Kazutoshi Kinjo

Expression of terpenoid synthase mRNA and terpenoid content in salt stressed mangrove

The halophytic Kandelia candel and Bruguiera gymnorrhiza are ideal model for studying the molecular mechanisms of salinity tolerance in mangrove plants. The correlation between mRNA expression of four oxidosqualene cyclase (OSC) genes namely, KcMS multifunctional terpenoid synthase and KcCAS cyloartenol synthase (K. candel), BgbAS beta-amyrin synthase and BgLUS lupeol synthase (B. gymnorrhiza) and salt concentration was examined. mRNA level of KcMS was increased with salt concentration in both roots and leaves of K. candel. Similarly, salt stress increased the mRNA levels of BgLUS and BgbAS in the root of B. gymnorrhiza. This result suggests that the function of terpenoids in root is associated with the salt stress. In contrast to these observations, the mRNA level of KcCAS was not modulated by salt stress in the roots, and decreased in the leaves. These results therefore suggest that the terpenoids but not phytosterols play an important role to cope with the salt stress in mangrove root. The content and proportion of beta-amyrin and lupeol increased with salinity in the root of K. candel and B. gymnorrhiza, providing additional evidence for the protective role of terpenoids. However, beta-amyrin and lupeol in B. gymnorrhiza leaves decreased with salt concentration, suggesting that the physiological significance for the terpenoids in the leaf may differ from that for the root.

Effect of Synthetic Soil Aggregates as a Soil Ameliorant to Enhance Properties of Problematic Gray (“Jahgaru”) Soils in Okinawa, Japan

Synthetic aggregates (SA) were developed using low productive red soil, paper, and starch waste and then utilized as a soil ameliorant to improve poor physical and chemical properties of a gray soil (“Jahgaru”). The gray soil was amended with SA at 10, 20, 30, 40, and 50% and then used for the cultivation of French marigold (Tagetes patula). The SA addition enhanced bulk density, porosity, water‐holding capacity, hydraulic conductivity, pH, organic matter, and carbon (C) content of original gray soil. Plant height, number of flowers per plant, shoot fresh weight, shoot dry weight, root length, root fresh weight, and root dry weight in 30% of SA addition were the greatest and were increased by 1.5, 2.9, 3.5, 4.7, 3.4, 4.3, and 9 times, respectively, compared to gray soil. It can be concluded that developed SA can be utilized as a soil ameliorant to improve poor physical and chemical properties of gray soil.

Growth and Nutrient Accumulation of Winged Bean and Velvet Bean as Cover Crops in a Subtropical Region

We examined biomass dry matter and nutrient uptake of live plant parts, leaf area index, and litter of winged bean (Psophocarpus tetragonolobus) and velvet bean (Mucuna pruriens) 12, 18, 24 and 30 weeks after sowing (WAS). The two plants had similar leaf and stem+petiole biomasses. At 30 WAS winged bean had a significantly lower pod yield than velvet bean. Between 18 and 30 WAS, winged bean produced less litter than velvet bean due to differences in growth stages. The total mulch of live parts and litter of winged bean and velvet bean completely covered the ground by 18 and 12 WAS, respectively. Compared to velvet bean, the leaf and stem+petiole of winged bean had a significantly higher N concentration; significantly higher N uptake at 24 and 30 WAS; significantly lower C/N ratio; and significantly higher P, K and Mg concentrations. In winged bean, P uptake was significantly higher in the leaf at 30 WAS and in the stem+petiole at all harvesting times. The total biomass of the leaf, stem+petiole and litter of winged bean was 317–561 g DM m-2, and their N content was 12.3–17.7 g m-2. The total biomass of live parts and litter of winged bean might be sufficient to suppress weeds and increase soil N. Winged bean is an appropriate legume cover crop and green manure due to its longer growing period and superior ground-covering ability and high N input.

Potential growth of hairy vetch as a winter legume cover crops in subtropical soil conditions

Abstract Soil acidity is one of the most serious causes of land degradation and limits crop production in subtropical agriculture. A number of legumes have adapted to P-limiting conditions, and the aim of the present study was to select an appropriate species for use as a winter legume cover crop under subtropical soil conditions in Okinawa, where P deficiency stems from soil acidification. Four vetch and four clover species were examined in pot trials. Of these, hairy vetch (Vicia villosa Roth) was found to be the most tolerant of P-limiting conditions. The shoot biomass of hairy vetch was also generally higher than that in the clover species when the P supply was non-limiting in the spring season. Hairy vetch was then compared in a pot trial with four clover species for an extended period of growth with adequate P supply. The N fixing activity of hairy vetch in the vegetative stage was 3.2-fold greater than that of the clover species. Nitrogen and P uptake in shoots and roots was significantly higher in hairy vetch than in the clover species in the vegetative and flowering stages. The C/N ratio in the shoots and roots of hairy vetch tended to be lower than that in the clover species. Shoot K uptake by hairy vetch was significantly higher in the vegetative stage than that in the clover species. In a field trial, shoot biomass and nutrient uptake of hairy vetch were similar on four different subtropical soils with pH values ranging from 5.7 to 7.5. Hairy vetch is an appropriate winter legume cover crop to improve subtropical soils by increasing organic matter and supplying nutrients to the subsequent crop.

High salinity leads to accumulation of soil organic carbon in mangrove soil

Although mangrove forests are one of the most well-known soil organic carbon (SOC) sinks, the mechanism underlying SOC accumulation is relatively unknown. High net primary production (NPP) along with the typical bottom-heavy biomass allocation and low soil respiration (SR) have been considered to be responsible for SOC accumulation. However, an emerging paradigm postulates that SR is severely underestimated because of the leakage of dissolved inorganic carbon (DIC) in groundwater. Here we propose a simple yet unique mechanism for SOC accumulation in mangrove soils. We conducted sequential extraction of water extractable organic matter (WEOM) from mangrove soils using ultrapure water and artificial seawater, respectively. A sharp increase in humic substances (HS) concentration was observed only in the case of ultrapure water, along with a decline in salinity. Extracted WEOM was colloidal, and ≤70% of it re-precipitated by the addition of artificial seawater. These results strongly suggest that HS is selectively flocculated and maintained in the mangrove soils because of high salinity. Because sea salts are a characteristic of any mangrove forest, high salinity may be one of mechanisms underlying SOC accumulation in mangrove soils.

Oil palm waste and synthetic zeolite: an alternative soil-less growth substrate for lettuce production as a waste management practice.

A study was conducted to assess the characteristics and the prospective utilization of oil palm waste (OP) and synthetic zeolite (SZ) developed by coal fly ash, as an alternative substrate to peat and commercial perlite for lettuce (Lactuca sativa L.) production. The SZ, OP, sphagnum peat (PE), perlite (PL) and two different SZ—OP mixtures (v/v) at the ratio of 1 : 3 and 1 : 10 were utilized as the substrates under this study. The substrates formulated by mixing SZ with OP at the ratio of 1 : 3 and 1 : 10 showed improved substrate physical and chemical properties such as air space, bulk density, particle density, water-holding capacity, pH and electrical conductivity (EC), which were in the ideal substrate range when compared with PL. Furthermore, the water-holding capacity of the substrate having a 1 : 10 mixing ratio of SZ with OP was higher than that of the PL by 28.23%, whereas the bulk density was lower than that of PL by 35%. A greenhouse experiment was carried out to assess the influence of the substrates on the growth and development of lettuce. The shoot fresh weight, shoot dry weight, root fresh weight, root dry weight and number of leaves per plant of the lettuce grown in the 1 : 10 mixing ratio of SZ and OP were the highest, which showed increased values compared with that of PL by 11.56, 9.77, 3.48, 17.35 and 16.53%, respectively. The shoot fresh weight, shoot dry weight, root fresh weight, root dry weight and number of leaves per plant of the lettuce grown in the 1 : 10 mixing ratio of SZ and OP showed increased percentages compared with that of PE by 12.12, 11.37, 3.74, 23.66 and 17.50%, respectively. In addition, the growth and yield parameters of lettuce grown in the 1 : 3 mixing ratio and the OP did not show any significant difference with PL and PE but differed from the 1 : 10 mixing ratio. The results of the study suggest that the SZ—OP-based substrates and OP can be successfully utilized as alternatives to the commercial perlite and to substitute the conventional peat substrate for lettuce cultivation. In addition, this can be proposed as an alternative waste management practice.

Contribution of humic substances to dissolved organic matter optical properties and iron mobilization

Humic substances (HS) are the primary constituents of dissolved organic matter (DOM) and play pivotal roles in aquatic systems. Optical indices of DOM, such as specific UV absorbance (SUVA254), the fluorescence index (FI) and biological index (BIX), have gained wide interest because of their ease of use. In this study, we explored the relationship between HS and the indices in the Trat River Basin (eastern Thailand) from headwaters to the river mouth through the distinct dry and rainy seasons to examine whether changes in index values reflect variability in the relative contribution of HS to DOM, or %HS. The results show that %HS and the indices did not exhibit significant linear relationships (FI and BIX, P > 0.05), or the relationships changed seasonally (SUVA254). However, analyzing the indices versus %HS did show clear DOM composition changes by season with more humic-like or terrestrial material in the rainy season. Relationships between DOM and dissolved iron (dFe) concentrations were also explored. Separating the relationships of DOM versus dFe into HS versus dFe and non-HS versus dFe provides us the opportunity to better understand which fraction contributes more to dFe mobilization. The results indicate stronger positive linear relationships between HS and dFe concentrations independent of river tributary. Overall, this study highlights the importance of quantifying HS for the study of DOM dynamics or compositional changes along a river transect as well as for DOM-induced iron mobilization.