摘要:

ABSTRACTMeasurements of net photosynthesis (PS, O2evolution), dark respiration (R, O2consumption), and light and dark carbon fixation (14C) were conducted on whole blades, isolated blade discs, sporophylls, apical scimitars and representative portions of stipe and holdfast of the giant kelpMacrocystis pyriferaL.C. Ag.On a dry weight basis, highest net PS rates were observed in apical scimitar segments and whole blades (3.81 and 3.07 mgC · g dry wt−1· h−1, respectively), followed by sporophylls (1.42 mgC·g dry wt−1· h−1) and stipe segments (0.15 mgC·g dry wt−1· h−1). No PS capacity was observed in holdfast material. Respiration rates showed similar ranking ranging from 1.22 mgC·g dry wt−1·h−1for apical scimitar to 0.18–0.22 mgC·g dry wt−1· h−1for holdfast material. Considerable within blade variability in both PS and R was also found. Steepest PS and R gradients on both an areal and weight basis were found within immature blades followed by senescent and mature blade material. Highest net PS rates were associated with the blade tips ranging from 3.08 (mature blades) to 10.3 mgC·dry wt−1·h−1(immature blades). Highest rates of R generally occurred towards the basal portions of blades and ranged from 1.03–1.80 mgC·g dry wt−1·h−1for immature blades. The variability within and between blades was high, with coefficients of variation approaching 50%. The observed patterns can be related to the decreasing proportionment of photosynthetic tissue and increasing proportionment of structural tissue as occurs from the blade tip to the blade base. Rates of light carbon fixation (LCF) revealed longitudinal profiles similar to oxygen measurements for the different blade types, with the absolute rates being slightly lower. Patterns of dark carbon fixation (DCF) were less easily interpreted. Highest rates of DCF (0.04–0.06 mgC·g dry wt−1·h−1) occurred at the basal portions of immature and senescent blades. Longitudinal profiles of total chlorophyll (a + c) on both an areal and weight basis were very similar to the profiles of PS. Normalized to chlorophylla,PS displayed an unusual longitudinal profile in immature tissue; however, such profiles for mature and senescent tissues were similar to those for PS on an areal basis.It was demonstrated that it is difficult, if not impossible, to select single tissue discs that are representative of whole blades. The metabolic longitudinal profiles reveal a characteristic developmental pattern; the previous working definitions of immature, mature, and senescent blades, based on morpholo

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00154.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTSilicon uptake kinetics of the diatomPhaeodactylum tricornutum(Bohlin) were examined at pH 8.8 ± 0.1 and pH 9.1 ± 0.1. Uptake follows hyperbolic saturation kinetics at both pH's, but at the higher pH the half‐saturation constant for uptake is 11.8 μM, as opposed to 54.8 μM at the lower pH. When the uptake rate is examined as a function of the calculated concentration of the monovalent conjugate base, SiO(OH)3−, the half‐saturation constant for uptake is 6.6 μM at

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00168.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTChroococcoid cyanobacteria (0.7–1.3 μm in diameter) were discovered to be a significant component of the Lake Ontario plankton. Using epifluorescence microscopy, the densities of these microorganisms were found to vary by four orders of magnitude with a single large peak in abundance (6.5 × 105cells mL−1) corresponding to the time of maximum water temperature. The morphology and abundance of these cyanobacteria were similar to those previously found in oceanic systems. They constituted 10% of the bacterial numbers in the epilimnion during this period, approximately 40% of the biomass of prokaryotes less than 2.0 μm, and 30% of the biomass of all microorganisms less than 20 μm in size. Size fractionation studies indicated that they were responsible for approximately 38% of the total primary production during times of peak abundance, and were important in phosphorus uptake. Cyanobacteria observed in the food vacuoles of heterotrophic microflagellates and in the guts of rotifers suggest that the latter organisms may be important consumers of this prokaryote pop

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00171.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY