摘要:

Epiphytic algal and bacterial in situ community metabolism and physiological—nutritional relationships of macrophyte—epiphyte systems were investigated in the littoral zone of a small temperate lake from April 1968 through May 1969. Annual primary productivity, chemo—organotrophy of dissolved organic compounds, and field and laboratory studies of macrophyte—epiphyte interactions were monitored by carbon—14 techniques. Productivity measurements of epiphytic algae on artificial substrates colonized in emergent (Scirpus acutus Muhl.) and submergent (Najas flexilis L. and Chara spp.) macrophytic vegetation sites were compared over an annual period with pigment (corrected chlorophyll a and total plant carotenoids) estimates of biomass. Changes in biomass are not proportional to changes in photosynthetic activity, except during periods of intense productivity. The mean daily productivity of epiphytic algae was higher per unit macrophyte surface area of emergent plants (336 mg C m—2day—1) than on submerged plants (258 mg C m—2day—1). Mean daily productivity per unit area of the littoral zone, for all of the macrophytic surface area colonized, was 195 and 1,807 mg C m—2day—1in the Scirpus and Najas—Chara dominated sites, respectively. The total annual production by algal epiphytes in the Scirpus and Najas—Chara dominated sites was 2.86 and 35.00 g C m—2of lake surface year—1, respectively. Estimates of annual net production of macrophytes and epipelic algae, derived from studies undertaken during the same time period as reported in this study, indicate that epiphytic algae were responsible for 31.3% of the total littoral production. The epiphytic algae were responsible for 21.4% of the total annual production for the whole lake when the production of the pelagial phytoplankton was added to that of the littoral communities. In comparison to the pelagial phytoplankton alone, the algal epiphytes fixed an amount of carbon equivalent to 75% of the phytoplankton production over the annual period. These results indicate that algal epiphytes on submerged macrophytes may be one of the dominant primary producers in shallow—water ecosystems and may be comparable to the phytoplankton. Deposition of14C—monocarbonates during in situ productivity measurements represented 38.5—71.7% of the total intracellular fixed carbon. Acidification of14C—productivity samples by rinsing with dilute hydrochloric acid (0.001 N) removed 24% of previously incorporated carbon and is not recommended as a routine procedure. Physiological interactions in macrophyte—epiphyte systems were investigated by bioassay procedure. Inorganic iron added at less than 10 mg liter—1, and at 100 mg liter—1in combination with organic compounds of chelatory or complexing ability, stimulated photosynthesis of epiphytic algae. Bioassay experiments in which vitamins, trace metals, and inorganic phosphorus were added to algal photosynthesis. Chlorophyll a, corrected for pheopigment degradation products, and total plant carotenoid levels are among the highest standing crops reported in the literature (annual maximum of chlorophyll a = 7.3 g m—2; plant carotenoids = 40.7 SPU m—2). Maximum concentrations were found during winter under ice cover. Epiphytic bacterial chemo—organotrophy with glucose and acetate substrates was measured at concentrations of 11—160 mg liter—1and evaluated through Michaelis—Menten enzyme kinetic analysis. First—order active transport kinetics dominated throughout the annual period. Uptake of acetate (submerged plant site, mean rate = 893 mg liter—1hr—1dm—2; emergent plant site, 106 mg liter—1hr—1dm—2) was greater than that of glucose (submerged plant site, 586 mg liter—1hr—1dm—2; emergent plant site, 54 mg liter—1hr—1dm—2). Scirpus acutus was labeled in situ during photosynthesis with natural concentrations of carbon dioxide (as14C). Epiphytic uptake of14C—labeled, extracellular products of macrophytic origin was determined. Extracellular release of14C—labeled organic matter was followed at various depths in the littoral water column. The nature of the extracellular release and the amount of14C fixed by the macrophyte and transferred into the epiphytic complex suggests nutritional interactions that may be prevalent in other macrophyte—epiphyte systems. Najas flexilis, germinated and grown under axenic conditions in a defined medium, was labeled during photosynthesis and placed into the center section of Plexiglas chambers separated by membrane filters free of organic carbon contamination. Over a 3.75—hr incubation interval, a mean of 7% of the total intracellularly fixed carbon was excreted as14C—labeled dissolved organic carbon. Cultured algal and bacterial epiphytes, separately and mixed in simulated natural communities, were able to utilize these extracellular products when placed into chamber sections adjoining the labeled Najas. The amount of extracellular products utilized by the mixed algal and bacterial communities changed with time, depending on the composition of the epiphytic community. The results suggest interspecific interactions where competition for specific external metabolites or organic solutes may have existed, or where toxic extracellular products may have accumulated. Laboratory uptake of low concentrations of glucose and acetate—14C at 5°, 11° to 12°, and 21° to 23° C by separate and mixed cultures of algal and bacterial epiphytes showed that uptake was strongly influenced by temperature, except at low temperatures where transport and diffusion mechanisms seemed to be inactivated. A sessile bacterium, Caulobacter, however, showed a highly efficient uptake system for both substrates under cold conditions. Uptake of both substrates by mixed cultures of algae and bacteria showed that bacterial uptake of both substrates by mixed cultures of algae and bacteria showed that bacterial uptake was little influenced at low substrate concentrations by the presence of algae. Epiphytic algal uptake following kinetics of simple diffusion was, however, increased in the presence of bacteria, suggesting uptake of14CO2previously respired by the bacteria. Macrophyte—epiphyte metabolism may be an important source of dissolved organic materials and extracellular metabolites and thus may help to sustain high levels of primary productivity and chemo—organotrophy in lakes.

ISSN:0012-9615    

DOI:10.2307/1942387

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The sexes of the Red—eyed Vireo, an abundant insectivorous bird in eastern deciduous woodlands, differed in their foraging heights, with an overlap of only about 35%. The males foraged higher than the females, and non—random sequences of movements were employed to maintain this separation. The foraging level and the nest height of female Red—eyes was similar, whereas the males foraged closer to their singing perches. Thus the foraging efficiency of both sexes was likely greater in accordance with their differing behavior roles. The "small" territory (1.3—1.7 acres) of this species actually consists of a cylinder extending from the forest canopy to the low understory. The associated White—eyed Vireo (Vireo griseus) was generally separated from Red— eyed Vireo by habitat, and the Yellow—throated Vireo (Vireo flavifrons) overlaps in habitat but possesses structural and behavioral differences which indicate different prey preferences. Foraging behavior of migrating Red—eyed Vireos differs markedly from that of breeding birds. Differences were also noted between summer and winter foraging behavior patterns in the White—eyed Vireo. All three vireo species exhibit species—specific patterns of foraging movements. Two other foliage—gleaning insectivorous birds occupying the same forests, the American Redstart (Setophaga ruticilla) and the Acadian Flycatcher (Empidonax virescens), also possess species—specific foraging behaviors (niche—exploitation patterns).

ISSN:0012-9615    

DOI:10.2307/1942388

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Black cherry occupies a key position in the dynamics of oak (Quercus spp.) forests in southern Wisconsin. Its relative importance in sapling and small—tree sizes averaged over 50%, and in some stands it was the only species in these strata. Age analysis of 854 cores showed that 58% of all black cherry stems were established between 1931 and 1941. The appearance of large amounts of black cherry in the 1930 decade was the result of drought and livestock—feed shortages. The latter were especially severe in 1934 and 1936 and resulted in large—scale disturbance of forests through grazing and possibly extensive cutting of forests for foliage. The presence of a strong shrub component exerted a major influence on the dynamics of the oak forest. An inverse relationship existed between overstory tree basal area and the importance of shrubs. Although density and cover of tree seedlings were independent of tree basal area and shrub cover, seedling numbers were insufficient for adequate restocking of most stands. In clear—cut forests the shrub layer was extensive, and regrowth of trees was largely confined to stump sprouts. Shrubs in disturbed forests averaged 38,635 stems/acre, 4,535 square inches basal area/acre, and 145.8% cover. In undisturbed forests, shrub competition (average 16,231 stems/acre, 1,036 square inches basal area/acre, and 51.4% cover) largely precluded seedling establishment by tree species, and maximum basal area levels in these forests were not maintained. Growth and survival of black cherry in the understory depended on the complex interaction of environmental factors. Tree overstory basal area and soil available water were the most significant factors controlling its vigor. Suppressed stems of cherry were as old as 60 years. Growth patterns in stem cores showed that stems responded to release after 39 years of suppression. The capacity of black cherry to develop basal sprouts and the occurrence of light intensities greater than 1,200 ft—c in the understory greatly aided its survival in this stratum. The important role of black cherry in the dynamics of the oak forests was based on opportunistic characteristics including widespread dispersal, delayed germination of seeds, and flexible seedbed requirements. Forest conditions, such as the isolation of forests as woodlots, pioneer environmental conditions, and widespread disturbance, predisposed invasion by opportunistic species. Dynamic processes were characterized by general rather than gradient compositional changes. Patterns of replacement were not orderly and predictable, but irregular as a result of chance dispersal and local catastrophe. Although not uncommon in oak forests in the northeastern United States, invasion by Acer saccharum is not occurring in southern Wisconsin. Succession to Acer—Tilia is confined to specific sites. The overall existing pattern is one of increasing diversity typical of many pioneer communities in an early phase of colonization.

ISSN:0012-9615    

DOI:10.2307/1942389

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY