Title:
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Comparative physiological ecology of Daucus carota subsp. carota and Daucus carota Subsp. gummifer
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A comparison was made between the physiological
ecology of Daucus carota subsp. carota and
D. carota subsp. gummifer, the first a widespread weed,
the latter restricted to exposed coastal cliffs in the
south-west. Experiments were carried out on germination,
growth and flowering both in the field and in the laboratory.
These included studies on reciprocal transplants
in the field, growth on different soils, culture experiments
on the effect of salinity, pH and nutrient concentration.
Experiments on the effect of temperature, shade
and wind were also conducted.
Germination in the field was found to take place
mainly in the spring for subsp. carota as the seeds need
to be after-ripened over winter, whereas there is no
requirement for after-ripening in most of the seeds of
subsp. gummifer, so that a large percentage of them can
germinate immediately on maturation in the autumn. The
optimum temperature for germination of subsp. carota is
20°C, but for subsp. gummifer it is between 200 and 25°C.
Weak acids inhibited the germination of both subspecies,
whereas alkaline solutions and KNO3 were stimulators, and
NaCl stimulated the germination of subsp. gummifer in the
dark.
Transplanted D. carota subsp. carota grew better
inland than subsp. gummifer, whereas transplanted subsp.
gummifer grew better at an exposed site at Portland Bill.
Wind at Portland Bill broke and killed plants of subsp. carota, whereas those of subsp. gummifer survived and were
undamaged.
Sodium chloride had a beneficial effect on the
growth of subsp. gummifer even at a concentration of 1 g/l,
which inhibited the growth of subsp. carota. The highest
wind speed produced in a wind tunnel (3 m/sec), decreased
the growth of subsp. carota, whereas growth of subsp.
gummifer increased with increasing wind speed.
The main conclusion of this study is that air
temperature, wind speed and the salinity of the soil are
the most important factors determining the distribution of
the two subspecies.
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