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  • Seed germination  (1)
  • Temperature fluctuations  (1)
  • semi-arid grassland  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Effects of soil disturbance, fire and litter accumulation on the establishment of Cistus clusii seedlings (1997)
    Springer
    Plant ecology 131 (1997), S. 207-213 
    Details
    ISSN: 1573-5052
    Keywords: Coloniser species ; Dormancy ; Drought ; Fire ; Impermeable seeds coats ; Mediterranean climate ; Seed germination ; Temperature fluctuations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cistus clusii is an early successional shrub, the most drought-resistant species of Cistus which colonises perturbed areas in the southern Iberian Peninsula and regenerates entirely from seeds after a fire. Some of the factors controlling germination and seedling establishment were examined in a field experiment in which we tested the effect of soil disturbance, fire, and litter accumulation on seedling emergence. In a first experiment, soil disturbance and fire were applied to plots in the field with a factorial design in April 1992. In a second experiment, we measured the effect of adding C. clusii litter. The number of seedlings, annual plants and grasses, and the coverage of mosses were recorded in 1993 and 1994. Soil disturbance increased the number of C. clusii seedlings almost seven-fold but did not change the number of grasses, annual plants nor moss cover. Fire significantly increased the number of C. clusii seedlings only in combination with soil disturbance, and it did not affect the presence of annuals, grasses nor moss cover. Litter increased the number of C. clusii seedlings in the following two years. Overall, soil disturbance as a single factor had the most significant effect on seedling emergence, though plots disturbed and treated with fire had the highest number of seedlings, implying that germination of C. clusii seeds was enhanced by processes that alter the hard seed coat and break the physical dormancy imposed by the testa. In addition, recruitment of C. clusii was dependent on rainfall, as drought significantly reduced the number of seedlings appearing in winter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009779820845
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  • 2
    Electronic Resource
    Electronic Resource
    Environmental control of canopy dynamics and photosynthetic rate in the evergreen tussock grass Stipa tenacissima (1999)
    Springer
    Plant ecology 145 (1999), S. 327-339 
    Details
    ISSN: 1573-5052
    Keywords: canopy age structure ; carbon assimilation ; leaf elongation ; semi-arid grassland ; soil water content
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seasonal changes in leaf demography and gas exchange physiology in the tall evergreen tussock grass Stipa tenacissima, one of the few dominant plant species in the driest vegetation of Europe, were monitored over a period of two years at a field site in semi-arid south-eastern Spain. Three age-classes of leaves – young, mature and senescent – were distinguished in the green canopy. Production of new leaves and extension growth of older leaves occurred exclusively from October–November to May–June. The rate of extension was significantly correlated with gravimetric soil water content. Leaf growth ceased after gravimetric soil water content fell below 0.015 g g−1 at the beginning of the dry season which corresponded to pre-dawn leaf water potentials of -3.0 MPa. Leaf senescence and desiccation reduced green leaf area by 43–49% during the dry season. Diurnal changes in the net photosynthetic rate of all three cohorts of leaves were bimodal with an early morning maximum, a pronounced midday depression and a small recovery late in the afternoon. Maximum photosynthetic rates of 10–16 μmol CO2 m−2 s−1 were attained from November 1993 to early May 1994 in young and mature leaves. Photosynthetic rate declined strongly during the dry season and was at or below compensation in September 1994. Gas exchange variables of young and mature leaves were not significantly different, but photosynthetic rate and diffusive conductance to water vapour of senescing leaves were significantly lower than in the two younger cohorts. Leaf nitrogen content of mature leaves varied seasonally between 2.9 and 5.2 g m−2 (based on projected area of folded leaves), but was poorly correlated with maxima of the photosynthetic rate. There was a stronger linear relationship between the daily maxima of leaf conductance and pre-dawn leaf water potential than with atmospheric water vapour saturation deficit. Seasonal and between-year variation in daily carbon assimilation were caused mainly by differences in climatic conditions and canopy size whereas the effect of age structure of canopies was negligible. Since water is the most important limiting factor for growth and reproduction of S. tenacissima, any future rise in mean temperature, which might increase evapotranspiration, or decrease in rainfall, may considerably reduce the productivity of the grasslands, particularly at the drier end of their geographical distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009892204336
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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