Tomomi Inoue

Interspecific differences in radial oxygen loss from the roots of three Typha species

A comparison was made of the radial oxygen loss (ROL) from the roots of three Typha species, Typha latifolia L., Typha orientalis Presl and Typha angustifolia L., which resemble each other in morphology. ROLs were evaluated in the laboratory for seedlings of T. orientalis and T. angustifolia in order to compare them with the ROL value for T. latifolia obtained in our previous study. Measurements were conducted using the highly oxygen-sensitive anthraquinone radical anion as an oxygen indicator, which enabled us to simulate the natural conditions in which the oxygen released from the root is immediately consumed by the soil. Among the three Typha species, the ROL was the highest in T. angustifolia, followed by T. latifolia and T. orientalis. Illumination significantly enhances the ROL of T. orientalis, and this effect was also observed for T. latifolia in our previous study, whereas it did not affect the ROL of T. angustifolia. These results indicate that ROL differs significantly between species, even among members of the same genus that are similar in morphology.

Growth strategy of an emergent macrophyte, Typha orientalis Presl, in comparison with Typha latifolia L. and Typha angustifolia L.

The growth strategy of an emergent plant, Typha orientalis Presl, was examined in experimental ponds in comparison with two other Typha species distributed in Japan, Typha latifolia L. and Typha angustifolia L. T. orientalis showed the greatest ability of vegetative reproduction at the expense of growth in height. T. orientalis started to produce new ramets earlier than T. latifolia and T. angustifolia. These results suggest that T. orientalis should be a rather pioneer-like species and would be restricted to disturbed habitats.

What happens to soil chemical properties after mangrove plants colonize

Understanding soil chemical properties is necessary to characterize the basic properties of ecosystems. In mangrove ecosystems, soil iron, phosphorus, methane and nitrogen have been well studied under field conditions. However, it is difficult to understand fundamental relationships between mangrove root functions and soil chemical properties, because of the multiple factors present in field data. The aim of this study was to clarify what will happen to soil chemical properties after mangrove plant colonize. To examine the effect of mangrove roots on these soil properties, three representative mangrove species (Avicennia marina, Rhizophora stylosa and Bruguiera gymnorrhiza) were cultivated in a greenhouse and selected soil chemical properties were monitored in comparison with those in unplanted soil. We detected oxidative effects in all three species, including deposition of iron oxide on root surfaces, lowered methane concentrations and increased oxidized inorganic nitrogen concentrations in the soil pore-water, suggesting that radial oxygen loss from mangrove roots had affected these soil chemical properties. Besides the oxidative effects, enhanced Fe2+ concentrations in the soil pore-water were present in A. marina, and enhanced phosphorus concentrations in the soil pore-water were present in all three species, suggesting that mangrove roots provide Fe- and phosphate-solubilizing substrates. The most remarkable change was in soil nitrogen enrichment. During the experimental period, amounts of nitrogen in the mangrove soils increased four times more than in uncolonized soil. Six months from the start of cultivation, bacterial nitrogen fixation (nitrogenase activity) was significantly higher in soil colonized by mangrove plants than in uncolonized soil, suggesting that mangrove roots stimulated bacterial nitrogen fixation. Among these properties, Phosphate mobilization and soil nitrogen enrichment are likely to be particularly important for the growth of mangrove plants, because phosphate and nitrogen are generally limited in mangrove ecosystems. This self-supporting ability of mangroves observed in this study could be one key to the high productivity of mangrove ecosystems.

Effect of acid solutions on plants studied by the optical beam deflection method.

The optical beam deflection method was applied to study the effects of acid solution on both a terrestial and aquatic plants Egeria and Cerastium, which are common aquatic plant and terrestial weed respectively. A probe beam from a He-Ne laser was passed through a vicinity of a leaf of the plants, which were put in culture dishes filled with acid solutions. Deflection signals of the probe beam were monitored and compared for acid solutions with different pH values. The results of Egria showed that the deflection signals changed dramatically when pH values of acid solutions were 2.0 and 3.0, while little at pH of 4.0 and 5.0. For Cerastium when pH were below 3.0, deflection signals changed greatly with time at the begining. After a certain period of time, deflection signals changed little with time. When pH value was above 4.0, deflection signals of Cerastium were still changing with time even after 20 hours. The results suggested that the damage threshold of pH was between 3.0 and 4.0 for both the land and aquatic plants.

Comparative Studies on Effects of Acid Solutions on Aquatic Plants by Beam Deflection and Absorbance Spectroscopy Methods

The beam deflection method and absorbance spectroscopy were applied to study effects of acid solutions on aquatic plants, and their results were compared. Aquatic plants Egeria densa and Ceratophyllum demersum L were used as model plants. In absorbance experiments, a piece of the plants was put in a beaker with 20 mL HCl solution, and absorbance of the HCl solution was measured every 30 min. In beam deflection experiments, a probe beam from a He-Ne laser was focused to a vicinity of the plants in a culture dish with HCl solution by an objective lens, and deflection signals of the probe beam were monitored by a position sensor. Absorbance spectra of the HCl solutions with immersing of the plants showed absorbance below 410 nm, suggesting that some compounds leaked from the plants into the HCl solutions. Changes of absorbance and deflection signals with immersion time were examined for different pH levels. The changing trends of the absorbance and deflection signals with time were similar, but the absorbance changes were delayed for about 2 - 3 h. The absorbance method could not detect the effect of the pH 5.0 HCl solutions on the aquatic plants, while the deflection method could.

Evaluation of plant contamination in metabarcoding diet analysis of a herbivore

Fecal DNA metabarcoding is currently used in various fields of ecology to determine animal diets. Contamination of non-food DNA from complex field environments is a considerable challenge to the reliability of this method but has rarely been quantified. We evaluated plant DNA contamination by sequencing the chloroplast trnL P6 loop region from food-controlled geese feces. The average percentage of contaminant sequences per sample was 1.86%. According to the results of generalized linear models, the probability of contamination was highest in samples placed in wet soil. The proportion of contaminant sequences was lowest at the earliest sampling point and was slightly higher in samples placed in open conditions. Exclusion of rare OTUs (operational taxonomic units) was effective for obtaining reliable dietary data from the obtained sequences, and a 1% cutoff reduced the percentage of contaminated samples to less than 30%. However, appropriate interpretation of the barcoding results considering inevitable contamination is an important issue to address. We suggest the following procedures for fecal sampling and sequence data treatment to increase the reliability of DNA metabarcoding diet analyses: (i) Collect samples as soon as possible after deposition, (ii) avoid samples from deposits on wet soil, and (iii) exclude rare OTUs from diet composition estimations.

Impacts of anthropogenic structural changes to the Mekong River watershed on seasonal hydrologic dynamics in the watershed and floodplain

Recent drastic economic and population growth in the middle region of Mekong River watershed has accelerated structural landscape changes, industria! development, and exploitation of natural resources (HoRI 1993, PLATE & lNSISIENGMAY 2005). Development in the watershed, including dam and levee construction and channel straightening, has modified the natural seasonal river-flow dynamics, gradually degrading those ecological interactions in the watershed that are sustained by the natural hydrological regime (DUDGEON 1992, 2005). From the perspective ofhuman society, river flooding constitutes a hazard; yet seasonal water movement is an essential component of the watershed ecosystem (HEILER et al. 1995, TocKNER et al. 2000, JENSEN 2001), enabling nutrient cycling (JuNK 1999, PHAM et al. 2002), seed dispersion, and freshwater fish migration (ÜALAT & ZWEIMULLER 2001, HOCUTT & JOHNSON 2001, HALLS & WELCOMME 2004). Although dams control downstream flooding during the rainy season, they also disrupt the natural hydrologic regime. We focus on 2 hypotheses: (l) that the seasonally flooded area downstream of the dam si te i s decreasing compared with before-dam construction as a result ofthe dams operation; and (2) the decrease in the flooded area will potentially reduce the movement of nutrients from the main river channel to the riparian flooded area; this movement is essential to conserve biophysical connectivity (NAIMAN et al. 2005). We quantify and evaluate the human impact on seasonal flooding in the middle region o f the Mekong Ri v er watershed. Our challenge is not only to resolve the perpetual dilemma between conservation ofthe natural environment and development for economic growth, but also to develop an assessment methodology that can harmonize environmental quality with sustainable economic growth (KITE 2001, DunA et al. 2007). These assessment tools must be both accurate and flexible. We performed a watershed hydrologic model simulation of a subcatchment along the middle reaches ofthe Mekong River. First, we simulated the hydro1ogical regime before (1945) and after (2002) watershed development. Second, we performed a flooded-area analysis and validated it with remote sensing data. Third, we classified the flooded areas according to the cumulative annual number of days. Finally, we evaluated the anthropogenic impact on the area of flooding by comparing cumulative flood data between 1945 and 2002.