Sixty years of environmental change in the world's largest freshwater lake – Lake Baikal, Siberia

High-resolution data collected over the past 60 years by a single family of Siberian scientists on Lake Baikal reveal significant warming of surface waters and long-term changes in the basal food web of the world's largest, most ancient lake. Attaining depths over 1.6 km, Lake Baikal is the deepest and most voluminous of the world's great lakes. Increases in average water temperature (1.21 °C since 1946), chlorophyll a (300% since 1979), and an influential group of zooplankton grazers (335% increase in cladocerans since 1946) may have important implications for nutrient cycling and food web dynamics. Results from multivariate autoregressive (MAR) modeling suggest that cladocerans increased strongly in response to temperature but not to algal biomass, and cladocerans depressed some algal resources without observable fertilization effects. Changes in Lake Baikal are particularly significant as an integrated signal of long-term regional warming, because this lake is expected to be among those most resistant to climate change due to its tremendous volume. These findings highlight the importance of accessible, long-term monitoring data for understanding ecosystem response to large-scale stressors such as climate change.     

New or rare chromosome counts in the genera Artemisia L. and Mausolea Bunge (Asteraceae, Anthemideae) from Uzbekistan

Seventeen chromosome counts of 14 Artemisia and one Mausolea species are reported from Uzbekistan. Five of them are new reports, two are not consistent with previous counts and the remaining are confirmations of very scarce (one to four) previous data. Two basic chromosome numbers (x = 8 and x = 9) and two ploidy levels (2x and 4x) were found. Some correlations between ploidy level, morphological characters and distribution are noted.     

ENDOSYMBIONTS OF DREISSENA POLYMORPHA IN IRELAND: EVIDENCE FOR THE INTRODUCTION OF ADULT MUSSELS

Although zebra mussels (Dreissena polymorpha) have invaded watersacross Europe for over 200 years, they colonized Ireland onlywithin the past decade. To test the hypothesis that Irelandwas colonized by adult D. polymorpha, we examined mussels fromdifferent sites along the Lower Shannon River system in Irelandfor the presence of host specific and generalist endosymbionts.Withinthe mantle cavity and/or associated with zebra mussel tissueswe found species specific-ciliates (Conchophthirus acuminatusand Ophryoglena hemophaga) and generalist symbionts (the ciliateAncistrumina limnica, nematodes, oligochaetes and chironomids).We found a significant difference in the prevalence of symbiontsamong sites, but all mussels at all sites harboured one specialistspecies C. acuminatus, and all of the mussels at three of thefour sites also had the second specialist, O. hemophaga. Thus,with the introduction of D. polymorpha into Ireland, at leasttwo additional species, their host-specific symbionts C. acuminatusand O. hemophaga, have also been introduced. The presence ofthese symbionts in Ireland supports the hypothesis that adultzebra mussels were introduced into Ireland, rather than larvalstages. This contrasts with the introduction of zebra musselsto North America, where adult zebra mussels are devoid of host-specificsymbionts. (Received 8 June 2005; accepted 7 November 2005)     

Proton cellular influx as a probable mechanism of variation potential influence on photosynthesis in pea

Electrical signals (action potential and variation potential, VP) caused by environmental stimuli are known to induce various physiological responses in plants, including changes in photosynthesis; however, their functional mechanisms remain unclear. In this study, the influence of VP on photosynthesis in pea (Pisum sativum L.) was investigated and the proton participation in this process analysed. VP, induced by local heating, inactivated photosynthesis and activated respiration, with the initiation of the photosynthetic response connected with inactivation of the photosynthetic dark stage; however, direct VP influence on the light stage was also probable. VP generation was accompanied with pH increases in apoplasts (0.17–0.30 pH unit) and decreases in cytoplasm (0.18–0.60 pH unit), which probably reflected H⁺‐ATPase inactivation and H⁺ influx during this electrical event. Imitation of H⁺ influx using the protonophore carbonyl cyanide m‐chlorophenylhydrazone (CCCP) induced a photosynthetic response that was similar with a VP‐induced response. Experiments on chloroplast suspensions showed that decreased external pH also induced an analogous response and that its magnitude depended on the magnitude of pH change. Thus, the present results showed that proton cellular influx was the probable mechanism of VP's influence on photosynthesis in pea. Potential means of action for this influence are discussed.