Genetic Variations In Morphological And Physiological Traits Of 18 Species In Different Sections Of The Genus Populus L.

Poplars (Populus L.), are fast-growing and high-yielding tree species,very important to industrial plantations in the world. The natural genetic resources of poplars are quire rich and widely distributed. The evaluation of poplar genetic resources is very important. In this study, phenotypic variation of 18 species, belonging to five sections of poplar, was evaluated for the first time, to show their genetic differences in growth, photosynthesis, water and nutrient utilization etc. Results obtained laid a good foundation for understanding the characteristics of poplar genetic resources and provided useful imformation in mining, creating and utiliziing those special germplasms.The main results are described as follows:1,Genetic variations in foliage traits and plant growth. Leaf size, growth traits (height, DBH, biomass) of 18 poplar species were remarkbly different(p<0.01). The top 5 fast growth species were P. alba, P. deltoides M."P12, P. nigra L."P11, P. deltoides M."P10, P. cathayana by comprehensive evaluation based on growth traits.2,Genetic variation in photosynthetic characteristics. Total chlorophyll content, stomatal frequency, gas exchange parameters (Pn, Gs, Ci, Tr, Pn/Ci) and chlorophyll fluorescence parameters(Fo, Fm, Fv/Fo) were remarkbly different between species. Big difference was also found in the photosynthetic potential of those species. Species such as P. nigra L."P11, P. deltoides"P14, P. nigra L."P16, P. nigra L."P15, P. deltoides M."P12, had higher light saturation point and lower CO₂ saturation point, were potential high photosynthetic production species. Those species are good genetic resources for the production of high light effciency new varieties.3,Genetic variation in nutrient accumulation and resorption. Main nutrients (N, P and K) concentration in 18 poplar species is remarkbly different. The nutrient concentration in leaves was higher than that of in roots and stems, and N concentration in popar organs was higher than K and P concentration. Species, such as P. lasiocarpa, P.trichocarpa, P. simonii and P. euphratica, were the low nutrient strorage tree species, while P. davidiana were high nutrient strorage species. After leaf shedding, transfer rates of N, P and K from the abscised leaves were also have remarkble difference in those poplar species. P. nigra L."P11 and P. nigra L."P15 had relatively higher N transfer rate, P. lasiocarpa. and P. trichocarpa had relatively higher P transfer rate and P. nigra L."P16 and P. deltoides M."P12 had higher K transfer rate. Comprehensive evaluation based on the transfer rate of N, P and K showed that P. deltoides M."P14, P. nigra L."P15, P. nigra L."P11, P. nigra L."P16, and P. alba were the high nutrient transfer efficiency species. In general, the nutrition transfer rate of species in Aigeiros is higher than others.4,Genetic variation in water use efficiency(WUE). Remarkble difference was found in theδ(13)^C values of the 18 poplar species. The range of theδ(13)^C values varied from -30.47‰to -33.77‰. Species such as P. lasiocarpa and P. trichocarpa had higherδ(13)^C values, P. nigra L."P15, P. deltoides M."P10, P. szechwan, P. trichocarpa, P. nigra L."P13 had relatively lowerδ(13)^C values.5,Genetic variation in wood physical properties. 18 poplar species had remarkble difference in basic density, fiber wire angle, fiber length, fiber width and fiber aspect ratio.Basic density varied from 0.34 g·cm^-3 to 0.48 g·cm^-3, and the density the P. maximowiczii, P. yvnnanensis, P. deltoides M."P10, P. nigra L."P11 and P. nigra L."P15, is higher than others. Fiber wire angle varied from 18.90°to 22.28°, fiber wire angle of P. nigra L."P11, P. nigra L."P15, P. cathayana and P. davidiana is smaller than others. The range of fiber length is 612.32μm to 753.86μm, P. alba, P. deltoides M."P10, P. deltoides M."P14, P. nigra L."P13, P. nigra L."P11 and P. nigra L."P15 had longer fiber than others.