Takayoshi Tsuchiya

Root aerobic respiration and growth characteristics of three Typha species in response to hypoxia

The responses of root aerobic respiration to hypoxia in three common Typha species were examined. Typha latifolia L., T. orientalis Presl, and T. angustifolia L. were hydroponically cultivated under both aerobic and hypoxic growth conditions to measure root oxygen consumption rates. Hypoxia significantly enhanced the root aerobic respiration capacity of the two deep-water species, T. orientalis and T. angustifolia, while it did not affect that of the shallow-water species, T. latifolia. T. angustifolia increased its root porosity and root mass ratio, while T. latifolia increased its root diameter under the hypoxic growth conditions. The relative growth rates in biomass of T. orientalis and T. angustifolia were 59 and 39% higher, respectively, under the hypoxic growth conditions than under the aerobic growth conditions. In contrast, that of T. latifolia did not differ between the two conditions. In T. orientalis and T. angustifolia, enhanced root aerobic respiration rates under the hypoxic growth conditions would have increased the nutrient uptake, and thus higher relative growth rates were obtained. For the deep-water species, T. orientalis and T. angustifolia, the root aerobic respiration capacity was enhanced, probably in order to maintain the generation of respiratory energy under hypoxia.

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 and leaf life-span of a floating-leaved plant, Trapa natans L., as influenced by nitrogen flux

Abstract Trapa natans L., cultured in tanks under varying nitrogen flux, was examined with particular reference to the change in foliage structure. Leaf initiation rate, leaf loss rate and leaf life-span were independent of nitrogen flux and ranged from 140 to 250 mg N m−2 day−1. In contrast, leaf and rosette size were positively correlated with nitrogen flux. The maximum biomass was estimated to be 487 g dry weight m−2 in the most nitrogen-enriched tank. With increasing nitrogen flux, proportions of petiole and reproductive parts (fruit) in the total biomass increased, while those of stem and root decreased. Net production of T. natans was also positively correlated with nitrogen flux and ranged from 5 to 14 g dry weight m−2 day−1 for all experimental tanks, excluding a tank with algal competition.

Population dynamics, productivity and biomass allocation of Zizania latifolia in an aquatic-terrestrial ecotone

The population and production ecology of a Zizania latifolia stand at a sheltered shore of the Hitachi-Tone River were investigated. Shoot emergence was observed twice a year; the fist was a synchronized shoot emergence in April and the second was from August to October. Aboveground biomass was mostly occupied by leaves and peaked at 1500 g dry weight m−2 in August. The belowground biomass also reached its peak, 750 g dry weight m−2, in August. The secondary shoots were small in spite of their high density. Leaves were produced continuously throughout the season. The leaf life span was as short as 55.6 days for cohorts that emerged from May through to September. Total annual net production of Z. latifolia could be more than 3400 g dry weight m−2. Shoot clusters of several centimeters were observed in April. The following self-thinning caused a regular distribution of the remaining shoots in August. Most shoots produced in August to October were found near a shoot persisting since April. They showed more concentrated distribution than shoots in April. A large biomass allocation to leaves and the ability to produce many clump shoots during the late growing period may facilitate dominance of Z. latifolia in relatively sheltered sites.

Production and population ecology ofPhyllospadix iwatensis Makino. I. Leaf growth and biomass in an intertidal zone

In an intertidal zone on Choshi coast, Japan,Phyllospadix iwatensis Makino emerges at daytime in spring and summer, while at night time in winter. The plants therefore experience seasonally different stresses caused by emergence, for example, intense light, ultraviolet rays, extreme temperature and desiccation, all of which the plants are unable to avoid during daytime emergence. Seasonal changes in the biomass and LAI suggest that the optimum periods for growth ofP. iwatensis would be in March when the emergent period is short or nil and light availability is high while water temperature is not too low. Dense foliage and low canopy height ofP. iwatensis in the intertidal zone relieve the plant from the stresses in emergent periods and from the disturbance caused by strong water movement in some coastal areas with active wave action.

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.

Indirect method to estimate convective gas flow through culms of a Phragmites australis stand

We propose an indirect method to estimate continuously the rate of convective gas flow in a Phragmites australis stand. In this method, the rate of gas flow is estimated using the dynamic pressure differential in a culm and the convective conductance of the culm. The rate of gas flow obtained by this indirect method coincided well with that obtained by the direct method in which a culm is detached and then reconnected to the stubble using a mass flow meter. We monitored the total gas flux through a P. australis stand in a field and found that it fluctuated diurnally with the dynamic pressure differential in culms, showing a highest rate of 26 l air m−2 ground area h−1 at noon. The total daily gas flux was about 170 l air m−2. Our indirect method has advantages in simultaneous and continuous measurements for a cluster of culms. This method will be of use not only to quantify various gas dynamics through aquatic plants in aquatic ecosystems but also to elucidate the ecosystem processes and properties that regulate these gas dynamics.

Production and population ecology ofPhyllospadix iwatensis Makino. II. Comparative studies on leaf characteristics, foliage structure and biomass change in an intertidal and subtidal zone

A seagrass in Japan,Phyllospadix iwatensis Makino, is distributed in the lower intertidal zone and upper subtidal zone making a dense population on the Choshi coast, Japan. IntertidalP. iwatensis is able to receive sufficient light for photosynthesis but experienced severe exposure to the air, which decreased a large amount of aboveground biomass in April to June (i.e. the daytime exposure season). SubtidalP. iwatensis was never exposed throughout the year and the aboveground biomass increased gradually over the daytime exposure season. However, the maximum aboveground biomass and shoot density of the subtidal plant never exceeded that of the intertidal plant. The dense foliage, large aboveground biomass and high shoot density of both intertidal and subtidal plants is likely to be an adaptation to heavy water movement, but the subtidal plants always received insufficient light for photosynthesis as a result of having dense foliage, particularly in turbid water. In choppy and swell sea,P. iwatensis did not seem to be adapted to growing in the subtidal zone where there was shortage of light.

Functional linkage between N acquisition strategies and aeration capacities of hydrophytes for efficient oxygen consumption in roots

We evaluated the specific strategies of hydrophytes for root O(2) consumption in relation to N acquisition and investigated whether the strategies varied depending on the aeration capacity. Aeration capacity of roots is an important factor for determining hypoxia tolerance in plants. However, some hydrophytes possessing quite different aeration capacities often co-occur in wetlands, suggesting that root O(2) consumption also strongly affects hypoxia tolerance. We cultivated Phragmites australis with high aeration capacity and Zizania latifolia with low aeration capacity in hypoxic conditions with NH(4)(+) or NO(3)(-) treatment and compared the growth, N uptake, N assimilation and root respiration between the two species. In Z. latifolia grown with NH(4)(+) treatment, high N uptake activity and restrained root growth led to sufficient N acquisition and decrease in whole-root respiration rate. These characteristics consequently compensated for the low aeration capacity. In contrast, in P. australis, low N uptake activity was compensated by active root growth, but the whole-root respiration rate was high. This high root respiration rate was allowed by the high aeration capacity. The O(2) consumption-related traits of hydrophyte roots were closely correlated with N acquisition strategies, which consequently led to a compensational relationship with the root aeration capacity. It is likely that this functional linkage plays an important role as a core mechanism in the adaptation of plants to hypoxic soils.