Sinosenecio jishouensis D.G. Zhang, Y. Liu & Q.E.Yang is a new Asteraceous species, and is considered as a critically endangered species because its population is extremely small. Currently, only several natural populations of S.jishouensis are discovered in Dehang canyon which is at northwestern Hunan, China, and is characteristic of low light intensity and high relative humidity. An interesting question is thus whether or not the distinct habitat conditions are related to its growth and distribution. Generally, its natural habitats consist of valley falls habitat, valley sidehill habitat and valley understory habitat. In order to reveal the adaptive ability to different environments and the underlying mechanisms, S. jishouensis were transplanted from valley to sun habitat and shade habitat. Since the light intensity and the relative humidity are different among 5 habitats, especially, there are higher light intensity and lower relative humidity in 2 artificial distribution habitats than in 3 natural distribution habitats, the leaf morphology and PSⅡchlorophyll fluorescence parameters in leaves of S. jishouensis within above 5 habitats were investigated.
The results showed that: as compared with 3 natural distribution habitats, the leaf area, specific leaf area of Sinosenecio jishouensis were smaller and their stomata density, SPAD value were higher in 2 artificial distribution habitats, especially in sun habitat. On the other hand, the rapid light-response curves of chlorophyll fluorescence parameters were measured at various light intensities (8, 16, 32, 90, 165, 245, 325, 430, 580, 770, 1100, 1400, 1700, 2100 μmol · m^-2 · s^-1) by PAM-2500 chlorophyll fluorimeter. We observed that the maximal PSⅡquantum yield (Fv/Fm), latent PSⅡ quantum yield (Fv/Fo), the quantum yield of regulated energy dissipation (Y(NPQ)) had no significant difference between 5 habitats. However, the maximal electron transport rate (ETR_max), minimum saturating irradiance(Ik), the coefficient of photochemical quenching (qP) and the effective PSⅡ quantum yield (Y(Ⅱ)) of S. jishouensis in sun habitat were higher than other 4 habitats, above 4 parameters in valley understory habitat were significantly lower than other 4 habitats, at the same time, those values showed no significant difference among valley falls habitat, valley sidehill habitat and shade habitat.
It thus indicated that S. jishouensis had tolerance to greater light intensity and moderate air humidity realized by reduced leaf area, specific leaf area, and increased stomata density, SPAD value, improved NPQ and Y(Ⅱ). while low light intensity and high relative humidity was not an important ecological factor in limiting development of S. jishouensis, providing a theoretical foundation for ex situ conservation of S. jishouensis. However, the major environment factors limiting distribution of S. jishouensis and the main causes for the endangered status of S.jishouensis still needed further investigation.