The Germination Characteristics Of Gramineous Species In The Alpine Meadow On The Qinghai-Tibet Plateau

Seeds germination are affected by many factors,and temperature is one of the most important ecological factors.This paper described the germination characters of 74 Gramineous species under 5 different temperatures(5℃,10℃,15℃,20℃,25℃),which might be a important supplement to the experiment on inter-specific seed germinability.The main results are as follows:1.According to different germination percentage of the tested species under 5 temperatures,these species showed four germination patterns.First:germination percentage of 42 species which remained with high germination pattern were high under 5 temperatures,average germination percentage of these species exceeded 70% and 22 of 42 species exceeded 83%germination;Second:germination percentage of 13 species which remained with middle germination pattern was 55%-70%;Third:5 species remained with intergrades,these species did not germinate or germination percentage was a very small quantity under one temperature,but germination percentage exceeded 75%under other temperatures.Fourth:average germination percentage of 18 species which remained with low germination pattern was lower than 50%.2.Of the 74 species tested,germination was inhibited at low temperature for 23 species,germination percentage of 17 species were higher under 10-25℃than at 5℃(p＜0.05);compared with 5℃and 10℃,germination percentage of 5 species were higher under 15-25℃(p＜0.05);germination percentage of Elymus dahuricus was significantly greater at 20 and 25℃than under 5-15℃(p＜0.05).Germination was inhibited at higher temperature for 5 species,the optimum temperature for seed germination was 5-20℃for Poa annua and Roegneria nutans and 5-15℃for Dactylis glomerata and Deyeuxia flavens;Stipa bungeara can only germinate at 5℃; the optimum temperature for seed germination was 10-20℃for Elymus tangutorum and Stipa tianschanica;germination percentage was not significant difference under 5 temperature for 44 species(p＜0.05). 3.The germination rates(the reciprocal of the duration for 50%germination) enhanced with temperature power-up,16 species maxed in 25℃,and the germination rates of 30 species were the rapidest at 20℃and reduced a little bit at 25℃. Germination rates were regressed against temperature,for all species a linear regression accounted for 90%of the variation in germination rates and temperatures (r~2＞0.90,p＜0.001).4.From the regressions,the base temperatures(Tb,below which no germination is expected) and the thermal constant(S,expressed in degree days) for 50%germination were calculated.For 90%the studied species,their Tb was under 3℃and S exceeded 60d℃.Although species with similar Tb values could have very different values of S,when the estimated S values for 50%germination were regressed against their corresponding values of Tb,there was a negative correlation,a linear regression accounted for only 35%of the variation(r~2=0.35,p＜0.001).