Taiichiro Hattori

Growth and Nutrient Use in Four Grasses Under Drought Stress as Mediated by Silicon Fertilizers

ABSTRACT Field water stress is a common problem in crop production, especially in arid and semi-arid zones and it is widely hypothesized that silicon (Si) could reduce water stress in plants. We set up a greenhouse study to evaluate some silicon sources—potassium silicate (K2SiO3), calcium silicate (CaSiO3) and silica gel for growth and nutrient uptake by four grass species under adequate and deficit irrigation. The four species studied were Rhodes grass (Chloris gayana), Timothy grass (Phleum pratense), Sudan grass (Sorghum sudanense) and Tall fescue (Festuca arundinacea). For all species, the biomass yield response to applied silicon under deficit irrigation was significantly better than under adequate irrigation. The yield response of Rhodes grass across silicon sources was 205% under deficit irrigation compared with only 59% under adequate irrigation; for Sudan grass it was 49% compared with 26% and for Timothy, it was 48% compared with a mere 1%. The higher responses under deficit irrigation suggest that the plants relied more on silicon to endure drought stress. Biomass yield of individual plants also differed according to soil water levels with Timothy grass being the most sensitive to water stress as it exhibited the highest yield response (209%) to adequate irrigation. This was followed by tall fescue (122%) and Rhodes grass (97%). Sudan grass was the least affected by deficit irrigation, possibly on account of improved root mass and its natural drought tolerance. Strong associations were noted between the uptake of silicon and those of nitrogen (N) and phosphorus (P) irrespective of soil water condition, but the uptake of potassium (K) was more strongly correlated with that of Si under deficit than adequate irrigation. Improvements in plant growth following Si application could therefore be linked to enhanced uptake of major essential nutrients.

Energy Crops for Sustainable Bioethanol Production; Which, Where and How?

Abstract Bioethanol is gathering attention as a countermeasure to global warming and as an alternative energy for gasoline. Meanwhile, due to the synchronous increase in bioethanol production and grain prices, the food-fuel competition has become a public issue. It is necessary to see the issue objectively and to recognize that the real background is the change in allocation of limited resources such as farmland and water. In this review, we discuss which, where and how energy crops shouldbe grown to establish a sustainable bioethanol production system. Several combinations of crops, areas and cultivation methods are recommended as a result of a survey of the bioethanol production system with various energy crops. In tropical and subtropical regions, sugarcane can be grown in agricultural and/or unused favorable lands. In other regions, cellulosic energy crops can be grown in abandoned and marginal lands, including lands contaminated with inorganic pollutant like heavy metals and some detrimental minerals. There also is the possibility that, for Japan and other Asian countries, rice can be grown as an energy crop in unused lowland paddy field. Regarding cultivation way, energy saving is beneficial for bioethanol production systems irrespective of energy efficiency. On the other hand, effective energy input should be consideredfor the systems with higher energy efficiency when available land area is limited. Exploring and developing new energy crops and varieties, which show higher biomass productivity and stress tolerances under marginal conditions, are necessary for sustainable bioethanol production because energy crop production would be restricted mostly to marginal areas in future.

Effects of Silicon on Photosynthesis of Young Cucumber Seedlings Under Osmotic Stress

ABSTRACT Effects of silicon (Si) application on photosynthesis of solution-cultured cucumber seedlings were investigated under osmotic stress and unstressed conditions. In unstressed conditions, silicon application had no effect on growth and photosynthetic parameters. The responses of the photosynthetic parameters to abruptly imposed osmotic stress did not differ between silicon treatments. After 1 week exposure to osmotic stress, growth reduction was observed, but it was less severe in seedlings grown with silicon than in those without silicon. Although there were no differences between silicon treatments in stomatal conductance, transpiration rate, cuticular transpiration, or xylem sap exudation rate under osmotic stress, leaf intercellular carbon dioxide (CO2) concentration was significantly lower and photosynthetic rate tended to be higher in seedlings supplied with silicon. These results suggested that the silicon-induced alleviation of growth reduction under osmotic stress in cucumber was due to amelioration of stress-induced damage of leaf tissues rather than to improvement of leaf water status.

Silicon Application by Sorghum Through the Alleviation of Stress-Induced Increase in Hydraulic Resistance

ABSTRACT In this study, it was verified whether silicon (Si) affected plant hydraulic resistance, which was one of the significant factors affecting water uptake. Sorghum bicolor (L.) Moench. was grown hydroponically under varying silicon levels and exposed to osmotic stresses. Under osmotic stress, reduction in growth, photosynthesis, and transpiration were alleviated as supplied silicon levels increased. These alleviative effects were ascribed to enhancement of water uptake. Although shoot/root ratio was not affected by silicon, estimated apparent hydraulic resistance was lower in silicon-supplied sorghum than silicon-deficient one under osmotic stress. Simultaneous measurement of transpiration and water uptake rates indicated that under osmotic stress silicon-deficient sorghums showed unbalanced water relation that transpiration rate exceeded water uptake rate, while they were balanced in silicon-supplied sorghums. The results indicated that silicon improved hydraulic resistance, allowing sorghum to avoid from decrease in water uptake rate that happens to silicon-deficient sorghum under water stress.

Suppression of tillering in Erianthus ravennae (L.) Beauv. due to drought stress at establishment.

Abstract We investigated the effect of drought stress on biomass productivity of newly established Erianthus ravennae (L.) Beauv. This species has recently drawn great attention as a novel cellulosic energy crop because of its excellent tolerance against various environmental stresses, but the shoot dry weight of the newly established E. ravennae was significantly decreased under drought compared to irrigated condition. A significant correlation between shoot dry weight and stem number suggested that the drought-induced decrease in stem number was ascribable to the reduced shoot dry weight in the drought condition. Decrease in soil water content was coincident with mid-day decrease in stomatal conductance, suggesting that limitation of CO2 diffusion into leaf due to lower stomatal conductance in the drought condition caused decrease in photosynthesis followed by suppression of stem number. The present study suggested that E. ravennae was susceptible to drought, at least, in the first establishment year.

Growth Enhancement of Rye by Silicon Application Under Two Different Soil Water Regimes

ABSTRACT To clarify whether silicon application could improve root growth of rye (Secale cereale L.) under drought, a pot experiment was conducted under two soil water regimes (soil water contents were kept at 0.015–0.030 or above 0.050 g g−1 for dry and well-watered conditions, respectively). Silicon increased dry weight of rye but did not affect shoot/root ratio under the well-watered condition, while it lowered the ratio under the dry condition. Water use and leaf water potential were increased by silicon under the well-watered condition, although photosynthetic rate, stomatal conductance and water use efficiency were not affected. Under the dry condition, silicon-supplied ryes showed higher photosynthetic rate, stomatal conductance, water use and leaf water potential than silicon-deficient ones. These results suggested that silicon increased dry matter production of ryes under drought, enabling them to allocate more assimilates to root. This resulted in lowering of the shoot/root ratio and better adaptation to drought.

Effect of Stubble Shaving after High-Level Cutting on the Growth and Yield of Forage Sugarcane, KRFo93-1, under Multiple Ratooning Cultivation

Abstract In the production of sugarcane, stubble shaving that cuts the residual stubble of the previous crop is carried out to promote ratoon crop growth. On the other hand, in the production of feed crops, it is generally considered that high-level cutting increases the yield of the regrowth crop. In this study, the growth and yield of the forage sugarcane subjected to high-level cutting without stubble shaving (HC) were compared with those of the plants subjected to stubble shaving (Control) to clarify the necessity of stubble shaving in the cultivation of a forage sugarcane variety, KRFo93-1. The influence of high-level cutting on the growth and yield of ratoon crop was evaluated from the first ratoon crop (RC1) to sixth ratoon crop (RC6). Tiller number in the Control plot was not different from that in the HC plots in all ratoon crops from RC1 to RC6. Stem length was significantly larger in HC than in the Control plot in all ratoon crops at the initial stage of regrowth, and in RC1, RC3, RC5 and RC6 around the harvest time. Dry matter yield was significantly higher in HC than in the Control plot in RC1, RC3, RC5, RC6 and in the sum of the ratoon crops. Although no significant difference was observed in RC2 or RC4, the dry matter yield of HC exceeded that of Control plot. The increase in the dry matter yield of HC was due to an enhancement of stem growth, since the single stem dry weight were larger in HC than in Control plot. Thus, cultivation management without stubble shaving is recommended in KRFo93-1.

Evaluation of the juice brix of wild sugarcanes (Saccharum spontaneum) indigenous to Japan

Abstract Modern sugarcane cultivars are derived from the interspecific crossing between Saccharum officinarum and wild sugarcane, Saccharum spontaneum. The introgression of valuable characteristics from wild sugarcane is recognized as extremely important, but this process typically requires long-term effort over multiple generations of backcrosses owing to the low sugar content of the initial interspecific hybrids. In this study, we aimed to identify Japanese wild sugarcanes with high juice brix in order to promote effective interspecific crossing of sugarcane. Sixty-four accessions from the Nansei Islands and 70 accessions from the Honshu were evaluated for juice brix. Wild sugarcanes with high juice brix were demonstrated to exist among wild sugarcanes indigenous to the Honshu. A significant difference was observed between the median juice brix values of wild sugarcanes of the Nansei Islands and those of the Honshu. The relationship between juice brix and stem traits was then examined in 20 wild sugarcanes, 10 each from the Nansei Islands and the Honshu. The reproducibility of juice brix value in both experiments was confirmed. In contrast to juice brix, stem traits, such as length, diameter, and volume, were typically smaller in wild sugarcanes from the Honshu. Moreover, a negative correlation was observed between the index of stem volume and juice brix. In this study, we identified outstanding wild sugarcanes with high juice brix. Using germplasms from the identified wild sugarcanes in interspecific crossing could contribute to the increases in both yield and sugar content.