Responses of germination and radicle growth of two Populus species to water potential and salinity

Abstract The effects of water potential, NaCl and Na2SO4 on germination and radicle growth of two riparian tree species, Populus euphratica Oliv. and P. pruinosa Schrenk （Salicaceae）, were tested. Growth chamber studies revealed an optimum temperature range for seed germination of both species between 15-35℃. The final germination percentage of both species decreases with decreasing water potential in all types of solution applied in the experiments. P. pruinosa was less tolerant to low ψw stress than P. euphratica, especially in salt solutions. Germination percentages fell below 20% for P. pruinosa at -0.6 MPa （NaCl） or -0.4 MPa （Na2SO4） and for P. euphratica at -1.2 MPa （NaCl） or -0.6 MPa （Na2SO4）. Radicle growth of both species was inhibited by high concentrations of PEG1 NaCl and Na2SO4. However, growth was enhanced at -0.13 and -0.29 MPa in PEG or at -0.13 MPa in NaCl solutions compared to distilled water. Radicle growth of P. euphratica was higher than that of P pruinosa. Germination and radicle growth of both species exhibited ion toxicity. Na2SO4 was more toxic than iso-osmotic solutions of NaCl. Radicle growth proved to be more sensitive than seed germination. Thus, flooding does not only yield the necessary soil moisture for germination but also favors seedling establishment of both species through leaching of salts from the soil surface. The different sensitivity of the species during their early growth stages might, moreover, contribute to the observed differences in their distribution in the Talim Basin （northwest China）.

Forest gaps regulate seed germination rate and radicle growth of an endangered plant species in a subtropical natural forest

The survival rate of Castanopsis kawakamii from seed to seedling is relatively low,leading to difficulties in the regeneration of its natural forests.Forest gaps play a vital role in plant regeneration and biodiversity maintenance in forest ecosystems.Unfortunately,our understanding of the effects of gap size and within-gap position on the seed germination and radicle growth of C.kawakamii is still limited.In particular,our knowledge on the relationship between gap size and environmental factors and their influence on seed germination and radicle growth is incomplete.In the present study,we studied the influences of forest gaps and within-gap position on seed regeneration on the germination and radicle growth of an endangered species C.kawakamii in a subtropical natural forest in China.We selected three large gaps(LG,gap size above 200 m^(2)),three medium gaps(MG,gap size 50-100 m^(2)),three small gaps(SG,gap size 30-50 m^(2)),and non-gap(NG),and planted the seeds of C.kawakamii in five positions within each gap.The results showed that(1)the influence of forest gaps on seed germination rate was,from highest to lowest,medium gaps(51%),non-gap(47%),small gaps(40%)and large gaps(17%),and the seed germination rate was the highest in all positions in medium gaps,with the exception of the east position.(2)Radicle length in forest gaps was,from highest to lowest,medium gaps,small gaps,large gaps and non-gap,and it was the highest in the east,south,west and north positions of medium gaps.(3)Canopy openness(gap size)and air temperature were the main factors influencing seed germination and radicle growth of C.kawakamii.We concluded that medium-sized gaps were the most suitable for seed germination and radicle growth of C.kawakamii,and they promote the regeneration of this endangered species in the investigated natural forest.