A Study On Early Growth Of Seeds And Its Correlation To Tree Nutrition In Torreya Grandis ‘merrillii’

Seed production in Torreya grandis‘Merrillii’has developed quickly in recent years,which is one of income sources for farmers in Zhejiang province and other places nearby suitable for planting of this species.But it has been found that some individuals have a low seed set rate of less than 3%due to severe post-flowering premature seed drop,which has directly influenced seed yield.Therefore,it is an important measure to increase the seed set rate for an increase in seed yield per unit area and economic return.With T.grandis‘Merrillii’trees located in Lin’an district and Fuyang district of Hangzhou,Zhuji,and Jinyun county of Lishui,such parameters were measured in March and June,respectively,when it was pre-and post-seed drop as tree height,basal trunk diameter,crown diameter,the seed number of two years,length and thickness of seed-bearing shoots of two years,the number of mixed buds and vegetative buds of one-year shoots to study the relationship between reproductive growth and vegetative growth;the relationship between seed traits,seed nutrition and nutrition of shoots and leaves before and after seed drop as well as the relationship between soil nutrition,nutrition of shoots and leaves,and seed-set rate were analyzed;and effects of girdling on floral bud differentiation and seed setting were also studied with a view to providing theoretical rationale for improvement in stand management.The main results are as follows:（1）Although individuals in T.grandis‘Merrillii’result from grafting,there were differences between individuals in terms of the 2^nd-year seed set percentage,the number,length and thickness of fruiting shoots,the number of new shoots,the number of new seeds each shoot,and the percentage of mixed buds.It has been found that the percentage of fruiting shoots was not small in T.grandis‘Merrillii’,but seed set rate was not high.Most of fruiting shoots were intermediate in both length and diameter.It has been revealed that fruiting shoots with a length of 7.11–10.30 cm and a thickness of 3.11–3.40 mm had more seeds.And over long or over short and over thin or over thick shoots were not high in the number of the 2^nd-year seeds.The length and thickness of fruiting shoots in the lower layer of the canopy were smaller than those in the middle and upper layers of the crown,so were the number of new shoots and the number of new seeds each shoot,but the seed set rate and the percentage of mixed buds in the lower layer were high as compared with those in the middle and upper layers.This is associated with nutrient accumulation in the“horizontally pulled shoots”resulting from fruiting on the shoots in the lower layer.It is also found that fruiting shoots on the south and west had a proper length and thickness,which might be associated with a good sunshine in the morning and afternoon.T.grandis‘Merrillii’trees regulate vegetative growth and reproductive growth themselves.（2）Volume growth of young seeds in T.grandis‘Merrillii’mainly depended on increase in the number of cells and the main component of a cell was water.N,P and K were necessary for seed growth and development,especially N and K.The Ca content in the leaves and shoots was found higher than that in the seeds and fluctuated greatly.Therefore,fertilization is good for seed growth and development,which should be based on soil diagnosis to determine whether it is necessary to apply fertilizers,which fertilizer should be applied and how much fertilizer to apply.（3）Multi-site investigations have found that the seed set rate was not high in T.grandis‘Merrillii’.K was one of main nutritive elements in the seed of T.grandis‘Merrillii’.The K content and the ratio of K to N in the shoot and leaves were positively correlated with the seed set rate most significantly.The total K content in the top surface soil was negatively correlated with the 2^nd-year seed set rate,so was the N in the soil and the 2^nd-year seed set rate as well as the K content in the top surface soil and that in the shoot and leaves,which indicates that the K in the seed is mainly from shoots and leaves.A low seed set rate indicates that soil is rich in nutrients.It is necessary to study how to regulate the proportion of various elements in favor of seed setting.（4）There was no significant difference in mineral elements between complete girdling or half-girdling and non-girdling of shoots（P>0.05）.Complete girdling of branches was superior to half girdling,which could be seen from the ratio of C/N in the shoot and leaves,percentage of mixed buds and seed set percentage.Girdling had almost or completely no effect on the transportation of mineral elements in the tree,but blocked the phloem,which influenced the transportation of organic nutrients.Differences in the 2^nd-year seed set rate and the proportion of mixed buds between girdling and non-girdling treatments mainly resulted from blocked transportation of organic nutrients leading to nutrient accumulation.Conclusions are as follows:the percentage of seed-bearing shoots is not small in T.grandis‘Merrillii’,but seed set rate is not high,which is popular everywhere.Most of the 2^nd-year seed are borned on the shoots with a moderate lenth and thickness.The length and thickness of seed-bearing shoots in the upper and middle layers of the crown are higher than those of shoots in the lower part of the crown,but the percentage of seed setting and mixed buds of shoots in the lower part of the crown is the highest.N,P and K are necessary for seed growth and development,especially N and K.K in the seed is mainly from shoots and leaves.Soil is rich in nutrition but sever in acidization.Complete girdling is better than half girdling in terms of C/N,proportion of mixed buds and 2^nd-year seed set rate.