Conservation Biology Of A Rare Herb Taihangia Rupestris (Rosaceae)

Cliffs are one of the relictual and least disturbed habitats which act as refuges for biodiversity. Numerous rare and endemic species are distributed in these special habitats, and most of them could only grow there. During the long process of evolution, these plants established an adaptable relationship with their stressing habitats. They present a new research aspect for conservation biology of rare species in special habitats. This dissertation reports the study on conservation biology of Taihangia rupestris Yu et Li, a naturally rare herb inhabiting north-facing vertical cliffs of the Taihang Mountains within a limited geographic area in China.Firstly, the genetic diversity and genetic structure of eight populations of T. rupestris as revealed by RAPD markers were analyzed. The results indicate high levels of genetic diversity within populations and no signs of severe genetic bottleneck effects were found in this rare species. Significant differentiation also exists between the populations, which is correlated with their geographical distances. The dendrogram of UPGMA is consistent with the division of the species into the two varieties, namely T. rupestris var. rupestris and T. rupestris var. ciliata.Greenhouse experiment were conducted to study the ability of acclimation and adaptation of T. rupestris in response to light intensity and nutrient availability. Light intensity had significant effects on photosynthetic parameters, and the ability of T. rupestris to acclimate photosynthetically to full light differed on the two different measuring dates. The photosynthetic rate was higher in high light (HL, full ambient light) than in medium light (ML, 50% of full light) on August 8, but was lower in HL than in ML on September 22. The photosynthetic light response curves showed the photosynthetic acclimation of T. rupestris to different light environments.Light intensity also had significant effects on the growth and morphological andanatomical characteristics of T. rupestris. It produced more numerous but smaller and thicker leaves under HL. A higher rate of new leaf formation could guarantee T. rupestris under HL to have higher photosynthetic rate at the whole plant level, resulting in larger biomass at harvest, although the single-leaf photosynthetic rate may become lower as indicated by the data on September 22. T. rupestris had greater petiole length, area per leaf, SLA (specific leaf area) and LAR (leaf area ratio) in ML than in HL. These responses are thought to be adaptive for plants growing in relatively low light conditions. Light intensity had no effects on stomatal density, stomatal index and the size of stomata. The effects of nutrient availability on the growth of T. rupestris were small. These results suggest that T. rupestris growing in shade possesses a latent capacity of acclimattion and adaptation to full light. Light and nutrient, therefore, may not be factors responsible for the restricted distribution of T. rupestris growing on vertical cliffs.The flower development process of T. rupestris was observed by scanning electron microscopy (SEM) for the first time. The existence of suppressed flower buds in the base of bracts suggests that the apparent solitary terminal flower of T. rupestris is actually a reduced determinate inflorescence, in which all the flower buds except for the terminal one abort in the development process in early spring. The ontogeny of pistils in T. rupestris was normal and no signs of suppression were found.The above results suggest that T. rupestris growing in the special habitats of cliff crevices with restricted distribution does not show reduced physiological and morphological acclimation and low levels of genetic diversity. The restricted distribution of T. rupestris on cliffs, therefore, is not due to genetic decline and lack of adaptation ability. It is concluded that T. rupestris evolves the ability of acclimation and adaptation to the stressing special habitats of cliffs in the long process of evolution. The efforts of conservation for this rare species should be i...