Browsing by Author "HOFFMANN, AJ"

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    DAYLENGTH AND LIGHT RESPONSES IN GROWTH AND FERTILITY OF GLOSSOPHORA-KUNTHII (PHAEOPHYTA, DICTYOTALES) FROM PACIFIC SOUTH-AMERICA
    (1988) HOFFMANN, AJ
    Excised ligulae of Glossophora kunthii (C. Ag.) J. Ag. were cultured in photoperiods of 4-24 h and photon fluence rates of 10-75 .mu.mol .cntdot. m-2 .cntdot. s-1. Daylength interacted with irradiance on the growth of the ligulae. Maximal growth of primary ligulae occurred in long-day regimes with high irradiances suggesting an effect of irradiance on photosynthesis and growth. In contrast, growth of secondary ligulae was greatest in short-day regimes. Differences were significant at the highest irradiance tested. Differentiation of tetrasporangia on the ligulae is a short-day photoperiodic response. Daylengths of 8.5 h or less induced a sharp increase in numbers of fertile ligulae and tetrasporangia attaining maturity. Interruptions of the dark period decreased the development of tetrasporangia; the number of interruptions had a cumulative inhibitory effect. Differentiation of reproductive structures was influenced by interactions of photoperiod and irradiance. Maximum numbers of tetrasporangia were formed at short-day regimes and low irradiances; differentiation was completely inhibited at long-day conditions and high irradiance.
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    EFFECTS OF LIGHT-INTENSITY AND NUTRIENTS ON GAMETOPHYTES AND GAMETOGENESIS OF LESSONIA-NIGRESCENS BORY (PHAEOPHYTA)
    (1982) HOFFMANN, AJ; SANTELICES, B
    Meiospores of L. nigrescens Bory collected in Central Chile, were cultivated under different light and nutrient conditions to test for their influence on the development of gametophytes and gametogenesis. The microscopic stages of the life cycle are described. Under 45 .mu.E [Einsteins] .cntdot. m-2 .cntdot. s-1 (12 h daily) and sea water enriched with nitrate and phosphate, development of few-celled gametophytes, gametogenesis and sporophyte differentiation occur within 35 days. At 10 .mu.E .cntdot. m-2 .cntdot. s-1, most gametophytes are multicellular and remain vegetative up to 65 days. Only enriched sea water or enriched sea water with double concentrations of phosphate lead to fertile few-celled gametophytes under 45 .mu.E .cntdot. m-2 .cntdot. s-1. The addition of double concentrations of nitrate - allows for the development of few-celled gametophytes but inhibits gametogenesis. The average gametophyte size progressively decreases when increasing amounts of nitrate and phosphate are added to the media.
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    FRUIT AND SEED CHARACTERISTICS OF WOODY SPECIES IN MEDITERRANEAN-TYPE REGIONS OF CHILE AND CALIFORNIA
    (1989) HOFFMANN, AJ; TEILLIER, S; FUENTES, ER
    The distribution and characteristics of propagules of woody species were compared in four community types along a gradient of increasing annual rainfall, between 30.degree. and 38.degree. latitude in Chile and California. The hypothesis tested was that in these two regions climatic constraints determine similar responses in phylogenetically unrelated organisms. The abundance of fleshy fruits less than 15 mm in diameter (corresponding to the syndrome of bird-dispersal), their sizes, and the frequency of black fruits increased from xeric towards mesic communities, both in Chile and in California; the largest variety of fruit colors was found in the evergreen scrub in both regions. These trends support the convergence hypothesis. In contrast, the distribution and characteristics of wind-dispersed propagules and of "small" dry, not wind-dispersed propagules showed different, apparently non-convergent trends, in Chile and California.
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    GROWTH HABITS AND PHENOLOGY OF DROUGHT-DECIDUOUS SPECIES IN AN ALTITUDINAL GRADIENT
    (1980) HOFFMANN, AJ; WALKER, MJ
    Several drought-deciduous species occur in the mediterranean type vegetation of central Chile, some of them extending to the slopes of the Coastal and Andean Ranges, up to 2300 m. The growth habits and phenology at different altitudes are compared in 2 drought-deciduous, malacophyllous shrubs: Talguenea quinquinervia, a species of restricted distribution, and Proustia cuneifolia, of widespread distribution. The morphology and timing of seasonal events of T. quinquinervia do not substantially change along its altitudinal range of distribution. In contrast, gradual displacement of phenology occurs in P. cuneifolia, with increasing altitude. Its growth habit varies from the presumably original chamaephyte to a phanerophyte, when under optimal conditions, or to a hemicryptophyte in the highest altitudes. Low temperatures and a prolonged snow cover constitute severe limiting factors for the survival of this drought-deciduous life form.
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    GROWTH-PATTERN AND SEASONAL BEHAVIOR OF BUDS OF COLLIGUAYA-ODORIFERA, A SHRUB FROM CHILEAN MEDITERRANEAN VEGETATION
    (1976) HOFFMANN, AJ; HOFFMANN, AE
    C. odorifera Mol., an euphorbian shrub, grows among the sclerophyllous scrub of central Chile. The growth pattern and seasonal behavior of the floral and vegetative buds are analyzed, with special reference to the climatic conditions (cool humid winters and dry hot summers). Observations were conducted on marked twigs and in sections of embedded material. The branching system is of a Y-shaped sympodial type. The growth season of C. odorifera extends from early winter to the beginning of summer. When the dry season starts, the vegetative apical meristem is converted into a floral bud, and in the leaf axils partly predetermined, unprotected vegetative buds develop. Both types of buds remain dormant during the drought period. Soon after the 1st winter rains begin, activity is resumed; the preformed flowers and leaf buds unfold and grow, and a few more leaf pairs develop during the current year. Buds are influenced partially by the climate of the previous and of the next year.
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    INTERACTIONS IN THE PATTERNS OF VEGETATIVE GROWTH AND REPRODUCTION IN WOODY DIOECIOUS PLANTS
    (1984) HOFFMANN, AJ; ALLIENDE, MC
    Interactions between vegetative growth and reproduction were evaluated in Peumus boldus, Lithraea caustica and Laretia acaulis, woody dioecious species in central Chile. Phenological observations were made periodically on marked branches of male and female plants, and biomass allocation (dry weight) to vegetative and reproductive tissues was measured. The magnitude of flowering was evaluated in groups of plants in 3 successive seasons. The patterns of activities are species- and sex-dependent, and cycles of 2-4 yr were established. Branches that produce flowers either do not grow or grow less than branches without flowers, and males and females have differential resource allocation: male branches attain higher biomass values. Groups of plants show seasonal behavior that suggest synchrony in their reproductive activities.
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    PLANTS INTRUDING LARETIA-ACAULIS (UMBELLIFERAE), A HIGH ANDEAN CUSHION PLANT
    (1985) ALLIENDE, MC; HOFFMANN, AJ
    Several plants invade the cushions of L. acaulis in the high Andean communities of central Chile. Humus develop among the rosettes, and 42 different spp. settle on the cushions. Most of these species are also found outside the cushions. Semi-woody chamaephytes, hemicryptophytes and cryptophytes have a similar cover on both substrates, while the cover of woody chamaephytes and therophytes is smaller on the cushions. The diversity and cover of invading plants, which vary with altitude, result from interations among the environmental conditions, cushion morphology and the surrounding vegetation.
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    Satureja gilliesii, a poikilohydric shrub from the Chilean mediterranean vegetation
    (1979) Montenegro Rizzardini, Gloria; HOFFMANN, AJ; ALJARO, ME; HOFFMANN, AE
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    SEASONAL CYCLES OF GROWTH AND TETRASPORE FORMATION IN GLOSSOPHORA-KUNTHII (PHAEOPHYTA, DICTYOTALES) FROM PACIFIC SOUTH-AMERICA - FIELD AND LABORATORY STUDIES
    (1990) MALBRAN, ME; HOFFMANN, AJ
    The seasonal patterns of growth and tetraspore formation in Glossophora kunthii (C. Agardh) J. Agardh were determined in plants collected in central Chile (32.degree.57'' to 33.degree.15''S) and compared with results obtained from cultures under laboratory conditions. The prostate phase of G. kunthii is apparently perennial. Erect fronds grow during winter. In some locations fronds are persistent, in others they disappear in summer, probably due to local environmental factors. Plants collected in the field showed two peaks of maximal tetraspore formation, in August-October and in January. Ligulae cultured under controlled experimental conditions showed seasonal variations in fertility similar to plants in the field, through the peaks appeared earlier.
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    SEASONAL GROWTH RHYTHMS IN PEUMUS-BOLDUS, A DIOECIOUS TREE OF THE CHILEAN MEDITERRANEAN VEGETATION
    (1981) HOFFMANN, AJ
    The relations between phenology, pollination and climate in P. boldus, a dioecious sclerophyllous evergreen tree of the Chilean Mediterranean vegetation, were studied. Observations were made on marked twigs of mature reproductive trees. Differences are observed between male and female individuals in the seasonal growth rhythms, shoot growth and duration of leaves. Insects visiting the flowers are identified as poorly selective pollinators. The adaptative strategies of this species probably evolved to meet the conditions of the Mediterranean climate, dioecy and their mutual interactions. The energetic cost of fruit development could affect the seasonal behavior of female trees and be related to the larger number of male individuals: in natural populations of P. boldus the male-female ratio is 1.5.
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    SINKING RATES AND VIABILITY OF SPORES FROM BENTHIC ALGAE IN CENTRAL CHILE
    (1989) HOFFMANN, AJ; CAMUS, P
    Spore-sinking rates and viability were studied in 12 species of benthic macroalgae from the intertidal zone in central Chile: two Chlorophyta, Enteromorpha intestinalis (L.) Link and Ulva rigida C. Ag.; one Phaeophyta, Lessonia nigrescens Bory; nine Rhodophyta, Ahnfeltia durvillaei (Bory) J. Ag., A. gigartinoides J. Ag., Gelidium Chilense (Mont.) Santelices et Montalva, G. lingulatum J. Ag., Gymnogongrus furcellatus (C. Ag.) J. Ag., oaIridaea ciliata Kutz, I. laminarioides Bory, Nothgenia fastigiata (Bory) Park., and Porphyra columbina Mont. In still water, interspecific differences in sinking rates were found. Whereas E. intestinalis swarmers remained near the water surface, suggesting a low sinking rate, concentration of spores gradually decreased in all species. After 2-5 h, the percentage of spores that remained near the surface, varied between 80% in A. gigartinoides and 20% in I. ciliata. The sinking rate of spores measuring < 15 .mu.m in diameter was significantly lower than that of spores > 15 .mu.m (P < 0.01). Sinking rate of spores under continuous water stirring was tested for spore suspensions of I. laminarioides and P. columbina. Spores remained suspended near the water surface for 12 h but their concentration decreased to < 50% of the initial value after 24 h. Differences in spore-germination capacity and viability were observed among species. A. durvillaei, G. furcellatus, N. fastigiata, and P. columbina seem to have seasonal fluctuations in germination capacity. Spores were viable from 4 to 11 days, depending on the species. Characteristics of the spores might influence their dispersal potential and, in some species, be related to the life-history strategies of the algae.
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    TEMPERATURE, PHOTOPERIOD AND LIGHT INTERACTIONS ON GROWTH AND FERTILITY OF GLOSSOPHORA-KUNTHII (PHAEOPHYTA, DICTYOTALES) FROM CENTRAL CHILE
    (1989) HOFFMANN, AJ; MALBRAN, ME
    Excised ligulae of Glossophora kunthii from central Chile were cultured at temperatures of 5-25.degree. C, photoperiods of 16:8 and 8:16 h LD cycles, with photon irradiances of 10 and 50 .mu.mol .cntdot. m-2 .cntdot. s-1. Growth of the ligulae, number of fertile ligulae and number of tetrasporangia forming on the ligulae were assessed. Ligulae tolerated temperatures between 10 and 23.degree. C. Temperature interacted with daylength and photon dose, determining quantitative responses in the growth and fertility of ligulae. Growth was least at 8:16 h LD and was not affected significantly by temperature. It was greatest at 16:8 h LD, 50 .mu.mol .cntdot. m-2 .cntdot. s-1 and increased with temperature up to 20.degree. C. Percentage of fertile ligulae and number of tetrasporangia increased with temperature at the 8:16 h LD cycle, reaching a maximum at 20.degree. C. Fertility was low at 16:8 h LD, except at 20.degree. C (and low photon dose) suggesting that reproduction at 20.degree. C is independent of daylength in this species. Ligulae grew larger at the lung-day photoperiods and the proportions of fertile ligulae were higher at the short-day photoperiods, irrespective of the total photon dose received. These results suggest that some aspects of growth and fertility are controlled by photoperiod.
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    THE ARRIVAL OF PROPAGULES OF MARINE MACROALGAE IN THE INTERTIDAL ZONE
    (1985) HOFFMANN, AJ; UGARTE, R
    The composition and abundance of macroalgal propagules contained in sea water arriving at intertidal rocky shores was estimated monthly at Pelancura, central Chile, from June to December, 1984. Samples from surface water and from water running off rocky platforms with mixed algal vegetation were cultured in laboratory conditions and examined for development of sporelings. Thirty eight macroalgal entities grew in the cultures, 75% of them with opportunistic life-styles. The total number of sporelings was similar in the surface water of sites separated by 300 m. Marked variability on composition and number of sporelings was, however, observed between samples taken simultaneously at one site and between different months, suggesting patchiness in the dispersal of propagules. Marked differences were established in the ratio run-off water/surface water in the number of sporelings, which could be related to the dispersal shadows of the various taxa. Sporelings of late successional algae showed marked spatial and temporal variations in number. Some taxa of opportunistic algae were characterized by the development of several thousand sporelings per litre of sea water while in others the number of sporelings was two or three orders of magnitude less, suggesting differences in reproductive effort.
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    TRISTERIX-TETRANDRUS (LORANTHACEAE) AND ITS HOST-PLANTS IN THE CHILEAN MATORRAL - PATTERNS AND MECHANISMS
    (1986) HOFFMANN, AJ; FUENTES, ER; CORTES, I; LIBERONA, F; COSTA, V
    Interactions between a Chilean mistletoe, quintral (Tristerix tetrandrus, Loranthaceae) and its potential host plants were studied at a site with mediterranean type climate. The results show that the distribution of T. tetrandrus is related to the behaviour of avian dispersers, which feed on its fruit, and evacuate the seeds at random in the field, but the distribution is also influenced by microenvironmental conditions, survival of seedlings is hampered at drier locations. The infection capacity of the seeds is increased after birds have eliminated the fruit coat. Survival of T. tetrandrus seeds differed depending on the species to which they were attached experimentally. Seeds germinated, and plants developed on Colliguaya odorifera and Kageneckia oblonga, previously reported as susceptible to infection. Survival was significantly higher on C. odorifera, although in the field it is infected less frequently than K. oblonga. In species on which no T. tetrandrus has been previously reported, resistance to infection might be ascribed to different mechanisms: in Quillaja saponaria, differentiation of cork layers apparently prevents penetration by haustoria; in Lithraea caustica haustoria enter the cortex and phloem, but no further development ensues. K. oblonga seldom bears more than one T. tetrandrus plant. Experimental inoculations showed that significantly more seeds developed into plants on K. oblonga individuals not previously infected with quintral, suggesting that they become resistant to infection.
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    VEGETATION CHANGE IN LARGE CLEARINGS - PATTERNS IN THE CHILEAN MATORRAL
    (1986) FUENTES, ER; HOFFMANN, AJ; POIANI, A; ALLIENDE, MC
    Previous studies have shown that in Chile the so called mature matorral can have the form of either a continuous matrix of shrubs (wet sites) or of multispecific clumps of shrubs (dry sites). After clearing, sites are known to be initially covered by annuals and then by Baccharis spp. or Acacia caven shrubs. Further vegetation changes are still not documented. In the first part of this contribution we show evidence indicating that the "seed rain" of plants dispersed by birds is important only around bird perches and that in general "seed shadows" of mature matorral shrubs are small. These results suggest that late recolonization of cleared areas occurs by a slow diffusion process in which the presence of perching sites for birds plays a significant role. Then we exhibit results regarding the importance of seasonal droughts and European rabbits in explaining transitions between the various types of plant cover. Here we conclude that nursing by older shrubs and not by rocks or fallen branches, is a requirement to insure the survival of seedlings belonging to mature matorral shrubs. Nurses are important regarding both summer desiccation and herbivory. These nurse effects seem to be more important at dry sites where rabbits are also more numerous, than at wet sites where conditions seem somewhat milder and vegetation change could be faster. In the last part we discuss a scheme of vegetation change that incorporates these processes and explains the relation between them, the vegetation types and the recolonization of wet and dry areas. Finally, a brief mention is made to the difference between these processes and the comparable ones in the California [USA] chaparral.