolite composition of spinach. The aim of the present study was to find an appropriate indicator of overall metabolic response to N source. The effect of the NH+ 4/NO− 3 ratio on spinach tissue was investigated, comparing two cultivars that differed in their ability to use N. There was wide variation in NH+ 4/NO− 3 absorption without any distinct growth inhibition in either cultivar. Statistical analysis revealed that the metabolites could be broadly divided into two types, correlating either positively or negatively with NH+ 4 uptake in the culture solution. Principal component analysis (PCA) was an effective tool that extracted the indexes of the effect of the ratio of N forms as PCA scores. Close relationships between metabolite profiles and NH+ 4 uptake were observed, indicating that metabolic profiling is able to distinguish the invisible metabolic change in mature leaves of spinach and may provide a new tool for the investigation of quality features or rhizosphere nutritional condition.

Soil microbial biomass phosphorus as an indicator of phosphorus availability in a Gleyic Andosol

Abstract The relationship between plant phosphorus (P) uptake and soil microbial biomass phosphorus (biomass P) or available phosphorus (Truog P) was estimated in a Gleyic Andosol in Sapporo, Hokkaido, in a 4-year field trial (2004–2007). Every year, the soil was treated in duplicate (each plot 36 m2) or triplicate (each plot 24 m2) with chemical fertilizer, cow manure compost or sewage sludge compost, and then kidney beans (Phaseolus vulgaris) were planted. Pooled data of the shoot content of P at harvest over the 4 years was significantly correlated with biomass P determined 1 month after the application of fertilizer (P < 0.01). A multivariate analysis revealed that the grain yield was significantly positively correlated with the shoot content of P (P < 0.01) and significantly negatively correlated with the shoot content of calcium (P < 0.05), but not correlated with the shoot content of either nitrogen or potassium. These results suggest that P is the most limiting element to affect the productivity of kidney bean plants in this trial and that biomass P is an important P source that explains the differences in P availability among soil amendments. Biomass P is a better indicator of P availability for kidney beans grown in Gleyic Andosols compared with Truog P, which is widely used in Japan.

Arbuscular mycorrhizal (AM) effects on maize growth and AM colonization of roots under various soil moisture conditions

Abstract The effects of arbuscular mycorrhizal (AM) inoculation on growth, P uptake, and AM formation of maize (Zea mays L.) were examined at different soil moisture levels. Arbuscular mycorrhizal inoculum was added to pots filled with sterilized Andosol at concentrations of 0, 10, 50 g kg-1 dry soil. From 11 to 75 d after sowing, the soil water potential was adjusted to around -10 (wet: W), -50 (moist: M), or < -63 kPa (dry: D). The effect of inoculation on maize growth and P uptake was distinct in dry soil, in which AM colonization of roots occurred significantly more frequently in inoculated than in non-inoculated soil. The effect, however, was less pronounced with the increase in the soil moisture status, despite wide differences in the AM spore population and AM colonization. The increased AM colonization with the increase in the soil moisture status indicated that a higher soil moisture status improved the efficiency of AM colonization of roots. The increase in the shoot weight of non-inoculated maize with the improvement in the soil moisture status was presumably due to a higher P availability under a higher soil moisture status. Such effects may in turn stimulate P uptake and enhance plant growth, thereby masking the influence of the AM population.

Metabolite profiling of Komatsuna (Brassica rapa L.) field-grown under different soil organic amendment and fertilization regimes

Among agricultural soil fertility management options, the environmental benefits of organic amendments have recently drawn particular attention. However, little information exists about their effects on crop metabolites or quality. Field plots of Komatsuna (Brassica rapa L. var. perviridis) were planted in a fractional factorial design with the following treatments: soil amendments of cattle manure (0, 2 or 4 kg m−2), wheat straw (0, 0.05 or 0.1 kg m−2), fast release nitrogen (N) (0, 6 or 12 g N m−2 of ammonium sulfate), slow release N (0, 3 or 6 g N m−2 of coated ammonium nitrate), phosphorus (P) [0, 5 or 10 g phosphorus pentoxide (P2O5) m−2 of lime superphosphate] and potassium (K) [0, 6 and 12 g potassium oxide (K2O) m−2 as potassium sulfate]. Metabolite profiling was carried out using a gas chromatograph/mass spectrometer (GC/MS), which yielded 62 and 67 metabolites in the leaves and the petioles, respectively. Metabolite peak areas were subjected to principal component analysis (PCA). The first component accounted for 44.1% of the total variance and bore a close relationship to N. The third component accounted for 8.8% of the total variance and was used to distinguish between different levels of manure application. An analysis of variance (ANOVA) of treatment factor effects on individual metabolites showed that the three most significant factors, from highest to lowest, were N absorption, manure amendments and slow release N. The effects of the manure amendments were not fully explained by its attendant N, P or K inputs. This result raises the question as to what mechanisms may bring about the metabolic changes caused by the manure amendment. The current findings will serve to direct further studies on the relationship between crop quality and cultivation procedures and will lead to more efficient quality control methods.