 |
|
|
|
|
|
 |
New Zealand Journal of Botany abstractB97061 Received 25 August 1997; accepted 19 December 1997
Germination, growth, reproduction, and population structure of three subspecies of Lepidium sisymbrioides (Brassicaceae) with respect to taxon rarityR. B. ALLEN
Landcare Research
Abstract Lepidium sisymbrioides comprises three
subspecies endemic to South Island, New Zealand. The taxa have very different
abundances: L. s. ssp. sisymbrioides is geographically
widespread, L. s. ssp. kawarau has a few populations in two
localities, and L. s. ssp. matau has only one main population.
This study sought ecological reasons for these differences in abundance.
Population structures, flowering, and seed production were recorded in two
populations of Lepidium sisymbrioides ssp. sisymbrioides
(Patearoa, Pisa Flats), two populations of L. s. ssp. kawarau
(Slapjack Creek, Falls Dam), and the only known population of L. s. ssp.
matau (Galloway). Seed germination for each population was tested in
vitro. Germination, growth, flowering, and rosette production were recorded
in reciprocal sowings of seed from the five populations in soils from each of
the sites. Taxonomic characters were compared between plants of these five and
a third population of L. s. ssp. kawarau also grown in these
soils. In vitro seed germination varied between populations and between
years. L. s. ssp. kawarau seeds from Falls Dam failed to
germinate in vitro, and their germination rates in soil were lower than
those of the other populations. Seedling growth rates were similar between
populations. Falls Dam L. s. ssp. kawarau plants grown from seed
flowered one (male) or two (female) years later than those of the same sexes
from other populations. Thereafter, flowering rate and frequency, and rosette
production, did not differ markedly between populations in cultivation, as was
also the case in the wild. Soil bioassay (Lolium perenne dry weights)
indicated that soils occupied by L. sisymbrioides plants were more
fertile than adjacent soils, but there were no differences in fertility between
the soils occupied by different populations of L. sisymbrioides. There
was a gradient of taxonomic characters between two populations of L. s.
ssp. sisymbrioides and L. s. ssp. matau, between three
populations of L. s. ssp. kawarau, and between these two main
groupings. Differences in germination, growth, reproduction, and population
structure between taxa and populations did not explain their relative abundance
in the wild. |