History vs. habitat type: explaining the genetic structure of European nine‐spined stickleback (Pungitius pungitius) populations

The genetic structure of contemporary populations can be shaped by both their history and current ecological conditions. We assessed the relative importance of postglacial colonization history and habitat type in the patterns and degree of genetic diversity and differentiation in northern European nine‐spined sticklebacks (Pungitius pungitius), using mitochondrial DNA (mtDNA) sequences and 12 nuclear microsatellite and insertion/deletion loci. The mtDNA analyses identified – and microsatellite analyses supported – the existence of two historically distinct lineages (eastern and western). The analyses of nuclear loci among 51 European sites revealed clear historically influenced and to minor degree habitat dependent, patterns of genetic diversity and differentiation. While the effect of habitat type on the levels of genetic variation (coastal > freshwater) and differentiation (freshwater > coastal) was clear, the levels of genetic variability and differentiation in the freshwater sites were independent of habitat type (viz. river, lake and pond). However, levels of genetic variability, together with estimates of historical effective population sizes, decreased dramatically and linearly with increasing latitude. These geographical patterns of genetic variability and differentiation suggest that the contemporary genetic structure of freshwater nine‐spined sticklebacks has been strongly impacted by the founder events associated with postglacial colonization and less by current ecological conditions (cf. habitat type). In general, the results highlight the strong and persistent effects of postglacial colonization history on genetic structuring of northern European fauna and provide an unparalleled example of latitudinal trends in levels of genetic diversity.     

CHANGES IN ACTIVITY OF DGLUCOSE-6-PHOSPHATE: NADP AND 6-PHOSPHO-D-GLUCONATE: NADP OXIDOREDUCTASES IN RELATION TO LIGNIFICATION OF BAMBOO

D-Glucose-6-phosphate: NADP oxidoreductase (glucose-6-phosphatedehydrogenase; EC 1.1.1.49[EC]) and 6-phospho-D-gluconate: NADPoxidoreductase (6-phosphogluconate dehydrogenase; EC 1.1.1.44[EC])were found to be present in immature bamboo. Optimal pHs ofthe glucose-6-phosphate- and 6-phosphogluconate dehydrogenaseswere found to be 8.0 and 8.5, respectively. Both enzymes were demonstrated to be NADP-specific and NADPcould not be replaced by NAD. Fructose-6-phosphate was indirectlyutilized after convrsion to glucose-6-phosphate by glucose-6-phosphateisomerase coexisting in the enzyme preparation. Pattern of enzyme activity and of respiratory breakdown of glucose-1-¹⁴Cand glucose-6-¹⁴C were investigated in connection with lignificationof bamboo and discussed in comparison with sugar metabolismof fungi-infected plant tissues. As for the changes in the enzymeactivity with growth of bamboo, it was recognized that therewas a tendency that the activity of both enzymes increased andwas maintained at a certain level even in the aged tissues.In addition there was a drop of the C₆/C₁ ratio toward the tissuesof lower parts containing considerable amount of lignin andthis phenomenon was the same as that observed in pentose phosphatemetabolism of fungi-infected plant tissues. (Received September 5, 1966; )     

Quantitative aspects of heterogeneity in soil organic matter dynamics in a cool-temperate Japanese beech forest: a radiocarbon-based approach

Soil is the largest carbon reservoir in terrestrial ecosystems; it stores twice as much carbon as the atmosphere. It is well documented that global warming can lead to accelerated microbial decomposition of soil organic carbon (SOC) and enhance the release of CO₂ from the soil to the atmosphere; however, the magnitude and timing of this effect remain highly uncertain due to a lack of quantitative data concerning the heterogeneity of SOC biodegradability. Therefore, we sought to identify SOC pools with respect to their specific mean residence times (MRTs), to use those SOC pools to partition soil respiration sources, and to estimate the potential response of the pools to warming. We collected surface soil and litter samples from a cool-temperate deciduous forest in Japan, chemically separated the samples into SOC fractions, estimated their MRTs based on radiocarbon (¹⁴C) isotope measurements, and used the data to construct a model representing the soil as a complex of six SOC pools with different MRT ranges. We estimate that a minor, fast-cycling SOC pool with an MRT of less than 10 years (corresponding to the O horizon and recognizable plant leaf fragments in the A1 horizon) is responsible for 73% of annual heterotrophic respiration and 44% of total soil respiration. However, the predicted response of these pools to warming demonstrates that the rate of SOC loss from the fast-cycling SOC pool diminishes quickly (within several decades) because of limited substrate availability. In contrast, warming will continue to accelerate SOC loss from slow-cycling pools with MRTs of 20–200 years over the next century. Although using a ¹⁴C-based approach has drawbacks, these estimates provide quantitative insights into the potential importance of slow-cycling SOC dynamics for the prediction of positive feedback to climate change.     

CHANGES IN ACTIVITY OF SHIKIMATE : NADP OXIDOREDUCTASE IN RELATION TO LIGNIFICATION OF BAMBOO

Shikimate : NADP oxidoreductase (5-dehydroshikimate reductase;EC 1.1.1.25 [EC] ) was extracted from immature bamboo and partiallypurified. The optimal pH of the enzyme was found to be 11.0.The enzyme was demonstrated to be NADP specific. Michaelis constants (Km) for NADP and shikimic acid as substratewere found to be 1.4 10^–4M and 2.0 10^–4M, respectively,at pH 8.0. No metal requirement could be demonstrated sincelittle change in enzyme activity was observed on addition ofethylenediamine-tetraacetic acid (EDTA). On the other hand,the enzyme was potently inhibited by p-chloromercuribenzoicacid (PCMB). 5-Dehydroshikimate reductase was demonstrated to be widely distributedin woody plants such as bamboo, udo (Aralia cordata), asparagus(Asparagus officinalis) and tulip tree (Liriodendron tulipifera)as well as other higher plants. Shikimic acid content was comparatively low at the top, butafter reaching maximal content in the part just below the top,it began to decrease toward lower parts of bamboo. The enzymeactivity at the top was the highest and seemed to decrease towardthe tissues of lower parts. However the fact that the activitywas still maintained at a certain level even in the aged tissuessuggests that 5-dehydroshikimate reductase might play a significantrole for biosynthesis of lignin. (Received September 5, 1966; )