The critical pressures of gas vesicles in Planktorhrix rubescens in relation tothe depth of winter mixing in Lake Zrich, Switzerland |
| |
Authors: | Walsby Anthony E; Avery Avril; Schanz Ferdinand |
| |
Institution: | School of Biological Sciences; University of Bristol Woodland Road, Bristol BS8 1 UG, UK
1Institut f Pflanzenbiologie der Universitat Zrich Limnologische Station, Seestrasse 187, CH-8802 Kilchberg, Switzerland |
| |
Abstract: | The vertical distribution of the cyanobacterium Planktothrir(Oscillazoria) rubescens in Lake Zrich was investigated fromMarch 1993 to June 1995 by collecting filaments on filters andmeasuring them by epifluorescence microscopy and computer imageanalysis. The initial population, which began to stratify inApril, decreased by up to 99% by June. During the summer, thepopulation peaked at depths of 815 m; it reached a maximumareal filament-volume concentration of -60 cm 3 of lakesurface in early September and was then entrained in the deepeningsurface layer. It became mixed progressively deeper, to thelake bottom in the cold winter of 199394, but less completelyin the milder winter of 199495. Most of the filamentsremained viable during the winter. At the end of the mild winterof 19945, 70% of filaments in the water column retainedbuoyancy, but after the cold winter of 19967 only 22%were buoyant. Few remained buoyant below 80 m, where the hydrostaticpressure caused gas vesicle collapse. The proportion that remainbuoyant decreases with the depth and duration of winter mixing,and increases with the critical collapse pressure (Pc) of thegas vesicles, which provide buoyancy. Strains of P.rubescensisolated from Lake Zrich differed in mean (Pc) of their gasvesicles, from 0.9 to 1.1 MPa, the highest values in freshwatercyanobacteria. Allowing for a turgor pressure of 0.2 MPa. thesestrains would remain buoyant at depths down to 70 and 90 m,respectively. Natural selection for gas vesicles of high (Pc)will operate by increasing the proportion of filaments thatremain buoyant in the upper parts of the water column aftercirculation to various depths during the winter because onlybuoyant filaments will form the inoculum for the following season. |
| |
Keywords: | |
本文献已被 Oxford 等数据库收录! |
|