An Eco-physiological Study On Syringa L. Under The Long-term Domestication

The study was carried out on the basis of rich collections in Syring genus in the past half century in Beijing Botanical Garden affiliated with the Chinese Academy of Sciences. The responding mechanisms to long-term domestication were studied with the methods of photosynthetic physiology. The differences in acclimation between S. pinnatifolia (endangered) and its congener S. oblata (widespread) were displayed by the gas exchanges. Lower light requirement, stronger stomatal restriction and weaker stomatal regulation on photosynthesis compared with the widespread species, as well as its evasive growth strategies presented on the level of day and growing season were quite distinctive. These traits might be the explanation for its limited distribution in the wild from the special aspect. The further study was performed on S. pinnatifolia in order to separate the high light or high temperature affection on the growth quality from the stress combination in ex-situ domestication. The experiments on those individuals grown in the full light-exposure and the 60 percent shading habitats were conducted and the chlorophyll fluorescence of PSⅡ was measured so as to evaluate the light inhibition extent. The results, expressed by the Fv/Fm along with Chla/Chlb, showed that high light in the summer did not damage the PSⅡ and the LHCⅡ. The shading individuals exhibited some adaptive traits in low light intensity not only by the higher foliar chlorophyll content but also the visible moderate growth in shading site. It looked like the high temperature might be the critical limited factor on the S. pinnatifolia ex-situ cultivation. In order to give a further evidence to this speculation and explore the real endangered reason for this species in the origin, the measurements and the investigations were performed in Helan National Natural Reserve, Ningxia Municipality of the Hui Nationality. We found that the individuals of S. pinnatifolia are distributed nearly in the bottom of half sun-faced slop in 1700 m in altitude and the hours of sun-exposure were more than 8h in the clear day. The current leaves were thick and the net photosynthetic rate was notably higher than those of plants in ex-situ conservation. The maximum quantum efficiency indicated that just slight light inhibition happened in the midday and the extent up to which the maximum quantum yield was recovered after one night dark adaptation, meanwhile, higher actual quantum efficiency was presented in the wild. It inferred that this plant acclimated itself to the light exposure very well in its origin, also, the cool temperature would be more favorable to the assimilation than the higher temperature in ex-situ site. Therefore, the high temperature was the primary stress that S. pinnatifolia tried to evade. The results of WUE got from the ex-situ and in-situ were analyzed synthetically in order to find the endangered reason for this species in the wild. The results showed that the individuals grown in botanical garden had higher water use efficiency than those in the wild. This point, for the species in the wild, was just a fatal factor, especially in the arid and semi-arid area. S. pinnatifolia, to be unexaggeratedly, was an enjoyer to the prompt available water and was not tolerant to the drought. An 'omnipotent' species and a 'subnormal' species made us to explore the domestication traits from the systematic level by eco-physiological approaches. The results from S. pinnatifolia showed a middle level in gas exchange parameters across six representative species from the evolutionary sections, just like its intermediate position in Syringa genus from the respect of systematic evolution. S. josikeae and S. sweginzowii, which had the terminal inflorescence and were classified to the original section (Ser. Villosae (Schneid.) Rehd.), had lower photosynthesis capacity, whereastheir higher capacity of water balance might be helpful to survive in the temperate region even though they were introduced from the high altitude area in sub-tropical region. S. vulgaris from a developed section (Ser. Syringa) had stronger transpiration and lower water use efficiency, it might explain the poor growth status in water scarceness in the growing season in ex-situ site. A higher water use efficiency in S. reticulata, an arboreal species, made it tolerant to the drought and could distribute widely in north-west — north-east — Japan. One realistic aim of domestication should be the application. The tolerance to the salt stress for Syringa cultivars was a problem when they were used in the salt areas. Our results from the salt-light interaction experiment simulating chloride -sulphate soil suggested that the Syringa cultivars derived from S. oblata could tolerate to the 0.2% soil salt content. The better tolerance to the salt would be displayed if the 60% shading was used in the habitat. Our eco-physiological study on the domestication traits of Syringa not only focused on the 'species', but also on 'development series' level. The demonstrations on the adaptation under long-term domestication were done from the view of the current status -the historic and ex-situ – in-situ aspects, and at last, these conclusions could go back to give some scientific instructions to the practice of introduction and domestication hopefully.