Studies On Conservation Biology Of Lilium Rosthornii Diels, An Endemic Plant To China

Lilium rosthornii Diels(Liliaceae) and its congeneric species,Lilium sargentiae Wilson,are two perennial herbs endemic to China.Both species have great values in horticulture and medicine science.L.rosthornii distributes in Sichuan,Chongqing,Hubei,and Guizhou provinces,mainly occurs in valley or riverside.L.sargentiae distributed in Sichuan,Chongqing,Yunnan provinces,and so on,mainly occurs in grasses or shrubs on mountain slopes.The number of L.rosthornii is decreasing and its natural distribution is also shrinking gradually,which indicates this species is becoming an endangered plant.Population distribution patterns,flowering phenology,floral syndrome,breeding system, pollination ecology,and seed germination characteristics of L.rosthornii and L.sargentiae were comparatively studied,and phenotypic plasticity under water stress,fertilizing and shading experiments were also done in this paper.For L.rosthornii,the endangered reasons and ecological strategies from the views of population ecology,reproductive ecology,and physioecology of this species were dicussed.The results are as follows:1.According to the spatial pattern analysis in L.rosthornii and L.sargentiae by using the fractal theory and the mean/variance ratio and indexes of aggregation degree,the relatively consistent results were obtained.L.rosthornii are all clumped distribution,however,the majority of L. sargentiae populations is clumped distribution,but they are tending to random and regular distribution.The populations of both species had low fractal dimension(far from 2),suggesting that their spatial occupation degrees were low and that they functioned as accompaniment populations in the communities.This status makes it easily supplanted by the dominant species.In 2006,in L. rosthornii populations,the mean box-counting dimension decreased by 14.15%and the mean correlation dimension decreased by 18.27%,while the mean information dimension increased by 100.32%,suggesting its lower spatial occupation degrees but a higher scale variation degrees,as compared with those of L.sargentiae populations.As compared with in 2005,populations of both species had lower mean box-counting dimensions,information dimensions,and correlation dimensions in 2006.This may be due to the particularly dry climate they experienced in 2006.The percentage by which the mean box-counting dimension decreased was 1.44 times higher in L. rosthornii(13.00%) than in L.sargentiae populations(9.04%).On the other hand,the percentage by which mean information dimension and correlation dimension decreased was much higher in L. rosthornii(22.71%and 5.71%,respectively) than in L.sargentiae populations(3.43%and 0.23%, respectively).These data indicated that the growth of both species was influenced by the hot and dry conditions and that L.sargentiae had stronger resistance to high temperature and drought as compared to L.rosthornii.Moreover,man-made disturbance is also a significant factor which affects the size of L.rosthornii populations.It can be concluded that L.rosthornii,compared with L. sargentiae,is a species more vulnerable to the exceptional climatic events.2.The studies on flowering phenology,floral syndrome,breeding system,and pollination ecology of L.rosthornii indicated that:(1) The flowering time of L.rosthornii was from July to September,anthesis of a single flower lasted from 4 to 6 days.The flowering span of the individuals and population was about 6 to 26 days,30 days respectively.The flowering process of L.rosthornii in wild populations shows a gradually single peak curve,belong to the so-called"Mass-flowering"pattern.As there were few flowers with individuals(single flower in minority but 2 to 9 flowers in majority with one individual),this pattern may be regarded as an adaptive strategy to ensure its reproductive success.(2) The distance from stigma to anthers usually was very short(sometimes connect each other).The stigma receptivity took precedence of dehiscence of anther of a flower.The out crossing index(OCI) of L.rosthornii was 3 or 4.The pollen-ovule ratio(P/O) was about 2000 to 3800.Combining with the results of emasculation,bagging,and artificial pollination studies,the breeding system of this species was mainly determined to be out-crossing,sometimes self-compatible,need pollinators.The out crossing index(OCI) of L.sargentiae was 4.The pollen-ovule ratio(P/O) was about 2400 to 4000.Thus the degree of outbreeding of L.rosthornii was lower than that of L.sargentiae,while the degree of inbreeding of the former was higher than the latter.This probably was due to environmental selection pressure and self-evolutionary,i.e., self-crossing reduced the risk of reproductive failure,which decreased the adaptability of the offspring.The pollen grains of the flower fell on its own stigma very easily.Pollen competition may be the major factor leading to the endangered status of L.rosthornii.(3) Large butterflies in Lepidoptera were the dominant pollinators of L.rosthornii,e.g.,Papilio bianor(Cramer),Papilio polytes polytes Linnaeus,Papilio memnon agenor Linnaeus,Eurema blanda hylama Corbet,Pieris rapae orientalis Oberth(u|¨)r and so on.There were relatively high correlation between visiting behaviors of pollinators and nectar secretion,which was helpful for the reproductive success of the species.But there were a few species of pollinators with bigger bodies,which was disadvantageous to reproductive success.3.The seeds germination of L.rosthornii and L.sargentiae showed that:In certain temperature extent,light illumination delayed the time of the seeds of both L.rosthornii and L.sargentiae starting to germinate,and shortened the time seeds germination reached the peak.Under light illumination,the mean seed germination rate of L.rosthornii was 18.60%lower than that of L. sargentiae,while it was 4.55%higher than that of L.sargentiae in the absence of light illumination. This showed that sunlight was beneficial for the seeds germination of the two plants,and the absence of sunlight had distinct inhibiting effect on the seeds germination of L.sargentiae,it also had some influences on the seeds germination of L.rosthornii.All these facts mean that shade tolerance of L. rosthornii stronger than that of L.sargentiae could also be reflected by the seeds germination.The temperature range for the seeds germination of L.rosthornii and L.sargentiae was 10～30℃,and the suitable range was 15～25℃.Besides,the appropriate temperature range for the seeds germination of L.sargentiae was wider than that of L.rosthornii,which showed that L.sargentiae had stronger adaptation ability for environment than L.rosthornii.The seed germination rate of L. rosthornii(58.47%) under the best combination of temperature and sunlight(20℃,24 h light illumination) was obviously lower than that of L.sargentiae(99.17%) under the best combination of temperature and light(15℃,24 h light illumination),this may be another reason why L.rosthornii was becoming more and more scarce.4.The experiment of response to water stress displays that:①heavily stressed plants of L.rosthornii,their leaf area is increased in the later process period,leaves are getting thinner,and they do not show the characteristics of anti-water stress;however,the L.sargentiae is the opposite, and shows the characteristics of anti-water stress.The features displayed in caudex and leaf of L. sargentiae show even higher phenotypic plasticity index compared to L.rosthornii.②In two important indicators of photosynthesis adaptation,the ratio of Chlorophyll a and Chlorophyll b of L. rosthornii is decreased when the stress is increased during the later process period,and the ratio of Carotenoid and Chlorophyll is also decreased when the stress is increased during most of the time, and these two changes experience a larger range difference an do not show the characteristics of anti-water stress;however,the ratios of L.sargentiae keep in constant high value with a little change, and show the characteristics of anti-water stress.③The plasticity index(PI) of activities of SOD and POD of L.rosthornii is less than the PI of activity of L.sargentiae,and its POD activity maintains at high level during the later process period following by decrepitude,and show lower ability of performing anti-water stress.Thus,compared with L.sargentiae,L.rosthornii's ability of performing anti-water stress is lower. 5.According to the experiment of fertilizing and shading treatments,it can be show that①In either fertilizing or non-fertilizing condition,the morphological indicators of plant height,crown diameter,leaf length,leaf width and leaf area of L.rosthornii are the highest in heavy shading,and its leaf thickness is the smallest,however,only crown diameter,leaf length and leaf area of L. sargentiae are the highest in heavy shading,and the leaf thickness is the smallest only during the later process period.With the same sunlight condition,the most morphological indicators of L. rosthornii in the fertilizing condition are larger than the non-fertilizing condition,but only plant height,leaf width and leaf thickness of L.sargentiae are larger in the fertilizing condition compared with the non-fertilizing condition.The PI of architectural traits of L.rosthornii is larger than that of L.sargentiae.②in two important indicators of photosynthesis adaptation,the ratio of Chlorophyll a and Chlorophyll b,and the ratio of Carotenoid and Chlorophyll for both L.rosthornii and L. sargentiae with either fertilizing or non-fertilizing condition,represent a lower value in heavy shading condition,but plasticity index,PI of L.rosthornii is higher than L.sargentiae.The ratio of Chlorophyll a and Chlorophyll b for both L rosthornii and L.sargentiae with the same sunlight condition,represent a lower value in fertilizing condition.The ratio of Carotenoid and Chlorophyll of L.rosthornii is decreased under the heavy shading condition,while the ratio is increased for L. sargentiae.The PI of the two above indicators and photosynthetic pigments of L.rosthornii is larger than L.sargentiae.③In non-fertilizing condition,CAT and SOD activity of L.rosthornii are increased when the degree of shading is increased,POD activity is the highest only during the later process period,but CAT activity of L.sargentiae shows dynamic changes in the growth and decline, SOD activity is decreased when the degree of shading is increased,POD activity with heavy shading is the highest during the later process period.In fertilizing condition,CAT,SOD and POD activity of L.rosthornii all reach the highest with shading condition,but CAT activity of L.sargentiae is only highest with the heavy shading condition,SOD activity reaches the highest with non-shading condition,POD activity is the highest under the shading condition.In the same sunlight condition, although the POD activity of L.rosthornii is lower under the fertilizing condition,the CAT and SOD activity are the highest under the same condition,and fertilizing has a inhibited effect on the CAT, SOD and POD activity of L.sargentiae.In the fertilizing and shading conditions,the protective enzymes activities of L.rosthornii has larger PI value than the protective enzymes activities of L. sargentiae.Therefore,L.rosthornii can easily adapt with fertilizing and shading habitats,and barren land and strong sunlight are harmful to their survival.6.According to the experiment results,the reasons that L.rosthornii is becoming increasingly scarced are:①Over-excavation by mankind make it difficult to restore this species in a short time.②The limited species number of pollinators,bigger bodies and pollen competition lead to the high incidence of inbreed seed rate between plant populations and reduce the probability of seeding rate, influencing its reproductive success.③Light and temperature are the two key environmental factors in affecting seed germination of L.rosthornii.Temperature which is too high or too low will directly lead to a low seed germination in natural environment,and a small regenerated seedling population.④Its populations have lower spatial occupation degrees and weaker resistance to high temperature and drought.⑤L.rosthornii do not show the characteristics of anti-water stress and the tolerance of barren soil,so it requires strict habitat,and are adaptable to grow up in habitat with relatively moist,fertile and deep soil.Based on the information available for L.rosthornii,two alternative conservation strategies are proposed.The first would consist of an in situ conservation plan that defines areas free from significant disruption for at least the genetically most diverse populations.This would guarantee the maintenance of most of the species' genetic variation.By that,the decreased trend of population can be inhibited,the individual number of populations for this species can be restored and the certain gene flow level can be maintained.So many small and dispersed populations of the species can be associated so that the species can have large populations to resist the pressure of the environment.At the same time,it is necessary to pay attention to protect pollinators of L.rosthornii during the protection process of ecological environment.The second management strategy would be a program of ex situ conservation.The program of ex situ conservation can be taken.The way to protect and restore this suffered populations of species can be implemented through the method of artificial regeneration.