|其他摘要||Nyssa L. is a remnant genus of Nyssaceae with the disjunct distibutional patterns between eastern Asia and North America. There are seven species in China (five endemic) according to Flora of China. A revision of Nyssa was proposed based on observation in the field, studying specimens, analyzing morphological characters and molecular phylogeny. The results revealed that N. yunnanensis W. C. Yin ex H. N. Qin & Phengklai was a distinct taxon. Besides, wild investigation, cytology, pollination ecology and conservation genetics have been studied on this species. The causes of critically endangered species of N. yunnanensis were discussed, and correspondent conservation strategies also were proposed according to the above-mentioned. The main results are summarized as follows:
Thirty-three qualitative characters and 19 quantitative characters of Nyssa in China were analysed via statistics and principle component analysis (PCA). The results showed that N. yunanensis was a distinct taxon and different from N. javanica (Bl.) Wanger. N. sinensis Oliv., N. shweliensis (W. W. Smith) Airy-Shaw, N. shangszeensis Fang et Soong and N. wenshanensis Fang et Soong were not distinct. N. leptophylla Fang et Chen was excepted because there were no information about its collecter and site on its type specimen.
Camptotheca acuminate Decne.and Davidia involucrata Baill were choosed as outgroup. Two species, N. sylvatica Marsh and N. aquatica L from North America, were also treated as ingroup, excepting those species of Nyssa in China. Phylogeny of Nyssa was studied by maximum parsimony analysis of nuclear ribosomal ITS and 5 chloroplast psbA-trnH, rps16r-f, trnL-F, trnL-rps32F, trnsr-sf gene sequence, respectively or unitedly. The results were same as that of morphology. N. yunnanensis was a distinct and basal taxon and affinities with N. javanica. N. sinensis, N. shwenliensis, N. shangzeensis and N. wenshanensis clustered togeter, and they were affinities with N. sylvatica.
3.Taxonomic revision of Nyssa in China
Combining the results of morphology and molecular phynology, we made the classification revision of Nyssa and concluded three species N. yunnanensis, N. javanica and N. sinensis distributing in China. N. leptophylla Fang et Chen were numerated as dubious taxa.
4.Biological traits of N. yunnanensis, a critically endangered species
N. yunnanensis is a canopy tree narrowly distributed species of nortern edge in tropical zone with 37 individual in the two wild populations. It grows nearby stream with conifer and broadleaf with poor natral regeneration. It was morphologically androdioecy.
5.Seed germination traits of N. yunnanensis
Seed morphology was observed and effects of substance types, light, destroying the endocarp artificially and gradient pH on germination percentage of the species, N. yunnanensis, were investigated primarily. The results showed that the average seed size with endocarp was 0.94cm×0.52cm×0.17cm (length×width×thickness), per- thousand-seed-weight about 234.3g, with germination valve. Among the three substance types, laterite/ humus soil/ peat (v/v/v, 1:1:1) was better for N. yunnanensis. Seeds could germinate in the both light and dark, the germination rate be increased by destroying the endocarp artificially obviously, and the seed germination of N. yunnanensis was stunted by treaded in lye, however, that of N. sinensis was promoted. Besides, the rarity causes of N. yunnanensis were discussed in this paper.
6.Cytology of N. yunnanensis
Chromosome numbers, 2n=44, of N.yunnanensis was investigated and reported here for the first time. It was same as other species of Nyssa but different in existing B-chromosome in this species which might be related to its ratity.
7.Pollination ecology of N. yunnanensis
We herein documented the flower phenology, pollen germination and morphology, sex ratio, pollinators, and mating system of N. yunnanensis. The results showed that the male flowers opened 10-15 days earlier than hermaphrodites, but ended at nearly the same time. The mean germination rate for pollen from males on the sucrose gradient solution was 97.8%, whereas that from hermaphrodites was 0%. Pollen morphology of males was tricolporate but that of hermaphrodite inaperturate. Thirty-six species of visitors to the flowers were collected, and four of them including bees and flies were the effective pollinators. Anemophilous and entomophilous pollination co-existed in N. yunnanensis, with the latter dominated the breeding system. The mating system was xenogamous and parthenogenesis was not detected. No seeds were produced in inflorescences with self-pollination or in those self-pollinated by pollen from hermaphrodites. In contrast, the mean seed set of male-pollinated inflorescences was 47%. The sex ratio of males: hermaphrodites in the two populations examined were 1:1.7 and 1:2, respectively, female-biased. Yet the flower sex ratio was 2.56:1, which was male-biased. These results indicate that N. yunnanensis is functionally dioecious. Strong xenogamy and biased sex ratio might be the reasons why it is so rare.
8.Conservation genetics of N. yunnanensis
ISSR markers were used to determine the genetic variation among different populations and between parents and progeny in different populations of N. yunnanensis. High genetic diversity of N. yunnanensis was detected. Except Well population, genetic diversity of progeny was higher than their parents in others.
In order to protect the critically endangered tree, some strategies should be recommended: reinforcement of public education and in-situ conservation, introduction by collecting seed to increase the number of individuals, and then reintroduction.|