Effects Of Simulated Animals Feeding Cotyledon Or Growth Of Two Quercus Seedlings Under Different Environmental Conditions

The seed diffusion of spermatophyte is one of the important links in the life history.It is an important way to ensure plant propagation and population renewal.It is also one of the most vulnerable and restricted stages in the plant life cycle.Animal activities play an important role in this process.The seeds of the Quercus L.,for example,are rich in nutrients and are important source of food for many kinds of animals.In the process of feeding on the acorn,the animals also spread the acorn everywhere,completing the diffusion of the seed.Quercus are widely distributed around the world and have important ecological and economic value.Investigations in recent years have found that the natural regeneration rate of oak is low,and environmental factors that affect the regeneration of oak have become a topic of concern to ecologists.Among biological factors,the feeding of seeds by vertebrates(such as rodents and birds)and insects(such as weevils)is an important cause of seeds' damage and seedlings' inability to survive.In this study,Q.acutissima and Q.dentata,which are common in warm temperate zone,were selected as the research objects.Cotyledons may be fed before or after emergence,and we simulated the effects of these two feeding patterns on seedling growth.Three levels of damage,no damage,mild damage(1/3 of cotyledon were removed from the base)and severe damage(2/3 of cotyledon were removed from the base),as well as different nutrient and light levels,were treated in the experiment where cotyledons were fed before seedling emergence.In the experiment where cotyledons were fed after seedling emergence,we set three time points for cotyledons to be removed,1,2 and 4 weeks after seedling emergence and different nutrient levels.Seed emergence rate,seedling survival rate,growth index,physiological index,total biomass and allocation were measured to explore the influence of different feeding ways and degrees of cotyledon on emergence and seedling growth of oak,as well as the compensation effect brought by the change of environmental factors.The results are as follows:Mild damage of the cotyledon before seedling emergence(1/3 of cotyledon were removed from the base)did not significantly affect the seedling emergence rate and survival rate of Q.acutissima seedlings,while severe damage(2/3 of cotyledon were removed from the base)resulted in reduced survival rate of Q.acutissima seedlings The partial damage of cotyledons had adverse effects on the growth,net photosynthetic rate and biomass of seedlings,and the restriction effect was enhanced with the increase of the proportion of cotyledons removed.The addition of soil nutrients can partially compensate for the adverse effects of cotyledon damage on the growth of Q.acutissima seedlings,but it cannot completely relieve the restriction of cotyledon damage on seedling growth.Under low light conditions,the growth of Q.acutissima seedlings was restricted.Compared with the high light experimental group,the plant height,base diameter,net photosynthetic rate,total biomass and other indicators at the end of the experiment were significantly reduced.In order to capture more light,the leaf area increased,and the chlorophyll content increased significantly.The compensation effect of soil nutrients on cotyledon damage weakened under low light.Remove cotyledons one week after emergence had a strong restrictive effect on the growth of Q.dentata seedlings.Compared with the control group with complete cotyledons,the growth of seedlings,development of lateral root,net photosynthetic rate,total biomass and the biomass of roots,stems and leaves were significantly affected.The growth of the experimental group that removed cotyledons two or four weeks after seedling emergence was also restricted.However,compared with the experimental group that removed cotyledons in the first week,the growth of the experimental group was better.The above indicators did not decrease significantly,and the net photosynthetic rate tended to increase.The results show that cotyledon plays an important role in the early growth of seedlings.The level of soil nutrition had a significant effect on the growth of the seedlings of Q.dentata.Sufficient nutrients improved the growth of the seedlings,and the content of N and P in the leaves also increased significantly,but it could not fully compensate for the effect of cotyledon removal on the growth of the seedlings.In short,under different environmental conditions,the cotyledons of Quercus were fed before or after emergence had an adverse effect on the growth of seedlings,but the magnitude of the impact was related to the degree of cotyledon damage and the time of cotyledon removal.Adequate nutrients in the soil can partially compensate for the adverse effects of cotyledons being fed.When the light is insufficient,the compensation effect is weakened.