Study On Physiological Ecology Of Seed Aging Of Koelreuteria Bipinnata Franeh.

Under natural conditions,the survival and reproduction of a plant species is determined to a great extent by its seeds,and seed is also important for the conservation of rare and endangered angiosperm and gymnosperm,the vegetation ecosystem management and agroforestry and horticultural production.As an excellent multipurpose garden tree of the family Sapidaceae,Koelreuteria bipingnan Franeh.has high ornamental and economic value and is widely distributed in the humid areas of central and southwestern China.In the present study,the seeds collected from the canopy seedbank of K.bipingnan were used as the experimental materials.By means of the artificial accelerated aging treatment,the hydration-dehydration cycling treatment simulated wet-dry cycling under natural conditions,and termly collecting seeds from canopy seedbank,the changes in the viability,the malondialdehyde(MDA)content,the activity of main antioxidant enzymes(SOD,APX,CAT and DHAR)and the content of main reserve substances(soluble protein,soluble sugar and crude fat)were detected in order to find out the change law of seed vigor and its physiological and ecological mechanism,and subsequently the ecological significance of canopy seedbank in K.bipingnan and other angiosperm and gymnosperm was discussed.The main results were as follows:1.If only the final average germination is taken into account,the optimum germination temperature range of K.bipingnan seeds under the constant temperature condition is 15~25°C.Nevertheless,if both the final average germination and the germination rate are taken into account,the optimum germination temperature range was 20~25°C.The final average germination were all more than 80% under the simulated alternative temperature in spring,summer and autumn,and there was no significant difference in germination rate.2.For the seeds treated with artificial accelerated ageing,the final average germination decreased rapidly under higher alternative temperature simulating summer,while under lower alternative temperature simulating spring and autumn,the final average germination decreased relatively slowly.This may be because the highertemperature aggravated the ageing of seeds,while the lower temperature may have a certain repair effect on the aged seeds.3.Lipid peroxidation of plasma membrane was more sensitive to artificial accelerated ageing than electrolyte leakage,i.e.lipid peroxidation occurred first and then electrolyte leakage.The activity of CAT decreased rapidly and the activity of SOD and APX decreased slowly with the artificial accelerated aging,while DHAR activity did not significantly changed,seeming to suggest that SOD and APX played a protective role in a certain extent.The content of soluble sugar in seeds decreased rapidly and the content of crude fat showed a change trend of "rise-fall-rise" with artificial accelerated ageing,while there was no significant change in the content of soluble protein.4.Under the simulated alternative temperature in summer,the seeds hydrated for different time followed by redried were more easier to lose their viability,while the simulated alternative temperature in spring and autumn seemed to be beneficial to maintain seed vigor,and which was consistent with the changes in the activity of main antioxidant enzymes and the contents of main reserve substances and MDA.Additionally,the simulated alternative temperature in spring could improve the activities of several main antioxidant enzymes to a certain extent.Under the simulated alternative temperature in summer,with the increase of the times of hydration-dehydration cycling treatment,the final average germination generally decreased despite occasionally occurring increase,and the MDA content in seeds did not change significantly,and the activity of the several main antioxidant enzymes decreased sharply except SOD.Nevertheless,under the simulated alternative temperature in spring,the seed viability could be maintained better with the increase of the times of hydration-dehydration cycling treatment,in spite of the activities of the main antioxidant enzymes also decreased sharply,and there was no significant change in MDA content too.Perhaps,in addition to the antioxidant defense mechanisms,there are other protective mechanisms in the seeds.5.Under the simulated alternative temperature in spring and summer,hydration-dehydration cycling treatment seemed to have no effect on the content ofsoluble sugar and crude fat but to have a significant effect on the content of soluble protein.With increasing the times of hydration-dehydration cycling treatment,the content of soluble protein increased first and then decreased,which may be due to occur an increase followed by an decrease in seed respiration with seed ageing.6.In the present study,the study on the canopy seedbank of K.bipingnan was not long enough(if only taking into account seeds reaching the physiological maturity,it was only carried out for four months),so the vigor loss of seeds from the canopy seedbank of K.bipingnan was not observed.While,the change of “rise-fall-rise” in seed viability in this study was probably resulted from the physiological processes such as physiological maturity,conditional dormancy and its release,and the changes in the relative conductivity,MDA content,the activity of main antioxidant enzymes and the content of main reserve substances also seemed to prove that.