Carbon autonomy of current-year shoots in flowering, and of current-year shoots plus 1-year-old shoots (1-year-old shoot system) in fruiting of Siberian alder (Alnus hirsuta var. sibirica) was investigated using a stable isotope of carbon, (13)C. The current-year shoot and 1-year-old shoot systems were fed (13)CO(2) and the atom% excess of (13)C in flowers and fruits was determined. The majority of photosynthate allocated to flower buds was originally assimilated in the leaves of the flowering current-year shoots. Of all the current-year shoots on fruiting 1-year-old shoots, only those nearest to the fruits allocated the assimilated photosynthate to fruit maturation. These results indicate that the current-year shoots and 1-year-old shoot systems are carbon-autonomous units for producing flowers and maturing fruits, respectively.
Two methods were developed for the quantitative sampling of rotifers and cladocerans attached to aquatic macrophytes while separating them from plankton. We named them the "covering method" and the "picking-up method." We consider the covering method to be better for estimating the abundance of animals on plants, but it requires hard work on a boat. In contrast, the picking-up method is simple and easy to perform, but it seems to estimate animal abundance with some errors. The densities of rotifers and cladocerans on emergent and submerged plants in two Japanese lakes were estimated by the two methods, and the results were compared. The densities of most animals (e.g., the rotiferans Brachionus, Mytilina, Lepadella, and Colurella, and the cladoceran Alona) estimated by the picking-up method did not differ from those estimated by the covering method. In contrast, the densities of the rotiferans Monostyla, Euchlanis, and Trichocerca estimated by the picking-up method tended to be lower than those estimated by the covering method. These suggest that the picking-up method is suitable for estimating many densities, except for some rotiferan genera.
Seasonal variation in NH4+ regeneration rates was examined by means of L5N-isotope dilution for different size fractions of organisms (< 1 pm, < 20 pm, < 100 ym, and > 100 ,um) in samples from mesotrophic Lakes Kizaki and Biwa, Japan. In both lakes, nanoflagellates and microzooplankton (mainly rotifers) accounted for a large fraction (17-55 and O-67%, respectively) of total NH,-+ regeneration (L. Kizaki, 0.0 1 l-O.26 1 hmol liter-1 h-l; L. Biwa, 0.040-O. 163 pmol liter-l h-l), suggesting that microbial food webs were primarily important in NH,+ regeneration. Contributions of crustacean mesozooplankton to NH,+ regeneration were generally minor (< 16%), except on one occasion in early summer when crustaceans accounted for 62% of total NH, t regeneration in Lake Kizaki. The weight-specific NH,+ regeneration rates (sR) of nanoflagellates and rotifers-ciliates were 20-30-fold greater than the corresponding rates for crustacean mesozooplankton, consistent with the general relationship between SR and body size of grazers. Bacterial contributions to NH4 + regeneration were high (26-5 1%) in summer but low (< 10%) in spring and winter, which was explained in part by the strong dependency of bacterial sR on temperature. Our data demonstrate that rates and major pathways of NH4 I regeneration may vary greatly depending on the size structure of planktonic food webs.
Spatial distributions of the biomass and species composition in submerged macrophytes in the southern basin of Lake Biwa were surveyed in September, 2002. Macrophyte samples were collected from 52 sites by SCUBA. The total biomass (dry weight) of and the vegetated area of macrophytes in the southern basin during the study period were estimated as 10735 ± 3030 t, and 43 km 2 , respectively. Potamogeton maackianus was dominant, and Hydrilla verticillata, Ceratophyllum demersum, Egeria densa and Myriophyllum spicatum were also abundant in the basin. Biomass of these five species accounted for 99% of the total macrophyte biomass. P. maackianus and C. demersum showed high niche overlap (Pianka's α = 0.71). Biomass of P. maackianus was positively correlated with the average transparency/water depth ratio (Spearman's ρ = 0.50), suggesting that P. maackianus tended to grow at the bottom under strong light. Biomass of C. demersum showed a positive correlation with transparency (ρ = 0.44). Biomass of E. densa was negatively correlated with the sediment diameter
The fluctuations of drift diatom assemblage and water quality in the lower reaches of the Nagara river part of a river system without large reservoirs, were surveyed
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