Study On Habitat Adaptation Of Two Karst-cave Dwelling Petrocodon(Gesneriaceae) Species

The original narrow Petrocodon Hance is a unique small genus of Gesneriaceae in China.Based on the classic morphological and molecular systematic studies of Weber and other scholars,the current general Petrocodon s.l.includes eight genus,33 species and 1 variant,i.e.the original Petrocodon,Calcareoboea,Paralagarosolen,Tengia,Lagarosolen,Dolicholoma,few species of Didymocarpus and W.tiandengensis of Wentsaiboea.Previous studies showed that Primulina and Petrocodon are the highly endangered species among all of the cave-dwelling Gesneriaceae plants in South China.There are no particular bottlenecks in the introduction and Ex-situ conservation of the former,while it is problematic in the introduction of the latter.However,less information concerning their conservation is available.In this study,Petrocodon jingxiensis and P.lui,two representative generalized Petrocodon in terms of quantity and endangered situation,were selected as the study objects to preliminarily study the relationship between target species and environment,between target species and associated species,and intraspecific breeding in relation to native environmental ecological factors,population niche and seed germination response.The aim of this study is to reveal the habitat adaptability,endangered status and possible reasons of two cave-dwelling Petrocodon species,and to provide a scientific theoretical basis for effective protection and germplasm resources rejuvenation.We obtained the following results.1.We investigated and monitored the respective karst environment of two Petrocodon species.The results showed that,(1)the habitats for these two species differed significantly in their geographical locations and spatial structures(2)the ambient temperature was stable;the atmospheric relative humidity was ?80%,the lighting conditions inside and outside of the cave was different;the soil was weakly alkaline(7.0?pH?8.0)and Ca content was high;(3)these two Petrocodon speices can survive in different lighting conditions and in a sterile soil environment.2.Two Petrocodon species,Petrocodon jingxiensis and P.lui,were distributed unevenly in their own habitats at each position.The results of population niche study showed that,(1)the relative dominance of Pet.lui in their habitats was 37.28%,and the Levins and Hurlbert niche breadth index ranked second,suggesting a broad available resources.Among these 20 dominant species,the niche overlap value among Pet.lui and the other 11 species was above 0.5.Due to different resources utilization ways of light and soil,Petie lui and other dominant species including Asplenium cornutissimum had higher niche overlap,but they could coexist wel.When the light and soil conditions were satisfied,the high level of niche overlap among Pet.lui and the other dominant species such as Begonia sinovietnamica,Ctenitopsis devexa and Elatostema longistipulum,led to a more pronounced competition.In this case,Pet.lui had a low dominance value,indicating that it was in a competitive inferiority.(2)In the habitats the relative dominance of Pet.jingxiensis was 20.50%,and its Levins and Hurlbert niche breadth index ranked 16 th.Thus its main community gathered on the stone surface of the cave which represents relatively poor resources,and its resources utilization degree was low.Among the 20 dominant species,the niche overlap value among Pet.jingxiensis and the other 5 species was greater than 0.5.This suggested that,due to its poor competitiveness,it was separated from most other species in space,and its community structure tended to be stable.3.We studied the effects of soil matrices which were collected from different locations in their habitat,pH values and soluble calcium salts on seeds germination of two Petrocodon species in laboratory conditions.The results showed that(1)Pet.lui seeds had dormancy.In its habitat,the soil matrix attached to the stone surface was more suitable for its seed germination.The soil matrices from the ground and boundary inhibited the germination of Pet.lui seeds to a certain extent since the soil had been disturbed by human activities.The results of pH and soluble calcium salt stress on seed germination showed that neutral to weak alkaline and high calcium content,low salinity environments were most suitable for Pet.lui seeds to break dormancy and al owed them to grow better.(2)Pet.jingxiensis seeds didn't have dormancy.The seeds could germinate in the soil matrix that were collected from different locations in its habitat.But in the process of seedling development,seedlings would be affected by biological and non-biological factors of the ground soil,resulting in lower number of survived seedlings.Combined with the results of seed germination in acidic or stronger alkaline environment and environment enriched with high salt concentration as well as the results of the one-variable germination experiment,it was clear that the distribution of Pet.jingxiensis in the habitat was inhibited not only by soil environment,but also the interaction of environment and biology,resulting in a massive distribution on the stone surface in the cave.4.Taken together,results of the study showed that Pet.lui had a higher environmental adaptation,and its demand for resources was not high,which al owed Pet.Lui to survive in sterile environmental condition.But Pet.lui had a very demanding requirement for interspecific relationships,so its weak interspecific competing ability was one of the reasons that cause endangering.And Pet.jingxiensis had strict requirements for environmental resources and interspecific relationships,so the main reason why Pet.jingxiensis was endangering was the the interactions between environment and biology.As a result,the native ecological environment of the two Petrocodon species had a significant protective effect on the survival of their population.Therefore,we suggest that management policies should be tuned to maintain the appropriate effective population size of two Petrocodon species and to protect their natural habitats,which is currently the most reasonable and effective means of species conservation.